Lung heterogeneity and deadspace volume in animals with acute respiratory distress syndrome using the inspired sinewave test

Abstract

Acute respiratory distress syndrome (ARDS) is associated with a high rate of morbidity and mortality, as patients undergoing mechanical ventilation are at risk of ventilator-induced lung injuries. Objective: To measure the lung heterogeneity and deadspace volume to find safer ventilator strategies. The ventilator settings could then offer homogeneous ventilation and theoretically equalize and reduce tidal strain/stress in the lung parenchyma. Approach: The inspired sinewave test (IST) is a non-invasive lung measurement tool which does not require cooperation from the patient. The IST can measure the effective lung volume, pulmonary blood flow and deadspace volume. We developed a computational simulation of the cardiopulmonary system to allow lung heterogeneity to be quantified using data solely derived from the IST. Then, the method to quantify lung heterogeneity using two IST tracer gas frequencies (180 and 60 s) was introduced and used in lung simulations and animal models. Thirteen anaesthetized pigs were studied with the IST both before and after experimental lung injury (saline-lavage ARDS model). The deadspace volume was compared between the IST and the SF6 washout method. Main results: The IST could measure lung heterogeneity using two tracer gas frequencies. Furthermore, the value of IST ventilation heterogeneity in ARDS lungs was higher than in control lungs at a positive end-expiratory pressure of 10 cmH2O (area under the curve = 0.85, p < 0.001 ). Values for the deadspace volume measured by the IST have a strong relationship with the measured values of SF6 (9 ml bias and limits of agreement from −79 to 57 ml in control animals). Significance: The IST technique has the potential for use in the identification of ventilation and perfusion heterogeneity during ventilator support.

Simulation-based optimisation to quantify heterogeneity of specific ventilation and perfusion in the lung by the Inspired Sinewave Test

“…A lung simulation was developed to work with the Inspired Sinewave Technique. The IST compares the tracer gas (N 2 O) inhaled and exhaled signals and applies an analytical model to calculate cardiopulmonary parameters 18 , 31 , 32 . In theory, the analytical model should be invertible, and we should be able to recalculate the lung parameters from this model.…”

“…The lung was simulated by ten dead-space compartments, 125 alveolar compartments (tidally ventilated) and five body compartments. A simple version of this lung simulation was implemented and validated previously in 31 , 38 . In this work, we increased the number of alveolar compartments to 125 and applied the fraction of ventilation and perfusion to each individual compartment to represent the heterogeneity of the lung.…”

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

“…The lung was assumed to be homogeneous and was represented by one compartment only. This lung simulation was introduced and validated elsewhere [6], [13].…”

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

“…IST uses available components commonly used in anaesthetic/intensive care practice and has proven efficacy in spontaneously ventilating healthy volunteers [13]. Lung heterogeneity measured by the IST was first introduced and conceptualised by Tran et al [14]. To date IST's measurements of lung heterogeneity have not been compared against any established method.…”