[Evaluation of halothane induced HPV inhibition with analysis of pressure-flow curve]

We investigated the effect of halothane on the hypoxic pulmonary vasoconstriction using in vivo measurement of the pressure-flow curve of the left lower lobe in the dog. With hypoxic ventilation of the left lower lobe, the pressure-flow curve shifted to the right and the slope of the curve became flatter. Although inhalation of 1 MAC halothane by the left lower lobe during hypoxic ventilation had no effect on the pressure-flow curve configuration, inhalation of 3, 5 MAC made the slope steeper. We analyzed these changes by the distensibility model proposed by W. Mitzner et al, and our data support the hypothesis that hypoxic ventilation decreases the small pulmonary vessels of 1-4 orders and also increases the compliance of the orders of vessel where the constriction has occurred, and halothane antagonizes the HPV response by further increasing the compliance of the constricted vessels. The inhibitory effect of halothane on HPV was weaker in in vivo preparation compared with the effect in in vitro preparation. Some humoral factors in the perfusate could contribute to this effect.