# Pressure–Flow Relation of Porcine Thoracic Duct Segment

## TL;DR

This study establishes a pressure-flow relationship for the thoracic duct in pigs, providing a model to simulate lymphatic flow and understand disease-related changes.

## Contribution

A validated pressure–flow relation for a single-valve thoracic duct segment in a large animal model is newly established.

## Key findings

- A sigmoidal model accurately predicts flow resistance in the thoracic duct with R²=0.985±0.010.
- The model can serve as a baseline for studying lymphatic dysfunction in diseases like heart failure or ascites.

## Abstract

The lymphatic system collects excess fluid and molecules from the interstitial space back into the venous system mainly via the thoracic duct (TD). Despite the importance of the lymphatic flow in health and disease, a validated pressure–flow relation of lymphatic fluid through the TD is lacking in a translational large animal model. The objective of this work was to establish a pressure–flow relationship for a TD segment with one valve in a swine model. Our methodology consisted of using a specialized bench experimental setup to measure the passive forward flow of 0.9% saline through single-valve TD segments (n = 5) under various pressure gradients. Using Poiseuille’s law, we computed the resistance to flow in the TD segment. Subsequently, we used a sigmoidal function to model the relation between valve resistance and pressure gradient across the valve. We estimated the model’s parameters using the Poiseuille-based resistance values and associated experimental pressure date then validated the model by comparing model predictions of flow to experimental measurements. We found that the model performs accurately (R2=0.985±0.010). The resistance model validated here for a single valve TD segment provides a fundamental element for computational simulations of lymphatic flow in the entire TD. Moreover, this work provides a baseline for future characterization of TD behavior under pathological conditions, such as congestive heart failure or hepatitis caused ascites.