Lymphatic flow dynamics under exercise load assessed with thoracic duct ultrasonography

The thoracic duct (TD) is the largest lymphatic vessel proximal to the venous system. It undergoes morphological changes in response to lymph flow from the periphery, with automatic contraction controlling the dynamics to propel lymph toward the venous system. Recent advancements in ultrasonography have facilitated non-invasive observations of the TD’s terminal, including its valve and wall motions. Observations of TD movements allow predictions of lymphatic flow dynamics. However, no studies have yet documented the changes in the TD under exercise-induced lymph flow enhancement in humans. Here, using 18-MHz high-frequency ultrasonography, we demonstrate for the first time that the TD diameter significantly expands under exercise load. This study analyzed 20 participants; the maximum TD diameters at rest and post-exercise were 2.69 ± 1.06 mm and 3.41 ± 1.32 mm, respectively (p = 0.00000056). While various methods exist for observing the TD, our approach—dynamically monitoring the TD diameter using sonography in real time and correlating it with lymphatic flow dynamics—offers a novel contribution.