Ventilatory compensation during the incremental exercise test is inversely correlated with air trapping in COPD.

Kuint R; Berkman N; Nusair S;

F1000Research [F1000Res] 2019 Sep 19; Vol. 8, pp. 1661. Date of Electronic Publication: 2019 Sep 19 (Print Publication: 2019).

Background: Air trapping and gas exchange abnormalities are major causes of exercise limitation in chronic obstructive pulmonary disease (COPD). During incremental cardiopulmonary exercise testing, ventilatory equivalents for carbon dioxide (V E /VCO 2 ) and oxygen (V E /VO 2 ) may be difficult to identify in COPD patients because of limited ventilatory compensation capacity. Therefore, we aimed to detect a possible correlation between the magnitude of ventilation augmentation, as manifested by increments in ventilatory equivalents from nadir to peak effort values and air trapping, detected with static testing.
Methods: In this observational study, we studied data obtained previously from 20 COPD patients who, during routine follow-up, underwent a symptom-limited incremental exercise test and in whom a plethysmography was obtained concurrently. Air trapping at rest was assessed by measurement of the residual volume (RV) to total lung capacity (TLC) ratio (RV/TLC). Gas exchange data collected during the symptom-limited incremental cardiopulmonary exercise test allowed determination of the nadir and peak effort values of V E /VCO 2 and V E /VO 2 , thus enabling calculation of the difference between peak effort value and nadir values of  V E /VCO 2 and V E /VO 2 , designated ΔV E /VCO 2 and ΔV E /VO 2 , respectively.
Results: We found a statistically significant inverse correlation between both ΔV E /VCO 2 (r = -0. 5058, 95% CI -0.7750 to -0.08149, p = 0.0234) and ΔV E /VO 2 (r = -0.5588, 95% CI -0.8029 to -0.1545, p = 0.0104) and the degree of air trapping (RV/TLC). There was no correlation between                ΔV E /VCO 2 and peak oxygen consumption, forced expiratory volume in the first second, or body mass index.
Conclusions: The ventilatory equivalents increment to compensate for acidosis during incremental exercise testing was inversely correlated with air trapping (RV/TLC) and may be a candidate prognostic biomarker.