Abstract
Introduction The relationship between limb hemodynamics and walking capacity in PAD is inconsistent. More precise predictive measures of functional capacity in PAD are needed. Methods Sixty-two patients with mild-to-moderate symptomatic PAD (35 M, mean age ± SD 65 ± 11 years, ABI 0.68 ± 0.13) underwent a Skinner-Gardner exercise treadmill test. Total treadmill time (TTT), time to claudication (TTC) and VO2max were measured. Six minute walk distance (6WD) was recorded. A runoff contrast-enhanced magnetic resonance angiogram was segmentally scored (MRAi) by number and degree of arterial stenoses distal to the aorta. Black blood MRI of the superficial femoral artery measured % plaque volume (%PV) as the ratio of plaque volume to total vessel volume. Calf muscle perfusion index (PI) was measured at peak exercise using an MRI-compatible pedal ergometer and first pass gadolinium-enhanced MRI and defined as the ratio of slopes of calf muscle perfusion to arterial input. 31 Phosphorus MR spectroscopy measured calf muscle phosphocreatine recovery time constant (PCr) immediately after exercise. Pearson correlation coefficients were measured between imaging and functional parameters. The bivariate relationship between them were tested using F-tests and stepwise linear regression models. Results Mean TTT was 517 ± 362s, TTC 130 ± 50s, VO2max 12.6 ± 4.2, 6WD 1028 ± 391ft. See Table . By stepwise linear regression, independent predictors of TTT were ABI (r 2 =0.12, p<0.01) and PCr (r 2 =0.09, p<0.03). Independent predictors of V02max were %PV (r 2 =0.24, p=0.0001), MRAi (r 2 =0.20, p<0.001), and ABI (r 2 =0.11, p<0.02). Conclusions The ABI, MRAi, %PV, and PCr correlate with TTT while all but PCr correlate with V02. No measured parameter correlates with 6WD. TTT is predicted by both ABI and calf muscle metabolism, whereas V02max is predicted by ABI and plaque burden. Thus, functional capacity in PAD is determined in part by flow, but metabolism and plaque burden play a significant role. Correlations Between Imaging and Functional Parameters
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