Investigation of the Methodology of Specific Airway Resistance Measurements in COPD

Introduction: Specific resistance (SRaw) measurements in Chronic Obstructive Pulmonary Disease (COPD) patients may be performed by panting or tidal breathing. The aim of this study was to compare how breathing frequency affected SRaw in COPD and compare different tangent plotting methods.Methods: Fifteen COPD patients participated. Three protocols were performed: tidal 1 - spontaneous tidal breathing; tidal 2 - tidal breathing with a flow of +/- 1 L/sec; panting - 60 breaths per min. Effective (SReff), total (SRtot), +/- 0.5 L/s (SR0.5), and mid (SRmid) specific resistance were assessed.Results: The tidal breathing protocols provided similar results. Panting resulted in higher SReff (p = 0.0002) and SRtot (p < 0.0001) versus tidal breathing, but not SR0.5 or SRmid. Breathing frequency did not affect intra-test variance. SReff and SRtot measurements were similar, and were higher than SR0.5, during tidal breathing (p = 0.0014 and p < 0.0001 respectively) and panting (p = 0.0179 and p < 0.0001 respectively). SRtot was higher than SRmid during tidal breathing (p < 0.0001) and panting (p < 0.0001). Intra-test variance of SReff and SRtot were similar and showed the lowest percent coefficient of variation during both tidal breathing and panting.Conclusion: Panting and tidal breathing manoeuvres are not interchangeable in COPD patients. Panting widens the clubbing in the SRaw loop. SR0.5 and SRmid may underestimate abnormal physiology in COPD. Plain Language Summary: The effort to breathe can be measured as specific airway resistance (SRaw), which is a measure of the airflow that a person can achieve. SRaw is calculated from a plotted loop, but may be affected by the way that the test is performed and calculated. SRaw can be measured during panting or tidal breathing, and can be calculated using different methods of plotting the SRaw slope. In COPD patients, we found that panting SRaw is higher than during tidal breathing, and the calculation methods that use the extremities of the SRaw loop give higher values and have the lowest variability.