Nineteen patients (12 male and seven female) with
essential hypertension (mean arterial pressure ranging from 113-162 mmHg) were studied at rest, supine and sitting, and during bicycle exercise (50, 100 and 150 W). Intra-arterial blood pressure and heart rate were recorded continuously. Cardiac output was measured by
dye dilution (
Cardiogreen). The patients were treated with
enalapril 10-40 mg (mean 33 mg) once-daily; seven patients received in addition 25-50 mg
hydrochlorothiazide daily. After 5-13 months (mean 10 months) patients were restudied. Blood pressure fell (P less than 0.001) in all - at rest sitting from 184/108 to 150/89 mmHg (-19%) and during 100 W bicycle exercise from 225/118 to 197/101 mmHg (-13%). Pretreatment total peripheral resistance index (TPRI) was markedly increased and fell at rest sitting from 4087 to 3514 dyn s/cm-5 m2 (-14%) (P less than 0.05). No significant change was seen in cardiac output, heart rate or stroke volume. Overall
body weight and body fluid volume (
isotope dilution technique) remained unchanged, but in the subgroup receiving
enalapril +
hydrochlorothiazide, blood volume fell by 12% (P less than 0.01). No side-effects were seen. In conclusion,
enalapril monotherapy reduces blood pressure in two-thirds of patients with moderately severe
essential hypertension at rest and during exercise, associated with a significant reduction in TPRI. One-third of patients require a
diuretic in addition to
enalapril. In this subgroup the reduction in TPRI was about twice the reduction seen during
enalapril treatment alone, and there was a fall in blood volume.