Real-time measurement of ventricular stroke volume variations by continuous arterial pulse contour analysis

Abstract

Ventricular stroke volume variation (SVV) is estimated as a function of the standard deviation of arterial blood pressure value measured over each of at least two cardiac cycles, preferably over each of the cardiac cycles in a computation interval covering a full respiratory cycle. In one embodiment, maximum and minimum standard deviation values are determined over the computation interval. SVV is then estimated proportional to the ratio of the difference between the maximum and minimum standard deviation values and the mean of the standard deviation values. In another embodiment, SVV is then estimated proportional to the ratio of the standard deviation of the standard deviation values and the mean standard deviation over the entire computation interval. A pre-processing arrangement for improving reliability of estimates of more general cardiac or hemodynamic parameters is also disclosed and involves smoothing with an approximating function, and sampling and low-pass filtering at an adjustable rate.

1 . A method for determining a cardiac or hemodynamic output value comprising:
 inputting a waveform data set corresponding to measurements of a measurement parameter;   generating a series of measurement values from the waveform data set;   computing an approximating function that best matches the measurement values according to a predetermined metric;   over each of at least one computation interval, creating a set of sampled, approximating values by sampling the approximating function at an interval-specific sampling rate;   low-pass filtering the sampled, approximating values; and   calculating an estimate of the output value as a function of the low-pass filtered, sampled approximating values.   
   
   
       2 . A method as in  claim 1 , in which the output value displays respiration-induced variation, further comprising:
 identifying respiratory cycles;   detecting cardiac cycles;   setting the computation interval to be a respiratory cycle; and   for each computation interval, setting the interval-specific sampling rate as a function of the number of cardiac cycles in each respective respiratory cycle.   
   
   
       3 . A method as in  claim 1 , in which the step of generating the series of measurement values includes pre-processing the waveform data set. 
   
   
       4 . A method as in  claim 1 , in which the waveform data set corresponds to blood pressure, further comprising computing each measurement value to be a function of the standard deviation of blood pressure over each respective computation interval. 
   
   
       5 . A method as in  claim 1 , in which the output value is systolic pressure variation. 
   
   
       6 . A method as in  claim 1 , in which the output value is pulse pressure variation. 
   
   
       7 . A system for determining a cardiac or hemodynamic output value comprising:
 an arrangement for determining and inputting a waveform data set corresponding to measurements of a measurement parameter;   a low-pass filter;   a processing system including computer-executable code for generating a series of measurement values from the waveform data set;
 for computing an approximating function that best matches the measurement values according to a predetermined metric; 
 over each of at least one computation interval, for creating a set of sampled, approximating values by sampling the approximating function at an interval-specific sampling rate; 
 calculating an estimate of the output value as a function of the sampled approximating values after filtering by the low-pass filter. 
   
   
   
       8 . A system as in  claim 7 , in which the output value displays respiration-induced variation, further comprising:
 an arrangement for identifying respiratory cycles;   an arrangement for detecting cardiac cycles;   in which the processing system further includes additional computer-executable code
 for setting the computation interval to be a respiratory cycle; and 
 for each computation interval, setting the interval-specific sampling rate as a function of the number of cardiac cycles in each respective respiratory cycle. 
   
   
   
       9 . A system as in  claim 7 , further including a pre-processing module, included in the processing system, that pre-processes the series of measurement values includes pre-processing the waveform data set. 
   
   
       10 . A system as in  claim 7 , in which
 the arrangement for determining and inputting the waveform data includes a mechanism for determining blood pressure,   the waveform data set corresponds to blood pressure,   in which the processing system further includes additional computer-executable code for computing each measurement value to be a function of the standard deviation of blood pressure over each respective computation interval.   
   
   
       11 . A system as in  claim 7 , in which the output value is systolic pressure variation.