Cardiorespiratory effects of large pneumothorax in conscious and anesthetized dogs

¹ Physiology Division, U. S. Army Medical Research and Nutrition Laboratory, Fitzsimons General Hospital, Denver, Colorado

Ventilation, arterial blood gases, diffusing capacity for carbon monoxide, and flow and pressure in the pulmonary circulation were measured in conscious and pentobarbital-anesthetized dogs at intervals up to 5 hr after intrapleural injection of air. Pneumothorax of twice the functional residual capacity increased the frequency of breathing and reduced physiological dead space in both conscious and anesthetized dogs, but conscious dogs were otherwise unaffected. In contrast, the arterial blood oxygen saturation fell, pulmonary artery pressure rose, and carbon monoxide diffusing capacity was reduced in anesthetized dogs despite greatly increased respiratory minute volume and alveolar ventilation. Ventilation was depressed by anesthesia alone in controls and improved gradually during the experiments. Pentobarbital anesthesia appeared to augment cardiorespiratory depression or abolish compensatory reactions evoked by pneumothorax to produce effects in anesthetized dogs which did not occur in their conscious counterparts. The potent effects of pentobarbital anesthesia on ventilation, pulmonary circulation, and carbon monoxide diffusing capacity, emphasize the advantage of conscious subjects in cardiorespiratory studies.

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