Effects of hypoxia and hypercapnia on patterns of sleep- associated
apnea in elephant seal pups.
Milsom, William, Michael Castellini, Michael Harris, Judith
Castellini, David Jones, Ralph Berger, Supriti Bahrma, Lorrie Rea,
Daniel Costa.
Department of Zoology, University of British Columbia, Vancouver,
B.C., Canada, V6T 1Z4, Institute of Marine Science, University of
Alaska, Fairbanks, AK 99775, Department of Biology, University of
California, Santa Cruz, CA 95064, Institute of Marine Sciences,
University of California, Santa Cruz, CA 95060
APStracts 3:0136R, 1996.
This project examined the effects of alterations in respiratory drive
on the occurrence of sleep apnea in northern elephant seal pups
(Mirounga angustirostris). Sleep pattern was unaffected by levels of
hypoxia ( nearly equal to 13%) or hypercapnia ( nearly equal to 6%)
that doubled respiratory frequency during slow wave sleep (SWS).
During sleep in air, short periods of continuous breathing (mean
length nearly equal to 2.6 min) alternated with periods of apnea
(mean length nearly equal to 6.1 min). Under hypoxic or hypercapnic
conditions the frequency of occurrence of apneas was reduced
primarily due to the occurrence of some sleep episodes without
periods of apnea. In episodes where apneas did occur, they began
later in the sleep episodes but their length and the length of the
periods of eupnea were not significantly altered. During each period
of eupnea, however, the instantaneous respiratory rate and the total
number of breaths increased. Breathing during sleep was restricted to
SWS, never occurring during rapid eye movement (REM) sleep,
regardless of the respired gas mixture. By raising the levels of
hypoxia and hypercapnia further, all episodes of apnea during sleep
could be eliminated together with all episodes of REM sleep. One
interpretation of the data is that the threshold for altering
breathing during eupnea (instantaneous breathing frequency and the
number of breaths per episode of eupnea) is lower than that for
altering the lengths of the periods of apnea and eupnea and that the
muscle atonia associated with REM sleep extends to all respiratory
muscles.
Received 31 August 1995; accepted in final form 20 March 1996.
APS Manuscript Number R546-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96