[Myocardial function and reactivity in thyrotoxicosis and in the post-thyrotoxic state (experimental-clinical study)]

A response of the heart to hypoxia was studied in experimental thyrotoxicosis and physical exercise in patients with the thyrotoxic goiter. A decrease in the duration of cardiac hyperfunction and acceleration in the suppression of cardiac function in hypoxia were observed in rats with thyrotoxicosis though myocardial sensitivity to noradrenaline increased. After the discontinuation of hormone administration these changes rapidly disappeared but the general resistance of the body to hypoxia remained lowered and a response of the heart to acetylcholine sharply increased. In the thyrotoxic goiter a degree of myocardial hyperfunction in physical exercise was lowered in accordance with the gravity of a process, and the recovery of myocardial function after exercise slowed down. After therapy in the presence of a normal blood level of T4 a response of the heart to physical exercise returned to normal though the recovery of external respiration after exercise remained inhibited for a long time. The role of hypoxia in change of myocardial reactivity in thyrotoxicosis and the meaning of disorders of external respiration in preserving hypoxic manifestations in the post-thyrotoxic condition were discussed.