Periodic Breathing, Arterial Oxyhemoglobin Saturation, and Heart Rate during Sleep at High

The aim of this study was to investigate the effects of acclimatization to high altitude on periodic breathing (PB), arterial oxygen saturation (Sao(2)), and heart rate (HR). Nine male elite climbers, age 24-52 years underwent overnight cardiorespiratory monitoring at sea level and at Everest North Base Camp (5180 m), during the first (BC1) and the tenth (BC2) nights. PB was commonplace in all subjects at high altitude. PB cycle duration increased (p<0.0001) from BC1 (21.7+/-1.9 s) to BC2 (26.7+/-2.1 s). Mean Sao(2) from BC1 to BC2, significantly increased during wakefulness (77.4+/-3.4% vs. 82.5+/-2.8%; p<0.001) and during sleep regular breathing (73.3+/-3.8% vs. 77.8+/-2.9%; p=0.022). During PB, mean higher Sao(2) was 75.3+/-3.6% at BC1 and 82.4+/-2.9% at BC2 (p<0.001); mean lower Sao(2) was 68.2+/-4.0% at BC1 and 74.5+/-4.3% at BC2 (p<0.01). During PB, mean higher HR was 72.4+/-8.8 b/min at BC1 and 63.3+/-6.0 b/min at BC2 (p<0.0002); mean lower HR were 53.6+/-7.5% at BC1 and 43.6+/-7.3% at BC2 (p<0.0001). The mean Sao(2) during PB compared with Sao(2) at night without PB was unchanged. Acclimatization to high altitude resulted in an overall increase in Sao(2) along with an increase in the PB cycle duration and a decrease in HR.