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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 Po2recordings 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. [ABSTRACT FROM PUBLISHER]

The validity of myocardial surface tissue Po2 (PtO2) as a reliable indicator of transmural myocardial tissue oxygenation was studied in six anaesthetised, open chest pigs. Epicardial surface Pto2 was correlated with other variables of myocardial tissue oxygenation such as regional blood flow, coronary venous Po2, O2 saturation, PCO2 and regional myocardial lactate extraction. The study design was based on an experimental model in which the effects of a pacing induced tachycardia on tissue oxygenation of ischaemic and normally supplied myocardium were measured.Two platinum multiwire surface electrodes were placed on the epicardium, on the areas supplied by the left anterior descending coronary artery (LAD) and the left circumflex coronary artery (CX). The LAD was constricted to reduce mean surface Pto2 in the LAD area to about 50% of its baseline value. This did not affect surface Pto2 in the CX area. The reduction of surface Pto2 in the LAD area was associated with decreases in coronary venous Po2 and O2 saturation and with increases in coronary venous lactate and PCO2. Subendocardial regional blood flow and the subendocardial to subepicardial flow ratio were significantly lower than in the CX area. Increasing the heart rate by pacing (+45 beats·min−1) led to an increased degree of ischaemia as shown by fall in surface Pto2 in the LAD area to values around zero kPa, by marked increase in coronary venous lactate and PCO2, by reduction in total (−10%) and subendocardial (−40%) LAD flow and by deterioration of the subendocardial to subepicardial flow ratio. The increased degree of ischaemia was not accompanied by an increase in O2 extraction. The marked decrease in surface Pto2 occurred in spite of a slight increase in the subepicardial regional blood flow (+10%); thus the increase in O2 delivery was not sufficient to meet the increase in O2 demand. Total flow was increased by 27% in the CX area without changes in the subendocardial to subepicardial flow ratio and in the surface Pto2 values. When pacing was stopped, surface values of Pto2 in the LAD area returned to prepacing values, as did lactate extraction and coronary venous PCO2.Clear and close relationships with surface Pto2 were found for regional lactate extraction, coronary venous PCO2 and the normalised subendocardial RBF. Poor or no correlations were found for the normalised subepicardial regional blood flow, the coronary venous O2 saturation and the absolute values of subendocardial and subepicardial regional blood flow. We conclude (1) that surface Pto2 reflects the net difference between subepicardial capillary O2 delivery and cellular O2 consumption and (2) that measurement of myocardial surface Pto2 is a sensitive method for determining both regional epicardial tissue oxygenation and also transmural oxygenation. [ABSTRACT FROM PUBLISHER]

Progenics Pharmaceuticals Inc and Wyeth Pharmaceuticals are developing methylnaltrexone, a micro-receptor opioid antagonist derived from naltrexone by the addition of a methyl group. The intravenous formulation of methylnaltrexone is currently in phase III clinical trials for the potential treatment of postoperative ileus.