FR2559051A1 - Method and devices for detecting the arterial pulse - Google Patents

Abstract

The subject of the invention is a method and devices for detecting the arterial pulse. A device according to the invention includes a pulse detector 1 which is fixed by straps 2 on the wrist of a patient. The detector 1 includes two notches 3a, 3b which are placed astride an artery. It includes a deformable membrane fitted with a sensor which is applied against the artery by a gas back pressure which is exerted on the inner face of the membrane. The detector 1 is connected by a flexible pipe 4 to a box 5. The tube 4 contains optical fibres 6 which illuminate a reflector carried by the membrane and which detect the reflected light. The box 5 contains a photoelectric receiver and electronic circuits which deliver an electrical signal which represents in analog manner the movements of the membrane and therefore the deformations of the artery. One application is the measurement of the pulse in well-determined back-pressure conditions.

Description

 Method and devices for sensing the arterial pulse

 The present invention relates to a method for sensing the arterial pulse and a sensor using this method.

 The technical field of the invention is that of the construction of measuring apparatus.

 It is known that measurement of the arterial pulse, that is, the number of heartbeats per minute, is indicative of the condition of a patient. It is generally measured, approximately, by pressing a finger on the artery at the wrist and counting the frequency of beats by means of a timer.

 Analog pulse sensors are known which convert the beats into oscillating electrical signals whose frequency is equal to that of the pulse.

 The MAREY capsule is a known pulse sensor, which has a capsule closed by a deformable membrane and filled with a fluid. This hand-held capsule is applied to the wrist of a patient in a position where a lug secured to the center of the membrane is pressed against the artery.

 Periodic deformations of the artery are transmitted to the membrane and are transformed into pressure variations. The capsule is connected to a transducer that converts pressure variations into electrical signals whose frequency measures the pulse.

 Systematic tests were carried out to study the influence of the pressure exerted on an artery on the amplitude of periodic deformations of the artery due to the heartbeat. These studies have shown that the amplitude of the deformations depends on the back pressure and goes through a maximum for a well-defined counterpressure.

 Moreover, if the pulse rate is measured under backpressure conditions which correspond to the maximum amplitude of the deformations, a curve is obtained which is the one which most faithfully reproduces the variations of the pressure in the artery. at the place of the measure.

 In order to obtain a very precise representation of the arterial blood pressure, it is therefore very important to be able to precisely adjust the back pressure exerted on the artery during the measurement of the pulse in order to maintain a counter-pressure during the entire measurement. uniform pressure, constant and well determined.

 Known pulse sensors comprising a membrane capsule associated with a transducer do not allow precise control of the back pressure exerted on the artery. They are held by hand and the back pressure varies with the operator. In addition, they have no means of regulating the pressure of the fluid contained in the capsule and it varies with the ambient temperature.

In addition, some of the energy that is transmitted by the membrane to the fluid is transformed into heat.

 An object of the present invention is to provide means for sensing the arterial pulse which makes it possible to adjust with very great precision the pressure exerted by the sensor on the artery in order to be able to choose the back pressure which corresponds to the maximum amplitude of the deformations of the artery and to be able to maintain a constant back pressure during a measurement and a reproducible counter pressure during successive measurements.

 Another object of the present invention is to provide means for performing very accurate and high fidelity pulse measurements.

 An arterial pulse analog record has rising portions that correspond to systoles and descending portions that correspond to diastoles.

 Studies have shown that the descending or diastolic part has an exponential shape of the form y = Ae u> that is, an exponential that tends to a horizontal asymptote of ordinate p. If the measurement of the arterial pulse is carried out under conditions of counterpressures such that the amplitude of the deformations of the artery is maxima, the ordinate p has a physiological significance.

It corresponds to the position of the wall of the artery at rest, which can not be measured directly.

 The measurement of the arterial pulse under reproducible counterpressure conditions thus provides an indirect means of determining the resting position of the artery and hence of determining whether the artery is distended. Measurements staggered over time on the same patient make it possible to determine the evolution of the state of the arteries of this patient.

 Optoelectronic sensors of physical quantities are known, in particular displacement sensors, which comprise optical fibers which direct a light beam perpendicularly to a reflector and which pick up the light reflected by the latter whose intensity varies linearly as a function of the distance of the reflector.

 Such sensors are described in the FR patent. 77 / 36,542 (BEAUFRONT J. and Company SEAT S.A.).

 The pulse sensors according to the invention constitute a new application of optoelectronic displacement sensors for sensing the deformations of an artery due to the pulse under specific operating conditions.

The objectives of the invention are achieved by a method for measuring the arterial pulse which comprises the following operations
in the path of an artery, preferably the artery of the wrist, a sensor comprising two notches which are placed astride said artery, which sensor comprises a deformable membrane provided with a probe on its external face and a reflector on its internal face;
the end of said probe is placed in contact with the skin on the path of the artery;
a slight back pressure is exerted on the inner face of the membrane, having a determined value corresponding to the maximum amplitude of the deformations of the artery, so that the thrust on the membrane keeps the probe in permanent contact with the skin;;
a luminous beam is sent on said reflector and the reflected light is captured by means of two optical fiber bundles whose end is placed very close to said reflector;
and the reflected light is converted by means of a photoelectric transducer into an electrical signal which analogically represents the artery deformations due to the pulse.

 A device according to the invention comprises a sensor which is provided with fixing means on the body of a patient in the path of an artery, which sensor comprises a deformable membrane which is equipped with a probe in the center of its outer face. and means for placing the end of said probe in contact with the skin in the path of the artery and said device comprises a flexible tube connecting said sensor to a measurement box which contains a light source, photoelectric transducers and a compressed gas source at a low adjustable pressure and said flexible tube contains two bundles of optical fibers, a first beam which conducts the light of said light source on the inner face of said membrane and a second beam which captures the light reflected by said membrane and which leads to said photoelectric transducer and said flexible tube further transmits the pressure of said gas to the inner face of said membrane.

 The sensor equipping a device according to the invention comprises a hollow cylindrical body whose end comprises two diametrically opposed notches which are placed astride the path of said artery.

 According to a preferred embodiment, the sensor of a device according to the invention comprises a finger which slides axially inside said cylindrical body and which is traversed by an axial bore and the end of said finger is equipped with a head. rounded which is pierced with an axial orifice and said deformable membrane is clamped between said head and the end of said finger, in a position such that said probe is engaged in said axial orifice and that the end of said probe is located in the plane tangent to the end of said head.

 The present invention results in means for measuring the arterial pulse and recording a highly amplified signal which is analogous to the deformations of an artery on which the pulse is taken.

 The method and the devices according to the invention make it possible to record the pulse under conditions in which the artery is compressed with a very small and determined back pressure, so that the amplitude of the movements of the artery is maxima.

 The pulse sensors according to the invention make it possible to perform pulse measurements under perfectly reproducible operating conditions and thus to compare records made on the same patient at different periods, to study an evolution.

 The pulse sensors according to the invention have the advantage that the pulse is captured by means of a membrane whose movements are captured by the reflection of a light beam, which introduces no braking of the movements of the membrane or no mechanical inertia.

 In addition, the sensor that is applied to the body of the patient does not include any portion turned on and the use of this sensor does not present any danger of electrocution.

 The pulse sensors according to the invention make it possible to obtain very precise pulse recording curves from which it is possible to deduce, by extrapolation, the ordinate of the asymptote of the falling part of the curve corresponding to the diameter at rest of the artery as well as the slope of the exponential.

 The following description refers to the accompanying drawings which show, without any limiting character, an exemplary embodiment of a device according to the invention.

 Figure 1 is an overview of a device for sensing the arterial pulse on the wrist of a patient.

 FIG. 2 is an axial half-section of a sensor equipping a device according to the invention.

 Figure I shows an overview of a device according to the invention for measuring the pulse. This device comprises a sensor I which is fixed on the anterior face of the wrist of a patient by means of a strap 2 which surrounds the wrist or by any other equivalent attachment means.

 The sensor 1 has two diametrically opposed notches 3a, 3b which are arranged in the path of the artery which is under the skin of the wrist and on which the pulse is to be sensed. These notches prevent compression of the artery by the sensor.

 The straps 2 are arranged in a diametral plane perpendicular to the plane passing through the notches 3a, 3b.

 The sensor 1 is connected by a flexible conduit 4 to a box 5.

The conduit 4 is a small tube having for example a diameter of 4 to 6 mm twist. Optical fibers 6 pass through the tube 4 and connect the box 5 to the head 1. The box 5 contains a light source, for example a light emitting diode and one or more optical fibers carry the reflected light to optoelectronic circuits contained in the cabinet 5. These circuits comprise a photoelectric cell or a phototransistor or any photoelectric transducer which transforms the reflected light into electrical signals and electronic circuits for filtering and amplifying the signals.

 The cabinet 5 delivers an electrical signal that analogically reproduces the pulse of the patient. This signal can be recorded graphically, displayed on a screen, or decomposed into numerical values that can be recorded and / or processed.

 The optical fibers 6 and the circuits contained in the box 5 are similar to those composing the optoelectronic devices described in the FR patent. 77 / 36.542 and it is not necessary to describe them in more detail.

 The conduit 4 is connected to a source of compressed gas under a very low pressure, for example of the order of a few tens of millibars and this pressure is adjustable. For example, the tube 4 is connected to a graduated syringe and the pressure in the tube is tilted by moving the plunger of the syringe.

 FIG. 2 is a half section of the sensor 1 passing through the plane II-II of FIG.

 The sensor 1 comprises a hollow body 7 which has a generally cylindrical shape and which delimits an axial bore 7a. A threaded ring 8 is screwed onto a male thread 9 of said hollow body. A ring 10 is interposed between an outer shoulder of the hollow body and the ring 8. This ring carries loops on which are fixed the straps 2 which surround the wrist and which hold the sensor on the wrist.

 On the left side of the figure is the notch 3a which is astride the path of the artery 39.

 The sensor 1 comprises a membrane support 11 which has the shape of a cylindrical finger which slides inside the bore 7a. This finger 11 is traversed through by an axial bore 12. The front end of the finger 11 has a male thread 13 on which is screwed a sensor head 14 in the form of a ring which extends beyond the end of the finger 11 by a rounded head 14a which is pierced with an axial orifice 15.

 A thin and very flexible deformable membrane 16 is placed across the front end of the finger 11. The membrane 16 is for example a thin sheet of latex or other elastomeric material. It is glued to a washer 17 which is clamped between the end of the finger 11 and a shoulder of the head 14a.

 The membrane 16 seals the front end of a chamber 18 which communicates with the bore 12 through orifices 19 pierced in a partition 20.

 A probe 21 is fixed to the center of the membrane 16 on the outer face thereof. This feeler is for example a small piece of cylindrical rod made of aluminum alloy. It has an outer diameter smaller than the diameter of the orifice 15 in which it is engaged. The free end of the probe 21 is located in the plane tangent to the end of the head 14a.

 A reflective patch 22 may be glued to the center of the inner face of the membrane. However, this reflector is optional and can be removed if the membrane is sufficiently reflective.

 The upper end of the sliding finger 11 carries a ring 23 which is placed across the bore 12 and which is pressed on a shoulder of the finger 11. This ring 23 is pierced with orifices 24. It carries an axial endpiece 25 in which are engaged the ends of the optical fibers 6.

 The tip 25 extends over the entire height of the bore 12 and its lower end is placed opposite the reflector 22 and at a very short distance therefrom, for example at a distance of 0.5 mm. The tip 25 is held by the partition 20, by elastic washers 26 and the ring 23 and is integral with the finger 11, so that the distance from the end of the tip to the reflector remains constant when the finger 11 is moved. The tip 25 contains a bundle of optical fibers which extend the fibers 6 passing through the flexible conduit 4 and the ends of these fibers are perpendicular to the reflector 22.

 The upper end of the finger 11 carries a female thread 27 in which is screwed a threaded plug 28 which has a skirt 29 which blocks the ring 23. A seal 30 is interposed between the cap 28 and the upper end of the finger 11. The plug 28 carries a rigid axial tube end 31 which emerges on the outside and on which is engaged a flexible tube 4.

 The sliding finger 11 carries an external thread 32 on which a threaded ring 33 provided with a knurled head 34 is screwed.

 The ring 33 is provided with an external flange 35 which is engaged under an internal flange 36 of the ring 8, so that the ring 33 can rotate freely, but can not move axially.

 The sliding finger 11 has a longitudinal groove 37 and the cylindrical body 7 carries a radial lug 38 which is engaged in the groove 37 and which prevents the finger from rotating while allowing it to move axially. It can thus be seen that by turning the knurled head 34, the finger 11 is moved axially, which thus makes it possible to position the convex head 14a with respect to the end of the body 7. It can also be seen that the inside of the tube 4 communicates with the chamber 18 by the nozzle 31 and the bore 12, so that the back pressure can be adjusted in the chamber 18.

 The operation is as follows.

 To record the pulse of a patient, the sensor is fixed around the wrist of the patient by means of the straps 2. It is fixed in the position where the artery of the wrist 39 is aligned with the two indentations 3a, 3b whose width is greater than the diameter of the artery, so that it is not compressed. By turning the knurled head 34, the finger 11 is slid until it just comes into contact with the skin without compressing it. The end of the probe 21 is then pressed against the skin by a slight thrust of the membrane 16 due to the back pressure exerted on the inner face thereof.

 The probe 21 follows the movements of the skin caused by the deformations of the artery due to the pulse and transmits these movements to the membrane 16.

 The reflector 22 moves periodically. The distance between the end of the optical fibers and the reflector 22 is chosen so that one is in a range where the intensity of the reflected light varies linearly with the distance between the light source and the reflector.

 The photoelectric transducer in the housing 5 receives a beam of reflected light whose intensity reproduces the movements of the membrane and transforms it into an amplified electrical signal which analogically represents the deformations of the artery due to pulse.

Claims (7)

 1. Method for sensing the arterial pulse, characterized by the following operations  in the path of an artery (39), preferably the artery of the wrist, is fixed a sensor (1) comprising two notches (3a, 3b) which are placed astride said artery, which sensor comprises a deformable membrane; (16) provided with a probe (21) on its outer face and a reflector (22) on its inner face;  placing the end of said probe (21) in contact with the skin in the path of the artery;  a slight back pressure, having a determined value, which corresponds to the maximum amplitude of the deformations of the artery, is exerted on the inner face of the membrane, so that the thrust on the membrane keeps the probe in permanent contact with the skin;;  a luminous beam is sent to said reflector and the reflected light is captured by means of two bundles of optical fibers (6) whose end is placed very close to said reflector (22);  and the reflected light is converted by means of a photoelectric transducer into an electrical signal which analogically represents the artery deformations due to the pulse.  2. Device for collecting the arterial pulse, characterized in that it comprises a sensor (1) which is provided with fixing means (2) on the body of a patient in the path of an artery (39), which sensor comprises a deformable membrane (16) which is equipped with a probe (21) in the center of its outer face and means for placing the end of said probe in contact with the skin in the path of the artery and said device comprises a flexible tube (4) connecting said sensor to a measurement box (5) which contains a light source, photoelectric transducers and a gas source compressed under a low adjustable pressure and said flexible tube contains two bundles of optical fibers ( 6), a first beam which conducts the light of said light source on the inner face of said membrane and a second beam which captures the light reflected by said membrane and which leads to said photoelectric transducer and said flexible tube (4) transm and, in addition, the pressure of said gas to the inner face of said membrane (16).  3. Device according to claim 2, characterized in that said sensor (1) comprises a hollow cylindrical body (7) whose end comprises two notches (3a, 3b) diametrically opposite which are placed astride the path of said artery (39).  4. Device according to claim 3, characterized in that said body is equipped with straps (2) which are arranged in a diametral plane perpendicular to the plane defined by said notches (3a, 3b) and which allow to fix said body around the wrist of a patient.  5. Device according to any one of claims 2 to 4, characterized in that said sensor comprises a finger (11) which slides axially inside said cylindrical body (7) and which is traversed by an axial bore (12). and the end of said finger is equipped with a rounded head (14, 14a) which is pierced with an axial orifice (15) and said deformable membrane (16) is clamped between said head and the end of said finger in a position such that said probe (21) is engaged in said axial orifice (15) and that the end of said probe is located in the plane tangent to the end of said head (14a).  6. Device according to claim 5, characterized in that said finger (11) has an external thread (32) and a longitudinal groove (37) in which is engaged a radial lug (38) integral with said cylindrical body (7) and said sensor further comprises a threaded ring (33) which is screwed onto said thread and which has a flange (35) which cooperates with a flange (36) of said body, so that said ring can rotate without moving axially relative to said body and the rotation of said ring makes it possible to deem axially said finger to bring said head (14a) in contact with the skin of the patient.  7. Device according to any one of claims 2 to 6, characterized in that said membrane comprises, in the center of its inner face, a reflector (22) and the ends of said optical fibers (6) are arranged perpendicularly to said reflector and to very short distance from it.