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.