Effect of ketamine on control of breathing in cats

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Abstract
Minute ventilation, breathing pattern, end-tidal CO2 partial pressure (PACO2) and tracheal occlusion pressure were studied in cats anesthetized with ketamine (40 and 80 mg/kg) before and after CO2 inhalation. Before CO2 administration ventilation was reduced and PACO2 increased relative to unanesthetized cats at both ketamine doses. Breathing pattern was of the apneustic type, being characterized by prolonged inspiratory duration and relatively short expiratory time, and markedly curvilinear (convex upward) inspiratory volume-time profile. The latter reflected a similar curvilinearity in the tracheal occlusion pressure waveform. During CO2 inhalation, the ventilatory response to CO2 was similar to that in unanesthetized cats despite a depressed tracheal occlusion pressure response. This discrepancy was due to the fact that in the presence of a convex upward inspiratory volume-time prolife, the shortening of inspiratory duration with increasing CO2 results in a marked increase of mean inspiratory flow, and hence the ventilatory response to CO2 remains high.