Use of a portable device to record maximum inspiratory flow in relation to dyspnoea in patients with COPD

Forced inspiratory measures have been described to reflect the reduction in dyspnoea upon bronchodilation in severe COPD. Based on this we evaluated the applicability and usefulness of a portable device for the assessment of forced inspiration. In 37 patients with COPD (GOLD II/II/IV n = 16/15/6, mean ± SD FEV(1) 46.2 ± 15.4%pred) lung function was recorded prior to inhalation of 24 μg formoterol and 30 min later. Assessments comprised spirometry including forced inspiration, body plethysmography, maximum inspiratory flow (InCheck, Clement Clarke), and changes in dyspnoea via visual analogue scale (VAS). The sequence was repeated on a second day to assess reproducibility. Bronchodilation by formoterol was detectable in all functional indices (p < 0.05 each) except total lung capacity. FEV(1) improved by (mean ± SD) 11.1 ± 10.3%, forced inspiratory volume in 1s (FIV(1)) by 11.6 ± 13.5%, inspiratory peak flow (PIF) by 10.7 ± 16.2%, and inspiratory flow determined by the InCheck device (IF-IC) by 11.9 ± 14.4%. Remarkably, the changes of IF-IC (p < 0.001) but not those of other measures except FIV(1) (p < 0.05) were related to those of dyspnoea. Effects on IF-IC showed reproducibility comparable to that of other indices. The results suggest that a simple, portable device for recording forced inspiration could be useful in monitoring COPD, as a functional correlate of acute changes in dyspnoea.