Altitude distress influence on cardiac function

To study the influence of altitude exposure on heart rate variability (HRV) and cardiac ventricular function, 11 male climbers performed 24-hour ECG and echocardiographic evaluation during an expedition to Mount Everest. Recordings were done as soon as they reached the altitude of 5000 m, after at least 15 days of acclimatization and at sea level (both before and after the expedition). HRV indices were computed (in the time and frequency domains) on the RR time series, and major cardiac measures were calculated from the best echocardiographic view. Significant changes in HRV and other cardiac indices were detected after altitude exposure. Altitude distress induced tachycardia and reduced some HRV indices. The respiratory pattern was used to document sleep apnea, which greatly interferes with RR-interval time series. It was concluded that altitude distress modifies the cardiac function, whose interference with the heart-rate reflex could explain the HRV changes.