Oxygen supply dependency in patients with obstructive sleep apnea and its reversal after therapy with nasal continuous positive airway pressure.

Recently, it was shown that under certain conditions, there is a linkage between oxygen delivery (DO2) and oxygen consumption (VO2) so that any increase in DO2 is accompanied by an increase in VO2. We investigated this phenomenon in 10 patients with severe obstructive sleep apnea who had nocturnal oxygen desaturations to less than 85% (Group I), 10 patients with mild sleep apnea and no significant desaturations (Group II), and six obese control subjects (Group III). VO2 was measured by respired gas analysis before and after passive leg raising, which has been shown to increase DO2 by 10 to 12%. This was verified by thermodilution cardiac output measurements in four obese patients. In patients with severe sleep apnea, mean apnea index was 53 +/- 11, and supine VO2 was 141 +/- 40 ml/min/m2, whereas with leg elevation it rose to 163 +/- 41 ml/min/m2 (p less than 0.005). In patients with mild sleep apnea and in obese control subjects (mean apnea indices of 24 +/- 6 and 4 +/- 1, respectively), supine VO2 was 144 +/- 11 and 152 +/- 10 ml/min/m2, respectively; with leg elevation, VO2 was 144 +/- 13 and 151 +/- 6 ml/min/m2, respectively (p greater than 0.6). The study was repeated in nine of the Group I patients after 8 wk of treatment with nasal CPAP (Group IA). The repeated supine VO2 in these patients was 138 +/- 28 ml/min/m2, and a significant difference was not observed after leg raising (140 +/- 29 ml/min/m2; p greater than 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)