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WO2008109185A2 - Procédé non invasif de détermination du travail du cœur, des compliances du système vasculaire, et de la résistance vasculaire périphérique - Google Patents

Procédé non invasif de détermination du travail du cœur, des compliances du système vasculaire, et de la résistance vasculaire périphérique Download PDF

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Publication number
WO2008109185A2
WO2008109185A2 PCT/US2008/003207 US2008003207W WO2008109185A2 WO 2008109185 A2 WO2008109185 A2 WO 2008109185A2 US 2008003207 W US2008003207 W US 2008003207W WO 2008109185 A2 WO2008109185 A2 WO 2008109185A2
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heart
blood
patient
pressure
value
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PCT/US2008/003207
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WO2008109185A3 (fr
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Kenneth R. Kensey
Daniel J. Cho
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Kensey Kenneth R
Cho Daniel J
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Publication of WO2008109185A2 publication Critical patent/WO2008109185A2/fr
Publication of WO2008109185A3 publication Critical patent/WO2008109185A3/fr

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    • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/026—Measuring blood flow
    • A61B5/029—Measuring blood output from the heart, e.g. minute volume
    • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/02007—Evaluating blood vessel condition, e.g. elasticity, compliance
    • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/02028—Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
    • 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 for evaluating the cardiovascular system, e.g. pulse, heart rate, blood pressure or blood flow
    • A61B5/021—Measuring pressure in heart or blood vessels
    • A61B5/022—Measuring pressure in heart or blood vessels by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers

Definitions

  • the present invention relates generally to a method of determining the work of the heart, proximal and distal compliances, and peripheral vascular resistance.
  • Every organ in the human body needs oxygen, which is supplied by blood through the work of the heart.
  • Diseases such as ischemia or hypoxemia often result from the lack of oxygen through improper work of the heart.
  • the heart works harder and pumps blood with a greater pressure, increasing the blood pressure.
  • hypertension is a consequence of increased work of the heart.
  • Hypertension if not corrected, becomes a cause of vascular occlusive disease that increases the peripheral vascular resistance, thus creating a condition of ischemia or hypoxemia.
  • the heart attempts to overcome vascular resistance by pumping blood with greater pressure, which increases the work of the heart and promotes hypertension.
  • arteriosclerosis i.e., hardening of arterial wall
  • atherosclerosis i.e., partial blockage of lumen
  • arteriosclerosis i.e., hardening of arterial wall
  • atherosclerosis i.e., partial blockage of lumen
  • CHF congestive heart failure
  • the currently available method for determining the work of the heart is invasive. Specifically, the currently available method uses a cardiac function analyzer (e.g., Leycom CFA-512), which measures the transient pressure P(t) and the left ventricular volume V(t).
  • a pressure-volume loop can be constructed using the transient pressure and left ventricle volume data as shown in Fig. 1.
  • the area enclosed by the pressure- left ventricle volume loop is mathematically determined by integration, which indicates the work of the heart per a cardiac cycle.
  • This method requires the measurement of the transient motion of the left ventricle, which requires the injection of a special dye into the arterial system for the angiography of the left ventricle. The introduction of the dye requires the penetration of a catheter, a non-trivial procedure which is conducted only when there is an absolute need for the procedure.
  • a noninvasive method is used to determine the work of the heart based on estimated or measured pulsatile pressure (e.g. measured from the upper exteremities, i.e. the arm, of a patient) and data related to the whole blood viscosity of the patient.
  • estimated or measured pulsatile pressure e.g. measured from the upper exteremities, i.e. the arm, of a patient
  • the cardiac output (i.e. blood flow rate) of the heart of the patient can be calculated based on fluid dynamic principles.
  • the work of the heart can be estimated by the integration of the product of the cardiac output and the pulsatile pressure over a cardiac cycle.
  • a modified Windkessel model is used to simulate the cardiovascular system.
  • a modified Windkessel model according to the present invention includes vascular hemodynamic impedance parameters such as proximal and distal compliances, and peripheral vascular resistance (PVR).
  • PVR peripheral vascular resistance
  • vascular hemodynamic and impedance parameters can also be calculated in addition to the work of the heart.
  • Fig. 1 illustrates two examples of a pressure-volume loop obtained using a method according to the prior art.
  • FIG. 2 illustrates steps in a method according to the present invention.
  • FIG. 3A illustrates schematically parts of a cardiovascular system.
  • Fig. 3B illustrates an equivalent circuit diagram for a modified Windkessel model used as a basis for a method according to the present invention.
  • Fig. 4 illustrates a method according to the first embodiment of the present invention.
  • Fig. 5 illustrates a method according to the second embodiment of the present invention.
  • Fig. 6 provides values for the power of the heart of nine human subjects calculated using a method according to the present invention.
  • Fig. 7 reports the values from Fig. 6 broken into four subgroups.
  • Fig. 8 provides ten pairs of values for Casson model constants selected randomly and used in a method according to the present invention to obtain values for the power of the heart.
  • Figs. 9A-9C graphically illustrate the relationship between the power of the heart and Casson model constants.
  • a method according to the present invention non-invasively determines the work of heart, the power of the heart, and other cardiovascular characteristics of a patient using data related to the blood viscosity of a patient.
  • the work of the heart of a patient can be calculated by providing a value for the pulsatile pressure S l , which can be estimated or measured, providing the blood viscosity of the patient S2 (for example, blood viscosity at a high shear rate (e.g. 300/s)), providing yield stress S3, calculating blood flow rate (cardiac output) S4 based on the values provided at S l , S2, S3, and calculating the work of heart of the patient S5 based on values obtained at S l and S4.
  • a value for the pulsatile pressure S l which can be estimated or measured
  • the blood viscosity of the patient S2 for example, blood viscosity at a high shear rate (e.g. 300/s)
  • yield stress S3 for example, blood viscosity at a high shear rate (e.g. 300/s)
  • cardiac output cardiac output
  • a value for the pulsatile pressure can be the patient's aortic pressure, which can be measured by taking the pulse of the patient at his/her upper extremity (e.g. forearm).
  • the blood viscosity of the patient and the yield stress can be determined using, for example, a scanning capillary tube viscometer, or any other desirable method.
  • the blood flow rate can be calculated using the patient's pulsatile pressure, blood viscosity of the patient, and the yield stress using preferably a mathematical relationship as disclosed herein (see Equation (6) below), and the work of the heart of the patient can be estimated/determined by first determining the power of the heart of the patient, and then integrating the power of the heart of the patient over a cardiac cycle as mathematically demonstrated below.
  • Blood is a non-Newtonian fluid which means that its viscosity varies with the shear rate of the flow thereof.
  • shear rate increases, whole blood viscosity decreases, which is referred to as the "shear-thinning characteristic" of whole blood.
  • a reason for the variation in blood viscosity with varying shear rate is that blood consists of a number of suspended particles such as erythrocytes, leukocytes, and platelets. Red blood cells, the main component of whole blood, cause blood's non- Newtonian behavior.
  • the Casson model contains two parameters: ⁇ y (yield stress) and k (the Casson model constant). These parameters can be obtained using a scanning capillary tube viscometer SCTV (available from Rheologics, Exton, PA, USA), or any other suitable method.
  • SCTV produces whole blood viscosity data (more specifically viscosity vs. shear rate) of a patient over a wide range of shear rates. In terms of blood viscosity, one can rewrite the above Casson model equation as
  • and f 2 represent two Casson model constants, k and ⁇ y , where fi represents the blood viscosity at a high shear rate (i.e., shear rate greater than 300 s * 1 ) and f 2 represents the yield stress.
  • Viscosity which is a measure of resistance to flow, critically affects the magnitude of peripheral vascular resistance (PVR).
  • PVR peripheral vascular resistance
  • the power of the heart can be estimated by the product of the pressure change in the left ventricle during a cardiac cycle and the cardiac output according to the following equation:
  • DP L v is the left ventricular pressure at the end of diastole
  • CO is a cardiac output [ml/min].
  • the left ventricular pressure at the end of diastole is approximately 5 mmHg for most people.
  • the aortic pressure at peak systole varies widely from person to person, but can be approximated by the systolic blood pressure measured at the forearm. It has been shown that the cardiac output CO can be estimated using a person's body weight W as
  • the power of the heart has a unit of [J/s].
  • the work of the heart can be obtained by multiplying the period of a cardiac cycle T (which is measured in seconds) to the power of the heart POH as
  • period of a cardiac cycle T [s] can be determined by the heart rate as
  • the left hand side ⁇ P represents a pressure drop due to friction between the moving fluid and the tube wall over a length L of a tube with an inside diameter d.
  • the blood pressure can be described as the product of the cardiac output and blood viscosity for a given geometry circulatory system, i.e., with fixed diameter and length. More specifically, since blood leaves the heart (i.e., left ventricle) only during systole, blood pressure can be replaced by the aortic blood pressure during systole minus the left ventricle pressure at the end of diastole, which is relatively small compared to the peak aortic pressure at the peak systole.
  • ⁇ P the aortic blood pressure at the peak of systole minus the venous pressure, or simply systolic pressure, ⁇ P can be qualitatively described as the product of the cardiac output, Q, and blood viscosity, ⁇ .
  • the cardiac output is the volumetric flow rate of blood per minute, it is the time-averaged value over a cardiac cycle, which is often constant and does not vary over time at resting conditions for most people.
  • the work of the heart can be simply expressed as a function of the whole blood viscosity as
  • both the instantaneous cardiac output Q(t) and the instantaneous aortic blood pressure P(t) vary with time. Therefore, one can determine the work of the heart using an integration of the product of the two over time as
  • T is the period of a cardiac cycle.
  • the above integration (Eq. 4g) of the product of the cardiac output and blood pressure (e.g. aortic pressure) over time is used to estimate the work of the heart.
  • left-hand side represents the inertial force (i.e., acceleration) of a fluid particle
  • the two terms in the right-hand side represent contributions from pressure gradient and viscous force
  • the human arterial system is a network of vessels that converts the intermittent flow pumped out of the heart into steady flow through the capillaries and the venous system.
  • One of the most elementary modeling approaches is the Windkessel model, where compliance, pressure wave reflection, vascular resistance, and inertance are the key parameters in the analysis of the pulsatile arterial flow.
  • a great deal of research has been performed to approximate these parameters, and a number of modified models have been created for this purpose.
  • More complex models have failed to capture the phenomenon and have limitations in reflecting the behavior of the real system.
  • each model that represents a segment of the whole arterial system is combined with the next segment model in series, forming a lumped parameter model to increase the accuracy of the model.
  • the lumping of parameters increases the uncertainty of the uniqueness of the solution.
  • a modified Windkessel model is used to analyze vascular hemodynamic impedance parameters that indicate the progressive state of the cardiovascular disease.
  • the modified Windkessel model uses the proximal compliance of the aorta, C / , and the peripheral vascular resistance, R s , to simulate the inertia (often called inertance) of blood, L.
  • the inertance L relates to the recoil effect of the arterial wall as the pressure wave propagates through the arterial system in each cardiac cycle.
  • a value of L 0.017 (mmHg S 2 AnI) can be used.
  • Pi(O is the instantaneous pressure at the aorta, i.e. the pulsatile pressure P ⁇ (t). Since the modified model assumes the venous pressure to be negligible for simplicity, Pi(O actually means the pressure difference between the aorta and the vein.
  • P ⁇ (t) represents aortic pressure, which can be mathematically described in three different ways, Eqs. (5a), (5b), and (5c).
  • Fig. 3B indicates the three different paths for the aortic pressure to propagate, and each path is marked by the corresponding equation number, Eqs. (5a), (5b), or (5c) in Fig. 3B.
  • Q ⁇ n(t) is the flow rate of blood pumped out of the left ventricle LV of the heart during systole.
  • Qm ⁇ t) is made of two components: the blood flow moving in the aorta, Qi(O > and the blood flow that is stored in an stretched aorta. is the flow rate of blood in an aorta, which simulates the blood moving in a hypothetical rigid arterial system toward the peripheral arterial system during systole.
  • the proximal compliance, C / during systole can be determined from Qm ⁇ t) - Q ⁇ t) .
  • the proximal compliance Cl can be expressed as:
  • Equation 5a-5c represents the blood flow passing through each path shown in the circuit diagram of the modified Windkessel model (Fig. 3B).
  • Eq. 5(a) describes the proximal blood pressure (i.e., aortic pressure), as
  • proximal blood pressure, Pi(O , is often clinically assumed to be equivalent in magnitude to that measured in the brachial artery.
  • a pulse pressure measured at the brachial artery is used.
  • the blood flowrate at the hypothetical rigid arterial system can be estimated based on the fluid mechanics principle.
  • the mathematical form for the relation between and Q ⁇ t) can be given using the Casson viscosity model by the following equation:
  • Equation (6) the stroke volume of the left ventricle can be obtained by integrating the Qm(t) curve over time for the period of a cardiac cycle.
  • the area under the Qm(t) curve during a cardiac cycle represents the stroke volume. Since the blood volume stored in the compliant proximal arterial wall is always constant from one cycle to another cycle, the integration of the Qm(t) curve must be equal to the integration of the Q ⁇ t) as shown below.
  • peripheral vascular resistance R s (t) can be obtained from the momentum equation using the Casson model as follows:
  • k and ⁇ y are the Casson model constants (see Eq. (I)), R is the radius of vessel, z 2 is another characteristic dimension for the whole arterial system, and r c is the radial distance where the shear stress is equal to the value of the yield stress ⁇ y .
  • Equation (5a) Qi(t) and Ci ⁇ t) are obtained in equation (5a), they should also satisfy Equation (5b) with the same values of Q ⁇ (t) and Pi(O .
  • Equation (5a) By differentiating Equation (5a) and rearranging it, one can obtain the following equation:
  • Qm(t) can be obtained from Equation ( 10). Then, preferably, iteration is used whereby more values are guessed for Ci(O until the flowrate estimated by the area under the curve of Qm(t) is equal to the area under the curve of Q ⁇ t) .
  • the flow rate ejected from the heart should be the same as the amount passing through the arterial system during one cardiac cycle. Using this "flow balance" concept in a closed system, one can confirm the validity of the results obtained using the mathematical approach set forth herein.
  • whole blood viscosity is one of the variables that dictates how hard the heart must work. Similar to Eq. 4(g), the important relationship between the circulating whole blood viscosity and the work of the heart can be mathematically expressed as follows:
  • WOH is the work of the heart [J] in a cardiac cycle
  • subscripts 1 and in indicate the location identified by Pi in Figs. 3A and 3B (i.e., at the ascending aorta) and the integrand, Q ⁇ (t)P ⁇ (t), represents an instantaneous power of the heart POH(i).
  • an average power of the heart can be calculated as follows:
  • T is the period of a cardiac cycle [s]
  • POH is the power of the heart [W].
  • Equations (1 1 - 13) show that the work of the heart depends on the aortic blood pressure and cardiac output, which is dictated by the peripheral vascular resistance and whole blood viscosity. Note that whole blood viscosity directly correlates with blood pressure through the peripheral vascular resistance as mentioned earlier. Hence, the work of the heart which is needed to overcome the peripheral vascular resistance can be estimated by using the blood flow rate, aortic blood pressure and viscosity of a patient's blood. When the whole blood viscosity is elevated, one can expect that the work of the heart increases. Similarly, when the blood pressure is elevated, one can expect that the work of the heart increases. A method according to another aspect of the present invention allows for the calculation of the changes in the work of the heart due to the elevated blood viscosity as indicated by Eq. (4f). EXAMPLE 1
  • the power of the heart can be determined using the procedure shown in Fig. 4.
  • the aortic pressure is measured SlO by, for example, taking the patient's systolic and diastolic blood pressures at his/her forearm, the blood viscosity (f
  • cardiac output values obtained at S 14 average cardiac output can be calculated S16 by integrating the instantaneous blood flow rate Q(t) over time during a period of time, for example, a cardiac cycle (e.g., Eq. 6a can be used to obtain an average over one minute), instantaneous POH values can be calculated S18 (see Eq. (12)), and average POH can be calculated S20 (see Eq. (13)). Note that by obtaining the area under a curve constructed using the instantaneous values of POH (i.e. by integrating the POH), the work of heart of the patient may be obtained.
  • a cardiac cycle e.g., Eq. 6a can be used to obtain an average over one minute
  • instantaneous POH values can be calculated S18 (see Eq. (12)
  • average POH can be calculated S20 (see Eq. (13)). Note that by obtaining the area under a curve constructed using the instantaneous values of POH (i.e. by integrating the POH), the work of heart
  • (t) is not used. Rather, initially the pulsatile pressure profile is estimated S22. Using the estimate from S22, the instantaneous blood flow rate Q(t) is calculated S24 using Eq. 6 and the blood viscosity information for the patient S26, i.e. fl and f2 from Eq. 2 . Then, the average blood flow rate over a cardiac cycle Q nvg is calculated S28 by integrating the instantaneous blood flow rate Q(t) over time during the cardiac cycle. The cardiac output CO estimated from the body weight, Eq. (4), is compared with that obtained using Eq. 6 S30.
  • a multiplying factor mf is obtained S32.
  • an mf 1.1 is selected for each iterative step in order to increase the pressure profile by 10% in each iteration when the calculated CO is less than the estimated CO.
  • the mf is multiplied by the initial estimated pulsatile pressure 34 to obtain a new estimated pulsatile pressure, and the procedure in steps S24, S28, S30 is continued until the cardiac output estimated from the body weight S36 is almost equal (i.e., difference is less than 5%) to the average cardiac output obtained using the Navier-Stokes Eq.
  • the Casson model constants fl and f2 are determined from the whole blood viscosity curve using, for example, a viscometer such as a scanning capillary tube viscometer, and used along with the following values to calculate Work of the heart [J], Power of the heart [W], Cardiac output [1/min], Proximal compliance Ci [ml/mmHg], Distal compliance C 2 [ml/mmHg], Peripheral vascular resistance R s [mmHg/ml].
  • Ci can be obtained using Eq. (5d);
  • C 2 can be obtained using Eq. (8), and R s can be obtained using Eq. (7).
  • a general purpose computer such as a personal computer, can be programmed to automatically calculate the work of the heart upon receiving the required input values such as shear rate, yield stress, estimated initial pulsatile pressure or measured pulsatile pressure profile.
  • FIG. 6 shows results of tabulation of two Casson model constants fl, f2 obtained from nine whole blood samples of human subjects.
  • represents a value for high shear viscosity of blood, which varies widely from 2.76 to 5.63.
  • f> is a value representing the yield stress of blood, which also varies widely from 2.55 to 18.32.
  • the average power of the heart POH was determined using the aforementioned modified Windkessel model illustrated by Figs. 3A and 3B and a method according the second embodiment. The time-average POH was found to vary from 0.892 to 1.794 [W].
  • the nine human subjects were grouped into four subgroups: women, men, polycythemia patients, and regular blood donors.
  • the average POH for each subgroup was calculated as shown in Fig. 7.
  • the subgroup representing polycythemia shows the highest value of POH, whereas the group representing blood donors shows the lowest value.
  • the POH for men was 1.2 [W], which is slightly greater than the value for women 1.1 [W].
  • the two Casson model constants fi and f 2 vary much more widely in reality than the data shown in Figure 6. Often, the value of f
  • Figure 8 tabulates 10 pairs of data for fi and f 2 and corresponding POH values.
  • Figs. 9A-9C show three graphs: POH vs. f, (Fig. 9A), POH vs. f 2 (Fig. 9B), and POH vs. f
  • represents a high shear blood viscosity.
  • 2 +f 2 ° 75 there is a strong one-to-one correlation between POH and f
  • POH was almost independent of f 2 .

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Abstract

La présente invention concerne un procédé pour l'estimation/la détermination du travail du cœur d'un patient qui comprend le calcul du débit cardiaque sortant basé sur le profil de pression pulsatile estimé ou mesuré et les caractéristiques du flux sanguin d'un patient.
PCT/US2008/003207 2007-03-06 2008-03-06 Procédé non invasif de détermination du travail du cœur, des compliances du système vasculaire, et de la résistance vasculaire périphérique WO2008109185A2 (fr)

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Cited By (4)

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Publication number Priority date Publication date Assignee Title
US9936885B1 (en) 2014-03-31 2018-04-10 Sensogram Technologies, Inc. Apparatus for ambient noise cancellation in PPG sensors
US10117586B1 (en) 2014-03-31 2018-11-06 Sensogram Technologies, Inc. Continuous non-invasive wearable blood pressure monitoring system
US10117598B1 (en) 2015-11-08 2018-11-06 Sensogram Technologies, Inc. Non-invasive wearable respiration rate monitoring system
US10327649B1 (en) 2014-03-31 2019-06-25 Sensogram Technologies, Inc. Non-invasive wearable blood pressure monitoring system

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US5054493A (en) * 1986-01-31 1991-10-08 Regents Of The University Of Minnesota Method for diagnosing, monitoring and treating hypertension
US5261412A (en) * 1992-11-20 1993-11-16 Ivac Corporation Method of continuously monitoring blood pressure
US6796168B1 (en) * 2000-08-28 2004-09-28 Rheologics, Inc. Method for determining a characteristic viscosity-shear rate relationship for a fluid
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US20050124864A1 (en) * 2003-10-27 2005-06-09 Mack David C. System and process for non-invasive collection and analysis of physiological signals
US20070135124A1 (en) * 2005-12-13 2007-06-14 Davolos Christopher J Method and system of multiple wireless HPLMN

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US5054493A (en) * 1986-01-31 1991-10-08 Regents Of The University Of Minnesota Method for diagnosing, monitoring and treating hypertension
US5261412A (en) * 1992-11-20 1993-11-16 Ivac Corporation Method of continuously monitoring blood pressure
US6796168B1 (en) * 2000-08-28 2004-09-28 Rheologics, Inc. Method for determining a characteristic viscosity-shear rate relationship for a fluid
US20040254483A1 (en) * 2003-01-24 2004-12-16 Proteus Biomedical, Inc. Methods and systems for measuring cardiac parameters
US20050124864A1 (en) * 2003-10-27 2005-06-09 Mack David C. System and process for non-invasive collection and analysis of physiological signals
US20070135124A1 (en) * 2005-12-13 2007-06-14 Davolos Christopher J Method and system of multiple wireless HPLMN

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9936885B1 (en) 2014-03-31 2018-04-10 Sensogram Technologies, Inc. Apparatus for ambient noise cancellation in PPG sensors
US10117586B1 (en) 2014-03-31 2018-11-06 Sensogram Technologies, Inc. Continuous non-invasive wearable blood pressure monitoring system
US10327649B1 (en) 2014-03-31 2019-06-25 Sensogram Technologies, Inc. Non-invasive wearable blood pressure monitoring system
US10117598B1 (en) 2015-11-08 2018-11-06 Sensogram Technologies, Inc. Non-invasive wearable respiration rate monitoring system

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