Haemodynamics in hypertensive patients before and during guanfacine treatment.

1. The haemodynamic mechanisms underlying the antihypertensive effect of guanfacine during chronic oral administration were studied. 2. Ten patients with essential hypertension were submitted to haemodynamic measurements at rest and during exercise, before and after 12 weeks' treatment with guanfacine alone at a daily dose of between 3 and 15 mg orally. 3. The relevant haemodynamic values were obtained by means of an arterial catheter in the aorta, a venous catheter in the right atrium, and the measurement of cardiac output using the thermodilution method. 4. The antihypertensive efficacy of guanfacine was confirmed. 5. In the seven patients with a high peripheral resistance the main effect of guanfacine was a marked decrease in total peripheral resistance. In three patients with hypertension characterized by high stroke volume and cardiac output, the main effect of guanfacine was to reduce these variables.