The sympathetic nervous system in human hypertension.

While animal models of hypertension have clearly shown an increase in sympathetic activity, a similar demonstration in humans has been more difficult to obtain for methodological reasons. There is now clear evidence, however, of an increase sympathetic activity in essential hypertension by the finding of either an increase in plasma norepinephrine and an increase in muscle sympathetic nerve traffic. Among the mechanisms responsible for this sympathetic activation the arterial baroreflex may play a role although probably a non specific and late one. Central neural influences associated with an excessive hypothalamic response to stress may also be involved, but conclusive evidence is still lacking due to the difficulty of assessing cardiovascular reactivity to stress in man. A deeper insight into the features of human sympathetic cardiovascular control may be offered now by new techniques which allow neural cardiovascular regulation to be assessed in daily life through computer analysis of noninvasive ambulatory beat-by-beat blood pressure and heart rate recordings.