The hemodynamics of thyrotoxicosis in man with special reference to coronary blood flow and myocardial oxygen metabolism.

For many years the hemodynamics of thyrotoxicosis have been of interest to clinicians. Blood flow through the extremities was assumed to be increased in thyrotoxicosis because of the high rate of heat elimination when the hand was placed in a calorimeter (1). Several workers found an increase in cardiac output in thyrotoxic subjects using the oxygen content of arm vein blood in the Fick formula (2-4). Similar findings were obtained using the nitrous oxide (5) and acetylene methods (6, 7). The velocity of circulation, as determined by the rate of transit of radioactive materials through the cardiovascular system is accelerated in thyrotoxicosis and becomes normal after effective treatment (8, 9). Circulation time measured by sodium dehydrocholate in patients with thyrotoxicosis is more rapid than normal (10). Blalock and Harrison using oxygen content of right ventricular blood in the Fick formula showed that in dogs thyroid feeding produced an increase in cardiac output while thyroidectomy produced a decrease in output (11). Experiments concerning the myocardium directly have shown an increase in 02 uptake/gram of muscle. Direct measurement of 02 consumption in the Warburg apparatus demonstrated an increase in oxygen utilization by the thyroid stimulated myocardium as shown in the isolated beating