Effect of aging on carotid baroreflex control of blood pressure and leg vascular conductance in women

Abstract

Recent work suggests that β-adrenergic vasodilation offsets α-adrenergic vasoconstriction in young women, but this effect is lost after menopause. Given these age-related vascular changes, we tested the hypothesis that older women would exhibit a greater change in vascular conductance following baroreflex perturbation compared with young women. In 10 young (21 ± 1 yr) and 10 older (62 ± 2 yr) women, mean arterial pressure (MAP; Finometer), heart rate (HR), cardiac output (CO; Modelflow), total vascular conductance (TVC), and leg vascular conductance (LVC, duplex-Doppler ultrasound) were continuously measured in response to 5-s pulses of neck suction (NS; -60 Torr) and neck pressure (NP; +40 Torr) to simulate carotid hypertension and hypotension, respectively. Following NS, decreases in MAP were similar between groups; however, MAP peak response latency was slower in older women (P < 0.05). Moreover, at the time of peak MAP, increases in LVC (young, -11.5 ± 3.9%LVC vs. older, +19.1 ± 7.0%LVC; P < 0.05) and TVC were greater in older women, whereas young women exhibited larger decreases in HR and CO (young, -10 ± 3% CO vs. older, +0.8 ± 2% CO; P < 0.05). Following NP, increases in MAP were blunted (young, +14 ± 1 mmHg vs. older, +8 ± 1 mmHg; P < 0.05) in older women, whereas MAP response latencies were similar. Interestingly, decreases in LVC and TVC were similar between groups, but HR and CO (young, +7.0 ± 2% CO vs. older, -4.0 ± 2% CO; P < 0.05) responses were attenuated in older women. These findings suggest that older women have greater reliance on vascular conductance to modulate MAP via carotid baroreflex, whereas young women rely more on cardiac responsiveness. Furthermore, older women demonstrate a blunted ability to increase MAP to hypotensive stimuli.

Impaired carotid baroreflex control of arterial blood pressure in multiple sclerosis

“…For this study, we focused on the baroreceptors located in the carotid sinus due to their accessibility for noninvasive manipulation. The responsiveness of the carotid baroreflex in the short-term regulation of heart rate and blood pressure can be examined quantitatively by utilizing a variable pressure neck chamber system to selectively load (simulated hypertension via neck suction) and unload (simulated hypotension via neck pressure) the carotid baroreceptors (Credeur et al 2014;Fadel et al 2003;Ludbrook et al 1977). In all familiarization and actual experimental trials, subjects were positioned semirecumbent (ϳ45°) on a patient table.…”

“…Five-second pulses of Ϫ60 Torr neck suction (NS) and ϩ40 Torr neck pressure (NP) were applied to load and unload the carotid baroreceptors, respectively (Credeur et al 2014;Fadel et al 2003; 2010; Kim et al 2011;Ogoh et al 2002). The neck collar (Physiology Research Instruments, Austin, TX) was fitted around the anterior two-thirds of the neck with each NS and NP stimulus being delivered 50 ms after the second consecutive R-R interval that did not vary by Ͼ50 ms using customized computer-controlled software as previously described (Credeur et al 2014;Fisher et al 2007;Potts and Raven 1995). A variable pressure source using a 3-stage vacuum/blower motor (Ametek Lamb, Berwyn, PA) in combination with a computer controlled throttle valve was used to generate the changes in neck collar pressure.…”

“…Ten trials for each NS and NP were performed with a minimum of 45 s of recovery allotted between trials to allow all physiological variable to return to prestimulus values. The rationale for performing 10 trials of NS and NP was to better characterize individual carotid baroreceptor responses for all cardiovascular variables as previous utilized by Credeur et al (2014).…”

“…No subject had a history or symptoms of cardiovascular or pulmonary disease. There is compounding evidence to show that sex, age, and race influence carotid baroreceptor function (Credeur et al 2014;Fisher et al 2007Fisher et al , 2009Fisher et al , 2012Holwerda et al 2001Holwerda et al , 2013Kim et al 2011). Thus, in an effort to minimize these variables, each individual with MS was matched to a healthy control of the same sex, age, race, height, and weight.…”

Sex differences with aging in nutritive skeletal muscle blood flow: impact of exercise training, nitric oxide, and α-adrenergic-mediated mechanisms

“…These results are in line with our previous findings (24). Credeur et al (4) have recently observed no difference in femoral artery blood flow between young and postmenopausal women; however, Moreau et al (44) have previously found that femoral artery blood flow is impaired in postmenopausal women compared with young women: a finding that remained when normalizing to leg fat-free mass. Interestingly, they also investigated a group of postmenopausal women taking hormone replacement therapy (HRT).…”