Some of the haemodynamic abnormalities in mild (borderline) human hypertension appear to be neurogenic, since they can be completely abolished by pharmacological autonomic blockade. 2. The cardiac output is elevated in 30% of patients through increased sympathetic drive and decreased parasympathetic inhibition. 3. In the remainder, the higher blood pressure is maintained by increased total peripheral vascular resistance. 4. In approximately 30% of this latter group, the higher vascular resistance is maintained solely by increased alpha-adrenergic tone. 5. Elevated plasma renin activities in a proportion of cases are probably due to generalized increase in sympathetic nervous activity. 6. Patients with mild hypertension thus show increased sympathetic drive to the heart and arterioles as well as decreased cardiac parasympathetic inhibition. It is presumed that the increased plasma renin is also neurogenic. 7. Such a widespread distribution of altered autonomic tone suggests aberration of the function of the integrative centres of cardiovascular control. 8. Evidence is presented of a possible psychosomatic origin of these changes in some cases.
