Detection of Parameters in Cardiac Output Related Waveforms

Abstract

Methods for detecting parameters in cardiac output related waveforms are described. The methods include methods for detecting individual heart beat cycles in a cardiac output related waveform, methods for detecting an error in an assigned starting point for an individual heart beat cycle in a cardiac output related waveform, methods for detecting a dichrotic notch for an individual heart beat cycle in a cardiac output related waveform, and methods for detecting an error in an assigned dichrotic notch for an individual heart beat cycle in a cardiac output related waveform. The identification of these parameters is important for a clinician as these parameters form the basis for the calculation of many other cardiac output related parameters.

What is claimed is: 
     
         1 . A method for detecting a dichrotic notch for an individual heart beat cycle in a cardiac output related waveform comprising:
 providing cardiac output related waveform data for an individual heart beat cycle to a processing system, the individual heart beat cycle having a previously determined starting time point;   using the processing system to calculate a first derivative function for the waveform data;   using the processing system to determine a first time point and a second time point from the first derivative function, the first time point being the first zero crossing after the starting time point for the first derivative function and the second time point being the second zero crossing after the starting time point for the first derivative function;   using the processing system to calculate a second derivative function for the waveform data;   using the processing system to determine a third time point and a fourth time point from the second derivative function, the third time point being the first zero crossing after the second time point for the second derivative function and the fourth time point being the second zero crossing after the second time point for the second derivative function; and   using the processing system to search the portion of the second derivative function between the third time point and the fourth time point for a local maximum, the local maximum occurring at a fifth time point,   wherein the fifth time point corresponds to the time point at which the dichrotic notch is located in the cardiac output related waveform data for the individual heart beat cycle.   
     
     
         2 . The method of  claim 1 , further comprising filtering the second derivative function using a low-pass filter. 
     
     
         3 . A method for detecting an error in an assigned dichrotic notch for an individual heart beat cycle in a cardiac output related waveform comprising:
 providing cardiac output related waveform data for an individual heart beat cycle to a processing system, the individual heart beat cycle having a previously determined dichrotic notch time point, a previously determined starting time point, a previously determined cardiac output maximum point, and a previously determined ending time point;   using the processing system to calculate a first derivative function for the waveform data;   using the processing system to find all the local maximums between the cardiac output maximum point and a search time point in the first derivative function, the search time point being the starting time point plus two-thirds of the time between the starting time point and the ending time point,   wherein if more than one local maximum is found, the dichrotic notch is assigned to the time point at the second local maximum.