The blood volume in hyperthyroidism

Thyrotoxicosis is almost invariably associated with a certain degree of cardiovascular disturbance. Tachycardia is always one of the first signs of this malady. Demonstrable enlargement of the heart fre-quently follows. Cardiac arrhythmia, especially auricular fibrillation, and congestive heart failure often constitute the important part of the clinical picture during the later part of the course of the disease. Occasionally the patient's death may be directly attributable to car-diac insufficiency. Although various views have been put forward, the cause and nature of these circulatory derangements remain in-completely understood. Attempts to find characteristic histological changes in the myocardium have been without success. The isolated reports of damage to the heart muscle (1) (2) (3) (4) give no convincing evidence that the lesion was specific. That the thyroid heart is not a permanent condition has been recently emphasized by Thomas (5). One of the patients reported by this author died from heart failure, but presented no significant myocardial damage on postmortem examina-tion. On the other hand investigations into the physiological pathol-ogy of the disease have been less disappointing. Years ago Plesch (6) demonstrated an increased minute volume in the patients suffering from exophthalmic goiter. Stewart (7) by his special technic found in Graves ' disease an exceptionally large blood flow in the hands and this he thought was in agreement with the flushing of the skin which is commonly seen. More recently the cardiac output in hyper-thyroidism has aroused a renewed interest (8) (9) (10) (11) (12). In spite of the widely different methods employed, all investigators with the single exception of Rabinowitch and Bazin (9) have come to the same conclusion as that reached by Plesch. Blumgart, Gargill and Gilligan (13) studied 13 thyrotoxic patients and showed that th