誘發性低酸素血症に於ける心筋糖質代謝に關する臨床的研究
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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% O_2 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 O_2 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 O_2 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. Lactate usage is maintained in the normal and pulmonary cases whereas it is reduced in the cardiac cases despite the increase in coronary flow. The changes in pyruvate usage do not show a constant trend and are small in general.(iii) Myocardial carbohydrate O_2 extraction ratio.It was found that the myocardial carbohydrate O_2 extraction ratio is 73.8% prior to and 81.2% after loading. Both are less than the 100% oxygen consumption of cardiac muscle. The extracted carbohydrate is therefore the main source of energy, but it is believed that non-carbohydrate substances and myocardial glycogen are also involved.(iv) Myocardial carbohydrate metabolism and myocardial R. Q. .Examination of the myocardial R. Q. shows that it is reduced in general after loading. The(glucose+lactate)O_2 extraction ratio however, shows two groups, increased or reduced, following loading. The pyruvate O_2 extraciton ratio is reduced in the former increased group is increased in the latter reduced group. The reduction in R. Q. in the former group suggests incomplete carbohydrate combusion following loading and the reduction in the myocardial R. Q. in the latter group suggests an increased involvement of metabolism of noncarbohydrate substances. This can also be assumed from the theory of the TCA cycle.(3) Comparison of metabolic behaviours between carbohydrate metabolites prior to and 15 minutes after low oxygen loading.(i) Glucose.The glucose extraction, extraction coefficient and usage in the normal, pulmonary and cardiaccases is reduced in general. Furthermore, there is a marked freeing from the cardiac muscle in the normal subjects and pulmonary disorder cases. The glucose O_2 extraction ratio is reduced in the nomal subjects and pulmonary cases whereas in the cardiac cases there is a tendency to maintain it.(ii) Lactate. The lactate extraction is reduced in general. The extraction coefficient and usage are maintained in the normal and pulmonary cases, but are reduced in the cardiac cases and a pulmonary case in a state of shock. The O_2 extraction ratio too, is increased in the normal and pulmonary cases but decreased in the cardiac cases and a case in shock.(iii) Pyruvate.The pyruvate extraction is reduced in general. Little change is seen in the pyruvate extraction coefficiant, usage and O_2 extraction ratio, and their trend is not clear. The pyruvate level is low so that as proposed by Bing and as suggested from the present reports ((2) : i, iv), it is more important as an indicator of myocardial metabolism in states of oxygen deficiency rather than as an energy source.(4) Comparison of the myocardial carbohydrate metabolism prior to and after low oxygen loading between some diseases.(i) Normal and pulmonary cases.In these healthy and relatively healthy hearts, myocardial utilization of glucose is reduced whereas that of lactate is increased in a state of induced hypoxemia.(ii) Cardiac case and a cases in a state of shock.In these unhealthy hearts, there is a tendency to maintain myocardial utilization of glucose, and that of lactate is reduced in a state of induced hypoxemia. In a pulmonary case in a state of shock (arterial O_2 content : 6.6 vol%), both utilization of glucose and lactate is reduced.So it can be summarized that in cardiac disorders, there is a defect in ability of the cardiac muscle in the utilization of lactate whereas glucose utilization is maintained in a state of induced hypoxemia, in contrast to the normal and nonsevere pulmonary cases in which the utilization of glucose is restricted and that of lactate is pronounced.
- 社団法人日本循環器学会の論文
- 1958-01-20