Direct Effects of Halothane and Isoflurane in Infant Rabbit Hearts with Right Ventricular Hypertrophy Secondary to Chronic Hypoxemia

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Abstract
In this study we compared the direct myocardial effects of halothane and isoflurane between chronically hypoxemic and normoxemic infant hearts with an isolated, perfused, nonworking rabbit heart model. Anesthetic effects were measured on heart rate, atrioventricular time, coronary flow, O2 consumption and extraction, and left and right ventricular peak systolic and end-diastolic pressures, nd -dP/dtmax; and tau, the time constant of isovolumic relaxation. Control values were similar between chronically hypoxemic and normoxemic groups except for variables affected by right ventricular (RV) hypertrophy in chronically hypoxemic hearts. For these variables values were significantly larger in the chronically hypoxemic group (P < or = 0.05): coronary flow (12.3 +/- 0.4 vs 10.3 +/- 0.3 mL.min-1.g-1), RV peak systolic pressure (68 +/- 3 vs 53 +/- 4 mm Hg), RV + dP/dtmax (1.42 +/- 0.07 vs 1.03 +/- 0.08 mm Hg/ms), and RV -dP/dtmax (-0.99 +/- 0.04 vs -0.78 +/- 0.08 mm Hg/ms). (Values are mean +/- SEM.) With anesthesia, values were similar between chronically hypoxemic and normoxemic groups except for coronary flow, which was significantly greater in chronically hypoxemic hearts for both anesthetics (14.1 +/- 0.9 vs 11.3 +/- 0.7 mL.min-1.g-1 for halothane and 15.4 +/- 1.1 vs 12.2 +/- 0.6 mL.min-1.g-1 for isoflurane). The degree of depression of RV peak systolic pressure and RV + dP/dtmax by both anesthetics, and of RV - dP/dtmax by isoflurane, was significantly larger in chronically hypoxemic hearts because these hearts had greater control values but similar anesthetic values to normoxemic hearts.(ABSTRACT TRUNCATED AT 250 WORDS)