Proximal feed artery regulation of skeletal muscle blood flow during exercise : the paraplegic model

[摘要] ENGLISH ABSTRACT:The mechanisms of blood flow (BF) control to skeletal muscle during dynamicexercise are still not clearly understood. The paraplegic subject (P) has reducedsympathetic innervation to the lower limbs. The current study was designed to focuson the contribution of neural control, specifically the sympathetic nervous system(SNS), as part of the central vascular mechanism to skeletal muscle BF duringdynamic exercise. Aims: We studied BF parameters in P vs. able-bodied subjects(AB) to determine whether the paraplegic can serve as a model for assessing thecontribution of the SNS to changes in active vs. inactive muscle BF during exercise.Further questions addressed include: the influence of level of fitness on resting andexercise BF, how lesion level affects BF control in the paraplegic, the 'muscle pump'theory and its hypothesized role in exercise hyperemia and whether blood poolingoccurs in the legs of paraplegics. Method: Noninvasive duplex Doppler studies of thelarge conduit arteries (brachial and common femoral) were performed on 10 eliteparaplegic athletes (EP), 10 sedentary paraplegics (SP) en 10 sedentary able-bodiedsubjects (AB). The paraplegic groups were further subdivided by lesion level with T6being the critical level. Tests were carried out at rest and after 2 bouts of armergometer exercise: a maximal incremental test and 3 minutes at 75% of maximal.Diameter, mean velocity, pulsatile index and blood flow were measured/calculated.Results: Resting heart rate was significantly higher in the paraplegic groups (EP = 80bpm ± 10, SP = 83 bpm ± 12) vs. the AB group (69 bpm ± 7), p < 0.05. Restingdiameter in the common femoral artery (CFA) was similar in EP (5.93 mm ± 1.54)and SP (6.52 mm ± 0.95), but significantly lower than in AB (7.87 mm ± 1.38), p <0.05. Similar resting pulsatile index (PI) in the CFA were contrary to that previouslyreported, casting doubt on venous blood pooling theories. Post-exercise values need tobe interpreted with caution in view of the large resting differences in CFA diameter.Percentage change values are therefore more appropriate. These differences were notstatistically significant, but may suggest interesting trends. Large variability existedfor most resting and post-exercise values. Conclusion: The paraplegic subject is anideal model for the study of the influence of the SNS on blood supply to exercisingskeletal muscle. The difference in CFA diameter at rest in the paraplegic vs. the ABgroup confirms previous results and is probably due to structural/non-physiologicalchanges. Our observation that the BA and CFA diameters in EP and SP subjects donot differ significantly at rest, suggests that training does not have a spillovervasomotor effect on lower limb conduit arteries in paraplegia. Similar BF and PIvalues post-exercise in the SP and AB groups challenge the muscle pump theory. TheSNS has an important role in the control of skeletal muscle blood flow - both at rest(vascular tone) and during exercise (redistribution). Suggestions for future researchare made.

[发布机构] Stellenbosch University