Elevated Muscle Sympathetic Nerve Activity Contributes to Central Artery Stiffness in Young and Middle-Age/Older Adults

Muscle sympathetic nerve activity (MSNA) influences the mechanical properties (ie, vascular smooth muscle tone and stiffness) of peripheral arteries, but it remains controversial whether MSNA contributes to stiffness of central arteries, such as the aorta and carotids. We examined whether elevated MSNA (age-related) would be independently associated with greater stiffness of central (carotid-femoral pulse wave velocity [PWV]) and peripheral (carotid-brachial PWV) arteries, in addition to lower carotid compliance coefficient, in healthy men and women (n=88, age: 19-73 years, 52% men). We also examined whether acute elevations in MSNA without increases in mean arterial pressure using graded levels of lower body negative pressure would augment central and peripheral artery stiffness in young (n=15, 60% men) and middle-age/older (MA/O, n=14, 43% men) adults. Resting MSNA burst frequency (bursts center dot min(-1)) was significantly correlated with carotid-femoral PWV (R=0.44, P<0.001), carotid-brachial PWV (R=0.32, P=0.004), and carotid compliance coefficient (R=0.28, P=0.01) after controlling for sex, mean arterial pressure, heart rate, and waist-to-hip ratio (central obesity), but these correlations were abolished after further controlling for age (all P>0.05). In young and MA/O adults, MSNA was elevated during lower body negative pressure (P<0.001) and produced significant increases in carotid-femoral PWV (young:Delta+1.3 +/- 0.3 versus MA/O: Delta + 1.0 +/- 0.3 m center dot s(-1), P=0.53) and carotid-brachial PWV (young:Delta+0.7 +/- 0.3 versus MA/O:Delta+0.7 +/- 0.5 m center dot s(-1), P=0.92), whereas carotid compliance coefficient during lower body negative pressure was significantly reduced in young but not MA/O (young:Delta-0.04 +/- 0.01 versus MA/O:Delta 0.001 +/- 0.008 mm(2)center dot mm Hg-1, P<0.01). Collectively, these data demonstrate the influence of MSNA on central artery stiffness and its potential contribution to age-related increases in stiffness of both peripheral and central arteries.