誘発性低酸素血症に於ける心筋糖質代謝に関する臨床的研究

Carbohydrate metabolism under hypoxemic conditions was first studied by Araki' in 1895, and since that time numerous reports have been published on this subject. With the introduction of the coronary catheterization method by Bing in 1949, it has become possible study the coronary flow and cardiac muscle metabolism directly. The influence of oxygen dificiency on carbohydrate metabolism in the human cardiac muscle, the relation to other factors and differences in cardiac conditions of various types however, have not yet been examined. In the present study, 52 cases of normal subjects and subjects with some disorder were placed in a state of hypoxemia induced by low oxygen loading (10% O₂ for 20 minutes), and in 25 cases of these, coronary catheterization was performed before breathing of low oxygen air. In the 52 cases, samples of the arterial blood and in the latter 25 cases samples of the arterial and the coronary venous blood were taken prior to, 5 minutes and 15 minutes after loading. The author measured the glucose, lactate and pyruvate levels, and the findings were considered in relation to the results obtained by the co-workers on the gas content of the blood and the amount of coronary flow.The results are presented here.(1) Changes in myocardial carbohydrate metabolism in the stage of low oxygen breathing.(i) Initial stage (after 5 minutes, arterial O₂ saturation 60-80%).In arterial levels, glucose is slightly increased, lactate is almost unchanged, pyruvate is slightly decreased and the L/P ratio shows a small increase. The percentage of each change is within ±3%. Examination of the myocardial extraction shows that the relation between extraction of glucose and the arterial concentration is more pronounced following loading with a trend for higher extraction with higher glucose concentration in the artery. This corresponds to the findings under anaerobic condition described Schumann. Lactate and pyruvate extractions show a slight decrease, but the relation between the lactate- and pyruvate extraction coefficient is clearer than before loading. Thus at this stage the influence of low oxygen loading still seems to be small, and it may be said that this stage is that of compensatory response to hypoxemia.(ii) Stage of constant hypoxemia (after 15 minutes, arterial O₂ saturation 45-70%).There is an increase in glucose, lactate, pyruvate and L/P ratio. The lactate especially shows a rise of 25%. The others, glucose pyruvate and L/P ratio show a rise of about 9%. Myocardial extraction however, is reduced despite the rise in glucose, lactate and pyruvate levels, and the relation between lactate- and pyruvate extraction coefficient no longer becomes apparent. In other words, distinct disturbances in myocardial carbohydrate metabolism are produced at this stage of induced hypoxemia.(2) Relation between carbohydrate metabolism and gas metabolism in hypoxemic myocardium.(i) The relationship between myocardial carbohydrate extraction and arterial oxygen content.With advance in the state of hypoxemia, extraction of blood carbohydrate metabolites decreases and there is a freeing of metabolites from the cardiac muscle. After 15 minutes, when a constant state is reached, there is a suppression of glucose, lactate and pyruvate extraction in the order named together with reduction in arterial oxygen content. The borderline is an arterial oxygen content of 12-10 Vol%.(ii) The relationship between myocardial carbohydrate metabolism and coronary flow.Calculation of the mean carbohydrate usage, by multiplying the extractions with the coronary flow, was performed prior to and 15 minutes after loading. Glucose usage is reduced in general in the normal, pulmonary and circulatory cases in which coronary flow is increased.