The hyperaemic response to passive leg movement is dependent on nitric oxide: a new tool to evaluate endothelial nitric oxide function

Key points Passive leg movement is associated with a ∼3‐fold increase in blood flow to the leg, but the underlying mechanisms remain unknown. Passive leg movement increased venous levels of metabolites of nitric oxide (NO) in young subjects, whereas they remained unaltered in the muscle interstitial space. Inhibition of NO synthesis lowered the vasodilatory response to passive leg movement by ∼90%. The increase in leg blood flow was lower in elderly subjects compared to young subjects and leg blood flow did not increase when passive leg movement was performed by elderly with peripheral artery disease. The results suggest that the hyperaemia induced by passive leg movement is NO dependent. The hyperaemic response to passive leg movement and to ACh was also assessed in elderly subjects and patients with peripheral artery disease. Abstract Passive leg movement is associated with a ∼3‐fold increase in blood flow to the leg but the underlying mechanisms remain unknown. The objective of the present study was to examine the role of nitric oxide (NO) for the hyperaemia observed during passive leg movement. Leg haemodynamics and metabolites of NO production (nitrite and nitrate; NOx) were measured in plasma and muscle interstitial fluid at rest and during passive leg movement with and without inhibition of NO formation in healthy young males. The hyperaemic response to passive leg movement and to ACh was also assessed in elderly subjects and patients with peripheral artery disease. Passive leg movement (60 r.p.m.) increased leg blood flow from 0.3 ± 0.1 to 0.9 ± 0.1 litre min −1 at 20 s and 0.5 ± 0.1 litre min −1 at 3 min ( P < 0.05). Mean arterial pressure remained unchanged during the trial. When passive leg movement was performed during inhibition of NO formation ( N G ‐mono‐methyl‐ l ‐arginine; 29–52 mg min −1 ), leg blood flow and vascular conductance were increased after 20 s ( P < 0.05) and then returned to baseline levels, despite an increase in arterial pressure ( P < 0.05). Passive leg movement increased the femoral venous NOx levels from 35 ± 5 at baseline to 62 ± 11 μmol l −1 during passive leg movement ( P < 0.05), whereas muscle interstitial NOx levels remained unchanged. The hyperaemic response to passive leg movement were correlated with the vasodilatation induced by ACh ( r 2 = 0.704, P < 0.001) and with age ( r 2 = 0.612, P < 0.001). Leg blood flow did not increase during passive leg movement in individuals with peripheral arterial disease. These results suggest that the hypaeremia induced by passive leg movement is NO dependent and that the source of NO is likely to be the endothelium. Passive leg movement could therefore be used as a non‐invasive tool to evaluate NO dependent endothelial function of the lower limb.