Gas exchange efficiency slopes to assess exercise tolerance in chronic obstructive pulmonary disease.

BACKGROUND: In patients with chronic obstructive pulmonary disease (COPD), the clinical use of the minute ventilation-carbon dioxide production ([Formula: see text]E-[Formula: see text]CO2) slope has been reported as a measure of exercise efficiency, but the oxygen uptake efficiency slope (OUES), i.e., the slope of oxygen uptake ([Formula: see text]O2) versus the logarithmically transformed [Formula: see text]E, has rarely been reported. METHODS: We hypothesized that the [Formula: see text]E-[Formula: see text]CO2 slope is more useful than OUES in clinical use for the pathophysiological evaluation of COPD. Then, we investigated the cardiopulmonary exercise testing parameters affecting each of these slopes in 122 patients with all Global Initiative for Chronic Obstructive Lung Disease (GOLD) COPD grades selected from our database. RESULTS: Compared with the GOLD I-II group (n = 51), peak [Formula: see text]O2 (p < 0.0001), OUES (p = 0.0161), [Formula: see text]E at peak exercise (p < 0.0001), and percutaneous oxygen saturation (SpO2) at peak exercise (p = 0.0004) were significantly lower in the GOLD III-IV group (n = 71). The GOLD III-IV group was divided into two groups by the exertional decrease in SpO2 from rest to peak exercise: 3% or less (the non-desaturation group: n = 23), or greater than 3% (the desaturation group: n = 48). OUES correlated only weakly with peak [Formula: see text]O2, [Formula: see text]E at peak exercise, and the difference between inspired and expired mean O2 concentrations (ΔFO2) at peak exercise, i.e., an indicator of oxygen consumption ability throughout the body, in the GOLD III-IV group with exertional hypoxemia. In contrast, the [Formula: see text]E-[Formula: see text]CO2 slope was significantly correlated with ΔFO2 at peak exercise, regardless of the COPD grade and exertional desaturation. Across all COPD stages, there was no correlation between the [Formula: see text]E-[Formula: see text]CO2 slope and [Formula: see text]E at peak exercise, and stepwise analysis identified peak [Formula: see text]O2 (p = 0.0345) and ΔFO2 (p < 0.0001) as variables with a greater effect on the [Formula: see text]E-[Formula: see text]CO2 slope. CONCLUSIONS: The OUES may be less useful in advanced COPD with exertional hypoxemia. The [Formula: see text]E-[Formula: see text]CO2 slope, which is independent of [Formula: see text]E, focuses on oxygen consumption ability and exercise tolerance in COPD, regardless of the exertional hypoxemia level and COPD grade. Therefore, the [Formula: see text]E-[Formula: see text]CO2 slope might be useful in establishing or evaluating tailor-made therapies for individual patient's pathologies in COPD as an indicator focusing on oxygen consumption ability.

Exercise intolerance and oxygen dynamics in nontuberculous mycobacteria with bronchiectasis.

BACKGROUND: Nontuberculous mycobacterial pulmonary disease (NTM-PD) patients often have exercise intolerance. Pulmonary rehabilitation (PR) to improve such patients' conditions is often not based on its exercise pathophysiology. We have reported that the oxygen consumption (ΔFO2) by expiratory gas analysis, i.e., the inspired-expired-expiratory mean oxygen concentration difference, is related to the minute ventilation-carbon dioxide output (V'E-V'CO2)-slope and oxygen uptake (V'O2) independent of the V'E. The aim of this study was to investigate how ΔFO2 is related to dynamic ventilatory variables, chest computed tomography (CT), and echocardiography findings in NTM-PD patients to understand their pathophysiological conditions. METHODS: Clinical data of NTM-PD patients with exertional dyspnea (n = 29) who underwent incremental exercise testing, chest CT, and echocardiography at the same time were compared with those of control participants (n = 12). RESULTS: In the NTM-PD group, 1) peak V'O2 decreased (NTM-PD: 17.6 vs. controls: 28.7 mL⋅min-1⋅kg-1), and 2) ΔFO2 at peak exercise was negatively correlated with respiratory frequency at peak exercise (correlation coefficient: r = -0.80, p < 0.0001), V'E-V'CO2-slope (r = -0.75, p < 0.0001), bronchiectasis CT score (r = -0.52, p = 0.0042), and the trans-tricuspid pressure gradient (r = -0.39, p = 0.0417), and positively correlated with peak V'O2 (r = 0.71, p < 0.0001) and the body mass index (r = 0.42, p = 0.0217), but it was not correlated with V'E at peak exercise and the cavity CT score. CONCLUSIONS: Exertional oxygen consumption, independent of ventilatory ability, is associated with exercise tolerance and ventilatory efficiency, while being related to tachypnea and bronchiectasis rather than cavitation in NTM-PD patients. These findings may be useful in considering exercise physiology-based PR for NTM-PD patients with exertional dyspnea.

Increased Oxygen Extraction by Pulmonary Rehabilitation Improves Exercise Tolerance and Ventilatory Efficiency in Advanced Chronic Obstructive Pulmonary Disease.

BACKGROUND: In cardiopulmonary exercise testing (CPET), oxygen uptake (V'O2) is calculated using the product of minute ventilation (V'E) and the difference between inspiratory and expiratory O2 concentrations (ΔFO2). However, little is known about the response of ΔFO2 to pulmonary rehabilitation (PR). The aim of the present study was (1) to investigate whether PR increases peak V'O2, based on whether ΔFO2 or V'E at peak exercise increase after PR, and (2) to investigate whether an improvement in ΔFO2 correlates with an improvement in ventilatory efficiency. METHODS: A total of 38 patients with severe and very severe COPD, whose PR responses were evaluated by CPET, were retrospectively analyzed. RESULTS: After PR, peak V'O2 was increased in 14 patients. The difference in ΔFO2 at peak exercise following PR correlated with the difference in peak V'O2 (r = 0.4884, p = 0.0019), the difference in V'E/V'CO2-nadir (r = -0.7057, p < 0.0001), and the difference in V'E-V'CO2 slope (r = -0.4578, p = 0.0039), but it did not correlate with the difference in peak V'E. CONCLUSIONS: The increased O2 extraction following PR correlated with improved exercise tolerance and ventilatory efficiency. In advanced COPD patients, a new strategy for improving O2 extraction ability might be effective in those in whom ventilatory ability can be only minimally increased.