Maximal inspiratory flow rates in patients with COPD

OBJECTIVES: To assess the relevance of maximal inspiratory flow rates (MIFR) in the assessment of airway obstruction in COPD. SETTING: University teaching hospital. PARTICIPANTS: Ten consecutive COPD patients (O group; mean [+/- SD] age, 58.5+/-8.3 years) and 10 matched healthy subjects (H group; mean age, 58.7+/-7.4 years). MEASUREMENTS: Lung volumes, FEV(1), specific airway conductance, single-breath lung diffusing capacity, MIFR, and maximal expiratory flow rates (MEFR). RESULTS: Mean FEV(1)/vital capacity (VC) was 74.7% in the H group and 37.8% in the O group (p<0.001). Total lung capacity was higher (p<0.001) in the O group compared with the H group. Lung diffusing capacity was less than half in the O group compared with the H group (p<0.001). MEFR at all lung volumes were lower in the O group (p<0.001). MIFR were comparable in the two groups, except at 25% inspired VC, where MIFR were lower in the O group (p< 0.05). CONCLUSION: MIFR are less sensitive than MEFR to detect airway obstruction in COPD patients. Yet, the interest of MIFR lay in the possibility to separate intrinsic from extrinsic involvement of airways. A normal MIFR associated with low MEFR, as in the present study, suggests either a lack of parenchymal support, an increased collapsibility of the airways, or a reversible peripheral airway narrowing. A fixed, generalized airway narrowing would be associated with a decrease of both MIFR and MEFR.