Postural reflexes in chronic Chagas's heart disease. Heart rate and arterial pressure responses.

Studies of heart rate and blood pressure responses to 70 degrees head-up tilt and 30 degrees head-down tilt were conducted in normal subjects and in chronic cardiac chagasic patients without past or present cardiac decompensation. During steady state of tilt, heart rate alterations were less marked in the chagasic than in the control group. Vasodepressor syncope supervened in three cardiac chagasic patients, two of whom showed the distinctive feature of hypotension without reflex bradycardia. In these patients, vagal control of cardiac rate could not be demonstrated either following a full blocking dose of atropine or during sudden elevation of systemic arterial blood pressure. These results are interpreted in the context of the pathologic and functional derangements of autonomic control which occur in Chagas' heart disease.