Inspiratory Fraction Correlates With Exercise Capacity in Patients With Stable Moderate to Severe COPD

Abstract

BACKGROUND: Exercise intolerance is the hallmark of COPD. Static lung hyperinflation and increased dynamic hyperinflation during exercise are associated with reduced functional capacity in COPD patients. Inspiratory capacity correction for the total lung capacity, 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 exercise capacity in patients with stable, moderate to severe COPD. METHODS: Fifty COPD subjects and 34 healthy volunteers constituted the study cohort. Pulmonary function and cardiopulmonary exercise testing were performed, and ventilation and gas exchange parameters were measured. RESULTS: IF was significantly correlated with percent-of-predicted peak oxygen consumption (V O 2 ) in the subjects with COPD (r ‫؍‬ 0.52, P < .001). IF was an independent predictor of reduced exercise capacity in the COPD subjects, and was more sensitive and specific than percent-of-predicted FEV 1 . Statistical analysis generated the equation: percent-of-predicted peak V O 2 ‫؍‬ 65.9 IF ؉ 0.45 percent-of-predicted FEV 1 ؉ 35.8 (R C 2 ‫؍‬ 0.39, P < .001). The subjects with IF < 0.23 had more severe lung hyperinflation and less exercise capacity than the subjects with IF > 0.23. At peak exercise, the breathing frequencies of the 2 groups were similar, whereas the low-IF subjects had reduced peak minute ventilation and peak tidal volume, relative to the high-IF subjects. CONCLUSIONS: Compared to FEV 1 , IF is a robust factor to reflect lung hyperinflation and to estimate the exercise capacity of subjects with stable moderate to severe COPD.

Combining Dynamic Hyperinflation with Dead Space Volume during Maximal Exercise in Patients with Chronic Obstructive Pulmonary Disease

“…In addition to EELV peak % >75% [25], the reciprocal IC peak /TLC <25% [26] has also been associated with lower O 2P and exercise capacity in patients with severe COPD. IC peak /TLC <23% has also been associated with lower O 2P and exercise capacity in patients with severe COPD [27]. Although OUES was not measured in this study, our previous study reported that IC peak /TLC was significantly correlated with O 2P and ∆O 2P (r = 0.35-0.36, both p < 0.05) [28].…”

Forced Mid-Expiratory Flow Can Predict Ventilatory Limitation and Exercise Capacity

“…A few small studies have demonstrated a significant correlation between resting pulmonary function test (PFT) parameters and overall exercise capacity in COPD patients. These studies however did not explore whether the exercise limitations observed were specifically related to subjects' underlying lung disease and compromised ventilatory capacity as opposed to concurrent co-morbidities [15][16][17][18][19].…”

“…FEV1 and FVC had significant (p < 0.001) associations with peak exercise capacity VO2 (area under curve of 0.62 and 0.71 respectively) [15]. Zhang and co-workers investigated the association of post-bronchodilator PFTs with exercise capacity in a cohort of 50 COPD subjects [17]. The area under the curve for FEV1% as predictor of peak VO2 was 0.853 (95% CI 0.751 -0.955, p < 0.001) [17].…”

“…Zhang and co-workers investigated the association of post-bronchodilator PFTs with exercise capacity in a cohort of 50 COPD subjects [17]. The area under the curve for FEV1% as predictor of peak VO2 was 0.853 (95% CI 0.751 -0.955, p < 0.001) [17]. Similarly, Albuquerque, et al studied exercise capacity in 44 patients with moderately severe COPD and found that the area under the receiver operating characteristic (ROC) curve was 0.86 (0.73 -0.99) for FEV1 [18].…”

Static hyperinflation is associated with ventilatory limitation and exercise tolerance in adult cystic fibrosis

“…The assessment of static hyperinflation may, therefore, be of value to clinicians working in pulmonary rehabilitation to predict whether the patient is more likely to experience an adverse response to exercise. In patients with chronic obstructive pulmonary disease, significant correlations between IC/TLC and exercise tolerance have been reported 24,25 and between the IC and exercise tolerance when defined as exercise endurance time. 26 The latter study reported a stronger relationship between exercise endurance time and static hyperinflation than airway obstruction (FEV 1 ).…”