The Role of Obesity on Neurovascular Responses to Exercise
thesisposted on 01.11.2017 by Kanokwan Bunsawat
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The prevalence of obesity increases drastically in the U.S., with more than a third of the adults being obese. Obesity is an important cardiovascular risk factor that may be associated with increased vasoconstriction and decreased vasodilation. Exercise is a lifestyle strategy recommended to combat obesity, yet obese individuals often exhibit reduced exercise tolerance and exaggerated cardiovascular responses that may not subside during the recovery period following acute exercise. Impaired functional sympatholysis may be a possible mechanism contributing to exercise intolerance in obesity due to impaired ability to blunt sympathetic vasoconstriction during exercise, resulting in malperfusion. Following exercise, obese individuals may not exhibit reductions in blood pressure (BP) during the recovery period, likely due to sustained vasoconstriction and reduced vasodilation. We tested the hypotheses that young obese individuals would exhibit impaired functional sympatholysis (study 1) and post-exercise hypotension (study 2) compared with age-matched lean individuals. In study 1, we monitored forearm blood flow (FBF) and forearm vascular conductance (FVC) responses to reflex increases in sympathetic vasoconstriction evoked by lower body negative pressure (LBNP) at rest and during handgrip exercise at low and moderate intensities. We found that LBNP evoked decreases in FBF and FVC at rest, but these responses were blunted during exercise in an intensity-dependent manner similarly in both groups. In study 2, we monitored BP (both brachial and central), leg blood flow (LBF), and leg vascular conductance (LVC) before and every 30 min until 90 min after a 60-min moderate intensity cycling exercise. We observed a lack of reductions in brachial BP in both groups, but both groups exhibited similar reductions in central BP (central systolic and mean arterial BP) below baseline values throughout exercise recovery, coupled with similar increases in LBF and LVC. Our findings suggested that young, otherwise healthy obese individuals may have preserved functional sympatholysis and may benefit from moderate-intensity aerobic exercise in terms of central BP reductions post-exercise.