II - Evaluation of Autonomic Control of Heart Rate in Various Clinical Conditions.

Through the comparison of responses of normal volunteers, assessment of autonomic function under abnormal clinical conditions focused on the detection of dysautonomia involving both the parasympathetic and adrenergic limbs in patients with Chagas heart disease, post-cardiac surgery, chronic heart failure, mitral valve prolapse, and hyperthyroidism. In particular, the autonomic impairment observed in Chagas disease patients involved predominantly the parasympathetic control of heart rate at the sinus node level, and the adrenergic innervation at the myocardial ventricular level. The autonomic derangements observed in Chagas cardiomyopathy patients have only recently been explored in terms of their prognostic relevance, and their potential clinical implications for therapeutic purposes remain to be investigated. Over the last nearly seven decades, our laboratory has accumulated significant expertise using several tests described above to evaluate autonomic control of heart rate, now focusing on various pathophysiological clinical conditions. The effect of endurance physical training and of aging was mostly focused on studies of normal volunteers whose responses at baseline served as controls to be compared during tests employed in individuals with some morbid clinical conditions. By far, the pathophysiology of Chagas heart disease involving the autonomic nervous system was the most predominant subject studied in our laboratory, since the early studies in the 1960s until the late studies just recently published in international journals (Central Illustration). Other pathological conditions focused on our studies were mitral valve prolapse, heart failure, post-cardiac surgery, and hyperthyroidism.