HK1083734A

HK1083734A - A method for measuring blood pressure variability

Info

Publication number: HK1083734A
Application number: HK06103978.4A
Authority: HK
Inventors: 张元亭; 顾颖颖; 郑振耀
Original assignee: 香港中文大学
Filing date: 2006-03-30
Publication date: 2006-07-14

Description

Method for measuring blood pressure change rate

Technical Field

The present invention relates to a method of measuring blood pressure, and more particularly to a method of measuring the rate of change of blood pressure corresponding to each or successive heart beats.

Background

Measuring blood pressure is a basic method for understanding health conditions and observing disease conditions, and is especially necessary for middle-aged and elderly people with cardiovascular diseases. Blood pressure often fluctuates greatly during the day and even within a certain period of time, so that a single or small measurement cannot provide accurate and reliable data and enough useful information, and various change rates of blood pressure corresponding to heart beating cannot be calculated. Specifically, each heart beat generates a corresponding blood pressure value, that is, the blood pressure value is actually continuously changed like the heart rate and corresponds to one of the heart beats, so that the continuously measured blood pressure value can be called a blood pressure value sequence corresponding to the heart beat, and the rate of change of the blood pressure corresponding to each heart beat can be obtained by calculating the rate of change of the sequence.

Continuous measurement of blood pressure for a long time and calculation of the continuous change rate of blood pressure corresponding to each heart beat over a certain period of time are essential for monitoring some physiological state changes of human body such as illness, pathology, emotional state, etc., especially for some people whose physiological state changes frequently, such as athletes and busy people, etc.

Blood pressure measurement is mainly divided into invasive measurement and non-destructive measurement. Invasive measurement is a direct measurement method in which a catheter is inserted into the artery and arterial pressure is measured by a transducer connected to a fluid column. The method needs to be operated by professional medical staff, is high in cost, easily causes medical risks such as bacterial infection and blood loss, is not suitable for daily measurement and health care, and is even impossible to carry out continuous blood pressure measurement and continuous change rate calculation of blood pressure.

The non-destructive measurement method is an indirect measurement method, and mainly adopts three types of equipment: pulse sphygmomanometers, tone measuring sphygmomanometers, and sphygmomanometers based on the pulse wave transmission time.

There are two measurement methods of pulse sphygmomanometers: auscultatory methods and oscillatory methods. The auscultation method is based on the collection of the korotkoff sounds and the whole device comprises an inflatable cuff, a mercury manometer (in recent years also an electronic pressure transducer) and a stethoscope. When measuring the blood pressure of the upper limb, the air in the sleeve belt is exhausted, then the sleeve belt is flatly and non-wrinkled wound on the upper arm, the pulse of the brachial artery is groped, and the chest piece of the stethoscope is placed at the position. And opening a mercury column switch, moving the mercury column or the gauge needle when the cuff is inflated by the balloon with the movable valve, and stopping inflation when the mercury column rises to a default value. Then, slightly opening the balloon valve to slowly deflate, slowly descending the mercury column (turning the gauge needle), observing the scale of the mercury column or the gauge needle, and if the first sound of the brachial artery is heard, the scale is the systolic blood pressure, called systolic pressure for short; when the mercury drops to the point where the sound is suddenly weakened or inaudible, the scale indicates diastolic blood pressure, referred to as diastolic pressure for short. However, this method can only determine systolic and diastolic pressures and is not suitable for some patients with weak or even inaudible 5 th korotkoff sounds.

The oscillation method can make up for the above-mentioned deficiencies of the auscultation method to some extent, and the blood pressure can be measured for patients with weak Korotkoff sounds. When in use, the cuff is flatly and non-wrinkled wound on the upper arm, and the cuff is inflated and deflated. The blood pressure value is determined by measuring the amplitude of the oscillations of the pressure in the inflated cuff, which are caused by the constriction and dilation of the arterial blood vessel. The values of systolic, mean, and diastolic pressures can be obtained from monitoring the pressure in the cuff as the cuff is slowly deflated. The average pressure corresponds to the pressure in the attenuating device of the cuff at the moment of the peak of the envelope. The systolic pressure is generally estimated as the pressure in the attenuating device of the cuff at a time before the peak of the envelope corresponding to the time at which the amplitude of the envelope equals a certain proportion of the amplitude of the peak. The diastolic pressure is typically estimated as the pressure in the attenuating device of the cuff at a time after the peak of the envelope corresponding to the time when the amplitude of the envelope equals a certain proportion of the peak amplitude. The use of different ratio values may affect the accuracy of the blood pressure measurement.

Most products on the market at present adopt an auscultation method or an oscillation method. However, since both methods require inflation and deflation of the cuff, frequent measurements are difficult to achieve, and continuous measurements are less likely to be achieved. Furthermore, the frequency of measurements using the cuff is also limited by the time required to inflate the cuff and the time required to deflate the cuff when the measurements are taken. Typically, a complete blood pressure measurement takes about 1 minute. In addition, the size of the cuff size also has an effect on the measurement of blood pressure. Combining the above factors, the conventional auscultation method or oscillation method cannot continuously measure a plurality of blood pressure values, or even a sequence of blood pressure values corresponding to each heart beat, and thus cannot calculate the continuous change rate of the blood pressure corresponding to each heart beat in a certain period.

The basic principle of the tonometer is as follows: when the blood vessel is compressed by an external object, the circumferential stress of the blood vessel wall is eliminated, and the internal pressure and the external pressure of the blood vessel wall are equal. The artery is flattened by pressurizing the artery. The pressure at which the artery remained flat was recorded. This pressure is measured using an array of pressure sensors placed on the superficial arteries, from which the blood pressure of the patient is calculated. However, this method has disadvantages in that the cost of the sensor used is high, and the measurement accuracy is easily affected by the measurement position, so that it is not popular in the market. It is obvious that with this method, it is not possible to continuously measure a plurality of blood pressure values, and thus it is not possible to calculate a continuous variation trend of the blood pressure over a certain period of time.

The sphygmomanometer based on the pulse wave transmission time determines the blood pressure from the relationship between the arterial blood pressure and the pulse wave transmission speed. When the blood pressure rises, the blood vessel expands, the transmission speed of the pulse wave is increased, and conversely, the transmission speed of the pulse wave is reduced, and the specific contents can be seen in the following documents:

1) "The Velocity of The pulse Wave in Man" by Messers.J.C.Bramwell and A.V.Hill, published in The Proceedings of The Royal Society of London, p.298-306, 1922;

2) gribbin, a. steptoe, and p. sleight, "Pulse Wave Velocity as a Measure of Blood Pressure Change", "Psychophysiology" vol 13 first phase, pages 86-90 (Psychophysiology, vol.13, No.1), 1976.

Such sphygmomanometers are used by acquiring photoplethysmographic and electrocardiographic signals from a photosensor positioned at a fingertip or other peripheral tissue location. The method can provide a simple and easy-to-use blood pressure measuring device, and has the advantages of lower development cost (the cost can be reduced by more than half), small volume (about hundreds of times), less power consumption (about hundreds of times), long-time continuous measurement of arterial blood pressure and the like compared with the traditional cuff type sphygmomanometer. Before the blood pressure is measured by the sphygmomanometer adopting the method, the sphygmomanometer is calibrated by a standard sphygmomanometer, namely the relationship between the upper arm blood pressure and the pulse wave transmission time is found. Then, a plurality of blood pressure values can be continuously measured according to the relation between the determined blood pressure and the pulse wave transmission time. Therefore, the blood pressure measurement method based on the pulse wave transmission time can realize continuous blood pressure measurement in a certain time. But since the method using ecg signals requires simultaneous acquisition of signals on both fingers (or other parts). This still brings certain inconvenience to the measurement, and it is also difficult to realize a long-time continuous measurement in a true sense.

The method for measuring blood pressure based on the characteristic parameters of the photoplethysmography signals only needs to acquire signals from one finger (or other parts), so that great convenience can be provided for measurement, and long-time nondestructive continuous measurement can be truly realized. However, no technique has been known for specifically determining the blood pressure or the continuous change rate of the blood pressure corresponding to one or several heart beats by using such a measurement method. In the present specification, the blood pressure corresponding to several heart beats is an average value of the blood pressures corresponding to the several heart beats. Thus, the continuous measurement of blood pressure and its rate of change corresponding to each or several heart beats remains a blank.

Disclosure of Invention

It is an object of the present invention to provide a method for obtaining a continuous rate of change (including an absolute rate of change and a relative rate of change) of blood pressure corresponding to each or every several heart beats over an arbitrary period of time through continuous blood pressure measurement, thereby providing new useful information for medical and health care.

To achieve the above object, the present invention provides a method of measuring a blood pressure parameter corresponding to one or more heart beats, comprising the steps of: a) collecting a signal related to a pulse wave from a human body; b) acquiring characteristic parameters from the acquired signals to obtain a corresponding characteristic parameter sequence; c) from the determined sequence of characteristic parameters of the signal, a blood pressure parameter corresponding to each or a plurality of heart beats is determined.

In the above method, the blood pressure parameter may include: blood pressure value, continuous rate of change of blood pressure, instantaneous rate of change of blood pressure, and rate of change of a plurality of blood pressure values corresponding to each (or several) heart beats.

The continuous blood pressure change rate is the change rate of the measured continuous blood pressure value. Continuous blood pressure values refer to a sequence of blood pressure values corresponding to each or several heart beats measured continuously over a certain time. And the sequence obtained by measuring one blood pressure value at intervals is called the blood pressure value of discontinuous measurement. The determination of the continuous change rate of the blood pressure is mainly solved in the invention.

The algorithm in which the continuous rate of change of blood pressure may include an absolute rate of change of blood pressure and/or a relative rate of change of blood pressure. The method of calculating the absolute rate of change of blood pressure may include time domain and frequency domain methods.

When a time domain approach is employed, one of the following approaches may be employed to determine the rate of change of blood pressure:

let T ═ T₁，t₂，t₃，……t_n}^TRepresenting a sequence of blood pressure values, T representing the mean of the sequence T, T₁＝{t₁′，t₂′，t₃′，……t_n-1′}^T＝{t₂-t₁，t₃-t₂，t₄-t₃，……t_n-t_n-1T' denotes the sequence T₁Average value of (a). )

(Standard deviation of sequence T)

(sequence T)₁Standard deviation of (2)

The frequency domain method is to perform fourier transform (or other time domain to frequency domain transform) on the sequence T to obtain the frequency spectrum of the sequence T.

The calculation method of the relative change rate of the blood pressure can be expressed as follows: (± absolute rate of change in blood pressure ÷ mean blood pressure) × 100%.

The instantaneous blood pressure rate of change is the slope of any point on a continuous waveform that reflects the change in blood pressure over time, i.e., dP/dt, where P represents the instantaneous blood pressure value. The continuous waveform of the blood pressure variation with time can be obtained by extracting characteristic parameters from signals related to the generation and transmission characteristics of the pulse wave and estimating. The algorithm for the instantaneous blood pressure change rate may include an instantaneous blood pressure relative change rate (dP/dt/P) and an instantaneous blood pressure absolute change rate (| dP/dt |).

The rate of change of the blood pressure value corresponding to each (or several) heart beats refers to the change between two consecutive blood pressure values corresponding to each (or several) heart beats. It may be the relative rate of change of blood pressure or the absolute rate of change of blood pressure, depending on the calculation method used. For example, if a method of dividing the difference between the two blood pressure values by the average of the two blood pressure values and multiplying by 100% is adopted, the instantaneous rate of change is a relative rate of change; if the method of dividing the absolute difference between the two blood pressure values by the time of the interval between the two blood pressure values is adopted, the instantaneous change rate is the absolute change rate.

Therefore, in the present invention, the continuous rate of change of blood pressure, the instantaneous rate of change of blood pressure, and the rate of change of blood pressure corresponding to each (or several) heart beats are three concepts in parallel. The relative change rate of the blood pressure and the absolute change rate of the blood pressure refer to a specific change rate calculation method.

In addition, the pulse wave is a fluctuation signal generated by contraction and expansion of the heart or a signal related to blood flow caused by the beating of the heart.

In a preferred embodiment of the invention, the pulse wave is measured by photoplethysmography, i.e. using a photoelectric sensor to acquire photoplethysmographic and electrocardiographic signals from the peripheral tissues of the human body. From the acquired photoplethysmograph signal, the start point and corresponding vertex of each waveform are determined, and a segment between the start point and vertex is intercepted as one of the characteristic parameters of the photoplethysmograph signal, which may be referred to as FY pitch. The FY interval segment may take the entire time from the start point to the vertex, or a partial segment thereof. E.g., a period of time from the start point to 90% of the vertex, a period of time from the start point to 80% of the vertex, etc., and so on.

In the above scheme, the relationship between FY interval and blood pressure can be determined by: blood pressure m, FYⁿ+ c, n ≠ 0, where FY denotes the FY interval, and m and c denote calibration coefficients obtained by calibrating different subjects with a standard sphygmomanometer, that is, the correlation coefficient between the upper arm blood pressure and the FY interval. During calibration, the contact pressure between the sensor and the measured position of the body is properly changed, and the calibration is completed under different contact pressure values.

In addition, when it is necessary to further improve the accuracy of blood pressure measurement, a blood pressure value can be calculated from the determined sequence of FY intervals in combination with the pulse wave transit time and another characteristic parameter YG interval of the photoplethysmography signal. The calculation formula is as follows: blood pressure m, FYⁿ+a/PTT²+ b.YG + d, n ≠ 0, where a ∈ [0, m/2]]，b∈[0，m/5]。

The step a) may include: determining corresponding waveform feature point positions of a series of collected signals related to pulse wave generation and transmission time; and determining one or several pulse wave transmission times corresponding to one or several heart beats according to the determined waveform characteristic points of the signals.

In the above method, for the photoplethysmograph signal, the waveform feature points are the top and/or bottom points of the waveform; for the electrocardiosignal, the waveform characteristic points are R wave top points and/or R wave starting points and/or R wave ending points, and any characteristic points on Q waves, S waves and T waves. In this case, the pulse wave transit time series can be obtained using the time difference between the apex time of the electrocardiographic signal or the nadir of the photoplethysmograph signal or using the time difference between the apex time of the electrocardiographic signal or the apex of the photoplethysmograph signal.

The present invention may further include obtaining a continuous rate of change of the blood pressure by a method that embodies a trend of change of the sequence of values based on the sequence of blood pressure values corresponding to each or several heart beats. The specific method may be one of the time domain or frequency domain methods of determining the rate of change already described above.

In another preferred embodiment of the present invention, the step of determining the relatively continuous rate of change of blood pressure may reflect the relative trend of change of the blood pressure value sequence corresponding to one or several heart beats by the relative trend of change of the FY interval sequence corresponding to one or several heart beats and the relative trend of change of the YG interval using the relationship between the FY interval, the YG interval, the blood volume and the blood pressure. That is, the relative percentage of fluctuation of the blood pressure values corresponding to the fluctuation of one or more FY intervals and the relative percentage of change of the YG intervals and the blood volume in a certain period can be reflected to reflect the relative trend of the blood pressure change in a certain period.

The blood volume amount can be found by using the waveform area of the photoplethysmograph signal (including the area of the rising edge of the waveform, the area of the falling edge of the waveform, and the area of the entire waveform).

The relationship between the FY pitch, the YG pitch, the blood volume and the blood pressure is as follows: blood pressure m, FYⁿ+ a, YG + b, SV + c, n is not equal to 0, wherein m and c represent calibration coefficients obtained by calibrating different testees by using a standard sphygmomanometer, namely, represent the relation coefficients between the upper arm blood pressure and the FY spacing, the YG spacing and the blood volume, the FY is represented by the FY spacing table, YG represents the YG spacing, SV represents the blood volume, a, b and m are constants, and a belongs to [0, m/2]]，b∈[0，m/5]。

The blood pressure calculation may also ignore the effect of heart rate when the rate of change of heart rate is less than a certain threshold over a specified period of time. In this case, a may be 0.

According to yet another embodiment of the present invention, the method of directly determining the continuous rate of change of blood pressure may comprise: determining the FY pitch rate, the YG pitch rate and the blood volume rate; the continuous change rate of the blood pressure corresponding to one or more heart beats is determined based on the determined FY pitch change rate, YG pitch change rate and blood volume change rate and on the relational expression between the blood pressure and these parameters.

Determining the FY pitch change rate FYV, the pulse wave transit time change rate PTTV, the YG pitch change rate YGV, or the blood volume change rate VR using a time domain method or a frequency domain method, wherein

The time domain method determines FYV for any of the following equations:

let T ═ T₁，t₂，t₃，……t_n}^TRepresenting the FY interval sequence, the pulse wave transmission time sequence, the YG interval sequence, or the blood volume sequence, T represents the average value of the sequence T, T₁＝{t₁′，t₂′，t₃′，……t_n-1′}^T＝{t₂-t₁，t₃-t₂，t₄-t₃，……t_n-t_n-1T' denotes the sequence T₁Average value of (a).

1) FYV, PTTV, YGV or

2) FYV, PTTV, YGV or

3) FYV, PTTV, YGV or

The frequency domain method comprises the following steps: and carrying out Fourier transform or other time domain to frequency domain transform on the sequence T to obtain the frequency spectrum of the sequence T.

In the above method of the present invention, the frequency domain method may further include: the method comprises the steps of finding out a very low frequency change rate, a low frequency change rate and a high frequency change rate in a continuously changing frequency spectrum of a obtained sequence T (such as a blood pressure value sequence, and the corresponding frequency spectrum is called a blood pressure frequency spectrum), and determining physiological conditions corresponding to the very low frequency change rate, the low frequency change rate and the high frequency change rate of the blood pressure frequency spectrum respectively.

The extremely low frequency change rate, the low frequency change rate and the high frequency change rate of the blood pressure frequency spectrum are defined by adopting an area method, namely the area of each frequency component is compared with the total area of the frequency spectrum to determine the change of each frequency component, so that the change of the physiological state related to the change of each frequency component is reflected.

In addition, the method for defining the ultralow frequency change rate, the low frequency change rate and the high frequency change rate of the blood pressure frequency spectrum comprises the following steps:

ultra-low frequency rate of change: the area of the blood pressure frequency spectrum/the total area of the blood pressure frequency spectrum within the range of 0-0.003 Hz;

very low frequency rate of change: the blood pressure frequency spectrum area/total area of the blood pressure frequency spectrum within the range of 0.003-0.04 Hz;

low frequency rate of change: the area of the blood pressure frequency spectrum/the total area of the blood pressure frequency spectrum within the range of 0.04-0.15 Hz;

high frequency rate of change: the area of the blood pressure frequency spectrum/the total area of the blood pressure frequency spectrum within the range of 0.15-0.4 Hz.

In addition, in all of the above related methods, pulse wave transit time (PTT) may be used instead of FY interval for estimation of blood pressure or rate of change of blood pressure.

The invention can be used for carrying out long-time continuous blood pressure measurement on middle-aged and old people with cardiovascular diseases and people with frequent changes of physiological states, such as athletes, busy people and the like, and further obtaining the continuous change rate of the blood pressure corresponding to each heart beat in the time period so as to reflect the change of the physiological state or emotional state of the human body and even reveal state changes which are difficult to be perceived, thereby providing enough useful information for medical treatment and health care.

Brief description of the drawings

The above objects, advantages and features of the present invention will become more apparent from the following description of the embodiments of the present invention taken in conjunction with the accompanying drawings. The drawings comprise:

FIG. 1 is a flow chart for explaining a method of measuring a continuous rate of change in blood pressure;

FIG. 2 is a flow chart for illustrating the determination of the rate of change of blood pressure;

FIG. 3 is a diagram illustrating how the ECG signal and the PPG signal are used to define FY intervals, pulse wave transit times, and various feature points on the PPG signal;

FIG. 4 is a diagram for explaining the fluctuation of the pulse wave transmission time over a short period of time;

FIG. 5 is a view for explaining the fluctuation of blood pressure during the day;

FIG. 6 is a diagram for explaining fluctuation of a blood pressure value corresponding to each heart beat over a short period of time;

FIG. 7 is a graph for illustrating fluctuations in blood pressure values over a short period of time corresponding to every five heart beats;

FIG. 8 is a graph illustrating the frequency spectrum of blood pressure values over a short period of time corresponding to each heart beat;

FIG. 9(a) is a graph illustrating the fluctuation of the FY interval corresponding to each heart beat in the photoplethysmograph signal over a short period of time, and FIG. 9(b) is a frequency spectrum corresponding thereto;

FIG. 10 illustrates a detailed definition of the spacing and amplitude of various features on a photoplethysmograph signal;

fig. 11 is a diagram for explaining a comparison between the blood pressure value estimated by the FY interval and the true value (n ═ 2).

Detailed Description

FIG. 1 is a flow chart of a method of measuring a continuous rate of change of blood pressure in accordance with one embodiment of the present invention. As shown in fig. 1, in this embodiment of the present invention, the method mainly includes a step 101 of acquiring signals from a human body, a step 102 of preprocessing the signals, a step 103 of determining corresponding waveform feature points in the signals, a step 104 of determining FY intervals, pulse wave transit time and YG interval sequences, a step 105 of determining FY interval change rate (FYV), pulse wave transit time change rate (PTTV), heart rate change rate (HRV), and blood volume change rate (VR), a step 106 of directly calculating blood pressure change rate (BPV) based on the determined parameters of FY v, PTTV, HRV, and VR, a step 107 of calculating relative change rate of blood pressure, a step 108 of calculating blood pressure using FY intervals (or combining other parameters), and a step 109 of calculating blood pressure change rate from the blood pressure value sequences.

The respective steps will be described in detail below.

● step 101: signal acquisition

This step 101 comprises acquiring a pulse wave-related signal, such as an electrocardiographic signal or a photoplethysmographic signal, from a peripheral portion (e.g. a finger, an earlobe, a toe, etc.) or other non-peripheral portion (including a wrist, a thigh, etc.) of a human body using a certain sensor, thereby determining a pulse wave-related characteristic parameter, such as a pulse wave transit time. The time of signal acquisition can be as desired. For technical details of such signal acquisition methods, reference may be made to:

1) "Variability of photoplethysmograph pulses measurements at the ears, thumbs and toes," published in IEEE Proceedings of science, measurements and Technology (IEEE science, measurements and technical exchange), volume 147, page 403-;

2) "comprehensive of regional variability in the pulse wave characteristics of multipoint photoplethysmography", published in First International conference on Advances in Medical Signal and Information Processing (pages 26-31, 2000);

3) chan, K.W., Hung, K.K., Zhang, Y.T. "Noninivance and clinical measurements of blood pressure for telemedicine", published in Proceedings of the 23rd Annual International conference of the IEEE Engineering in Medicine and Biology Society (the 23 nd International Annual meeting Collection of the IEEE medical and biological Society Engineering), Vol.4, p.3592, 3593, 2001. Etc. of

● step 102: signal pre-processing

This step 102 includes preprocessing such as noise removal and smoothing of a series of signals acquired in step 101 with respect to the pulse wave transit time. Of course, whether or not pre-processing is performed depends on the quality of the acquired signal and the functionality of the associated hardware. The noise removal is mainly performed by filtering the signal, and the smoothing process may be performed by, for example, subdividing the signal into segments and replacing the values of the points in each segment with the average value of the segment. The signal preprocessing methods can adopt the existing technology, and are not described in detail here.

● step 103: determining corresponding waveform feature points in a signal

This step 103 is used to determine the FY pitch intercept method of the photoplethysmography signal and the corresponding waveform landmark positions between a series of signals related to the pulse wave transit time. Specifically, the physiological significance of certain points of the signal can be used to determine whether to use the points to calculate the pulse wave transmission time, as shown in fig. 3. Corresponding parameters such as FY interval, YG interval, and pulse wave transmission time can be defined. For example, the method for intercepting the FY pitch segment includes: the entire time from the start point to the vertex, the time from the start point to 90% of the vertex, the time from the start point to 80% of the vertex, and so on. The pulse wave transmission time calculation method comprises the following steps: for a photoplethysmograph signal, the waveform feature points may include the apex, the base, and any point in between the two points of the waveform. For the electrocardiosignal, the waveform characteristic points can comprise an R wave vertex, an R wave starting point, an R wave ending point and other arbitrary characteristic points on the R wave, as well as arbitrary characteristic points on the Q wave, the S wave and the T wave.

● step 104: determining FY spacing, pulse wave transit time, and YG spacing sequences

In step 104, each FY interval, YG interval, and pulse wave transit time are calculated by a predetermined method based on the respective waveform feature points of the signals determined in step 103.

Fig. 3 illustrates how characteristic points F, Y, G, etc. of the photoplethysmograph signal in the signal and corresponding pulse wave waveform characteristic points are determined, and the FY interval, the YG interval, and the pulse wave transit time are calculated using the determined waveform characteristic points. The pulse wave transmission time is defined by the electrocardio signals and the photoplethysmography signals. As shown in fig. 3(a), time 301 represents the position of the vertex of the R-wave on the electrocardiographic signal on the time axis, and time 302 and time 303 represent the positions of a bottom point and a vertex on the photoplethysmograph signal on the time axis, respectively. These time values can be used to determine the pulse wave transit time in different ways. One way to determine this is to calculate the time difference between time 301 and time 302 to obtain the pulse wave transit time Ts 304. Another determination method is to calculate the time difference between the time 301 and the time 303 to obtain the pulse wave transmission time Td 305.

Since either Td 304 or Td 305 is calculated from the characteristic points of the different photoplethysmograph signals, the information they convey is both physiologically and numerically different. The individual characteristic points of the photoplethysmograph signal are defined as follows: 1) f309: the starting point of the rapid rise of the waveform amplitude (or the turning point of the waveform amplitude from the fall to the rapid rise); 2) y310: the highest point of the waveform amplitude; 3) w311: the first inflection point of the falling edge of the waveform (for signals without this inflection point, point W is defined as the point on the falling edge of the waveform that reaches 50% of the highest amplitude of the waveform); 4) g312: the first lowest amplitude point on the falling edge of the waveform, as indicated by G313 in FIG. 3 (b); or the point on the falling edge of the waveform up to 1% of the maximum amplitude of the waveform, as shown at G312 in FIG. 3 (b); or a point coincident with point F, as shown in fig. 3(b) at g (F)314 (different definitions depend on different signals). Wherein the FY interval is defined by the photoplethysmograph signal, as shown in fig. 3(a), the method for truncating the FY interval segment includes: the entire period of time FY307 from the start point to the vertex may also include the period of time FY308 from the start point to 50% of the vertex, and so on.

The pulse wave transmission time series described by Td 305 or Td 306, and the FY intervals and YG intervals determined by F309, Y310, and G312 are obtained by a plurality of calculations.

If the calculation of the relative change rate of the blood pressure is not carried out at this time, the step 105 is entered to determine FYV, PTTV, HRV and VR and further determine BPV; otherwise, the relative rate of change of blood pressure is calculated (step 107).

● step 105: determining FYV, PTTV, YGV and VR

This step 105 is used to calculate the FY interval rate of change (FYV), the rate of change of pulse wave transit time (PTTV), the YG interval rate of change (YGV), and the rate of change related to blood Volume (VR) using a time and frequency domain rate of change analysis. For example, the specific method may be:

when the frequency domain method is adopted, let T ═ T₁，t₂，t₃，……t_n}^TRepresenting the FY interval sequence, or the pulse wave transit time, or the YG interval, T representing the average of the sequence T, the corresponding rate of change FYV, PTTV, or YGV can be calculated using any of the following equations.

1) FYV, PTTV or(Standard deviation of sequence T)

In addition, let T₁＝{t₁′，t₂′，t₃′，……t_n-1′}^T＝{t₂-t₁，t₃-t₂，t₄-t₃，……t_n-t_n-1T' denotes the sequence T₁Average value of (a). The above-mentioned rate of change can also be obtained by the following calculation:

2) FYV, PTTV or

3) FYV, PTTV or(sequence T)₁Standard deviation of (2)

In addition, a frequency domain algorithm may be adopted for the sequence T or T₁A fourier transform (or other time-to-frequency domain transform) is performed to obtain the spectrum of the sequence T.

Where the frequency domain analysis mainly involves several frequency components: very low frequency components (including ultra low frequency components) between about 0 Hz and about 0.04 Hz; a low frequency component of about 0.04 to 0.15 Hz; and a high frequency component of about 0.15 to 0.4 Hz. The amplitude, area, etc. over the spectrum can be calculated to obtain the corresponding rate of change.

Fig. 4 exemplarily illustrates a case of a pulse wave transit time change rate PTTV corresponding to a pulse wave transit time series corresponding to one or more heart beats. As shown in fig. 4, the length of the continuous recording of the signals is about 5 minutes, so that a pulse wave transmission time series corresponding to each heart beat and a pulse wave transmission time series corresponding to every five heart beats can be obtained.

Although the present invention is not strictly limited to the number of heart beats, the number of heart beats is too large to reflect some rapid blood pressure changes, i.e., the high frequency component of the rate of blood pressure change will not be reflected, so the number of heart beats is preferably smaller. The time length of the continuous recording of the signal depends on the time needed to be monitored by the tested person, so that the change conditions such as illness state in the time period can be reflected. The length of time for continuous recording is unlimited.

The change rate 401 and the change rate 402 in fig. 4 are respectively the standard deviations of the corresponding pulse wave transmission time series. Fig. 4(a) shows the pulse wave transit time corresponding to each heart beat, and fig. 4(b) shows the pulse wave transit time corresponding to each five heart beats, i.e., each value of the sequence is an average of every five values shown in fig. 4 (a). As shown in the figure, the pulse wave transmission time series of the example shown by fig. 4(a) and 4(b) has a large fluctuation between 0.3 seconds and 0.34 seconds. Let T ═ T₁，t₂，t₃，……t_n}^TRepresenting the pulse wave transmission time sequence, T represents the average value of the sequence T, and the change rate PTTV 401 and the change rate PTTV 402 can be obtained by any one of the above calculation formulas 1) -3), or the PTTV is calculated by using a frequency domain analysis method, i.e., fourier transform (or other time domain to frequency domain transform) is performed on the sequence T to obtain the frequency spectrum of the sequence T. And analyzing the frequency components to find out the corresponding physiological parameters and the represented physiological conditions.

Wherein, the analysis of the frequency components mainly comprises: the signal is observed through the frequency spectrum, and significant components exist in the frequency bands, so that the area of the corresponding frequency band or the ratio of the area of the corresponding frequency band to the total area of the frequency spectrum can be calculated, and the physiological parameters corresponding to the frequency band and the represented physiological conditions can be reflected. For example, the activity status of sympathetic nerve and parasympathetic nerve can be reflected by calculating the area or the ratio of the area of the frequency band of 0.04-0.15Hz in the frequency spectrum of the heart rate; while a frequency component of 0.15-0.4Hz may reflect respiration and parasympathetic activity.

Similarly, the YG pitch change rate YGV (see above) and the blood volume change rate (VR) can be calculated by a method embodying the trend of the numerical sequence. The calculation method can still be realized by the above equations 1) to 3) or by frequency domain analysis.

In addition, in the invention, the heart rate signal can be obtained by an electrocardiosignal or a photoelectric volume signal; the blood volume sequence can be extracted from the waveform area of the photoplethysmograph signal, including the area of the rising edge of the waveform, the area of the falling edge of the waveform, and the area of the entire waveform. After the heart rate sequence and the blood volume sequence are obtained, the calculation method of the change rate can also adopt the calculation method of the time domain and the frequency domain.

Furthermore, the calculation of the blood volume rate of change (VR) can also be derived from a sequence of waveform areas of the photoplethysmographic signal.

For example, in the case of calculating the whole area sequence, since the photoplethysmography signal has a more regular waveform, each single waveform can obtain an area value, that is, the area value of the waveform can be obtained from the starting point of one waveform to the starting point of the next waveform, so as to obtain a sequence of waveform areas, and the change rate can be calculated by the above method, or the blood volume change rate can be obtained by performing differential derivation on the area sequence.

● step 106: the blood pressure rate of change BPV is determined. BPV generally refers to the continuous rate of change of blood pressure and may include the relative rate of change of blood pressure as well as the absolute rate of change of blood pressure.

This step 106 directly calculates the absolute blood pressure change rate BPV using the FY interval change rate (FYV), the YG interval change rate (YGV), and the relational expression between the blood volume change rate (VR) and the BPV obtained in step 105. Fig. 2 is a flowchart for explaining the above-described calculation of the blood pressure change rate. In step 201, the FY pitch rate (FYV), the YG pitch rate (YGV), and the blood Volume Rate (VR) are calculated according to the method described in step 105.

The relation for calculating BPV may be expressed as BPV ═ f (FYV, YGV, VR, c) or BPV ═ f (PTTV, YGV, VR, c), the specific form of f () depending on the specific method of determining the rate of change, based on the relationship between blood pressure and FY or PTT, HR and SV: blood pressure m, FYⁿ+ a, YG + b, SV + c or blood pressure m/PTT²+ a.YG + b.SV + c, n ≠ 0. Wherein m and c represent calibration coefficients obtained by calibrating different testees by using a standard sphygmomanometer, namely representing the relation coefficients between the upper arm blood pressure and the FY distance, the YG distance and the blood volume, the FY table type FY distance, PTT represents the pulse wave transmission time, YG represents the YG distance, SV represents the blood volume, a, b and m are constants, and a belongs to [0, m/2]]，b∈[0，m/5]. And can be derived according to a specific change rate method. These constants can be determined using a calibration method, i.e. using one or several measurements made with conventional standard instruments as a standard.

For example, if BP ═ m · FY²+ c (where m and c represent calibration coefficients obtained by calibrating a standard sphygmomanometer to various subjects), can be obtained by simple mathematical derivationBy analogy, when the calculation formula of the blood pressure comprises a plurality of parameters: FY, YG, and SV, the corresponding BPV ═ f (FYV, YGV, VR, c) can also be obtained.

Further, it may be determined whether the heart rate change rate HRV (standard deviation) over a specified period of time is greater than a certain threshold Th. The threshold may be determined by calculating a ratio of the standard deviation of the heart rate variation to the heart rate mean over a specified time period, and if the ratio is less than 3%, the effect of the heart rate variation rate HRV may be ignored. If so, the BPV is calculated using the above equation (step 203); otherwise, the blood pressure rate of change is calculated by neglecting the effect of the heart rate of change HRV, which is calculated by the equation BPV ═ f (PTTV, VR, c) (step 204).

The relative percentage of fluctuation of the blood pressure value corresponding to the relative percentage of fluctuation of one or more FY intervals and the relative change percentage of parameters such as YG intervals and blood volume in a certain period of time can be reflected, so that the relative change trend of the blood pressure in a certain period of time can be reflected, and the absolute change rate of the blood pressure value can not be reflected. This is because the fluctuation tendency of the blood pressure values is a linear superposition of the fluctuation tendencies of the parameters such as the FY interval, the YG interval, and the blood volume, and therefore the fluctuation tendency of the pulse wave transmission time and the heart rate is known, that is, the fluctuation tendency of the blood pressure can be roughly determined.

● step 107: calculating the relative rate of change of blood pressure

This step 107 includes calculating the relative rate of change of blood pressure using the relationship between the pulse wave transit time and the blood pressure (systolic pressure and diastolic pressure), which can be expressed as:

blood pressure m, FYⁿ+ a, YG + b, SV + c or blood pressure m/PTT²+a·YG+b·SV+c，

Wherein n ≠ 0, m and c represent calibration coefficients obtained by calibrating different testees by adopting a standard sphygmomanometer, namely represent the relation coefficients between upper arm blood pressure and FY spacing, YG spacing and blood volume, FY tabular FY spacing, YG represents YG spacing, SV represents blood volume, a, b and m are constants and a belongs to [0, m/2], b belongs to [0, m/5 ].

Based on this relational expression, the relative change rate of the blood pressure value sequence corresponding to each (or several) heart beats can be reflected by the relative change rate of the parameters such as the FY interval, the YG interval, and the blood volume without calibration. I.e., the relative percentage of fluctuation of the blood pressure values corresponding to the relative percentage of fluctuation of each (or several) FY interval and the relative percentage of change of parameters such as YG interval and blood volume in a certain period of time.

Fig. 6 and 7 are used to illustrate the relative fluctuation of blood pressure values. Fig. 6(a) shows the variation of the sequence of systolic blood pressure values corresponding to each heart beat over five minutes. As can be seen from fig. 6(a), even in a short 5 minutes, the systolic pressure corresponding to each heart beat fluctuates largely between 110mmHg and 118 mmHg.

It should be noted that fig. 6 and 7 only show the fluctuation of blood pressure, i.e. the value sequence obtained by subtracting the average value from the original sequence. The rate of change 601 is the standard deviation of the sequence of systolic blood pressure values. Fig. 6(b) shows the variation of the diastolic blood pressure value sequence corresponding to each heart beat within five minutes. As can be seen from fig. 6(b), within 5 minutes, the diastolic pressure corresponding to each heart beat fluctuates greatly between 68mmHg and 73mmHg, and the rate of change 602 is the standard deviation of the diastolic pressure value sequence. Let BP be { P ═ P₁，P₂，P₃，……P_n}^TThe sequence of blood pressure values corresponding to each heart beat is shown, P represents the average value of the sequence BP, and the rate of change 601 and the rate of change 602 can be obtained by the following calculation formula:

formula 4:

fig. 7 illustrates the fluctuation of the blood pressure value corresponding to every five heart beats over a short period of time.

Fig. 7(a) shows the variation of the sequence of systolic blood pressure values corresponding to every five heart beats over five minutes. As can be seen from fig. 7(a), the systolic pressure corresponding to each heart beat also fluctuates greatly between 110mmHg and 117mmHg, and the variation rate 701 is the standard deviation of the systolic pressure value sequence. Fig. 7(b) shows the case where the sequence of diastolic blood pressure values corresponding to every five heart beats changes within five minutes. As can be seen from fig. 7(b), within 5 minutes, the diastolic pressure corresponding to each heart beat fluctuates greatly between 68mmHg and 73mmHg, and the variation rate 702 is the standard deviation of the diastolic pressure value sequence. The method of calculating the rate of change 701 and the rate of change 702 is described above in equation 4.

● step 108: calculating blood pressure using FY spacing (or in combination with other parameters)

Blood pressure m, FYⁿ+ c, n ≠ 0, where m and c represent calibration coefficients obtained by calibrating different subjects with a standard sphygmomanometer, that is, represent the relationship coefficients between the upper arm blood pressure and the FY pitch, and FY represents the FY pitch. During calibration, the contact pressure between the sensor and the measured position of the body is properly changed, and the calibration is completed under different contact pressure values.

In addition, when it is necessary to further improve the accuracy of blood pressure measurement, the following method can be adopted to determine the pulse wave transmission time and another characteristic parameter YG interval of the photoplethysmography signal (which is defined as shown in fig. 10) according to the determined FY interval sequence: blood pressure m, FYⁿ+a/PTT²+ b.YG + d, where a ∈ [0, m/2]]，b∈[0，m/5]。

● step 109: calculating blood pressure rate of change from a sequence of blood pressure values

The corresponding blood pressure value sequence of each (or a plurality of) heart beats measured by using the FY interval (or combining other parameters) is calculated and analyzed by a certain time domain and frequency domain change rate analysis method. The above-described method can be used to obtain the variation trend of blood pressure in a certain period of time to reflect the corresponding change of physiological status.

Fig. 5 is a diagram for explaining the absolute change in blood pressure during one day (from about 8 am to about 4 pm). As shown in FIG. 5, the systolic and diastolic pressures vary significantly at different times of the day or under different conditions. The blood pressure 501 at the time of driving to work corresponds to around 9 am, during which period and in which state both the systolic and diastolic blood pressure are at relatively low values during the day. The blood pressure 502 at the preparation time corresponds to around 11 am, during which period and in which state both the systolic and diastolic blood pressure are at relatively high values during the day. The blood pressure 503 at meal outing corresponds to around 12 am, during which time and in which state the systolic pressure and the return fall again to relatively low values during the day; although there is some fall back in diastolic pressure, the magnitude of the fall back is not as great as systolic pressure. The blood pressure 504 while the office is working busy corresponds to around 2 pm, during which time and in which state the systolic pressure rises again to a relatively high value during the day; while the diastolic pressure is relatively stable and does not change significantly. The blood pressure 505 in class corresponds to about 3 pm, and the systolic pressure in this period and state falls back to a relatively high value in a day, although it is higher than that in the case of busy office work; the diastolic pressure is also at a relatively high value during the day, which is higher than the diastolic pressure when the office is busy.

Furthermore, the invention can observe ultralow frequency, low frequency and high frequency components from the frequency spectrum of the blood pressure, thereby defining the change rate of each frequency component and better reflecting the change of the physiological state related to the change rate. The definition method of the frequency change rate mainly includes an area method, etc., that is, the area ratio of each frequency component to the total area of the spectrum determines the change of each frequency component.

Fig. 8 serves to illustrate the frequency spectrum of the blood pressure values corresponding to each heart beat measured in accordance with the method of the invention over a short period of time. Fig. 8(a) shows the frequency spectrum of the systolic pressure corresponding to each heart beat, with 3 more prominent frequency components 801, 802, and 803. 801 is a very low frequency component (including an ultra-low frequency component) which is approximately between 0 and 0.04 Hz; 802 is a low frequency component, approximately between 0.04-0.15 Hz; 803 is a high frequency component, and is between about 0.15Hz and about 0.4 Hz. Fig. 8(b) shows the spectrum of the diastolic pressure corresponding to each heart beat, in which there are also 3 frequency components 804, 805, and 806 that coincide with the frequency components in (a). These frequency components have important physiological significance and can be associated with sympathetic, parasympathetic activity, respiratory motion, and the like, respectively.

Fig. 9 is a diagram illustrating the fluctuation of the FY interval of the photoplethysmograph signal over a short period of time and its corresponding frequency spectrum. Fig. 9(a) shows fluctuations in FY spacing within 1 minute, ranging within approximately ± 0.03 seconds. Fig. 9(b) is a frequency spectrum corresponding to the FY pitch sequence shown in fig. 9 (a). Two frequency components can be clearly seen in fig. 9 (b): approximately around 0.05Hz and around 0.3 Hz. These two frequency components may be associated with sympathetic, parasympathetic activity, and respiratory motion, respectively. Therefore, the FY interval also contains frequency components similar to the heart rate and the blood pressure, and can represent important physiological significance.

Fig. 10 is a diagram illustrating specific definitions of various feature spacings and amplitudes on a photoplethysmograph signal, including FY spacing 1001, YW spacing 1002, WG spacing 1003, GF spacing 1004, FG spacing 1007, FY amplitude 1005, and YW amplitude 1006. Wherein F, Y, W and G are defined as described in FIG. 3. The representation of the FY pitch may also include any segment in the FY pitch 1001.

Fig. 11 is a diagram for explaining a comparison of a blood pressure value estimated by the FY interval with a true value (n ═ 2) according to the present invention. The estimation equation may be: blood pressure m, FY²+ c, where m and c represent calibration coefficients obtained by calibration with a standard sphygmomanometer for different subjects, that is, represent the relationship coefficient between the upper arm blood pressure and the FY interval, and FY represents the FY interval. During calibration, the pressure between the sensor and the contact end of the body is appropriately changed and selectedThe calibration is performed under different pressure values. FIG. 11(a) shows a comparison of estimated systolic pressure with true values, with 7 measurements taken at 7 different pressure values on the abscissa and the values of systolic pressure on the ordinate; the mean error of the measurement was only-1.8 mmHg, while the standard deviation was 2.4 mmHg. FIG. 11(b) is a graph showing the comparison of the estimated diastolic pressure with the true value for the same subject, wherein 7 different pressure values indicated on the abscissa thereof correspond to the respective pressure values in FIG. 11(a), respectively; the mean error of the measurement was only-2.2 mmHg, while the standard deviation was 3.3 mmHg.

The preferred embodiments of the present invention have been described in detail for illustrative purposes, but those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A method of measuring a blood pressure parameter corresponding to one or more heart beats, comprising the steps of:

a. collecting a signal related to a pulse wave from a human body;

b. acquiring characteristic parameters from the acquired signals to obtain a corresponding characteristic parameter sequence;

c. from the determined sequence of characteristic parameters of the signal, a blood pressure parameter corresponding to each or a plurality of heart beats is determined.

2. The method of claim 1, wherein the blood pressure parameters comprise: blood pressure values, relative and/or continuous rates of change of blood pressure, instantaneous rates of change of blood pressure, and rates of change of blood pressure corresponding to each heart beat.

3. The method according to claim 2, wherein the pulse wave-related signal is a pulse wave-related signal related to generation and transmission characteristics of the pulse wave, including a fluctuation signal generated by contraction and expansion of the heart, or a signal related to blood flow caused by the beating of the heart.

4. The method according to claim 3, wherein the pulse wave is measured by a light sensor, a pressure sensor, an acoustic sensor, a photoelectric sensor, an acceleration sensor, a displacement sensor, or an electrode.

5. The method according to claim 1, wherein said step a employs a photoplethysmography method for acquiring a photoplethysmography signal related to a transit time of a pulse wave, and said step b further comprises:

determining a starting point and a corresponding vertex of each waveform from the acquired photoplethysmograph signal, and intercepting a section between the starting point and the vertex as an FY spacing, wherein the FY spacing is one of characteristic parameters of the photoplethysmograph signal,

wherein the FY pitch comprises: the whole time from the starting point to the vertex or the partial time thereof.

6. The method of claim 5, wherein step c further comprises: according to the determined FY spacing and the relationship between the FY spacing and the blood pressure: blood pressure m, FYⁿ+ c, to obtain a blood pressure value sequence, wherein n ≠ 0, FY represents the FY interval, and m and c represent calibration coefficients obtained by calibrating a standard sphygmomanometer for different testees.

7. The method of claim 6, wherein step c further comprises a calibration step, wherein during calibration, the contact pressure between the sensor and the measured position of the body is changed, and calibration is performed at different values of the contact pressure.

8. The method of claim 5, wherein step c further comprises: from the determined sequence of FY intervals, the pulse wave transit time, and another characteristic parameter YG interval of the photoplethysmograph signal, a blood pressure value is calculated using the following calculation:

blood pressure m, FYⁿ+a/PTT²+ b.YG + d, where n is not equal to 0, a belongs to [0, m/2]]，b∈[0，m/5]

Wherein the YG spacing is a spacing between a Y point and a G point on a photoplethysmograph signal waveform, wherein the Y point is a vertex of the photoplethysmograph signal waveform; point G is the first lowest amplitude point on the falling edge of the waveform; or the point that the falling edge of the waveform reaches 1% of the highest amplitude of the waveform; or a point coinciding with the next starting point.

9. Method according to claim 3, characterized in that the continuous rate of change of the blood pressure BPV is determined by a time domain or frequency domain method from the determined sequence of blood pressure values corresponding to each or several heart beats, wherein

The time domain method comprises the following steps:

let T ═ T₁，t₂，t₃，……t_n}^TRepresenting a sequence of blood pressure values, T representing the mean of the sequence T, T₁＝{t₁′，t₂′，t₃′，……t_n-1′}T＝{t₂-t₁，t₃-t₂，t₄-t₃，……t_n-t_n-1T' denotes the sequence T₁Average value of (2)

The method comprises the following steps:

the second method comprises the following steps:

the third method comprises the following steps:

the frequency domain method is to perform Fourier transform or other time domain to frequency domain transform on the sequence T to obtain the frequency spectrum of the sequence T.

10. The method of claim 8, further comprising: extracting relevant information from the waveform area of the photoplethysmograph signal, the relevant information including the area of the waveform rising edge, the area of the waveform falling edge and the area of the entire waveform to determine the blood volume amount.

11. The method according to claim 10, wherein the relative rate of change of the sequence of blood pressure values corresponding to one or several heart beats is determined using the relationship between the FY intervals or pulse wave transit times, the YG intervals, the blood volume and the blood pressure, based on the relative rate of change of the sequence of FY intervals corresponding to one or several heart beats, and the relative rates of change of the YG intervals and the blood volume.

12. The method of claim 11, further comprising: the relative percentage of fluctuation of one or more FY intervals over a period of time, and the relative rate of change of the YG intervals and blood volume, are used to determine the corresponding relative percentage of fluctuation of blood pressure values.

13. The method according to claim 10, wherein the relationship between the FY pitch, the YG pitch, and the blood pressure is determined as follows: blood pressure m, FYⁿ+ a.YG + b.SV + c, n ≠ 0, where m and c represent calibration coefficients obtained by calibration of a standard sphygmomanometer for different subjects, represent the relationship between upper arm blood pressure and FY pitch, YG pitch and blood volume, FY represents FY pitch, YG represents YG pitch, SV represents blood volume, a and b are constants, and a ∈ [0, m/2]]，b∈[0，m/5]。

14. The method of claim 13, wherein when the rate of change of heart rate is less than a threshold over a specified period of time, the effect of heart rate is ignored in determining blood pressure, when a is 0.

15. The method of claim 8, further comprising: determining the FY pitch change rate FYV, the pulse wave transit time change rate PTTV, the YG pitch change rate YGV, or the blood volume change rate VR using a time domain method or a frequency domain method, wherein

The time domain method determines FYV for any of the following equations:

let T ═ T₁，t₂，t₃，……t_n}^TRepresenting the FY interval sequence, the pulse wave transmission time sequence, the YG interval sequence, or the blood volume sequence, T represents the average value of the sequence T, T₁＝{t₁′，t₂′，t₃′……t_n-1′}^T＝{t₂-t₁，t₃-t₂，t₄-t₃，……t_n-t_n-1T' denotes the sequence T₁Average value of (a).

1) FYV, PTTV, YGV or

2) FYV, PTTV, YGV or

3)FYV、PTTV, YGV or

16. The method of claim 15, further comprising directly determining the blood pressure change rate BPV using the following relationship BPV ═ f (FYV, YGV, VR, c), wherein the specific form of f () depends on the specific calculation of the parameter change rates FYV, YGV, VR, and c represents a calibration coefficient obtained by calibrating each of the different subjects using a standard sphygmomanometer.

17. The method of claim 9, further comprising determining the very low frequency rate of change, the low frequency rate of change, and the high frequency rate of change of the blood pressure spectrum using an area method, wherein the area method determines the change of each frequency component relative to the total area of the blood pressure spectrum.

18. The method of claim 17, wherein the frequency components of the blood pressure spectrum comprise: the frequency range of the ultralow frequency component is between 0 and 0.003 Hz; the frequency range of the extremely low frequency component is between 0.003Hz and 0.04 Hz; low-frequency components with the frequency range of 0.04-0.15 Hz; and a high frequency component, wherein the frequency range of the high frequency component is between 0.15Hz and 0.4Hz, and the method for determining the ultralow frequency change rate, the low frequency change rate and the high frequency change rate of the blood pressure frequency spectrum comprises the following steps:

19. The method of any one of claims 5, 6, 8, 13, and 14, further comprising: in making an estimate of blood pressure or rate of change of blood pressure, the FY interval is replaced by pulse wave transit time.

20. The method of claim 19, further comprising: determining the position of a corresponding waveform feature point of the acquired pulse wave generation and transmission time related signals, and calculating a pulse wave transmission time sequence corresponding to one or more heart beats by using the determined position of the waveform feature point,

wherein, for a photoplethysmograph signal, the waveform characteristic points are the top and/or bottom points of the waveform;

for the electrocardiosignals, the waveform characteristic points are R wave vertexes and/or R wave starting points and/or R wave ending points, and any characteristic points on Q waves, S waves and T waves.

21. The method of claim 20, wherein the pulse wave transit time series is determined using the time difference between the apex times of the electrocardiographic signals or the nadirs of the photoplethysmographic signals, or the time difference between the apex times of the electrocardiographic signals or the vertices of the photoplethysmographic signals.