Mechanisms of tachycardia on standing: studies in normal individuals and in chronic Chagas’ heart patients

• Published in: Cardiovascular research Vol. 14; no. 9; pp. 541 - 550
• Main Authors: NETO, J A MARIN, GALLO, L, MANCO, J C, RASSI, A, AMORIM, D S
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.09.1980
• Subjects: Adult; Chagas Cardiomyopathy - physiopathology; Heart Rate; Humans; Middle Aged; Parasympathetic Nervous System - physiopathology; Posture; Sympathetic Nervous System - physiopathology; Tachycardia - physiopathology
• ISSN: 0008-6363; 1755-3245
• DOI: 10.1093/cvr/14.9.541

The reflex tachycardia induced by change from the supine position to a 70° head-up tilt was studied in conscious normal individuals and in patients with chronic Chagas’ heart disease, known to constitute a model of parasympathetic denervation of the sinus node, in the absence of cardiac failure. Chagas’ patients showed markedly decreased heart rate responses during the initial 10 s following tilt to upright posture. A similar response was obtained in normals after parasympathetic blockade with atropine. β-adrenergic blockade failed to produce a significant effect on the initial heart rate response of normals, but heart rate increment, at 1 and 5 min of tilt, was significantly reduced in normals and abolished in patients. These results indicate a biphasic mode of tachycardia elicited by the upright posture: initially it depends on parasympathetic withdrawal, sympathetic stimulation becoming the predominant mechanism when stabilisation is attained in the orthostatic position.