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Objectives: In this study, we evaluate changes in blood flow in individuals with spinal cord injury (SCI) participating in arm crank exercise alone or in conjunction with lower extremity functional electric stimulation (FES). Our objectives were to assess the distribution of upper and lower limb blood flow both before and after maximal exercise and to determine whether the hemodynamic response was enhanced by the addition of lower extremity FES.
Clinical Relevance: The adaptive capacity of the arterial system is compromised in individuals with SCI. Hypokinesis in the lower extremities results from blood pooling secondary to a lack of sympathetic tone and diminished or absent venous "muscle pump." This puts individuals with SCI at risk for blood clots, increased fatigueability, and decreased cardiovascular fitness. If hybrid exercise can be demonstrated to increase blood flow, this will have important implications for improved cardiovascular health and aerobic potential. The current pilot study has only evaluated the influence on blood flow of an acute bout of exercise. Future studies will evaluate whether an exercise training program can improve hemodynamic function in individuals with SCI.
Methods: Arterial diameter and flow velocity were measured by duplex doppler ultrasonography in seven male subjects with SCI. Subjects were characterized by level of injury (3 tetraplegic and 4 paraplegic) and habitual activity (5 active and 2 sedentary). Hemodynamic measures were taken in the subclavian and femoral arteries at rest and immediately after a session of maximal exertion exercise in one of three exercise protocols. The exercise protocols included: 1) arm crank exercise alone (ACE); 2) arm cranking combined with FES applied simultaneously to opposing muscle groups of the lower limbs to create isometric co-contractions (Static Hybrid); and 3) arm cranking combined with FES applied to leg muscles to produce cycling (Dynamic Hybrid).
Results: Upper extremity arterial diameter increased by 12% (from 7.35 to 8.24 mm) and upper extremity blood flow increased nearly 4-fold (from 336.3 to 1299.3 ml/min) after maximal exercise. No change was observed with exercise in either arterial diameter or blood flow in the lower extremity. The change in upper limb blood flow was much greater in paraplegic than tetraplegic subjects, as expected. The difference in upper limb arterial diameter was detectable only in paraplegic but not tetraplegic subjects. There appeared to be a greater effect on upper extremity blood flow in active compared with sedentary subjects although this was not significant due to a high variance. While there was a trend toward greater upper limb blood flow increment in the dynamic hybrid protocol, there were no significant differences in hemodynamic response among exercise protocols.
Conclusions: Arm cranking exercise elicits an increase in upper extremity blood flow in both paraplegic and tetraplegic individuals, but upper extremity arterial diameter is only increased in paraplegic individuals. We were unable to discern a statistically significant benefit attributable to the addition of FES although the dynamic hybrid protocol appeared to elicit a greater blood flow response. No effect was observed in the lower limb with exercise.
Acknowledgments: VA Rehabilitation R & D Merit Review Grant #B2110-RA.