GB1574869A

GB1574869A - Veinclosure plethysmograph

Info

Publication number: GB1574869A
Application number: GB47830/77A
Authority: GB
Original assignee: Medicor Muvek
Current assignee: Medicor Muvek
Priority date: 1976-11-17
Filing date: 1977-11-17
Publication date: 1980-09-10
Also published as: PL112328B1; DE2751004C3; DD132403A5; DE2751004B2; ES464181A1; CS209806B2; GR64026B; HU173760B; DE2751004A1; NL7712555A; PL202209A1

Description

(54) VEIN-CLOSURE PLETHYSMOGRAPH (71) We, MEDICOR MUVEK, an enterprise organised and existing according to the Laws of Hungary of 11-13., Rontgen utca, Budapest XIII, 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:- The present invention relates to an apparatus by means of which it is possible to undertake a plethysmographic examination of the extremities of the body by veinclosure.

With the aid of the apparatus according to the invention the pathological changes in the capillary blood-vessels, and also those of the venous or arterial circulatory systems, can be ascertained in non-invasive fashion.

Moreover, the results of surgical intervention and the effects of the various chemicals in adults or in infants can also be observed.

Modern man is becoming increasingly vulnerable to disorders of the circulatory system in the extremities. For some time now requirements have been laid down concerning measurement procedures and apparatus by means of which various disorder conditions of the peripheral circulation including the closure of distal arteries, may be observed quite simply during outpatient treatment of these conditions. Equipment developed for this purpose which is basically identical in concept but appears in various technical embodiments, is termed plethysmographic apparatus.

The known procedures in general use at the present time will be readily understood from Fig. 1. An inflatable sphygmomanometer cuff M I is applied in the vicinity of the extremity area to be examined and is filled by a pumping action to subdiastolic pressure. Venous reflux is thereby blocked for a considerably period of time but arterial influx has not yet been prevented in the first seconds so that there is an increase in volume distally of the cuff Ml. This volume increase is measured by a transducer G located distally of the cuff Ml.

The character of the volume increase, with the arterial pulse curve superimposed on the average value A, is illustrated in Fig. 2.

Here, and also hereinafter throughout the description, the relative volume change is shown as AVID0 since this expression enables the various measurements at the extremity areas to be compared with various initial volumes VO It follows logically that the variation in relative volume change, that is to say, the initial acclivity of the curve occurring as a result of the pulsating increase in pressure in the cuff Ml in the moment of time t=0 may be determined in the arterial circulatory system since the increase in pressure of the venous circulatory system does not as yet affect the arterial influx.

When, after the quasi-stationary condition thus described, the pressure in the cuff M1 is suddenly interrupted, venous efflux, the area begins proximally in the direction of the cuff Ml. A volume decrease is thus recorded by the transduer G as shown in Fig. 3, together with the arterial pulse curve superimposed on an average value B. It should be noted here that the form of the pulse curve is also influenced by the venous pulse but that this effect is negligible. It will be readily observed that the alteration in relative volume change dV/VJdt at the moment of pressure decrease, that is to say the initial declivity of the curve, yields important diagnostic information concerning the condition of the venous circulatory system since the venous efflux is not influenced by bloodless veins located in the vicinity of the cuff. If only the cuff M I is employed (as described above), the examination may extend over the entire area of the extremity distal to the cuff M1.

If, however, only a predetermined location is required to be examined, for example between the cuffs M1 and M2, the pressure produced in the cuff M2 should exceed the systolic pressure. Thus, the area located distally of the cuff M2 can be excluded from examination.

The diversity of apparatus for carrying out the measurement procedure arises from the various forms of construction of the transducer G.

A so-called water-plethysmograph is provided with a transduer G comprising a closed water-filled container which peripherally encloses the extremity at any level and, which has a measuring aperture whose outer wall is rigid, the water in the water-filled container being heated to body temperature. When the cuff Ml is placed under pressure, a change in volume occurs which can be observed by means of a calibrated glass tube inserted into the measurement aperture, or by a capacitive based transducer or the like.

A further device is similar in operation in which, instead of water, the container holds air. In the case of a closed container volume changes may be indicated by observing pressure differences and, in the case of an open container, by means of a pneumotachograph. More recently volume changes may be deduced from measuring the peripheral dimension changes in a part of a given extremity. Thus, it can be proved that the following equation gives a close approximation: dV dL =2 (1) V L O O i.e. the relative volume change is equal to twice the value of the relative peripheral change.

If the arterial, or the venous circulatory system, is being examined, in practice one is faced with the same problem: the initial acclivity or declivity of a curve in the moment of time t=0 must be determined, whereby the spontaneous (and from our point of view, undesirable) volume changes caused by the pulse, are superimposed upon this curve (See for this Figs. 2 and 3).

In the case of the conventional procedure, the alteration in relative volume change is undertaken manually by noting that tangent to a recording which is judged to be most suitable (see Figs. 2 and 3, lines A, B) and by calculating magnitude of relative volume change and duration of time involved. It is obvious that this procedure is laborious and cannot offer an acceptable degree of accuracy.

In the case of another known system, a more speedy but even less accurate measurement is obtained. This type of system is described in the case of the examination of the arterial circulatory system with reference to Fig. 4. If, after inflating the cuff M1, the volume, or relative volume change in the extremity sector under examination exceeds a predetermined value (AVk/Vo), a timer device is triggered and after a specific period of time At, at a moment tv, the apparatus determined the actual relative volume change (AVv/Vo) From the difference in relative volume change existing in the moments tk, tv and from the duration of time At, the initial acclivity of the curve can be determined mechanically and indicated directly. Although this measurement is speedy and the evaluation does not require any manual operation or recording apparatus, its weakness is apparent.

Irrespective of how the selected interval At, the pulse wave frequency and the amplitude thereof, behave relative to each other, the apparatus can give widely incompatible results in the case of the same cardiovascular disorders.

If, for example (with constant pulse frequency and amplitude) one alters the value At to At' (as will be seen in Fig. 4), the end of the interval, i.e. the moment tv' falls on the diastolic area of the pulse wave.

The initial acclivity, which may be calculated from the associated values At', AVk/VO and AVV'/VO, is much smaller than the initial acclivity calculated with the associated values At, AVk/Vo and aVV/VO.

The apparatus according to the present invention eliminates the above-described interference affects of the pulse beat and enables the initial acclivity of the curve of relative volume change to be determined clearly, accurately and automatically.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figs. 1, 2 and 3 and 4 show the manner of the measuring procedures in conventional apparatus; Fig. 5 is the block circuit diagram of the apparatus according to the present invention, and Figs. 6a and 6b show operating results of the apparatus according to the present invention; Fig. 7 shows a block circuit diagram of a further method of realisation of the apparatus according to the invention.

Referring now to Fig. 5 the output of a transducer G is connected to the input of an a.c. potentiometer K' which functions as a comparator, and to the input of at least one scanner and storage circuit S,, S2...Sn. The inputs of a monitor PA (which determines the characteristic points, i.e. points of like phases of the pulse curve, or of an ECG signal) are taken from the output of the transducer G, and or from pulsimeter P and electrocardiograph apparatus, (ECG). The output of the monitor PA is connected to the first input of a control unit VA, whilst the second input of the latter is connected to the output of the a.c. potentiometer K.

The first output of the control unit VA is connected to the input of a pneumatic unit PN; and the second output is connected to the input of a timer device T, whilst its third output is connected to the first input of a calculator RA. Its fourth, fifth and subsequent outputs however are connected to the other inputs of the aforementioned scanner and storage circuits Ski . . . Sn. The output of the timer T is connected to the second input of the calculator RA, whilst the outputs of the scanner and storage circuits S, . . . Sn are connected to its third, fourth and subsequent inputs. An indicator M is connected to one output of the calculator RA and a recording instrument D is connected second to the output. One output of the pneumatic unit PN is connected to the inflatable cuff Ml and the other output to the second cuff M2.

In the case of a further method of realisation, the apparatus as shown in Fig. 7 is connected as follows). The output of the transducer G is connected to the input of the a.c. potentiometer K and also to the first input of a scanner and storage circuit and/or a A/D transducer SD. The output of the transducer G, or of the pulse recorder P or ECG channel, is connected to the input of the analyser PA which determines the characteristic points, or points of like phases of the pulse curve, or ECG curve, whilst the output of the analyser PA is connected to the first input of a control unit VD. The output of the aforementioned a.c.

potentiometer K is connected to the second input of the control unit VD, whilst the first output of the said control unit is connected to the input of the pneumatic unit PN and the second output is connected to the input of the timer T. The third output of unit VD is connected to the first input of a calculator and storage unit RD, and the fourth output of unit VD is connected to the second input of the scanner and storage circuit and/or of the A/D converter SD.

The output of the scanner and storage circuit and/or A/D transformer SD is the second input to the calculator and storage unit RD, whilst the output of the timer T is the third input of said unit RD. One output of the pneumatic unit PN is connected to the inflatable cuff Ml and its other output to the second cuff M2. An indicator M is connected to one output of the calculator and storage unit RD, and a recording instrument D to the other output.

The manner of operation of the apparatus according to the invention will now be described in the case of an examination of the arterial circulatory system. Reference is made to the block circuit diagram of Fig. 5, based in the first place on a similar measuring technique, and also to Figs. 6a and 6b which characterise the relative volume changes AVp/Vo produced by the pulse.

At the beginning of the measurement the pneumatic unit PN is set in motion by the control unit VA. By means of the pneumatic unit the inflatable cuff M1 is filled with water by a pump-like action to a subdiastolic pressure (appx. 50 mmHg), and possibly also, depending upon the particular extremity area to be examined, the inflatable cuff M2 is also filled so that the pressure exceeds the systolic value.

The transducer G indicates the volume change in the extremity between cuffs Ml and M2, its output being connected to the input of the scanner and storage circuits Si Sn and of the a.c. potentiometer K. The output of the pulsimeter P is connected to the input of the analyser PA. The pulsimeter P should preferably be located in the immediate vicinity of the measurement area. It is also possible for the pulsimeter P to be incorporated with the transducer G.

The function of the analyser PA is to determine the pulse curve times relating to the characteristic points, preferably the systolic and/or diastolic points. At these times the analyser PA sends to the input of the control unit VA synchronous or recognition impulses. Meanwhile, the transducer G monitors the relative volume change in the extremity sector. When the volume change, or relative volume change, exceeds a predetermined value, which is preferably greater than the volume change produced by the systolic part of the pulse, or as the case may be, when the temporary phenomena occurring during operation of the pneumatic unit PN have completely subsided (see Fig. 6a, value Vk/Vo), the a.c. potentiometer produces a preparatory impulse for the control unit VA. Thereupon, the control unit VA receives the synchronous or recognition impulses provided by the analyser PA and relating to one (preferably the next) characteristic point in the pulse curve (see Figs. 6a and 6b, time t1 the systolic time in the pulse curve), whilst at the same time the timer unit T is set in motion and sends an instruction for the scanner and storage circuit S, which stores the amplitude value AV1IV0. The control unit VA then selects only that synchronous or recognition impulse which coincides with the one which arrived first, i.e. which belongs to the same phase of the pulse curve. (See Figs. 6a and 6b, time t2 the next systolic point on the pulse curve). At the same moment t2 the control unit VA switches off the timer unit T and sends an instruction for the scanner and storage circuit S2 which stores the amplitude value V2/VO at the time t2. Thereupon, the initial acclivity of the curve of relative volume change is determined, in accordance with the instruction of the control unit VA, by the calculator RA from the output signal of the timer unit T proportional to the duration of time t2-t1=At, and from the output signals of the scanner and storage circuits S1 and S2 proportional to the relative volume changes V1/VO and VJVO, and is shown in the indicator M.

The relationship for this is:

The value thus obtained corresponds closely to the theoretically anticipated initial acclivity of the curve of relative volume change.

Referring now to Figs. 6a and 6b, we discuss a case in which the pulsimeter P is placed in the immediate vicinity of the transducer G or is incorporated with said transducer.

In this case there is no phasedisplacement between the corresponding points of the signals produced by the transducer G and pulsimeter P. The same is true of the case where the output of the transducer G is connected to the input of the analyser PA instead of to the output of the pulsimeter P. In this case the analyser PA processes the pulse curve separated from the output of the transducer. If, however, the pulsimeter P is placed at any other point on the body, a phasedisplacement caused by the speed of the pulse wave, occurs between the corresponding points on the signals produced by the transducer G and the pulsimeter P. This phase-displacement does not interfere in the working of the apparatus because the initial acclivity of the curve of relative volume change is also determined in this case by the points of like phase in the pulse curve superimposed on the signal given by the transducer G. Such a case can be seen in Fig. 6a at the line t1, and t2,. The phase displacement here is t1'-t1 and the initial acclivity cu,' coincides with the initial acclivity a, determined by the times t1 and t2 From the above it will be realised that the times relating to the characteristic points (preferably to the R waves) of ECG signals may also be employed for synchronisation instead of the pulse curve. Thus, the output signal of an ECG channel can be passed to the input of the analyser PA. In this case, the time relating to the characteristic points on the ECG curve are determined by the analyser PA.

The control unit VA may also be constructed in such a manner that the initial acclivity of the curve of relative volume change is determined, not by the two consecutive points of like phase of the signal given by the transducer G, but by means of points of like phase which are more widely separated. If, for example, the timer unit T is set in motion by the control unit VA at the moment t and is switched off at the moment t4, and if the scanner and storage circuits S1 or S2 receive an instruction at the same moments ti and t2, the expression of the initial acclivity of the curve of relative volume change assumes the following modified form (see Fig. 6a):

This solution ensures a lower measurement value than that according to expression (2) but the accuracy is sufficiently high, especially in the case of infants since in this case a higher pulse frequency is to be expected. It should also be noted that this solution improves the reliability of measurement.

The control units VA and RA may also be so constructed that, by employing the scanner and storage circuits S1 . . . Sn to any desired number, the relevant part of the curve describing the relative volume change can be followed on the track. In this way also the acclivity of any region where measurements or the described behaviour thereof can be determined, or the curve can be recorded by the recording instrument D without the disturbing effects of the pulse beat. This type of construction is especially useful if it is desired to observe the flat, socalled filtration sector of the curve describing the relative volume change. If, however, it is desired to examine a longer sector, or to observe the characteristics of the entire curve, another form of construction may be employed which is better suited to this purpose and which is based on the principles of the digital measuring techniques. This apparatus is shown diagrammatically in Fig. 7.

In the embodiment of Fig. 7 the functions of the inflatable cuffs M1, M2, the transducer G, the pulsimeter P, the ECG channel, the analyser PA, the pneumatic unit PN, and timer Unit T correspond to those of Fig. 5. The output of the transducer of G, however, is connected to an input of a scanner and multiple storage circuit, an A/D converter SD, whilst the control unit VD is connected to the second input of the latter.

At the times corresponding to the characteristic points on the pulse or ECG curve, the control unit VD sends instructions for the scanner and storage circuit, and, by means of other instructions, sets in motion the processing of the scanned signals by a calculator and storage unit RD.

The initial acclivity of the curve of relative volume change, or as the case may be, any other parameters of said curve, are determined by the calculator and storage unit RD and indicated by the recording instrument D or on the indicator M.

With reference to Figs. 5, 6a, 6b and 7, we have now described the functioning of the apparatus as applied to the examination of the arterial circulatory system. If the venous system is to be examined, the measurement procedures are identical with the one exception that, in the latter case, the measurement is taken when an impulse-like interruption of the pressure of the cuff Ml occurs. In fact, the influence of the venous pulse upon the measurement is negligible.

WHAT WE CLAIM IS: 1. Apparatus for measuring the rate of change of volume of a limb of a subject when the venous circulation is interrupted, said apparatus comprising, a cuff adapted to be located on the limb, a limb volume measuring transducer capable of being located on the limb distally of the cuff, an arterial pulse measuring means, a signal storage means, a comparator connected to the output of said transducer, a timer, a processing and calculating means, a control unit connected to said storage means, the pulse monitor and the comparator output, the timer and, the processing and calculating means, the arrangement being such that, in use, during interruption of the venous circulation when the tranducer signal exceeds a predetermined value the comparator produces a response signal which activates the control circuit, said control circuit thereafter monitors the output of said pulse monitoring means and repeatedly detects a characteristic point on successive cycles of the pulse waveform and, on occurrence of a first said detection enables a first transducer signal amplitude to be stored in said storage means and initiates the timer simultaneously and, on receipt of a second said detection the control enables a second transducer signal amplitude to be stored in said storage means and stops the timer, said control unit then directs said processing and calculating means to receive said first and second stored tranducer signal amplitude and the time elapsed between storage of said signal amplitudes, so that said processing and calculating means indicate the rate of change of volume of the limb.

2. Apparatus as claimed in Claim 1, including a further cuff disposed apart from said first cuff on the limb, the arrangement being such that when the distalmost cuff is inflated to occlude the arterial circulation distally thereof and the venous circulation is interrupted by the proximal cuff, the rate of change of limb volume in the portion between the cuffs is indicated by said processing and calculating means.

3. Apparatus as claimed in Claim I or Claim 2, wherein the, or each, cuff is pneumatically inflatable and is controlled by the control unit.

4. Apparatus as claimed in any preceding claim, wherein said processing and calculating means includes a visual display which indicates the measured rate of change of volume of the limb.

5. Apparatus as claimed in any preceding claim wherein said storage means comprises first and second storage circuits connected to receive the first and second transducer signals respectively.

6. Apparatus substantially as hereinbefore described with reference to Figs. 5 to 7 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. curve, the control unit VD sends instructions for the scanner and storage circuit, and, by means of other instructions, sets in motion the processing of the scanned signals by a calculator and storage unit RD. The initial acclivity of the curve of relative volume change, or as the case may be, any other parameters of said curve, are determined by the calculator and storage unit RD and indicated by the recording instrument D or on the indicator M. With reference to Figs. 5, 6a, 6b and 7, we have now described the functioning of the apparatus as applied to the examination of the arterial circulatory system. If the venous system is to be examined, the measurement procedures are identical with the one exception that, in the latter case, the measurement is taken when an impulse-like interruption of the pressure of the cuff Ml occurs. In fact, the influence of the venous pulse upon the measurement is negligible. WHAT WE CLAIM IS:

1. Apparatus for measuring the rate of change of volume of a limb of a subject when the venous circulation is interrupted, said apparatus comprising, a cuff adapted to be located on the limb, a limb volume measuring transducer capable of being located on the limb distally of the cuff, an arterial pulse measuring means, a signal storage means, a comparator connected to the output of said transducer, a timer, a processing and calculating means, a control unit connected to said storage means, the pulse monitor and the comparator output, the timer and, the processing and calculating means, the arrangement being such that, in use, during interruption of the venous circulation when the tranducer signal exceeds a predetermined value the comparator produces a response signal which activates the control circuit, said control circuit thereafter monitors the output of said pulse monitoring means and repeatedly detects a characteristic point on successive cycles of the pulse waveform and, on occurrence of a first said detection enables a first transducer signal amplitude to be stored in said storage means and initiates the timer simultaneously and, on receipt of a second said detection the control enables a second transducer signal amplitude to be stored in said storage means and stops the timer, said control unit then directs said processing and calculating means to receive said first and second stored tranducer signal amplitude and the time elapsed between storage of said signal amplitudes, so that said processing and calculating means indicate the rate of change of volume of the limb.