A controlled study of the effects of mental relaxation on autonomic excitatory responses in healthy subjects.

Circumstantial evidence indicates that, in the presence of a suitable substratum, sudden, behaviorally induced increases in sympathetic drive to the cardiovascular system might play an important physiopathological role in various conditions, ranging from arterial hypertension to sudden coronary death. Accordingly, it might be useful to study the effects of behavioral interventions, such as mental relaxation, that might be capable of blunting excitatory autonomic responses. It would also be preferable to study healthy subjects in whom autonomic control is not modified by the presence of disease, and to use noninvasive approaches to minimize the possible emotional impact produced by invasive recordings. We examined healthy subjects who were either subjected to relaxation training (N = 13) or sham relaxation (N = 12). An additional group, treated with beta-adrenergic blockade (N = 12), was also examined. Spectral and cross-spectral analysis of RR interval and systolic arterial pressure (SAP) variabilities provided quantitative markers of sympathovagal balance modulating the sinoatrial (SA) node, of sympathetic vasomotor modulation, and of the gain of the arterial pressure/heart period baroreflex (index alpha). Subjects were studied at rest, during standing, and during mental arithmetic. Data indicate that both beta-adrenergic blockade and relaxation training significantly blunted the excitatory autonomic responses to standing and to mental arithmetic. Indices of sympathetic modulation also seemed reduced by beta blockade at rest. No changes were observed with sham training. Frequency domain analysis of cardiovascular variabilities, using a totally noninvasive approach, indicates that relaxation training significantly blunts the excitatory autonomic changes produced by standardized behavioral laboratory stimuli.