Method, a system and a computer program product for determining a beat-to-beat stroke volume and/or a cardiac output

• US 8,465,435 B2
• Filed: 07/20/2007
• Issued: 06/18/2013
• Est. Priority Date: 07/20/2007
• Status: Active Grant

• Current Assignee: Bmeye B.V. (Edwards Lifesciences Corporation)
• Original Assignee: Bmeye B.V. (Edwards Lifesciences Corporation)
• Inventors: Van Goudoever, Jeroen, Schraa, Olaf, Wesseling, Karel H.
• Primary Examiner(s): Natnithithadha, Navin
• Assistant Examiner(s): BERHANU, ETSUB D
• Application Number:
  US12/669,890
• Publication Number:
  US 20100217134A1
• Time in Patent Office: 2,160 Days
• Field of Search: 600/485, 600/526
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/022 by applying pressure to close blood vessels, e.g. against the skin; Ophthalmodynamometers
• CPC Class Codes: A61B 5/02233 Occluders specially adapted therefor tourniquets A61B17/132
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: G16H 50/30 for calculating health indices; for individual health risk assessment

Abstract

The invention relates to a method 10 for determining a beat-to-beat stroke volume 9a and/or a cardiac output 9b based on a measurement 2 of suitable arterial pressure data. At the step 4 a waveform of the arterial pressure pulse is assessed based on data obtained during the measurement of step 2. At step 6 a compliance or impedance in dependence of at least one measurement of arterial pressure data is computed using a non-linear model 7. The non-linear model may comprise an arctangent model. The arctangent model may be differentiated numerically or analytically to obtain the compliance or the impedance of an aortic portion. The thus obtained compliance or impedance may then be substituted into a linear model 8. The linear model 8 may comprise a Windkessel model 8a, or a Waterhammer model 8b or any other suitable linear pulse contour model 8c. As a result, the beat-to-beat stroke volume 9a and/or cardiac output 9b are computed.

Claims

1. A method for determining a beat-to-beat stroke volume or a cardiac output based on at least one measurement of arterial pressure data, the method comprising the steps of:

obtaining at least one measurement of arterial pressure data using a measurement unit;

providing the at least one measurement of arterial pressure data to a processor; and

causing the processor to perform the steps of;

computing a compliance or impedance in dependence of at least one measurement of arterial pressure data using a non-linear model, said non-linear model being given by the following equation;

A(p)=Am(0.5+(1/π

)arctan((p−

p0)/p1),

wherein A(p) is the pressure-dependent cross-sectional area of the aorta in cm²,

Am is the maximal area of the aorta at very high pressure;

p0 is a parameter indicating an inflection point of a pressure curve A(p); and

pl is a parameter describing a half-width of the pressure curve;

using said compliance or impedance in a pulse contour method for determining the beat-to-beat stroke volume or cardiac output based on the measured arterial pressure data;

approximating parameters of the non-linear model based on a further model based on a person-specific characteristic;

using the approximated parameters for the non-linear model; and

computing the aortic compliance for an effective pressure, wherein for the effective pressure a mean pressure during systole is selected that is computed beat-to-beat for a contraction frequency of the heart.

2. A method according to claim 1, wherein for the arterial pressure data an arterial pressure waveform is selected.

3. A method according to claim 2, wherein said non-linear model is conceived to approximate a pressure dependency of a cross-sectional area of a portion of aorta.

4. A method according to claim 1, wherein the non-linear model is used to approximate mechanical properties of the total aorta.

5. A method according to claim 4, wherein the mechanical property is a pressure dependent volume V(p) of the aorta, the pressure dependent volume V(p) of the aorta being approximated by an equation of:

V(p)=A(p)Le,

wherein Le is an effective length of the aorta.

6. A method according to claim 5, wherein the effective length of the aorta is taken to be about 0.5 a height of the person.

7. A method according to claim 1, wherein a compliance per unit length is derived from the non-linear model, and wherein a total effective aortic compliance is calculated by the processor by taking into account the compliance per unit length in combination with an effective length of the aorta dependent on the person-specific characteristics.

8. A method according to claim 1, wherein for the pulse contour method a Waterhammer model is used, given by an equation of:

Z(w, pe)=Z₀+R Zc/(R+Zc)

wherein;

Z is a total impedance of the aortic portion;

Z₀ is a characteristic impedance of the aorta;

Zc is 1/jwC;

w=2π

f, with f the heart rate in Hz;

R is a resistance;

pe is an effective pressure level for the beat; and

C is an aortic compliance.

9. A method according to claim 8, further comprising the step of causing the processor to determine a value of the resistance R iteratively.

10. A method according to claim 9, wherein iterations comprise:

determining a stroke volume for an initial value of the resistance R;

determining a cardiac output from the stroke volume;

determining a further value for the resistance based on a means pressure and a cardiac output;

repeating a new stroke volume computation using the further value of the resistance; and

updating the value for the resistance R based on a new value of the stroke volume.