BP regulation VI: elevated sympathetic outflow with human aging: hypertensive or homeostatic?

Abstract

Though conventional wisdom suggests that a rise in blood pressure is a reality of advancing age, in fact, it appears that progressive elevation in sympathetic activity, not necessarily accompanied by increased blood pressure, is intrinsic to cardiovascular aging in humans. The mechanism behind this elevation would seem to reside in homeostatic cardiovascular regulation; nonetheless, the balance of factors that result in elevated sympathetic outflow with age remains elusive. Age-related increases in sympathetic nervous outflow cannot be fully explained by increases in body mass, body adiposity, or other metabolic factors; interrelations among cardiac output, peripheral resistance, and blood pressure may not reflect a determinative hemodynamic interrelation but rather parallel phenomena; and there is no simple linear relationship between baroreflex control and resting levels of sympathetic activity. In contrast to systemic relationships, available data suggest that elevated sympathetic outflow may derive from the inter-relationship between centrally driven sympatho-excitation and a decline in the ability of sympathetic outflow to effect peripheral vascular responses. This review aims to integrate the current knowledge of mechanisms underlying elevated sympathetic outflow with age. It seeks to synthesize these data in the context of proposing that an age-related decline in the ability of sympathetic outflow to effect regional vascular responses incites a compensatory elevation in resting sympathetic activity to maintain homeostatic balance, presumably to maintain adequate control of blood pressure.

Alterations in the Medullary Endocannabinoid System Contribute to Age-related Impairment of Baroreflex Sensitivity

“…Progressive autonomic imbalance with blunted sympathetic or parasympathetic reflex control over the heart and vasculature during normal aging is accepted as a primary contributor to elevated blood pressure during aging (17). Several factors within the brain may contribute to the development of age-related autonomic dysfunction, including the RAS (8) and the metabolic hormones insulin and leptin (18).…”

Upward resetting of the vascular sympathetic baroreflex in middle-aged male runners

“…Vascular sympathetic baroreflex "resetting" with age occurs in the absence of a change of reflex "gain" (i.e., responsiveness to acute changes in blood pressure) (11,25,26). Notably, however, it appears that a rise in arterial pressure does not necessarily follow progressive elevation in resting vascular sympathetic activity with advancing age (49). In contrast, baroreflex-mediated cardiac parasympathetic control (i.e., cardiovagal baroreflex gain) is progressively impaired with advancing age (11,32).…”

Blood pressure regulation XI: overview and future research directions

“…Taylor and Tan (Taylor and Tan 2014) raise the intriguing question as to whether the age-related increase in muscle sympathetic nerve activity is obligatory for an age-related increase in mean arterial blood pressure. The authors raise the question because not all middle-aged and older individuals that have high sympathetic activity have hypertension.…”