1. The haemodynamics of ten patients with essential hypertension were studied before treatment (study 1) and again 1 week after cessation of 1 year's antihypertensive drug therapy (study 2). On each occasion measurements of mean arterial pressure (MAP), cardiac index (CI) and total peripheral resistance index (TPRI) were made before and after ‘total’ pharmacological autonomic blockade (with intravenous propranolol, atropine, phentolamine and clonidine); measurements after ‘total’ autonomic blockade were used to assess the magnitude of the ‘non-autonomic’ component of TPRI, which reflects humoral or structural alterations in the vasculature.

2. The findings before ‘total’ autonomic blockade during study 2 showed that MAP was 18 ± 8 mmHg below the value (135 mmHg) observed during study 1 before treatment, and TPRI had fallen by 33% (P < 0·05) and CI had increased by 23% (P < 0·05).

3. After ‘total’ autonomic blockade the differences in the ‘non-autonomic’ components of the different variables were similar, with ‘non-autonomic’ MAP 14 ± 4 mmHg lower in study 2, TPRI 42% lower (P < 0·005) and CI 28% higher. The value in ‘non-autonomic’ TPRI was now the same as values previously observed in normotensive subjects.

4. We conclude that after 1 year's successful treatment there is complete restoration of ‘non-autonomic’ TPRI as a secondary consequence of the blood pressure reduction.

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