Heart rate variability measurement

Abstract

A method and apparatus for quantitative measurement of the long-term and short-term variability of a subject's heart rate. Long-term variability is measured by apparatus which receives a signal having a magnitude proportional to a subject's instantaneous heart rate with each successive heart beat during a measuring interval consisting of a fixed number of heartbeats. Each heart rate signal magnitude is compared with the previous maximum and minimum heart rate signal magnitudes in the measuring interval and the sampled heart rate magnitude is substituted for the previous maximum signal magnitude if the maximum is exceeded and for the previous minimum signal magnitude if it exceeds the magnitude of the instant sampled heart rate signal. The difference between the maximum and minimum heart rate signal magnitudes, after occurrence of the predetermined number of heartbeats, is a measure of long-term heart rate variability. To measure short-term variability the apparatus determines the average of the differences in time between successive heart beats for the predetermined number of heartbeats by comparing each latest time difference with the previous time difference and incrementing or decrementing the previous time difference until it equals the latest time difference. The number of increments or decrements are counted and divided by the predetermined number of heartbeats comprising the measuring interval to yield a measure of short-term variability.