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.