Myocardial metabolism during dynamic exercise]

The development of Webster catheterization has enabled us to make clinical measurement of coronary sinus blood flow and to estimate the kinetics in myocardial substrate uptake. In this study, exercise tolerance test using supine multistage bicycle ergometer test was performed and exercise-induced hemodynamic alteration was evaluated in 18 patients with ischemic heart disease (16 males and 2 females, average age 56.3 years). The change in substrate kinetics in myocardial metabolism was also examined in terms of two indexes; myocardial uptake rate and myocardial uptake. The following results were obtained. 1) The myocardial uptake rates of glutamate and free fatty acid were significantly decreased by exercise, while those of glucose and lactate showed no significant change. 2) The myocardial uptakes of glutamate, glucose and lactate were significantly increased by exercise, but that of free fatty acid did not change significantly. 3) A significant negative correlation (r = -0.52, p < 0.05) was observed between the change in myocardial glutamate uptake and the change in pulmonary artery wedge pressure induced by exercise, suggesting that patients with ischemic heart disease might fail in glutamate uptake induced by exercise. The difference in the kinetics of myocardial uptake rate and myocardial uptake for glutamate, alanine, glucose, free fatty acid and lactate is observed. This difference occurs from the decrease in uptake rate due to the increase in coronary sinus blood flow. Myocardial uptake, which directly reflects myocardial energy metabolism is regarded as a more useful index of myocardial metabolism than myocardial uptake rate.