Heart rate variability measures: a fresh look at reliability.
Level 3 - non-randomized controlled study
Prospective test-retest reliability study in a single cohort without clinical outcome endpoints
PubMed 17381425 · doi:10.1042/CS20070055
What was done
Researchers evaluated the absolute and relative test-retest reliability of standard short-term heart rate variability (HRV) metrics in 39 healthy adults (aged 26–56 years; 18 men, 21 women). Five-minute supine electrocardiograms were recorded during spontaneous breathing and paced breathing (15 breaths/min), and repeated the following day under identical conditions. Standard HRV metrics calculated were SDNN, RMSSD, LF and HF power (absolute and normalized), and the LF/HF ratio. Reliability was quantified using 95% limits of random variation and intraclass correlation coefficients (ICC), alongside sample size estimations to detect a mean difference of at least 30% of the between-subject standard deviation.
What was found
There were no significant group-level mean differences between the two recording days. However, individual-level absolute day-to-day variation was wide: the second measurement ranged from 0.5 to 1.9 times the first measurement for SDNN (best case) and from 0.3 to 3.5 times for LF/HF (worst case). Relative reliability remained high, with most parameters demonstrating an ICC > 0.8 (overall range: 0.65–0.88). Required sample sizes to detect moderate differences ranged from 24 to 98 participants. Paced breathing systematically improved reliability metrics.
Why it matters
While short-term HRV reliably ranks individuals relative to one another (high ICC), large day-to-day random swings in single individuals mean that individual monitoring requires substantial caution. Controlling respiratory rate with paced breathing reduces this noise and improves measurement precision.
Limits
The sample was relatively small (n = 39) and restricted to healthy adults across a limited age range, limiting generalizability to clinical populations with cardiovascular or autonomic disease. The retest interval was limited to 24 hours, so longer-term reliability was not assessed.
Cited by
- supports Even under strictly controlled laboratory conditions controlling time of day, diet, and breathing depth and rate, day-to-day heart rate variability shows a plus or minus 25% variation.