Continuous measurement of intramyocardial pH: Correlation to functional recovery following normothermic and hypothermic global ischemia

Abstract

The continuaus measurement of imtramyocardial pH was used to follow the progression of ischemia and was correlated to the recovery of left ventricular function following normothermic (38 °C) and hypothermie (25 °C) global ischemia. New miniature myocardial transducers, which incorporate fiberoptic technology and dual pH- and temperature-sensing capability, were placed into the left ventricular free wall and seplum of 52 sheep undergoing cardiopulmonary bypass, Left ventricular stroke work as a functional mean left atrial pressure curves were generated before and after cardiopulmonary bypass by volume loading wilh whole blood. Functional recovery was determined by the ratio of the integrats of the preischemic and postischemic function curves. Control sherp (N = 11) did not undergo ischemia. Three groups (N = 41) or 6.6. The prelschemic myocardial pH averaged 7.42 ± 0.01. Following both normothermic and hypothermic global ischemia, no significant difference was demonstrated in recovery of function between control (pH 7.4) ery of function of the pH 6.8 and pH 6.6 groups was significantly decreased ( p < 0.01) versus cortrol and pH 7.0 groups at both temperatures. No significant difference in recovery of function was demo trated at any pH level when normothermic versus hypothermic groups were cornpared. However, hypothermia provided increased time ( p < 0.001) before each level of function was reached with a slower rate of change of pH ( p < 0.01) compared with the corresponding same pH graup in sheep undergoing normyocardial pH lower than 7.0 at the termination of ischemia resulted in a marked decrease in left ventricular function following both normothermic and hypothermic global recovery at 38 °C and 25 °C, and rate of change of myocardial pH predicted the interval of ischemia required to achieve a give functional level of recovery.