Which plantar region can predict peripheral arterial disease by using laser speckleflowgraphy?

Laser speckle flowgraphy (LSFG) is a new device that can measure skin blood flow and capture the movement of erythrocytes. However, there are a few reports on the use of LSFG to estimate skin blood flow, especially in the lower extremities. We aimed to compare plantar skin blood flow between patients with and without peripheral arterial disease (PAD) to discern the extent to which LSFG could accurately predict PAD. We prospectively measured the plantar skin blood flow in 28 patients with PAD and 37 participants without PAD at two hospitals from 2017 to 2021, using the ankle-brachial index (ABI) and LSFG. We partitioned the plantar into 12 parts: digits 1-5, medial metatarsal, middle metatarsal, lateral metatarsal, medial arch, middle arch, lateral arch, and heel, and compared the difference between the two groups and the area under the curve (AUC) of each point. Statistical analyses were performed to determine the sensitivity, specificity, false-positive rate, and false-negative rate at high accuracy points of AUC and ABI. There was a significant difference among the 12 points between the two groups, and the ratio using toe 1 and toe 5 was highly accurate. The ratio using toe 1 indicated higher sensitivity (89 vs. 82%), higher false-positive rate (22 vs. 4%), lower specificity (81 vs. 97%), and an equivalent false-negative rate (9 vs. 12%) to that of the ABI. These findings could facilitate the use of LSFG to estimate the skin blood flow condition in the plantar skin. Our results indicate that measuring toe 1 using LSFG could be used to somewhat assess PAD.