<p> Physical inactivity or deconditioning has been shown to be an independent risk factor for
cardiovascular disease. Contrary to the previously demonstrated effects of exercise training on the cardiovascular system, the vascular adaptations that occur with a deconditioned state have not been adequately characterized within a young, healthy population. Thus, it was the interest of the present study to examine vascular adaptations to 12 days of unilateral lower limb immobilization (ULI) in young, healthy humans. Previous studies have used other models to mimic a deconditioned state such as paraplegia, simulated micro gravity and bed rest; however, such models are also associated with factors that are not physiologically applicable to normal deconditioning in the able-bodied population. Fifteen young, healthy participants [age: 20.6±0.51 (mean ± SEM)] participated in the 12-day knee-braced immobilization period that consisted of PRE and 12-DAY time point testing sessions. Measurements of supine common carotid, popliteal and common femoral artery cross sectional compliance as well as popliteal artery endothelial function (using flow mediated vasodilation (FMD)) were acquired prior to the 12-day immobilization (PRE) and on the 12th day of the immobilization (12-DAY).
Arterial characteristics of the Immobilized legs (IMM) and NON-Immobilized (NIM) legs were assessed by echo Doppler ultrasound and applanation tonometry.</p> <p> Resting carotid artery cross sectional compliance and blood flow showed no change throughout the 12-day time period, (Compliance: PRE = 0.001209 ± 0.000067 mm^2/mmHg, 12-DAY= 0.001230 ± 0.00085 mm^2/mmHg; Blood Flow: PRE = 242.8±14.2 mL/min, 12-DAY = 226.0±14.27 mL/min). Popliteal artery cross sectional compliance decreased significantly over the 12 day time period in both legs (p<0.05) (IMM PRE = 5.7±0.4 10^-4mm^2/mmHg, IMM 12-DAY = 3.8±0.4 10^-4mm^2/mmHg; NIM PRE= 6.7±0.9 10^-4mm^2/mmHg, NIM 12-DAY = 5.5±0.6 10^-4mm^2/mmHg). Common femoral artery cross sectional compliance decreased in the immobilized leg but not in the non-immobilized leg (p<0.05) over 12 days of immobilization (PRE= 1.2±0.1 10^-4mm^2 /mmHg, 12-DA Y =: 0. 79±0.1 10^-4mm^2/mmHg). Neither popliteal nor common femoral artery mean blood flow changed throughout the 12 days of immobilization. Popliteal arterial mean diameter decreased significantly over time in both the IMM and NIM legs showing greater decreases in the IMM leg, while common femoral arterial mean diameter decreased in both the IMM and NIM legs through the 12 days (Popliteal: IMM PRE = 0.57±0.02 cm, IMM 12-DAY = 0.50±0.02 cm; NIM PRE = 0.59±0.02 cm, NIM 12-DAY = 0.55±0.02 cm; Common Femoral IMM PRE = 0.83±0.04 cm, IMM 12-DAY = 0.77±0.03 cm; NIM PRE = 0.81±0.03 cm, NIM 12-DAY = 0.77±0.03 cm).
Popliteal artery endothelial function, calculated as both relative FMD and FMD normalized to shear stress, increased (p<0.05) throughout the 12 days in the immobilized leg while showing no change in the non-immobilized leg (Relative FMD: IMM PRE 6.0 ± 1.4%, IMM 12-DAY = 12.6 ± 2.7%; NIM PRE = 5.8 ± 1.4%, NIM 12-DAY = 8.3 ± 1.6 %; Normalized FMD: IMM PRE = 0.023 ± 0.007%/^sec-1, IMM 12-DAY = 0.037 ± 0.008%/^sec-1; NIM PRE = 0.016 ± 0.003%/^sec-1, NIM 12-DAY = 0.022 ± 0.004%/^sec-1).</p> <p> In conclusion, 12 days of deconditioning by ULI was able to cause structural and functional changes in the arteries of the immobilized leg, but not the central elastic artery in the neck in healthy young humans. Specifically in the legs, a decrease in arterial compliance, increases in mean blood velocity and increases in endothelial function were noted, with no change in volumetric blood flow. Surprisingly, our results suggest, with regards to endothelial function, that the vascular effects of deconditioning are not simply the inverse of exercise training which also shows increases in endothelial function. Thus the present study concludes that there exists a very short time course to arterial adaptations in healthy young humans with significant changes within the vasculature occurring within 12 days of deconditioning.</p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/21680 |
| Date | 08 1900 |
| Creators | Crozier, Jennifer L. |
| Contributors | MacDonald, Maureen J., Human Biodynamics |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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