First report of intramyocardial pH in man: I. Methodology and initial results

Continuous in vivo measurements of intramyocardial pH (MpH) have not been previously obtained in man. To achieve this goal, we developed in our laboratory a new, steel-jacketed, glass electrode, and circumvented temperature-related problems by recording the output in millivolts along with the adjacent myocardial temperature. A computer program was devised to calculate MpH in accordance with the Nernst equation. The need in this system for a remote, subcutaneous, reference electrode prompted two sets of experiments. The first set of experiments demonstrated in vitro that the adverse effect of varying the temperature of the reference electrode on the calibration of the pH electrode could be avoided if the reference electrode was placed in a potassium chloride (KCl) solution outside the body and connected to the subcutaneous tissues with a salt bridge. The second set of experiments, which were conducted in vivo in dogs, demonstrated that MpH measurements made with the reference electrode in the limb were not affected by ischemic electrocardiographic changes. This system was then used successfully in 10 patients undergoing coronary artery bypass surgery. Reliable, reproducible, and uniform changes were observed. Baseline MpH prior to revascularization was 6.81 +/- 0.07. Myocardial protection with cold K+ cardioplegia resulted in a significant rise in MpH to 7.45 +/- 0.06. Throughout the period of cross-clamping, MpH remained high. After revascularization and discontinuation of cardiopulmonary bypass, MpH stabilized at 6.93 +/- 0.04.(ABSTRACT TRUNCATED AT 250 WORDS)