Sympathetic activity increases with age. Relationship to blood flow volume and long-term smoking.

Basal venous plasma noradrenaline and muscle sympathetic nervous activity both increase with age. It has been reported that during exercise venous plasma noradrenaline increased more in elderly subjects both at the same relative as well as the same absolute work load, compared to younger subjects. Recent studies have shown that increased basal levels of plasma noradrenaline in elderly subjects were confined to elderly long-term smokers, whereas values in elderly non-smokers and young smokers were not different from values obtained in young non-smokers. At present, the pathophysiological mechanism of increased levels of basal plasma noradrenaline in long-term smokers has not been clarified, but cardiac output and total blood volume were not different in smokers and non-smokers. This may be due to a reduced sensitivity of alpha-adrenoceptors to noradrenaline or a compensatory mechanism to vascular dilatation induced by chronic smoking. Reported values of increases in plasma noradrenaline during exercise are conflicting. However, recent studies have shown that the increase in plasma noradrenaline was not different in young and elderly subjects when correcting for the generally lower physical fitness in the latter group. During exercise at relatively high work loads, plasma noradrenaline increased more in young than in elderly subjects. This may be explained by lack of a continuous increase in plasma noradrenaline during exercise in elderly subjects.