System and method for determining stroke volume of an individual
View Patent ↗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.
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.