Night 1. Eleven patients were studied on the first night (N1). The suboptimal pressure was 7.1 2.7 cmH2O. After reaching stage 2 or stage 3 sleep, the subjects breathed room air for five minutes (control period), followed by three minutes of hypoxic gas (eight percent O2); this sequence was repeated 10 timnes. Hypoxia was rapidly induced by having the subject breathe one or two breaths of 100 percent nitrogen followed by continuous eight percent O2 for three minutes to maintain hypoxia (O2 saturation: 80-84 percent). Care was taken to ensure that arterial CO2 pressure remained constant or unchanged throughout the hypoxia period by measuring end-tidal CO2 (PETCO2), and five percent CO2 was supplemented as needed. Hypoxia was abruptly terminated with one breath of 100 percent O2. The breathing pattern was monitored at 5, 20, and 40 minutes of the recovery period after the 10th exposure to hypoxia.

Night 2. Each patient received a nasal CPAP machine set to the optimal volumetric analysis pressure and was asked to use it for a minimum of six hours a night for at least four weeks. After four weeks of treatment with optimal pressure CPAP, eight patients returned for the second night (N2) study, which followed the same protocol as the first night study.

Sham study. Seven patients had a third study during which the CPAP was reiterated to suboptimal pressure (mean = 5 1.4 cmH2O). The pressure was maintained throughout the study night without any hypoxic periods.

Wakefulness/sleep stage was scored according to standard criteria. The subjects were in stable stage 2 or stage 3 (slow wave percentage = 20-25 percent) sleep during the hypoxic exposures and data collection, and there were no ar
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Contact: Donna Krupa
djkrupa1@aol.com
703-527-7357
American Physiological Society
10-Jan-2002