Pressure-based system and method for determining cardiac stroke volume

• US 7,220,230 B2
• Filed: 12/05/2003
• Issued: 05/22/2007
• Est. Priority Date: 12/05/2003
• Status: Active Grant

• Current Assignee: Edwards Lifesciences Corporation
• Original Assignee: Edwards Lifesciences Corporation
• Inventors: Roteliuk, Luchy, McKown, Russell, Meyer, Doug Jr.
• Primary Examiner(s): Getzow; Scott M.
• Application Number:
  US10/728,705
• Publication Number:
  US 20050124903A1
• Time in Patent Office: 1,264 Days
• Field of Search: 600485-507
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• 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

Abstract

Cardiac stroke volume (SV) of a subject is estimated as a function of a value derived from a measured arterial pressure waveform. The value may be the standard deviation, or a function of the difference between maximum and minimum pressure values, or a function of either the maximum value of the first time derivative or the absolute value of the minimum of the first time derivative of the pressure waveform, or both, or a function of the magnitude of one or more spectral components of the pressure waveform at a frequency corresponding to the heart rate. Cardiac output is then estimated as the product of the subject'"'"'s heart rate and SV, scaled by a calibration constant. Arterial pressure may be measured invasively or non-invasively.

Claims

1. A method for determining a parameter proportional to the cardiac stroke volume of a subject comprising:

sensing an input signal that is proportional to arterial blood pressure;

calculating the standard deviation of the input signal over a measurement interval; and

calculating an estimate of the cardiac stroke volume as a function of the standard deviation of the input signal.

2. A method as in claim 1, further comprising:

measuring the heart rate of the subject; and

estimating current cardiac output of the subject by calculating the product of the heart rate and the standard deviation and scaling the product by a calibration constant.

3. A method as in claim 2, further comprising:

measuring a calibration cardiac output value; and

calculating the calibration constant as the quotient between a calibration cardiac output estimate and the product of the heart rate and the standard deviation.

4. A method as in claim 1, further comprising sensing the input signal non-invasively.

5. A method as in claim 1, in which the measurement interval extends over more than one cardiac cycle.

6. A method as in claim 5, in which the measurement interval is a plurality of cardiac cycles.

7. A method as in claim 5, further comprising:

calculating a component standard deviation value of the input signal for each of a plurality of measurement intervals;

computing a composite standard deviation value as an average of the component standard deviation values; and

using the composite standard deviation value in calculating the estimate of the cardiac stroke volume.

8. A method as in claim 5, further comprising:

for each of a plurality of cardiac cycles, calculating a mean pressure value;

and adjusting the measurement interval as a function of change in the mean pressure value.

9. A method as in claim 5, further comprising high-pass filtering the input signal before the step of calculating the standard deviation.

10. A method as in claim 1, in which the input signal is a measurement of the arterial blood pressure.

11. A method as in claim 10, further comprising:

determining a maximum value and a minimum value of the arterial blood pressure; and

calculating the standard deviation as a function of the difference between the maximum and minimum values.

12. A method as in claim 1, in which the step of calculating the estimate of the cardiac stroke volume as a function of the standard deviation of the input signal comprises calculating the product of the standard deviation and a calibration factor.

13. A method for determining cardiac stroke volume of a subject comprising:

sensing arterial blood pressure;

converting the sensed arterial blood pressure to a pressure signal;

calculating the standard deviation of the pressure signal over a measurement interval;

calculating an estimate of the stroke volume as a function of the standard deviation of the pressure signal.

14. A method as in claim 13, further comprising:

measuring the heart rate of the subject; and

estimating current cardiac output of the subject by calculating the product of the heart rate and the standard deviation and scaling the product by a calibration constant.

15. A method as in claim 14, further comprising:

measuring a calibration cardiac output value; and

calculating the calibration constant as the quotient between a calibration cardiac output estimate and the product of the heart rate and the standard deviation.

16. A method for estimating cardiac output of a subject comprising:

sensing arterial blood pressure;

converting the sensed arterial blood pressure to a pressure signal;

calculating the standard deviation of the pressure signal over a measurement interval;

calculating an estimate of stroke volume as a function of the standard deviation of the pressure signal;

measuring the heart rate of the subject; and

estimating current cardiac output of the subject by calculating the product of the heart rate d the standard deviation and scaling the product by a calibration constant.

17. A system for determining a parameter proportional to the cardiac stroke volume of a subject comprising:

a sensor located in or on the body of the subject and generating a sensor signal that is proportional to arterial blood pressure;

conversion circuitry that receives the sensor signal and converts it to an input signal;

a processing system that receives the input signal and that includes processing modules for calculating the standard deviation of the input signal over a measurement interval and for calculating an estimate of the cardiac stroke volume as a function of the standard deviation of the input signal; and

a display for presenting the estimate of the cardiac stroke volume to a user.

18. A system as in claim 17, further comprising a heart rate monitor measuring the he rate of the subject;

the processing system estimating current cardiac output of the subject by calculating the product of the heart rate and the standard deviation and scaling the product by a calibration constant.

19. A system as in claim 17, further comprising a high pass filter connected between the sensor and the processing system.

20. A system as in claim 17, in which the sensor is a direct blood pressure sensor.

21. A system for determining a parameter proportional to the cardiac stroke volume of a subject comprising:

a sensor located in or on the body of the subject and generating a sensor signal that is proportional to arterial blood pressure;

conversion circuitry that receives the sensor signal and converts it to an input signal;

a processing system including computer-executable code for calculating the standard deviation of the input signal over a measurement interval; and

for calculating an estimate of the cardiac stroke volume as a function of the standard deviation of the input signal; and

a display for presenting the estimate of the cardiac stroke volume to a user.

22. A system as in claim 21, further comprising a heart rate monitor measuring the he rate of the subject, the processing system further including computer-executable code for estimating current cardiac output of the subject by calculating the product of the heart rate and the standard deviation and scaling the product by a calibration constant.

23. A system as in claim 22, further comprising a calibration system measuring a calibration cardiac output value, the processing system further including computer-executable code for calculating the calibration constant as the quotient between a calibration cardiac output estimate and the product of the heart rate and the standard deviation.

24. A system as in claim 21, in which the sensor is non-invasive.