Quantitative indices of short- and long-term heart rate variability

Two quantitative indices of heart rate variability are proposed. Instantaneous variability is defined as the average of the absolute value of instantaneous rate differences over a 30 second interval. It is sensitive to short-term variability changes. Bandwidth variability is defined as twice the standard deviation of instantaneous heart rates over a 30 second interval, and it is a measure of long-term variability. The rationale for the choice of these indices is discussed, and they are compared with other published indices of variability. Samples of computer printout of instantaneous and bandwidth variability obtained from fetal heart rate records are given.