Pentobarbital anesthesia alters pulmonary vascular response to neural antagonists

We investigated the effects of pentobarbital sodium anesthesia on vasoregulation of the pulmonary circulation. Our specific objectives were to 1) assess the net effect of pentobarbital on the base-line pulmonary vascular pressure-to-cardiac index (P/Q̇) relationship compared with that measured in conscious dogs, and 2) determine whether autonomic nervous system (ANS) regulation of the intact P/Q̇ relationship is altered during pentobarbital. P/Q̇ plots were constructed by graded constriction of the thoracic inferior vena cava, which produced stepwise decreases in Q̇. Pentobarbital (30 mg/kg iv) had no net effect on the base-line P/Q̇ relationship. In contrast, changes in the conscious intact P/Q̇ relationship in response to ANS antagonists were markedly altered during pentobarbital. Sympathetic α-adrenergic receptor block with prazosin caused active pulmonary vasodilation (P < 0.01) in conscious dogs but caused vasoconstriction (P < 0.01) during pentobarbital. Sympathetic β-adrenergic receptor block with propranolol caused active pulmonary vasoconstriction (P < 0.01) in both groups, but the magnitude of the vasoconstriction was attenuated (P < 0.05) during pentobarbital at most levels of Q̇. Finally, cholinergic receptor block with atropine resulted in active pulmonary vasodilation (P < 0.01) in conscious dogs, whereas vasoconstriction (P < 0.01) was observed during pentobarbital. Thus, although pentobarbital had no net effect on the base-line P/Q̇ relationship measured in conscious dogs, ANS regulation of the intact pulmonary vascular P/Q̇ relationship was altered during pentobarbital anesthesia.