Ventilation, EELV and diaphragmatic activity in rats during chronic normobaric hypoxia

We determined the effects of chronic hypoxia on end-expiratory lung volume (EELV), end-expiratory diaphragmatic activity (DE) and ventilation ((V)over dot E) in 27 intact (awake and anesthetized) and six carotid body-denervat ed (CBD, anesthetized) rats. Twenty-nine control animals were also studied. Recordings were made during hypoxia and normoxia before and after 2 or 3 w eeks of hypoxia ( + 3 days of recovery from chronic hypoxia). In awake rats , 2 weeks of chronic hypoxia increased only normoxic (V)over dot E, while 3 weeks of chronic hypoxia did not change (V)over dot E or DE. In anesthetiz ed intact rats. after both exposures, hypoxic and normoxic (V)over dot E te nded to decrease, DE did not change and hypoxic and normoxic EELV were enla rged. In CBD animals. 2 weeks of chronic hypoxia did not affect hypoxic (V) over dot E but decreased normoxic ventilation and enlarged EELV similar to the intact animals. After 3 days of recovery in normoxia, all parameters ex cept EELV were restored to prehypoxic values. Also. transition from hypoxia to normoxia induced parallel changes in EELV and DE while chronic hypoxia increased only EELV. Therefore, chronic normobaric hypoxia induced, ( 1) an increase in normoxic ventilation reflecting a process of acclimatization: (2) an enlargement of EELV that did not depend on changes in DE and carotid chemoreceptors. (C) 2001 Elsevier Science B.V. All rights reserved.