Abstract
Tidal volume at peak exercise and vital capacity ratio (VTpeak/VC) and VTpeak/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 VTpeak/TLC is more significantly correlated with static air trapping and lung hyperinflation in patients with COPD than VTpeak/IC, VTpeak/FVC, and VTpeak/SVC (study 1), and developed a marker to replace dynamic IC maneuvers by evaluation of the relationship between end-expiratory lung volume (EELV) and VTpeak/TLC and identification of a cutoff value for VTpeak/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 VTpeak/TLC. In study 1, VTpeak/TLC was more significantly associated with airflow obstruction, static air trapping and hyperinflation. In study 2, VTpeak/TLC was highly correlated with EELV in the patients (r = −0.83), and VTpeak/TLC ≥ 0.27 predicted that 18% of the patients with static air trapping and hyperinflation can expand their VT equivalent to the controls. In conclusions, VTpeak/TLC was superior to other VTpeak/capacities. VTpeak/TLC may be a marker of dynamic hyperinflation in subjects with COPD, thereby avoiding the need for dynamic IC maneuvers. VTpeak/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.
Highlights
(EELV) and VTpeak/total lung capacity (TLC) and identification of a cutoff value for VTpeak/TLC
VTpeak/TLC and VTpeak/SVC were significantly lower in the subjects in study 1 than in the chronic obstructive pulmonary disease (COPD) group in study 2, while VTpeak/FVC and VTpeak/IC were similar between the two COPD groups
The key findings of this study were that VTpeak/TLC was the best marker for dynamic expandability of lungs compared to VTpeak/SVC, VTpeak/FVC, and VTpeak/IC in the subjects with COPD (Table 3, |r| = 0.45–0.62 vs. 0.001– 0.49)
Summary
(EELV) and VTpeak/TLC and identification of a cutoff value for VTpeak/TLC (study 2). One hundred adults with COPD (study 1) and 23 with COPD and 19 controls (study 2) were analyzed. VTpeak/TLC < 0.27 identified approximately 82% of subjects with COPD who could not adequately expand their tidal volume. VT/VC tends to be more variable because of variations in SVC and FVC in subjects with COPD due to pseudorestriction (i.e., low FVC%pred but normal total lung capacity, TLC). In this context, variations in operating VT at peak exercise and the “false” restriction of FVC www.nature.com/scientificreports/. (or SVC or IC) lead to inconsistent values of VT/FVC, VT/SVC, and VT/IC These variables are not recommended to differentiate obstructive from restrictive ventilatory limitations[8]. The ramp-pattern protocol is a widely used protocol to test incremental exercise
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