Estimating respiratory mechanics in the presence of flow limitation

Dynamic collapse of the pulmonary airways, leading to flow limitation, is a significant event in a number of respiratory pathologies, including obstru ctive sleep apnea syndrome and chronic obstructive pulmonary disease. Quant itative evaluation of the mechanical status of the respiratory system in th ese conditions provides useful insights into airway caliber and tissue stif fness, which are hallmarks of such abnormalities. However, assessing respir atory mechanics in the presence of flow limitation is problematic because t he single-compartment linear model on which most assessment methods are bas ed is not valid over the entire breath. Indeed, even deciding which parts o f a breath are flow limited from measurement of mouth flow and pleural pres sure often proves to be difficult. In this study, me investigated the use o f two approaches to assessing the overall mechanical properties of the resp iratory system in the presence of inspiratory flow limitation. The first me thod is an adaptation of the classic Mead-Whittenberger method, and the sec ond method is based on information-weighted histograms obtained from recurs ively estimated signals of respiratory resistance and elastance. We tested the methods on data simulated by using a computer model of the respiratory system and on data collected from obese sleeping pigs. We found that the in formation-weighted histograms provided the more robust overall estimates of respiratory mechanics.