Abstract 3427: Uncoupling of Skeletal Muscle Perfusion and Metabolism in Peripheral Arterial Disease
Introduction Studies suggests that limb hemodynamics do not correlate with functional capacity in patients with peripheral arterial disease (PAD). Alterations in microcirculatory function and muscle metabolism are postulated to account for part of this inconsistency. We sought to further characterize the relationship between macrovascular obstruction, tissue perfusion and cellular metabolism in patients with PAD.
Methods Sixty-two patients with mild-to-moderate PAD (35 males, mean age±S.D. 65±11 years) had their most symptomatic leg studied (resting ankle-brachial index (ABI) 0.68±0.13). To assess macrovascular disease, a runoff magnetic resonance angiogram was segmentally scored (MRAi) according to the number and degree of arterial stenoses distal to the aorta. A calf muscle perfusion index (PI) was measured at peak exercise with a magnetic resonance imaging (MRI) compatible pedal ergometer using first pass gadolinium-enhanced MRI. PI was defined as the ratio of slopes of calf muscle tissue perfusion to arterial input. 31Phosphorus MR spectroscopy measured calf muscle phosphocreatine recovery time constant (PCr) immediately after peak exercise. Correlations between ABI, MRAi, PI, and PCr were examined by Pearson’s correlation coefficient.
Results Mean MRAi was 0.97±0.74, PI was 0.45±0.15, and PCr was 73.1±30.0 sec. For reference, values in normal subjects are 0, 0.69±0.17 and 34.7±16.6 sec, respectively. The ABI correlated with PI (r=0.46, p<0.001), inversely with MRAi (r=−0.39, p<0.005) and modestly inversely with PCr (r=−0.27, p = 0.05). The MRAi showed a trend towards an inverse correlation with PI (r=−0.27, p<0.06), but did not correlate with PCr (p = 0.29). PCr likewise did not correlate with PI (p=0.85).
Conclusions In mild to moderate PAD, lower limb blood pressure relates to macrovascular obstruction and both calf muscle perfusion and metabolism at peak exercise. However, calf muscle perfusion does not correlate with cellular metabolism as determined by PCr recovery at peak exercise. Thus, there is uncoupling between calf muscle perfusion and metabolism, supporting the concept that factors independent of blood flow and intrinsic to skeletal muscle are critical in PAD.