CA1060226A - Apparatus and process for determining systolic pressure - Google Patents

Abstract

Abstract A conventional pressure cuff is attached to a living test subject. First means are provided for changing pressure in the cuff and thereby applying pressure to the subject.
Second means communicating with the cuff are provided for measuring a quantity proportional to a time-dependent fluctuating component representative of pulsatile pressure within a blood vessel of the subject, the second means having a frequency response adequate to accurately follow the subject's blood pressure waveform, for instance at least about five times the subject's pulse rate, whereby the fluctuating quantity is proportional to amplitude of pulsatile pressure. The maximum value of the fluctuating quantity is determined as applied cuff pressure is changed. Third means are provided for determining when the fluctuating quantity is about a particular fraction of its maximum value for applied cuff pressure greater than the pressure applied when the maximum value occurred or resulted, the particular fraction corresponding with that fraction of the total length of the blood vessel within the cuff which extends from its upstream (proximal) end to the point at which the cuff applies maximum pressure to the blood vessel wall between diastolic and systolic pressure and typically being about one-half. Systolic pressure, which is equal to applied cuff pressure when the fluctuating quantity is about equal to the particular fraction of the maximum value of the fluctuating quantity, is then read out on suitable instrumentation.

Description

-` 1060;~Z6 sackyround of the Invention 1. Field of the Invention The present invention relates generally to the field of blood pressure monitoring, and more particularly to automatic monitoring of systolic blood pressure.

2. Description of Prior Art The prior art is replete with devices for measuring systolic pressure of a living subject. An old and simple device is a pre-ssurizable cuff used in combination with a mercury manometer which reads pressure in the cuff and a stethoscope which is used to listen to Korotkoff sounds. More complicated methods and appar-atus based on the same principle of listening to the Korotkoff sounds replace the mercury manometer with a mechanical or electro-mec~anical pressure gauge and utilize microphonic detection of the Korotkoff sounds which are analyzed electrically. In another advanced method of measuring blood pressure, the distance from a blood pressure cuff to the wall of an artery is accurately deter-mined by measuring Doppler shifts of sound waves reflected by the artery. The distance to the artery varies as a function of pre-ssure within the somewhat pliable walls thereof. In yet othermethods for measuring blood pressure intrus~ve devices are often inserted directly into blood vessels.
Oscillometric methods of determining systolic pressure are also well known in the art. In such methods, the operator observes a representation of the strength of pulsations of pressure within an artery. This can be done visually, as by watching the extent of bouncing of the top of a mercury column in a mercury manometer which is in pressure-co~munication with a cuff, or indirectly as by 29 measuring the occlusion which occurs to a blood vessel in the pinna ~, ~
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of the ear as pressure is exerted thereon, as in U. S. Patent No. 3,227,155. Oscil]ometric methods of determining systolic pressure generally define systolic pressure to be the maximum applied pressure at which thresllold oscillations are observed to occur, With a typical mercury manometer and pressurizable cuff, this pressure would then be the highest pressure at which tlle operator noted bouncing in the top of the mercury column as the pressure in the cuff was slowly and relatively uniformly reduced. ~-Iowever, there are inaccuracies associated with this method for determining threshold oscillations, since the mercury column does not noticeablyrespond to narrow-width pressure pulses;
i.e., the energy associated with a narrow-width pulse is insuffi-cient to no~iceablymove the comparatively high inertia mercury column. In other words, because of relatively slow response time of a mercury manometer (or the apparantly selectively slow occlusion rate of the pinna of the ear) the quantity actually being measured is proportional to an integral of the pressure pulse rather than actual amplitude thereof. Oscillometric methods based on observing threshold oscillations are thus inherently somewhat inaccurate, where "threshold" is a para-meter or term that generally may be hard to rigorously and exactly define anyway.
Nevertheless, methods based on listening to Korotkoff sounds are relatively accurate for measuring systolic pressure but are burdened w~th requiring use of a microphonic detector if they are to be instrumented. The method based on Doppler shifts is also accurate, but also is burdened with requiring special measuring apparatus, and has a further shortcoming in 29 that it is sensitive to positioning of the measuring apparatus cb/

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` 1060Z26 relative to the artery.
The present invention provides a solution to the prob-lems associated with inaccurate systolic blood pressure measure-ment and monitoring provided by sa~ple devices of the prior art.
The present invention also provides a solution to the problems associated with complex and special microphonic and other apparatus employed in the more accurate prior art devices for measuring and monitoring systolic blood pressure. The present invention thus provides apparatus and method for automatically measuring and monitoring systolic blood pressure, employing a simple cuff and automatically controlled instrumentation.
Applicant's U. S. Patent No. 3,903,872, issued September 9, 1975, entitled "Apparatus and Method for Producing Sphygmo-metric Information", is directed to related subject matter but involving diastolic blood pressure.

Summary of the Invention In one sense, the invention comprises apparatus for determining systolic pressure, comprising: a pressure cuff attachable to a living test subject adjacent a blood vessel;
means for changing pressure in the cuff and thereby applying pressure to the subject; means communicating with the cuff for measuring a quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel whereby the quantity is proportional to amplitude of the pulsatile pressure; means for determining the maximum value attained by said quantity as the applied pressure is changed;
~eans for storing a representatlon of the maximum value, means for determining when the quantity is substantially equal to about 29 one-half of the maximum value for an applied pressure greater cb/

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and means for reading out the applied pressure corresponding to said quantity being substantially equal to about one-l~alf of the maximum value, said read-out pressure correspondin~ to the systolic pressure of said subject.
In another sense, the invention comprises a process for method for determining systolic pressure, comprising: applying pressure to a living tes~ subject by changing pressure in a pre-ssure cuff attached to the subject adjacent a blood vessel; measur-ing at said cuff a quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said quantity being proportional to amplitude of the pulsatile pressure; determining the maximum value attained by said quantity as the applied pressure is changed;
storing a representation of the maximum value; determining when the quantity is substantially equal to about one-half of the ma~imum value for an applied pressure greater than the pressure applied ~Ihen the maximum value occurs or result and reading out the applied pressure corresponding to the quantity being sub-stantially equal to about one-half of the maximum value the read-out pressure corresponding to the systolic pressure of the subject.
The advantages of employing the present invention in automatic blood pressure monitoring thus include at least:
simple cuff.hookup to the subject, automatic cuff inflation and pressure measurement, and accurate systolic pressure monitor-ing.
It is thus a general object of the present invention to provide an improved apparatus and process/method for taking blood 29 pressure measurements.

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- 1060Z2~i It is anotller object o~ the present invention to provide an improved apparatus and process/method for automatically monitor-ing systolic blood pressure, in which the need for a double-cuff and/or an arm-mounted transducer is eliminated.
It is yet another object of the present invention to pro-vide an apparatus and process for determining systolic pressure, which apparatus and process are extremely accurate and compatible witll pressure-transducer-based measurements of diastoljc pressure witllout requiring extra instrumentation.
Other objects and advantages of the present invention will be apparent to those skilled in the art after referral to the detailed description of the preferred embodiment in conjunc-tion with the appended drawings.
~rief Description of the Drawings Figure 1 illustrates in a block diagram the apparatus and process of the present invention;
Figure 2 illustrates a typical oscillometric envelope obtainable using the apparatus and me~hod of the present inven-tion;
Figure 3 illustrates an oscillometric envelope utilizing measuring means so that the pulses each represent the integral of the actual pulsatile pressure fluctuation within a blood vessel;
Figure 4 illustrates the pressure applied to an artery as a function of arterial location witnin a cuff when the applied cuff pressure is between the systolic and diastolic pressure of the test subject;
Figure 5 illustrates the pressure applied to an artery as a function of arterial location within a cuff and the effect upon the artery when the pressure applied to the cuff is slightly . - . . - . .

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greater than the systolic pressure of the test subject.
Fi~ure 6 illustrates an arm and the collapse of the brachial artery at point L/2 (half cuff length~ when systolic pressure equals cuff pressure at L/2, as shown in Figure 5; and Figure 7 illustrates an arm and the brachial artery without collapse, as would be obtained from cuff pressure less than systolic pressure, e.g., as shown in Figure 4.
Detailed Description of the Preferred Embodimen_ ~ eferring first to Figure 1, there is arm 11 of a test subject with artery 13 therein, the arm be;ng surrounded by a typical blood pressure cuff 15. Typically, the brachial artery located in the upper arm is employed for this type of blood pressure measurement. Attached to the cuff via conduit 17 is pump 19. Also attached to the cuff via conduit 21 is pressure transducer 23 having a frequency response of at least about five times the pulse rate of the test subject, which is adequate to accurately follow the subject's blood pressure waveform. The pressure transducer 23, in order to satisfy the criterion of having a frequency response of at least about five times the pulse rate of the subject, will generally have a frequency res-ponse of at least about ten Hertz. The pressure transducer serves to measure pressure within the cuff, which pressure is the sum of pressure supplied by the pump and a fraction of pressure pro-duced by blood pressure fluctuation within the artery. Since the transducer has the required frequency response, the fluctuating portion of output thereof represents amplltude of pulsatile pressure rather than the integral thereof. O~tput of transducer 23 proceeds as represented by line 25 to amplifier 27, wherein 29 the signal is amplified and passed therefrom, as represented by ~/ 7 .. .. .: . . .. ~ . : ~ . . .
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-- 106~)2Z6 line 29, to analog-to-digital (~/D) converter 31. Output of the analog-to-digital converter is fed, as represented by line 3 to digital peak-to-peak detector 35, in which a quantity pro-portional to the time-dependent fluctuating component represent-ative of pulsatile pressure within the blood vessel is calculated.
An output comprising said quantity from the digital peak-to-peak detector 35 proceeds, as represented by line 37, to averaging unit 39, wherein an updated average value for the present and three immediately previous quantities proportional to the time-dependent fluctuating component representative of the pulsatile pressure within the artery 13 .is determined. This average value is fed, as represented by line 41, to comparator 43. The comparator 43, as represented by line 45, controls gate .
47. The gate 47 serves to allow the averaging unit 39, as rep-resented by line 49, to load a selected value of the quantity, as represented by line 51, into storing unit 53. The value of the quantity being stored in storing unit 53 is supplied to the comparator 43, as represented by line 55. Within comparator 43, stored tentative previous representations of the maximum value of said quantity are compared with current values of said quantity introduced into the comparator 43, as represented by line 41.
When a value of said quantity supplied to the comparator 43, as represented by line 41, is greater-than the quantity tentatively stored in the storage unit 53, as supplied to the comparator 43, as represented by line 55, then gate 47 is activated by the com-parator 43, as represented by line 45, and the larger value of said quantity replaces the tentative maximum value in storage unit 53.
29 The tentative maximum value of said quantity is intro-~/ - 8 -' .~ . . ~ : . . .
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`` 106~Z26 duced, as represented by line 57, into a halving unit (divide-by-two) 59 wherein it is divi~ed in half. The divided-in-half value is then introduced, as represented by line 61, to a systo-lic comparator 63. ~lso supplied to the systolic comparator 63 is the (now) current average of four most previous measurements of said quantity. This is supplied from the averaging unit 39, as represented by line 65. When systolic comparator 63 determines that the average quantity being supplied thereto, as represented by the line 65, is less than or equal to one-half of the tentative maximum value being supplied thereto,as represented by line 61, the systolic comparator 63 orders, as represented by line 67, the switching means 69 to stop the pump 19 and bleed the cuff 15 through solenoid control valve 18 and conduit 20, the stop-and-bleed order being rep-resented by line 71.
The switching means 69, as represented by line 73, and systolic comparator 63 as represented by line 74, also order interpolating unit 75 to interpolate between values of the applied -pressure, that is, the pressure being applied to cuff 15 by pump 19, so as to determine the precise applied pressure corres-ponding to said quantity being about one-half of said maximum value.
Values of applied pressure are supplied to interpolation unit 75, as represented by lines 77 and 79. Line 77 represents introduction of the applied pressure value for measurement just before the quantity became less than one-half the maximum value,and line 79 represents applied pressure when the quantity was equal to or slightly less than one-half the maximum value. These values 28 of the applied pressure are supplied as represented by lines 77 cb/

-106~226 and 79, ~rom storaye unit 8] and computing and averaging unit 83 respectively. The values of the applied pressure are supplied to averaging unit 83 by gate 85, as represented by line 87. The value of the just-previous applied pressure is supplied to stor-age unit 81 from averaging unit 83, as represented by line 89.
The value of the applied pressure is supplied to gate 85 from digital peak-to-peak detector 35, as represented by line 91.
The gate 8~ is triggered ~y the output of the analog-to-digital converter 31, as represented by the line 93. Hence, one value of applied pressure passes into the average unit 83 or each pulse which passes into the averaging unit 39. The applied pre-ssure and pulse pressure values are easily separated from one another because of their very different frequencies, the applied pressure being usually a slow ramp function and the pulse pressure having a frequency of about 1 E~ert~. In the preferred embodiment -of the invention, pump 19 is adjusted to repetitively apply an increasing ramped pressure to cuff 15.
The apparatus and process of the invention can also, how-ever, be made to operate with a pump which sequentially applies a decreasing pressure including decreasing ramped pressure to the cuff. In this case it is necessary to provide a memory unit wherein successiye values of applied pressure and of corresponding amplitude of the pulsatile quantity measured are stored for later comparison with one-half of the eventually determined maximum amplitude. The maximum value of the pulsatile quantity will not be determined until after the cuff pressure corresponding to systolic pressure has been passed as the pressure drops. In other words, the half amplitude is not determined when it occurs, but 29 only after the peak amplitude is determined, the peak amplitude . . . . . . ~ . , . . :

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~060ZZ6 occurring later in time.
It is understood by those skilled in the art that imple-mentation of the various functions represented in Figure 1 is accomplished from commercially available component parts. The pressure transducer employed conyerts pressure to an electrical analog current which is digitized by A/D converter 31. The remaining functional blocks are constructed primarily from commercially available microprocessors and other digital cir-cuitry, excluding those items associated with the pneumatics and pneumatics controls. Power supplies are not shown, but are to be understood to be employed as required.
Referring now to Figures 2 and 3, one can observe the improved accuracy of systolic pressure measurements made with apparatus of the present invention. Figure 2 is a plot of ampli-tude of the pulse height obtainable with apparatus and method of the present invention. The measuring means has a frequency response of preferably at least five times the subject's pulse rate. The maximum amplitude is labeled A and the half amplitude point (at cuff pressure higher than maximum amplitude cuff pressure) is labeled A/2. Corresponding applied cuff pressure is clearly discernable.
By contrast, Figure 3 depicts an oscillometric envelope, as may be generated by a bouncing mercury column of a mercury manome~er, or other integrator device. One observes that the threshold peak corresponding to half amplitude of Figure 2 is difficult, at least, to define well.
Theory Referring to Figures 4 and 5 there is illustrated an 29 explanation of our discovery as to why this relationship between cb/ - 11 -::

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.; 10602;~6 maximum amplitude and one half maximu~ amplitude e~ists for determining systolic pressure. While it is belieyed that the following explanation of this phenomenon is correct, it is to be understood that the invention is not meant to be limited thereby. ~he ~igures illustrate arm 11 with artery 13 therein ~- surrounded by cuff 15. The artery within th~ cuff is of length L. The pressure versus distance curve i5 aligned under the artery to illustrate pressure at the artery wall correspending ~; to an applied pressure between systolic and diastolic for Figure 4 and slightly above systolic for Figure 5. It will be noted r ~ that pressure at the artery wall, for the illustrated arm and cuff, is highest opposite the center of the cuff and drops off near edges thereof. This results because some of the cuff pressure adjacent ends of the cuff leads to the arm thereat being squeezed out of the cuff.

When pressure in the cuff is between diastolic and systo-:
lic pressure of the test subject, there is no part of the artery which is completely closed during an entire pulse. The artery is, of course, closed during the period when the pulse pressure is below the cuff pressure (in Figure 4 when the pulse pressure is between 80 torr and 100 torr) but it is also, of course, open when the blood pressure is between cuff pressure (100 torr) and systo-lic pressure a20 torr). In this situation the artery 13 changes volume along its entire length L as the pressure changes from below to above 100 torr and vice versa. On the other hand, in the situation sho~n in Figure 5 wherein applied pressure is just yery slightly greater than systolic pressure of the test subject, it will be noted that one-half of the artery, namely that part 29 of the artery distal from the heart, will for all practical pur--b/ - 12 -......... . ~ . , . . . . . .: . .

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1~60226 poses be constantly closed, since pulsatile pressure within the artery will never rise high enough to open it. This effect on ' one-half of the artery occurs because of the previously mention-ed fact that, in the illustrated embodiment, only at the center of the cuff is the full applied cuff pressure also applied to the artery. This means that only one-half of the length of the artery changes volume as the blood pressure surges from diastolic to systolic during a pulse beat since only the portion of the artery proximal to the heart is opened against the pressure exert-ed at the artery wall by the cuff. Accordingly, the ~mplitudeof the pressure fluctuation, ~hich is just that quantity illustrat-ed in Figure 3, is to a good approximation, in the illustrated embodiment, one-half of the maximum fluctuation thereof which would comprise a fluctuation of the entire length L of the artery.

:. , The invention may be embodied in yet other specific forms without departing from the spirit or essential characteristics thereof. For example, the applied cuff pressure may variably increase or decrease in any fashion including linear, nonlinear and stepped ~discontinuous~ fashion. The apparatus for process-ing the transducer-generated electrical analog signal can be constructed from analog circuitry, digital circuitry, or both;
specifically, discrete electronic components, discrete digital chips, microprocessor technology and structure, or a digital computer can be employed. The pressure cuff may be of the ordin-ary single cuff variety, but could also be a double cuff, or'guard-ed cuff, etc. The cuff need not be an arm cuff, but could function on other limbs, fingers, etc.
Thus, the present embodiments are to be considered in 29 all respects as illustrative and not restrictive, the scope of cb/ - 13 -., .
, the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are 4 therefore intended to be embraced therein. - :

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~060Z26 Supplementary Disclosure The preferred embodiment uti.lizes the relationship between maximum amplitude and one-halE maximum amplitude of measured pressure for determining systolic pressure in tle situation where the pressure cuff applies maximum pressure midway of its total length. It has been determined that in some circumstances systolic pressure may correspond with a pulsatile pressure other than one-half of said maximum value if the patient s arm is particularly obese and/or the pressure cuff is structured such as to apply maximum pressure other than at its midpoint.
Although in the illustrated embodiment and under most common conditions the structure of the cuff and/or the subject s arm (leg, etc.) are such that the highest pressure at the artery wall between diastolic pressure and systolic pressure occurs at the center of the cuff and of the length of blood vessel within the cuff, it will be appreciated that the cuff might be so designed and/or the radial size gradient of the subject s arm be so great as to shift this point of highest pressure from the center toward the proximal or distal end relative to the source of blood supply. For instance, this point of maximum pressure might be within a range of fifteen percent or more of the total length L to either side of the center position, as may be predetermined either empirically and/or through knowledge of the cuff design and arm geometry.
Accordingly, with a predetermination of the point of maximum pressure on the blood vessel wall by the cuff between diastolic and systolic pressure, a particular fraction xL is obtained in which the total length L of the blood vessel within 0 the cuff comprises the denomir.ator and the numerator x is .. ' ~ ' ' comprised of that ]ength of blood vessel within the cuffmeasured from its end proximal to the blood supply to said point of maximum pressure by the cuff. This particular fraction then represents the sensed artery volume change at applied systolic press~lre relative to the maximum sensed artery volume change which occurs between applied diastolic and systolic pressures. Accordingly, when the sensed fluctuation value bears this particular fractional relationship to the maximum sensed fluctuation value, the cuff pressure is then indicative of the subject's systolic pressure. The value of x in the fractional expression L is seen to be 2 in the embodiment illustrated in Fig. 5.
Thus the invention comprises apparatus for determining systolic pressure, comprising: a pressure cuff attachable to a living test subject adjacent a blood vessel; means for changing pressure in the cuff and thereby applying pressure to the subject;
means communicating with the cuff for measuring a quantity proportional to a time-dependent fluctuating component repre-sentative of the pulsatile pressure within the blood vessel whereby the quantity is proportional to amplitude of the pulsatile pressure; means for determining the maximum value attained by said quantity as the applied pressure is changed; means for storing a representation of the maximum value; means for determining when the quantity is substantially equal to about a particular fraction of the maximum value for an applied pressure greater than the pressure applied when the maximum value occurs or results, the particular fraction corresponding with that fraction of the total length of the blood vessel within the cuff which extends from its upstream (proximal) end to the point at w-lich the cuff applies maximum pressure to the jvb/kh `` 1060226 b]ood vessel wal.l betweell diastolic and systolic pressure and typically being about one-half; and means for reading out the applied pressure corresponding to said quantity being substantially equal to about the particular fraction of the maximum value, said read-out pressure corresponding to the systolic pressure of said subject.
In another sense, the invention comprises a process or method for determini.ng systolic pressure, comprising: applying pressure to a living test subject by changing pressure in a pressure cuff attached to the subject adjacent a blood vessel;
measuring at said cuff a quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said quantity being proportional to amplitude of the pulsatile pressure; determining the maximum value attained by said quantity as the applied pressure is changed; storing a representation of the maximum value; deter-mining when the quantity is substantially equal to about a particular fraction of the maximum value for an applied pressure greater than the pressure applied when the maximum value occurs or results, the particular fraction corresponding with that fraction of the total length of the blood vessel within the cuff which extends from its upstream (proximal) end to the point at which the cuff applies maximum pressure to the blood vessel wall between diastolic and systolic pressure and typically being about one-half; and reading out the applied pressure corresponding to the quantity being substantially equal to about the particular fraction of the maximum value, the read-out 28 pressure corresponding to the systolic pressure of the subject.

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Claims (23)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for determining systolic pressure, compris-ing a pressure cuff attachable to a living test subject adjacent a blood vessel; means for changing pressure in the cuff and thereby applying pressure to the subject, means communicating with said cuff for measuring a quantity proportional to a time--dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said means having a frequency response of at least about five times the pulse rate of the subject whereby said quantity is proportional to the amplitude of said pulsatile pressure, means for determining the maximum value attained by said quantity as the applied pressure is changed, means for storing a representation of said maximum value, means for determining when said quantity is substantially equal to about one-half of said maximum value for an applied pressure greater than the pressure applied when said maximum value results, and means for reading out applied pressure correspond-ing to said quantity being substantially equal to about one-half of said maximum value, said read-out pressure corresponding to the systolic pressure of said subject.

2. An apparatus as in claim 1, wherein said quantity-measuring means comprises a pressure-transducer having a frequency response of at least about ten Hertz.

3. An apparatus as in claim 2, wherein said pressure-changing means comprises a pump which applies an increasing pressure to said cuff between lower and upper pressure limits in a repetitive manner.

4. An apparatus as in claim 3 including means for stopping said pump and means for bleeding said cuff as said read-out of systolic pressure occurs.

5. An apparatus as in claim 4, wherein said means for determining said maximum value comprises a comparator wherein each successive representation of the value of said quantity is compared with a tentative previous representation of a maximum value thereof stored in said storing means, the lesser of the compared representations of the values of said quantity is dis-carded and the greater of the compared representations is stored in said storing means.

6. An apparatus as in claim 5, wherein said means for deter-mining when said quantity is substantially equal to about one-half of said maximum value comprises a comparator wherein each successive representation of the value of said quantity is com-pared with one-half of the tentative representation of the maximum value of said quantity stored in said storing means, said stopping means and said bleeding means being activated when a value of said quantity is less than or equal to about one-half of said maximum value.

7. An apparatus as in claim 6, including a memory unit which temporarily stores a value of the applied pressure corres-ponding to each successive representation of the value of said quantity and also temporarily stores at least a value of the applied pressure corresponding to the previous to each success-ive representation of the value of said quantity.

8. An apparatus as in claim 7, including means for inter-polating between stored values of representations of said quantity and between temporarily-stored values of the respective corres-ponding applied pressure to calculate an interpolated value of the applied pressure corresponding to when said quantity is sub-stantially equal to about one-half of said maximum value.

9. A process for determining systolic pressure, comprising changing the pressure in a pressure cuff attached to a living test subject adjacent a blood vessel so as to apply different pressure to the subject, measuring at said cuff with a measuring device having a frequency response of at least about five times the pulse rate of the subject at said cuff, a quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said quantity being proportional to the amplitude of said pulsatile pressure, deter-mining the maximum value attained by said quantity as the applied pressure is changed, storing a representation of said maximum value, determining when said quantity is substantially equal to about one-half of said maximum value for an applied pressure greater than the pressure applied when said maximum value results and reading out the applied pressure corresponding to said quantity being substantially equal to about one-half of said maximum value, said read-out pressure corresponding to the systolic pressure of said subject.

10. A process as in claim 9, wherein said quantity is measured utilizing a pressure transducer having a frequency response of at least about ten Hertz.

11. A process as in claim 10, wherein said pressure is sequentially increased.

12. A process as in claim 11, including stopping said pump and bleeding said cuff as said read-out of systolic pressure occurs.

13. A process as in claim 12, including the step of inter-polating between stored values of representations of said quantity and between temporarily-stored values of the respective corres-ponding applied pressure to calculate an interpolated value of the applied pressure corresponding to when said quantity is substantially equal to about one-half of said maximum value.

14. An automatic blood pressure monitoring system for measuring and monitoring systolic blood pressure of a person comprising transducer means in pressure-communication with said person for converting said person's blood pressure to a varying electrical analog signal, pump means for applying a controllably variable pressure to said transducer means, said transducer means including cuff means for applying said controllably variable pressure to a blood vessel of said subject, converter means for receiving said electrical analog signal and converting said electrical analog signal to a digital signal, digital processing means adapted to receive said digital signal for determining (1) maximum blood pressure of said person and a first value of said controllably variable pressure corresponding thereto, (2) one-half said maximum blood pressure when occurring at a second value of said controllably variable pressure higher than said first value, and (3) the magnitude of said second value, and means for providing read-out of said second value as systolic blood pressure.

15. A method for automatically measuring and monitoring systolic blood pressure of a person including the steps of:
A) converting said person's blood pressure to a vary-ing electrical analog signal;

claim 15 cont'd....

B) applying a controllably variable pressure to said person in a manner which affects said electrical analog signal;
C) converting said affected electrical analog signal to a digital signal, D) digitally processing said signal to provide (1) maximum blood pressure of said person and a first value of said controllably variable pressure corresponding thereto;
(2) one-half said maximum blood pressure when occurring at a second value of said controllably variable pressure higher than said first value; and (3) the magnitude of said second value; and E) providing read-out of said second value.

16. An apparatus for determining systolic pressure, compris-ing a pressure cuff attachable to a living test subject adjacent a blood vessel, means for changing pressure in the cuff and thereby applying pressure to the subject, means communicating with said cuff for measuring a quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said means having a frequency response such that said quantity is proportional to the amplitude of said pulsatile pressure, means for determining the maximum value attained by said quantity as the applied pressure is changed; means for storing a representation of said maximum value, means for determining when said quantity is substantially equal to about a particular fraction of said maximum value for an applied pressure greater than the pressure applied when said maximum value results, said particular fraction corresponding with that fraction of the total length of said blood vessel within said cuff which extends from its end proximal the blood supply to the location at which the cuff applies maximum pressure to its wall when the pressure applied to the cuff is between diastolic and systolic pressure, and means for reading out applied pressure corresponding to said quantity being substantially equal to about said particular fraction of said maximum value, said read-out pressure corresponding to the systolic pressure of said subject.

17. The apparatus of claim 16 wherein said particular fraction is substantially within the range of thirty-five percent to sixty-five percent.

18. The apparatus of claim 17 wherein said location at which said cuff applies maximum pressure to the blood vessel wall when the pressure applied to said cuff is between diastolic and systolic pressure is predetermined whereby said particular fraction is also predetermined.

19. The apparatus of claim 18 wherein said frequency res-ponse of said means for measuring said quantity proportional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel is at least about five times the pulse rate of the subject.

20. A process for determining systolic pressure, compris-ing changing the pressure in a pressure cuff attached to a living test subject adjacent a blood vessel so as to apply different pressure to the subject, measuring at said cuff a quantity portional to a time-dependent fluctuating component representative of the pulsatile pressure within the blood vessel, said measuring device having a frequency response such that said measured quantity is proportional to the amplitude of said pulsatile pressure, determining the maximum value attained by said quantity as the applied pressure is changed, storing a representation of said maximum value, determining when said quantity is substantially equal to about a particular fraction of said maximum value for an applied pressure greater than the pressure applied when said maximum value results, said particular fraction corresponding with that fraction of the total length of said blood vessel within said cuff which extends from its end proximal the blood supply to the location at which the cuff applies maximum pre-ssure to its wall when the pressure applied to the cuff is bet-ween diastolic and systolic pressure, and reading out the applied pressure corresponding to said quantity being substantially equal to about said particular fraction of said maximum value, said read-out pressure corresponding to the systolic pressure of said subject.

21. The process of claim 20 wherein said particular fraction is substantially within the range of thirty-five percent to sixty-five percent.

22. The process of claim 21 wherein said location at which said cuff applies maximum pressure to the blood vessel wall when the pressure applied to said cuff is between diastolic and systolic pressure is predetermined whereby said particular fraction is also predetermined.

23. The process of claim 22 wherein said frequency response of said means for measuring said quantity proportional to a time dependent fluctuating component representative of the pulsatile pressure within the blood vessel is at least about five times the pulse rate of the subject.