Photobiomodulation combined with dynamic thermal imaging as a diagnostic tool for chronic leg ulcers

Venous ulcers (VUs) and diabetic foot ulcers (DFUs) are the most common types of chronic leg ulcers but arise from distinctly different pathophysiologies. Photobiomodulation (PBM) has been shown to accelerate wound healing potentially through effects on microvascular perfusion. Chronic VUs respond less well to PBM therapy than DFUs. Previously, we showed a correlation between photobiomodulation-induced skin temperature changes and microvascular blood flow. The current study was designed to compare the acute microvascular response to photobiomodulation between venous and diabetic foot ulcers as assessed by dynamic thermal imaging. In this prospective study, 33 chronic wounds (22 DFUs, 11 VUs) were evaluated in 20 patients and treated with PBM (808 nm, 250mW peak-power, 15 kHz). Thermal images were captured before PBM, and every 5-minutes (min) thereafter, for 30 min. Minimum and maximum wound temperatures were recorded. Linear regression analysis was used to determine predictors of response. At baseline, wound bed temperatures (27.7 ± 2.9 °C) were significantly lower than the surrounding margins (difference of 4.6 ± 2.2 °C, p < 0.001) in both ulcer types. PBM treatment resulted in a sustained rise in wound bed temperatures in DFUs (ΔT = 2.10 ± 2.25 °C, p < 0.001) but not of VUs (ΔT = 0.68 ± 2.49 °C, p = 0.385). The thermal response to PBM of DFUs correlated inversely with baseline temperature (β=–0.521, p = 0.008; R²=0.399), indicating that colder DFUs showed the greatest response. These findings show that dynamic thermal imaging is useful for distinguishing between wounds likely, and those less likely, to benefit from photobiomodulation-induced stimulation of microvascular flow and may provide an important physiologically relevant diagnostic tool for patient-specific optimization of treatment.