Evaluation of the use of heated cross-thermo-couples for assessments of regional myocardial blood flow.

The applicability of heat clearance for assessments of regional myocardial blood flow was examined in dogs. The axial and radial temperature field around the heated junction of the cross-thermocouples, sewn into the subepicardial layers of normally beating left ventricle of open-chest dog, was about 3.5mm. The heated tissue volume was approximately 0.31ml. The blood outflow from the cylinder introduced into the ventricular wall and the deflections in the thermoelectromotive voltage generated between the heated and reference junctions of the cross-thermocouples showed nearly a linear relationship, when the blood outflow was within 15ml./cm.2/min. Alterations in the temperature of a block of the myocardium, at the center of which the cross-thermocouples were settled, caused no obvious change in the thermoelectromotive voltage. At the room temperature of 26•}0.4•Ž, a temperature gradient of about 1•Ž was observed between the subendocardial layer and the subepicardial layer of the normally perfused left ventricle. In the ventricular wall of open-chest dog, the difference in the temperature alteration of the 2 different sites produced by coronary occlusion and by isoproterenol injection was within 0.026•Ž in most instances with an exception of 0.032•Ž, when the difference in distance of the measuring sites from the epicardium was within 2mm. The atmospheric temperature and the luminal flow caused no obvious change in the thermoelectromotive voltage, when the 2 junctions were implanted into the layers 2 and 1.5mm. apart from the epicardium and the endocardium, respectively. The change in voltage