FR2495772A1 - Pen-type blood pressure measuring device - has flexible membrane containing compressible fluid to which counter-pressure is applied for opto-electronic detection of liq. level - Google Patents

Abstract

The pressure arterial blood pressure to be measured is applied to a flexible membrane across the opening of a capsule contg. opaque liq. In the neck of the capsule a smaller quantity of transparent liq. floats on the opaque liq., and the interface level is sensed by a photocell facing an optical projector. Rapid restoration of the membrane to follow instantaneous variations of the pressure is aided by an ar pocket trapped between the transparent liq. and the plug sealing the top of the capsule. The capsule is housed in a tapered cavity in the tip of a probe with wires for the projector supply and photocell output. The transparent liq. can be gelatine, and the opaque liq. mercury.

Description

Device for capturing and exploiting pressure
including fluid
There are very many cases in which it is necessary
be able to capture a pressure, in particular of fluid, and
use it either as a measurement or as a signal
transcodable.

We can cite, for example, the production of sounds at
from the engravings of a disc and which uses the pres
variable sion that the engravings subject to a point of
reading, measuring atmospheric pressure for the cons
truction of barometers or altimeters, the pressure of a body placed on the pan of a scale to measure its weight, the blood pressure in the arteries of a living body to deduce medical information, etc.

 Among these innumerable cases, there is one which is particularly remarkable and which is that of blood pressure. Indeed, in the case of an operation performed on the human body, one must take into account not only physiological data but also psychological factors, particularly with regard to the possible pain that this measure could cause.

 The present invention provides a new solution to the problems of measuring pressure using simple and very effective means.

 The invention will be better understood from the detailed description below made with reference to the accompanying drawing. Of course, the description and the drawing are given only by way of an indicative and nonlimiting example.

 Figures 1 and 2 are two partial schematic sectional views of a device according to the invention according to a first embodiment.

 Figure 3 is a schematic view showing an embodiment of a complete apparatus comprising the device according to the invention.

 Figures 4 and 5 are two schematic sectional views of a second embodiment of the invention.

 FIG. 6 is a diagram showing the association: of a device according to the invention with devices allowing the exploitation of the information given by a device according to the invention.

 Referring to FIGS. 1 and 2, it can be seen that a device according to the invention is intended to capture a pressure, in particular of fluids, and to use it either as a measurement or as a transcodable signal, and is ca characterized in that it comprises a capsule 1 provided with two opposite openings and unequal sections 2 and 3, the largest of which, 2, is closed by a flexible membrane 4 accessible to the pressure to be captured and the smallest, 3, by an elastically compressible member, the capsule 1 containing at least one incompressible liquid 5.

 According to the embodiment shown, the smaller, 3, of the two openings is located at the end of a neck 6.

 According to this same mode. of embodiment, represented in FIGS. 1 and 2, the elastically compressible member is constituted by the combination of a gas such as air 7 placed in the capsule 1 and a rigid shutter 8.

 It is thus seen that by subjecting the membrane 4 to the pressure to be measured, and fitting the capsule 1 so that it remains stationary, the pressure deforms the membrane 4 by varying the internal volume of the capsule 1 in the direction a decrease, which has the consequence of causing the incompressible liquid 5 to rise in the neck 6.

 The volume moved in the wide area of the capsule 1 necessarily remains the same as that which moves in the neck 6, but this being much narrower it is clear that the height over which the movement of liquid 5 occurs is much greater than that which the membrane 4 undergoes in the same direction.

 As a result, a very small displacement of the membrane 4 results in a much more sensitive displacement of the liquid 5 inside the neck 6, which makes it possible to carry out a very precise measurement by detecting the level of the liquid 5.

 In order to be able to detect not only a given pressure but instantaneous variations in this pressure, it is essential that the incompressible liquid 5 be subjected to a back pressure ensuring automatic and instantaneous return of the membrane 4.

 In Figures 1 and 2, we see that this is achieved by providing a small volume of air 7 which is trapped between the incompressible liquid 5 and a plug 8 made, for example, by pouring a synthetic material.

 Thus, the displacement of the incompressible liquid 5 has the effect of compressing the air 7 against the shutter 8 while the relaxation of the membrane 4 is automatically followed by expansion of the air 7 previously compressed.

 A device according to the invention can be produced practically by placing the filled and closed capsule 1 in a slightly frustoconical opening 9 of a support 10 and then covering the assembly by means of a part 11 pierced in its center to receive the upper part of the capsule 1, the latter being blocked by means of a screw 12 with a flat hopper which bears on the shutter 8.

 According to a characteristic of the invention, the device comprises an incompressible liquid level detector.

 According to a particular embodiment, the detector is of the optical type and placed opposite the capsule 1.

 According to a variant, the capsule 1 is transparent and the incompressible liquid 5 is opaque.

 In FIGS. 1 and 2, there is shown an embodiment of the invention according to which the detector is constituted by a set of photoelectric cell 13 projector 14 whose light axis is transverse to that of the capsule 1.

In practice, this is obtained by providing two aligned transverse orifices 15 and 16 communicating with housings, s larger 17 respectively for the cell 13 and 18 for the projector 141
With the housings 17 and IS, there are passages 19 and 20 for electrical wires 21 and 22.

 The operation of this detector is well known in itself and it is known that by supplying the bulb of the projector 14 with an electric current conducted by the wires 22, this projector 14 emits a light beam which crosses the passage 16, the transparent material which constitutes the capsule 1 and the passage 15 to reach the photoelectric cell 13 which sends by the wires 21 an electric current proportional to the illumination which it receives from the beam emitted by the projector 14.

 As long as the opaque and incompressible liquid 5 has its upper level below the light beam, the electric current coming from the cell 13 is exploited in an apparatus of any known type possibly associated with a reading screen so that this situation corresponds at the indication of an absence of pressure. When the liquid level 5 reaches the electric beam, the current created by the cell 13 has a different value and the apparatus indicates this difference which can be either the simple indication of the existence of a pressure, or a precise indication of this pressure by establishing a relationship between its value and the fraction of light beam occulted by the opaque liquid 5.

 Since the level of this liquid undergoes relatively large displacements compared to the minute displacements of the membrane 4, it is easy to detect these large displacements and to deduce therefrom information in the form of very precise electrical pulses.

 In FIGS. 1 and 2, it can be seen that the capsule 1 contains an opaque incompressible liquid 5 and a transparent incompressible liquid 23 both of which are immiscible with one another in order to determine a clear and contrasting contact line which constitutes the level to be detected.

 This avoids possible reading errors due to the very large difference in nature which exists between the incompressible liquid 5 and the air 7.

We chose to illustrate 1 invention with a device suitable for measuring blood pressure and we see in Figure 3 that the device itself as shown in Figures 1 and 2 can be associated with a body 24 secured on the part 11 in such a way that the practitioner can handle the complete apparatus in the manner of a pencil,
The invention is, in fact, particularly interesting for this application because the devices with an inflatable cuff do not allow blood pressure to be taken in arteries such as the carotid artery, the abdominal aorta, the central artery of the retina and many 'others because they are in areas where it is impossible to place the tourniquet that constitutes the inflatable cuff.

 In addition, the measurement of blood pressure cannot be carried out continuously and requires the intervention of the practitioner.

 it is therefore not possible to measure the arterial elasticity or to measure the speed of propagation of the blood pressure wave.

 Naturally, we know the process which consists in acting by bloody way but this is only possible during a surgical intervention and, in any case, this process does not allow the study of all the pulse arteries by pulse.

 The device according to the invention, on the contrary, due to the transduction of the purely mechanical information of the membrane 4 into electrical information then allows the exploitation of this electrical signal by means of devices of all kinds, known in themselves .

It is thus possible to obtain a graphic or a permanent display on a screen or a storage or an operation.
IT is independent, or it is itself associated with complementary devices such as cardiac modulators, alarm systems, etc.

 It can be seen, in fact, that thanks to the invention, it is possible to measure the arterial pressure by applying the membrane 4 to any pulse, including in a non-parkable area.

 The device indicates the pressures exerted on the membrane 4 placed in contact with the skin A while the displacement of the membrane 4 is less than the displacement of the same surface of the wall of the artery B when the latter is not subjected to the device, the less the displacement absorbed by the intermediate fabric B subjected to these pressures.

 The volume increase of arterial segment B during the passage of the blood pressure wave must receive the antagonistic action of the back pressure created in the device and not by the reaction of the wall of artery B.

 The volume increase of segment B is therefore easily measurable since the reference used is the displacement of the upper level of the incompressible liquid 5 which displacement is much greater than that of artery B at equal pressure.

 In order for these conditions to be properly fulfilled, one can either hold the device as shown in FIG. 3, that is to say for a short time, or use rigid holding members such as an inelastic bracelet.

 By associating the device no longer with a pencil-shaped body 24 but with a low base, it is possible to fix the device in the desired location for relatively long times and, for example, for a few days or a few nights. intensive monitoring justified by a serious condition of the patient.

 Several devices can also be placed in the most representative places, for example during a surgical intervention or during in-depth examinations.

 It was indicated above that it could be interesting to combine two liquids 5 and 23 both incompressible and immiscible but one being opaque and the other transparent. By way of example, mention may be made of mercury for the opaque liquid and glycerin for the transparent liquid.

 However, according to another embodiment of the invention, the capsule 1 is made of frosted material and contains a liquid which makes it transparent at least in the area where they are in contact.

 Thus, the displacements of the liquid correspond to the creation of a screen at. light beam from the photocell.

 According to a particular embodiment of the invention, the elastically compressible member is constituted by a membrane possibly associated with a spring.

 In Figures 4 and 5, there is shown such an embodiment.

 We see that here the capsule is not constituted by an independent container placed inside a support but is created by a cavity suitably shaped inside a part 25 which has a tip 26 on which the membrane 4 is held by means of links 27 which surround the assembly.

 The cavity, or capsule, is completely filled with an incompressible liquid 28 and the small opening is closed by an elastic membrane 29.

 We see that according to this embodiment, the detector is constituted by a photoelectric cell 13 - projector 14 assembly, the light axis of which is transverse to a movable screen 30 kinematically connected to an elastic membrane 29 which closes the small opening of the capsule, which is completely filled with at least one incompressible liquid 28.

 According to a variant, the screen 30 is constituted by a bent end of an elastic blade 31 secured by its other end to a fixed part 32 and provided with a pin 33 applied against the outer face of the membrane 29 by the elastic blade 31.

 The fixed part 32 is connected by any known means to the part 25 and is pierced with a hole 34 in which the pin 3: passes freely.

 With these arrangements, it can be seen that small displacements of the membrane 4 cause greater displacements of the membrane 29 which repels the pin 33 and, consequently, the blade 31 and the screen 30 which is placed more or less completely in look of the light beam to obscure it at least in part from which it results in a variable current in the wires 21.

When the membrane 4 is subjected to a lower or zero pressure, the incompressible liquid 28 and the membrane
elastic 29 return to their original position under the effect of the pin 33 which is pushed by the elastic blade 31.

 These provisions can be adopted for reasons of space or construction facilities. They have the advantage of being more stable to shocks since the action of the elastic blade 31 is more constant than that of the air bubble provided with the embodiment of FIGS. 1 and 2.

 Another advantage of these arrangements results from the fact that the device is completely stabilized with heat since the elastic blade 31 is practically insensitive to temperature variations while the air bubble can expand more or less depending on the atmosphere in which the device is found.

 According to another embodiment of the invention, an optical deflector is not used but it is provided that the capsule is internally provided with at least two studs externally connected to an electrical circuit and contains at least one incompressible and conductive liquid. current in order to establish an electrical contact between the two studs.

 One can foresee, for example, that the electric circuit includes a resistor which becomes, therefore, a variable resistor according to the pads that the conductive liquid brings together.

 It is also possible to power the electrodes which the conductive liquid covers more or less to create variable electrical signals as a function of the pressure undergone by the membrane 4.

 When using an optical detector with a photocell, the projector 14 can be omitted, which decreases the consumption of electric current by using ambient light. Two photowelectric cells are then rocked, which both receive ambient light but one is associated with a screen of type 30 so that ultimately the one which receives direct ambient light without being influenced by the device, serves as reference to the one associated with the screen.

To measure the displacement of an arterial wall in order to calculate an arterial elasticity index, a device according to the invention of one of the types described must have a back pressure (of air, of membrane or of elastic blade) lower than the back pressure exerted by the arterial wall. In FIG. 3, the displacement of the membrane 4 is then equal. at the displacement of the same surface of the wall of the artery B minus the displacement absorbed by the intermediate tissue C. The device then indicates an amplified displacement. The relationship between this displacement of a surface and the pressure variation on this same surface gives the elasticity index of the artery.

 FIG. 6 shows an example of the combination of a portable device according to the invention and of fixed devices.

 In this figure, it can be seen that the entire installation includes a supply 40 of electric current, preferably at low voltage such as 12 volts, a rectifier 41 at the input of the projector, an amplifier 42 at the output of the cell. photoelectric and, finally, a display device 43 comprising here a series of indicator lights 44 whose switching on and off are controlled by the amplified signals of the photoelectric cell, which are created by the movements membrane 4.

 It emerges from the description above, that a device according to the invention makes it possible to transform into electrical signals mechanical implusions born of a pressure whose value varies more or less quickly.

 The invention therefore finds a very large number of applications and, depending on the case, it is easy to vary the two essential components which are the volume displacement on the one hand and the back pressure on the other hand.

One can, for example, apply the invention to the manufacture of barometers, altimeters or tachometers (according to the principle of the Pitot tube using the lateral fluid flow back pressure) or any system
liquid gauge.

You can use a rigid intermediate plate
to make a balance.

By associating a mobile mass with the membrane 4, we
can measure the acceleration or deceleration experienced by
the device.

The materials currently available allow
to minimize the inertia of the incompressible liquid
so that the invention can be applied to the fabrica
reading heads for turntables, or in manufacturing
microphones, being stressed that we can tune the external surface
of the device at the wavelength to be studied.

The invention can also be applied according to the
balance principle for monitoring and maintenance
plants placed in a tank: when the humidity of the
earth mass decreases, the pressure exerted on the membrane
ne of the device fixed under the tank decreases and one can
provide that from a certain threshold, the device com
requires the opening of a solenoid valve which feeds the tank
in irrigation water.

We can also study the propagation of a pressure wave in a wind tunnel by placing a line
series of devices and simultaneously recording
the value given by each of the devices so that
we obtain both the pressures and the speed of
wave propagation.

According to a particular embodiment, the organ
elastically compressible is associated with an element of
transcoding of mechanical information transmitted by
said body in exploitable information such as electronic
triques, electronic and the like.

For example, the embodiment shown on
Figures 4 and 5 can no longer include a set
optical and a mobile screen but a piezoresistive plate
aunt (not shown) applied against the membrane 29
in order to transform the pressures into an electric current
absolute or differential transmitted to the wafer
by the membrane 29, Any other transcoding element
sensitive to the pressures and / or movements of the elastically compressible member can be used depending on the case and this choice is within the reach of the skilled person (variations of capacities, variations of magnetic fields, etc.).

 When the device is applied to the measurement of blood pressure, one can seek sufficient miniaturization to implant it in the body. One can, in particular, place it in the cardiac region, against a rib, which immobilizes it.

 In this case, the solutions most suitable for reducing the size of the device and the constraints that it could impose must be retained. We can, for example, use an internal assembly comprising on the one hand the "sensor" proper consisting of the capsule and its membrane and on the other hand two optical fibers leading to an external reading device (projector and photoelectric cell).

 In order to remove the connecting electrical wires, a miniature radio transmitter can be provided, installed with the sensor and an external receiver associated with any desired device: display, alarm, IT, etc.

 The invention is therefore not limited to the embodiments described and shown but on the contrary embraces all variants.

Claims (16)

1 - Device for capturing a pressure, in particular of fluid  and to use it either as a measure or as a ti  tre transcodable signal, characterized in that it comprises  takes a capsule (1) provided with two opposite openings  and unequal sections (2 and 3), the largest of which (2)  is closed by a flexible membrane (4) accessible to  the pressure to be captured and the smallest (3)  by an elastically compressible member, the capsule (1)  containing at least one incompressible liquid (5). 2 - Device according to claim 1, characterized in that  that the smaller (3) of the two openings (2 and 3) is  located at the end of a neck (6). 3 - Device according to claim 1, characterized in that  that the elastically compressible member is made up  by a membrane (29) possibly associated with a res  exit (31). 4 - Device according to claim 1, characterized in that  that the elastically compressible member is made up  by the combination of a gas such as air (7) placed  in the capsule (1) and a rigid shutter (8). 5 - Device according to claim 1, characterized in that  that it includes a detector of the incom liquid level  pressable.  opposite the capsule (1).  that the detector is of the optical type (13-14) is placed  6 - Device according to claim 5, characterized in that 7 - Device according to claim 5, characterized in that  the capsule (1) is transparent and the liquid (5)  opaque. 8 - Say positive according to claim 6, characterized in that  that the capsule (1) is made of frosted material and contains a  liquid which makes it transparent in the area where they are  in touch. 9 - Device according to claim @, characterized in that the capsule (@) contains an opaque uncompressible liquid (5) and  an incompressible transparent liquid (23), all those not misci  between them to determine a clean contact line and  contrast which constitutes the level to be detected. 10 - Device according to claim 5, characterized in that  that the detector is made up of a cell assembly  photoelectric (13) - projector (14), whose axis read  the mineral is transverse to that of the capsule (1). 11 - Device according to claim 5, characterized in that  that the detector is made up of a cell assembly  photoelectric (13) - projector (14) whose lumi axis  neux is transverse to a mooile screen (30) connected to cine  matically to an elastic membrane (29) which seals the  small opening (3) of the capsule (1), which is  completely filled with water minus an incompressible liquid (5). 12 - Device according to claim 11, characterized in that  that the screen (30) is constituted by an even end  bent bent with an elastic blade (31) secured  by its other end to a fixed part (32) and provided  a pin (33) applied against the outer face of  the membrane (29) by the elastic blade (31). 13 - Device according to claim 5, characterized in that  that the capsule (1) is internally provided with at least  two studs externally connected to an electrical circuit  that and contains at least one incompressible liquid and  current conductor in order to be able to establish a con  electric tact against the two studs.  14 - Device according to claim 1, characterized in that  that it includes a body (10-11-24) which has exterior  laughingly the flexible membrane (4) which is adapted to  be kept for a longer or shorter time in a place  read from the surface of a living body so that the membrane  (4) is subjected to the pressure resulting from the increased  radial volume tion of an arterial segment in which  blood pressure develops. 15 - Device according to claim 14, characterized in that  that the body (10-11) is associated with hand organs  yours rigid like an inelastic bracelet. 16 - Device according to claim 1, characterized in that  that the elastically compressible member (7-8, 29-31) is  associated with an information transcoding element  mechanical transmitted by said body in information  usable such as electrical, electronic and  analogues.