Brain hypoxia and control of breathing: neuromechanical control

brain hypoxia on respiratory cycle timing, the lung inflation reflex, and respiratory compensation for an inspiratory flow-resistive load were studied in unanesthetized goats. Two models, inhalation of CO and acute reduction of brain blood flow (BBF) were used to produce comparable levels of brain hypoxia. The lung inflation reflex was assessed as the ratio of inspiratory time of an occluded breath to that of the preceding spontaneous breath (TI~JTI~~~~~). Compensation for flow-re-sistive loading was assessed as the effect of the load upon the airway occlusion pressure response to rebreathing CO2 (APO.,/ APcoz). Major findings were I) severe brain hypoxia (HbCO of 60 % or BBF of 42%) caused tachypnea due to a 50 % or more reduction of expiratory time but only a 20 % or less reduction of inspiratory time; 2) moderate carboxyhemoglobinemia (HbCO of 25-30%) enhanced ~~~~~~~~~~~~~~ ~ from 1.5 t 0.1 at control t