LEFT-VENTRICULAR SURFACE TISSUE OXYGEN PRESSURES DETERMINED BY OXYGEN SENSITIVE MULTIWIRE ELECTRODES IN PIGS

Study objective - Polarographic oxygen sensitive electrodes can be used to measure tissue oxygen pressures on the surface of the beating heart. The purpose of the study was to clarify the significance of these Po2 determinations. Design - Changes in left ventricular surface oxygen pressures, subendocardial or subepicardial wall functions (ultrasonic dimension technique), and blood flow (radioactive microsphere technique) were correlated during different degrees of acute coronary artery stenoses in pigs. Experimental material - 19 anaesthetised open chest pigs, 28-40 kg body weight, were studied during different degrees of constriction of the left anterior descending artery which did not influence overall left ventricular function or irreversibly damage the myocardium. Measurements and main results - Highly significant (p < 0.001) correlations (each % delta) were obtained for surface tissue oxygen pressures (y) with subepicardial (y = 0.002 e0.10x; r = 0.89) and subendocardial (y = 1.44 e0.04x; r = 0.98) blood flow values, as well as with subendocardial function (y = 82.4 + 0.22x; r = 0.89); a significant correlation was also obtained for subendocardial function (y) with subendocardial blood flow (y = 66.0 + 0.28x; r = 0.69). However, no significant correlation was obtained for polarographic tissue PO2 with subepicardial segment function, indicating that regional function was maintained when tissue PO2 recordings were not much above 0 kPa and when blood flow was reduced by 25 to 30%. Conclusions - Oxygen pressures of the superficial layers of the left ventricle are relatively high at normal values of oxygen consumption but decrease rapidly if blood supply is reduced. Regional wall function is preserved at low oxygen pressures. Polarographic surface PO2 electrodes hence can be used to study influences of experimental interventions on oxygenation of the normally perfused and of the moderately ischaemic myocardium.