Effects of breathing control on cardiocirculatory modulation in Caucasian lowlanders and Himalayan Sherpas

This study was performed to investigate the influence of breathing control on the autonomic cardiac regulation at high altitude in adapted and non-ada pted awake subjects. We recorded electrocardiogram and pulse oximetry in 14 short-term acclimatized lowlanders and 14 Himalayan Sherpas during resting conditions at an altitude of 5,050 m. Spectrum analysis was performed on s ynchronized 15 min periods of R-R intervals and the oxygen saturation of ar terial blood (SaO2). Despite mean SaO2 being similar in lowlanders and Hima layan Sherpas [78.5 (SD 7.0)% compared to 79.4 (SD5.8)%, respectively], flu ctuations in SaO2 were significantly increased in lowlanders compared to Sh erpas, thus indicating an unstable regulation of respiration control in low landers. Regression analysis demonstrated a significant relationship betwee n spectrum power of SaO2 and the relative power of R-R intervals in the fre quency band between 0.01 and 0.08 Hz in lowlanders, but not in Sherpas. Our results demonstrate differences in respiratory and autonomic cardiac contr ol between non-adapted lowlanders and Himalayan high-altitude residents and indicate that unstable breathing control during chronic hypobaric hypoxia is significantly correlated with the autonomic cardiocirculatory regulation .