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Inspiratory fraction and exercise impairment in COPD patients GOLD stages II–III

Pulmonary Function and Clinical Exercise Physiology Unit, Dept of Medicine, Division of Respiratory Diseases, Federal University of Sao Paulo (UNIFESP), São Paulo, Brazil.

CORRESPONDENCE: J. A. Neder, Pulmonary Function and Clinical Exercise Physiology Unit (SEFICE), Respiratory Division, Dept of Medicine, Federal University of Sao Paulo, Paulista School of Medicine (UNIFESP-EPM), Rua Professor Francisco de Castro 54, Vila Clementino, CEP, 04020-050, Sao Paulo, Brazil. Fax: 55 1155752843. E-mail: albneder{at}pneumo.epm.br

Keywords: Chronic obstructive pulmonary disease, dyspnoea, exercise, inspiratory fraction, lung hyperinflation, lung volumes

Received: March 21, 2006
Accepted June 29, 2006

The inspiratory-to-total lung capacity ratio or "inspiratory fraction" (inspiratory capacity(IC)/total lung capacity (TLC)) may be functionally more representative than traditional indices of resting airflow limitation and lung hyperinflation in patients with chronic obstructive pulmonary disease (COPD).

In the present retrospective study, a comparison was made of the individual performance of post-bronchodilator IC, IC/TLC and forced expiratory volume in one second (FEV₁) in predicting a severely reduced peak oxygen uptake (V'_O2; <60% predicted) in 44 COPD patients Global Initiative for Chronic Obstructive Lung Disease stages II-III (post-bronchodilator FEV₁ ranging from 31–79% pred).

Patients with lower IC/TLC values (0.28) showed increased lung volumes and reduced exercise capacity as compared with other subjects. Following a multiple linear regression analysis, only IC/TLC and FEV₁ remained as independent predictors of V'_O2 (r² = 0.33). A receiver operating characteristic (ROC) curve analysis revealed that an IC/TLC 0.28 had the highest specificity (89.6%), positive predictive value (80%) and overall accuracy (86.3%) in identifying patients with V'_O2 <60% pred. In addition, the area under the ROC curve tended to be higher for IC/TLC than IC.

In conclusion, post-bronchodilator total lung capacity-corrected inspiratory fraction provides useful information in addition to forced expiratory volume in one second and inspiratory capacity, to estimate the likelihood of chronic obstructive pulmonary disease patients to present with severely reduced maximal exercise capacity.