Small airway disease assessed by parameters of small airway dysfunction in patients with asthma, asthma-chronic obstructive pulmonary disease-overlap, and chronic obstructive pulmonary disease

Abstract

Aim: There is an increasing interest in defining the role of small airway disease (SAD) in asthma, chronic obstructive pulmonary disease (COPD), and asthma with coexisting COPD. Based on the specific pathophysiologic components of small airway dysfunction (SAdf) of these diseases, single lung function parameters characterize only fractional aspects of SAdf and that the phenotypic diagnosis of SAD, and therefore, the functional assessment must be based on more than one parameter, reflecting airway dysfunction, pulmonary hyperinflation (PHI), energy costs, trapped gases, and/or gas transfer disturbances. Methods: The present study was undertaken to define the interactive contribution of several spirometric and plethysmographic parameters such as forced expiratory flow between 25% and 75% of vital capacity (FEF25–75), effective specific airway resistance (sReff), plethysmographic functional residual capacity (FRC; FRCpleth), the parameter defining PHI, the aerodynamic resistive work of breathing at rest (sWOB), the volume of trapped gas at FRC (VTGFRC), and the carbon monoxide diffusion capacity (DLCO) as the parameter of the gas transfer. Results: The study clearly demonstrates that the diagnosis of SAD cannot be based on one single lung function parameter, especially not on the spirometric FEF25–75 only. Interestingly, sWOB has a high discriminatory power to define SAD in these diseases. Conclusions: Within a future framework including functional and treatable traits, it is mandatory to define SAdf parameters diagnosing unambiguously SAD, for a successful concept of precision medicine.