The importance of the autonomic nervous system in health and disease.

Baroreceptor control of the circulation is now generally thought to be concerned only with short term buffering of changes in arterial pressure, rather than with long term setting of pressure levels. This paper reviews evidence to the contrary, which suggests that impairment of the baroreflex, either by local changes in the carotid sinus or by environmental or genetic influences working through cortical modulation of the reflex gain, may have an important influence on long term arterial pressure. Further interest in the baroreflex has been revived by the demonstration in several large studies that autonomic control, measured either by baroreflex sensitivity (BRS) or heart rate variability (HRV), is a powerful independent prognostic factor, which adds to other clinical measures of risk stratification in patients with left ventricular damage, or who have survived a myocardial infarction. The inter-relationships are complex, poorly understood, and subject to many confounding factors. Nevertheless, BRS and HRV are promising techniques. Further understanding holds out the hope of new therapeutic approaches to these patients.