The Minute Volume Output and the Work of the Heart in Hypothyroidism 12

Abstract

Close association between aberrations in the function of the thyroid gland and disturbances in the physiology of the cardiovascular system has long been recognized. Because of the frequent occurrence of evidences of heart disease in patients with thyrotoxicosis many investigators have studied the cardiac minute volume output and other aspects of the circulation in this disease. In hypothyroidism, on the other hand, evidences of disturbed cardiovascular function are less prominent, and the cardiac output accordingly has been less thoroughly investigated.In 1925, Means (1) reported marked dinminution in the cardiac minute volume output in two cases of myxedema studied by Field and Bock. Two years later, Mobitz (2) observed a decrease in the cardiac output in one patient with myxedema, and Kininmonth (3) likewise observed a decrease in two additional cases. The results of the two latter observers are difficult to interpret, since the validity of the original ethyl iodide method (4) which they utilized has been questioned. Several years later, Bansi (5) (6) using the methods of Douglas and Haldane (7) and of Grollman (8), also found decreased cardiac output in three patients with myxedema.The recent work of Blumgart and his associates (9) (10) (11) in establishing the value of total ablation of the normal thyroid gland in the treatment of chronic intractable heart disease made it advisable to study the cardiac output and related aspects of the circulation in hypothyroidism induced by this operation. tion of the thyroid gland performed for the relief of angina pectoris. Studies were made in two, both before, and at different levels of basal metabolism after operation; in one other, observations were made at three different levels of metabolism after operation. Patients with no history of congestive failure were chosen for this study in order to avoid the complicating effect of cardiac decompensation on the output of the heart. Four subjects were males and three females; the ages varied from 53 to 65 years. Several patients showed slight elevation of the blood pressure; all presented slight to moderate sclerosis of the peripheral arteries. The hemoglobin in every instance was 90 per cent or above. Studies were made only in patients with hypothyroidism who could be trained to breathe as deeply and as rapidly as is necessary for measurement of the cardiac output by the acetylene method. The decreased oxygen consumption in hypothyroidism results in a diminution of the oxygen difference between the consecutive gas samples taken for analysis. This increases the percentage deviation from the average of repeated measurements of the cardiac output; it was not possible to obtain reliable results in several patients. As indicated in Table I, many patients were receiving small doses of dessicated thyroid gland (Armour) at the time of study.All measurements were made in the postabsorptive state, under basal conditions with the patients in the semi-recumbent position, after a rest of. one-half to one hour. The basal metabolic rate...

Physiologic Effects of Obesity Upon the Heart: The Incidence of Obesity in Coronary Disease†

“…In a typical case the cardiac output was 2.76 liters per minute when the basal metabolic rate was —34 per cent, and it rose to 4.15 liters per minute when the metabolic rate was only — 5 per cent. The findings are similar to those in hypothyroidism (22) but in these coronary patients the undernutrition did not produce clinical evidence of hypothyroidism or other untoward effects, even when the metabolism fell to —30 per cent or lower. The drop in metabolism appears to be a protective adaptation of the body to the low caloric intake.…”

Left ventricular function at rest and during exercise in acute hypothyroidism.

“…The heart rate an hour before the study was similar to that recorded upon completion of cardiac instrumentation in both euthyroid and hypothyroid patients, suggesting that the anxiety level associated with right heart catheterisation was low (68 (12) v 70 (11) beats/ min and 81 (15) v 80 (14) beats/min respectively). (14) Systolic blood pressure 124 (14) 134 (22) (mm Hg) Pulmonary capillary wedge 6 (2) 8 (2) pressure (mm Hg) Right atrial pressure (mm Hg) 3 (2) 4 (2) Cardiac output (1/min) 4 1). The values for heart rate tended to be higher in euthyroid patients (70 (11) v 80 (14) beats/min) but this difference did not reach statistical significance.…”

A Correlation of Clinical and Hemodynamic Studies in Patients With Hypothyroidism1

“…Physiologic studies in patients with hypothyroidsm have established that the cardiac output is low and that the circulation time is often moderately prolonged. In the majority of patients studied the reduction in cardiac output has been found to be proportional to the decreased oxygen consumption with the arteriovenous difference normal; other investigators have noted a somewhat greater reduction in cardiac output than in oxygen consumption with a somewhat increased arteriovenous difference (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Pressures within the heart and the pulmonary and systemic 1 Nebraska. circulations have been found to be within normal limits (22,26).…”