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

Abstract

SUMMARYHigh-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 cardiorespiratory monitoring in the following conditions: (1) sea level; (2) first/ second night at an altitude of 3400 m; (3) first/second night at an altitude of 5400 m and after a 10 day sojourn at 5400 m. At sea level, a normal breathing pattern was observed in all subjects throughout the night. At 3400 m the apnea-hypopnea index was 40.3 AE 33.0 in males (central apneas 77.6%, central hypopneas 22.4%) and 2.4 AE 2.8 in females (central apneas 58.2%, central hypopneas 41.8%; P < 0.01). During the first recording at 5400 m, the apnea-hypopnea index was 87.5 AE 35.7 in males (central apneas 60.0%, central hypopneas 40.0%) and 41.1 AE 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 10 days. With increasing altitude, there was also a progressive reduction in respiratory cycle length during central apneas in males (26.9 AE 3.4 s at 3400 m and 22.6 AE 3.7 s at 5400 m). 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 AE 5.8 s at 5400 m). 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 10 days at 5400 m gender differences in the apnea-hypopnea index similar to those observed after acute exposure were still observed, accompanied by differences in respiratory cycle length. IN TROD UCTI ONPeriodic breathing (PB) is an abnormal ventilatory pattern in which apneas and hypopneas alternate with periods of hyperventilation. Central apneas occur when arterial pCO 2 (paCO 2 ) falls below the threshold required to stimulate breathing, while hyperpnea occurs with reduced arterial pO 2 (paO 2 ), pulmonary congestion or increased chemosensitivity. paO 2 changes represent the most important modulator of peripheral chemoreceptor activity, while 322 ª

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