Title

The effects of exercise training on venous function in humans with hypertension

Date of Award

2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Exercise Science

Advisor(s)

Jill A. Kanaley

Keywords

Exercise training, Venous function, Hypertension, Baroreflexes

Subject Categories

Exercise Physiology

Abstract

The purposes of these studies were to: (1) examine the effects of baroreflex-mediated compared to non-baroreflex mediated increases in sympathetic nervous system activity on calf venous compliance in subjects with prehypertension and stage-1 hypertension (high blood pressure group, HBP) compared to subjects with normal blood pressure (NT), (2) determine the effects of aerobic exercise training on calf and forearm venous compliance in HBP compared to NT group, and (3) examine the effects of aerobic exercise training on baroreflex-mediated modulation of venous compliance in HBP individuals. To address the first purpose, calf venous compliance was measured in 20 subjects with high blood pressure (HBP, age: 46 ± 1 yr) and 13 normotensive controls (NT, age: 44 ± 2 yr) at baseline, during lower body negative pressure (LBNP), and during post-handgrip exercise ischemia (HGI). To address the second purpose, both NT and HBP groups underwent a 4-wk cycling exercise training program (4d/wk, 30-45 min per session, 65% heart rate reserve) and calf and forearm venous compliance were measured before and after training. To address the third purpose, calf venous compliance was measured at baseline, during LBNP and during lower body positive pressure (LBPP) in the HBP group before and after the exercise training. A 4-wk control (non-exercising) period preceded the exercise training program. Changes in calf and forearm volume were measured via a deflation protocol using venous occlusion plethysmography, at baseline and during each task (LBNP, LBPP, HGI). Venous compliance was assessed from the pressure-volume and pressure-compliance curves that were generated from the collecting-cuff pressures and changes in volume during the deflation period of the protocol. Baseline calf and forearm venous compliance were not different between groups ( p >0.05). The NT group but not the HBP group showed a significant reduction in venous compliance during LBNP ( p <0.05). Venous compliance did not respond to HGI in any of the groups ( p >0.05). Exercise training reduced systolic blood pressure from 130 ± 1 mm Hg to 123 ± 2 mm Hg ( p <0.05) and diastolic blood pressure from 91 ± 1 mm Hg to 87 ± 1 mm Hg ( p <0.05) in the HBP group, and improved cardiovascular fitness in the HBP and NT groups ( p <0.05). Exercise training affected neither baseline calf nor baseline forearm venous compliance in any of the groups ( p >0.05). Application of LBPP but not LBNP reduced venous compliance in the HBP group but this response was not altered with training (p>0.05). In conclusion, venous compliance was reduced in response to baroreceptor loading (LBPP), but did not change in response to baroreceptor unloading (LBNP) and metaboreflex activation (HGI) in a cohort of subjects with prehypertension and stage-1 hypertension. Four wks of aerobic exercise training at moderate intensity reduced blood pressure and improved cardiovascular fitness but did not affect either baseline venous compliance or baroreflex-mediated modulation of venous compliance in this population. These findings indicate that short-term exercise training does not induce adaptations in sympathetic modulation of venous compliance in prehypertensive and stage-1 hypertensive individuals.

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