Periodic breathing in dogs

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Abstract
Periodic breathing, similar to that observed by Haldane and Douglas in man after voluntary hyperventilation, occurred in anesthetized dogs after mechanical hyperventilation. The periodic breathing was regularly preceded by apnea; the lower the arterial O2 saturation and CO2 tension at end apnea, the more likely was breathing to be periodic once spontaneous breathing resumed. Neither hypoxia, per se, nor cerebral ischemia reproduced the characteristic pattern of posthyperventilation periodic breathing, although occasionally these devices did produce some irregularity in breathing. The lowest values of arterial O2 saturation and the highest values of arterial CO2 tension occurred during the period of augmented ventilation. Periodicity disappeared as the arterial CO2 tension and O2 saturation returned to the levels existing prior to mechanical hyperventilation. The experimental results obtained are used to assess the accuracy of a mathematical model of the respiratory control system described in the accompanying paper.