Lung mechanics and end-expiratory lung volume during hypoxia in rats

We investigated whether an hypoxia-induced increase in airway resistance me diated by vagal efferents participates in the increase in end-expiratory lu ng volume (EELV) observed in hypoxia. We also assessed the contribution of the end-expiratory activity of the diaphragm (DE) to this phenomenon. There fore, we measured EELV total lung resistance (RL), dynamic lung compliance (Cdyn), DE, and minute ventilation (VE) in anesthetized rats during normoxi a and hypoxia (10% O-2) before (control) and after administration of atropi ne or saline. In the control group, hypoxia increased EELV, Cdyn, DE, and V E but slightly decreased RL. These changes were unaffected by saline or atr opine, except that, in the atropine-treated rats, hypoxia did not change RL . These results suggest that I)the increase in EELV observed in hypoxia can not result from an increase in airway resistance; 2)the increased and persi stent activity of inspiratory muscles during expiration is the most likely cause of the increase in EELV during hypoxia; and 3) the decrease in RL ind uced by hypoxia could result from the increase in lung volume including EEL V.