Decreased cardiopulmonary reflexes with aging in normotensive humans.

Arterial baroreflex is impaired in the normotensive elderly. However, no information is available on the effects of aging on another major reflex mechanism of cardiovascular control, i.e., cardiopulmonary reflex. Three groups of normotensive subjects divided according to age were evaluated during leg raising, which increased central venous pressure, and during lower body negative pressures, which reduced central venous pressure without altering blood pressure and heart rate. These maneuvers stimulated and deactivated cardiopulmonary receptors with only little involvement of arterial baroreceptors. During lower body negative pressures, central venous pressure decreased similarly in three groups, but reflex increases in forearm vascular resistance, plasma norepinephrine, and plasma renin activity were smaller in elderly than in middle-aged and young subjects. Furthermore, during leg raising, comparable increases in central venous pressure caused reflex vascular and humoral responses that were smaller in elderly than in middle-aged and young subjects. Elderly subjects had smaller changes in left ventricular diameter in response to changes in central venous pressure. Blood pressure and vascular responses to cold pressor test were similar in the three groups, excluding a hyporeactivity of older subjects to neural stimuli. Thus aging is associated with an impairment of the cardiopulmonary reflex. This may originate from an impaired ability of cardiac receptors to sense alterations in central blood volume because of an age-dependent reduction in cardiac compliance.