The effect of a spinal cord injury (SCI) on vascular function has been clouded by both the physiological and mathematical bias of assessing vasodilation in arteries with differing diameters both above and below the lesion and when comparing with healthy, non-disabled controls (CTRL). Thus, we measured vascular function, with flow mediated vasodilation (FMD), in 10 SCI and 10 CTRL with all arteries matched for diameter (≈0.5cm): brachial (BA, arm, functional-limb in both groups) and popliteal artery (PA, leg, disused-limb in SCI, functional-limb in CTRL). PA %FMD was significantly attenuated in SCI (5.6±0.6%) compared to CTRL (8.4±1.3%), with no difference in the BA (SCI: 8.6±0.9%; CTRL: 8.7±0.7%). However, unlike the arm, where muscle mass was preserved, the legs of the SCI were significantly smaller than CTRL (~70%). Thus, reactive hyperemia (RH), which is heavily dependent upon the volume of muscle occluded, in the PA was attenuated in the SCI (144±22ml) compared to CTRL (258±16ml), but not different in the BA. Consequently, shear rate was significantly diminished in the PA of the SCI, such that %FMD/shear rate (vascular responsiveness) was actually greater in the SCI (1.5±0.1%・s-1) than CTRL (1.2±0.1%・s-1). Of note, this was significantly greater than both their own BA (0.9±0.1%・s-1) and that of the CTRL (0.9±0.1%・s-1). Therefore, examining vessels of similar size, this study reveals normal vascular function above the lesion and vascular dysfunction below the lesion. However, below the lesion there was, actually, evidence of increased vascular responsiveness in this population.
Spinal cord injury and vascular function: Evidence from diameter matched vessels