Sympathetic vasomotor control does not explain the change in femoral artery shear rate pattern during arm-crank exercise

Abstract

Thijssen DH, Green DJ, Steendijk S, Hopman MT. Sympathetic vasomotor control does not explain the change in femoral artery shear rate pattern during arm-crank exercise. Am J Physiol Heart Circ Physiol 296: H180 -H185, 2009. First published November 21, 2008 doi:10.1152/ajpheart.00686.2008.-During lower limb exercise, blood flow through the resting upper limbs exhibits a change characterized by increased anterograde flow during systole, but also large increases in retrograde diastolic flow. One explanation for the retrograde flow is that increased sympathetic nervous system (SNS) tone and concomitant increased peripheral resistance generate a rebound during diastole. To examine whether the SNS contributes to retrograde flow patterns, we measured femoral artery blood flow during arm-crank exercise in 10 healthy men (31 Ϯ 4 yr) and 10 spinal cord-injured (SCI) subjects who lack sympathetic innervation in the legs (33 Ϯ 5 yr). Before, and every 5 min during 25-min arm-crank exercise at 50% maximal capacity, femoral artery blood flow and peak anterograde and retrograde shear rate were assessed using echo Doppler sonography. Femoral artery baseline blood flow was significantly lower in SCI compared with controls. Exercise increased femoral artery blood flow in both groups (ANOVA, P Ͻ 0.05), whereas leg vascular conductance did not change during exercise in either group. Mean shear rate was lower in SCI than in controls (P Ͻ 0.05). Peak anterograde shear rate was higher in SCI than in controls (P Ͻ 0.05), whereas peak retrograde shear rate did not differ between groups. Arm-crank exercise induced an increase in peak anterograde and retrograde shear rate in the femoral artery in controls and SCI subjects (P Ͻ 0.05). This suggests that the SNS is not obligatory to change the flow pattern in inactive regions during exercise. Local mechanisms may play a role in the arm-crank exercise-induced changes in flow pattern in the femoral artery. inactive areas; shear pattern AT THE ONSET OF EXERCISE, substantial cardiovascular adjustments are necessary to continue exercise for more than a few seconds (6). To optimally meet the increased metabolic demands of the contracting muscles, blood flow to inactive regions is relatively decreased, resulting in a net redistribution of blood toward vascular beds in metabolically active regions (1,6,21). Recent studies suggest that changes in the pattern of blood flow in inactive areas during exercise may have important effects on exercise training-mediated improvements in vascular function in these nonactive regions (11,12). Green et al. (11) recently observed that, during lower limb cycle exercise, brachial artery blood flow in the resting upper limbs exhibits an oscillatory pattern of anterograde flow during systole, followed by substantial retrograde diastolic flow. This reproducible change in blood flow pattern during cycling exercise results in a shear rate-mediated release of endothelium-derived nitric oxide (NO) (10, 11). The synthesis of NO is of special interest, given the anti-ather...

Increased muscle sympathetic nerve activity acutely alters conduit artery shear rate patterns

“…Based on the lack of a group difference, it was concluded that the sympathetic nervous system does not play a role in promoting retrograde shear in the inactive regions. While this was the logical interpretation of the results at that time, our finding that increased blood pressure offsets the impact of MSNA on retrograde shear may also offer new insights into the data of Thijssen et al (34). Interestingly, the control subjects, but not the patients with spinal cord injury, exhibited an increase in blood pressure during the upper-body exercise bout.…”

“…In this regard, the findings of the present study support the observations by Green et al (16) and Thijssen et al (32) that, during lower limb exercise, brachial artery retrograde and oscillatory shear in the resting arm are augmented. In a timely follow-up study (34), the same authors compared femoral retrograde shear during arm-crank exercise between spinal cord injury patients and matched controls. Based on the lack of a group difference, it was concluded that the sympathetic nervous system does not play a role in promoting retrograde shear in the inactive regions.…”

Muscle perfusion of posterior trunk and lower-limb muscles at rest and during upper-limb exercise in spinal cord-injured and able-bodied individuals

“…This magnitude of reduction in perfusion of VL in SCI is in accordance with the reduction (35-70%) previously reported in studies that measured whole limb flow, conduit artery flow, or peak reactive hyperemic response. 2,7,8 Several physiological observations may collectively explain the reduced resting muscle perfusion of paralyzed limbs in SCI. First, skeletal muscle perfusion is mainly regulated by microcirculation.…”

“…Previous studies that examined blood flow to the legs of SCI or able-bodied individuals during ACE assessed changes in limb volume or in femoral artery and cutaneous circulation. One study reported a minimal increase in SCI and able-bodied individuals in femoral artery blood flow, 7 whereas, others reported a small decrease in calf volume 5 or no changes in cutaneous and femoral artery blood flow in SCI. 6,8 In agreement with those reports showing unchanged blood flow in lower limbs of SCI and able-bodied individuals during ACE, we document no effect of ACE at the level of muscle microcirculation.…”

“…4 Thus, the potential of ACE to enhance blood flow to non-exercising muscles, seems as an attractive intervention to increase the arteriole/capillary diameter, elicit capillarization and diminish the microvascular maladaptations in the paralyzed legs of SCI. The few studies that examined the effects of ACE on leg circulation in SCI have focused only on changes in limb volume, 5 cutaneous microcirculation, 6 and femoral artery blood flow 7,8 and reported equivocal results. Changes in limb volume and conduit artery blood flow, however, may not entirely reflect changes in muscle perfusion, and the blood flow response between the conduit artery and the microvasculature may vary substantially.…”