Bronchodilator response of advanced lung function parameters depending on COPD severity.

Background: COPD is defined as partly irreversible airflow obstruction. The response pattern of bronchodilators has not been followed in advanced lung function parameters.
Purpose: The aim of this study was to investigate bronchodilator response pattern in advanced lung function parameters in a continuous fashion along forced expiratory volume in 1 second (FEV ₁ ) percent predicted (%p) in COPD patients and controls.
Patients and Methods: Eighty-one smokers/ex-smokers (41 controls and 40 COPD) performed spirometry, body plethysmography, impulse oscillometry and single-breath helium dilution carbon monoxide diffusion at baseline, after salbutamol inhalation and then after an additional inhalation of ipratropium.
Results: Most pulmonary function parameters showed a linear increase in response to decreased FEV ₁ %p. The subjects were divided into groups of FEV ₁ %p <65 and >65, and the findings from continuous analysis were verified. The exceptions to this linear response were inspiratory capacity (IC), forced vital capacity (FVC), FEV ₁ /FVC and expiratory resistance ( R _ex ), which showed a segmented response relationship to FEV ₁ %p. IC and FVC, with break points (BP) of 57 and 58 FEV ₁ %p respectively, showed no response above, but an incresed slope below the BP. In addition, in patients with FEV ₁ %p <65 and >65, response of FEV ₁ %p did not correlate to response of volume parameters.
Conclusion: Response of several advanced lung function parameters differs depending on patients' baseline FEV ₁ %p, and specifically response of volume parameters is most pronounced in COPD patients with FEV ₁ %p <65. Volume and resistance responses do not follow the flow response measured with FEV ₁ and may thus be used as a complement to FEV ₁ reversibility to identify flow, volume and resistance responders.
Competing Interests: The authors report no conflicts of interest in this work.