Multiple measurement of intranural myocardial oxygen tension

A method was developed for measuring the intramural oxygen tension in the ventricular wall (MpO2). The 10 electrodes of intramural needles are employed simultaneously for measurement of MpO2, and, by means of the same amplifiers and registration system, of the electrogram. In this way information could be obtained about the local MpO2 and the local electrical activity obtained from over 100 points in the ventricular wall. In the normal in situ dog heart we found an MpO2 of 5-90 mm Hg (mean 32 mm Hg). When the arterial pO2 was raised, the mean value of MpO2 was decreased. Directly after the start of a period of severe hypoxia a marked fall in MpO2 could be observed, which was reversible after return to the normoxic situation, provided that the hypoxic period was short. Changes in heart rate had only transient effects on the MpO2. Heart massage of the fibrillating heart in the open-chested dog was effective in restoring the arterial pO2, but gave no significant rise in MpO2 which did not exceed 5 mm Hg.