Developing a New Marker of Dynamic Hyperinflation in Patients with Obstructive Airway Disease - an observational...

Tidal volume at peak exercise and vital capacity ratio (V_Tpeak/VC) and V_Tpeak/inspiratory capacity (IC) were used to differentiate lung expansion in subjects with normal health and chronic obstructive pulmonary disease (COPD) from that in subjects with restrictive ventilation. However, VC and IC variably change due to pseudorestriction of lung volumes. Thus, these variables are currently not recommended. In contrast, total lung capacity (TLC) does little change during exercise. The aims of the study investigated whether V_Tpeak/TLC is more significantly correlated with static air trapping and lung hyperinflation in patients with COPD than V_Tpeak/IC, V_Tpeak/FVC, and V_Tpeak/SVC (study 1), and developed a marker to replace dynamic IC maneuvers by evaluation of the relationship between end-expiratory lung volume (EELV) and V_Tpeak/TLC and identification of a cutoff value for V_Tpeak/TLC (study 2). One hundred adults with COPD (study 1) and 23 with COPD and 19 controls (study 2) were analyzed. Spirometry, lung volume, diffusing capacity, incremental cardiopulmonary exercise tests with dynamic IC maneuvers were compared between groups. An ROC curve was generated to identify a cut off value for V_Tpeak/TLC. In study 1, V_Tpeak/TLC was more significantly associated with airflow obstruction, static air trapping and hyperinflation. In study 2, V_Tpeak/TLC was highly correlated with EELV in the patients (r = -0.83), and V_Tpeak/TLC ≥ 0.27 predicted that 18% of the patients with static air trapping and hyperinflation can expand their V_T equivalent to the controls. In conclusions, V_Tpeak/TLC was superior to other V_Tpeak/capacities. V_Tpeak/TLC may be a marker of dynamic hyperinflation in subjects with COPD, thereby avoiding the need for dynamic IC maneuvers. V_Tpeak/TLC < 0.27 identified approximately 82% of subjects with COPD who could not adequately expand their tidal volume. As most of our participants were male, further studies are required to elucidate whether the results of this study can be applied to female patients with COPD.