TY - JOUR T1 - Inspiratory Fraction is Correlated with Exercise Capacity of Patients with Stable Moderate to Severe Chronic Obstructive Pulmonary Disease JF - Respiratory Care DO - 10.4187/respcare.01927 SP - respcare.01927 AU - Yan Zhang AU - Xing-guo Sun AU - Wen-lan Yang AU - Xiao-yue Tan AU - Jin-ming Liu Y1 - 2013/04/16 UR - http://rc.rcjournal.com/content/early/2013/04/16/respcare.01927.abstract N2 - BACKGROUND: Exercise intolerance is the hallmark of chronic obstructive pulmonary disease (COPD). Static lung hyperinflation and increased dynamic hyperinflation during exercise have been associated with the reduced functional capacity in these patients. Inspiratory capacity (IC) correction for the total lung capacity (TLC), defined as inspiratory fraction (IF) may be functionally more representative than other traditional indices in these patients. OBJECTIVE: To investigate the association between IF and the exercise capacity of patients with stable moderate to severe COPD. METHODS: Fifty patients and thirty-four healthy volunteers constituted the study cohort. Pulmonary function tests (PFT) and cardiopulmonary exercise testing (CPET) were performed, parameters of lung ventilation and gas exchange were measured. RESULTS: IF was significantly correlated with peak V̇ O2%pred of patients with stable moderate to severe COPD(r = 0.52, p < 0.001). IF was an independent factor in predicting a reduced exercise capacity of COPD patients, and was more sensitive and specific than forced expiratory volume in one second (FEV1%pred). Statistical analysis generated the final model as: peak V̇ O2%pred = 65.9IF + 0.45FEV1%pred + 35.8 (RC2 = 0.39, p < 0.001). Patients with IF lower than 0.23 had more severe lung hyperinflation and less exercise capacity than the patients with IF higher than 0.23. At peak exercise, breathing frequencies of two groups were similar, whereas low IF patients had reduced peak minute ventilation and peak tidal volume relative to the patients with high IF. CONCLUSIONS: IF is a robust factor to reflect lung hyperinflation and to estimate the exercise capacity of patients with stable moderate to severe COPD compared to FEV1. ER -