Abstract
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 (VE/VCO2) and oxygen (VE/VO2) 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 VE/VCO2 and VE/VO2, thus enabling calculation of the difference between peak effort value and nadir values of VE/VCO2 and VE/VO2, designated ΔVE/VCO2 and ΔVE/VO2, respectively. Results: We found a statistically significant inverse correlation between both ΔVE/VCO2 (r = -0. 5058, 95% CI -0.7750 to -0.08149, p = 0.0234) and ΔVE/VO2 (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 ΔVE/VCO2 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.
Highlights
Chronic obstructive pulmonary disease (COPD) patients often demonstrate significant effort limitation, resulting from gas exchange abnormalities and ventilation-perfusion mismatching1
We found a statistically significant inverse correlation between both ΔVE/CO2 output (VCO2) (r = -0.5058, 95% CI -0.7750 to -0.08149, p = 0.0234) and nadir to peak value of VE/oxygen consumption (VO2) (ΔVE/VO2) (r = -0.5588, 95% CI -0.8029 to -0.1545, p = 0.0104), with the degree of air trapping as estimated by the residual volume (RV)/total lung capacity (TLC) ratio (Figure 1)
We found that the ability to increase ventilation during incremental exercise testing in response to metabolic acidosis, as normally occurs in higher exercise intensities beyond the ventilatory compensation point, was diminished in chronic obstructive pulmonary disease (COPD) patients and in correlation with the severity of air trapping as represented by RV/TLC obtained at rest
Summary
Chronic obstructive pulmonary disease (COPD) patients often demonstrate significant effort limitation, resulting from gas exchange abnormalities and ventilation-perfusion mismatching. Chronic obstructive pulmonary disease (COPD) patients often demonstrate significant effort limitation, resulting from gas exchange abnormalities and ventilation-perfusion mismatching1 This situation is often compounded by hyperinflation and air trapping with dynamic hyperinflation during exercise and gradual reduction of inspiratory capacity. 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 (VE/VCO2) and oxygen (VE/VO2) may be difficult to identify in COPD patients because of limited ventilatory compensation capacity. 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. 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
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