Reliability of inspiratory capacity for estimating end-expiratory lung volume changes during exercise in patients with chronic obstructive pulmonary disease

The inspiratory capacity (IC) maneuver is increasingly used to monitor exercise-induced dynamic hyperinflation in patients with COPD. However, the reliability of this method in patients with COPD exercising to symptom limitation has not been systematically studied and presented. The purpose of the present study was therefore to evaluate the reliability of the IC maneuver in assessing changes in end-expiratory lung volume (EELV) by assessing the pressure developed during IC maneuvers, in patients with COPD during incremental bicycle exercise to exhaustion. Fifteen patients with stable COPD performed bicycle exercise to symptom limitation. During the experiment, the patients performed IC efforts during resting breathing and at the end of each exercise work load. Esophageal pressure (Pes) measured at peak inspired volume plateau (zero flow) was -13.5 +/- 1.9 and -13.4 +/- 1.9 cm H2O (p = 0.79) during IC maneuvers at resting breathing and during the final exercise work load, respectively. When the Pes values at the peak inspired volume plateau during IC efforts at each exercise level were expressed as a percentage of those during resting breathing, the great majority of the ratios were above 90% with the lowest at 84%, and these ratios were independent of exercise intensity. Despite a constant Pes during IC, there was a progressive decrease in IC with increasing exercise work load in most patients, suggesting an increase in EELV. At the highest exercise work load achieved, Delta EELV calculated as the decrease in IC was 0.26 +/- 0.06 L (p < 0.001). We conclude that repeated IC maneuver is a simple and reliable method for estimating EELV changes during exercise to exhaustion in patients with COPD.