Consequences of inspired oxygen fraction manipulation on myocardial oxygenpressure, adenosine and lactate concentrations: A combined myocardial microdialysis and sensitive oxygen electrode study in pigs

Adenosine is a potent vasodilator whose concentration has been shown to inc rease in cardiac tissue in response to hypoxia. However, the rime-dependent relationship between the levels of myocardial interstitial adenosine and t issue oxygenation has not yet been completely established. Therefore, the p urpose of this study was to investigate the complex relationship between ti ssue myocardial oxygen tension (PtiO(2)) and interstitial myocardial adenos ine and lactate concentrations by developing a new technique which combines a cardiac microdialysis probe and a Clark-type PO2 electrode. The combined and the single microdialysis probes were implanted in the left ventricular myocardium of anesthetized pigs. The consequences of the combined use of m icrodialysis and PO2 probes on myocardial PtiO(2) and microdialysis perform ances against glucose were evaluated. A moderate but significant reduction in the relative recovery against glucose of the combined probe was observed when compared to that of the single microdialysis probe (42 +/- 2 v 32 +/- 1%, mean +/- S.E.M.; n = 5; P<0.05), at 2 mu l/min microdialysis probe per fusion flow. Similarly, myocardial oxygen enrichment, measured by the PO2 e lectrode, was negligible when microdialysis probe perfusion flow was 2 mu l /min. Systemic hypoxia (FiO(2) = 0.08) resulted in a significant decrease i n PtiO(2) from 30 +/- 4 to 11 +/- 2 mmHg, limited increase in coronary bloo d now (CBF), and a significant increase in myocardial adenosine and lactate concentrations from 0.34 +/- 0.05 to 0.98 +/- 0.06 mu mol/l and from 0.45 +/- 0.05 to 0.97 +/- 0.06 mmol/l respectively (P<0.05). Increasing the FiO( 2) to 0.3 restored the PtiO(2) and hemodynamic parameters to baseline value s with no changes in interstitial adenosine and lactate concentrations. Nev ertheless, myocardial interstitial adenosine remained significantly higher than baseline values. In conclusion, this study demonstrates the ability of a combined probe to measure simultaneously regional myocardial PtiO(2) and metabolite concentration during hypoxia. The hypoxia-induced increase in m yocardial adenosine persists after correction of hypoxia. The physiological significance of this observation requires further studies. (C) 2000 Academic Press.