Bronchodilator Responses in Respiratory Impedance, Hyperinflation and Gas Trapping in COPD

ABSTRACT

Hyperinflation, gas trapping and their responses to long-acting bronchodilator are clinically important in COPD. The forced oscillation technique (FOT) measures of respiratory system resistance and reactance are sensitive markers of bronchodilator response in COPD. The relationships between changes in resistance and reactance, and changes in hyperinflation and gas trapping, following long-acting bronchodilator (LA-BD) have not been studied.

15 subjects with mild-moderate COPD underwent FOT, spirometry then body plethysmography, before and 2 hours after a single 150 microg dose of the LA-BD indacaterol. Hyperinflation was quantified as the inspiratory capacity to total lung capacity ratio (IC/TLC), and gas trapping as residual volume to TLC ratio (RV/TLC).

At baseline, FOT parameters were moderately correlated with IC/TLC (|r| 0.53–0.73, p < 0.05). At 2 hours post-LA-BD, there were moderate correlations between change in FOT and change in RV/TLC (|r| 0.60–0.82, p < 0.05). Baseline FOT parameters also correlated with the subsequent post-LA-BD change in both IC/TLC (|r| 0.54–0.62, p < 0.05) and RV/TLC (|r| 0.57–0.76, p < 0.05).

FOT impedance reflects hyperinflation and gas trapping in COPD, and the potential for long-acting bronchodilator responsiveness. These results provide us with further insight into the physiological mechanisms of action of long-acting bronchodilator treatment, and may be clinically useful for predicting treatment responses.

KEYWORDS:

• Airways disease
• indacaterol
• forced oscillation technique
• lung mechanics

Declaration of interests

SM reports personal fees from Novartis Pharmaceuticals, Boehringer Ingelheim and Menarini, outside the submitted work

CH and SW report no conflicts of interest

CSF reports personal fees from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Menarini, and Mundipharma, outside the submitted work.

CT reports membership of the ATS/ERS Task Force for Technical Standards for Forced Oscillation Technique, and intellectual property arrangements (non-financial) with Thorasys and Restech.

GGK reports grants from National Asthma Foundation, National Health and Medical Research Council, Boehringer Ingelheim, GlaxoSmithKline, Menarini, Mundipharma; fees for consultancy paid to the Woolcock Institute and used for funding the research group from AstraZeneca, GlaxoSmithKline, Boehringer Ingelheim, Novartis and MundiPharma; personal travel support from AstraZeneca, Boehringer Ingelheim, GlaxoSmithKline, Menarini, Mundipharma and Novartis; co-chair of the ATS/ERS Task Force for Technical Standards for Forced Oscillation Technique; intellectual property arrangements (non-financial) with Thorasys and Restech.

Prior presentation

Preliminary data from this study have been presented in abstract form:

•	Thoracic Society of Australia and New Zealand Annual Scientific Meeting 2016 (Perth, Australia) 5 March 2016. Published as: Milne S, Hammans C, Watson S, Farah CS, Thamrin C, King GG. Forced oscillation technique measurements relate to hyperinflation and lung volume improvements following long-acting bronchodilator in COPD [abstract]. Respirol 2016;21:75–76
•	American Thoracic Society Congress 2016 (San Francisco, CA) 17 May 2016. Published as: Milne S, Hammans C, Watson S, Farah CS, Thamrin C, King GG. Forced Oscillation Technique Measurements Relate to Hyperinflation and Lung Volume Improvements Following Long-Acting Bronchodilator in Chronic Obstructive Pulmonary Disease [abstract]. Am J Respir Crit Care Med 2016;193:A6358

Additional information

Funding

SM is supported by a National Health and Medical Research Council (NHMRC) Postgraduate Research Scholarship. CT is supported by a NHMRC Career Development Fellowship.