Airways resistance and specific conductance for the diagnosis of obstructive airways diseases.

Marko Topalovic,Marc Decramer,Eric Derom,Wim Janssens,Christian R Osadnik,Thierry Troosters,Belgian Pulmonary Function Study Investigators

doi:10.1186/s12931-015-0252-0

Abstract

BackgroundAirway resistance (RAW) and specific airway conductance (sGAW) are measures that reflect the patency of airways. Little is known of the variability of these measures between different lung diseases. This study investigated the contribution of RAW and sGAW to a diagnosis of obstructive airways disease and their role in differentiating asthma from COPD.Methods976 subjects admitted for the first time to a pulmonary practice in Belgium were included. Clinical diagnoses were based on complete pulmonary function tests and supported by investigations of physicians’ discretion. 651 subjects had a final diagnosis of obstructive diseases, 168 had another respiratory disease and 157 subjects had no respiratory disease (healthy controls).ResultsRAW and sGAW were significantly different (p < 0.0001) between obstructive and other groups. Abnormal RAW and sGAW were found in 39 % and 18 % of the population, respectively, in which 81 % and 90 % had diagnosed airway obstruction. Multiple regression revealed sGAW to be a significant and independent predictor of an obstructive disorder. To differentiate asthma from COPD, RAW was found to be more relevant and statistically significant. In asthma patients with normal FEV1/FVC ratio, both RAW and sGAW were more specific than sensitive diagnostic tests in differentiating asthma from healthy subjects.ConclusionsRAW and sGAW are significant factors that contribute to the diagnosis and differentiation of obstructive airways diseases.

Highlights

Airway resistance (RAW) and specific airway conductance are measures that reflect the patency of airways
As the manoeuvre to determine airway resistance is dependent on thoracic gas volume, specific airway resistance is divided by thoracic gas volume to obtain RAW
This study demonstrated that regular measurement of airway resistance, one of four most commonly used pulmonary function tests (PFTs), significantly contributes to a reduction in the number of differential diagnoses and accuracy of final diagnosis [7]

Summary

Introduction

Airway resistance (RAW) and specific airway conductance (sGAW) are measures that reflect the patency of airways. Plethysmography applies the gas law of Boyle-Mariotte [3] to evaluate the difference in the pressure of the closed box (in which the subject is breathing) in conjunction with flows measured at the subject’s mouth by breathing out of the box [4, 5]. RAW reflects changes in alveolar pressure over changes in flow [6] representing true resistance of the airways. As the manoeuvre to determine airway resistance is dependent on thoracic gas volume (with larger volumes resulting in opened airways), specific airway resistance (sRAW) is divided by thoracic gas volume to obtain RAW. SGAW is the inverse of sRAW and reflects the conductance of the airways independent of lung volumes

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Conclusion