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.