Effects of ageing on the cardiopulmonary receptor reflex in normotensive humans.

This study examined the effects of ageing on the cardiopulmonary receptor regulation of vasomotor tone in skeletal muscle and renin release by the kidney. To this end, the changes in forearm vascular resistance (mean arterial pressure divided by plethysmographically measured forearm blood flow), plasma noradrenaline concentration and plasma renin activity were measured in eight young (23 +/- 2 years, mean +/- s.e.m.) and seven elderly healthy subjects (69 +/- 2 years) during manoeuvres which altered cardiopulmonary receptor activity. The cardiopulmonary receptors were stimulated by increasing central venous pressure through passive leg-raising and deactivated by reducing central venous pressure through non-hypotensive (-15 mmHg) and hypotensive (-40 mmHg) levels of lower body negative pressure. During either manoeuvre, central venous pressure changed by the same amount in both groups, but the reflex changes in forearm vascular resistance, plasma noradrenaline and plasma renin activity were significantly less in elderly subjects. Since the increase in forearm vascular resistance induced by a cold pressor test was comparable in young and elderly subjects, a non-specific depression of cardiovascular responsiveness to neural stimuli can be excluded. Thus, healthy normotensive elderly subjects show an impairment of both vascular and neurohumoral influences exerted by cardiopulmonary receptors. This may be involved in the decreased ability of the elderly to cope with gravity challenges.