A comparison of two methods of heart rate variability assessment at high altitude.

Heart rate variability (HRV) is a useful index of autonomic function and has been linked to the development of high altitude (HA) related illness. However, its assessment at HA has been undermined by the relative expense and limited portability of traditional HRV devices which have mandated at least a minute heart rate recording. In this study, the portable ithlete(™) HRV system, which uses a 55 s recording, was compared with a reference method of HRV which utilizes a 5 min electrocardiograph recording (CheckMyHeart(™) ). The root mean squares of successive R-R intervals (RMSSD) for each device was converted to a validated HRV score (lnRMSSD × 20) for comparison. Twelve healthy volunteers were assessed for HRV using the two devices across seven time points at HA over 10 days. There was no significant change in the HRV values with either the ithlete (P = 0·3) or the CheckMyHeart(™) (P = 0·19) device over the seven altitudes. There was also a strong overall correlation between the ithlete(™) and CheckMyHeart(™) device (r = 0·86; 95% confidence interval: 0·79-0·91). The HRV was consistently, though non-significantly higher with ithlete(™) than with the CheckMyHeart(™) device [mean difference (bias) 1·8 l; 95% CI -12·3 to 8·5]. In summary, the ithlete(™) and CheckMyHeart(™) system provide relatively similar results with good overall agreement at HA.