Parasympathetic cardiovascular control in human disease: a critical review of methods and results

A variety of experimental approaches have been used to alter reflex parasympathetic cardiovascular control in normal human subjects and in patients with cardiovascular diseases. This review critically appraises several of these methods (the Valsalva maneuver, upright tilt, lower body negative pressure, pressor drug infusion, neck suction, and coronary arteriography) and summarizes the normal response patterns of healthy subjects and the abnormal response patterns of some patients with cardiovascular disease. Tests of parasympathetic function tend to be heterogeneous; they are not standardized, and, therefore, valid comparisons between results from different studies may be difficult to make. Moreover, although most of these tests are simple to perform, they may provoke surprisingly complex alterations of afferent and efferent autonomic activity. Notwithstanding these methodological difficulties, the research area of human parasympathetic cardiovascular control may have great importance, because parasympathetic reflex mechanisms are involved in diseases of major public health significance for which animal models may be imperfect or nonexistent.