Oxygen saturation during breath-holding and during apneas in sleep

The rate of fall in oxygen saturation is said to be greater during obstructive apneas than during breath-holding in wakefulness. Using an ear oximeter, a face mask and flowmeter, and measurements of thoracoabdominal motion, we determined in six healthy subjects the rate of fall in arterial oxygen saturation (SaO2) during breath-holding which simulated obstructive and nonobstructive apneas. Breath-holding maneuvers were performed during progressive isocapnic hypoxia and were initiated at the same end-expiratory thoracoabdominal configuration. We found that at any given initial SaO2 the rate of fall in SaO2 was similar during simulated obstructive (y = 5.5-0.06 x; r = 0.83) and nonobstructive (y = 6.8-0.07 x; r = 0.92) apneas. In two healthy subjects and 13 patients with obstructive and nonobstructive apneas during sleep, the rate of fall in SaO2 at any initial SaO2 was similar to that found in healthy subjects during breath-holding in wakefulness. We conclude that during wakefulness the presence or absence of respiratory efforts does not affect the rate of fall in SaO2 during breath-holding and that the rate of fall of SaO2 during sleep apnea is largely dependent on the initial SaO2 at the onset of apnea.