Transmural coronary venous O2 saturations in normal and isolated hearts

Abstract

Blood O2 saturations were measured by microscopic oximetry in the small coronary veins of wither open-chest or isolated and blood-perfused dog hearts. Subendocardial saturations (average 34%) were significantly lower than subepicardial (average 52%) in isolated hearts contracting isovolumically at systolic and coronary perfusion pressures of 100 mmHg. Saturations of botb regions fell and were not significantly different from each other (both averaged 16%) with partial coronary occlusion. When MVo2 was increased by calcium infusion, subendocardial saturations fell sharply to about 2% and were significantly, lower than subepicardial (average 10%). Conversely, when MVo2 was decreased by ventricular decompression, saturations rose equally in subendocardium (average 40%) and subepicardium (average 45%) (not significant). These data illustrate the efficacy of cascular autoregulation in isolated hearts. In open-chest dogs, as in isolated hearts with partial coronary occlusion, subendocardial (average 20%) saturations were not significantly diffenent from each other and ranged from 0 to 70%, suggesting the possibility of significant differences either in regional coronary flow or MVo2, or both, in closely adjacent areas throughout the myocardium.

Left ventricular mechanics related to the local distribution of oxygen demand throughout the wall.

“…As seen, the endocardial layers at normal preloads consume about 8% more oxygen than the epicardial layers, which is within the range obtained in experimental measurements (Gamble et al, 1974;Monroe et al, 1975;Weiss et al, 1978). However, the relative difference between the endocardial and epicardial layers seems to be highly preload dependent, actually inversing at very low preloads and increasing to 25% at high preloads.…”

“…However, data for the latter comparison is unattainable, and most of the techniques for measuring regional oxygen consumption encompass at least one-fourth of the wall thickness. The experimentally observed 20% higher oxygen consumption of the endocardial layers relative to the epicardial layers (Monroe et al, 1975;Weiss et al, 1978) is indeed consistent with our results.…”

“…Further support for the present approach should rely on experimental measurements of transmural metabolic gradient, and the literature provides some indications for the validity of the model. For instance, it is a well-known fact that the endocardial layers consume more oxygen than the epicardial ones, al- though the quantitative differences between the layers are rather controversial (Gamble et al, 1974;Monroe et al, 1975;Weiss et al, 1978;Feigl, 1983).…”

Effects of pulsatile and non-pulsatile perfusion on the isolated canine heart

“…As the distribution of coronary flow between the epicardium and endocardium is one important factor for myocardial oxygen supply [24] an improved endocardial oxygen extraction can be expected in hearts perfused with pulsatile flow. The vulnerability of the endocardium to ischemia has been well documented [21,22] and higher oxygen extraction in this layer has been reported [17]. It seems that shorter periods of ventricular fibrillation in the presence of a coronary stenosis are well tolerated as no differences appeared between both types of perfusion during the first 20 min.…”

Regularities of changes in microcirculatory flow through different parts of the heart in patients with acquired valvular disease before and after surgery

“…In the 1970s, experiments with animals showed that coronary flow is characterized by heterogeneity, reflected in a considerable difference in the myocardial capillary transit time [34] and in blood O 2 saturation [35]. This is easily explained by the fact that the mechanical load on the myocardial wall and, therefore, its metabolic activity are heterogeneous [2,3].…”