A tidal lung simulation to quantify lung heterogeneity with the Inspired Sinewave Test

TL;DR

This study develops a tidal lung simulation to evaluate the Inspired Sinewave Test (IST) for quantifying lung heterogeneity, demonstrating its accuracy and ability to distinguish emphysema and embolism in models and animals.

Contribution

The paper introduces a novel tidal lung simulation and a method to assess lung heterogeneity using IST results, validated through sensitivity analysis and animal data.

Findings

IST is highly accurate with ~5% underestimation.

Ratios of IST results at different frequencies identify lung heterogeneity.

Simulated emphysema and embolism show significant differences in IST metrics.

Abstract

We have created a lung simulation to quantify lung heterogeneity from the results of the inspired sinewave test (IST). The IST is a lung function test that is non-invasive, non-ionising and does not require patients' cooperation. A tidal lung simulation is developed to assess this test and also a method is proposed to calculate lung heterogeneity from IST results. A sensitivity analysis based on the Morris method and linear regression were applied to verify and to validate the simulation. Additionally, simulated emphysema and pulmonary embolism conditions were created using the simulation to assess the ability of the IST to identify these conditions. Experimental data from five pigs (pre-injured vs injured) were used for validation. This paper contributes to the development of the IST. Firstly, our sensitivity analysis reveals that the IST is highly accurate with an underestimation of about 5% of the simulated values. Sensitivity analysis suggested that both instability in tidal volume and extreme expiratory flow coefficients during the test cause random errors in the IST results. Secondly, the ratios of IST results obtained at two tracer gas oscillation frequencies can identify lung heterogeneity (ELV60/ELV180 and Qp60/Qp180). There was dissimilarity between simulated emphysema and pulmonary embolism (p < 0:0001). In the animal model, the control group had ELV60/ELV180 = 0.58 compared with 0.39 in injured animals (p < 0.0001).