Internal pressure driven finite element model of a single pulmonary acinus

James Campbell,Alkiviadis Tsamis,Simon Gill,Salman Siddiqui,S Pantelakis,G Lampeas,K Tserpes

doi:10.1051/matecconf/202134903008

James Campbell, Alkiviadis Tsamis + Show 5 more

Open Access

https://doi.org/10.1051/matecconf/202134903008

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Abstract

A computer simulated, poroelastic, hyperelastic model was developed to replicate the pressure-volume response of a single pulmonary acinus (15th branch of the respiratory tree and daughter branches) with air flow at its core. An internal pressure driven approach was taken upon a small spherical geometry (99.2 mm3 in volume) representing this small segment of lung parenchyma. A reference porcine tracheal pressure at tidal breathing was adjusted from 1471 Pa to 998 Pa to accommodate for pressure drop, and the pressure of 998 Pa was applied to the model for parametric analysis of its pressure-volume characteristics. In targeting a proportional tidal volume change of approximately 15% while also inducing a pressure-volume hysteresis, material parameters of Young’s modulus of 4 kPa, Poisson’s ratio of 0.4, and a permeability of 5×10-5 cm3s-1cm-2 were identified as suitable. The energy loss over a single pressure-volume cycle for a pulmonary acinus was found to be 6.3×10-6 J. This model was qualitatively compared to the pressure-volume relationship of the original porcine data source, and then with experimental findings of the material parameters for lung parenchyma in medical literature, demonstrating same-order agreement.

Highlights

The human lungs provide a huge point of interest in the field of clinical and computational medicine, not least with the increasing incidence of lung pathologies worldwide due to factors such as air pollution
Its enormous liquid-lined surface area, and site of surface tension, is responsible for the phenomenon of hysteresis: observed as the inspiration of the breathing cycle requiring a greater pressure gradient to ‘reopen’ the lungs for any given volume compared to the expiratory part of the cycle [1]
Of particular note is that the internal pressure model shares the same, desired, directionality of cycle – though rather than being the result of surface tension forces seen physiologically, the model’s hysteresis arises from a sufficiently low permeability causing flow during ‘inspiration’ to require a higher pressure gradient than that during ‘expiration’

Summary

Introduction

The human lungs provide a huge point of interest in the field of clinical and computational medicine, not least with the increasing incidence of lung pathologies worldwide due to factors such as air pollution. The acinar airway – the site of gas exchange in the lungs and the vast majority of their surface area – is vitally important in the physiological function of the human body. Its enormous liquid-lined surface area, and site of surface tension, is responsible for the phenomenon of hysteresis: observed as the inspiration of the breathing cycle requiring a greater pressure gradient to ‘reopen’ the lungs for any given volume compared to the expiratory part of the cycle [1]. A limitation of literature data on the smallest parts of the lung tissue (lung parenchyma) is that of the difficulty in probing airways so small on a living, breathing patient to determine their material properties. There may be a difficulty in the computational demand required to model a full set of lungs with the inclusion of the smallest airways

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