The effects of thyroid hormone excess on myocardial hemodynamics and carbohydrate metabolism were determined in a group of subjects, and the findings compared with those obtained in a group of normal individuals. The results indicate that in thyrotoxicosis there tends to be an increase in coronary blood flow and myocardial oxygen consumption and a normal per cent extraction of oxygen by the myocardium. The metabolism of glucose, lactic acid, and pyruvic acid was virtually identical in the 2 groups. No relationship was demonstrable between the arterial levels of the carbohydrate substances and their extraction by the heart.T HE pronounced clinical effects of hyperthyroidism upon the cardiovascular system strongly suggest a direct participation of cardiac tissue in the metabolic effects of excess thyroid hormone. Although limited study of the human heart has failed to support this view,1 experimental hyperthyroidism has revealed an increased myocardial oxidative activity2 3 and diminished myocardial concentration of high-energy phosphate compounds.4 This limitation in the source of immediately available energy for muscular contraction, and, hence, of cardiac work capacity, might represent a biochemical lesion responsible for the clinical demonstration of impaired exercise response in hyperthyroid patients.5To explore further the influence of thyroid hormone excess on the myocardium, a study of carbohydrate metabolism, oxygen consumption, and coronary flow was undertaken in a group of individuals with typical hyperthyroidism and, for comparative purposes, in a group of hospitalized individuals free of cardiac and metabolic disease. This investigation was supported by research grants H-1492 from the National Heart Institute, U. S. Public Health Service, and a grant from the Michigan Heart Association.
METHODS AND MATERIALThe data presented were obtained from 17 normal individuals and 13 hyperthyroid patients. The former group was made up of individuals convalescent from a variety of acute diseases, and at the time of study had no detectable cardiovascular or metabolic disease. The latter group was made up of patients with history, physical, and laboratory findings typical of hyperthyroidism.The 17 normal individuals ranged in age from 22to 54 years, with a mean age of 34.4 years. The 13 hyperthyroid individuals had an age range from 18 to 54 years, and a mean age of 26.6 years. All subjects were fasting for at least 8 hours prior to study. No attempt was made to modify the ward diet in the days preceding the study. The patients in both groups were sedated with Nembutal, 100 mg., or demerol, 50 mg., to obtain a reasonably basal state. Catheterization of the coronary sinus was carried out in the right anterior oblique position' and an indwelling needle inserted in either the radial or brachial artery. Coronary blood flow was determined by the nitrous oxide method of Kety and Schmidt as modified for the heart, utilizing the saturation technic and a coefficient of 1.1 for the partition of nitrous oxide between myocard...