Visualising lymphatic flow dynamics during complex physical therapy: A photoacoustic imaging study.

Background: Complex physical therapy (CPT), which combines compression and exercise therapies, is the cornerstone of lymphedema treatment. However, assessing lymphatic flow in living humans is challenging owing to the small size and transparent nature of lymphatic vessels. Herein, we introduce a novel approach utilising photoacoustic imaging (PAI) to visualise lymphatic flow dynamics under CPT conditions. Compared with existing modalities, PAI offers superior details, enabling real-time evaluation of lymphatic vessels during compression and exercise. Real-time evaluation of lymphatic flow may enable advanced research on optimal perioperative compression therapy and exercise therapy. Methods and Results: Herein, PAI was used to assess lymphatic flow in four healthy subjects. Detailed images of lymphatic and blood vessels were obtained using photoacoustic lymphangiography, which utilises indocyanine green as a light absorber. The participants underwent simulated compression using a transparent film dressing, with a pressure of approximately 20 mmHg. Exercise stress was applied to mimic CPT conditions. Compression facilitated the collapse of superficial veins while lymphatic vessels remained intact. Additionally, the lymphatic pumping frequency was the highest during combined compression and exercise, highlighting the synergistic effect of these therapies on lymphatic flow. Conclusion: Our findings underscore the potential of PAI in elucidating the mechanisms underlying the efficacy of CPT. PAI may enable comprehensive assessments of vascular changes during CPT by allowing simultaneous delineation of veins and lymphatic vessels. While our study represents a significant step forward, its limitations, including small sample size and exercise regimen specificity, warrant further investigations.