Thermal quantification of region myocardial perfusion and heat generation

Abstract

A technique for experimental determination of regional myocardial blood flow and heat generation has been developed, based on a heat-clearance method. This method allows repetitive and frequent measurements of regional blood flow without necessity for biopsy or microspheres. Testing was performed on a pedicle preparation, an intact segment of left ventricular myocardium dependent on a single diagonal coronary artery and situated in situ in the left ventricular free wall. Total blood flow to the pedicle was measured by an electromagnetic flow probe. A specially designed 3-thermistor microprobe was positioned in the pedicle to continuously sense temperature changes in the subepicardium, midmyocardium, and subendocardium. The theory underlying this method is based on a heat balance that includes local myocardial heating, conduction, and convection. Comparison of the predicted time- and position-dependent temperature with that measured experimentally allows extraction of the local myocardial blood flow and heating rates. This method allows resolution of differential flows in subendocardial, midmyocardial, and subepicardial myocardium and provides quantification of dynamic flow changes in each layer in response to various stimuli such as ischemia or pressor agents, without in itself causing damage to the myocardial microvasculature. Our data show total flow, based on summation of thermally calculated regional flows, to have correlation coefficients of 0.88 with both the flowmeter and microsphere results. Resting flow values for Nembutal-anaesthetized, open-chest dogs of 0.66 ml/(g . min) compare favorably with values obtained by microsphere studies. Infusion of norepinephrine increased total flow and all layer flows, but the increase in subendocardial flow with norepinephrine was less than the increase of the other layers, perhaps accounting for the vulnerability of this region during catecholamine stress. Local myocardial heating rates in subepicardial, midendocardial, and subendocardial layers are shown to follow the same dependence on local myocardial blood flow in response to anoxic stress or norepinephrine-induced vasodilation. Specifically, local heating rate increases to a factor of 10 at flow below resting level.

Dynamic Redistribution of Coronary Blood Flow in the Dog as Measured by a Thermistor Technique

“…1979;Shitzer & Eberhart, 1979). This approach, based upon analysis of the kinetics of local temperature change following temperature perturbation, has been analysed theoretically by Shitzer & Eberhart (1979) and verified experimentally (Hernandez et a!. 1979 Thus, all measurements must be expressed in terms of percentage change from control.…”

“…The same principle has been applied in the dog kidney in which thermal conductivity was measured after heating a small adjacent area (Muller-Schauenburg et al 1975;Olshausen et al 1976). Similarly, the principle of heat clearance has recently been applied to quantitative measurement of regional tissue blood flow in the myocardium (Hernandez et a!. 1979;Shitzer & Eberhart, 1979).…”

“…Gibbs(1967) has measured metabolic heat directly in the papillary muscle, and reported values which were an order of magnitude lower than the heat changes measured as a function of coronary blood supply. Hernandez et al (1979) and Shitzer & Eberhart (1979) also showed that heat changes produced by changes in local blood flow are much greater than those produced by metabolic heat. Fig.…”

AN EXPERIMENTAL APPROACH FOR EVALUATION OF THE O2 BALANCE IN LOCAL MYOCARDIAL REGIONS IN VIVO

“…Gibbs (1967) has measured metabolic heat directly in the papillary muscle, and reported values which were an order of magnitude lower than the heat changes measured as a function of coronary blood supply. Similarly, Hernandez, Hoffman, Fabian, Siegel & Eberhart (1979) showed that heat changes produced by changes in local blood flow are much greater than those produced by metabolic heat.…”