Investigation of the Methodology of Specific Airway Resistance Measurements in COPD

Abstract

Introduction

Specific resistance (SR_aw) 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 SR_aw 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 (SR_eff), total (SR_tot), ±0.5 L/s (SR_0.5), and mid (SR_mid) specific resistance were assessed.

Results

The tidal breathing protocols provided similar results. Panting resulted in higher SR_eff (p = 0.0002) and SR_tot (p < 0.0001) versus tidal breathing, but not SR_0.5 or SR_mid. Breathing frequency did not affect intra-test variance. SR_eff and SR_tot measurements were similar, and were higher than SR_0.5, during tidal breathing (p = 0.0014 and p < 0.0001 respectively) and panting (p = 0.0179 and p < 0.0001 respectively). SR_tot was higher than SR_mid during tidal breathing (p < 0.0001) and panting (p < 0.0001). Intra-test variance of SR_eff and SR_tot 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 SR_aw loop. SR_0.5 and SR_mid may underestimate abnormal physiology in COPD.

Plain Language Summary

The effort to breathe can be measured as specific airway resistance (SR_aw), which is a measure of the airflow that a person can achieve. SR_aw is calculated from a plotted loop, but may be affected by the way that the test is performed and calculated. SR_aw can be measured during panting or tidal breathing, and can be calculated using different methods of plotting the SR_aw slope. In COPD patients, we found that panting SR_aw is higher than during tidal breathing, and the calculation methods that use the extremities of the SR_aw loop give higher values and have the lowest variability.

Keywords:

• specific resistance
• COPD
• panting
• tidal
• plethysmography

Abbreviations

SR_aw, specific airway resistance; COPD, chronic obstructive pulmonary disease; SR_eff, effective specific resistance; SR_tot, total specific resistance; SR_0.5, specific airway resistance at a flow of ±0.5 L/s; SR_mid, specific airway resistance at a flow of ±0.5 L/s through the middle of the loop; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; Hz, hertz; ATS, American thoracic society; ERS, European respiratory society; CAT, COPD Assessment Test; mMRC, Modified Medical Research Council dyspnoea scale; CoV, percent coefficient of variation; GOLD, Global Initiative for Chronic Obstructive Lung Disease; EFL, expiratory flow limitation; FRC, functional residual capacity; IOS, Impulse Oscillometry; VTG, volume of thoracic gas; Vol, Volume; LABA, long acting beta2 agonist; LAMA, long acting muscarinic antagonist; ICS, Inhaled Corticosteroid; FEF_25%-75%, forced expiratory flow between 25% and 75% of FVC; SD, standard deviation; IQR, Interquartile range; TLC, total lung capacity; RV, residual volume; CI, confidence interval.

Data Sharing Statement

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Ethics Approval and Patient Consent

All patients provided written informed consent using a protocol approved by Greater Manchester East Research Ethics Committee (North West: 05/Q1402/41).

Acknowledgments

The authors would like to thank Leanne Archer and Natalie Jackson (Medicines Evaluation Unit, Manchester, UK) for their assistance during data collection.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

JD declares no competing interests in this work. DS has received personal fees from Aerogen, AstraZeneca, Boehringer Ingelheim, Chiesi, Cipla, CSL Behring, Epidendo, Genentech, GlaxoSmithKline, Glenmark, Gossamerbio, Kinaset, Menarini, Novartis, Orion, Pulmatrix, Sanofi, Synairgen, Teva, Theravance and Verona.

Additional information

Funding

The study was funded by the Medicines Evaluation Unit.