Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
  • A61B5/021—Measuring pressure in heart or blood vessels
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
  • A61B5/021—Measuring pressure in heart or blood vessels
  • A61B5/02108—Measuring pressure in heart or blood vessels from analysis of pulse wave characteristics

Definitions

• the present invention relates generally to blood pres- 5 sure evaluation procedures and more particularly to non-invasive techniques for determining certain waveform information associated with blood pressure.
• a more specific object of the present invention is to provide a different uncomplicated and yet reliable technique for generating non-invasively a waveform closely approximating an individual's true blood pres ⁇ sure waveform which, heretofore, has been obtainable by invasive means only.
• Another particular object of the present invention is to provide a new way for measuring and calculating the mean arterial pressure of an individual.
• a suitably sized cuff for example one which is 20 inches long and 5 inches wide, is positioned around the upper arm of an individual, a human being specifically or a mammal in general (hereinafter referred to as the patient) and initially pressurized to a level which is believed to be clearly greater than the patient's systolic pressure, for example 180 Torr. It is assumed that this pressure will also cause the patient's artery within the sleeve to completely collapse.
• cuff pressure is gradually reduced toward zero during which time the cuff continuously changes in pressure in an oscillating fashion due to the combination of (1) the internal blood pressure changes in the patient's artery and (2) changes in cuff pressure.
• the latter at any given time in the procedure is known and oscillatory changes in cuff pressure can be readily measured, for example with an oscilloscope.
• the typically 5" wide pressure cuff entirely surrounds a corresponding 5" length of artery.
• the tissue of the arm is for the most part incompressible, and therefore any change in the volume of the artery, caused for example by pulsations of blood, results in a corresponding change in the volume of air in the air bladder which is within the cuff and therefore adjacent to the arm.
• This change in air volume produces a small but accurately measurable pressure change in the air.
• This equivalence of pressure pulsations in the cuff bladder to volume pulsations of the artery is the essence of oscillometry.
• FIGURE 1 (corresponding to Figure 6 in United States Patent 3,903,872) diagrammatically illustrates the shapes of successive cuff pressure versus time pulses (cuff pulses) as the measured cuff pressure changes from 90 Torr to 80 Torr to 70 Torr, assuming the patient has a diastolic pressure of 80 Torr;
• FIGURE 1A diagrammatically illustrates a full series of cuff pulses corresponding to those in Figure 1 from a cuff pressure of 160 Torr to a cuff pressure of zero;
• FIGURE 2 diagrammatically illustrates a curve corre ⁇ sponding to arterial or cuff volume (V), that is, the volume of the patient's artery within the cuff (as measured by cuff volume) versus wall pressure (Pw) across the artery wall within the cuff and, super ⁇ imposed on this curve, a curve which is intended to correspond to the actual blood pressure waveform of a patient, the two curves being provided together in order to illustrate the principles of oscillometry, as relied upon in the above-recited patents;
• V arterial or cuff volume
• Pw wall pressure
• FIGURES 3 and 4 diagrammatically illustrate the cuff curve of Figure 1 in ways which display techniques for obtaining a given patient's systolic and diastolic blood pressures in accordance with the Link and Link et al patents recited above;
• FIGURE 5 diagrammatically illustrates a compliance curve for the patient's artery, that is, a curve which displays the ration ⁇ V/ ⁇ P against the arterial wall pressure Pw, where ⁇ v is the incremental change in the arterial volume corresponding to a preselected constant change in blood pressure ⁇ P.
• This curve is initially determined in order to provide the cuff or arterial volume curve (V/P curve) of Figure 2 by means of inte ⁇ gration, as will be seen.
• FIG. 1 this figure diagrammaticallv illustrates three successive waveforms lOh, lOi and lOj which correspond to the change in volume in a pres- surized cuff, as described above, at three different cuff pressures, specifically cuff pressures of 90 Torr, 80 Torr and 70 Torr.
• cuff pulses a greater number of waveforms (hereinafter referred to as cuff pulses) are generated starting at a cuff pressure of 160 Torr and ending at a cuff pressure of zero, as will be seen in Figure 1A.
• each waveform has what may be referred to as a systolic rise Sr at one end of the waveform, a diastolic decline D, at the opposite end and a maximum amplitude A.
• the generally S-shaped ' curve 12 illustrated is shown within a horizontal/vertical coordinate system where the horizontal axis represents the wall pressure P across the artery wall of a given patient, within the confines of the applied cuff, and the vertical axis represents arterial volume V of the artery within the cuff, as measured by the internal volume of the cuff itself.
• this V/P curve hereinafter merely referred to as an arterial or a cuff curve
• P The wall pressure P of the artery of the patient at any given time is equal to the blood pressure P. of the patient within the artery at that time less the applied pressure of the cuff Pc.
• This 40 Torr measuring band is illustrated by dotted lines in Figure 2 at 14 and actually represents the patient's pulse pressure ⁇ P which is equal to 40 Torr in this case.
• the patient's actual blood pressure waveform 15 is superimposed on the V/P coordinate system in Figure 2 within the pulse pressure band 14. As seen there, this waveform is made up of a series of actual blood pressure pulses 16, each of which corresponds to a single beat of the patient's heart. Note that each pulse starts at a minimum pressure (the diastolic pressure of the patient) and sharply increases along its leading edge which is the systolic rise S until it reaches a maximum (the patient's systolic blood pres ⁇ sure) , at which time it drops back down along a trailing edge which includes a dichrotic notch and a diastolic decline D, to the minimum pressure again.
• a minimum pressure the diastolic pressure of the patient
• a maximum the patient's systolic blood pres ⁇ sure
• the volume of the patient's artery and therefore the volume of the cuff is fixed by the arterial curve at the value indicated at Vi, .
• the 30 Torr value is determined by subtracting the cuff pressure P of 50 Torr from the diastolic blood pressure P fe (D) of 80 Torr and the 70 Torr value is determined by subtracting the same P of 50 Torr from the systolic blood pressure ? h (D) of 120 Torr.
• P oscillates back and forth along a steeper segment of the arterial curve so as to cause the volume of the patient's artery and therefore the volume of the cuff to oscillate between the values V- and V..
• each cuff pulse 101 is greater than the amplitude of each cuff pulse lOq. This is because the 40 Torr band 14* at a cuff pressure of 50 Torr is on a steeper part of the volume slope than the band 14 at a cuff pressure of zero. Indeed, as we increase the cuff pressure P (which decreases P ) and therefore move the pressure band to the left on the horizontal axis, we first continue to move along steeper sections of the arte ⁇ rial curve and thereafter less steep sections.
• the amplitude A (see Figures 1 and 1A) of the corresponding cuff pulses lOq, 101 and so on will first increase to a maximum and then decrease again.
• a cuff pressure P of 100 the entire 40 Torr pressure band is shifted to the left so as to uniformly straddle opposite sides of the vertical axis, as indicated at 14". This results in a corresponding cuff pulse lOg having approximately a maximum amplitude ( ⁇ V ax in Figure 2) .
• the entire 40 Torr band is moved a substantial distance to the left of the vertical axis, as indicated at 14' ' ' such that the resultant change in volume (amplitude of the corre ⁇ sponding cuff pulse 10a) is quite small.
• the band is moved still further to the left, eventually producing very small changes in volume V. From a physical standpoint, this represents a collapsed artery. In other words, sufficient cuff pressure.P is being applied over and above the internal blood pressure P, to cause the wall of the artery to col ⁇ lapse.
• a blood pressure increase causes an arterial volume increase.
• This arterial volume increase causes a cuff bladder air volume decrease which in turn causes a cuff bladder air-pressure increase. Therefore a blood pressure increase results in a cuff air pressure increase.
• a maximum change in volume ⁇ V max results from a cuff pressure P of about 100 Torr (e.g. the pressure band 14" in Figure 2) .
• the amplitude A of the resultant cuff pulse 10 is about one-half of the amplitude of the cuff pulse having a maximum amplitude. Therefore, a patient's systolic blood pressure can be determined by first generating a series of cuff pulses across the - cuff pressure spectrum, as in Figure 1A.
• the one having maximum amplitude Amax is determined and then the cuff pulse having half that amplitude (at a greater cuff pressure) is found.
• the cuff pressure P used to generate that pulse corresponds to the patient's systolic pressure.
• the one corre ⁇ sponding to the band 14' 1 ' 1 illustrated in Figure 3 can be found.
• its associated cuff pressure is assumed to be equal to the patient's systolic pressure. This is discussed in more detail in Link et al United States Patents 4,009,709 and 4,074,711 and means are provided in these latter patents for electronically making these evaluations.
• each blood pressure pulse 16 making up this waveform is identical to the next one. Both of these aspects of the waveform are assumed for purposes herein. Moreover, each pulse has its own systolic rise S and diastolic decline D,, as mentioned hereto ⁇ fore. It should also be noted that the arterial curve 12 dictates the relationship v between V and Pw at each and every point on the waveform 15 of individual blood pressure pulse 16, not merely at the extreme diastolic and systolic end points of each pulse.
• the measuring band (e.g. the pressure difference between the two measuring points) is substantially narrower than band 14.
• ⁇ V. ' is determined for a cuff pressure P of zero using the pressure band 18 which encompasses a small part of the diastolic decline of each blood pressure pulse 16.
• ⁇ V_' is determined for a cuff pressure of P of 50 Torr by shifting the band to 18' and, ⁇ V,' is determined for a cuff pressure P of 80 Torr (e.g. the patient's diastolic blood pres ⁇ sure) by shifting the band to 18".
• ⁇ V is maximum when the cuff pressure P is equal to the patient's diastolic blood pressure. Therefore, by determining the change in volume ⁇ V at the end of the diastolic slope of the patient's actual blood pressure waveform for each and every cuff pressure, the one cuff pressure producing a maximum change will correspond to the patient's diastolic blood pressure.
• the lowest pressure part of the diastolic decline D, forming part of each pulse 16 is particularly suitable for this purpose since it can be readily located during each cycle of the waveform. This is because it immediately precedes the systolic rise S which is readily distinguishable each time it appears. This procedure is described in more detail in the previous ⁇ ly recited Link Patent 3,903,872 along with means for carrying out this procedure electronically.
• this curve represents incremental changes in volume with incremental changes in pressure or dV/dP ( Figure 5) .
• FIGURE 6 diagrammatically illustrates an arterial v/p cure of a given individual with specific emphasis on the degree of linearity of its segments;
• FIGURE 7 diagrammatically illustrates the use of the arterial curve of Figure 6 in combination with the given individual's cuff pulses at a fixed cuff pressure to approximate the individuals actual blood pressure curve;
• FIGURE 8 schematically illustrates an arrangement for providing the approximated curve just referred to in association with Figure 7;
• FIGURE 9 (a) - (d) diagrammatically illustrate four blood pressure waveforms having different blood pressure constants K and equivalently, different mean blood pressures.
• FIG. 6-9 a technique is provided for generating a waveform which closely approximates the actual blood pressure waveform of a patient.
• this technique reference is again made to Figure 2. It may be recalled that a particular patient's cuff pulses at any given cuff pressure is dictated by the S-shaped cuff curve 12 in Figure 2. For example, assuming a systolic pressure of 120 Torr and a diastolic pressure of 80 Torr, the resultant measuring (pulse pressure) band may be moved along any section of the S-shaped curve by selecting a particular cuff pressure.
• the band With a cuff pressure of zero, the band is located to the far right, as viewed in Figure 2 and by providing a cuff pressure of 160, the band is located to the far left.
• the most linear sections of the arterial curve provide cuff pulses which most approximate the actual blood pressure waveforms.
• the S-shaped cuff curve of Figure 2 is shown in Figure 6 divided into three sections, sections 2 and 3 being the least linear while section 1, is the most linear.
• the pulse pressure band of Figure 6 has its center along section 2 for example, that is, at a fixed cuff pressure of around 50 Torr, the resultant cuff pulses are not close approximations of the patient's actual blood pressure waveform.
• section 3 there is practically no gain at the diastolic end of the waveform, that is, this section of the curve is practi ⁇ cally horizontal, resulting in very bad waveform distortions.
• section 1 which is more linear and which displays moderate to low gain, that is, a gradual slope. This can be achieved by operat ⁇ ing at a fixed cuff pres ' sure of anywhere from zero to approximately 80 Torr.
• cuff pulses are shown at 10m' in Figure 7 and correspond to a cuff pressure of, for example, 40 Torr (see Figure 1A) .
• the patients systolic and diastolic pressures and arterial curve are used in combination with the cuff pulses to provide ultimately an approximation of the patients blood pressure waveform, as will be seen below.
• the patient's arterial curve is reproduced in Figure 7 at 12'. Both the systolic and diastolic pressures of the patient and curve 12' can be readily provided.
• a waveform 16' can be generated between fixed wall pressures (P ) which are dictated by the patients systolic and diastolic pressures and the cuff pressure selected.
• P fixed wall pressure
• the patients systolic pressure P is 125 and his diastolic pressure P, is 85
• the operating P W band B is between 45 Torr and 85 torr, as illustrated in Figure 7.
• These wall pressures dictate the section of curve 12' which produces waveform 16'.
• a first point P.. at the beginning of pulse 10m* is found and a corresponding point P..
• band B is plotted. This is easily done since both of these points represent the diastolic pressure of the patient and the beginning of the pulse and waveform.
• a second point P- at time t ⁇ (as referenced from time t 1 ) can be found and so on until a series of points are found, as shown. From these points, the waveform 16 can be generated.
• the shape of waveform 16' correctly represents the true blood pressure waveform whereas the shape of waveform 10m from which 16' is derived may be highly deformed by the arterial V/P curve.
• suitable cuff means generally indicated at 30 in Figure 8 is positioned around the arm of a patient in the normal operating manner and maintained at one of these preferably low pressures, for example, a cuff pressure of 40 Torr by pump means 32.
• a cuff pressure of 40 Torr for example, a cuff pressure of 100 Torr could be selected but higher cuff pressures of this type might be uncomfortable for the patient.
• the resultant cuff pulses are continuously monitored by transducer 34.
• Suitable and readily providable electronic circuitry 36 is also provided with the patients arterial curve and his svstolic and diastolic pressures and uses the information to generate the waveform 16'.
• This waveform can be placed on an oscilloscope or monitor 38 or read out permanently as an approximation of the patient's actual blood pressure waveform, as shown in Figure 1A. Moreover, in its displayed or readout state, the waveform can be appropriately labeled with its systolic and diastolic points in order to more aptly represent the patient's true blood pressure waveform.
• any single one or many of the cuff pulses obtained when the cuff pressure is ramped slowly down or up in pressure can be transformed by the apparatus described above into a waveform 16' which accurately represents the shape of the true blood pressure waveform.
• a single or many cuff pulses can be transformed into accurate representations of the blood pressure waveform and suitably presented on a monitor for a doctors examination.
• the mean pressure M can be calculated by integrating the waveform (its pressure amplitude P) over time T (the duration of the waveform) so that:
• the Figure 9a waveform can be shown to have a K value (which is commonly referred to as the blood pressure constant) of about 0.50.
• the Figure 9b waveform approximates a K value of 0.6 while the Figure 9c waveform approximates a K value of 0.2.
• a diagnostic tool can be provided which not only provides for a patient's diastolic and systolic blood pressures non-invasively but also a close approximation of the patient's actual blood pressure waveform as well as his mean pressure and blood pressure constant, again non-invasively.
• the means 30 shown in Figure 8 can be provided with circuitry for calculating the mean pressure P. (M) and blood pressure constant K from this waveform and equations 2-4 above.

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• 1985
  • 1985-06-17 WO PCT/US1985/001120 patent/WO1986000209A1/fr not_active Application Discontinuation
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