Irregular nocturnal breathing patterns at high altitude in subjects susceptible to high-altitude pulmonary edema (HAPE): A preliminary study

We studied nocturnal breathing patterns and symptoms of acute mountain sickness (AMS) during trekking in the Japanese Alps (altitude: 2,760-2,920 m) for 4 d in five subjects susceptible to high-altitude pulmonary edema (HAPE-S-S) and five control volunteers. Breathing patterns were evaluated with the impedance plethysmograph, and symptoms of AMS were evaluated by the environmental symptoms questionaire-III score for AMS of cerebral type (AMS-C score). In both groups, the percentage of time with periodic breathing significantly increased at high altitude and the percentage in controls was significantly higher than in HAPE-S-S on the second night. In four HAPE-S-S, other disordered breathing patterns, termed 'irregular breathing' were observed frequently by night at high altitude. Irregular breathing patterns were characterized by irregularly repeated oscillatory or nonoscillatory clusters of breaths with augmented tidal volume, follewed by expiratory pause, apnea, or hypoventilation of various durations. All controls did not show significant changes in AMS-C score, but four HAPE-S-S showed the increase in AMS-C score on the next morning after frequent irregular nocturnal breathing. There was significant correlation between the percentage of time with irregular nocturnal breathing and AMS-C score on the next morning. These results suggest that HAPE-S-S are prone to irregular nocturnal breathing patterns at high altitude, which is associated with the development of AMS, but it was not possible to determine whether these abnormal breathing patterns are a cause or an effect of AMS.