Measurement of surface tissue pO2 (
ptO2) with surface
electrodes is increasingly applied in experimental medicine. Its use on the beating heart may seem to be problematic because transmural gradients of tissue pO2 would reduce the validity of pO2 determinations in the epicardial layers. This study attempted to determine whether
ptO2 may be a valid and sensitive
indicator of transmural myocardial oxygenation. In order to measure
ptO2, two eight-channel Clark-type
electrodes were placed on a beating porcine left ventricle (n = 13). Measurements were made at different degrees of acute
stenosis of the left anterior descending artery (LAD). A 24-F
cannula was inserted into the great cardiac vein, draining the poststenotic myocardium to obtain coronary venous blood samples. Transmural metabolic changes were detected simultaneously by coronary venous blood gas parameters and
lactate levels. Epicardial tissue pO2 was 49 +/- 2 mm Hg (mean +/- SEM) before
stenosis and decreased to a mean value of 25 +/- 2 mm Hg during
stenosis. Different degrees of LAD
stenosis (
ptO2 range: 12-35 mm Hg) were substantial enough to alter arterio-coronary venous
lactate difference (avd
lactate) from +0.31 +/- 0.07 mmol/l (control) to -0.62 +/- 0.15 mmol/l (
stenosis). A significant linear correlation between changes of
ptO2 (delta
ptO2) and changes of avd
lactate (delta avd
lactate) resulted (y = 0.59 + 0.62x; r = 0.86; p less than or equal to 0.001). However, linear regression analysis between delta
ptO2 correlated with the corresponding data from coronary venous pO2 (delta pO2cv)
oxygen content (delta O2contcv), and oxygen saturation (delta O2satcv) showed no significant correlations. We conclude that measurement of
ptO2 is a sensitive and valuable
indicator of transmural oxygenation in ischemic myocardium, whereas pO2cv, O2contcv and O2satcv do not seem to be valid predictors of
ischemia in myocardial oxygenation.