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SUMMARY The purpose of this study was to find a method to assess the sensitivity of the baroreceptor reflex avoiding the use of a pressor amine. Following the release of the Valsalva maneuver (VM), there is usually a pressor rise similar to the one obtained by phenylephrine administration. We were able to assess the baroreceptor reflex sensitivity index (BRSI) using this phase of the VM. Included in this study were nine healthy subjects, 25 patients with chronic Chagas' disease, and 10 hypertensive patients

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The purpose of this study was to investigate the sympathetic nervous system function in 34 patients with chronic Chagas' disease. The tilting test was selected as an appropriate means to assess the adrenergic system function. Our results demonstrate that (a) all chagasics respond with a significantly smaller rise in diastolic blood pressure (0-3.8 mmHg) than normal subjects (9-12 mmHg), when submitted to the tilting test and (b) chagasic patients with heart failure have a significantly lower heart rate than normal subjects and nonchagasic heart failure patients (P < 0.05 and 0.001, respectively). With these results we may speculate that the damage in chronic Chagas' disease should be located in the sympathetic pathway. Therefore, the faulty orthostatic mechanism would be the consequence of a diminished adrenergic activity, with a defective arteriolar vasoconstriction and a decreased basal heart rate. At the same time we note that our results differ from the results of similar tests performed on the same kind of chagasic patients in Brazil, where a predominantly decreased parasymphathetic activity has been demonstrated.