Leg blood flow and skeletal muscle microvascular perfusion responses to submaximal exercise in peripheral arterial disease

Peripheral arterial disease (PAD) is characterized by stenosis and occlusion of the lower limb arteries. While leg blood flow is limited in PAD, it remains unclear whether skeletal muscle microvascular perfusion is affected. We compared whole-leg blood flow and calf muscle microvascular perfusion following cuff occlusion and submaximal leg exercise between PAD patients (n=12, 69±9 years) and healthy age-matched control participants (n=12, 68±7 years). Microvascular blood flow (microvascular volume x flow velocity) of the medial gastrocnemius muscle was measured before and immediately after: 1) 5 min of thigh-cuff occlusion; and 2) a 5-min bout of intermittent isometric plantar-flexion exercise (400N) using real-time contrast-enhanced ultrasound (CEU). Whole-leg blood flow was measured after thigh-cuff occlusion and during submaximal plantar-flexion exercise using strain-gauge plethysmography. Post-occlusion whole-leg blood flow and calf muscle microvascular perfusion were lower in PAD patients than controls, and these parameters were strongly correlated (r=0.84; p<0.01). During submaximal exercise, total whole-leg blood flow and vascular conductance were not different between groups. There were also no group differences in post-exercise calf muscle microvascular perfusion, although microvascular blood volume was higher in PAD patients than control (12.41±6.98 vs 6.34±4.98 aU; p=0.03). This study demonstrates that the impaired muscle perfusion of PAD patients during post-occlusion hyperemia is strongly correlated with disease severity, and is likely mainly determined by the limited conduit artery flow. In response to submaximal leg exercise, microvascular flow volume was elevated in PAD patients, which may reflect a compensatory mechanism to maintain muscle perfusion and oxygen delivery during recovery from exercise.