Effect of tachycardia on intracellular PO2 and reserves of O2 transport in subendocardium of mouse left ventricle.

Intracellular PO2 (PmbO2) was determined by cryospectrophotometry in individual cardiac myocytes. The rate of progression of the freezing front was sufficient to trap the O2 distribution across the wall of the mouse left ventricle. The transmural PmbO2 distribution was uniform despite moderate tachycardia. Maximal heart rate produced a small but statistically significant transmural O2 gradient but no hypoxic myocytes in subendocardium. Reserves of diffusive as well as convective transport contribute to maintenance of aerobic metabolism during tachycardia.