Changes in the arterial baroreflex arc contribute to elevated sympathetic outflow
and altered reflex control of blood pressure with human aging.
Using ultrasound and sympathetic microneurography (muscle sympathetic
nerve activity, MSNA) we investigated the relationships between
aortic and carotid artery wall tension (indices of baroreceptor
activation) and the vascular sympathetic baroreflex operating point
(OP; MSNA burst incidence) in healthy, normotensive young (n 27,
23 3 yr) and middle-aged men (n 22, 55 4 yr). In young men,
the OP was positively related to the magnitude and rate of unloading
and time spent unloaded in the aortic artery (r 0.56, 0.65, and 0.51,
P 0.02, 0.003, and 0.03), but not related to the magnitude or rate of
unloading or time spent unloaded in the carotid artery (r0.32,
0.07, and 0.06, P 0.25, 0.81, and 0.85). In contrast, in middleaged
men, the OP was not related to either the magnitude or rate of
unloading or time spent unloaded in the aortic (r 0.22, 0.21, and
0.27, P 0.41, 0.43, and 0.31) or carotid artery (r 0.06, 0.28, and
0.01; P 0.48, 0.25, and 0.98). In conclusion, in young men, aortic
unloading mechanics may play a role in determining the vascular
sympathetic baroreflex OP. In contrast, in middle-aged men, barosensory
vessel unloading mechanics do not appear to determine the
vascular sympathetic baroreflex OP and, therefore, do not contribute
to age-related arterial baroreflex resetting and increased resting
MSNA.