Metabolic studies on the human heart in vivo: I. Studies on carbohydrate metabolism of the human heart

Abstract

The myocardial extraction and usage of glucose, lactate and pyruvate were measured in fifty-three patients with and without cardiac failure. The relative contribution of the catabolism of these substances to the oxidative metabolism of the heart (the oxygen extraction ratio) and the conversion of oxidative energy from these carbohydrates into cardiac work (the energy conversion factor) were estimated. Usually, the total aerobic metabolism of glucose, lactate and pyruvate combined fell short of the total oxygen consumption of the heart. Consequently, the heart used for provision of energy either heart muscle glycogen or non-carbohydrate substances. The latter possibility appeared more likely. Spontaneous rises in arterial glucose and lactate concentration were followed by an increase in their myocardial extraction and usage. The myocardial extraction of glucose is a function of the logarithm of its arterial concentration while the myocardial lactate extractions plotted against the logarithm of the arterial lactate level followed a parabolic curve. At glucose blood concentrations above 110 mg. per cent no further uptake of glucose by the myocardium was noticeable. When the arterial blood glucose concentration was suddenly raised, as the result of infusion, an upper limit of glucose extraction appeared to be absent. This might have resulted from glycogenesis as well as increased oxidation of glucose. Pyruvate was utilized by the human heart. In low and high output failure myocardial glucose and lactate extractions and the glucose and lactate oxygen extraction ratios were elevated; the glucose and lactate energy conversion factors were lowered. This indicates that the hyper- and hypokinetic heart in failure has become deficient in converting the energy derived from the aerobic breakdown of glucose and lactate into mechanical work.