Vascular adaptation to deconditioning and the effect of an exercise countermeasure: results of the Berlin Bed Rest study

Abstract

Deconditioning is a risk factor for cardiovascular disease. The physiology of vascular adaptation to deconditioning has not been elucidated. The purpose of the present study was to assess the effects of bed rest deconditioning on vascular dimension and function of leg conduit arteries. In addition, the effectiveness of resistive vibration exercise as a countermeasure for vascular deconditioning during bed rest was evaluated. Sixteen healthy men were randomly assigned to bed rest (BR-Ctrl) or to bed rest with resistive vibration exercise (BR-RVE). Before and after 25 and 52 days of strict horizontal bed rest, arterial diameter, blood flow, flow-mediated dilatation (FMD), and nitroglycerin-mediated dilatation were measured by echo Doppler ultrasound. In the BR-Ctrl group, the diameter of the common femoral artery decreased by 13 +/- 3% after 25 and 17 +/- 1% after 52 days of bed rest (P < 0.001). In the BR-RVE group this decrease in diameter was significantly attenuated (5 +/- 2% after 25 days and 6 +/- 2% after 52 days, P < 0.01 vs. BR-Ctrl). Baseline blood flow did not change after bed rest in either group. After 52 days of bed rest, FMD and nitroglycerin-mediated dilatation of the superficial femoral artery were increased in both groups, possibly by increased nitric oxide sensitivity. In conclusion, bed rest deconditioning is accompanied by a reduction in the diameter of the conduit arteries and by an increased reactivity to nitric oxide. Resistive vibration exercise effectively attenuates the diameter decrease of leg conduit arteries after bed rest.

The effect of bed rest and an exercise countermeasure on leg venous function

“…This difference in diameter response suggests that the venous and arterial vascular systems are susceptible to different stimuli, when exposed to deconditioning. As arterial adaptations were ascribed to mainly regional factors due to (the lack of) physical exercise, such as changes in blood flow and (peak) shear stress to the vessel wall (Bleeker et al 2005b;Miyachi et al 2001), veins might be primarily responsive to changes in pressure or blood volume (Arbeille et al 2001). …”

“…Exercise was performed on a specific vibration system that was developed for application under microgravity and bed rest conditions (Galileo Space, Novotec, Pforzheim, Germany). The used equipment and the countermeasure exercise are previously described in detail (Bleeker et al 2005b). In short, the training device consisted of a vibration platform, which was vertically suspended on a trolley.…”

“…In both studies, the absence of exercise effect on vein response to bed rest might be ascribed to the lack of muscle mass directly surrounding the vein. On the contrary, resistive vibration exercise was previously shown to be an effective countermeasure against deterioration of the arterial dimension (Bleeker et al 2005b), muscle mass and muscle function (Akima et al 2003;Mulder et al 2006), and tendon function (Kubo et al 2004). Resistive vibration exercise is also known to increase heart rate and oxygen uptake (Rittweger et al 2000) and blood flow (Kerschan-Schindl et al 2001).…”

“…Both venous capacitance and compliance are major determinants in the vital functions of the venous system, and a numerous amount of studies have been performed to specify their role in orthostatic intolerance after bed rest and space flight in humans. To study the effect of physical deconditioning on the venous vascular system, several human deconditioning models have been used, such as leg immobilisation (Bleeker et al 2005a), space flight (Arbeille et al 2001;Fomina and Kotovskaia 2005;Watenpaugh et al 2001), bed rest (Arbeille et al 1999(Arbeille et al , 2001Belin de Chantemele et al 2004;Bleeker et al 2005b;Bonde-Petersen et al 1994;Buckey et al 1992;Christ et al 2001;Convertino et al 1989;Louisy et al 1997;Melchior and Fortney 1993;Xiao et al 2005) and spinal-cord injury (Frieden et al 1987;Hopman et al 1994;Wecht et al 2000). Sparse data on venous diameter show a reduction in cross-sectional area of femoral venous diameter after bed rest (Arbeille et al 1999(Arbeille et al , 2001), but no change in tibial and gastrocnemial venous diameter (Belin de Chantemele et al 2004).…”

“…Applied during bed rest, training in the modality of resistive vibration exercise has been shown to attenuate the reduction in arterial vascular dimension and function (Bleeker et al 2005b). However, an efficient countermeasure effect of this physical exercise during deconditioning on the venous vascular system is not demonstrated yet.…”