Impact of Bed Rest on Conduit Artery Remodeling

Abstract

Abstract-Physical inactivity is a potent stimulus for vascular remodeling, leading to a marked decrease in conduit artery diameter. However, little is known about the impact of physical inactivity on artery wall thickness or wall:lumen ratio or the potential of exercise countermeasures to modify artery wall thickness. The purpose of the study was to examine the impact of 60 days of bed rest, with or without exercise countermeasures, on carotid and superficial femoral artery wall thickness. Eighteen men were assigned to bed rest (second Berlin Bed Rest Study) and randomly allocated to control, resistive exercise, or resistive vibration exercise. Both exercise countermeasures were applied 3 times per week while the subjects were in the supine position on the bed. Sonography was used to examine baseline diameter and wall thickness of the carotid and femoral arteries. Bed rest decreased diameter of the superficial femoral artery (Pϭ0.001) but not the carotid artery (Pϭ0.29). Bed rest induced a significant increase in carotid and superficial femoral artery wall thickness (Pϭ0.007 and 0.03) and wall:lumen ratio (Pϭ0.009 and 0.001). Exercise prevented the increase in wall thickness of the carotid artery. In addition, exercise partly prevented the increased wall:lumen ratio in the superficial femoral artery. In conclusion, 8 weeks of bed rest resulted in Ϸ20% increase in conduit artery wall thickness. Exercise countermeasures completely (carotid artery) or partly (superficial femoral artery) abolished the increase in wall thickness. These findings suggest that conduit artery wall thickness, a vascular characteristic associated previously with atherosclerosis, can rapidly adapt to physical inactivity and exercise in humans. (Hypertension. 2010;56:240-246.)

WISE 2005: responses of women to sublingual nitroglycerin before and after 56 days of 6° head-down bed rest

“…It is possible that the women in the present study were not as physically active prior to HDBR as the men so there was less difference between pre-and post-HDBR values, but technical difficulties reduced the sample size to 5 so the negative findings in the women should be viewed with caution. In the present study, the EX group showed no differences in pre-and post-HDBR baseline diameter values, suggesting that the exercise countermeasures, which included treadmill running, were sufficient to maintain vascular properties, while resistance or vibration exercise in men was not sufficient to maintain femoral artery diameter (40).…”

“…Also, there were no changes in the response to sublingual NG in either the CON or the EX groups with HDBR. Previous research with men found reduction in leg artery diameter after 52 days horizontal bed rest (5) and after 60 days HDBR with or without resistance or vibration exercise countermeasures (40). It is possible that the women in the present study were not as physically active prior to HDBR as the men so there was less difference between pre-and post-HDBR values, but technical difficulties reduced the sample size to 5 so the negative findings in the women should be viewed with caution.…”

Impact of body position on central and peripheral hemodynamic contributions to movement-induced hyperemia: implications for rehabilitative medicine

“…In such populations vascular health is reduced and appears to deteriorate over time since the positive benefits of physical activity and the associated shear stress are absent (17,38). Hellsten et al (15) and Hoier et al (16) have documented that acute and chronic passive exercise training in healthy able-bodied individuals resulted in an angiogenic stimulus characterized by enhanced vascular endothelial growth factor, endothelial cell proliferation, and capillary growth.…”

Acute Change in Vascular Tone Alters Intima-Media Thickness

“…Our current data demonstrate that artery wall thickness should be regarded as a dynamic part of the vascular system that is able to change acutely and over the short term. 3 A plausible explanation for the changes in wall thickness to GTN relates to the conservation of arterial wall mass. The strong correlation of the arterial wall cross-sectional area before and after GTN supports this hypothesis.…”

“…[1][2][3][4] Conduit arterial wall thickening, particularly of the carotid artery, is regarded as a surrogate marker of the atherosclerotic process and has been used in intervention trials as a primary outcome measure. 4 -8 Noninvasive ultrasound is widely used to assess wall thickness, sometimes referred to as intima-medial thickness (IMT), which is an established independent predictor for future cardiovascular events.…”