JP2009058444A - Ventilator flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flowmeter excellent in response when measuring a flow rate of a gas flowing in a tube for an artificial respirator, by adopting an ultrasonic type flowmeter having no protruding object in a flow channel and making its pressure loss low. <P>SOLUTION: An ultrasonic method is adopted as a flow rate measuring method for the artificial respirator-use flowmeter, and a flow rate measuring apparatus with a structure having an ultrasonic transducer which does not protrude in the flow channel, is realized. In the structure, a pair of ultrasonic transducers facing each other are arranged so as to be slightly shifted from their just facing position, thereby preventing a multiple reflection of a transmitted/received ultrasonic wave from being repeated many times between the ultrasonic transducers, and enabling its reverberation to be converged rapidly. Moreover, transceivers are disposed in two systems, and their transmission operations are carried out alternately, thereby shortening a repetition period. Furthermore, two pairs of ultrasonic transducers are disposed at a branch tube near the mouth of a patient, thereby enabling both an inspiration flow rate and expiration flow rate to be measured correctly. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a device for measuring the flow rate of a gas flowing in a tube for a ventilator, particularly in the medical field.

  A ventilator is a medical device used from a newborn baby to an elderly person, especially for a highly urgent patient who has trouble breathing. In recent years, the development of ventilators has been remarkable and succeeded in significantly reducing the risk of lung damage caused by the use of ventilators. In such a ventilator, not only the measurement management of the airway pressure measured conventionally, but also the flow rate of inspiration and expiration is measured and managed.

As a flow meter for gas flowing through a tube for a ventilator, a hot-wire flow meter is often used. The hot wire type flow meter is small, has good response, and has a wide dynamic range.
However, in the case of the hot-wire type, a hot-wire part that is a sensor protrudes in the flow path, and the sensor becomes dirty or bacteria adheres due to exhalation.
In addition, the presence of protrusions in the tube is not preferable because it tends to cause pressure loss in the tube and places a burden on the patient on breathing.

  On the other hand, the ultrasonic flowmeter for gas used in industrial use, particularly in a semiconductor manufacturing factory, can overcome the problems of pressure loss and contamination of the sensor part because there are no protrusions in the flow path (see Patent Document 1). However, it is often used when observing a stable flow rate, and is inferior to the hot-wire flow meter described above in terms of responsiveness.

The reason why the responsiveness of the ultrasonic flowmeter has been reduced is that “the reverberation of the ultrasonic wave is generated in the tube when the ultrasonic wave is irradiated. Therefore, the next time the ultrasonic wave is irradiated, the reverberation disappears. It must be said.
That is, since the measurement repetition cycle becomes long, the responsiveness deteriorates.

Also, in an industrial ultrasonic flowmeter, when an ultrasonic transducer is electrically driven to emit ultrasonic waves, a large voltage impulse signal or step signal is added from the transmission circuit and transmitted. Is common.
In that case, in order to drive the ultrasonic transducer next time, it is necessary to wait the circuit for a certain time. The time is the time required for the voltage to return to the original state after driving.
This is particularly referred to as the baseline recovery time of the received signal (returning the received signal to zero).
That is, at least at this time, the next transmission must be waited. This also causes the repetition cycle to become longer and the responsiveness to deteriorate.

Also, in the ultrasonic flowmeter, a pair of transmission / reception circuits, in some cases, an upstream transducer is driven to receive a signal from a downstream transducer, and in other cases, a downstream transducer The receiver circuit was not installed immediately after the transmitter / receiver in order to switch and use it to receive the signal from the upstream transmitter / receiver.
Therefore, since the signal obtained with the high impedance of the transducer propagates through the signal line, it is easily affected by external noise.
Furthermore, even if there is a difference in sensitivity between the pair of transducers, since the transmission / reception circuit is one set, the difference cannot be adjusted. These were all one of the causes of errors.

Next, the ventilator flowmeter often measures both the inspiratory flow and the expiratory flow inside the ventilator main body (see Patent Document 2).
In that case, the flow rate measured by each flow meter is measured at a position away from the patient's mouth, and is measured including the loss in the middle, so it must be somewhat inaccurate. There is also a problem.

JP 2006-208159 A JP 2006-506723 A

The present invention employs an ultrasonic flowmeter to measure the flow rate of the gas flowing in such a ventilator tube, eliminates protrusions into the flow path, reduces pressure loss, and provides responsiveness. It provides an excellent flow meter.
In addition, both the inspiratory flow rate and the expiratory flow rate are measured near the mouth, thereby enabling more accurate flow rate measurement.

The present invention relates to a flow meter incorporated in a breathing or inhalation pipe of a ventilator,
(A) a pair of ultrasonic transducers S _U , S _D arranged to face the upstream side and the downstream side of the measurement pipe channel so as not to protrude into the channel;
(B) the upstream ultrasonic transducer ultrasonic propagation time t _D and the downstream side from S _U from radiates ultrasound into the flow path until ultrasound reaches the downstream ultrasonic transducer S _D Means for measuring the ultrasonic propagation time t _{U from the} time when the ultrasonic wave is emitted from the ultrasonic transducer _SD to the upstream ultrasonic transducer S _U after the ultrasonic wave is radiated to the flow path;
(C) means for calculating the flow rate of the fluid flowing through the flow path using the measured propagation times t _U and t _D ;
(D) comprising means for outputting the calculated flow rate value to a ventilator, etc.
(E) A pair of opposing ultrasonic transducers S _U and S _D are arranged to face each other so as to form an angle δ within 5 ° from the angle at which the ultrasonic transmission / reception surfaces face each other. A flow meter for a ventilator having the structure

Also,
(A) Two systems of a transmission circuit for driving an ultrasonic transducer and a reception circuit for amplifying a signal received by the ultrasonic transducer are installed.
Transmitting circuit T _D and the receiving circuit R _U in (b) one of the lines connected to the ultrasonic transducer S _U upstream, (c) the transmission circuit T _U and the receiving circuit R _D of the other system downstream of being connected to the ultrasonic transducer _{S D,} (d) transmitting circuit _T D, _{T U} is exclusively driven ultrasonic transducer _S U, the _{S D} respectively,
(E) The receiving circuits R _U and R _D exclusively amplify the signals from the ultrasonic transducers S _U and S _D , respectively. (F) The transmitting circuits T _D and T _U are the ultrasonic transducers S _U , Drive each of _SD alternately at a constant cycle,
(G) A structure in which the receiving circuits R _U and R _D are installed immediately after the ultrasonic transducers S _U and S _D respectively, and a sensitivity adjustment function is added to each receiving circuit. A flow meter for a ventilator having

further,
(A) a branch pipe that branches an exhalation duct, an inhalation duct, and an airway guidance duct that leads to the patient's airway or oral cavity;
(B) Two pairs of ultrasonic transducers arranged in a branch pipe so as not to protrude into the flow path, that is, S _IU , S _ID and S _EU , S _ED ,
(C) Of the two pairs of ultrasonic transducers, one pair is composed of an ultrasonic transducer S _{IU on the} intake duct side and an ultrasonic transducer S _{ID on the} airway guide duct side,
(D) the other pair consists of an ultrasonic transducer S _EU ultrasonic transducer S _ED and airway guiding tube roadside expiratory tube roadside,
(E) In each pair, the ultrasonic waves are emitted from the upstream ultrasonic transducers S _IU and S _EU to the flow path until the ultrasonic waves reach the downstream ultrasonic transducers S _ID and S _ED. Ultrasonic wave propagation time t _ID, t _ED and downstream ultrasonic transducers S _ID , S _ED after radiating ultrasonic waves into the flow path, the ultrasonic waves are upstream ultrasonic transducers S _IU , S _EU Means for measuring ultrasonic propagation times t _IU, t _EU until reaching
(F) The flow rate Q _{I of the} fluid flowing from the inspiratory conduit to the airway guiding conduit using the two measured propagation times t _IU t _ID and t _EU t _ED and the expiratory air from the airway guiding conduit Means for calculating a flow rate Q _E of the fluid flowing in the pipe line;
(G) a means for outputting the values of the obtained flow rates Q _I and Q _{E to} a ventilator, etc.
(H) The two opposing ultrasonic transducers S _IU and S _ID and S _EU and S _ED are opposed to each other so as to form an angle δ slightly deviating from the angle at which the ultrasonic transmission / reception surfaces face each other. Arranged,
(I) A flow meter for a ventilator having a structure characterized in that two flow meters are arranged at the position of the branch pipe, and the inspiratory flow Q _I and the expiratory flow Q _E can be simultaneously measured at the mouth.

  The present invention adopts an ultrasonic method and has a structure in which the ultrasonic transducer is not protruded into the flow path, so that the ultrasonic transducer is not contaminated or exfoliated by exhalation, and at the same time pressure Loss can also be significantly reduced.

  In addition, by arranging a pair of opposing ultrasonic transducers slightly shifted from the directly facing position, the transmitted and received ultrasonic waves have a structure that can reduce reverberation without repeating multiple reflections between the ultrasonic transducers. Therefore, the repetition cycle of measurement can be shortened and the responsiveness of the flow measuring device can be improved.

Further, a receiving circuit and the transmission circuit 2 to lines established, the receiving circuit R _U a transmitting circuit T _D is connected to the ultrasonic transducer S _U, the transmission circuit T _U and the receiving circuit R _D is an ultrasonic transducer connect to S _D, the transmission circuit T _D, T _U ultrasonic transducer S _U, since the alternating transmission scheme for driving the respective S _D alternately in a constant cycle, the baseline is zero one transceiver system The transmitter / receiver can be driven by the transmission circuit of the other transmission / reception system with a waiting time that is approximately half of the return time.
As a result, the repetition cycle for driving the transmission circuit can be halved, and the response can be improved accordingly.

In addition, since the receiving circuits R _U and R _D are installed immediately after the ultrasonic transducers S _U and S _D , respectively, the ultrasonic transducers having a high output impedance are converted into low impedances to extract signals. Thus, the influence of noise from the outside can be reduced, and the sensitivity adjustment function is added to each receiving circuit, so that errors due to fluctuations in the received waveform due to variations in the ultrasonic receiver can be reduced.

Furthermore, two pairs of ultrasonic transducers are placed in the branch pipe that branches the exhalation duct, the inspiratory duct and the airway guiding duct that leads to the patient's airway and oral cavity, and these are used for inhalation. Having the inspiratory flow Q _I and airway guiding conduit to flow from the conduit to the airway induced conduit to seek expiratory flow Q _E expiratory conduit can be measured more accurately inspiratory flow and expiratory flow.

The present invention employs an ultrasonic method as a flow measurement method in a ventilator flow meter, and a flow measurement device having a structure in which an ultrasonic transducer is not protruded into a flow path. And by arranging the pair of opposing ultrasonic transducers slightly shifted from the directly facing positions, the transmitted and received ultrasonic waves do not repeat multiple reflections between the ultrasonic transducers, and the reverberation can be quickly converged. The structure.
In addition, two systems of transmitters / receivers are provided, and the repetition cycle can be shortened by alternately transmitting these.
In addition, two pairs of ultrasonic transducers were placed near the patient's mouth so that both inspiratory flow and expiratory flow could be measured accurately.

FIG. 1 shows the structure of the cell portion of the flow rate measuring device that represents the features of the present invention.
As shown in FIG. 1, the flow path is a straight pipe having a diameter D, and a pair of ultrasonic transducers S _U and S _D are arranged at positions opposed to the upstream and downstream portions with the flow path interposed therebetween. Has been.
The measuring tube to which the ultrasonic transducer is attached and the flow path intersect at an angle θ.
The pair of ultrasonic transducers are mounted so as to be shifted by an angle δ within 5 ° from the position facing directly behind the measurement tube.
Distance ultrasound propagates is the sum of the propagation distance L ₀ of the propagation distance _{L 1 (L 1/2 +} L 1/2) and a portion where the flow to the presence of non-existent part of the flow.
X is the length obtained by taking the propagation distance L ₀ of the portion where the flow exists along the axial direction of the flow path.

The flow measuring principle, by using the symbols shown in Figure 1, the propagation time until the ultrasonic waves transmitted from the ultrasonic transducer S _D on the downstream side to reach the ultrasonic transducer S _U on the upstream side t _U and the propagation time t _D until the ultrasonic wave transmitted from the upstream ultrasonic transducer S _U reaches the downstream ultrasonic transducer S _D is expressed as follows.

ここで、ｔ_Ｕ'とｔ_Ｄ'とを次のように表すこととする。

Here, t _U ′ and t _D ′ are expressed as follows.

これらを用いて整理すると式は次のように変形される。

ここで、（１）〜（４）式を用い、音速Ｃ＝340m/s が流速Ｖ=１〜5m/s に比較して相当に大きいことを考慮するとｔ_Ｕ'とｔ_Ｄ'は近似的に次のように表され

流速Ｖは次式で表される。

If these are arranged, the formula is transformed as follows.

Here, using the equations (1) to (4) and considering that the sound velocity C = 340 m / s is considerably larger than the flow velocity V = 1 to 5 m / s, t _U ′ and t _D ′ are approximate. Is expressed as

The flow velocity V is expressed by the following equation.

ここで、音速Ｃは、流速Ｖ＝０のときの伝搬時間ｔ_０から求められ、また音速Ｃが流速Ｖに比較して相当に大きいことを考慮すると、ｔ_０を近似的に相加平均でも相乗平均にでも置き換えて良いので、次式で表される。

Here, the sound velocity C is obtained from the propagation time t ₀ when the flow velocity V = 0, and considering that the sound velocity C is considerably larger than the flow velocity V, t ₀ can be approximated by arithmetic mean. Since it can be replaced by a geometric mean, it is expressed by the following formula.

（６）式を用いると、流速Ｖは次式で表される。

Using the equation (6), the flow velocity V is expressed by the following equation.

したがって、流量Ｑは流速Ｖに管の断面積Ａを乗じて求められる。

Therefore, the flow rate Q is obtained by multiplying the flow velocity V by the cross-sectional area A of the pipe.

The material of the tube and measuring tube should be appropriate depending on the application, such as metal or plastics.
The ultrasonic transducer has a structure in which a diaphragm made of a piezoelectric material is fixed to a front wall of a case.
The front surface of the diaphragm is covered with plastics resin.
The lead wire of the ultrasonic transducer is taken from the back and connected to the flow rate measuring device.

FIG. 2 shows a circuit block diagram relating to an embodiment of the flow rate measuring apparatus according to the present invention.
Various command signals are output from the control unit, and each part of the circuit operates.

For example, the main synchronization trigger signal in the controller, the ultrasonic transducer applied driving voltage input to the S _U channel on the upstream side control unit operates the transmission circuit T _D by transmitting the driving trigger signal Ultra Sound waves are emitted.
This ultrasonic wave is received by the ultrasonic transducer _SD on the downstream side, converted into an electric signal, and input to the receiving circuit _RD .

Since this time transceiver circuit is in the two systems independently drive signal when the transmitting circuit T _D is driving the ultrasonic transducer S _U on the upstream side is not to be input to the receiving circuit R _D.
Since the receiving circuit R _D only signals from the ultrasonic transducer S _D of the downstream side is inputted, SN of the received signal is kept in good condition.

Further, when the driving signal of the receiving circuit R _U upstream of the ultrasonic transducer S _U in is inputted as it is limited below a predetermined voltage by the limiter provided in the preceding stage in the receiving circuit simultaneously, the receiving circuit The base line is restored by the time constant determined by the input resistance and the capacitance of the ultrasonic transducer, and functions normally as a receiving circuit.

The output of the receiving circuit _RD becomes a received pulse signal via the switch / comparator and is input to the time measuring gate generator of the propagation time measuring means.
Ultrasonic up the timekeeping gate generator using the received pulse signal outputted from the comparator to the driving trigger signal transmitting circuit T _D which is output from the control unit ultrasound is reception from being transmitting It generates gate pulses with a length corresponding to the propagation time t _D sends the counter.
Counter converts the ultrasonic wave propagation time t _D into a digital number, is input to the arithmetic unit of the flow rate calculation means.

Next, a delay constant cycle T from the previous primary synchronization trigger signal, the control unit the driving voltage input to the ultrasonic transducer S _D of the downstream side operates the transmission circuit T _U to disseminate the driving trigger signal In addition, ultrasonic waves are emitted to the flow path.
The ultrasonic waves are inputted to the receiving circuit R _U is received in the ultrasonic transducer S _U on the upstream side is converted into an electric signal. Reception circuit output of R _U is input to the gate generator when measuring the propagation time measuring means becomes a received pulse signal via the switcher-comparator.
Ultrasonic up the timekeeping gate generator using the received pulse signal outputted from the comparator to the driving trigger signal transmitting circuit T _U output from the control unit an ultrasonic wave is received wave since the wave transmitting It generates gate pulses with a length corresponding to the propagation time t _U send counter.
Counter converts the ultrasonic wave propagation time t _U into a digital number, is input to the arithmetic unit of the flow rate calculation means.

In this apparatus performs while repeating measurement of as described above ultrasonic wave propagation time t _U and t _D are alternately every predetermined period T, and inputs these values to the calculator.
The computing unit always uses the new values of t _U and t _D to calculate the following formula to calculate the instantaneous flow rate Q at that time.
^{_{Q = K 1 A (L 2}} / 2X) (t U over _{t D) / (t U *} t D) (1)
However, K ₁ is the flow rate correction coefficient, A is the cross-sectional area of the flow channel, L is the distance between the transducer, X is the effective distance along the flow path direction between the transducer.
L and X are indicated by symbols in FIG. K depends on the cell shape and flow rate, and is determined experimentally.

The value of the instantaneous flow rate Q obtained above is updated every period T and displayed on the display unit of the data output means. Various displays and display methods are used, and a display in which a horizontal axis represents time and a vertical axis represents a flow rate is displayed on a CRT or the like.
Further, since this cycle is as short as several ms, in some cases, a smoothed value may be displayed in order to make it less likely to be affected by abnormal values by averaging over time.
The degree of smoothing is determined according to the purpose and measurement environment.

(Other embodiments of the cell)
Another embodiment is shown in FIG. 3 as the structure of the cell portion of the flow rate measuring device.
As shown in FIG. 3, the ultrasonic transducers S _U and _SD are installed on the same side of the flow path, and the ultrasonic wave radiated from one ultrasonic transducer is reflected once by the inner wall of the tube. After that, it is structured to be received by another ultrasonic transducer.
Again, the pair of ultrasonic transducers are mounted at a position that is offset by a slight angle δ from the directly facing position. Similarly the distance the ultrasonic wave is propagated is the sum of the propagation distance L ₀ of the propagation distance _{L 1 (L 1/2 +} L 1/2) and a portion where the flow to the presence of non-existent part of the flow.
X is the length obtained by taking the propagation distance L ₀ of the portion where the flow exists along the axial direction of the flow path.
By adopting such a structure, it is possible to increase the ultrasonic propagation distance, and as a result, improvement in measurement accuracy can be expected.

The formula representing the instantaneous flow rate Q in the case of the embodiment shown in FIG. 3 is as follows.
^{_{Q = K 2 A (L 2}} / 2X) (t U over _{t D) / (t U *} t D) (2)
However the flow correction factor _{K 2} is made different from the _{K 1} (1) below.

(Cell structure for measuring Q _I and Q _E with a branch pipe)
FIG. 4 shows an embodiment of a cell structure for measuring Q _I and Q _E with a branch pipe.
As shown in FIG. 4, an ultrasonic transducer S _IU is arranged inside the entrance from the inspiratory tube, and an ultrasonic transducer S _ID is arranged outside the airway tube on the expiratory tube side, so that the inspiratory flow rate Q _I is taking measurement.
In addition, an ultrasonic transducer S _EU is installed outside the airway on the inspiratory tube side, and an ultrasonic transducer S _ED is arranged inside the exit to the expiratory tube to measure the expiratory flow Q _E.
Again, the pair of ultrasonic transducers are mounted at a position that is offset by a slight angle δ from the directly facing position.
By adopting such a structure, the inspiratory flow rate and the expiratory flow rate can be simultaneously measured at a position closest to the mouth.

Another embodiment is shown in FIG. 5 as the structure of the cell portion of the flow rate measuring device.
As shown in FIG. 5, the inside length of the inspiratory tube and the expiratory tube is made as long as possible in the ultrasonic wave propagation path.
Therefore, the ultrasonic transducer S _IU on the outside of the intake pipe, has a structure in which even ultrasonic transducer S _ED is located outside the expiratory tube. This can be expected to be a method with good measurement accuracy.

FIG. 4 is a structural diagram of a cell portion of a flow rate measuring device that represents a feature of the present invention. It is a circuit block diagram regarding the Example of the flow measuring device by this invention. It is a structural diagram of another Example as a structure of the cell part of a flow measuring device. Q _I in the branch _pipe, a structural view of an embodiment of a cell structure for measuring the Q _E. It is a structural diagram of another Example as a structure of the cell part of a flow measuring device.

Claims (4)

In a flow meter built into the breathing or inspiratory piping of a ventilator,
(A) a pair of ultrasonic transducers S _U , S _D arranged to face the upstream side and the downstream side of the measurement pipe channel so as not to protrude into the channel;
(B) Ultrasonic propagation time t _{D from the} time when the ultrasonic wave is radiated from the upstream ultrasonic transducer S _U to the flow path until the ultrasonic wave reaches the downstream ultrasonic transducer S _D , and the downstream Means for measuring an ultrasonic propagation time t _U from when the ultrasonic wave is emitted from the side ultrasonic transducer _SD to the upstream ultrasonic transducer S _U after radiating the ultrasonic wave to the flow path;
(C) means for calculating the flow rate of the fluid flowing through the flow path using the measured propagation times t _U and t _D ;
(D) comprising means for outputting the calculated flow rate value to a ventilator, etc.
(E) For a ventilator, a pair of opposing ultrasonic transducers are arranged to face each other so as to form an angle δ within 5 ° from the angle at which the ultrasonic transmission / reception surfaces face each other. Flowmeter. (A) Two systems of a transmission circuit for driving an ultrasonic transducer and a reception circuit for amplifying a signal received by the ultrasonic transducer are installed.
Transmitting circuit T _D and the receiving circuit R _U in (b) one of the lines connected to the ultrasonic transducer S _U upstream,
(C) receiving circuit R _D and the transmission circuit T _U of the other system is connected to the ultrasonic transducer S _D of the downstream side,
(D) The transmission circuits T _D and T _U exclusively drive the ultrasonic transducers S _U and S _D , respectively. (E) The reception circuits R _U and R _D exclusively operate the ultrasonic transducers S _U and S _D. Amplify the signal from
(F) A flow meter for a ventilator, wherein the transmission circuits T _D and T _U drive the ultrasonic transducers S _U and S _D alternately at a constant period. 3. The ultrasonic flowmeter according to claim 2, wherein the receiving circuits R _U and R _D are respectively installed immediately after the ultrasonic transducers S _U and S _D , and a sensitivity adjustment function is provided to each receiving circuit. A ventilator flowmeter characterized by the addition. In a flow meter built into the breathing or inspiratory piping of a ventilator,
(A) a branch pipe for branching an exhalation duct, an inhalation duct, and an airway guidance duct for guiding to the patient's airway or oral cavity; and (b) facing the branch duct so as not to protrude into the flow path. Two arranged ultrasonic transducers, namely S _IU , S _ID and S _EU , S _ED ;
Among the ultrasonic transducer of the (c) two pairs, one pair is composed of a ultrasonic transducer S _ID of the ultrasonic transducer SIU and airway guiding tube roadside intake pipe roadside,
(D) the other pair consists of an ultrasonic transducer S _EU ultrasonic transducer S _ED and airway guiding tube roadside expiratory tube roadside,
(E) In each pair, the ultrasonic waves are emitted from the upstream ultrasonic transducers S _IU and S _EU to the flow path until the ultrasonic waves reach the downstream ultrasonic transducers S _ID and S _ED. ultrasonic propagation time tID, tED the downstream ultrasonic transducer _{S ID, S} ultrasound from radiates ultrasonic waves to the flow path upstream ultrasonic transducer from _{ED S IU,} reached _{S EU} Means for measuring ultrasonic propagation times t _IU and t _EU until
(F) The flow rate Q _{I of the} fluid flowing from the inspiratory conduit to the airway guiding conduit using the two measured propagation times t _IU t _ID and t _EU t _ED and the expiratory air from the airway guiding conduit Means for calculating a flow rate Q _E of the fluid flowing in the pipe line;
(G) a means for outputting the values of the obtained flow rates Q _I and Q _{E to} a ventilator, etc.
(H) The two pairs of ultrasonic transducers facing each other are disposed so as to face each other so as to form an angle δ slightly deviating from the angle at which the ultrasonic transmission / reception surfaces face each other.
(I) A flow meter for a ventilator, wherein two flow meters are arranged at the position of the branch pipe, and the inspiratory flow Q _I and the expiratory flow Q _E can be simultaneously measured at the mouth.

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