The effect of respiration and body position on terminal thoracic duct diameter and the lymphovenous junction: An exploratory ultrasound study.
Level 4 - case-series / case-control
Exploratory cross-sectional physiological study in healthy volunteers
PubMed 34658062 · doi:10.1002/ca.23801
What was done
High-resolution (13–5 MHz) ultrasound was used to scan the left supraclavicular fossa in 33 healthy, non-fasted volunteers. The study evaluated the visibility of the terminal thoracic duct (TD) and lymphovenous valve (LVV), and measured internal TD diameter across respiratory phases (inspiration vs. expiration) and body positions (supine vs. Trendelenburg).
What was found
The terminal TD was successfully visualized in 20 of 33 volunteers (61%), and an LVV was identified in 4 of 20 (20%). Mean terminal TD diameter in the supine position was 1.7 mm (range 0.8–3.1 mm). Diameter increased during full inspiration (mean 1.8 mm, range 0.9–3.2 mm, p < 0.05) and in the Trendelenburg position (mean 1.8 mm, range 1.2–3.1 mm, p < 0.05). The smallest mean diameter occurred during full expiration (mean 1.6 mm, range 0.7–3.1 mm, p < 0.05).
Why it matters
It provides preliminary in vivo evidence that respiratory cycles and gravitational positioning induce small, measurable changes in terminal thoracic duct diameter, supporting theoretical models of respiration-assisted lymph propulsion.
Limits
The sample was small (33 volunteers), and the terminal TD could only be visualized in 61% of subjects (with the LVV identified in only 20%). The study measured anatomical diameter changes rather than direct lymph flow rates or pressures. All participants were healthy non-fasted volunteers, so findings may not generalize to fasting states or patients with lymphatic disorders.