# The physiology of thoracic duct pressure and flow: A review of the literature

## TL;DR

This review examines how breathing and blood circulation affect lymph flow in the thoracic duct, finding inconsistent results across studies.

## Contribution

The study systematically reviews and compares the effects of respiration and circulation on thoracic duct lymph dynamics across species.

## Key findings

- Respiratory activity influenced thoracic duct flow and/or pressure in most human and animal studies.
- Circulatory influences were less consistently reported, with limited evidence in both human and animal studies.
- Intrinsic thoracic duct contractility was identified as a potential independent driver of lymph propulsion.

## Abstract

The thoracic duct (TD) is the largest vessel of the lymphatic system, transporting interstitial fluid, macromolecules, and immune cells into the venous circulation via the lymphovenous junction. Respiratory and circulatory forces have been proposed as key drivers of TD lymph propulsion; however, the literature reports inconsistent findings. This study systematically reviews the effects of respiration and circulation on TD lymph flow and pressure in humans and non‐human mammals. A systematic review was conducted in accordance with PRISMA guidelines using MEDLINE, Embase, and Google Scholar databases. Studies published up to August 2025 were included with no language or past date restrictions. Twenty‐three human and animal studies met the inclusion criteria. Respiratory activity influenced TD flow and/or pressure in 5/6 human and 12/17 animal studies. Circulatory influences were reported in 3/6 human and 8/17 animal studies. Intrinsic TD contractility was described in 3/6 human and 6/17 animal studies and was identified as an independent contributor to lymph propulsion. Overall, reported effects ranged from absent to highly synchronous physiological coupling. Evidence regarding respiratory and circulatory influences on TD lymphodynamics remains inconsistent, reflecting methodological heterogeneity. Findings should be considered hypothesis‐generating and highlight the need for modern imaging and standardized physiological protocols.