Untersuchungen über den Erregungszustand des sympathischen Nervensystems und des Nebennierenmarkes bei kardiovaskulären Erkrankungen

Autonomic nervous cardiovascular regulation in borderline hypertension

Borderline hypertension attracts investigative interest since it is an early predictor of established hypertension and its sequelae. This condition offers the opportunity of studying arterial hypertension at its inception, before the development of secondary pressure-related changes. A number of abnormalities of the circulation have been described in borderline hypertension. The peripheral resistance is either elevated or inappropriately adjusted to the prevailing increased cardiac output and blood flow. Cardiac output, heart rate and stroke volume are elevated in a proportion of patients. Decreased plasma volume, enhanced pressor responsiveness and elevated plasma renin activity have also been noted. All these changes could hypothetically be explained by a neurogenic mechanism. Although the experimental evidence supporting a neurogenic origin of borderline hypertension is incomplete and often indirect, most findings point toward an abnormal autonomic control of the circulation in this disorder. It is postulated that in a subgroup of patients with borderline hypertension a neurogenic mechanism is in fact operative. There is a need for further characterization of this category of borderline hypertension and for description of its natural history, particularly in relation to the possible subsequent development of essential hypertension.

Role of parasympathetic inhibition in the hyperkinetic type of borderline hypertension

Eleven patients with borderline hypertension and high cardiac output were compared to 16 paid healthy volunteers. Cardiac output, heart rate, and intraarterial blood pressure were determined at rest, after administration of 0.2 mg/kg of propranolol i.v., and after administration of an additional 0.04 mg/kg of atropine. In four additional patients, response to infusion of isoproterenol before and after administration of 0.2 mg/kg of propranolol i.v. was evaluated. Resting heart rate and cardiac output in patients with borderline hypertension were elevated. After propranolol infusion, the values decreased more in the patients with borderline hypertension, but remained significantly elevated. After atropine administration, the difference in cardiac output and heart rate between the two groups disappeared. Consequently, patients with borderline hypertension and hyperkinetic circulation simultaneously exhibit an increase of sympathetic and a decrease of parasympathetic tone.

Hemodynamic responses to tilt and beta-adrenergic blockade in young patients with borderline hypertension

Seventeen young patients with borderline hypertension (one female) and 18 normotensive paid volunteers (two females) were studied at rest and in the tilted position after 10 min of 45° head-up tilt. Cardiac output, heart rate, and intra-arterial pressure were recorded. The measurements at rest and during the tilt were repeated after betaadrenergic blockade with propranolol.

By comparison with the normotensives, cardiac output and heart rate in those with borderline hypertension were elevated initially, after 50 min of rest, and during tilt. The change of the cardiac output and heart rate to tilt was of the same magnitude in patients and control subjects. Consequently, regulation of the rate and flow in borderline hypertensives appears to be normal but starts from a higher base line level.

After blockade with propranolol, cardiac output in patients with borderline hypertension was still slightly elevated, but the difference from controls was not significant. The heart rate, however, remained significantly elevated at rest and during tilt. Elevation of the heart rate in borderline hypertensives is not mediated through the beta-adrenergic system and may result from decreased parasympathetic inhibition or from different intrinsic myocardial pacing.