Inspiratory Fraction (IC/TLC) and Exercise Impairment in COPD Patients GOLD Stages II-III

¹ Pulmonary Function and Clinical Exercise Physiology Unit Dept of Medicine, Division of Respiratory Diseases, Federal University of Sao Paulo (UNIFESP), São Paulo, São Paulo, Brazil

^* To whom correspondence should be addressed. E-mail: albneder{at}pneumo.epm.br.

	Abstract

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

On a retrospective study, we contrasted the individual performance of post-bronchodilator IC, IC/TLC and FEV₁ in predicting a severely-reduced peak V'O₂ (<60% predicted) in 44 COPD patients GOLD stages II-III (post-bronchodilator FEV₁ ranging from 31% to 79 % predicted).

Patients in the lowest IC/TLC tertile (0.28) showed increased lung volumes and reduced exercise capacity as compared to other subjects (p<0.05). On a multiple linear regression analysis, only IC/TLC and FEV₁ remained as independent predictors of peak V'O₂ (r²=0.33, p <0.01). A 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 peak V'O₂ <60% predicted. In addition, the area under the ROC curve tended to be higher for IC/TLC than IC (p=0.06).

In conclusion, post-bronchodilator TLC-corrected IC (inspiratory fraction) adds useful information to FEV₁ and IC in order to estimate the likelihood of COPD patients to present with severely-reduced maximal exercise capacity.