Published ahead of print on February 25, 2005, doi:10.1164/rccm.200405-595OC Am. J. Respir. Crit. Care Med., Volume 171, Number 11, June 2005, 1305-1311 A more recent version of this article appeared on June 1, 2005
Submitted on May 20, 2004 Habituation of Arousal Responses After Intermittent Hypercapnic Hypoxia in PigletsKaren A Waters1* and Kellie D Tinworth21 Department of Medicine, The University of Sydney, Sydney, NSW, Australia; Department of Paediatrics and Child Health, The University of Sydney, Sydney, NSW, Australia, 2 Department of Medicine, The University of Sydney, Sydney, NSW, Australia * To whom correspondence should be addressed. E-mail: kaw{at}med.usyd.edu.au.
Rationale: Clinical studies have demonstrated arousal deficits in infants suffering obstructive sleep apnea and some infant deaths have been attributed to such an arousal deficit. Objectives: To evaluate whether arousal deficits can be induced by intermittent asphyxia during normal development. Methods and measurements: Young piglets were exposed to intermittent hypercapnic hypoxia for 4 days from age 9.55 ± 0.5 days. Arousal responses were compared between controls and animals exposed to intermittent hypercapnic hypoxia. Outcome measures included time to arouse after onset of the respiratory stimulus and frequency of arousals during recovery. Main Results: Arousal deficits emerged after successive exposures to hypercapnic hypoxia on Day 1, and were exacerbated on Day 4, although following overnight recovery the deficit only became evident during the second & subsequent episode of hypercapnic hypoxia. On Day 1, time to arouse increased from 16.9 ± 7.1 s in the first epoch to 41.7 ± 28.6 s in the fourth epoch (p=0.004 between cycles; oneway ANOVA). In the recovery periods after hypercapnic hypoxia, there were 64% fewer arousals than baseline on Day 1 and 90% fewer arousals on Day 4. Respiratory effort, measured by Vt across 10 breaths before the arousal increased from 25.7 ± 7.6 on Day 1 to 29.1 ± 6.8 ml/kg on Day 4 (p<0.001 two-way ANOVA, Day 4 vs Day 1, respectively). Conclusions: These studies demonstrate that acute and chronic arousal deficits can be induced by intermittent asphyxia, on a background of otherwise normal postnatal development. Key words: OSA, SIDS, postnatal, intermittent hypoxia
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