System and method for determining stroke volume of an individual

• US 9,357,937 B2
• Filed: 09/06/2012
• Issued: 06/07/2016
• Est. Priority Date: 09/06/2012
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Watson, James Nicholas, Addison, Paul Stanley
• Primary Examiner(s): Le, Long V
• Assistant Examiner(s): PONTIUS, KEVIN LANE
• Application Number:
  US13/605,626
• Publication Number:
  US 20140066785A1
• Time in Patent Office: 1,370 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61B 5/0265 using electromagnetic means, e.g. electromagnetic flowmeter
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• 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 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography

Abstract

A system for determining stroke volume of an individual. The system includes a skew-determining module that is configured to calculate a first derivative of photoplethysmogram (PPG) signals of the individual. The first derivative forms a derivative waveform. The skew-determining module is configured to determine a skew metric of the first derivative, wherein the skew metric is indicative of a morphology of at least one pulse wave detected from blood flow of the individual in the derivative waveform. The system also includes an analysis module that is configured to determine a stroke volume of the individual. The stroke volume is a function of the skew metric of the first derivative.

Claims

1. A pulse oximetry system for determining stroke volume of an individual, the system comprising:

a pulse oximetry sensor configured to generate a photoplethysmogram (PPG) signal, wherein the pulse oximetry sensor detects light attenuated by the individual; and

a pulse oximeter coupled to the pulse oximetry sensor, the pulse oximeter comprising;

a skew-determining circuitry configured to calculate a first derivative of the PPG signal of the individual, the first derivative forming a derivative waveform, wherein the skew-determining circuitry is configured to determine a skew metric of the first derivative, wherein the skew metric is indicative of a symmetry or asymmetry of at least one pulse wave detected from blood flow of the individual in the derivative waveform;

an analysis circuitry configured to determine a stroke volume of the individual based on a function of the skew metric of the first derivative; and

a display configured to display physiological information based on the determined stroke volume.

2. The system of claim 1, wherein the skew metric is determined for each pulse wave or from a pulse-ensemble average that is based on a plurality of the pulse waves.

3. The system of claim 1, wherein the pulse oximeter further comprises an identification circuitry that identifies individual pulse waves from at least one of the derivative waveform or a PPG waveform that is formed by the at least one PPG signal, wherein the pulse waves are approximately defined from a first upstroke to a second, adjacent upstroke in the corresponding waveform, each of the first and second upstrokes corresponding to an increase in blood volume caused by a heartbeat.

4. The system of claim 1, wherein the skew metric is determined using at least one of Pearson'"'"'s skewness, Fisher-Pearson standardized moment coefficient, quartile-based measurements, distance skewness, Cyhelsky'"'"'s skewness coefficients, or a morphological metric of the derivative waveform.

5. The system of claim 1, wherein the pulse waves are pulse waves detected from a finger of the individual.

6. The system of claim 1, wherein the stroke volume is determined based on at least one of a constant or a coefficient, the at least one of the constant or the coefficient being determined by observed historical data and/or characteristics of the at least one PPG signal.

7. The system of claim 1, wherein the skew metric is a calculated value that is indicative of a distribution of values in a data set that includes the data points that define the pulse wave in the derivative waveform.

8. A method for determining stroke volume of an individual by a pulse oximeter, the method comprising:

acquiring, using the pulse oximeter, at least one photoplethysmogram (PPG) signal of the individual from a pulse oximetry sensor, the at least one PPG signal corresponding to pulse waves detected by the pulse oximetry sensor from blood flow of the individual;

calculating, using the pulse oximeter, a first derivative of the at least one PPG signal, the first derivative forming a derivative waveform;

determining, using the pulse oximeter, a skew metric of the first derivative, wherein the skew metric is indicative of a symmetry or asymmetry of at least one of the pulse waves in the derivative waveform;

determining, using the pulse oximeter, a stroke volume of the individual based on a function of the skew metric of the first derivative; and

displaying, using a display, physiological information based on the determined stroke volume.

9. The method of claim 8, wherein the determining the skew metric of the first derivative includes determining the skew metric for each pulse wave or for a pulse-ensemble average that is based on a plurality of the pulse waves.

10. The method of claim 9, wherein the pulse waves are defined from a first upstroke to a second, adjacent upstroke, each of the first and second upstrokes corresponding to an increase in blood volume caused by a heart beat.

11. The method of claim 8, wherein the pulse waves are pulse waves detected from a finger of the individual.

12. The method of claim 8, wherein the determining the skew metric of the first derivative includes determining at least one of Pearson'"'"'s skewness, Fisher-Pearson standardized moment coefficient, quartile-based measurements, distance skewness, Cyhelsky'"'"'s skewness coefficients, or a morphological metric of the derivative waveform.

13. The method of claim 8, wherein the stroke volume is determined based on at least one of a constant or a coefficient, the at least one of the constant or the coefficient being determined by observed historical data and/or characteristics of the at least one PPG signal.

14. A pulse oximetry system for determining stroke volume of an individual, the system comprising:

a pulse oximetry sensor configured to generate a photoplethysmogram (PPG) signal, wherein the pulse oximetry sensor detects light attenuated by the individual; and

a pulse oximeter coupled to the pulse oximetry sensor, the pulse oximeter comprising;

at least one processor or circuit configured to determine a skew metric of a first derivative of the PPG signal of the individual, and determine a stroke volume of the individual based on a function of the skew metric of the first derivative, wherein the skew metric is indicative of a symmetry or asymmetry of at least one pulse wave detected from blood flow of the individual in first derivative of the PPG signal; and

a display configured to display physiological information based on the determined stroke volume.

15. The system of claim 14, wherein the skew metric is determined using at least one of Pearson'"'"'s skewness, Fisher-Pearson standardized moment coefficient, quartile-based measurements, distance skewness, Cyhelsky'"'"'s skewness coefficients, or a morphological metric of the derivative waveform.

16. The system of claim 14, wherein the stroke volume is determined based on at least one of a constant or a coefficient, the at least one of the constant or the coefficient being determined by observed historical data and/or characteristics of the at least one PPG signal.