[Hemodynamic mechanisms of the decrease in physical work capacity in hypothyroidism and thyrotoxicosis]

A study of 21 patients with hypothyroidism, 22 patients with thyrotoxicosis and 18 normal subjects, using echocardiography and bicycle ergometry, demonstrated different mechanisms of reduced working capacity, associated with those conditions. The decrease in chronotropic and inotropic heart reserve, associated with hypothyroidism, is shown to be rooted in slowed-down relaxation of left ventricular posterior wall in the presence of diastolic arterial hypertension, while limited working capacity, associated with thyrotoxicosis, is rooted in resting myocardial hyperfunction due to hyperkinetic circulation.