Age-Associated Differences in Central Artery Responsiveness to Sympathoexcitatory Stimuli.

BACKGROUND: Age-associated arterial stiffening may be the result of greater tonic sympathetic nerve activity. However, age-associated changes in central artery responsiveness to sympathoexcitatory stimuli are understudied. Therefore, we examined changes in central-artery stiffness and wave reflection in response to sympathoexcitatory stimuli in young and older adults.

METHODS: Fourteen young (25±4yrs) and 15 older (68±4yrs) subjects completed 3min of the cold pressor test (CPT) and lower-body negative pressure (LBNP) separated by 15min. Carotid-femoral pulse wave velocity (cfPWV), central augmentation pressure (cAP), and augmentation index (AIx) were measured in duplicate during rest and the final minute of each perturbation.

RESULTS: Young subjects had lower baseline cfPWV, cAP, and AIx compared to older subjects (p<0.05 for all). During the CPT MAP, cfPWV, cAP, and AIx increased in both groups (p<0.05 for all); however, changes (Δ) in mean arterial pressure (MAP, 18±7 vs. 9±5mmHg), cfPWV (1.3±0.7 vs. 0.6±0.9m·sec-1), cAP (4±2 vs. 6±3mmHg), and AIx (18±9 vs. 7±4%) were greater in young versus older subjects, respectively (p<0.05 for all). With MAP as a covariate, cfPWV, cAP, and AIx responses to the CPT were no longer significantly different between groups. During LBNP, changes in MAP (-1±3 vs. -3±5mmHg), cfPWV (0.5±0.3 vs. 0.5±0.7 m·sec-1), cAP (-2±2 vs. -2±3mmHg), and AIx (-7±7 vs. -3±6%) were similar between young and older groups, respectively (p>0.05 for all).

CONCLUSIONS: Collectively, our data suggest the sympathetic nervous system may directly modulate central hemodynamics and that age-associated differences in central artery responsiveness to sympathoexcitatory stimuli are largely attributable to differential blood pressure responses.