Blood Flow
Blood flow was measured for 5 minutes at the beginning of each test day using a noninvasive laser Doppler (LDF 100C; Biopac Systems, Inc, Goleta, CA). Laser Doppler flowmetry has been used to measure blood flow in tissue, but no research on the validity and reliability of this device has been published.25–29 The laser Doppler includes a probe that emits infrared light into the tissue and specifically measures blood perfusion units (BPUs) and percentage of backscatter. Blood perfusion units are defined as the number of moving blood cells in the area measured multiplied by the velocity of those blood cells. Percentage of backscatter is the amount of infrared light that is reflected back to the probe by red blood cells during the time of measurement. Participants were instructed to lie prone on the testing table and remain still during the test time. The laser Doppler probe was secured on the skin 5 in (12.7 cm) below the popliteal fossa. To ensure consistent placement of the laser Doppler probe throughout the 3 test days, we drew a crosshair design around the targeted area that remained on the skin for the duration of the testing days (Figure 1). We used AcqKnowledge software (version 3.7.3; Biopac Systems, Inc) to record and store the blood flow data. The BPU and percentage of backscatter data were collected for 5 minutes, and the average of each was used for statistical analysis.
Blood Flow
Blood flow was measured for 5 minutes at the beginning of each test day using a noninvasive laser Doppler (LDF 100C; Biopac Systems, Inc, Goleta, CA). Laser Doppler flowmetry has been used to measure blood flow in tissue, but no research on the validity and reliability of this device has been published.25–29 The laser Doppler includes a probe that emits infrared light into the tissue and specifically measures blood perfusion units (BPUs) and percentage of backscatter. Blood perfusion units are defined as the number of moving blood cells in the area measured multiplied by the velocity of those blood cells. Percentage of backscatter is the amount of infrared light that is reflected back to the probe by red blood cells during the time of measurement. Participants were instructed to lie prone on the testing table and remain still during the test time. The laser Doppler probe was secured on the skin 5 in (12.7 cm) below the popliteal fossa. To ensure consistent placement of the laser Doppler probe throughout the 3 test days, we drew a crosshair design around the targeted area that remained on the skin for the duration of the testing days (Figure 1). We used AcqKnowledge software (version 3.7.3; Biopac Systems, Inc) to record and store the blood flow data. The BPU and percentage of backscatter data were collected for 5 minutes, and the average of each was used for statistical analysis.
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