Short term reproducibility of indices of heart rate variability

Spectral analysis of heart rate variability (HRV) has been tauted as a noninvasive means of assessing cardiac autonomic tone. Little agreement exists on optimal measures (i.e., peak vs. area absolute value vs. ratio, RR intervals vs. differences in successive RR intervals). The authors compared analyses of the first and last 128 beats of a 5 minute EKG acquisition in 81 healthy adults (age 21-65). It is concluded that: 1) most spectral indices of HRV are independent of resting heart rate; 2) the percent change between first and last segments showed no significant differences between any of the indices measured; 3) large short term changes in measures of HRV may limit their use for assessing changes in autonomic tone in individual subjects in response to physiologic stimuli such as tilt or standing.<>