Effects of pH changes on O2 uptake and plasma catecholamine levels in the dog

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Abstract
During hypercapnic acidosis induced by ‘apneic oxygenation,’ one observes in the dog a rise in plasma catecholamine levels in the presence of a constant oxygen uptake (Qo2) and a rise in mean blood pressure. When pH is maintained constant or alkaline by infusion of T.H.A.M. (2 amino 2 hydroxymethyl 1–3 propane diol), Qo2 remains constant while plasma catecholamines and blood pressure do not change although total plasma CO2 shows a twofold increase. When blood pH is rapidly shifted from 6.99 ± .03 to 7.52 ± .02, Qo2 increased by 39%, while plasma catecholamine levels were rapidly re-established to normal. The infusion of 1 µg/kg/min. of epinephrine, norepinephrine or isoproterenol will also produce a significant increase in Qo2 and blood pressure in the apneic dog when arterial blood pH is maintained normal or alkaline; but the same dose of epinephrine fails to change significantly Qo2 or blood pressure when arterial blood pH is maintained between 6.97 and 7.28.