Effects of Exercise Training on Calf Muscle Oxygen Extraction and Blood Flow in Patients with Peripheral Artery Disease

We employed near-infrared optical techniques, diffuse correlation spectroscopy (DCS) and frequency-domain near-infrared spectroscopy (FD-NIRS), to test the hypothesis that supervised exercise training increases skeletal muscle microvascular blood flow and oxygen extraction in patients with peripheral artery disease (PAD) who experience claudication. PAD patients (n=64) were randomly assigned to exercise and control groups. Patients in the exercise group received three months of supervised exercise training. Calf muscle blood flow and oxygen extraction were optically monitored before, during, and after performance of a graded treadmill protocol at baseline and at three months in both groups. Additionally, measurements of the ankle-brachial index (ABI) and peak walking time (PWT) to maximal claudication were made during each patient visit. Supervised exercise training was found to increase the maximal calf muscle blood flow and oxygen extraction levels during treadmill exercise by 29%(13%,50%) and 8%(1%,12%), respectively (p<0.001; median (25th percentile, 75th percentile)). These improvements across the exercise group population were significantly higher than corresponding changes in the control group (p<0.004). Exercise training also increased PWT by 49% (18%, 101%), (p = 0.01). However, within statistical error, the ABI, the resting calf muscle blood flow and oxygen extraction, and the recovery half-time for hemoglobin/myoglobin desaturation following cessation of maximal exercise, were not altered by exercise training. The concurrent monitoring of both blood flow and oxygen extraction with the hybrid DCS/FD-NIRS instrument revealed enhanced muscle oxidative metabolism during physical activity from exercise training, which could be an underlying mechanism for the observed improvement in PWT.

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