Twenty patients with mild or moderate essential hypertension participated in a double-blind crossover randomized trial aimed at assessing, by echocardiography, the hemodynamic effects of the antihypertensive therapy with atenolol administered once daily (100 mg) alone or combined with chlortalidone (25 mg) in fixed combination. Blood pressure and heart rate were measured at rest and during bicycle exercise before and after four-week periods of treatment. Both atenolol and atenolol plus chlortalidone reduced significantly blood pressure and heart rate. The reduction in blood pressure was mediated by a reduction in cardiac output. However, the combined treatment was also able to prevent the increase in stroke volume observed after atenolol alone. Furthermore, the combined treatment was able to significantly lower blood pressure during exercise, while atenolol alone failed. These results suggest that the association of chlortalidone potentiates the antihypertensive effect of atenolol by acting through a different mechanism.
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