Assessment of Circuit Rebreathing During CPAP Therapy

To understand the existence and severity of circuit rebreathing during treatment with continuous positive airway pressure (CPAP) using different sizes of the exhaust ports in individuals with obstructive sleep apnea (OSA).

Flow-adjusted end-tidal oxygen (PetO2) and carbon dioxide (PetCO2) will be assessed to determine the magnitude of hypoxic load during both wakefulness and sleep. To systematically assess these conditions, the conditions were defined as follows:

• 5A: 35 L/s exhaust flow with 5 cmH₂O PAP
• 5B: 23 L/s exhaust flow with 5 cmH₂O PAP
• 5C: 18 L/s exhaust flow with 5 cmH₂O PAP
• 5D: 13 L/s exhaust flow with 5 cmH₂O PAP
• 5E: 8 L/s exhaust flow with 5 cmH₂O PAP
• 0P: 35 L/s exhaust flow with 0 cmH₂O PAP
• 10A: 35 L/s exhaust flow with 10 cmH₂O PAP
• 10B: 23 L/s exhaust flow with 10 cmH₂O PAP
• 10C: 18 L/s exhaust flow with 10 cmH₂O PAP
• 10D: 13 L/s exhaust flow with 10 cmH₂O PAP
• 10E: 8 L/s exhaust flow with 10 cmH₂O PAP Primary endpoint is to evaluate the effect of exhaust flow on flow-adjusted average inspired oxygen fraction (FiO₂) during (1) wakefulness and (2) sleep between 5B vs. 5D.

Inclusion criteria

• Moderate to severe OSA (AHI>20)
• Self-reported CPAP users or have previously used CPAP
• Self-reported holding pressure of maximum 13 cmH2O (if known)
• Age: 21-70
• BMI: 18-40 kg/m2

Exclusion criteria

• Self-reported severe mouth-breathing
• Requirement for nocturnal supplemental oxygen or other ventilatory support
• Severe cardiovascular or pulmonary disease
• Any unstable or acute medical condition
• Any additional sleep disorder, including insomnia, except for OSA.