Motor Pathophysiology Related to Dyspnea in COPD Evaluated by Cardiopulmonary Exercise Testing

The relationship between homocysteine and cardiopulmonary exercise testing in patients with acute coronary syndrome after percutaneous coronary intervention

OBJECTIVE

The purpose of this study was to investigate the relationship between homocysteine (Hcy) levels and cardiopulmonary exercise testing (CPET) in patients with acute coronary syndrome (ACS) after percutaneous coronary intervention (PCI). We also explored the relationship between Hcy levels and cardiac ultrasonography.

METHODS

This study comprised 261 patients with ACS who underwent coronary angiography and PCI at Yulin First Hospital from January 2020 to June 2021. All subjects completed basic data collection, laboratory examination, CPET and cardiac ultrasonography. The CPET includes the peak oxygen uptake (peak VO₂), anaerobic threshold (AT), metabolic equivalents (METs), exercise load (load), oxygen pulse (O₂ pulse), end-tidal CO₂ partial pressure (PETCO₂), ventilatory equivalents for carbon dioxide (VE/VCO₂) and Oxygen uptake efficiency (OUES). Cardiac ultrasonography was used to evaluate the left ventricular end diastolic diameter (LVEDD), interventricular septal thickness (IVST), left ventricular posterior wall thickness (LVPWT) and left ventricular ejection fraction (LVEF). A serum Hcy level ≥ 15 µmol/L was defined as hyperhomocysteinemia (HHcy). The patients were divided into the Hcy < 15 µmol/L group (n = 189) and the Hcy ≥ 15 µmol/L group (n = 72).

RESULTS

The average age of the participating patients was 58.9 ± 10.1 years. The majority of participants were male (86.6%). The CPET indices of METs, load, VO₂/kg, and PETCO₂ were significantly decreased in the Hcy ≥ 15 µmol/L group compared with the Hcy < 15 µmol/L group. Additionally, the CPET index of the VE/VCO₂ slope and the cardiac ultrasonography indices of IVST and LVPWT were significantly increased in the Hcy ≥ 15 µmol/L group compared with the Hcy < 15 µmol/L group. These differences were statistically significant (P < 0.05). Correlation analysis showed that Hcy levels were negatively correlated with METs, VO₂/kg and PETCO₂ and positively correlated with the VE/VCO₂ slope (P < 0.05). Partial correlation analysis showed that Hcy levels were negatively correlated with METs and VO₂/kg in the AT state. The correlation coefficients were - 0.172 and - 0.172, respectively (P < 0.05). Hcy levels were negatively correlated with METs, VO₂/kg and PETCO₂ in the peak state. The correlation coefficients were - 0.177, -0.153 and - 0.129, respectively (P < 0.05). After further adjustment for confounders, multiple linear regression analysis showed that Hcy levels were negatively correlated with METs and VO₂/kg in the AT state and peak state. The standardized regression coefficients were - 0.035, -0.122, -0.048 and - 0.128, respectively (P < 0.05). Correlation analysis showed that Hcy levels were positively correlated with the IVST and LVPWT (P < 0.05), but after adjusting for confounding factors, partial correlation analysis showed that there was no correlation between them.

CONCLUSION

A high Hcy level is associated with lower METs and VO₂/kg and worse cardiopulmonary function in patients with ACS after PCI.

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.

Oxygen Extraction Based on Inspiratory and Expiratory Gas Analysis Identifies Ventilatory Inefficiency in Chronic Obstructive Pulmonary Disease

Aims: In contrast to cardiovascular disease, low rather than high ventilatory inefficiency, evaluated by the minute ventilation-carbon dioxide output (V'_E-V'_CO2)-slope, has been recognized as being related to greater disease severity in chronic obstructive pulmonary disease (COPD). To better care for patients with cardiopulmonary disease, understanding the physiological correlation between ventilatory inefficiency and exercise limitation is necessary, but remains inadequate. Given that oxygen uptake (V'_O2) evaluated by cardiopulmonary exercise testing (CPET) depends on both the ventilatory capability and oxygen extraction, i.e., the difference between inspiratory and expiratory oxygen concentration (ΔFO₂), the aim of this study was to investigate the correlations between V'_E-V'_CO2-slope and the ΔFO₂ during exercise and their physiological implications in patients with COPD.

Methods: A total of 156 COPD patients (mean age, 70.9 ± 7.2 years) with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages I–IV and 16 controls underwent CPET with blood gas analysis.

Results: With the progression of COPD, mechanical ventilatory constraints together with a slower respiratory frequency led to exertional respiratory acidosis. In GOLD IV cases, (1) decrease in the dependence of reduced peak V'_O2 on V'_E led to an increase in its dependence on peak ΔFO₂ during exercise; and (2) the ΔFO₂-V'_CO2-slope became steeper, correlating with the severity of exertional respiratory acidosis (r = 0.6359, p < 0.0001). No significant differences in peak exercise ΔFO₂ or V'_E-V'_CO2-slope were observed among the various GOLD stages. In all subjects, including controls, peak exercise ΔFO₂ had the strongest correlation with the V'_E-V'_CO2-slope (r = −0.8835, p < 0.0001) and correlated well with body mass index (r = 0.3871, p < 0.0001), although it did not correlate with the heart rate-V'_CO2-relationship and V'_E.

Conclusions: Ventilatory efficiency related to CO₂ clearance might depend on exertional oxygen extraction in the body. Measuring ΔFO₂ might be a key component for identifying ventilatory inefficiency and oxygen availability. Increasing ΔFO₂ would help to improve ventilatory inefficiency and exercise tolerance separately from cardiac and ventilatory capability in COPD patients.