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

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).

Validating the Inspired Sinewave Technique to Measure Lung Heterogeneity Compared to Atelectasis & Over-Distended Volume in Computed Tomography Images

“…This work fitted into a bigger picture of measuring the lung heterogeneity using a non-invasive technique. The IST has been developed and validated to be used as a clinical tool for lung monitoring at the bedside [6], [19]. In this paper, the IST analysis used a simple one, well-mixed, lung compartment and the heterogeneity of the lung was calculated according to the degree of breakdown of this model.…”

“…Besides, IST shown its advantages to measure accurate value when the patient breathes stably. A sensitivity analysis has pointed out stable breathes and unchanged tidal volume during IST could minimise its technical error [6].…”

“…Heterogeneity of the lung is the mismatch between ventilation (air coming into the lung), alveolar volume and perfusion (pulmonary blood flow) [5]. Lung heterogeneity has been considered as a critical tool or to support respiratory diseases classification [6], [7]. Therefore, measuring lung heterogeneity at the bedside could provide the clinician with valuable information with which to optimise the ventilatorsettings for patients with lung conditions.…”

“…IST has the potential to provide bedside measurement of deadspace volume, effective lung volume (ELV), pulmonary blood flow (Qp) and lung heterogeneity. Measurements of the first three parameters have been validated elsewhere [6], [10]- [12]. IST uses available components commonly used in anaesthetic/intensive care practice and has proven efficacy in spontaneously ventilating healthy volunteers [13].…”

Lung simulation to support non-invasive pulmonary blood flow measurement in Acute Respiratory Distress Syndrome in animals

“…According to the lung physiological parameters monitored at the bedside, clinicians can benefit patients by providing optimal/least injurious ventilator settings. The inspired sinewave test (IST) is a noninvasive method to quantify lung function parameters, including lung heterogeneity, effective lung volume and pulmonary blood flow [6]- [8]. The IST does not use ionising radiation and does not require patient effort.…”