Introduction/purpose: During exercise, redistribution of blood takes place to enhance blood flow to exercising muscles. To examine the role of sympathetic control in blood redistribution, we assessed blood flow in inactive regions (leg-splanchnic area) during arm-crank exercise in controls and in subjects with spinal cord injury (SCI) who lack central sympathetic control.
Methods: SCI with a low lesion (≤T7; SCI-L) have no leg sympathetic control and SCI with high lesion (≥T6; SCI-H) lack sympathetic control in the legs and splanchnic area. This enables us to compare inactive regions between subjects with (controls, SCI-L; splanchnic) and without sympathetic innervation (SCI-L: leg, SCI-H: leg-splanchnic). Before and every 5 min during a 25-min arm-crank exercise bout at 50% of the individual maximal capacity, portal vein and femoral artery blood flow were measured.
Results: Before exercise, portal vein blood flow was not different among groups. Arm-crank exercise induced a significant decrease in portal vein blood flow in subjects with splanchnic sympathetic control (able-bodied controls + SCI-L; ANOVA, P < 0.05), whereas SCI-H showed no change in portal vein blood flow. Baseline femoral artery blood was significantly lower in SCI compared with able-bodied controls. Exercise increased femoral artery blood flow in subjects with leg sympathetic control (controls; ANOVA, P < 0.05) but not in persons lacking sympathetic control in the leg (SCI). Leg vascular conductance did not change during exercise in both groups.
Conclusions: In summary, portal vein blood flow decreases in subjects with sympathetic control of the splanchnic area, whereas exercise-induced changes in femoral artery hemodynamics did not differ between groups. These observations primarily indicate the presence of regional differences regarding the magnitude of exercise-induced blood redistribution in vivo in humans.