The Haemodynamic Effects of Clonidine in Patients with Grade III to IV Hypertension

Abstract

In 10 patients (aged 46 to 72 years) with essential hypertension (grade III to IV), the acute effects on the haemodynamics in the systemic and pulmonary circulation were analysed following intravenous administration of clonidine. Pressure measurements in the right atrium (RA), right ventricle (RV), and the pulmonary artery (PA) were taken using cardiac catheterisation. Cardiac output was calculated according to the Fick principle. After determination of the initial values, 150 micrograms clonidine was administered intravenously and the haemodynamic parameters measured up to the 90th minute. Cardiac output and the peripheral vascular resistance were determined before and 15 and 30 min after clonidine administration. Heart rate decreased on average from 87 +/- 18 to 78 +/- 20 beats/min (p less than 0.01) 30 min after clonidine. Systolic blood pressure dropped from 215 +/- 33 to 164 +/- 26 mm Hg (p less than 0.01); the diastolic value from 117 +/- 15 to 98 +/- 14 mm Hg (p less than 0.01). At the same time, the systolic PA pressure decreased from 40 +/- 13 to 32 +/- 11 mm Hg (p less than 0.01) and the diastolic pressure decreased from 20 +/- 8 to 15 +/- 8 mm Hg (p less than 0.01). The mean PA pressure dropped from 29 +/- 11 to 23 +/- 10 mm Hg (p less than 0.05). Likewise, the mean RA value decreased from 8 +/- 1.6 to 5.3 +/- 1 (p less than 0.01) following clonidine administration. Cardiac output was not changed significantly.(ABSTRACT TRUNCATED AT 250 WORDS)