High-altitude hypoxia and periodic breathing during sleep: gender-related differences

High-altitude exposure is characterized by the appearance of periodic breathing during sleep. Only limited evidence is available, however, on the presence of gender-related differences in this breathing pattern. In 37 healthy subjects, 23 male and 14 female, we performed nocturnal cardio-respiratory monitoring in the following conditions: (1) sea level; (2) first/second night at an altitude of 3400m; (3) first/second night at an altitude of 5400m and after a 10day sojourn at 5400m. At sea level, a normal breathing pattern was observed in all subjects throughout the night. At 3400m the apneahypopnea index was 40.3 +/- 33.0 in males (central apneas 77.6%, central hypopneas 22.4%) and 2.4 +/- 2.8 in females (central apneas 58.2%, central hypopneas 41.8%; P<0.01). During the first recording at 5400m, the apneahypopnea index was 87.5 +/- 35.7 in males (central apneas 60.0%, central hypopneas 40.0%) and 41.1 +/- 44.0 in females (central apneas 73.2%, central hypopneas 26.8%; P<0.01), again with a higher frequency of central events in males as seen at lower altitude. Similar results were observed after 10days. With increasing altitude, there was also a progressive reduction in respiratory cycle length during central apneas in males (26.9 +/- 3.4s at 3400m and 22.6 +/- 3.7s at 5400m). Females, who displayed a significant number of central apneas only at the highest reached altitude, were characterized by longer cycle length than males at similar altitude (30.1 +/- 5.8s at 5400m). In conclusion, at high altitude, nocturnal periodic breathing affects males more than females. Females started to present a significant number of central sleep apneas only at the highest reached altitude. After 10days at 5400m gender differences in the apneahypopnea index similar to those observed after acute exposure were still observed, accompanied by differences in respiratory cycle length.