FR2569158A1 - DIGITAL DECOMPRESSIMETER WITH VARIABLE INFUSIONS - Google Patents

Abstract

The decompressemeter is intended to take into account the excercise of the diver and/or the temperature of the ambient medium to determine more accurately the optimum decompression program. Thus, the determination process in real time of the decompression program of a diver or a hyperbar worker comprises essentially: - measuring during exposure the time and the ambient pressure, - measuring and/or determining also during exposure at least one of the following additional parameters: 1) perfusion of one or a plurality of tissues, 2) heart flowrate, 3) pulmonar ventilation, 4) oxygen consumption, 5) heart pulse rate, 6) ambient temperature, - and deducing an estimation of the saturation stages of a diver and the appropriate decompression program.

Description

DESCRIPTION
Digital decompressimeter with variable infusions.

 The invention relates to a new method, more precise than the previous methods, of determining the minimum non-pathological decompression program for a person (diver, hyperbaric worker, aviator, cosmonaut, etc.) who has stayed and breathed a gas mixture. containing one or more non-metabolizable gases at ambient pressures higher than that of the "surface" that it ultimately wants to reach, as well as an automatic device for determining and indicating said program and related parameters applying said method, as well as 'a diving set incorporating said device.

 The need for such a program stems from the fact that, during the stay under pressure, said non-metabolizable gases have dissolved via the lungs and the blood in the tissues of the organism in greater quantities than those which may exist there at pressure. from the surface, and that too rapid decompression would release in situ, rather than in the exhalation gases via the blood and the lungs, the excess of said gases which are not consumable by the body in the form of so-called "pathological" bubbles, that is to say capable of inflicting lesions on the tissues in which they appear and / or of interrupting the blood circulation in certain vessels, the spectrum of observable and generally delayed consequences of these decompression sicknesses ranging from slight localized itching until the death of the person concerned.

 The two main types of decompression are continuous decompression and step decompression. Continuous decompression consists in reducing the ambient pressure continuously or in small steps, and is faster but less practical than decompression in stages, which consists in making stops of relatively long duration at predetermined ambient pressures relatively distant one on the other, generally spaced 3 mem (meters of seawater) 3 ms to the surface, the speed of movement to the first level and between the levels being limited by a given maximum admissible value, generally between 10 and 20 mem / min.

 Whatever type of decompression is used, the ideal decompression program is the minimal program, that is to say the one whose total duration is the shortest without compromising the safety of the person concerned. The reasons for this are obvious, especially in the professional diving environment where a few tens of minutes lost in unnecessary decompression time can lead to losses of several thousand francs due to the high hourly cost of divers and the people and equipment that surround. A method for determining decompression programs is precise when the program prescribed by this method for a given exposure comes as close as possible to the minimum program, any deviation going in the direction of safety.

 Two critical factors limit the accuracy of a given method.

The first is the accuracy of determining the state of saturation of the person interested in non-metabolizable gases after a given exposure. The second is the precision with which the constraints which said saturation state must obey during decompression are known to avoid the appearance of pathological bubbles. These two factors are not independent; indeed, the more the errors committed in the determination of the state of saturation, the more severe must be the constraints to which it must have subjected said state during decompression If one wants to avoid a sub-minimal decompression and therefore pathological. The method of the invention has a better first factor and, in turn, a better second factor than conventional methods. Before describing how this is accomplished, it is necessary to explain conventional methods in more detail.

These methods, whether they are applied to fictitious ambient pressure / time scenarios such as for the establishment of decompression tables or to the actual profile of an exposure as in apparatuses of the analog or digital decompressimeter type, are numerous but all have, or at least the most reliable and therefore the most used, a common basic architecture due to the pioneering work of the British physiologist 3.S. Haldane at the beginning of this century
The state of saturation of the organism is represented by the tensions of
gases which cannot be metabolized in a certain number of tissues.
represent scaled dissolved gas concentrations of
such that at saturation of a given tissue for a given gas (we
will use Saturation here with a capital S in the sense of the state
equilibrium where the tissue contains in solution all the gas which can
reside stably), the gas tension in the tissue is numbered
rique equal to the partial pressure of said gas in the mixture
breathed, itself equal to the product of the ambient pressure and the
molar concentration of gas in the mixture. These fabrics do not represent
not feel - well defined anatomical tissue, but rather
sets of diverse anatomical tissues united by behavior
common with regard to the dynamics of trade in a gas not
metabolizable given with respiratory gases.
finely finished (rarely more than 7) of fabrics taken into account by
various methods constitute a sampling which is intended to represent
tative of the theoretically almost infinite number of such sets possi
wheat. Each tissue is characterized for a gas given by a cons
aunt called period or half-life, which can - depending on the alier tissue of
a few minutes to a few hundred minutes which is defined
as the time required for the voltage of this gas in this
tissue pathway halved the difference separating it initially from
Saturation voltage, equal to the partial pressure of the gas in the
respiratory mixture, the latter being assumed to be constant.
definition implies that the voltage varies exponentially depending
of time t, according to a law which can be expressed-differentially from the
as follows:
(Eq. I) dq / dt = k [gp - q] where q is the tension of the gas dissolved in the tissue
g is the molar fraction of the gas in the mixture
p is the ambient pressure
k = Log2 / h is the exponential coefficient of the tissue
or
Log2 is the natural logarithm of 2
h is the period of the tissue
or, if the product gp and k are constant, in the integrated form
(Eq. 2) q = qo + [gp - qo] [l-exp (-kt)]
where qo is the initial value (at time 0) and q is the final value (at time
time t) of the voltage.

In addition, some methods employ calculation devices to
the estimation of the tensions when the ambient pressure is high,
as the "magnification" of the times actually spent under pressure
ambient over 70 mem by a factor of 1.5 or 2.

The state of saturation of the organism being thus represented, the con
which he must obey during decompression is com
essentially pose maximum allowable voltages for each
fabric and for each gas which are increasing functions, generated
generally linear but not necessarily passing through the origin,
of ambient pressure.These maximum allowable voltages
given ambient pressure for a given gas are greater than said
ambient pressure and therefore obviously higher than the pressure
partial gas at this ambient pressure, thus tuning the tissues
a certain degree of supersaturation (tension in excess of the tension of
Saturation) permitted and thereby the possibility for at least one
of them to desaturate at each stage of decompression, the
desaturation rate being proportional to the amplitude of the
supersaturation as indicated (Eq. 1). Another constraint which he has
already been reported is the maximum decompression speed or
rise, which is sufficient to ensure the non-pathological desaturation of
faster tissues, like blood.

 In order to understand how conventional methods are likely to improve, one can refer for example to paragraph 3.4.1 of research report 6-65 of the U.S. Navy Experimental Diving Unit by R.D.

Workman (1965), where it says in essence
"It is also recognized that the admission of inert gas during work is more important than at rest, due to the increase in cardiac output and tissue perfusion. Likewise, the elimination of inert gas during rest periods will be slower than during work. Determining the maximum allowable voltages from work dives takes this difference into account to some extent. "
The perfusion of anatomical tissue (tissue blood flow) is indeed an important factor in the processes of saturation and desaturation in non-metabolizable gases. Boycott, Damant and Haldane (The prevention of compressed air illness; J. Hyg. London. 8, 445-456, 1908) estimate that the characteristic exponential coefficient k of a given tissue for a given gas which, as we have seen, is inversely proportional to the period of this fabric for this gas, can be expressed as follows:
(Eq. 3) k = a CB / S where a is a constant
C is the blood perfusion of the tissue
B is the solubility of gas in the blood
S is the solubility of the gas in the tissue.

 According to these authors, therefore, the period of any tissue would vary in inverse proportion to the perfusion of this tissue, all other things being equal. However, it is nowadays agreed that this would only be true for well-vascularized tissues, and that the periods of poorly vascularized tissues, that is to say those where the gas in solution must diffuse over a comparatively distance long before encountering a blood vessel, would depend more or less on infusions of these tissues. These latter tissues would also be those with the longest periods.

 The perfusion of an increasing metabolism tissue, like an exerting muscle, increases by dilation of the blood vessels which supply it in response to the temporary hypoxia caused by said increased metabolism. This vasodilatation is accompanied by an increase in cardiac output in order to maintain a constant blood pressure.

 Between rest and a sustained effort the cardiac output in humans can vary between 5 and 25 I / min, i.e. by a factor of 5, or even more: cardiac outputs of around 40 I / min have been measured in well-trained athletes providing maximum effort. The simple act of walking slowly increases the cardiac output by about 50% compared to the value at rest. However, by conserving flow rates, a multiplication of cardiac output by a factor x greater than 1 must necessarily be associated with a multiplication by a factor y at least equal to x of the perfusion of tissues whose increased metabolism is - at the origin increase in cardiac output. If Boycott, Damant and Haldane are to be believed, this means that the exponential coefficients and therefore the gas exchange rates of said tissues are multiplied by the same y factor. Since the factors x and therefore y can be greater than 5, it can be seen that the errors due to this effect, made by conventional methods in determining the state of saturation of an individual, to which Workman alludes in the extract from his report presented above, are potentially enormous.

 If we consider a simplified model of the organism where the exponential coefficients of all the tissues would vary in proportion to the cardiac output, and if we admit that a diver can work at the bottom at a cardiac output of 25 I / min then decompress then at cardiac output 5 I / min according to a conventional method in complete safety - which it is allowed to doubt -, then it is simple to see, by interchangeability of k and t in (Eq.

2), that the same diver could have safely undergone the same decompression program after a dive at the same depth but lasting 5 times higher if his cardiac output at the bottom was only 5 I / min, c that is to say if he had made no effort at bottom. In fact, its state of saturation when it started to rise would have been exactly the same in both cases. In other words, it would be perfectly safe, in some cases, to use conventional tables by entering a fictitious duration 5 times less than the actual duration of the dive, for example if one used the dive table at the air annexed to the 1974 decree of the French Ministry of Labor governing the special protection measures applicable to hyperbaric workers (Official Bulletin, special issue no. 74-48 bis), one could, in certain cases, go up safely from a dive from 50 min to 57 m in a total time of 11.4 min (duration of the ascent recommended for a dive of 50/5 = 10 min to 57 m) which can be compared to the 141.6 min of the decompression program obtained by strict application of the table, thus achieving a significant saving of more than two hours or 92% on the decompression time.

 It goes without saying that a diver who would let himself be tempted by the saving of time achieved in the above example would run into serious trouble given the simplicity of our hypotheses, which were only intended to provide an order of magnitude of possible impact on actual decompression times of changes in cardiac output during a given exposure to pressure.

 The method of the invention consists in monitoring during exposure (including decompression), in addition to time and ambient pressure as do conventional digital decompressimeters, ie the cardiac output of the person concerned or any related parameter allowing the calculation of said cardiac output, to estimate the instantaneous values of the exponential coefficients or periods of a certain number of representative tissues of the organism as a function of said cardiac output, to be deduced therefrom by real-time integration of (Eq. 1) the current values of the tensions in each tissue of each of the main non-metabolizable gases present in the breathed mixture, to predict the evolution of these voltages in simulated decompression at presumed constant cardiac output under constraints of maximum admissible tensions as a function of the ambient pressure on the one hand and d '' a maximum decompression speed on the other hand, to display or otherwise indicate the minimum progressive decompression program a so obtained, and to assist the diver as much as possible while respecting the said program.

In order to avoid the difficulties inherent in direct measurement of cardiac output under real operational conditions, one can make use of the correlation, the observation of which is a daily banality between the cardiac and respiratory activities of an individual, these activities being both determined. by the metabolism of the individual. Detailed studies have shown that the average ventilatory flow rate ("respiratory volume minute") of an individual varies approximately from 6 to 120 I / min in direct proportion to his oxygen consumption, which can be expressed as the product of cardiac output by the difference in oxygen concentration between the arterial blood and the venous blood respectively at the exit and the entry of the lungs. This difference in concentration, or oxygen extraction rate, also increases significantly with metabolism, so that cardiac output, unlike ventilatory output, is not directly proportional to oxygen consumption. There is however a relation between the cardiac output and the average ventilatory output, which, for a normal individual breathing air at atmospheric pressure can be represented by the following linear approximation
(Eq. 4) c = 0.18v + 3.95 where c is the cardiac output in I / min
v is the average ventilation flow in I / min.

 The lying position and the vertical immersion of the body affect this relationship in similar ways in that they cause an increase in cardiac output (from 15 to 30%) without appreciable modification of the average ventilatory flow.

Variations in ambient pressure are also likely to modify this relationship, in particular by the variations in partial pressure of oxygen in the breathed mixture (and therefore in oxygen tension in arterial blood) that they cause. Anyway, we can admit that there exists, with a respiratory mixture given function of the ambient pressure, an analytical expression giving the cardiac output of an individual according to his ventilatory flow or his consumption of oxygen and of ambient pressure with sufficient precision to allow the application of the method of the invention by monitoring the subject's consumption of respiratory gases. The precision of this method of determining cardiac output, which is not critical in measure that it is enough that it is better than 60 96 to allow to determine the state of saturation of the subject with more precision than the conventional methods, can be very good (certainly better than 20%) if the analytical expression on which it is based is determined experimentally in a box for the same subject to which it must be applied, and under conditions of respiratory mixture, attitude, immersion and temperature as pro as possible real operational conditions at equal ambient pressure. A determined mean expression experimentally from measurements on a large number of individuals would also have sufficient precision for our application. The expression could for example take the following linear form
(Eq. 5) c = a (p) v + b (p) where a (p) and b (p) are functions of ambient pressure, or a polynomial form of higher order according to the required precision.

The ventilatory flow can in turn be determined by monitoring the pressure of the respiratory gas tank for an open circuit respiratory device or that of the oxygen tank for a neutral gas recycling device, according to the expansion expression next isotherm
(Eq. 6) vp = -KV dP / dt or K is equal to 1 for an open circuit device or equal to the
proportionality constant between the ventilatory flow and the
oxygen consumption in the case of a recycling device.

In the latter case K can be determined beforehand by
box, depending on the ambient pressure.

Alternatively for a recycling device the flow because
diac can be directly expressed according to the consumption
oxygenation, which would then be substituted for v in the
equations 5 and 6 where a (p) and b (p) would be new functions
of the ambient pressure p, and K would be equal to 1.

V is the volume of the tank concerned
P is the pressure of the tank concerned. dP / dt is obviously
negative at constant temperature.

 Knowing P has other obvious safety advantages by allowing proper management of respiratory reserves.

où Ps est la valeur de P prédite à l'arrivée en surface
vo est la valeur présumée du débit ventilatoire lors de la décom
pression. Afin de majorer pour raisons de sécurité la chute de
pression P-Ps et aussi de simplifier les calculs, on pourra utiliser
une valeur constante (par exemple 20 I/mn) pour vo partout
supérieure à celle correspondant par (Eq. 5) à la valeur présumée
du débit cardiaque, également choisie constante (par exemple
7 I/mn). This management is made all the easier since the present method makes it possible, thanks to the simultaneous knowledge of P and of the minimum decompression program, to predict the value of P on arrival at the surface by application of the following equation obtained by integration of (Eq. 6)

where Ps is the value of P predicted on arrival at the surface
vo is the presumed value of the ventilatory flow during the decom
pressure. In order to increase for safety reasons the fall of
P-Ps pressure and also to simplify the calculations, we can use
a constant value (for example 20 I / min) for vo everywhere
higher than that corresponding by (Eq. 5) to the presumed value
cardiac output, also chosen to be constant (e.g.
7 I / min).

 The mention "prog." under the integral sign means that integration is performed on the ambient pressure / time profile of the minimum decompression program. If K is equal to 1 we see that the integral is equal to the area under this profile, an approximation of which in the context of decompression in stages is the sum of the products (ambient pressure X duration) for all the stages.

 Having described a possible method of determining cardiac output and the additional gain that can be obtained in terms of safety, we will now examine as an example a decompression calculation method using this parameter.

The mathematical model of the organism is made up, whatever the non-metabolizable gas concerned, of seven tissues numbered according to an index i ranging from 1 to 7. The exponential coefficients of these tissues are the following functions of cardiac output, in units of 10 5 5-1 for c expressed in I / min
(Eq. 8) kl = 22.3168 c
(Eq. 9) k2 = 11.1584 c
(Eq. 10) k3 = 5.5792 c
(Eq. Il) k4 = 2.7896 c
(Eq. 12) k5 = 1.10 c + 2.0636
(Eq. 13) k6 = 0.55 c + 1.0318
(Eq. 14) k7 = 2.4409
Three criteria governed the choice of these functions, in addition to their linearity
The first criterion is the proportionality of the exponential coefficients, and therefore the inverse proportionality of the periods, of the fastest tissues in cardiac output.

The second criterion is consistency with the periods of the 7 fabrics which served as the basis for calculating the official tables of the French Ministry of Labor (Official Bulletin 74-48 bis). These tissues were affected by different periods according to the immersion conditions respectively 7.5, 15, 30, 60, 120, 240, and 480 min in immersion (exposure and decompression), and 10, 20, 40, 80, 150, 300 and 480 my during the surface interval. We thank in passing 3.P. COMEX lmbert for having communicated these values to us. If we calculate for each tissue the ratio between the submerged period and the non-submerged period, we obtain respectively 0.75, 0.75, 0.75, 0.75, 0.80, 0.80 and 1.00 These reports seem to take into account the 32% increase, reported by several authors, in a subject's cardiac output when it passes from the vertical immersed rest state to the immersed vertical rest state, by a variation of the periods of the 4 fastest tissues in inverse proportion to the cardiac output (0.75 = 1 / 1.33), a slower variation of the periods of the following 2 tissues, and no variation at all for the last tissue. The periods corresponding to the exponential coefficients that we have chosen are respectively 7.40, 14.79, 29.58, 59.16, 118.32, 236.64 and 473.29 min for a cardiac output of 7 I / min typical of submerged rest, and 9.86, 19.72, 39.44, 78.88,
147.38, 294.76 and 473.29 min for a cardiac output of 5.25 I / min typical of non-submerged rest. Note that, although close to the periods used in the calculation of the official tables respectively for immersion and for
The surface interval, and although respecting the geometric progression of reason 2 of the latter in the case of immersion, our periods slightly deviate from it when it would have been possible to make them coincide: the reasons for this reside in the third criterion.

The third criterion is that, at cardiac output 7 I / min, presumed value of cardiac output during the simulated ascent in this method to establish the minimum decompression program, and for a convenient time interval dt, the product k.dt is for any tissue a whole negative or positive power of 2, allowing the simple and rapid integration of (Eq. 1) for the estimation of the tensions of the tissues during said ascent simulated by means of calculation with binary notation. As it happens,
The convenient time interval chosen is 2.5 s or the product of this value by any integer power of 2. This 2.5 s value leaves us "convenient" in that it divides exactly one minute (60 = 24 x 2.5) and in that eile corresponds to a pressure reduction of 0.5 mem at the nominal decompression speed of 12 mem / min which we prefer to the 15 mem / min of the official tables for safety reasons . 0.5 mem happens to be the precision with which we intend to measure the ambient pressure, as well as the internal unit of representation of this quantity by the means of calculation, which will thus be able to represent on a single byte (8 bits d 'information) all ambient pressures on a range of variation of 128 mem, quite sufficient for most applications. In addition, 0.5 mem exactly divides the usual distance of 3 mem between the bearings.

 Simultaneous or alternating monitoring of ambient pressure, time and cardiac output make it possible to calculate at any time and for each gas considered the real tensions of this gas prevailing in each of the 7 tissues, by real-time integration of (Eq. 1 ), where k is a function of the tissue and the instantaneous value of the cardiac output according to equations (Eq. 8) to (Eq. 14), and where g is the molar fraction of the - gas considered in the respiratory mixture, possible function of ambient pressure and known in advance.

From these real tensions prevailing at the present time in the tissues, one can predict future tensions by means of the following hypotheses
- Decompression starting at the present time.

 - Constant cardiac output (7 I / min) during decompression.

 - Decompression speed either zero or equal to a nominal value (12 mem / min).

 - Stops authorized only at certain ambient pressures or "decompression stops". The usual steps are located at all ambient pressures distant from the surface pressure (known here as the multiple of 0.5 mem closest to its real value) by a multiple of 3 mem. If all ambient pressures are authorized, we are in a continuous decompression situation, equivalent here to decompression in stages where the stages are located at all ambient pressures multiple of G, 5 mem.

 - Tensions everywhere less than or equal to maximum allowable voltages also called control voltages which, for each gas considered and each tissue, are linear functions of the ambient pressure (see below).

 - Decompression as fast as possible while respecting the previous assumptions.

 - Decompression ending on arrival at the surface.

 The ambient pressure / time profile resulting from these assumptions constitutes the minimum decompression program appropriate to this state of saturation.

 At the start of the calculation of the minimum decompression program, which is carried out every few seconds, we ensure that all the current tensions in the tissues are lower than the control tensions in force at the current ambient pressure. When this is not the case, we block the "real" voltages and the decompression program in the state where these quantities were before the detection of the anomaly, to let them vary again from the end detection 'anomaly. This arbitrary measure is intended to prohibit the prescription of artificially short decompressions induced by the abnormally rapid reduction of tensions when a level is not respected.

 The fabric which, for a given gas, controls stopping at a given level because the voltage of this gas is too high to allow it to reach the next level without exceeding the control voltage, and which determines the time of stop at this level, is called the directing tissue of this level.

 When, as is the case in most methods of decompression calculation where a single non-metabolizable gas is present, certain conditions involving the periods and control voltages of the various tissues and the molar fraction of the gas considered in the mixture breathed at each level are combined, the director fabric of a given level is always greater than or equal to that of the director fabric of the previous level. In this case, it is possible to speed up the calculation of the decompression program by considering, as the simulated decompression is concerned, only tissues with a period greater than or equal to that of the current director tissue.

The control voltages at the various levels of the various tissues for each non-metabolizable gas constitute the cornerstone of any method of calculating the minimum decompression program for a given initial state of saturation. As we saw above, taking into account the cardiac output by our method gives it better precision in determining the state of saturation than conventional methods, allowing the use of less severe control voltages (therefore higher) because the share of the error is smaller. The question of determining these control voltages therefore arises. A simple method which has the advantage of benefiting from the hundreds of thousands of human experiments which have led to establishment and which have confirmed through use security conventional tables authorizing work at the bottom is as follows
For each scenario of one or more confirmed conventional tables authorizing work at the bottom, such as for example the tables of GERS (now GISMER) or of the Ministry of Labor in France, or those of the US
Navy, we can calculate thanks to (Eq. 2) the state of saturation at the end of exposure (start of decompression) of each of our seven tissues affected by constant exponential coefficients given by equations (Eq. 8) to (Eq 14) for a cardiac output typical of constant moderate work at the bottom, for example 15 I / min. From the tensions at the end of exposure of our seven tissues, we can calculate the tensions reached at the different decompression stages by the same tissues affected this time by exponential coefficients given by the same equations for a cardiac output typical of decompression, by example 7 I / min. The overall comparison of these results for all the scenarios considered makes it possible to determine the maximum tensions reached by the various tissues at the various stages, possibly eliminating for safety reasons the individual results that are too much higher than the maximum tensions reached by most scenarios. way of making this determination is to retain, as and when the scenarios considered, the ten highest tensions reached by each tissue at each level, then to keep only the values constituting the lowest close group. The control voltages can finally be determined for each tissue as preferably linear functions of the ambient pressure which are everywhere less than or equal to the maximum tensions obtained as described above. It is easy to see that the minimum decompression programs which will be prescribed by our method from these control voltages will be, for profits ambient pressure / equal times, respectively shorter or longer than the programs obtained from the conventional tables used in the determination of said control tensions, when the average cardiac output measured during exposure will respectively be less than or more than 15 1 / pan. This is how our method will allow a faster ascent and just as safe as the tables when the work done at the bottom has been unimportant, a rise close to the tables when a moderate work has been provided, and a slower ascent and safer than the tables for a particularly important work at the bottom.
Having exposed the invention in its theoretical aspect (method of the invention), we will in the following focus on its technical aspect (device of the invention).

 The device of the invention is an instrument: - for determination by measurements and calculations - and for automatic indication, in real time and at any time - of the minimum integral or partial program of continuous non-pathological decompression or in stages of the user from the ambient pressure of the moment to a predefined pressure, - as well as numerical or logical parameters related to said program which may either have participated in the establishment of said program, or may be likely to facilitate or make safer execution by the user of said program, either result from or depend on said program, comprising on the one hand: - means for measuring time capable of producing output signals representative of said time, - as well as means for measuring ambient pressure suitable to produce output signals representative of said ambient pressure, - as well as automatic memory means at least partly in memory capable of receiving and inter read the output signals of said time measuring means as well as those of said ambient pressure measuring means, as well as to estimate, by real-time integration of quantities partly dependent on said signals, the current state of gas saturation not metabolizable by the user, as well as calculating, as a function of said saturation state, said decompression program, as well as producing output signals representative of said decompression program and of said related parameters, - as well as means of indication suitable for receiving the output signals from said calculation means as well as possibly those from all or some of the measurement means present in said device, as well as for producing output signals representative of said signals in a form directly interpretable by the user, - as well as supply means capable of supplying electrical energy to all the active components of said device, - as well as a housing suitable for containing and protecting against shock and harmful effects of the ambient environment said device, as well as facilitating the wearing of said device by the user, as well as allowing communications of the means of indication to the user, characterized : - in that it also comprises means for measuring the cardiac output of the user or any related parameter which would allow, taking into account other information to which the calculation means otherwise have access, to estimate said cardiac output, capable of producing output signals representative of said cardiac output or related parameter, - and in that said calculation means are adapted to receive and interpret the output signals of said means for measuring cardiac output or related parameter, thus to deduce therefrom, possibly taking into account other information to which they also have access, an estimate of said cardiac output, as well as to involve said cardiac output in the s real-time integration calculations mentioned above leading to the evaluation of the user's saturation state, for example by varying the periods (semi-saturation time) of the mathematical tissues representative of the said organism user in inverse proportion to said cardiac output in order to model the effect of variations in blood / tissue transfusion on the gas exchanges of the anatomical counterparts of said tissues, or according to a slower or even constant function of said cardiac output for those of said tissues on which the anatomical counterparts would depend largely or even completely diffusion phenomena for their gas exchanges and / or whose perfusion of the anatomical counterparts would vary less quickly than in proportion to the cardiac output, or even according to a more rapid function of said cardiac output for those of said tissues whose perfusion of the anatomical counterparts would vary faster than proportional to cardiac output.

 The measurement of the cardiac output can be carried out indirectly by measuring the average value over a few tens of seconds of the ventilatory output ("volume minute") and the application of the existing physiological correlation, with respiratory mixture given function trivial or not of ambient pressure, between ventilatory flow, cardiac output and ambient pressure. The coefficients of the analytical expression used by the computing means to represent this correlation can be mean coefficients determined from measurements on a large number of individuals, or the user-specific coefficients.

 To do this, the device of the invention may include means for measuring the pressure P, defined as the pressure prevailing inside the respiratory gas reservoir in the case of an open circuit breathing apparatus or as that prevailing inside the oxygen tank in the case of a closed or semi-closed breathing apparatus. The means of calculation and possibly the means of indication are sensitive to the signals coming from said means of measuring P. The said means of calculating evaluate the speed of variation of P according to the signals coming from said means of measuring P and those coming from means for measuring time at the ends of a small time interval. Said calculating means determine the ventilatory flow rate of the user as a function of said speed of variation due ?, ambient pressure, volume of the reservoir concerned, type of breathing apparatus used, and of the percentage of oxygen in the respiratory mixture as a function of ambient pressure in the case of a closed or semi-closed circuit breathing apparatus, the latter three information being contained in explicit or implicit form in the memory of the computing means.

 The calculation means also use the current measured value of the pressure P to predict, on the basis of and possibly simultaneously with the current decompression program, the value of P when arriving at the surface in the event that the user performs immediately its ascent according to the indications of the device and where its ventilatory flow during said ascent would have a presumed given value, said value being able or not to depend on the values measured until the moment when the prediction is carried out. Said calculation means are able to warn the user by means of one or more of the indication means as soon as the value of P predicted upon arrival at the surface becomes lower than a given safety threshold.

The means for measuring the pressure or pressures are based on one or more sensors which can be reactive or resistive, electro-mechanical or electrical, passive or active, precalibrated or not, with or without internal thermal compensation of the sensitivity and / or zero, sensitive to absolute pressures or to pressures relating to that prevailing inside the housing or one of its compartments, which may or may not include bellows,
Bumblebee, levers, converters for displacement into electrical signal, membranes, intermediate pressure transmitting fluids, flexible or rigid pipes or conduits putting in equilibrium the sensitive parts of the sensors and the environments where the pressures are measured, including the part may consist of one or more discrete or integrated electronic components, which may behave electrically as a "bridge
Wheatstone "whose resistance of one or more of the branches varies as a function of the pressure measured, thus varying the output voltage of said bridge, or as a differential or non-electric oscillator whose impedance of one or more of the elements varies in as a function of the pressure measured, thus varying the frequency of oscillation of said oscillator. Said means for measuring the pressure or pressures may also include circuits for amplification and / or external thermal compensation of the input signals (excitation) and / or output from the basic sensor (s), said circuits being able to be integrated in a single component or made up of operational amplifiers and passive components (resistances, capacities), said circuits being able to be moreover common to several sensors by insertion of a or several analog demultiplexers and / or multiplexers controlled by the calculation means between said circuits and the inputs and / or outputs of said sensors. Said means for measuring the pressure or pressures can also comprise at least one analog-digital converter which can be of the voltage-frequency type and which can be used for the conversion of analog signals coming from various sources by insertion between said sources and the input of said converter. an analog multiplexer controlled by said calculating means, the output or outputs of said converter (s) being connected to one or more lines of said calculating means. Said means for measuring the pressure or pressures can comprise at least one constant voltage source of which the output is connected either directly or via said amplification and / or thermal compensation circuits to the input (excitation) of the sensor (s), said constant voltage source being able, according to an arrangement called "ratiometric", to be one that calibrates internally or externally the analog to digital converter (s).

 The device according to the invention may also include means for measuring the ambient temperature, the basic sensor of which may be of the resistive temperature detector (RTD), thermistor, thermocouple, diode or integrated circuit type. Said temperature measurement means may have parts in common with other elements of the device, the basic sensor being able in particular to be integrated into a pressure sensor or to an analog-digital converter being able to be of the voltage-frequency type. The signals from said temperature measuring means can be used to compensate the thermal coefficients of the other measuring means and possibly of the indicating means. Said compensations can be carried out analogically, either by direct excitation of the member to be compensated by output voltage of said temperature measurement means either by the use of operational amplifiers which may or may not be part of amplifier stages, or numerically in which case said temperature measurement means can comprise at least one analog-digital converter which can be of the voltage-frequency type which they can share with other measurement means if an analog multiplexer is added thereto, ia or the outputs of said converter being connected to one or more lines of the calculation means, said converter being able moreover to contain the base temperature sensor.

The indication means can be sensitive, directly, through amplification circuits or via calculation means, to signals from said temperature measurement means and capable of informing the user of the value of said temperature.

 The device of the invention may also include data input means allowing the possible modification, for the purposes of experimentation or adaptation to new diving conditions or simply for reasons of personal preferences, of some of the quantities that can be explicitly or implicitly kept in the memory of the calculation means such as pressure prevailing at the surface, volume of the tank in which the pressure P is measured, type of respiratory device used, safety threshold of the pressure P predicted on arrival in surface, composition of the respiratory mixture possibly in the form of a function of the ambient pressure, number and basic periods (for a given basic cardiac output) of the tissues constituting the mathematical model of the organism, initial values of the tensions of the various gases not metabolizable in said tissues, maximum admissible values of said tensions in the form of functions of ambient pressure, maximum ascent rate, desired decompression mode (continuous or stepwise), depths or ambient pressures authorized for the execution of steps in the case of step decompression, coefficients of the correlation cardiac output / ventilatory output / ambient pressure , coefficients of the cardiac output / period correlation for each tissue, dive time not to be exceeded, depth or ambient pressure not to be exceeded, calibration constants of the measurement means, thermal sensitivity and / or zero coefficients of the measurement means measurement and / or indication means, desired indication mode, optimal reading angle and / or display illumination request in the case of a liquid crystal display. Said data input means can be composed of magnetic action switches of the "Reed" or Hall effect type located inside the housing, controlling the binary state of lines of the calculation means, and one or more several magnets encapsulated in or covered with a material suitable for protecting them from corrosion located outside said housing and capable of being moved in translation, rotation or a combination of these movements by the user in order to selectively and distance said switches.

Said data entry means may include a locking device capable of protecting said constants against any accidental modification during use or transport of the device.

 The computing means consist of a microcomputer which can be essentially of CMOS construction, comprising in one or more housings one or more microprocessors with 4, 8, 16, 32 or even 64 bits, one or more clock signal generators, one or more elements of random access memory which can be of the static or dynamic type or a combination of the two, possibly one or more elements of read-only memory programmable or not, possibly one or more timers (counting registers), possibly one or more decoders, possibly one or more binary signal amplifiers ("buffers", "drivers", buffers, transmitters, receivers, transmitters), possibly one or more auxiliary logic boxes (gates, inverters, single tables, multiplexers, counters, Schmidt flip-flops), possibly one or more passive components (resistors, capacitors), possibly one or more communication interfaces, programmable or not, para Models (PIA, PIO) or synchronous or asynchronous series (SCI, UART, USART, CFIA). The said clock signal generator (s) allow the said microprocessor (s) to execute in sequence the machine code instructions stored in the memory (dead or in the absence of a living fault) of which the various operations for entering, processing and transmitting assigned information are made up. to the means of calculation. Said random access memory can be kept under permanent voltage so that its content is preserved even during periods of device shutdown. Said microprocessor (s) can operate in various modes such as "active", "sleep", "standby" corresponding to various energy levels. Said means of calculation can have one or more interruption facilities hierarchical or not, maskable or not, internal and / or external, by hardware and / or software, allowing the execution of specific algorithms according to the state of the measurement means and / or display means and / or the timers or timers if necessary and / or data input means if necessary and / or electrical energy supply means. One of said interruption facilities, preferably of the non-maskable type, controlled by the data input means, can trigger an organized system closure procedure which guarantees the backup of the contents of the RAM. Said timers, if present, can fulfill all or part of the functions of the time measurement means in association with said clock signal generator (s). Said clock signal generator (s) can be composed of oscillators (crystalline , for example quartz, or others, for example RLC circuits) independent or of outputs from those of the time measurement means, if any, which are distinct from the calculation means. The communications between the various components, if there are several, of the calculation means (internal communications) and between the calculation means and the other components of the device (input-output communications) take place via programmable ports. or not, with or without latches ("latches"), one-way or two-way or mixed, which may have an inhibition facility (high impedance state) and / or via interrupt lines (by example for reception of frequency type signals) and / or via control lines (such as selection lines, handshake lines) and / or via parallel or serial communication interfaces . Some of said ports can be interconnected in a so-called "bus" arrangement. The input-output ports can be specialized or projected in memory. Said calculating means can fulfill part of the functions of the various measuring means, in particular by performing thermal calibrations and / or compensations for sensitivities and / or zeros, by generating analog signals via digital-analog converters allowing to evaluate the signals to be measured by the use of comparators, or by measuring the frequency of an alternating signal using a timer and the associated external interruption facility ("input capture interrupt"). Said calculation means can modify one or more excitation voltages of the measurement and / or indication means by means of digital-analog converters or analog multiplexers associated with potential dividers and possible operational amplifiers and components. associated liabilities in order, for example in the case of a liquid crystal display, to modify the optimum reading angle to satisfy the requests expressed by r the user via the data entry means or in order to keep said angle constant by compensating for the thermal effects which affect it. The sequences of instructions executed by said calculation means may include various tests of the correct functioning of the device, in particular likelihood tests, leading to a warning of the diver via the indication means in the event of a malfunction detected.

Said calculation means can, thanks to one or more switches of the "solid-state" type (for example Darlingtons or power Mosfets) or mechanical relays (for example of the "Reed" type), selectively or globally control the power supply other components of the system, in order to direct their operation (on / off of lamps, horns, etc.) and / or to save energy for example by temporarily deactivating some of the measurement means while the output signals said measurement means are not "online" (active on the input lines of the calculation means) or when said output signals are observed to vary very slowly allowing infrequent sampling.

 The means for supplying electrical energy may consist of rechargeable batteries which may be of the cadmium-nickel type or of non-rechargeable batteries which may be of the lithium or mercury type. Said electrical energy supply means can occupy a separate and possibly detachable and replaceable compartment of the housing, hermetically isolated from the other compartment or compartments of said housing while being electrically connected to them. Said supply means if they are of the rechargeable type can be connected to two stainless steel contacts, which may be gold or gold-plated, located outside the housing and allowing recharging of said supply means, at least one of the two connections being made via a diode or d a switch prohibiting the discharge of said supply means via said contacts in seawater or the ambient environment of the user, whoever it may be, said switch if it is a switch that can be of the Reed type controlled from the outside of the housing using a magnet by the user or a relay controlled by the calculation means according to the ambient pressure and / or the requests expressed by the user via the data entry means. The compartment of the box containing said supply means can be provided with an ease of manual opening or with a valve authorizing the elimination of gases released by said means. feeding while prohibiting the entry of fluids or foreign bodies. The device of the invention may also include means for determining the state of charge of said supply means, said means for determining may consist of a constant voltage source, possibly a potential divider to which is applied the potential difference between the terminals of said supply means, and of a comparator, said means being able to be totally or partially integrated into a single component, the output or outputs of said determination means being connected to one or more ports of the means of calculation and / or the means of indication. Said means of determining the state of charge may be capable of triggering, after possible expiration of a delay and possible warning of the diver via the means of indication, an organized closure of the system guaranteeing the backup of the contents of the RAM.

 The indicating means may consist of any combination of visual, audible or tactile indicating means. Said visual means may include one or more simple light emitting diodes or arranged in segment displays and / or dot matrix and / or "bar graphs", one or more reflective or transflective liquid crystal displays, with parallel or multiplexed excitation, illuminable or not, with segments and / or matrices of predefined points and / or symbols and / or "bar-graphs", one or more plasma screens, one or more cathode-ray tube screens, one or more needle dials, one or more incandescent lamps, one or more flashlights, a bu from electroluminescent tubes or screens, painted and / or engraved legends. Said visual means are visible to the user through one or more transparent windows or walls of the housing and are suitable to be represented, in digital or analog form or as a "bar-graph" or binary (two-state display, such as an LED that lights up when a certain quantity exceeds a certain threshold), simultaneously or alternatively, automatically or on request via the data entry means, any combination of the following information that the calculation means and possibly the measurement means are capable of providing them: decompression program in full or partial steps consisting of couples (depth or ambient pressure , time) and possibly the total duration of the ascent, depth or minimum ambient pressure accessible for continuous decompression, duration of this dive (stay at ambient pressures higher than that prevailing on the surface), time, date, possible residual duration diving at this depth or ambient pressure depending on the estimated present state of saturation of the user's body and its residual amount of respiratory gas and possibly on the request it has expressed via the means of data entry for maximum dive time, depth or maximum ambient pressure reached during this dive, prof inverter or current ambient pressure, current ascent rate, residual amount of respiratory gas present (pressure P or equivalent volume for a given ambient pressure which may be the pressure prevailing at the surface), residual amount of respiratory gas predicted at the end of the prescribed ascent by the device, the user's ventilatory flow and / or cardiac output, ambient temperature, any information that may have been stored by the user via the data entry means, answer to the question "the maximum admissible depth ( may have been defined by the user) exceeded? ", answer to the question" maximum dive time (may have been defined by the user) exceeded? ", answer to the question" the time maximum dive will be exceeded at the end of the ascent prescribed by the device? ", answer to the question" does the residual amount of breathing gas allow to go up as indicated of the device (taking into account a safety threshold which may have been defined by the user)? ", answer to the question" has the maximum admissible ascent speed been exceeded? ", answer to the question" the current depth is it less than that of the first bearing to be executed? ", answer to the question" is the current depth less than the minimum admissible depth of continuous decompression? ", answer to the question" the state of charge of the means d is the supply of electrical energy satisfactory? ". Said sound means may include one or more electro-acoustic transducers adapted to the ambient environment (for example hydrophones in marine or freshwater environments) as well as their generator circuits and amplifiers. associated electrical waves, said transducers being able to be electromagnetic or piezoelectric, monotone or multitone, capable of informing the user qualitatively (alarms and signals differentiated or not salted on the information transmitted, particularly suitable for information of binary type), or even quantitative for example by speech synthesis if they are associated with one or more speech synthesis circuits receiving their instructions from the calculation means, the information transmitted by said sound means can be any combination of those listed above with reference to visual means. Said tactile means may consist of mechanical appendages driven by electromagnets or electric motors and capable of coming into contact with any part of the body of the user or of fixed electrodes in permanent contact with the skin of the user capable of causing slight discharge.

Said tactile means, if present, are capable, in the event of important information to be transmitted to the user (see list referring to visual means), to draw their attention to said visual means even under ambient noise conditions which would make ineffective sound means.

 The present invention also relates to a diving set comprising, in addition to a device according to the invention, a breathing apparatus composed of reserves of compressed gas carried or not by the diver, one or more regulators, and optionally a breathing bag provided valves and a carbon dioxide absorption cartridge and an automatic oxygen dosing device, possibly a waterproof lamp, possibly orientation instruments (compass, goniometer), a diving mask or helmet, possibly means of propulsion (fins, underwater "scooter"), possibly means of protection against the cold (heated suit or not), possibly means of adjusting the buoyancy of the diver and his equipment (buoy, ballasts or dry suit) with or without an inflation gas reserve independent of the breathing gas reserves, possibly a turret or caisson or decompression chamber. It may include a turbine-electric generator assembly (dynamo or rectified alternator) associated with a regulator and capable of extracting the energy for expansion of the respiratory gases and / or inflation of the means for adjusting the buoyancy and to maintain in a state of load satisfying the means of supplying electrical energy to the assembly during the dive. Said device according to the invention can be incorporated into the diving helmet and may include a corrective optical assembly based on lenses and / or mirrors and / or prisms and / or semi-reflecting plates allowing close-up vision, and possibly superimposed on the normal field of vision, - visual indication means, may also include conventional sound indication means (speakers, headphones) operating in the gaseous volume of the headset, and may include voice type data input means consisting of a microphone or laryngophone connected to the calculation means via a m speech recognition module. The dive unit can include two solenoid valves controlled by the calculation means, binary via relays or switches called "solid-state" or proportionally via digital-analog converters followed by amplifiers, one controlling the entry of inflation gas into the jacket or dry suit and the other controlling the exhaust of said gas to the ambient environment, said solenoid valves allowing said means of calculation as a function of time, of ambient pressure and possibly its time derivatives - easily calculated as a function of the output signals over a period of time of the time measurement means and the ambient pressure measurement means -, possibly of information previously stored in memory by the user via the data entry means (such as the mass of the diver, its volume, its coefficient of resistance to movement in water, the compression coefficient suit and surface volume of his suit), and possibly the current decompression program, to stabilize the diver at a given depth (at the diver's request via the data entry means) or at all depths, to make him execute an ascent "in disaster" or at controlled speed (after possible warning, via the means of indication, of the diver, leaving the latter the option of aborting the procedure via the data entry means or by simply disconnecting the solenoid valves) in the event of detection of an emergency condition (for example drowning made probable by apnea - no ventilatory flow - of abnormally long duration, or abnormally high ambient pressure making it probable a state of narcosis in the diver), or to make him execute the continuous ascent or in stages prescribed by the device (at the request of the diver via the data entry means). The means of calculating said device according to the invention can be able to similarly control a solenoid valve responsible for decompressing a diving turret or chamber or decompression chamber and possibly another responsible for its compression, thus automating the operation of said turret or chamber or chamber with regard to decompression and possibly as for compression.

 The invention is in no way limited to the embodiments and applications of the device given here. On the contrary, it embraces all the variants which would remain in accordance with its essence.

A preferred embodiment among the combinations of embodiments given for each - of the main components of the device, particularly suitable for the use of scuba divers, and which has the advantages of being economical, versatile and relatively simple, is the following
The ambient and reservoir pressures are transmitted to the "pressure" inputs, mouthed on one side of the housing, of two monolithic absolute pressure sensors (with single semiconductor substrate) of the "bridge type".
Wheatstone "whose measurable pressure ranges are compatible with their respective measurands, via a rot-proof stainless membrane and an incompressible, non-corrosive and electrically non-conductive intermediate fluid in both cases, also via a flexible hose designed for high pressures (armed) connected to the HP output of the regulator in the second case.

 The two bridges are excited by constant voltages obtained by amplification of the constant voltage output of the single voltage-frequency converter ("ratiometric" arrangement), on the "voltage to measure" input from which are multiplexed, after amplification and offset, the output signals of said bridges as well as the "temperature" output with which said converter is also provided.

 The means of calculating and measuring time, consisting of a CMO & 8 bit microcomputer in a box (microprocessor, read only memory or ROM, RAM or RAM, 16 bit timer or timer, 29 output lines), control the multiplexing the analog signals to be measured by two of their input-output lines, and receive the output frequency of the converter on their "frequency to be measured" line. They are therefore able to know at any time the uncalibrated values of the ambient pressure, the tank pressure and the temperature, to calibrate them and, as regards the pressures, to apply thermal compensations to them. calibration and thermal compensations are introduced into the RAM of the microcomputer by means of data input means of the "reed" type controlling the state of input-output lines of said microcomputer. This manipulation does not need to be repeated each time the device is turned on, but can be repeated at annual intervals if a deterioration in the accuracy of the device was observed. The constants stored in the RAM survive the periods of device shutdown and even at full discharge of the main batteries (cadmium-nickel), "sintered cells", 5 X 1.2V, 0.5Ah) thanks to automatic switching to "Standby" mode (consumption of a few microamperes , RAM saved) of the microcomputer during the shutdown of the device or the detection by an appropriate device of an advanced state of discharge of the main batteries, as well as when using a back-up battery up "(cadmium-nickel," mass plate ", 3 X 1.2V, 0.1 Ah) with low self-discharge losses intended to take over in the event of exhaustion of the main batteries as regards exclusively the power supply of the standby microcomputer and its essential satellites d in this mode, which it can provide for several months. The rest of the time, that is to say when the main batteries are charged, they keep the said "back-up" battery charged by "trickle charging" at 0.25 mA. On the other hand, the device is provided with a second charge level detector for the main batteries, constituted like the first with a potential divider and a threshold detector, which changes the state of a line of microcomputer input-outputs when said charge level only allows a few hours of operation, so that the user is notified.

This arrangement is advantageous for several reasons:
a) It allows the use of non-calibrated and non-thermally compensated pressure sensors, therefore inexpensive (hundreds of francs instead of thousands for fully calibrated and compensated sensors).

 b) It allows calibration without delicate manipulation of potentiometers or other variable components and even without opening the device housing, by simply reading the indications of the device subjected to known pressures and temperatures and introduction of constants easily calculated from said indications and said known values.

 c) It provides precise calibration / compensation because downstream of all analog circuits.

 d) It authorizes recalibrations as frequent as necessary, which can possibly be carried out by the user himself.

 e) It allows the display of the water temperature for the benefit of the diver.

 f) It allows the entry of other constants such as surface pressure, composition of the respiratory mixture, etc., which will also be preserved when the device is stopped or discharged.

 The main batteries are simply charged via two bare stainless coritacts emerging from the housing, the discharge of said batteries by the same path being prevented by the interposition of a diode. This diode can be short-circuited by an externally controlled reed switch authorizing in rapid emergency a total discharge of the main batteries via the external contacts, a condition necessary for the subsequent execution of a rapid total charge at 2A in 15 min safe for batteries. Upstream of this diode, that is to say between the diode and the external positive contact, a second diode connected to the positive pole of the back-up battery via a resistor performs a 1 mA bypass of the charging current, allowing a relatively rapid recharging of said back-up battery when it has been used for a prolonged period, which the trickle charging current cannot guarantee. The maximum permanent charge current of the assembly is 68 mA.

 There are two types of indication: visual and audible. The visual means consist of a transflective LCD screen module (can be lit either from behind or from the front) with 32 alphanumeric multiplexed characters, in a resistance scale associated with an analog multiplexer allowing the optimal reading angle of the screen to be adjusted. by that of the excitation voltage of the liquid crystals, into an electroluminescent panel underlying the screen and into a wave generator intended to supply said panel. The calculation means control said visual means by 15 of their input-output lines It is dedicated to data transmissions, 3 to control the multiplexer 8-1, 1 to the wave generator of the panel E.L.

ordered via a Darlington.

 The audible indication means consist of a piezoelectric transducer connected to the "frequency output" line of the microcomputer via an amplifier.

In conclusion, here are the advantages of a device such as the one whose realization has just been described, applying the method of calculation of the decompression program described above, compared to one or the other (all, in this which concerns at least a, b and c) existing or already proposed devices and methods
a) Better precision in determining the saturation state of the user, leading to the establishment of decompression programs more appropriate to the real saturations of the tissues, therefore generally more reliable than those prescribed by existing devices and processes.

 b) This better precision leads in many cases to a decompression program substantially shorter than that obtained by another method.

c) The time savings mentioned in (b) translates into significant financial savings for hyperbaric works companies, allowing the execution of a given task at a lower cost.
d) The device measures and displays the dive time, the ambient pressure, the tank pressure, the ambient temperature.

 e) The - device takes charge of all the calculations relating to the decompression of the user, going until the determination of the moment when this decompression should start according to the residual quantity of respiratory gases.

 f) The decompression program is progressive, that is to say that even during decompression, the program which remains to be carried out adapts to the conditions in which the decompression was actually carried out up to this time. This adaptability can even go as far as applying the therapeutic rule of half-pressure or that of half-depth in the event of a significant violation of the decompression constraints, said application presenting no difficulty from the software point of view.

 g) Good communications from the device to the diver by means of indication addressing several of the diver's senses. Good readability of visual aids whatever the ambient light. Flexible display on screen, allowing, in addition to the routine display of digital parameters relating to exposure and decompression, the occasional display of explicit alphanumeric messages (warnings, alarms, reminders) accompanied by an audible signal.

 h) Flexibility of calibration, thermal compensation, adaptation to new diving conditions (surface pressure, composition of the respiratory mixture, etc.), and possibility of personalization of the device (constants defining the relation ventilatory flow / cardiac output / pressure , control voltages, etc.) thanks to the data input means.

 i? The device is suitable for both professionals and amateurs, thanks to its calculation method which takes account of the work done at the bottom, as well as its price which should not exceed 2500 F for sale.

 j) Technical reliability and long service life of the device, thanks to the possibility of sealing the case in the factory in an inert atmosphere, due to the ease of external charging of the batteries.

 k) Low electrical consumption, allowing the continuous operation of the device on its energy reserves for several days and the calculation of tissue desaturation during surface int + ryalles ...

 I) User warning several hours before the total discharge of the main batteries.

 m) Back-up battery ensuring the backup of the calculation constants in all circumstances (except abandonment of the device for several months without recharging it, in which case a reinitialization of the constants is necessary; this circumstance will in any case be detected by the device and reported to the user).

 n) Indefinite recharging (after 10h the main batteries are fully recharged but an indefinite extension of the charging time does not endanger them) or rapid (15 min, a prior discharge being necessary and made possible by the bypass switch the charging diode, an extension of the charging time (risk of damaging the batteries) at the user's choice and depending on the urgency of the situation. A relatively simple automatic device can ensure constant current charging of the batteries in either of these two modes (including the remote triggering of the reed bypass switch by creating a magnetic field the along the reed using a coil traversed by a current, including also the discharge prior to rapid charging (using a switching and threshold detection device) in complete safety, the timing of the quick charge that can be done using a simple timer. Such an automatic charging device can be designed to operate indifferently from a mains supply or from a 12 or 24 V vehicle battery.

Claims (11)

1 - Method characterized in that it consists in monitoring during exposure (including decompression), in addition to time and ambient pressure as do conventional digital decompressimeters, the cardiac output of the person concerned or any related parameter allowing to calculate said cardiac output, to estimate the instantaneous values of the exponential coefficients or periods of a certain number of representative tissues of the organism as a function of said cardiac output, to be deduced therefrom by integration in real time of (Eq. 1) the values current of the tensions in each tissue of each of the main non-metabolizable gases present in the breathed mixture, to predict the evolution of these tensions in simulated decompression at presumed constant cardiac output under constraints of maximum admissible tensions according to the ambient pressure of a part and a maximum decompression speed on the other hand, to display or otherwise indicate the minimum decompression program evolutionary thus obtained, and to assist the diver as much as possible while respecting the said program. 2 - Method according to claim 1, characterized in that the measurement of the cardiac output is carried out indirectly by measuring the average value over a few tens of seconds of the ventilatory output ("minute volume") and the application of the correlation physiological existing, with respiratory mixture given trivial function or not of the ambient pressure, between the ventilatory flow, the cardiac flow and the ambient pressure, and in that the coefficients of the analytical expression used by the means of calculation to represent this correlation can be average coefficients determined from measurements on a large number of individuals, or user-specific coefficients. 3 - Device - for determination by measurement and calculation - and for automatic indication, in real time and at any time - of the minimum integral or partial program of continuous non-pathological decompression or in stages of the user from the ambient pressure from the moment until '' at a predefined pressure, - as well as numerical or logical parameters related to said program which may either have participated in the establishment of said program, or be likely to facilitate or make safer the execution by the user of said program, or result or depend on said program, comprising on the one hand - time measurement means capable of producing output signals representative of said time, - as well as ambient pressure measurement means capable of producing output signals representative of said ambient pressure, - as well as automatic memory means at least partly in memory capable of receiving and interpreting the output signals of said m means for measuring time as well as those for said means for measuring ambient pressure, as well as for estimating, by real-time integration of quantities partly dependent on said signals, the current state of saturation with non-metabolizable gases of the user, as well as calculating, as a function of said saturation state, said decompression program, as well as producing output signals representative of said decompression program and said related parameters, as well as indicating means suitable for receiving the output signals from said calculation means as well as those from all or some of the measurement means present in said device, as well as for producing output signals representative of said signals in a form directly interpretable by the user, - as well as supply means capable of supplying electrical energy to all the active components of said device, - as well as a housing capable of containing and protecting against e the shocks and the harmful effects of the ambient environment said device, as well as to facilitate the wearing of said device by the user, as well as to allow communications of the means of indication towards the user, characterized - in that on the other hand, it comprises means for measuring the cardiac output of the user or any related parameter which would allow, taking into account other information to which the calculation means otherwise have access, to estimate said cardiac output, capable of producing output signals representative of said cardiac output or related parameter, and in that said calculating means are able to receive, interpret and deduce the output signals from said means for measuring cardiac output or related parameter, possibly taking into account other information to which they also have access, an estimate of said cardiac output, as well as to include said cardiac output in real-time integration calculations m mentioned above leading to the evaluation of the saturation state of the user, for example by varying the periods (half-saturation time) of the representative mathematical tissues of the organism of said user in inverse proportion to said cardiac output in order to model the effect of variations in blood / tissue transfusion on the gaseous exchanges of the anatomical counterparts of said tissues, or according to a slower or even constant function of said cardiac output for those of said tissues whose anatomical counterparts would largely or even totally depend on the phenomena diffusion for their gas exchanges and / or whose perfusion of the anatomical counterparts would vary less quickly than in proportion to the cardiac output, or even according to a more rapid function of said cardiac output for those of said tissues whose perfusion of the anatomical counterparts would vary faster than in proportion to the flow cardiac. 4 - Device according to claim 3, characterized in that it comprises means for measuring the pressure P, defined as the pressure prevailing inside the respiratory gas tank in the case of an open circuit breathing apparatus or as that prevailing inside the oxygen tank in the case of a closed or semi-closed circuit breathing apparatus, in that the calculation means and possibly the indication means are sensitive to the signals coming from said means of measurement of P, in that said calculating means evaluate the speed of variation of P as a function of the signals coming from said means for measuring P and those coming from the means for measuring time at the ends of a small time interval, and in that said calculation means determine the ventilatory flow rate of the user as a function of said rate of variation of P, of the ambient pressure, of the volume of the reservoir concerned, of the type of respiratory apparatus used, and of the percentage d oxygen in the respiratory mixture as a function of the ambient pressure in the case of a closed or semi-closed circuit breathing apparatus, the latter three information being contained in explicit or implicit form in the memory of the calculation means. 5 - Device according to claim 4, characterized in that the calculation means also use - the current measured value of the pressure P to predict, on the basis of and possibly simultaneously with the current decompression program, the value of P during the '' arrival at the surface in the event that the user would immediately make his ascent according to the indications of the device and where his ventilatory flow during said ascent would have a presumed given value, said value may or may not depend on the values measured until the moment when the prediction is carried out, and in that said calculation means are able to warn the user by means of one or more of the indication means as soon as the value of P predicted upon arrival at the surface becomes lower at a given security threshold. 6 - Device according to any one of the preceding claims, characterized in that the means for measuring the pressure or pressures are based on one or more sensors which can be reactive or resistive, electro-mechanical or  electric, passive or active, precalibrated or not, with or without a compensator  internal thermal sensitivity and / or zero, pressure sensitive  absolute or pressures relative to that prevailing inside the housing or a  of its compartments, which may or may not include bellows,  Bumblebee, levers, displacement converters to electrical signal,  membranes, intermediate pressure transmitting fluids, pipes or  flexible or rigid piping equipping the sensitive parts of the  sensors and the environments where the pressures are measured, including the electrical part  can be composed of one or more discrete or integrated electronic elements,  which can behave electrically like a "Wheatstone bridge" whose  the resistance of one or more of the branches varies depending on the pressure  measured thus varying the output voltage of said bridge, or as a  electric oscillator differential or not whose impedance of one or more of  elements varies according to - the pressure measured thus varying the  frequency of oscillation of said oscillator, in that said means for measuring  the pressure (s) may also include amplification circuits  and / or external thermal compensation of the input signals (excitation) and / or  of the base sensor (s), said circuits being able to be integrated into a  single component or consisting of operational amplifiers and components  passive (resistances, capacities), said circuits possibly also being common to  several sensors by insertion of one or more demultiplexers and / or multi  analog plexers controlled by the calculation means between said circuits and  the inputs and / or outputs of said sensors, in that said means for measuring  the pressure or pressures may also include at least one converter  analog-digital which can be of the voltage-frequency type and which can be  used to convert analog signals from various sources by  insertion between said sources and the input of said converter of a multiplexer  analog controlled by said computing means, the one or more outputs of said one or more  converters being connected to one or more lines of said means of  calculation, and in that said means for measuring the pressure or pressures can  include at least one constant voltage source, the output of which is connected either directly or via said amplification circuits and / or  thermal compensation at the input (excitation) of the sensor (s), said source  of constant tension which, according to an arrangement called "ratiometric", can be  one that calibrates the analog converter (s) internally or externally  digital. 7 - Device according to any one of the preceding claims, characterized in that it comprises means for measuring the ambient temperature, the basic sensor of which may be of the resistive - temperature detector (RTD), thermistor, thermocouple, diode type. or integrated circuit, in that the said temperature measurement means may have parts in common with other elements of the device, the basic sensor being able in particular to be integrated into a pressure sensor or to an analog-digital converter being able to be of the voltage-frequency type, in that the signals from said temperature measuring means can be used to compensate the thermal coefficients of the other measuring means and possibly of the indicating means, in that said compensations can be effected analogically, either by direct excitation of the member to be compensated by the output voltage of said temperature measuring means. either by the use of operational amplifiers which may or may not be part of amplifier stages, or numerically in which case said temperature measurement means can comprise at least one analog-digital converter which can be of the voltage-frequency type which they can share with other measurement means if an analog multiplexer is added thereto, the output or outputs of said converter being connected to one or more lines of the calculation means, said converter possibly also containing the base temperature sensor, and in that the indication means may be sensitive, directly, via amplification circuits or via calculation means, to signals from said d & commat measurement means; of the temperature and capable of informing the user of the value of said temperature. 8 - Device according to I1 any one of the preceding claims, characterized in that it also comprises data input means allowing the possible modification, for purposes of experimentation or adaptation to new diving conditions or simply for reasons personal preferences, some of the quantities that can be held explicitly or implicitly in the memory of the calculation means such as surface pressure, volume of the tank in which the pressure P is measured, type of respiratory system used, safety threshold of the pressure P predicted on arrival at the surface composition of the respiratory mixture possibly in the form of a function of the ambient pressure, number and basic periods (for a cardiac output dz given base) of the tissues constituting the mathematical model of l 'organism, initial values of the tensions of the various non-metabolizable gases in said tissues, maximum admissible values of said t ensions in the form of functions of the ambient pressure, maximum ascent rate, desired decompression mode (continuous or in stages), depths or ambient pressures authorized for the execution of stages in the case of a decompression in stages, coefficients correlation of cardiac output / ventilatory flow / ambient pressure, coefficients of correlation of cardiac output / period for each tissue, dive time not to be exceeded, depth or ambient pressure not to be exceeded, calibration constants of the measurement means, coefficients thermal sensitivity and / or zero measurement means and / or indication means, desired indication mode, optimal reading angle and / or display illumination almond in the case of a display with liquid crystal, in that said data input means may be composed of magnetic action switches of the "Reed" type or of Hall effect located inside the housing, controlling the bin state area of lines of the calculation means, and of one or more magnets encapsulated in or covered with a material suitable for protecting them from corrosion situated outside said housing and capable of being moved in translation, rotation or a combination of these movements by the user in order to selectively and remotely actuate said switches, and in that said data input means may comprise a locking device capable of protecting said constants against any accidental modification during use or transport of the device. 9 - Device according to any one of the preceding claims, characterized in that the calculation means consist of a microcomputer which may be essentially of CMOS construction, comprising in one or more housings one or more microprocessors with 4, 8, 16, 32 or even 64 bits, one or more clock signal generators, one or more random access memory elements which may be of the static or dynamic type or a combination of the two, possibly one or more programmable or non-programmable read only memory elements, possibly one or several timers (counting registers), possibly one or more decoders, possibly one or more binary signal amplifiers ("buffers", "drivers", buffers, transmitters, receivers, transmitters), possibly one or more auxiliary logic boxes (gates , inverters, monostable, multiplexers, counters, Schmidt rockers), possibly one or more passive components (resistors, condensate eurs), possibly one or more programmable or non-programmable communication interfaces, parallel (PIA, PIO) or synchronous or asynchronous series (SCI, UART, USART, CFIA), in that the said clock signal generator (s) allow the said microprocessor (s) to execute in sequence the machine code instructions stored in memory (dead or hard-fault) of which the various input, processing operations are made up and transmission of information allocated to the calculation means by the claims, in that said random access memory can be kept under permanent voltage so that its content is preserved even during periods of device shutdown, in that said microprocessor (s) can operate in various modes such as "active", "sleep", "standby" corresponding to various energy levels, in that said calculation means can have one or more interruption facilities, hierarchical or not, internal or concealable and / or external, by hardware and / or software, allowing the execution of specific algorithms according to the state of the measurement means and / or display means and / or the tim ers if necessary and / or data entry means if necessary and / or means for supplying electrical energy, in that one of said interruption facilities, preferably of the non-maskable type, controlled by the data input means, can trigger an organized system closure procedure which guarantees the backup of the contents of the RAM, in that said tjmers if they are present can fulfill all or part of the functions of the time measuring means in association with the said clock signal generator (s), in that the said clock signal generator (s) may be composed of oscillators (crystalline, for example quartz, or others, for example RLC circuits) independent or from those of the time measuring means, if any, which are distinct from the calculation means, in that the communications between the various components, if there are several, of the calculation means (internal communications) and between means and the other components of the device (input-output communications) are via programmable or non-programmable ports, with or without latches ("latches"), one-way or two-way or mixed, which may have ease of inhibition (high impedance state) and / or via interrupt lines (for example for receiving frequency type signals) and / or via control lines (such as selection lines, handshake lines -) and / or via parallel or serial communication interfaces, in that some of said ports can be interconnected in a so-called "bus" arrangement, in that the ports input-output can be specialized or projected in memory, in that said calculation means can fulfill part of the functions of the various measurement means, in particular by performing calibrations and / or thermal compensations of sensitivities and / or calculated zeros , by generating by means of analog digital converters of the analog signals making it possible to evaluate the signals to be measured by the use of comparators, or by measuring the frequency of an alternating signal using a timer and the ease of interruption associated external "input capture interrupt"), in that said calculation means can modify one or more excitation voltages of the measurement and / or indication means via digital-analog converters or associated analog multiplexers to potential dividers and possible operational amplifiers and associated passive components so, for example in the case of a liquid crystal display, of modifying the optimal reading angle to satisfy the requests expressed by the user via the means of data entry or in order to keep said angle constant by compensating for the thermal effects which affect it, in that the sequences of instructions executed by said means calculation can include various tests of proper operation of the device, in particular likelihood tests, leading to a warning of the diver via the indication means in the event of a malfunction detected, and in that said calculation means can, thanks to a or several switches of the "solid-state" type (for example Darlingtons or power Mosfets) or mechanical relays (for example of the "Reed" type), selectively or globally controlling the supply of electrical energy to the other components of the system, in order to direct their operation (start-stop of lamps, audible warning devices, etc.) and / or save energy for example by temporarily deactivating some of the measuring means while the output signals from said measuring means are not "in line "(active on the input lines of the calculation means) or when said output signals are observed to vary very slowly allowing infrequent sampling. 10 - Device according to any one of the preceding claims, characterized in that the means for supplying electrical energy may consist of rechargeable batteries which may be of the cadmium-nickel type or non-rechargeable batteries which may be of the lithium type or with mercury, in that said means for supplying electrical energy can occupy a separate and optionally detachable and replaceable compartment of the housing, hermetically isolated from the other compartment or compartments of said housing while being electrically connected to them, in that said means of power supply if they are of the rechargeable type can be connected to two stainless steel contacts which may be gold or gold-plated located outside the case and allowing the recharging of said power supply means, at least one of the two connections being made by via a diode or a switch preventing the discharge of said supply means via said contacts in water sea or the ambient environment of the user, whoever it may be, said switch if it is a switch that can be of the Reed type controlled from the outside of the housing using a magnet by the user or a relay controlled by the calculation means cn as a function of the ambient pressure and / or of requests expressed by the user via the data input means, in that the compartment of the housing containing said supply means can be fitted with a facility for manual opening or with a valve authorizing the elimination of gases released by said dialimentation means while preventing the entry of fluids or foreign bodies and in that it also includes means for determining the state of load of said supply means, said means of determination can! consist of a constant voltage source, possibly of a potential divider to which the potential difference is applied between the said terminals: supply means, and a comparator, said means being able to be totally or partially integrated into a single component, ia or the outputs of said determination means being connected to one or more ports of the calculation means and / or to the indication means, and in that said means for determining the state of charge may be capable of triggering, after possible expiration of a delay and possible warning of the diver via the indication means, an organized closure of the system guaranteeing the backup of contents of the RAM 11 - Device according to any one of the preceding claims, characterized in that the indication means may consist of any combination of visual, audible or tactile indication means, in that said visual means may include one or more light-emitting diodes simple or arranged in segment displays and / or dot matrix and / c "bar-graphs", one or more reflective or transflective liquid crystal displays, with parallel or multiplexed excitation, illuminable or not, with segments and / or dots and / or predefined symbols and / or "bar-graphs", one or more plasma screens, one or more CRT screens, one or more needle dials, one or more incandescent lamps, one or more lamps with flashes, one or more electroluminescent tubes or screens, painted and / or engraved legends, in that said visual means are visible to the user through one or more transparent windows or walls of the housing and are capable of representing, in the form digital or analog or "bar-graph" or binary (two-state display, such as an LED illuminating when a certain quantity exceeds a certain threshold), simultaneously or alternatively, automatically or on request via the input means of do nnées, any combination of the following information that the means of calculation and possibly the means of measurement are capable of providing them: decompression program in full or partial steps consisting of couples (depth or ambient pressure, time) and possibly the total duration ascent, depth or minimum ambient pressure accessible for continuous decompression, duration of this dive (stay at ambient pressures higher than that prevailing on the surface), time, date, residual duration ~ possible dive at this depth or ambient pressure as a function of the estimated present state of saturation of the user's body and of its residual quantity of respiratory gas and possibly of the request which it has expressed via the data entry means in terms of duration maximum dive, depth or maximum ambient pressure reached during this dive, current depth or ambient pressure, vi current ascent rate, residual amount of respiratory gas present (pressure P or equivalent volume for a given ambient pressure which may be the pressure prevailing on the surface), residual amount of respiratory gas predicted at the end of the ascent prescribed by the device, flow rate user's ventilatory and / or cardiac output, ambient temperature, any information that may have been stored by the user via the data entry means, answer to the question "the maximum admissible depth (which may have been defined by user) exceeded? ", answer to question" maximum dive time (may have been defined by user) exceeded? ", answer to question" maximum dive time aura- has it been exceeded at the end of the ascent prescribed by the device? ", answer to the question" does the residual amount of respiratory gas allow it to go up as indicated by the device (taking into account a threshold may have been defined by the user)? ", answer to the question" has the maximum admissible ascent speed been exceeded? ", answer to the question" is the current depth less than that of the first landing at execute? ", answer to the question" is the current depth less than the minimum admissible depth of continuous decompression? ", answer to the question" is the state of charge of the electrical energy supply means satisfactory ? ", in that said sound means may comprise one or more electroacoustic transducers adapted to the ambient environment (for example hydrophones in a marine or freshwater environment) as well as their associated generator and electric wave amplifier circuits, said transducers being able to be electromagnetic or piezoelectric, monotone or multitone, capable of informing the user in a qualitative manner (alarms and signals differentiated or not according to the information transmitted, particularly suitable for binary type information), or even quantitative for example by speech synthesis slils are associated with one or more speech synthesis circuits receiving their instructions from the calculation means, the information transmitted by said sound means being able to be a any combination of those listed above with reference to visual means, in that said tactile means may consist of mechanical appendages driven by electromagnets or electric motors and capable of coming into contact with any part of the body the user or fixed electrodes in permanent contact with the skin of the user capable of causing a slight discharge, and in that said tactile means, if present, are suitable, in the event of important information to be transmitted to the user. user (see list referring to visual means), to draw their attention to said visual means even under ambient noise conditions that i would make the sound means ineffective. 12 - Diving assembly characterized in that it comprises a device for determining and indicating according to any one of the preceding claims, a breathing apparatus composed of reserves of compressed gases carried or not by the diver, of one or more regulators, and possibly a breathing bag fitted with valves and a carbon dioxide absorption cartridge and  an automatic oxygen metering device, possibly a lamp  waterproof, possibly orientation instruments (compass, goniometer), a  diving mask or helmet, possibly means of propulsion (fins,  underwater "scooter"), possibly means of protection against the cold  (heating suit or not), possibly means for adjusting the  buoyancy of the diver and his equipment (lifeline, ballast or  dry suit) with or without an independent inflation gas supply  of the respiratory gas reserves, possibly a turret or box or  decompression chamber, in that it may include a turbine assembly  electric generator (dynamo or rectified alternator) associated with a regulator and  able to extract the relaxation energy from the respiratory gases and / or the inflation of the  means of adjusting the buoyancy and of maintaining it in a state of charge  satisfying the means of supplying electrical power to the assembly in  diving course, in that said determination and indication device can  be incorporated into the diving helmet and may include an optical assembly  corrective based on lenses and / or mirrors and / or prisms and / or blades  semi-reflective for close-up vision, and possibly super  placed in the normal field of vision, visual indication means, can include  also wear conventional means of sound indication (loudspeakers,  earphones) operating in the gaseous volume of the helmet, and may include  voice type data input means consisting of a microphone or - laryngophone connected to the calculation means via a recognition module  speech, and in that it can include two solenoid valves controlled by the  means of calculation, in a binary way via relays or switches called "solid  state "or proportionally via digital-to-analog converters  followed by amplifiers, one controlling the entry of inflation gas into the  vest or dry suit and the other controlling the exhaust of said gas  towards the ambient environment, said solenoid valves allowing said means to  calculation as a function of time, ambient pressure and possibly its  time derivatives - easily calculated according to the output signals on  a time period of the time measuring means and the measuring means  ambient pressure-, possibly information previously set  memory by the user via the data entry means (such as the mass of the  diver, its volume, its coefficient of resistance to movement in water, the  compressibility coefficient and the surface volume of his suit), and possibly the current decompression program, to stabilize the diver at a given depth (at the diver's request via the data entry means) or at all depths, from him execute a ascent "in disaster" or at controlled speed (after possible warning, via the means of indication, of the diver, leaving the latter the option of aborting the procedure via the data entry means or by disconnecting simply the solenoid valves) in the event of detection of an emergency condition (for example drowning made probable by apnea - zero ventilatory flow - of abnormally long duration, or abnormally high ambient pressure making it probable a state of narcosis in the diver), or to make him execute the continuous ascent or in stages prescribed by the device (at the request of the diver via the data entry means), and in that said means of calculating dud it determination and indication device may be able to similarly control a solenoid valve responsible for the decompression of a diving turret - or chamber or decompression chamber and possibly another responsible for its compression, thus automating the operation of said turret or chamber or chamber for decompression and possibly for compression.