The oxygen pressure histogram in the left ventricular myocardium of the dog.

Myocardial PO2 in its relation to arterial and coronary venous PO2 was measured in anesthetized open-chest dogs by means of polarographic methods. At normal arterial O2 supply, there exists a broad PO2 spectrum in the myocardium, ranging from about 0 Torr to arterial values (mean 19.3 Torr, median 14 Torr). 60% of the values are below the mean coronary venous PO2 of 18.8 Torr, the maximum is in the class of 0 to 5 Torr. Neither the shape of the histogram nor the mean coronary venous PO2 are significantly changed under moderate arterial hypoxemia (mean arterial PO2 63.7 Torr). Also increases in arterial PO2 to more than 300 Torr cause no distinct change in coronary venous PO2, whereas myocardial PO2 shows heterogeneous reactions. Myocardial as well as coronary venous PO2 seem to be well regulated over a wide range of arterial PO2.