Blood Flow In The Human Anterior Tibial Artery Following Ischemic Isometric Exercise

Studies involving handgrip exercise have shown forearm reactive exercise hyperemia to be immediate, however, this response is not well known in the leg. PURPOSE To characterize the hyperemic response in the anterior tibial artery of the leg under two conditions: 1) cuff occlusion (SHAM) and 2) cuff occlusion +electrical stimulation exercise (ES). METHODS Subjects participated in two protocols (N=8 healthy males). Doppler ultrasound was used to measure arterial diameter and blood flow velocity during rest and recovery from ischemia. Anterior tibial blood flow (ATBF) was calculated as the product of mean blood velocity and vessel cross-sectional area. The SHAM protocol involved 1 min rest, 3 min ischemia (260mmHg) and 5 min recovery in the left leg. The ES protocol involved 3 min rest, 3 min ischemia +ES and 20 min recovery in the right leg. ES of the peroneal nerve at 20Hz (1:1 duty cycle) with 4 periodic 10, 20 and 50Hz simulations was used to produce contractions and elicit fatigue ∼2.56 min. Mean arterial pressure (MAP) and heart rate (HR) were measured continuously throughout the experiment. RESULTS Baseline ATBF (mean±SE) was similar (p > 0.05) in ES (9.70±1.04mL/min) and SHAM (12.32±1.74mL/min). Peak ATBF in recovery was similar (p > 0.05) in ES (44.13±8.18mL/min) and SHAM (38.04±5.79mL/min). End Exercise MAP and HR were greater (p < 0.05) in the ES vs. SHAM condition. Time to peak for vessel diameter, flow velocity and ATBF was higher (p < 0.05) in ES (172.50±36.63sec, 97.50±32.45sec, 153.75±36.49sec, respectively) compared with SHAM (35±5.98sec, 13.75±1.83sec, 15.00±2.67sec). In the SHAM condition, diameter, flow velocity and ATBF had returned to baseline after 5 min (p > 0.05); however, in ES these parameters were still elevated (p < 0.05) after 20 min of recovery. CONCLUSION These data suggest that the peak reactive exercise hyperemia in human anterior tibial artery is delayed and prolonged following ischemic electrical stimulation exercise compared to ischemia alone. This anterior tibial artery response may prove to be useful in studies investigating endothelial function and flow-mediated dilation to an isolated muscle.