Haemodynamic Changes in Hypertension and Their Modification by β-Blockers and Prazosin

The haemodynamic disturbances in essential hypertension differ depending on the age of the subject and the stage of the hypertensive disorder. In young subjects in WHO stage I, the cardiac output at rest is usually higher than in age-matched controls due to an increase in heart rate, and the total peripheral resistance at rest is within “normal limits.” However, during muscular exercise, the total peripheral resistance is increased. In older subjects in stage I, II, or III, the cardinal disturbance is an increase in the total peripheral resistance at rest as well as during exercise. The cardiac output is normal in stage I, but low in stage II or III due to a subnormal stroke volume. A 10-year follow-up in subjects 18-39 years old with mild essential hypertension left untreated demonstrated that in spite of insignificant changes in blood pressure at rest, there was a deterioration of the circulatory system reflected in a marked increase in total peripheral resistance and a decrease in cardiac output and stroke volume at rest as well as during exercise. It is possible that these changes are caused by a gradual restructuring of the left ventricle and of the arteriolar wall. The various antihypertensive drugs reduce blood pressure through different modes of action and through different alterations of central haemodynamics. The long-term haemodynamic changes induced by prazosin differ from those seen by long-term treatment with diuretics and β-blockers. Prazosin induces reduction in total peripheral resistance without a decrease in cardiac output at rest and with an increase in cardiac output and stroke volume during exercise.