GB1598984A

GB1598984A - Apparatus for the non-invasive determination of blood pressure primarily for babies

Info

Publication number: GB1598984A
Application number: GB2043578A
Authority: GB
Original assignee: Medicor Muvek
Current assignee: Medicor Muvek
Priority date: 1977-12-21
Filing date: 1978-05-18
Publication date: 1981-09-30
Also published as: JPS5486990A; PL207193A1; PL119631B1; DD136451A5; DE2821037B2; HU176288B; FR2412298A1; DE2821037C3; DE2821037A1; BG28983A3

Description

(54) APPARATUS FOR THE NON-INVASIVE DETERMINATION OF BLOOD PRESSURE, PRIMARILY FOR BABIES (71) We, MEDICOR MijVEK, a body corporate organised under the laws of Hungary, of 1389 Budapest, Röntgen utca 11-13, Hungary do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention concerns apparatus for the non-invasive determination of blood pressure primarily for babies. Furthermore, the apparatus is suitable for carrying out vein-occluding plethysmographic examinations serving for judging the condition of the arterial and venous circulation systems of limbs as well as their capillaries somewhat in the manner of a screen examination, in an ambulant condition. Thus, the apparatus is in essence a complex measuring system which is suitable for simultaneous measurement of interrelated and mutually complementary parameters.

DESCRIPTION OF THE PRIOR ART It is a known fact that as a consequence of environmental and other damage, an increasing proportion of babies are born with some damage in their health requiring longer-term medical supervision and care. This fact requires the creation of medicaltechnological means suitable for the rapid, accurate and preferably non-invasive measurement of the various vital functions of babies.

It is a further fact that one of the most important vital functions is the value of the blood pressure. Innumerable attempts have been made to measure this. However, a reliable convenient and risk-free method of measurement involving arterial puncture cannot be used for babies because of the dimensions of the baby's arterial system and because of the dangers involved, except in the period immediately after birth when the umbilical cord is treated. The non-invasive measurement based on the auscultatory principle developed by Riva-Rocci-Korotkoff is not reliable because of the low intensity of the sounds from the veins since the sensitivity of the stethoscope or microphone cannot be increased because of "noise" from the environment. Another process, the so-called "flush" or continuous flow process, is suitable for determining the systolic pressure value. Its essence is that a tourniquet or cuff (hereafter, for simplicity, cuff) placed on a limb is inflated to a pressure higher than the systolic pressure, then the pressure is slowly decreased and the systolic pressure is regarded as that cuff pressure at which the section of the limb after the cuff starts to redden. The inaccuracy and subjective nature of this method are manifest.

An earlier known process suitable also for the determination of the diastolic value of blood pressure is described in connection with Figures 1, 2, 3, 4, and 5. A cuff M (Figure 1) placed on the limb of the baby is inflated to a pressure above the systolic pressure value whereupon the flow of blood ceases into the section of the limb after the cuff M. Then by gradually releasing the pressure PM of the cuff, when the systolic pressure Ps is achieved Figure 2) the blood flow restarts and the section of the limb distal from the cuff M starts to increase in volume from its rest or normal volume VO. The volume increase is monitored by a sensor G (Figure 1) and/or is registered by a suitable apparatus (Figure 3). The cuff pressure PM arising when the limb volume begins to increase agrees with the systolic blood pressure Ps.

The determination of the diastolic pressure PD takes place as follows: The cuff is deflated in several steps to a gradually reducing pressure lower than the already known systolic pressure Ps (Figure 4) and the gradient of the curve of the volume change is registered (Figure 5). The cuff pressure associated with that gradient of change of volume which no longer changes with further decreases in cuff pressures PM is regarded as the diastolic blood pressure PD. The explanation of this phenomenon is that if the cuff pressure agrees with the diastolic pressure PD or is less than that (PMAPD) then the flow of blood into the section of the limb distal from the cuff M is no longer impeded by the pressure of the cuff M.

The above-described process is cumbersome, time-consuming and above all inaccurate, and for two reasons: on the one hand, a fine graduation of the cuff pressure PM is difficult to ensure because the repeated inflation and deflation of the cuff represent a coarse interference with the circulation mechanism, which inherently makes it doubtful that the measured values are accurate and on the other hand, the determination by manual registration of the gradient of the curve describing the volume change is rendered difficult by a pulse wave superposed on the curve (Figures 3 and 5).

SUMMARY OF THE PRESENT INVENTION The apparatus in accordance with the invention is defined in claim 1 or claim 2 appended hereto. It eliminates or reduces the above drawbacks: it is suitable for the rapid, accurate automatic and non-invasive determination of systolic and diastolic arterial blood pressure values as well as the venous blood pressure. Furthermore, it is suitable for carrying out so-called vein-occluding plethysmographic examinations. This latter is particularly significant because expert medical opinion agrees that for judging the general condition of the circulation system, the value of the blood pressure and the data obtained by the vein-occluding plethysmographic tests supplement each other in promoting the formation of a correct diagnosis.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described, purely by way of example, with reference to the accompanying drawings. In the drawings, known processes are described in Figures 1 to 5, wherein: Figure 1 represents one possible mode of placing the cuff M and the volume sensor Cl for measuring the volume change of the limb, Figure 2 represents the change in the pressure PM of the cuff M as a function of time in the course of determining the systolic pressure value P5, Figure 3 illustrates the characteristic of the volume change of that section of the limb of normal or rest volume V0 which is distal from the cuff M, in the course of the determination of the systolic pressure Ps, Figure 4 illustrates the pressure programme of cuff M in the course of determining the diastolic pressure PD, and Figure 5 illustrates the characteristic of the change in the gradient of the volume change measured by the volume sensor G during the determining of the diastolic blood pressure PD.

and Figure 5 illustrates the characteristic of the change in the gradient of the volume change measured by the volume sensor G during the determining of the diastolic blood pressure PD.

Figures 6 to 15 refer to the apparatus according to the invention. More particularly: Figure 6 illustrates the pressure change in the cuff M of the apparatus according to the invention as well as the blood pressure curve, as a function of time, Figure 7 illustrates the change in volume of the limb section distal from the cuff M as measured by the volume sensor G and illustrates the pulse train superposed on the useful signal, Figure 8 illustrates one embodiment of the apparatus according to the invention Figure 9 illustrates a possible refinement of the pressure programme of Figure 6, Figure 10 illustrates a pressure programme achievable with the apparatus according to the invention, but different from the foregoing, Figure 11 illustrates the volume change characteristic of the limb associated with the cuff pressure programme according to Figure 10 and illustrates also the pulse train superposed on the useful signal, Figure 12 illustrates a possible refinement of the pressure programme according to Figure 10, Figure 13 shows another preferred embodiment of the apparatus according to the invention, Figure 14 shows a further preferred embodiment of the apparatus according to the invention, and Figure 15 illustrates yet another preferred embodiment of the apparatus according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

Referring to the drawings, the apparatus is constructed as follows: The inflatable cuff M that can be placed on the limb is connected with a pressure sensor GM the output of which is connected to the input of a sampling and holding circuit S1.

The output of a volume sensor G disposed distally from the cuff M is on the other hand connected with the input of a further sampling and holding circuit S2.

A pulse sensor GP is disposed at any desired location on the body and its output is connected to the input of an analyser PA. Analyser PA serves for periodically determining respective points in the same phase of the pulse curve or an ECG signal. The outputs of the sampling and holding circuits S1 and S2 are connected to the first and second inputs of a multiplexing unit C1 the output of which is connected to the input of an analog-digital converter D. The output of the latter is connected to the input of a demultiplexing unit C2 the output of which is connected to one input of a read/write (random access) memory R.

The other input of the read/write memory R is connected with an arithmetical unit PR which is connected so as to be suitable for handling bidirectional data and address traffic.

At least one indicating instrument K is connected with the output of the arithmetical unit PR. A control unit V1 is incorporated in the apparatus and has several inputs and outputs.

One output of the control unit V1 is connected with a pneumatic unit N the output of which is connected to the cuff M.

One input of the control unit V1 is connected to an output of the already mentioned analyser A while another input thereof is connected to the output of a clock generator T.

The other output of the control unit V1 is connected to the second input of the first sampling and holding circuit S1 while its third output is connected to the second input of the second sampling and holding circuit S2. Its fourth output is connected to the third input of multiplexing unit C1 while its fifth input is connected to the second input of the analog-digital converter D; at the same time, the sixth output thereof is connected to the second input of the also previously mentioned demultiplexing unit C2. The control unit V1 is connected to the arithmetical unit PR and the read/write memory R in such a manner as to be capable of handling bi-directional data and address traffic.

The output of analyser PA is connected to one input of the control unit V1 while the second input of the same analyser PA is connected either to the output of an ECG channel E or to pulse sensor GP.

The operation in principle of the apparatus should take place as follows: The cuff M is inflated to a pressure exceeding the systolic pressure PM > PS, then the pressure is slowly reduced e.g. at a rate of 1 Hgmm/sec. so that when the systolic pressure is reached, the limb section distal from the cuff M rises in volume from its initial volume V0 (Figures 6 and 7, tj). The gradient of the change of volume monitored by the sensor G (the slope of the curve m Figure 7), rises in a gradually steepening manner because the gradually decreasing cuff pressure enables an increasing volume of blood to reach the limb section distal from the cuff M (Figure 6, the quantity corresponding to the shaded area of the blood pressure curve). Thereafter, when the pressure of the cuff M reaches the diastolic pressure PD or becomes smaller than that (PM ' PD) the gradient of the curve describing the volume change becomes constant (Figure 7, the section following the time tk), since the pressure of the cuff M no longer impedes the flow of blood.

The task therefore is to determine the cuff pressure associated with time tj and corresponding to the systolic pressure Ps and the cuff pressure associated with the time tk and corresponding to the diastolic pressure PD. Since essentially one is concerned with the determination of the gradients of given sections of the curve illustrated in Figure 7, or more precisely with the comparison of the gradients of the preceding sections, one requires apparatus which can determine these values while eliminating or ignoring the disturbing effect of the superposed pulse train.

The apparatus according to the invention shown in Figure 8 is capable of solving this task.

This takes place as follows: At the commencement of measurement, on the command of the control unit V1 the pneumatic unit N inflates the cuff M to a value exceeding the systolic pressure (Figure 6, PM > Ps) then gradually decreases it. The pressure of the cuff M is measured by the pressure measuring or transducing device GM. The change in volume, which starts at time tj and can be characterised by a curve the gradient of which becomes increasingly steep up to the time tk, is monitored by the volume sensor G. At the same time, a pulse sensor GP placed at any desired part of the body senses the pulse curve and connects it to the input of analyser PA.

The analyser PA selects in each period of the pulse curve a respective point of identical phase and at the instant of time appropriate to these points, sends synchronous signals to the control unit V1.

To simplify the discussion, in the description that follows, it is assumed that the selected points are the systolic points of the pulse curve and that the phase of the pulse train (Figure 7) superposed on the curve describing the volume change and the phase of the pulse curve registered by the pulse sensor GP are in agreement. (This condition is satisfied if the pressure wave starting from the left chamber of the heart arrives at the same point in time to the volume change sensor G and to the pulse sensor GP. This for the time being means a certain limitation regarding the positioning of the pulse sensor GP). At the instant of time corresponding to the systolic point of the pulse train, the control unit V1 sends sample taking commands to the sampling and holding circuits S1 and S2; the sampling and holding circuit S1 sends samples from the output signals of the pressure sensor GM to the multiplexing unit C1 while the sampling and holding circuit S2 sends samples from the output signals of the volume sensor G to the multiplexing unit C1. On the command of the control unit V1 the multiplexing unit C1 alternates the output signals from the sampling and holding circuits S1 and S2 and connects them to the transforming input of the analog-digital converter D. The output signal of the analog-digital converter is separated by the demultiplexing unit C2 controlled by the control unit V1 into signals proportional to the cuff pressure and to the volume change of the limb and then the signals are connected to the input of the read/write memory R.

In parallel with the described operations, the control unit V1 continuously forms signals proportional to the periodicity of the pulse train of the clock generator T in accordance with the synchronous signals coming from the analyser PA and connects them to the input of the read/write memory R whilst at the same time it also fulfils the control tasks connected with the storage of signals arriving from the demultiplexing unit C2. Accordingly, therefore, the read/write memory R contains the following associated values: the cuff pressures Pj-1, Pj, Pj+1... Pk-1, Pk, the limb volume values Vj-1, Pj, Vj+1...Vk+1, Vk, Vk+1...

associated with the times.. .tj-1, tj, tj+1...tk-1, tk, tk+1...

the Period times Atj4 = (tj tji), #tj = (tj+1-tj).., Atki= (tk - tk l), Atk = (tk+1 - tk) or the pulse trains immediately following the times ....tj-1, tj, tj, tj+1....tk-1. tk, tk+1.....

On the command of the control unit V1 the arithmetical unit PR connected to the read/write memory R determines the volume changes in the pulse period immediately following the above times: .... #Vj-i = Vj - Vj-1; #Vj = Vj+1 - Vj....; aik-l = k-1,Ak = Vk+l - Vk---- (1) Or, in other words, it computes the change in the gradient of the curve describing the volume change of the limb according tote following: #Vj-1, #Vj, #Vj+1 ... #Vk-1, #Vk = #tj #tj+1 #tk-1 #tk (2) = #Vk+1 #tk+1 The gradients associated with the individual points in time are compared by the arithmetical unit PR which determines the point t1 when the volume change of the limb started and the point tk from which onwards the gradient of the volume change of the limb no longer increases but is constant. The cuff pressure Pj associated with the point tj agrees with the systolic blood pressure while the cuff pressure PK arising at the point tk corresponds to the diastolic blood pressure (Figures 6 and 7). The indication of the pressures Pi and Pk takes place on at least one indicating instrument K connected to the arithmetical unit PR.

The curve according to Figure 7 may also be examined by utilising several points spaced apart by a pulse period for the determination of the gradient. By way of example, this is illustrated by the following relation used in the determination of the diastolic blood pressure: .Vk - Vk-2 < Vk+1-Vk-1 < Vk+2-Vk = Vk+3 Vk+1 = ...(3) tk - tk-2 tk+1 - tk-l tk+2-tk tk+3 - tk+l Naturally, with this last procedure, again it is the cuff pressure Pk which corresponds to diastolic blood pressure at the time tk.

It can be seen further that the determination of the gradient of the curve in Figure 7 is not disturbed by the fact that there is a phase shift between the pulse train superposed on the curve and the signal of the pulse sensor GP i.e. that the points selected by the analyser PA, e.g. the systolic points, do not coincide with the systolic points of the pulse train superposed on the curve according to Figure 7.

Let the phase shift be, for instance: tk7 - tk (Figure 7); in this case the computed value of the gradient does not change since Atk' = Atk and AVk' = #Vk (Figure 7). However, a different cuff pressure is associated with the time tk, thus the measured value of the diastolic pressure does not agree with that determined previously. (Figure 6, Pk = P'k). This difference can however be neglected because in practice its maximal value is one-half that of the cuff pressure drop falling within one pulse period. This latter is for example 120 per minute, which is 0.25 Hgmm in the case of the pulse frequency and sleeve pressure drop rate of lHgmm/sec usual for babies.

The above description is mutatis mutandis valid also for the determination of the systolic pressure.

It follows from the above therefore that the pulse sensor GP may be placed in any position on the body and that the ECG signal can also be used for synchronisation. Thus, the ECG channel can also be used for synchronisation. Thus, the ECG channel can also be connected to analyser PA (Figure 8, block R).

The measurement can be refined by altering the time dependent change of the cuff pressure shown in Figure 6. An exemplary embodiment of this is shown in Figure 9. Its essence is as follows: on the command of the control unit V, the pneumatic unit N inflates the cuff M to a pressure PM > Ps and thereafter decreases it rapidly e.g. at a rate of 3Hgmm/sec. Meanwhile, in the manner described above, the arithmetical unit PR continuously computes from the data passed into the read/write memory R the gradient describing the volume change and approximately determines the time of reaching the systolic pressure; thereafter it sends a signal to the control unit V1 which then so controls the pneumatic unit N that the cuff pressure is raised suddenly in an impulse-like manner somewhat above the systolic pressure e.g. 3 Hgmm above that, and is then decreased slowly e.g. 3 Hgmm above that, and is then decreased slowly e.g. at a rate of 0.5 Hgmm/sec. The accurate determination of the value of the systolic pressure takes place in this interval in the manner described above. Thereafter, the pneumatic unit N decreases the cuff pressure M rapidly once again, e.g. at a rate of 3Hgmm/sec while the arithmetical unit PR approximately determines the time of reaching the diastolic pressure and thereafter sends a signal to the control unit V1. The control unit V1 commands the pneumatic unit N to raise the cuff pressure suddenly somewhat above the diastolic pressure e.g. 3 Hgmm above that, and then slowly to reduce the pressure e.g. at a rate of 0.5 Hgmm/sec. The accurate determination of the diastolic pressure takes place in the manner described above during this interval of slow pressure change (Figure 9).

A process suitable for determining venous blood pressure is described in connection with Figures 10 and 11. The performance of the measurement process also takes place with the apparatus according to Figure 8 and there is no essential change as regards the function of the individual elements and therefore only the operation in principle is described below.

As an example, in the embodiment of Figure 10 the cuff pressure M is increased at a rate of 1 Hgmm/sec and when the venous blood pressure is reached, the blood outflow from the vein ceases from the portion of the limb distal from the cuff M, thus at a point ti the change in volume of the limb starts (Figure 11). The sleeve pressure at the time ti accords with the blood pressure in the vein. A further increase in the cuff pressure M does not impede the arterial flow so that the change in volume of the limb remains uniform until the pressure reaches the diastolic pressure value at time tj. Thereafter, the curve describing the volume change becomes less and less steep in gradient in accordance with the fact that in the course of a given cycle of the heart less and less blood reaches the portion of the limb. Thus, the cuff pressure arising at time tj accords with the diastolic blood pressure. As the cuff pressure increases further until at time tit reaches the value of the systolic blood pressure the inflow of blood ceases thus the curve describing the volume change becomes horizontal or nearly horizontal. The cuff pressure arising at point tk accords with the systolic blood pressure.

The determination of the cuff pressures arising at points ti and tk takes place in the same way as has been described above in connection with Figures 6 and 7.

The measurement can be further refined by modification of the time-dependent change of the cuff pressure shown in Figure 10 and the duration of the measurement can be decreased. On exemplary embodiment of this is shown in Figure 12. In this case, the control unit V1 commands the pneumatic unit N to increase the cuff pressure relatively fast e.g. at a rate of 3 Hgmm/sec.

Meanwhile, the arithmetical unit PR continuously computes the gradient of the curve describing the volume change from the data passed to the read/write memory R and with an approximative accuracy determines the time of reaching the venous pressures and at that time sends a signal to the control unit V1 which in turn commands the pneumatic unit N suddenly to decrease the pressure of the cuff M e.g. by 3 Hgmm and then to raise it slowly at a rate of 0.5 Hgmm/sec. The determination of the venous blood pressure (Figure 12, time ti, pressure Pv) takes place in the manner described above in this slowly rising interval.

Thereafter, the pneumatic unit N increases the cuff pressure fast once again, e.g. at a rate of 3 Hgmm/sec while the arithmetical unit PR determines with approximative accuracy the time of reaching the diastolic pressure and at the same time sends a signal to the control unit V1. The control unit V1 commands the pneumatic unit N to decrease the cuff pressure in an impulse-like manner, e.g. by 3 Hgmm and thereafter to increase it slowly, e.g. at a rate of 0.5 Hgmm/sec. The determination of the diastolic pressure takes place in the manner described above during this slowly rising interval (Figure 12, point tj, pressure PD) - Thereafter the pressure of the cuff M once again rises rapidly e.g. at a rate of 3 Hgmm/sec and then analogously with the foregoing is decreased suddenly e.g. by 3 Hgmm on reaching the systolic pressure, and thereafter is raised slowly, e.g. at a rate of 0.5 Hgmm/sec. In the manner already described, the systolic pressure is determined in this slowly rising interval (Figure 12, point tk pressure Ps).

The pressure programmes illustrated in Figures 6, 9, 10 and 12 are exemplary embodiments. Naturally, there is no reason why they should not be combined to give a new pressure programme or why any desired curves or curved sections should not replace the straight lines representing linear pressure changes.

A further preferred embodiment of the apparatus according to the invention and illustrated in Figure 8 can be seen in Figure 13. In the apparatus according to Figure 13, the sampling and holding circuits S1 and S2 the multiplexing units C1 and the demultiplexing unit C2 are omitted, as compared with Figure 8. The output of the pressure sensor Gm and the output of the volume sensor G are respectively connected to respective inputs of converter D1 and converter D2, the outputs of which are connected to the input of the read/write memory R. Naturally, the function of the apparatus agrees with that described in connection with Figure 8, having a unit PR and a unit V1.

The apparatus according to the invention can be realised in a further embodiment (Figure 14) omitting the sampling and holding circuits S1 and S2 but having a unit PR and a unit V, wherein the pressure sensor GM and the volume sensor G are directly connected to the multiplexing unit C1 controlled by the control unit V1. Since one is here concerned with the transformation of signals which vary slowly with time, the above solution is permissible since the use of even an averagely fast A/D converter or multiplexing unit C1 would not result in any significant asynchronism between the two signals resulting from the sequential transformation or conversion.

An embodiment of the apparatus according to the invention founded on microprocessor technology can be seen in Figure 15. According to this apparatus, there is a data line H1 and an address line H2 to which are connected an arithmetical unit PR a read/write memory R and a clock generator T which essentially function in a manner already described above, as well as a control unit V2, a programme store Q and a matching unit I. Fundamentally, the control unit V2 fulfils the same tasks as the control unit V1 but does not operate autonomously: instead, it controls the system and the operation of the arithmetical unit PR according to a programme in the programme store Q. The pressure sensor GM, the volume sensor G and the analyser PA are connected to the inputs of the matching unit I, the outPut of which is connected to the pneumatic unit N. The indicating instrument K is connected to the data line H1.

The microcomputer structure provided with a separate data line and address line naturally only represents one possible embodiment. The essence of the invention is not affected by it and there is no reason why the data flow between the component units of known function should not be organised in a different manner.

It can be seen without further description that the apparatus according to the invention is also suitable for carrying out plethysmographic examinations with vein occlusion. If, for instance, on the command of the control unit V1 or V2, the pneumatic unit N inflates the cuff M in a pulse like sudden manner to a value greater than the venous pressure but

The initial slope of the curve describing the volume change is also determinable in the manner described in connection with Figure 8 by means of the apparatus-accPrding to. the invention, in a manner free from the. disturbing effect of the arterial pulse train It can be seen therefore that the extra requirement of the examination process using vein occluding plethysmography need only be taken into account in the constructiòn of. the control unit V1, i.e. the programme in the programme store Q relating to the function of the control unit V2 has to be formed accordingly; It is remarked that in the case of blood pressure -measurement it is sufficient for the sensor G to provide signals proportional to the change of volume of the limb, but in the case of plethysmographic examinations involving vein occlusion it is necessary that the sensor G should also measure the instantaneous - absolute value of the volume, in an accurate manner.

WHAT WE CLAIM IS: 1. Apparatus for the non-invasive determination of arterial and venous blood pressure values, comprising an inflatable cuff to be placed on a limb of a patient, a limb volume sensor to be placed on the limb and distally of the cuff, a pulse sensor to be placed on any part of the body of the patient, a pressure transducer associated with the cuff, means for changing the cuff pressure from a value exceeding the systolic Pressure to zero or vice versa, means for determining the values of the slope of the curve describing the volume change with respect to time of the limb distal of the cuff, and computing means to determine those instants in time when the cuff pressure agrees with the systolic and diastolic pressure or the venous pressure by computing the slope of the curve describing the limb volume change with respect to time in a manner free from interference from any superposed pulse trains.

and control means for controlling the functional inter-relationshlp of the determining and computing means and of the means for changing the cuff pressure.

2. Apparatus for the determination of the systolic and diastolic values of arterial blood pressure and venous blood pressure, primarily for babies as well as for effecting plethysmographic examinations with vein occlusion, which apparatus comprises a cuff to be placed on a limb, a volume sensor disposed distally from the cuff, a pressure sensor serving to measure the pressure in the air space of the cuff, wherein the output of the pressure sensor is connected to the input of a sampling and holding circuit, the output of the volume sensor being connected to a further sampling and holding circuit, the input of an analyser serving for the periodical determination of the same phase point in each pulse curve or in each ECG signal cycle being connected to the output of a pulse sensor placed on any part of the body, or to the output of an ECG channel; the output of the first sampling and holding circuit being connected to a first input of a multiplexing unit while the output of the second sampling and holding circuit is connected to a second input of the multiplexing unit, and the output of the latter is connected to one input of an analog-digital converter the output of which is connected to one input of a demultiplexing unit, the output of which is connected to one input of a read/write memory a second input of which is connected to the output of an arithmetical unit capable of handling two-directional data traffic, at least one indicating instrument being connected to the output of the arithmetical unit, and wherein one output of a control unit incorporated in the apparatus is connected to the input of a pneumatic unit the output of which is connected to the input of the cuff, one input of the control unit being connected to the output of the analyser while another input thereof is connected to the output of a clock generator; and wherein a second output of the control unit is connected to the second input of one of the sampling and holding circuits, its third output being connected to the second input of the other sampling and holding circuit, while its fourth output is connected to the third input of the multiplexing unit, its fifth output is connected to the second input of the analog-digital converter, its sixth output is connected to the second input of the demultiplexing unit, while the control unit is connected to the read/write memory and the arithmetical unit so as to handle two-way data traffic.

3. Apparatus according to claim 1, wherein the output of the pressure transducer is connected to an analog-digital converter, the output of the limb volume sensor is connected to the input of a further analog-digital converter, both analog-digital converters having their outputs connected to a respective input of a read/write memory.

4. Apparatus according to claim 1 wherein the output of the pressure sensor and the output of the volume sensor are directly connected to a respective input of a multiplexing unit.

5. Apparatus according to claim 1 further comprising a read/write memory, an arithmetical unit, a clock generator, a control unit, a programme store and a matching unit, all the aforesaid being connected to a data line and an address line in a manner enabling two-directional matching or association; and at least one indicating instrument connected to the data line, one input of the matching unit being connected to the output of the pressure transducer while its second input is connected to the output of the limb volume sensor, its

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The initial slope of the curve describing the volume change is also determinable in the manner described in connection with Figure 8 by means of the apparatus-accPrding to. the invention, in a manner free from the. disturbing effect of the arterial pulse train It can be seen therefore that the extra requirement of the examination process using vein occluding plethysmography need only be taken into account in the constructiòn of. the control unit V1, i.e. the programme in the programme store Q relating to the function of the control unit V2 has to be formed accordingly; It is remarked that in the case of blood pressure -measurement it is sufficient for the sensor G to provide signals proportional to the change of volume of the limb, but in the case of plethysmographic examinations involving vein occlusion it is necessary that the sensor G should also measure the instantaneous - absolute value of the volume, in an accurate manner. WHAT WE CLAIM IS:

1. Apparatus for the non-invasive determination of arterial and venous blood pressure values, comprising an inflatable cuff to be placed on a limb of a patient, a limb volume sensor to be placed on the limb and distally of the cuff, a pulse sensor to be placed on any part of the body of the patient, a pressure transducer associated with the cuff, means for changing the cuff pressure from a value exceeding the systolic Pressure to zero or vice versa, means for determining the values of the slope of the curve describing the volume change with respect to time of the limb distal of the cuff, and computing means to determine those instants in time when the cuff pressure agrees with the systolic and diastolic pressure or the venous pressure by computing the slope of the curve describing the limb volume change with respect to time in a manner free from interference from any superposed pulse trains.

third input being connected to the output of an analyser while its output is connected to the input of a pneumatic unit.

6. Apparatus according to claim 1 substantially as hereinbefore described with reference to and as shown in Figure 8 or Figure 13 or Figure 14 or Figure 15 of the accompanying drawings.