Abnormalities of autonomic nervous control in borderline hypertension

The systemic hemodynamic was investigated in 145 young male patients with borderline hypertension and 85 control subjects. Response of the cardiac output, stroke volume and the heart rate to sequential parasympathetic, beta-adrenergic and alpha-adrenergic blockade was used for assessment of the autonomic nervous tone. These investigations suggest that the apparently "innocent" minimal blood pressure elevation in borderline hypertension is associated with a number of physiologic abnormalities: The cardiac output, heart rate and stroke volume can be elevated. In all patients the peripheral resistance is abnormal. An abnormal distribution of plasma renin values is detectable. The plasma volume is decreased in a proportion of patients. A number of these abnormalities can be explained by a neurogenic mechanism. The elevation of the cardiac output is entirely neurogenic. In a substantial minority of patients, the elevation of peripheral resistance is attributable to increased sympathetic drive. Indirect evidence indicates that the plasma renin elevation in borderline hypertension may also be neurogenic. Hypothetically the decreased plasma volume may stem from sympathetic effects on postcapillary vessels, but at the present there is no experimental evidence of support this view. The change in autonomic function in borderline hypertension involves both the sympathetic and parasympathetic efferents. Increased sympathetic stimulation is coupled with decrease parasympathetic inhibition. This points toward abnormal integration of the autonomic control, presumably in the medulla oblongata. The mechanism of the autonomic abnormality is not fully elucidated. The role of baroreceptors requires further investigation. In some patients the altered autonomic integration appears to be related to psychosomatic mechanisms.