Preserved flow-mediated dilation in the inactive legs of spinal cord-injured individuals

Abstract

.-The aim of the study was to assess endothelial function, measured by flow-mediated dilation (FMD), in an inactive extremity (leg) and chronically active extremity (arm) within one subject. Eleven male spinal cord-injured (SCI) individuals and eleven male controls (C) were included. Echo Doppler measurements were performed to measure FMD responses after 10 and 5 min of arterial occlusion of the leg (superficial femoral artery, SFA) and the arm (brachial artery, BA), respectively. A nitroglycerine spray was administered to determine the endothelium independent vasodilatation in the SFA. In the SFA, relative changes in FMD were significantly enhanced in SCI compared with C (SCI: 14.1 Ϯ 1.3%; C: 9.2 Ϯ 2.3%), whereas no differences were found in the BA (SCI: 12.5 Ϯ 2.9%; C: 14.2 Ϯ 3.3%). Because the FMD response is directly proportional to the magnitude of the stimulus, the FMD response was also expressed relative to the shear rate. No differences between the groups were found for the FMD-to-shear rate ratio in the SFA (SCI:0.061 Ϯ 0.023%/s Ϫ1 ; C: 0.049 Ϯ 0.024%/s Ϫ1 ), whereas the FMD-to-shear rate ratio was significantly decreased in the BA of SCI individuals (SCI: 0.037 Ϯ 0.01%/s Ϫ1 ; C: 0.061 Ϯ 0.027%/s Ϫ1 ). The relative dilatory response to nitroglycerine did not differ between the groups. (SCI: 15.6 Ϯ 2.0%; C: 13.4 Ϯ 2.3%). In conclusion, our results indicate that SCI individuals have a preserved endothelial function in the inactive legs and possibly an attenuated endothelial function in the active arms compared with controls. vascular endothelial function; deconditioning; ultrasound THE ENDOTHELIUM plays an essential role in vascular homeostasis and is able to respond to physical and chemical stimuli by the synthesis and release of vasoactive, thromboregulatory, and growth factor substances (37). Impaired endothelial function has been suggested as a key early event in the development of atherosclerosis, and a high correlation between endothelial dysfunction and risk factors for cardiovascular diseases, including hypertension, hypercholesterolemia, cigarette smoking, diabetes, and aging, has been reported (6 -8, 12, 29, 33, 47, 48). Besides the above-mentioned traditional risk factors, it is well known that physical inactivity is associated with an increased risk of developing cardiovascular diseases (32). However, at present, the relationship between inactivity and endothelial dysfunction is not clear. In individuals with paraplegia, the part of the body below the lesion level is paralyzed and thus extremely inactive (20,39). In contrast, the upper limbs are often relatively active because the arms are used for ambulation due to their wheelchair-bound life-style (43). A spinal cord injury (SCI), therefore, offers a unique "human model of nature" to assess peripheral vascular adaptations to inactivity (legs) and activity (arms) on endothelial function within one subject.Healthy vessels are capable of accommodating to an increase in blood flow by dilating the internal vessel diameter, a phenomenon called fl...

Peripheral vascular function in spinal cord injury: a systematic review

“…79,80 In the only study to investigate resistance artery remodeling in SCI, individuals with chronic SCI exhibited a 40-60% reduction in SFA-reactive hyperemia compared with AB individuals. 67 This far exceeds values that occur in healthy AB individuals who undergo acute 81 or chronic 82 bed rest. Remodeling of resistance arteries appears to be at least partly attributable to general muscle atrophy, as lower-limb-reactive hyperemia corrected per unit muscle volume is similar between SCI and AB.…”

“…61 In the only study to investigate brachial artery FMD, it was reported that absolute brachial artery FMD is not different between SCI and AB individuals, whereas brachial artery FMD expressed relative to the shear rate stimulus (in this case the change in shear rate ratio from rest to peak hyperemic response) was reduced in SCI compared with AB. 67 Enhanced or preserved FMD below the lesion and a reduction in FMD above the lesion appears counterintuitive given the known positive relationship between the degree of physical activity and FMD in AB. [70][71][72] Such differences in FMD above and below the lesion may be attributed to the structural adaptations that occur following SCI.…”

“…In individuals with SCI, FMD has been examined in the superficial femoral artery (SFA), 62,66,67 the posterior tibial artery, 68 brachial artery 67 and the radial artery. 68 In the SFA, individuals with SCI exhibit an increased absolute FMD compared with AB individuals; 69 however, this difference is no longer present when the degree of FMD is corrected for area under the shear rate curve, from the time of occluding cuff deflation to that of peak diameter attainment.…”

The effects of functional electrical stimulation leg cycle ergometry training on arterial compliance in individuals with spinal cord injury

“…Thus it is somewhat counterintuitive to have research show that with deconditioning flowmediated dilatation (FMD), a method of noninvasively assessing endothelial health, is actually increased in the legs of individuals with SCI and decreases to normal levels with training. 14,18 It has been suggested that this results from increased shear stress, a strong stimulator of NO release, in the leg vasculature of individuals with SCI, 18 which may increase endothelial nitric oxide synthase (eNOS). With larger arterial diameters following FES-LCE training, 19 shear stress is reduced which may decrease eNOS and FMD while concurrently increasing arterial compliance.…”

Rapid and Extensive Arterial Adaptations After Spinal Cord Injury

“…[3][4][5] In humans with longstanding SCI, extensive adaptations occur in the peripheral circulation such as a 30% decrease in diameter, a reduction in blood flow, and an almost doubling of stress levels in the femoral artery. 1,[6][7][8] Results on vascular changes derived from other models of deconditioning like bedrest studies [9][10][11] conflict with some studies showing a decrease in leg blood flow and others showing no changes after a period of bedrest varying from 10 to 41 days. However, none of these studies provides information related to changes in diameter size, and the magnitude of physical inactivity during bedrest may vary, because movements of the legs are still possible.…”