Ventilatory response of the cat to hypoxia in sleep and wakefulness

1 Texas Tech University School of Medicine, Department of Physiology, Lubbock, Texas 79430-6551; 2 Information Transmission Problems Institute, Russian Academy of Science, Moscow 101447, Russia; and 3 University of Wisconsin Medical School, Department of Population Health Sciences, Madison, Wisconsin 53705-2368 Submitted 18 November 2002 ; accepted in final form 23 April 2003 This study characterized ventilation, the airflow waveform, and diaphragmatic activity in response to hypoxia in the intact adult cat during sleep and wakefulness. Exposure to hypoxia for up to 3 h caused sustained hyperventilation during both wakefulness and sleep. Hyperventilation resulted from significant increases in minute ventilation due to increases in both tidal volume and frequency. Diaphragmatic activity changed significantly from augmenting activity with little postinspiratory-inspiratory activity (PIIA) in normoxia to augmenting activity with increased PIIA in hypoxia. The increase in PIIA was least in rapid eye movement sleep. These changes in diaphragmatic activity were associated with changes in airflow waveforms in inspiration and expiration. We conclude that the ventilatory response to hypoxia involves a change in the output of the central pattern generator and that the change is dependent in part on the state of consciousness. airflow waveform; periodic breathing; diaphragmatic activity; postinspiratory-inspiratory activity; rapid eye movement sleep Address for reprint requests and other correspondence: J. M. Orem, Texas Tech Univ. School of Medicine, Dept. of Physiology, Lubbock, TX 79430-6551 (E-mail: john.orem{at}ttuhsc.edu ).