Shear stress levels in paralyzed legs of spinal cord-injured individuals with and without nerve degeneration

Abstract

The purpose of this study was to assess the relationship between inactivity and shear stress, the frictional force of blood against the endothelium, in spinal cord injury (SCI) subjects. SCI group offers a unique "model of nature" to study the effects of inactivity. Nine SCI subjects with upper (SCI-U) and 5 with a lower (SCI-L) motoneuron lesion and 10 able-bodied controls (C) were included. A venous blood sample was withdrawn to determine blood viscosity. Red blood cell velocities and arterial diameters of the common carotid artery (CCA) and common femoral artery (CFA) were measured by using echo-Doppler ultrasound in a supine position. No differences were observed in wall shear stress in the CCA between groups. In the CFA, peak and mean wall shear stress were significantly increased in SCI (14.1 and 1.2 Pa, respectively) compared with C (10.2 and 0.9 Pa, respectively). Because SCI-U and SCI-L showed no differences in shear stress levels, inactivity and not nerve degeneration seems to cause the elevated shear stress levels in the CFA in SCI. However, the lack of central neural control as a causal factor cannot be ruled out.

Peripheral vascular function in spinal cord injury: a systematic review

“…However, shear stress and shear rate in the common femoral artery in individuals with SCI are Peripheral vascular function in spinal cord injury CR West et al 50-100% greater than in AB individuals. 51,53,54 The almost doubled shear rate appears to be a consequence of the inactivity rather than loss of supraspinal sympathetic control, as both tetraplegics (decreased sympathetic tone to a nearly all of the vasculature) and low paraplegics (decreased sympathetic tone to approximately half of the vasculature) demonstrate similar increases in shear stress compared with AB controls. 51 It should be noted that shear stress is inversely proportional to arterial diameter cubed at constant flow and viscosity.…”

“…54,55 Compared with the inactive lower limbs, the active upper limb vasculature is relatively well preserved. For example, the diameters of the common carotid artery 51,53 and brachial artery 50 are similar between SCI and AB. Thus, it appears the structural adaptations below the injury are primarily an adaptation to the reduced metabolic demands of the lower limb vasculature.…”

“…Acute alterations are mediated primarily by changes in sympathetic activity to the smooth muscle, whereas chronic changes are mediated primarily by changes in blood flow and pressure, which alters shear stress and consequently the number of smooth muscle cells in vessel walls. 48 Remodeling of peripheral arteries in paralyzed limbs occurs soon after SCI; within weeks there is a significant reduction in systemic blood volume 49 and a consequent inward remodeling of the arterial wall, 50 such that the diameter of the common femoral artery is 30-50% smaller [51][52][53][54] and resting blood flow in the leg is 30-40% lower than in AB individuals. 54,55 Compared with the inactive lower limbs, the active upper limb vasculature is relatively well preserved.…”

Physiological effects of lower extremity functional electrical stimulation in early spinal cord injury: lack of efficacy to prevent bone loss

“…Although this apparent lack of therapeutic efficacy may be explained by Type 2 error or protocol inadequacies, the discrepancy between the postulated and observed response to exercise may also be attributed to overlapping behavioural, physical, endocrine [35][36][37]51 or physiological effects [52][53][54] relative to acute/subacute or rehabilitation/recovery phases. Further study is warranted to explore the mechanisms underlying the low therapeutic efficacy of FES to promote clinically relevant bone remodelling in the present study.…”

Rapid and Extensive Arterial Adaptations After Spinal Cord Injury

“…31 The present study shows that already within 3 to 6 weeks postinjury, basal shear rate levels are doubled in the conduit arteries of the inactive and denervated legs of patients with SCI (see fig 6B), which is in agreement with findings in chronic SCI. 6,7,32 FMD is a measure of NO production in response to shear stress stimulus. Absolute and relative FMD responses increased significantly during the first 6 weeks of extreme inactivity, with most changes evident at 3 weeks postinjury.…”