Administration of nocturnal
oxygen for 1 night to patients with
obstructive sleep apnea (OSA) causes a moderate reduction in
apnea frequency without improving
hypersomnolence. Therefore, we administered
oxygen chronically to patients with OSA to determine: whether
apnea frequency would be further reduced, whether the effect of
oxygen upon
apnea frequency is correlated with an increased ventilatory response to
hypoxia and
hypercapnia, and whether
hypersomnolence improves with more prolonged
oxygen administration. In a single-blinded, nonrandomized trial, we compared the effects of 1 month of
oxygen (4 L/min by
nasal cannula) with room air (4 L/min by
nasal cannula) placebo during sleep in 7 men and 1 woman with
obstructive sleep apnea. During non-REM sleep, acute
oxygen administration elevated the average low oxy-
hemoglobin saturation during apneic events and decreased
apnea frequency. These acute effects persisted during chronic
oxygen administration but reverted to the preoxygen effects immediately upon discontinuing
oxygen. One month of
oxygen did not affect the waking ventilatory response to
hypoxia or
hypercapnia; however, waking PaCO2 increased from 40 +/- 1 mm Hg (mean +/- SE) after placebo to 43 +/- 1 mm Hg after
oxygen (p less than 0.01). Neither subjective nor objective
hypersomnolence consistently improved after 1 month of
oxygen administration. We conclude that: first,
oxygen has no effect upon
apnea frequency beyond the period of administration, and the reduction of
apnea frequency is not correlated with an increased sensitivity to chemical ventilatory stimuli. The reduced
apnea frequency may be related to an increased PaCO2 stimulating ventilation during sleep.(ABSTRACT TRUNCATED AT 250 WORDS)