THE RESPONSE TO EXERCISE BEFORE AND AFTER TREATMENT OF MYXEDEMA WITH THYROXINE

Five hypothyroid patients were studied before and after three months of treatment with thyroxine. Treatment resulted in improvement of symptoms and restored basal metabolic rate to normal. Exercise performance was improved by treatment, greater work loads were achieved and the cardiac output for a given level of O2 intake was increased. The increase in cardiac output was achieved by an increase in heart rate. However, blood lactate levels during exercise were similar in the two studies suggesting that the increase in cardiac output did not result in improved blood distribution to muscle. Ventilation during exercise was higher in four patients after treatment, due to an increase in alveolar ventilation, but this was not accompanied by any improvement in abnormal pulmonary gas exchange, shown by an increased alveolar to arterial difference in oxygen pressure. The improvement in peripheral distribution of systemic blood flow and in the distribution of ventilation and blood flow in the lung may be delayed due either to the general effects of a chronic illness or to the slow rate at which myxedematous changes in tissues resolve.