Ryan J. Willoughby, Jalyn A. Boyles, Hieu Vu, Zabilon Dessalegn, Chloe Blum, Abisola R. Akinbobola, Kevin McCully, FACSM. University of Georgia, Athens, GA.

Background: Peripheral Arterial disease (PAD) is a common cardiovascular disease. The ankle-brachial index test (ABI) is used to evaluate PAD, but it lacks sensitivity in detecting mild disease. Additionally, the hardening of arteries commonly associated with diabetes confounds ABI results. This study evaluated an alternative method for testing for PAD that used near-infrared spectroscopy (NIRS) to measure the blood flow response to leg lifts. NIRS uses cuff ischemia, which is poorly tolerated by some patients. We hypothesized that the blood flow response to lifting the leg of the subject to 45 degrees would have good reproducibility and validity compared to reactive hyperemia after cuff ischemia. Methods: Young, healthy adults were tested on two separate days (males: n=6 and females: n=1). Blood flow was measured as the half-time of recovery (T1/2) of the NIRS tissue saturation index (TSI) after leg lifts or cuff ischemia. The total signal was measured as the change in TSI due to the leg lifts or ischemia. NIRS devices were placed on the vastus lateralis, medial gastrocnemius, and the arch of the foot pad. T-tests and correlations (sample size permitting) were made to compare values between days and between tests. Results: All subjects preferred the leg lifts to cuff ischemia as a method of measuring blood flow. Two people were not retested. Out of 12 possible tests: all of the 180s cuffs and all foot leg-lifts produced analyzable data. Only 9 calf tests and 5 thigh tests were analyzable. T1/2 values for 60 seconds and 120 seconds of leg lifts were 7.8+3.4 and 8.4+2.6 for the thigh, 5.9+2.5 and 6.9+3.2 for the calf, and 12.4+5.4 and 12.7+6.6 for the foot. For comparison, the values were 6.2+1.7, 6.2+1.7, and 12.7+3.7 for 180 seconds of ischemia. The mean values were not different between values for all measures. The magnitudes of the blood flow response were ~10-30% of the signal for the 180 seconds cuff ischemia, which contributed to the difficulty in making the T1/2 measurements with leg lifts. Conclusions: Leg lifts are a subject-preferred method to measure blood flow in the leg. However, the low success rates support performing additional studies or protocol adjustments before leg lifts can be recommended for use in evaluating PAD.

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