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EXERCISE AND RESPIRATORY PHYSIOLOGY

Hypocapnia increases the prevalence of hypoxia-induced augmented breaths

Penn State University College of Medicine, Heart and Vascular Institute, Milton S. Hershey Medical Centre, Hershey, Pennsylvania

Submitted 11 August 2008 ; accepted in final form 11 December 2008

Augmented breaths promote respiratory instability and have been implicated in triggering periods of sleep-disordered breathing. Since respiratory instability is well known to be exacerbated by hypocapnia, we asked whether one of the destabilizing effects of hypocapnia might be related to an increased prevalence of augmented breaths. With this question in mind, we first sought to determine whether hypoxia-induced augmented breaths are more prevalent when hypocapnia is also present. To do this, we studied the breath-by-breath ventilatory responses of a group of freely behaving adult rats in a variety of different respiratory background conditions. We found that the prevalence of augmented breaths was dramatically increased during hypocapnic-hypoxia compared with room air conditions. When hypocapnia was prevented during exposure to hypoxia by adding 5% CO₂ to the inspired air, the rate of occurrence of augmented breaths was no greater than that observed in room air. The addition of CO₂ alone to room air had no effect on the prevalence of augmented breaths. We conclude that in spontaneously breathing rats, hypoxia promotes the generation of augmented breaths, but only in poikilocapnic conditions, where hypocapnia develops. Our results, therefore, reveal a means by which CO₂ exerts a stabilizing influence on breathing, which may be of particular relevance during sleep in conditions commonly associated with respiratory instability.

sighs; carbon dioxide; hypocapnia; respiratory instability

This article has been cited by other articles:

				H. J. Bell and P. Haouzi Acetazolamide suppresses the prevalence of augmented breaths during exposure to hypoxia Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2009; 297(2): R370 - R381. [Abstract] [Full Text] [PDF]