Objective: To correlate the postbronchodilator (post-BD) inspiratory capacity (IC), % of predicted, with other markers of severity and prognostic factors in chronic obstructive pulmonary disease (COPD).
Methods: Eighty stable patients with COPD performed forced vital capacity and slow vital capacity maneuvers, as well as the 6-min walk test, prior to and after receiving albuterol spray (400 microg). Patients were divided into four groups, based on post-BD forced expiratory volume in one second. Several variables were tested to establish correlations with the post-BD distance walked, using univariate and multivariate analysis. Post-BD IC was found to correlated with Global Initiative for Chronic Obstructive Lung Disease (GOLD) staging and with the Body mass index, airway Obstruction, Dyspnea, and Exercise capacity (BODE) index.
Results: Multivariate regression analysis revealed that the distance walked, % predicted, correlated significantly with the IC post-BD, % predicted (p = 0.001), long-term oxygen use (p = 0.014), and number of medications used in the treatment (p = 0.044). IC < 70% was observed in 56% patients in GOLD stages 3 or 4 vs. 20% in GOLD 1 or 2 (p < 0.001). IC < 70% was observed in (60%) patients with BODE score 3 or 4 vs. (33%) BODE score 1 or 2 (p = 0.02).
Conclusion: Post-BD IC% predicted is the best functional predictor of distance walked and is significantly associated with GOLD staging and BODE index. Therefore, We propose that the inspiratory capacity should be added to the routine evaluation of the COPD patients.