1. Vascular resistance at maximal vasodilatation was examined in two vascular beds in two groups of hypertensive patients and in normotensive control subjects before and during anti-hypertensive therapy in the hypertension groups.
2. In one group of twelve untreated patients with essential hypertension, examined with plethysmography and intra-arterial blood pressure recording, a significantly higher vascular resistance at maximal vasodilatation was found in the hands compared with normotensive control subjects matched for age, sex, weight and height. This indicated a structural vascular abnormality in the patient group.
3. After 5 years of anti-hypertensive therapy in the patient group the difference in vascular resistance between patients and control subjects had decreased significantly, indicating a reversibility of the structural vascular abnormality.
4. Vascular resistance at maximal vasodilatation was examined in the calves of twelve untreated patients with essential hypertension and fourteen normotensive control subjects. Plethysmographic technique and indirect blood pressure recordings were used. A significantly higher vascular resistance was found in patients than in control subjects, indicating a structural vascular abnormality also in this vascular bed.
5. Anti-hypertensive treatment for 6 months in the patient group did not change vascular resistance at maximal dilatation, indicating that the structural vascular abnormality remained.
6. During acute reduction of blood pressure in hypertension by means of trimethaphan infusion, blood pressure and blood flow to the hands were reduced proportionally with no change of vascular resistance at maximal vasodilatation.
7. This indicates that resistance at maximal dilatation was unaffected by the acute reduction of blood pressure, in contrast to the findings after prolonged reduction of blood pressure in this vascular bed.