EFFECTS OF HYPOXIA AND HYPERCAPNIA ON PATTERNS OF SLEEP-ASSOCIATED APNEA IN ELEPHANT SEAL PUPS

This project examined the effects of alterations in respiratory drive on the occurrence of sleep apnea in Northern elephant seal pups (Mirou nga angustirostris). Sleep pattern was unaffected by levels of hypoxia (similar to 13%) or hypercapnia (similar to 6%) that doubled respirat ory frequency during slow-wave sleep (SWS). During sleep in air, short periods of continuous breathing (mean length = similar to 2.6 min) al ternated with periods of apnea (mean length = similar to 6.1 min). Und er hypoxic or hypercapnic conditions, the frequency of occurrence of a pneas was reduced primarily due to the occurrence of some sleep episod es without periods of apnea. In episodes in which apneas did occur, th ey began later in the sleep episodes, but their length and the length of the periods of eupnea were not significantly altered. During each p eriod of eupnea, however, the instantaneous respiratory rate and the t otal number of breaths increased. Breathing during sleep was restricte d to SWS, never occurring during rapid eye movement (REM) sleep, regar dless of the respired gas mixture. If the levels of hypoxia and hyperc apnia were raised further, all episodes of apnea during sleep could be eliminated together with all episodes of REM sleep. One interpretatio n of the data is that the threshold for altering breathing during eupn ea (instantaneous breathing frequency and number of breaths per episod e of eupnea) is lower than that for altering the lengths of the period s of apnea and eupnea and that the muscle atonia associated with REM. sleep extends to all respiratory muscles.