Evaluation of carbon dioxide rebreathing during exercise assisted by noninvasive ventilation with plateau exhalation valve

Abstract

Noninvasive ventilation with a plateau exhalation valve (PEV) is often used as an adjunct to exercise to achieve a physiologic training effect in severe chronic obstructive pulmonary disease (COPD) patients. However, during exercise, with the increase of exhalation flow and respiratory rate and limited capability of PEV to exhale gases out of the circuit, it is still unknown whether CO₂ rebreathing occurs in COPD patients ventilated during exercise assisted by single-limb circuit with a PEV. A maximal symptom-limited cycle exercise test was performed while ventilated on pressure support (inspiratory:expiratory pressure 14:4 cmH₂O) in 18 male patients with stable severe COPD (mean ± standard deviation, forced expiratory volume in 1 s: 29.5%±6.9% predicted). At rest and during exercise, breathing pattern, mean expiratory flow, mean expiratory flow of PEV, and the mean inspiratory fraction of CO₂ (tidal fractional concentration of inspired CO₂ [FiCO₂]) reinsufflated from the circuit was measured for each breath. In comparison with rest, with the significant increase of mean expiratory flow (0.39±0.15 vs 0.82±0.27 L/s), fractional concentration of end-tidal CO₂ (2.6%±0.7% vs 5.5%±0.6%), and the significant decrease of mean expiratory flow of PEV (0.41±0.02 vs 0.39±0.03 L/s), tidal FiCO₂ significantly increased at peak exercise (0.48%±0.19% vs 1.8%±0.6%) in patients with stable severe COPD. The inflection point of obvious CO₂ rebreathing was 0.67±0.09 L/s (95% confidence interval 0.60–0.73 L/s). Ventilated by a single-limb tubing with PEV caused CO₂ rebreathing to COPD patients during exercise. Patients with mean expiratory flow >0.60–0.73 L/s may be predisposed to a higher risk of CO₂ rebreathing.

Keywords:

• carbon dioxide rebreathing
• noninvasive ventilation
• exercise
• chronic obstructive pulmonary disease
• single-limb circuit
• pulmonary rehabilitation

Acknowledgments

The authors thank colleagues from the pulmonary function test room (Division of Respiratory Diseases Department, Guangzhou Institute of Respiratory Disease, First Affiliated Hospital of Guangzhou Medical University, People’s Republic of China) for their collaboration, and Doctors Yi Gao, Wei-jie Guan, and Li-ping Zhong for technical support.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosure

The authors report no conflicts of interest in this work.