System and method for determining stability of cardiac output

Abstract

A PPG system for determining cardiac stability of a patient includes a PPG sensor configured to be secured to an anatomical portion of the patient, wherein the PPG sensor is configured to sense a physiological characteristic of the patient. The PPG system includes a monitor operatively connected to the PPG sensor. The monitor receives a PPG signal from the PPG sensor. The monitor includes a cardiac stability analysis module configured to determine an amplitude variance of the PPG signal over a predetermined time period and configured to determine a pulse period variance of the PPG signal over the time period. The cardiac stability analysis module is configured to determine cardiac stability as a function of the amplitude variance and the pulse period variance.

What is claimed is: 
     
         1 . A PPG system configured to determine cardiac stability of a patient, the PPG system comprising:
 a PPG sensor configured to be secured to an anatomical portion of the patient, wherein the PPG sensor is configured to sense a physiological characteristic of the patient; and   a monitor operatively connected to the PPG sensor, the monitor receiving a PPG signal from the PPG sensor, the monitor comprising a cardiac stability analysis module configured to determine an amplitude variance of the PPG signal over a predetermined time period and configured to determine a pulse period variance of the PPG signal over the time period, the cardiac stability analysis module configured to determine cardiac stability as a function of the amplitude variance and the pulse period variance.   
     
     
         2 . The PPG system of  claim 1 , wherein the cardiac stability is calculated as a function of the amplitude variance and as a function of an inverse of the pulse period variance. 
     
     
         3 . The PPG system of  claim 1 , wherein the cardiac stability analysis module determines a cardiac stability ratio as the amplitude variance over the pulse period variance, the cardiac stability analysis module calculating the cardiac stability as a product of the cardiac stability ratio and a scaling factor. 
     
     
         4 . The PPG system of  claim 1 , wherein the cardiac stability analysis module determines a cardiac stability ratio as a function of the amplitude variance and the pulse period variance, a numerator of the cardiac stability ratio is configured to decrease as the cardiac stability of the patient decreases, a denominator of the cardiac stability ratio is configured to increase as the cardiac stability of the patient decreases, wherein the cardiac stability ratio is configured to decrease as the cardiac stability of the patient decreases. 
     
     
         5 . The PPG system of  claim 1 , wherein the cardiac stability analysis module determines the amplitude variance as an average of the squared differences of each of the amplitudes from the mean amplitude over the time period. 
     
     
         6 . The PPG system of  claim 1 , wherein the cardiac stability analysis module determines the pulse period variance as an average of the squared differences of each of the pulse periods from the mean pulse period over the time period. 
     
     
         7 . The PPG system of  claim 1 , wherein the PPG signal forms a PPG waveform, the cardiac stability analysis module analyzing a contour of the PPG waveform along the primary peak to identify a minimum amplitude and a maximum amplitude for each pulse, the cardiac stability analysis module calculating the amplitude variance based on the absolute amplitude of each pulse. 
     
     
         8 . The PPG system of  claim 1 , wherein the monitor includes an alarm, the monitor storing a threshold cardiac stability, the monitor activating the alarm when the determined cardiac stability crosses the threshold cardiac stability. 
     
     
         9 . The PPG system of  claim 1 , wherein the monitor displays an output of the cardiac stability on a display. 
     
     
         10 . A method of determining cardiac stability of a patient from a PPG system, the method comprising:
 securing a PPG sensor to an anatomical portion of the patient;   sensing a physiological characteristic of the patient with the PPG sensor;   receiving a PPG signal from the sensor at a monitor having a cardiac stability analysis module;   analyzing an amplitude component of the PPG signal at the cardiac stability analysis module to determine an amplitude variance of the PPG signal over a predetermined time period;   analyzing a temporal component of the PPG signal at the cardiac stability analysis module to determine a pulse period variance of the PPG signal over the time period; and   calculating cardiac stability of the patient at the cardiac stability analysis module based on the amplitude variance and the pulse period variance.   
     
     
         11 . The method of  claim 10 , wherein the analyzing an amplitude component operation comprises calculating an inverse variance of the pulse period variance, the cardiac stability being a function of the inverse variance of the pulse period. 
     
     
         12 . The method of  claim 10 , wherein the calculating operation comprises:
 determining a cardiac stability ratio as the amplitude variance over the pulse period variance; and   calculating the cardiac stability as a product of the cardiac stability ratio and a scaling factor.   
     
     
         13 . The method of  claim 10 , wherein the calculating operation comprises determining a cardiac stability ratio as a function of the amplitude variance and the pulse period variance with a numerator of the cardiac stability ratio decreasing as the cardiac stability of the patient decreases and with a denominator of the cardiac stability ratio increasing as the cardiac stability of the patient decreases, wherein the cardiac stability ratio is configured to decrease as the cardiac stability of the patient decreases. 
     
     
         14 . The method of  claim 10 , wherein the analyzing an amplitude component operation comprises determining the amplitude variance as an average of the squared differences of each of the amplitudes from the mean amplitude over the time period. 
     
     
         15 . The method of  claim 10 , wherein the analyzing a temporal component operation comprises determining the pulse period variance as an average of the squared differences of each of the pulse periods from the mean pulse period over the time period. 
     
     
         16 . A tangible and non-transitory computer readable medium that includes one or more sets of instructions configured to direct a computer to:
 receive a PPG signal from a sensor secured to an anatomical portion of a patient over a predetermined time period;   determine an amplitude variance of the PPG signal over the time period;   determine a pulse period variance of the PPG signal over the time period; and   calculate cardiac stability of the patient based on the amplitude variance and the pulse period variance.   
     
     
         17 . The tangible and non-transitory computer readable medium of  claim 16 , further configured to calculate an inverse variance of the pulse period variance, the cardiac stability being a function of the inverse variance of the pulse period. 
     
     
         18 . The tangible and non-transitory computer readable medium of  claim 16 , further configured to:
 determine a cardiac stability ratio as the amplitude variance over the pulse period variance; and   calculate the cardiac stability as a product of the cardiac stability ratio and a scaling factor.   
     
     
         19 . The tangible and non-transitory computer readable medium of  claim 16 , further configured to determine a cardiac stability ratio as a function of the amplitude variance and the pulse period variance with a numerator of the cardiac stability ratio decreasing as the cardiac stability of the patient decreases and with a denominator of the cardiac stability ratio increasing as the cardiac stability of the patient decreases, wherein the cardiac stability ratio is configured to decrease as the cardiac stability of the patient decreases. 
     
     
         20 . The tangible and non-transitory computer readable medium of  claim 16 , further configured to:
 determine the amplitude variance as an average of the squared differences of each of the amplitudes from the mean amplitude over the time period; and   determine the pulse period variance as an average of the squared differences of each of the pulse periods from the mean pulse period over the time period.