SHORT-TERM AND LONG-TERM REPRODUCIBILITY OF TIME AND FREQUENCY-DOMAINHEART-RATE-VARIABILITY MEASUREMENTS IN NORMAL SUBJECTS

Objective: To obtain data relating to the reproducibility of the time and frequency domain measurements obtained from 10-min ECG recordings. Methods: Eighteen normal volunteers underwent evaluations of time and frequency domain heart rate variability 2 weeks and 7 months after ba seline analysis. The time domain parameters were mean NN, the standard deviation of NN intervals, the percentage of successive NN intervals > 50 ms and the root mean square successive difference of NN intervals . The frequency domain evaluations (total power, low frequency, and hi gh frequency) were made by means of both the Fast Fourier Transform al gorithm (FFT) and the autoregressive method (AR) from 10-min ECG recor dings made under three different conditions: rest, controlled respirat ion, and after a passive head-up tilt-lest. Reproducibility was evalua ted by means of the interclass correlation coefficient (ICC), comparin g baseline values with the results obtained at the second week and the seventh month, Time domain evaluation were also made from 10-min EGG. Results: All of the time domain measurements had an ICC greater than or equal to 0.75, except for the standard deviation of NN intervals, w hich had an ICC of 0.57. The frequency domain parameters obtained by m eans of either FFT or AR showed similar reproducibility, Low frequency was reproducible under all three conditions, total power only at rest , and high frequency only during controlled respiration. conclusion: T he reproducibility of frequency domain parameters depends on the analy sed condition. These results are of primary importance when the effect s of drugs or other interventions on heart rate variability are under investigation.