A shift from central and mixed sleep apnea to obstructive sleep apnea resulting from low-flow oxygen

Low-flow oxygen decreases the frequency of the 3 types of apnea (central, mixed, and obstructive) in patients with predominantly obstructive sleep apnea. The decrease in frequency appears to be accompanied by a shift in apnea distribution, consisting of a decrease in the proportion of central and mixed apneas and an increase in that of obstructive apneas. To determine whether this shift represents a greater inhibitory effect on central and mixed apneas or an increased tendency toward obstructive apneas, we administered low-flow oxygen during sleep to 9 patients who demonstrated predominantly central and mixed sleep apnea (51 ± 33% and 33 ± 21% of apneic events, respectively, mean ± SD) and had resting, room air, oxygen tensions of 83 ± 11 mmHg. During non-REM sleep, oxygen increased the baseline oxyhemoglobin saturation while reducing the average peak fall in oxyhemoglobin saturation during each apneic event. Oxygen reduced the overall apnea frequency from 66 ± 7.8 (mean ± SE) to 43.0 ± 10.7 episodes per hour (p < 0.02). Central and mixed apneas decreased markedly from 31.4 ± 0.6 to 6.4 ± 4.3 episodes per hour (p < 0.02) and from 20.9 ± 5.0 to 4.9 ± 1.5 episodes per hour (p < 0.02), respectively. However, obstruction apnea frequency more than doubled from 13.9 ± 7.0 to 32.1 ± 9.2 episodes per hour (p < 0.02). We conclude that in these patients oxygen tension altered both the frequency and distribution of sleep-induced apnea, with a lower oxygen tension increasing the frequency of central and mixed apneas and a higher oxygen tension increasing the frequency of obstructive apneas. These findings are compatible with the hypothesis that the 3 types of apnea represent a continuum of destabilized ventilatory control.