Low Exercise Tidal Volume in Chronic Obstructive Pulmonary Disease Is a Manifestation of Hyperinflation During Exercise

Mumtaz Zaman

PURPOSE: The purpose of this study is to investigate the unsettled relationship between resting hyperinflation and exercise ventilation among patients with chronic obstructive pulmonary disease (COPD) undergoing incremental treadmill exercise testing.

METHODS: Fifty five patients with COPD and 25 normal subjects underwent resting pulmonary function testing and incremental exercise test (IET) on treadmill. Ventilation and gas exchange data were collected on all subjects and exercise duration determined.

RESULTS: Inspiratory capacity/total lung capacity (IC/TLC) ratio was lower in COPD patients compared to normal subjects (0.39 vs 0.47 P=0.009) and so was exercise duration (5.4 vs 8.5 minutes, P=0.0001). The tidal volumes during exercise were lower in COPD patients compared to normal subjects (1.27L vs 2.01L, P < 0.001). There was a correlation between a reduced IC/TLC and peak oxygen consumption (peak VO2) among COPD patients (r=0.35) but not among controls. The reduced exercise capacity in COPD patients was associated with a reduced forced expiratory volume in one second (FEV1) and lower IC/TLC. Also among COPD patients, those with an IC/TLC < 0.25 had lower exercise capacity compared to those with an IC/TLC > 0.25 (peak VO2 0.95 L/min vs 1.26 L/min; P=0.05). The low IC/TLC ratio group had lower FEV1 (0.94L vs 1.5L; p=0.01) and lower tidal volumes (0.93 L vs 1.33 L; P=0.01) compared to high IC/TLC group.

CONCLUSIONS: The mechanisms of reduced exercise tolerance in patients with COPD are several and include combination of airflow obstruction, static and dynamic hyperinflation and dead space ventilation during exercise. A low resting IC/TLC, FEV1 and low exercise tidal volume are predictors of reduced exercise tolerance among patients with COPD.

Chest. 2014;146(4_Meeting