Reproducibility of resting heart rate variability with short sampling periods

The purpose of this study was to determine whether resting heart rate variability (HRV) is reproducible with short sampling measurement periods using an office-based personal computer measurement system. Eight healthy active women participated in ECG analyses on 2 days within 1 week under controlled environmental and physiological conditions. After they rested for 10 minutes, a 10-min ECG was recorded. HRV was determined from a 2.5- and 5-min sample period using both time domain variables (meanRR and SDNN) and frequency domain variables (LF, HF, LF:HF). Repeated measures ANOVA found no significant differences between Day 1 and Day 2 for either sampling period (p > or = 0.23). For both the 2.5- and 5-min sampling periods, the intraclass correlations between days for the time domain variables showed good reproducibility (R = 0.86-0.90). The reproducibility of the frequency domain variable was only average (R = 0.67-0.96), with the LF:HF ratio yielding the higher R values.