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 µg 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 < 0.01) 30 min after clonidine. Systolic blood pressure dropped from 215 ± 33 to 164 ± 26 mm Hg (p<0.01); the diastolic value from 117 ± 15 to 98 ± 14 mm Hg (p<0.01). At the same time, the systolic PA pressure decreased from 40 ± 13 to 32 ± 11 mm Hg (p < 0.01) and the diastolic pressure decreased from 20 ± 8 to 15 ± 8 mm Hg (p < 0.01). The mean PA pressure dropped from 29 ± 11 to 23 ± 10 mm Hg (p < 0.05). Likewise, the mean RA value decreased from 8 ± 1.6 to 5.3 ± 1 (p < 0.01) following clonidine administration. Cardiac output was not changed significantly. The peripheral vascular resistance was initially increased considerably to 3,004 ± 971 dynes/s/cm-5 and decreased after clonidine to 2,359 ± 365 dynes/s/cm-5 (p < 0.05). An initial increase in blood pressure by slow administration was not observed in any of the patients.
A decrease in afterload following clonidine leads to simultaneous improvement of the haemodynamic situation in the pulmonary circulation and in the right heart as a result of pressure release of the left ventricle. The findings confirm the very good efficacy and tolerance of the substance after intravenous administration.
Address correspondence and reprint requests to Dr. V. Mitrović, Städtisches Krankenhaus, Innere Abteilung, Ludwigstraβe 41, D-6350 Bad Nauheim, Federal Republic of Germany.
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