Background: Hyperthyroidism affects the circulatory system, producing an increase in cardiac output and an enhanced vascular bed volume. These phenomena are important in the regulation of blood pressure. The present study was designed to evaluate the effects of short- and long-term treatment of hyperthyroidism on arterial pressure, taking into account the indices of cardiac function and peripheral vessel resistance.
Material/Methods: Fifty-one patients with hyperthyroidism and 30 healthy controls were investigated. The patients were examined before treatment, two weeks after initiation of therapy, and after attainment of a euthyroid state. Thiamazole was used as the antithyroid agent. Blood pressure and serum thyroid hormones were determined and ultrasonographic examination was performed on all the subjects, after the application of a diet containing 120 mmol of sodium and 70 mmol of potassium for three days.
Results: Patients with hyperthyroidism had higher systolic blood pressure and lower diastolic blood pressure than the healthy controls. After short-term treatment, systolic blood pressure returned to normal, while diastolic blood pressure was normalized only after long-term treatment.
Conclusions: Regulation of blood pressure in patients with hyperthyroidism is a complex process. Systolic blood pressure is mainly related to cardiac output and returns to normal range shortly after the initiation of therapy, while diastolic blood pressure is related to peripheral vascular resistance and is normalized after long-term treatment.

Keywords: arterial pressure, hyperthyroidism, therapy