FR2475881A1 - BLOOD PRESSURE MEASURING DEVICE WITH MICROPHONE OR SENSOR OF EQUIVALENT SOUND - Google Patents

Abstract

THE BLOOD PRESSURE MEASURING DEVICE INCLUDES AN INFLATABLE DEFORMABLE AIR CHAMBER 31 AND MICROPHONE 33 CUFF 1 AS WELL AS AN APPARATUS 3 TO MEASURE AND INDICATE SYSTOLIC AND DIASTOLIC BLOOD PRESSURE. THE SOUND FREQUENCY SIGNALS PROVIDED BY THE MICROPHONE 33 DURING THE MEASUREMENT ARE ADDRESSED, THROUGH FILTERING MEANS 51, TO A DISCRIMINATOR 53 WHICH GENERATES A PULSE AT EACH NOISE OF KOROTKOFF. DIASTOLIC PRESSURE IS MEASURED DURING THE LAST PULSE FORMED WHEN THE PRESSURE FALLS IN AIR CHAMBER 31. FILTER MEDIA TRANSFER FUNCTION 51 IS SWITCHABLE SO THAT DIASTOLIC PRESSURE IS ELECTED MEASURED DURING FOURTH OR FIFTH. NOISE OF KOROTKOFF.

Description

The invention relates to a device for measuring blood pressure.

  comprising a microphone for picking up noise caused by blood in an artery

and filter means connected to the microphone.

A blood pressure measuring device known from US Patent 2,827,040 has a

microphone intended to pick up the sounds of Korotkoff provo-

  qués by the sanà flowing in an artery. The microphone is connected, via an amplifier, a

  bandpass filter and an image shaping circuit

  drives, to a coincidence circuit. An inflatable cuff, capable of being fixed to the arm of the person to be examined, is connected to an air tank having an outlet nozzle which, during the measurement, creates a flow of air passing in front of a thermistor. The thermistor, used for the detection of pressure pulses, is also connected, via an amplifier and a pulse shaping circuit, to the coincidence circuit. In addition, there is a pressure gauge for detecting systolic pressure and a pressure gauge for detecting diastolic pressure. The two pressure gauges are each connected by

  an air tank valve. The air tank is

  core connected, via a valve, to a compressor

and in addition, via a drain valve

cuation of air, to the ambient atmosphere. In addition, there is also a control device for actuation.

different valves.

When measuring a blood pressure, the pressure in the air reservoir is gradually increased. As a result, in certain pressure zones, pulses are obtained both because of Korotkoff noises and pressure oscillations, these pulses being addressed to the coincidence circuit. During the first coincidence of pulses, that is to say that which is established for the lowest pressure, the manometer used to measure the diastolic pressure is temporarily connected to the air reservoir, so that it measures and

  indicates diastolic pressure. We then increase more

  pressure. When the pulses coincide

  occurring at the highest pressure, we connect tempo-

  the pressure gauge used to measure the air tank

monitor the systolic pressure and thus measure the pressure

systolic sion.

Another device for measuring blood pressure known from US Patent 3,450,131 has a

microphone which is connected via an amplifier

set ficitor, at the inputs of three different bandpass filters. These have pass frequencies of 40 and 1000 Hz. The outputs of the three bandpass filters are connected to a logic circuit. The device further includes an inflatable cuff and a pressure sensor which is connected to a pressure recording device

via an analog / digital converter

disconnectable risk and a door circuit.

  During a blood pressure measurement, the cuff is inflated to a pressure higher than the systolic pressure and then deflated slowly. Korotkoff noises are thus obtained, in a certain pressure zone, which are transformed into electrical signals by the microphone. The logic circuit connected to the outputs of the filters is then constituted in such a way that it identifies as parasitic noises, the signals which have a component at 1000 Hz while it identifies as Korotkoff noises the signals which have a component at 40 Hz and a component at 100 Hz but no component at 1000 Hz. For each signal identified as Korotkoff noise, the analog / digital converter and the gate circuit are controlled by the logic circuit so that the pressure measured at this time by the sensor

  pressure is stored in the input device

pressure recording.The first recorded pressure value therefore corresponds to the systolic pressure and the last recorded pressure value to the pressure

  diastolic. In addition, it also mentions the possibility of

  lity to provide an auxiliary circuit designed in such a way

  that only systolic pressure and diastolic pressure

that are recorded.

  In pressure measuring devices

  blood known from two US patents 2,827.

040 and 3.450.131, we therefore measure as diastolic pressure the smallest pressure for which a noise from Korot} koff still occurs. For this, we establish the presence

  Korotkoff noise by the fact that the electrical signals

corresponding triques that pass the pass filters

band dispond in the device, exceed a certain

threshold value.

We have now carried out comparative measurements.

ratives, in which the pressure values dias-

tolioue are measured on the one hand indirectly, i.e.

  using an inflatable cuff, and on the other hand

  hold or bloody, that is to say by connecting di-

  arteries to a pressure measuring device

  if we. It follows from these comparative measurements that the

  indirect and bloody methods are more or less in good agreement depending on the different patients, sometimes noticeable deviations may occur. If you consider blood pressure measured by blood as the

true blood pressure, the measurement methods indi-

errors cause measurement errors, the size of which depends on the individual characteristics of the patients examined. As such, it has been known for a long time that Korotkoff noises do not only become weaker but also modify their frequency when the

  cuff pressure to the vicinity of the dias-

  tolerant. One can quote on this subject for example the "Handbuch der inneren Medizin", volume 9, fifth part, "Herz und

Kreislauf "by G. von Begmann, W. Frey and H. Schwiegk, pu-

blied in 1960 by the German publishing house Springer-

Verlag.

  In professional parlance, doctors make a distinction in particular between "fourth" and "fifth" noises from IKorotkoff. This fifth noise is weaker and more serious than the fourth noise. Medical authorities are currently recommending measuring diastolic blood pressure at Korotkoff's fourth noise. Experiments have now shown that the diastolic blood pressure, measured at the time of the third Korotkoff noise, is 7 to 15% higher than the blood pressure measured at the time of the fifth noise.

Korotkoff, in approximately 80 to 90% of those examined.

  Such a difference is generally unimportant if

we consider variations in blood pressure over-

  normally coming in the short term. However, for approximately 20% of those examined, the diastolic pressure measured at the fourth Korotkoff noise is up to 70% higher than the pressure measured at the fifth Korotkoff noise. With the known blood pressure measuring devices described above, the diastolic blood pressure is always measured for the same noise of t Korotkoff, in this case probably the fourth noise. As a result, significant measurement errors may occur in a certain proportion of the people examined.

  The invention has therefore given itself, inter alia,

  my objective, to make a device for measuring the pressure

  indirect action, thanks to which the measurement errors mentioned above can be eliminated or

to say the least diminished.

  The invention now rests on bringing

profit from the observation that we can reduce the er-

  measurement errors during indirect pressure measurement

  if you don't just look at the change

  tion of the sound intensity but also the frequency spectrum of Korotkoff noises which changes;% so

variable depending on the individual.

  This objective is achieved by a system

  measuring blood pressure of the kind defined in

ambule, characterized in that it comprises an adjustment member, by means of which it is possible to develop, as desired, at least one of two different transfer functions

  filtering means, and in that the trans-

  mission of the filtering means, for the two functions of

  transfer, depends in different ways on the frequency.

  Other advantageous features of

  the invention will appear on reading the description

next.

For the purpose of clarification, we must note

  quer que, by 'blood pressure' and 'pressure in the chamber

  bre ci air ", we always designate the relative pressure

safe compared to ambient atmospheric pressure.

The invention will now be described in more detail with regard to a particular embodiment shown in the accompanying drawings in which: FIG. 1i shows, in top view, a device for measuring blood pressure, FIG. 2 represents a block diagram of the blood pressure measurement device, FIG. 3 represents the diagram of the filtering means used to collect various Kcrotkoff noises as desired, cub ds in FIG. 4 is a diagram illustrating the

frequency transfer curve of the mo-

filter yen, and Figure 5 is a diagram illustrating the

  time course of a blood pressure measurement.

The pressure measuring device

guine shown in figure 1 has a cuff 1 sus-

capable of being attached to the arm of the person to be examined and an apparatus designated as a whole by 3. The cuff 1 contains a deformable inflatable air chamber, formed of a rubber pocket, as well as a microphone and it is connected detachably to the device 3 using a pipe 5 which has a flexible hose connected to the air chamber as well as a cable connected to the microphone and, on the side of

  the device, a plug-in connector 7. The device 3 has

  sàde a housing 9 with a threaded connection 9a on which is

  detachably fixed with a union nut

  ment 11, a pump 13 with a substantially cylindrical pump body made of rubber. On the case 9 are fixed an air connection 15 of the grooved type and an electrical connection 17, formed by a chassis plug, on which the connector 7 can be inserted. In addition, there is provided a connector 19 formed by a chassis plug for the connection of a headset. The apparatus further has three push-button switches 21, 23, 25, a digital display unit 27

  and various constructive, pneumatic and electrical elements

  triques, arranged inside the boot 9.

  In Figure 2, there is shown schematically the inflatable air chamber 31 and the microphone 33 which belong to the cuff 1, as well as part of the constructive elements, pneumatic and electric, arranged in the device 3. The chamber air-31 is connected, by the flexible pipe contained in the pipe 5 and by air ducts arranged in the device 3, to the pump 13 by means of a non-return valve 35 as well as to an exhaust valve 37 electrically controllable and with a pressure sensor 39. The pump 13 is also provided with an air inlet provided with a non-return valve 41. The two non-return valves 35 and 41 are mounted so

  such that, by alternating manual compression and release

pump body, air can be drawn into

  the atmosphere and pushed back into the inner tube 31.

  The microphone 33 is connected by conduc-

electric torers at the input of filtering means 51

  the outlet of which is connected as well to the drain connection

19 to a discriminator 53 which has a potentio-

  setting meter 54, for setting a lower value

  threshold, as well as a pulse shaping circuit.

  The output of this potentiometer 54 is connected to an organ of lun maonut aoc

  control 55. The pressure sensor 39 includes / in the bridge

measurement vertisseur, consisting of piezo-resistive elements and connected to the input of an amplifier 57. The output thereof is connected to the control member 55 on the one hand by a differentiator 59, on the other leaves by a parallel link which short-circuits the latter. The pressure sensor 39 and the amplifier 57 are also connected to an automatic zeroing device 75 which is connected by a conductor to an output of the control member 55. The output of the differentiator 59 is also connected to the control member 55 and furthermore to an input of a regulator 61. The control member 55 is also connected to an input of regulator 61 whose output is connected to the electromagnetic actuation member of the discharge valve 37. The control unit 55 also has two connections connected, respectfully: to capacitors 63 e J crnmant an analog memory. The controller

is no longer connected to a display control unit -

67 which notably includes an analog / digital converter

  which is connected to the display unit 27. A discri-

timer 69 has an input still connected to the output of the differentiator 59 and an output connected to an input of a heart rate meter 71 as well as to the organ

55. The heart rate monitor 71 pos-

  Another control input connected to the control member 55 and a control system connected to the control member 55. The push-button switch 21 is connected to the control member 55 and the push-button switch 23 to the display control element F7. In addition, a supply voltage source 73 is provided, comprising

a battery, which is connected to the supply voltage terminals

  tion of the various active elements and to the ground connection.

  The push-button switch 25 as well as the control member are connected to the supply voltage source 73 which,

  in addition to the battery, still has some-

logic elements as well as a regulator for stabilization

the supply voltage. The battery is contained

  in a container capable of being closed by a cover.

The taicrophone 33 is connected to the input terminal 81 and to the earth terminal 83 of the filtering means 51 which are shown separately in FIG. 3. The terminal 81 is connected via a capacitor 34 to the non-inverting input 85a and via a resistor 37 to the inverting input 85b of an amplifier 85. The non-inverting input o30 85a is connected to two resistors 89, 91

montoeson parallel, resistor 39 being directly connected

  resistance 91 through an interrup-

tor 93, at the mass terminal $ 3. Via a resistor 95 and a capacitor 97 mounted in parallel with the latter, the output 85c of the amplifier 35 is connected to the inverting input 35b, which is also connected to the terminal of ground 33 via a resistor 99 and a capacitor 1.G connected in series. The S5c output of amplifier 85

  is connected to the output terminal 103 of the filtering means.

In addition, the amplifier 85 is still connected to the source

of supply voltage 73 by conductors not re-

  presented. The adjustment potentiometer 54 and the switch 93 are arranged inside the housing 9, so

  that they can only be set or activated after or

the cover that closes the battery tray.

  Let us designate by "transmission factor" T the ratio between the measured voltage, relative to the mass, at the output terminal 103 and the measured voltage, compared to the mass, at the input terminal 81. The variation of the factor

  of transmission T with respect to the frequency f is represented

shown in figure 4 for the two positions of the inter-

  1D- switch 93. When the switch 93 is open as shown in FIG. 3, the function for transferring

  filtering means 51 is rendered by the trans-

  mission according to curve 111. On the contrary, when the inter-

  switch 93 is closed, the transmission factor varies

  - 20 according to curve 113. At frequency f2, the transmission factor rendered by curve 111 has a fairly sharp maximum, the value of this maximum being designated by T2 and being for example 100. The low limit frequency, for which the transmission factor according to curve 111 is T2 / rV, is designated by f1. Curve 113 goes up

  slowly, reaches a plateau-shaped maximum and re-

  then goes down, the maximum transmission factor for curve 113 having the value T1. The lower limit frequency of the transfer function represented by the

  curve 113 is designated by f3. The flat-shaped part

teau and the descending part of the curve 113 coincide, at least approximately, with parts of the curve 111. As can be seen in FIG. 4, this therefore results, for the variation of the frequency represented by the curve 113, a lower limit frequency f3 which is greater than the limit frequency f1 and the frequency f2 The lower limit frequency f1 of the frequency curve 111 is at least Hz. Furthermore, it is at most 30 Hz, and preferably at most 25 Hz, for example about 20 Hz. On the other hand, the limit frequency f3 is at least 35 Hz and preferably at least 40 Hz and at most about 60 Hz, for example of the order of 50 Hz. The frequency f2, for which the curve 11-1 reaches its maximum, is between 25 and Hz approximately and for example 30 Hz. The maximum in the form of a plateau of the curve 113 is found at - above f2 and extends from O0 to 120 Hz approximately. For both curves, the

upper limit frequency is around 130 to 200 Hz.

  The maximum transmission factor T2 of curve 111 is 0 at least 30% and for example 50% greater than the

  maximum transmission factor T1 of curve 113.

  It should also be noted that the electronic constructive blocks and elements shown in the figures

  2 and 3 can be condensed into integrated circuits.

  In the following, we will now describe the operation of the pressure measuring device

using the diagram in Figure 5. For ef-

  take a measurement, connect the cuff 1 by the pipe to the device 3 and fix the cuff on the arm of the

person to examine.

The apparatus 3 is designed in such a way that it can be conveniently held with one hand, the pump

  13 serving as a handle. If necessary, the three interrup-

pushers 21, 23 and 25 can also be operated

with the hand holding the device.

We will first discuss the variation of the pressure p in the air chamber 31, as a function of time t. The temporal variation of the pressure p is represented by the curve 121 on the diagram in FIG. 5. When the cuff is fixed, the device is started up at the instant to with a short pressure on the on / off push-button switch 250 In the time interval between instant t and instant t1, the pressure sensor 39 is automatically reset to zero by the zero reset device 75. The end of this reset is indicated by the fact that the display unit 27 indicates the value zero. Between instants t1 and t2, air is discharged successively into the air chamber 31 with the pump 13, so that an air pressure is established in this chamber which is higher than the pressure systolic. Shortly after the completion of pumping, air begins, at time t3, to exit from the inner tube 31

  through the valve 37, escaping to the atmosphere, so.

  as the pressure drops in the air chamber 31. As a result,

  the pressure sensor 39 generates a voltage proportion-

nelle at the pressure p and the differentiator 59 determines the differential quotient dp / dt. The regulator 61 acts on the evacuation valve 37 so that the quotient

differential dp / dt remains constant during the measurement phase

  itself, up to the pressure oscillations which are caused by cardiac activity and which will

described in more detail below.

  When now the pressure p begins to decrease from a maximum greater than the systolic pressure pS, one observes from time t4 pressure oscillations which are due to the cardiac pulsations. These pressure oscillations are captured by

  the differentiator 59. The discriminator 69 creates an im-

  impulse at each pressure swing, caused by

a heartbeat, for which the quotient differs

  ferential dp / dt exceeds a predetermined threshold of at least Pa / s and for example 400 Pa / s. These impulses form

  a series of pulses which is designated by 123 in the figure

re 5.

  When the pressure in the air chamber 31, decreasing, is inside a certain area, the blood causes by its flow in the artery surrounded by the cuff 1, for each blood stream caused by a heartbeat , breaths, i.e.

  sounds of Korotkoff. These Korotkoff noises are trans-

  formed by the microphone 33 into electrical signals of sound frequency and addressed to the discriminator 53, by means of the filtering means 51, which preferably also cause amplification. When the voltage of the Korotkoff noise signals exceeds the lower threshold value, established by the discriminator 53, the pulse shaping circuit belonging to this discriminator brings each faith. a pulse to the command -14 orane 55. This series of pulses is designated by in FIG. 5 and extends from the instant t5 to the instant t6 'In the control member 55, the pulses created by the pressure oscillations and the pulses created by Korotkoff noises are sent to an AND gate. As shown in Figure 5, the pulses due to pressure oscillations are wider than the

pulses due to Korotkoff noises. The door AND cons-

sets up a coincidence circuit and, during each pulse

Sion of the series of pulses 123, it opens a window for the pulses of the series of pulses 125. The signals coming from the microphone therefore continue to be processed only when they fall into a window opened by a pressure oscillation, that is to say when there is a coincidence between the noise signals and the pressure oscillations. Korotkoff noise can thus be distinguished from parasitic noise and the latter

be eliminated.

The control member 55 has a switch

electronic sensor which connects the amplifier output

  57 to memory 63, from switching on the device

the same. The control unit -55. Also has first means for detecting the appearance of the Korotkoff signal.

which crosses the above door AND. When the first if-

of Korotkoff occurs, memory 63 is separated from

the conductor coming from the amplifier 57 of the measurement channel

sure of the pressure. In this memory 63 is therefore stored

siné the value of the pressure present at the time of the first noise signal of Korotkoff, i.e. that

systolic pressure.

  When now the pressure drops in air chamber 31, the first sound of Korotkoff is followed by other sounds of Korotkoff. The controller comprises means which briefly connect the output of the amplifier 57 to the memory 65 for each Korotkoff noise, that is to say for each pulse in the series of pulses 125. At each noise of Korotkoff, a new pressure value is therefore stored in the

  memory 65, the amplitude of these values of the di-

gradually diminishing. As already described, the series of im-

  impulses 125 extends to time t6 - As no other impulses occur after time t6, the

value of the pressure p measured at time-t6 remains em-

  stored in the Moire 65 until the appliance stops.

  This memory value then represents the pressure dias--

  tolique PD 'The controller 55 also has

a circuit which determines when, during an interval

the predetermined time from 2 to 10 s, for example from 5 s; he

no more noise appears - from Korotkoff. At the end of this in-

  tervalle, that is to say at time t7: the control member 7 '55 sends the regulator 61 a signal which causes it to fully open the valve 37. The pressure p then decreases very quickly and reaches again at moment t8

  zero value, i.e. atmospheric pressure am-

  biante. The control member 55 is further designed so that it connects the output of the amplifier

577, to the display control element 67, until the ins-

  both t7 at regular intervals of for example 0.3 s.

  The display unit 27 therefore displays the momentary pressure each time. The control member 55 could however be constructed in such a way that the pressure is displayed

  each time, during each pulse of the pulse series

  sions 123, during the time interval extending from time t4 to time t7

The control member 55 furthermore puts momen-

  temporarily in action the heart rate meter 71 so that it measures the heart rate during the occurrence of the series of pulses 123 and calculates the average value of these pulses. This average value is stored in the memory of the frequency measurer

71.

  The control member 55 is still designed

so that memory 63 or 65 or memory em-

  storing the heart rate can be interrogated cyclically by a short push on the push button 21. The relevant memory value, stored

  in analog form, is then brought to the element of pi-

display lot 57 and transformed by this into a nu.uric signal. The latter is brought to the display unit 27 so that the latter optionally indicates the pressure

systolic, diastolic pressure or heart rate

  devil. The display control element 67 contains a network interposed between the conductors of the memories 63, 565 and the analog / digital converters, this network

  can be switched by pushbutton 23.

  When displaying the pressure, this allows you to choose an indication in k-lopascals or in Torrs, switching being effected by a short press on the switch

23.

  When the three memory values have been read, the device3 can be stopped by a short press on the on-off push-button

  so that the measurement is finished.

  The general operation of the device having

et [exposed, it remains to explain the purpose of the com-

  mutability of the transfer function of the wire means

trage 51.

  As appears from the preceding discussion, the momentary pressure which prevails in the air chamber 31 during the last pulse of the series of pulses 125 is identified and measured as the diastolic pressure PD 'When

  pressure approaches diastolic pressure decreases

Health from higher values, Korotkoff noises become less strong. At the same time, their spectrum of

frequency shifts to lower frequencies.

  Such a shift towards low frequencies occurs between the noises designated, in professional professional language, by quatrieimn / àruits de Korotkoff. It is because of their relative sound intensities and their different sounds that doctors distinguish these two noises from one another. As the analysis of the frequency spectra has shown, the high intensity components

  sound of the frequency spectrum, at the fourth noise of Korot-

  koff, are well above a value between 50 and 80 Hz. On the contrary, the fifth noise of

  Korotkoff reaches its maximum intensity around 30 Hz.

When the switch 93 is opened and the transfer function of the filtering means 51 is rendered

by the curve 111 of FIG. 4, the frequencies are re-

  raised to the region of frequency f2 which, as already mentioned, is for example equal to around 30 Hz. In this case, the electric sound frequency signal, created by the fifth Korotkoff noise and brought to the discriminator 53, is so strongly raised that it exceeds the threshold value of this discriminator and causes the emission of a

pulse from the series of pulses 125. The dias-

  tolic is then measured during the fifth noise of Ko-

rotkoff.

  On the contrary, when the switch 93 is closed and the transfer function of the filtering means

51 is represented by curve 113 of FIG. 4, the fac-

transmission factor T has only a relatively low value

* ble near frequency f2. The electrical signal, created by the aforesaid fifth noise of Korotkoff and brought

discriminator 53, is no longer sufficient to

pass the threshold value of this discriminator. In this case, the last pulse in the 125 pulse series is created by Korotkoff's fourth noise, so

  that diastolic pressure is measured during the

  Korotkoff's third noise. fourth quaflème e% It should again be noted that the / Fifth

Korotkoff noises are identified by doctors due to

sound of their relative intensity and their sound. The fourth and fifth sounds of Korotkoff are therefore not necessarily identical respectively to the fourth and

fifth pulse in the 125 pulse series.

The pressure measuring device

guine which has just been described is intended in particular for patients who measure. themselves, their own blood pressure and who present the results of these measurements from time to time to their doctor. As already explained

  in the preamble, the individual characteristics of the pa-

  tients, in particular the particular conformation of their arteries, can influence the sound intensity and the frequency spectrum of Korotkoff noises. By examining his patient, the doctor can measure his blood pressure or blood pressure using the device. The doctor then has the possibility of listening to Korotkoff noises using a stethoscope or a headset plugged into connector 19 and of then continuously reading the

  blood pressure. Based on his acous interpretation

tick of Korotkoff noises and other acquaintances

that he has from his patient, the doctor can decide if he

  comes, in a particular case, from measuring the pressure

  at the fourth or fifth noise of Korot-

  koff. In case the sound intensity of Korotkoff noises differs significantly from the normal value, the doctor can,

  using the adjustment potentiometer 54, adapt to the charac-

individual patient's threshold threshold value

discriminator 53. By selection of the fourth or fifth

  5th Korotkoff noise as a criterion for measuring the diastolic pressure and if necessary by varying the threshold value of the discriminator 53, it is possible to improve the agreement of the measured values of the diastolic pressure with the effective diastolic pressure.

which is measured bloody. In addition, this improves

  increases the expressiveness of the measurements which are made easier to compare with the values of the measurements carried out

on other patients.

The device can be modified under different

  many aspects. This is how, for example, we could

  arrange the filtering means interposed between the micro-

phone and the discriminator so that not only two transfer functions such as

  different, corn of your choice three or more functions.

  In this way, the transfer function could be better adapted to the individual characteristics of a patient. In addition, the transfer function could be selected using not a switch but another manual control adjustment organ such as a potentiometer; it would then be possible to continuously influence the frequency stage of the function

transfer.

It should be noted that three other requests

  were filed the same day by the application-

  resse about this measuring device. It should also be pointed out that instead of a separate microphone and a separate pressure sensor, a sound and pressure sensor could be provided which is used to capture not only the noise caused by the blood but also the blood pressure. quasi static and the pressure modulation created by the beating of the heart. This combined sound and pressure sensor could be contained either in the airbag or in the device with the electronic components. The electrical signals emitted by the sound and pressure sensor could be sorted by a frequency switch before being directed according to the

case to the sound or pressure channel of the electro-

fuck.

Claims (8)

1. Saniuirce pressure measurement device _corprenant a microphone (33) for picking up the noises caused by the blood in an artery and filtering means (51) connected to the microphone (33) characterized in that q'i cor.iporte un regulating member (93) by means of which it is possible to develop one of at least two different transfer functions of the filtering means (51V e ei that the transmission factor (T) of the wire means! rago (51), for the two transfer functions,   depends on different ways of the frequency. 2. Device according to claim 1, characterized in that the regulating member is an interrup- eur (93). 3. Device according to one of claims % eF 2, characterized in that the lower limited frequency (f-- f3) of the filtering means (51) is different from various transfer functions.   i. Device according to claim 3, charac- terized in that the value of the lower limit frequency   (f%, f3) is between 10 and 30 Hz at one of the functions   transfer tions and at least 35 'z to each other or one other transfer functions.   5. Device according to one of claims 23 1 to -., Characterized in that the maximum transmission factor (T1, T2) of the filtering means (51) is different to the different transfer functions. 6. Device according to claim 5, taken in combination with one of claims 3 and 4, charac- terized in that the maximum transmission factor, at the transfer function which corresponds to the lowest lower limit frequency (fl), is greater than the   maXimal transmission, to the transfer function which responds to the highest lower limit frequency (f3).   7. Device according to any one of the re- vendications i to 6, characterized in that the output of the filtering means (51) is connected to a control member (55) by means of a discriminator (53); in that a pressure sensor (39), serving to sense the pressure in an inflatable deformable chamber (31) which is intended born to be attached to the person to be examined, is related to the control member (55) by means of a different   renciateur (59) and a discriminator (69); in that the discriminators (53, 69) include means for sending pulses to the control member (55) when the signals sent to them by the filtering means (51) or the differentiator (59) exceed a threshold value; and in that the control member (55) has means for detecting noises which appear at the same time as a pressure oscillation due to the heartbeat.   8. Device according to claim 7, ca- characterized in that the chamber (31) is connected to a discharge member (37) to deflate the chamber (31); in that the device comprises a memory (65); and in that   the control member (55) comprises means for storing sine, in the memory (65), that <pD) of the pressure measurement values which is evaluated by the pressure sensor (39) when the noise which appears at the lowest pressure occurs at the same time as an oscillation of pressure due to a heartbeat.   9. Device according to one of claims 7 and 8, characterized in that the microphone (33) and the cap-   pressure sensors (39) are combined into a sound sensor. and pressure which is contained either in an inflatable cuff (1) intended to be fixed to the person to be examined, or in an apparatus (3) detachably connected to this cuff by a pipe (5).