Heart rate variability modified by altitude exposure

To study the influence of altitude exposure on heart rate variability (HRV) and the possible detection of apnea by ECG 11 male climbers performed 24-hour ECG and respiratory signal monitoring during an expedition to the Everest. Recordings were done as soon as they reached the altitude (=>5000 m, P1), after at least 15 days of acclimatization (P2) and at sea level (before and after the expedition, B1, B2). HRV indices were computed on the RR time series, and their mean hourly values were fitted by a harmonic regression model to quantify the circadian periodic structure. Significant changes of HPV indices were detected after altitude exposure: altitude distress induces tachycardia, reduces HRV indices and blunts circadian heart rate variability. Respiratory pattern greatly interferes with RR interval time series