Comparison of forearm blood flow responses to incremental handgrip and cycle ergometer exercise: relative contribution of nitric oxide

Abstract

The contribution of endothelium-derived nitric oxide (NO) to exercise hyperaemia remains controversial. Disparate findings may, in part, be explained by different shear stress stimuli as a result of different types of exercise. We have directly compared forearm blood flow (FBF) responses to incremental handgrip and cycle ergometer exercise in 14 subjects (age ± S.E.M.) using a novel software system which calculates conduit artery blood flow continuously across the cardiac cycle by synchronising automated edge-detection and wall tracking of high resolution B-mode arterial ultrasound images and Doppler waveform envelope analysis. Monomethyl arginine (L-NMMA) was infused during repeat bouts of each incremental exercise test to assess the contribution of NO to hyperaemic responses. During handgrip, mean FBF increased with workload (P < 0.01) whereas FBF decreased at lower cycle workloads (P < 0.05), before increasing at 120 W (P < 0.001). Differences in these patterns of mean FBF response to different exercise modalities were due to the influence of retrograde diastolic flow during cycling, which had a relatively larger impact on mean flows at lower workloads. Retrograde diastolic flow was negligible during handgrip. Although mean FBF was lower in response to cycling than handgrip exercise, the impact of L-NMMA was significant during the cycle modality only (P < 0.05), possibly reflecting the importance of an oscillatory antegrade/retrograde flow pattern on shear stress-mediated release of NO from the endothelium. In conclusion, different types of exercise present different haemodynamic stimuli to the endothelium, which may result in differential effects of shear stress on the vasculature.

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

“…Physical exercise is a physiological scenario during which sympathetic outflow is increased in the inactive muscle beds (1). 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.…”

“…While it is already well established that chronic exposure to oscillatory and retrograde shear is a deleterious signal to the vasculature (5, 6), it is possible that repeated episodes of disturbed flow, as it occurs in the inactive limb during exercise (16,32), may provide favorable vascular adaptations over time; however, this interesting hypothesis has not been directly tested.…”

Retrograde Flow and Shear Rate Acutely Impair Endothelial Function in Humans

“…25,[32][33][34][35] However, this model is importantly confounded by a concurrent increase in antegrade SR, heart rate, blood pressure, and other systemic changes associated with cycling exercise. In the present study, we increased retrograde SR in a dose-dependent manner without impacting on the antegrade SR.…”

“…Retrograde shear stress patterns may result from increased vascular tone in the downstream resistance vessel beds. 34 Advanced age, 36,37 obesity, 38 and hypertension 38 -40 are characterized by elevated peripheral vascular tone, which may, as a consequence, be associated with elevated retrograde SR levels in the upstream conduit arteries. Interestingly, such conditions are also associated with an impaired endothelial function.…”

Effect of 4 weeks of aerobic or resistance exercise training on arterial stiffness, blood flow and blood pressure in pre- and stage-1 hypertensives

“…Increases in vasodilatory capacity are due to factors such as nitric oxide availability, the presence of antegrade or retrograde flow and an intact endothelial lining. [55][56][57] Resistance training may upregulate nitric oxide signalling more than aerobic training, leading to greater increases in flow, 58 and possibly signal other endothelium-dependent dilators (prostaglandins, endothelium-derived hyperpolarizing factor and acetylcholine), [58][59][60] leading to an increase in RH-induced flow. If so, this is likely related to the repeated shear stress experienced in the arm during resistance training, whereas the generalized effect from leg training may not have been as great.…”