Background: Inhalation of low-dose CO₂ (for example 2.5% CO₂) using a traditional tightly fitting mask could eliminate central sleep apnea in patients with heart failure.   However, the reduction of central sleep apnea events with CO₂ inhalation is associated with increased arousal index, greater sleep disturbance and increased sympathetic nervous activity.  It is unknown whether these side effects associated with CO₂ therapy are because of hypercapnia or intolerance of the mask.

Objectives: We recently invented a device including a novel open mask which is able to supply CO₂ in accurate concentration comfortably.

Methods: Two overnight full polysomnography studies during inhalation of room air or 2.5 % CO₂ were performed in seventeen healthy subjects (aged 36 ± 12 years, BMI 21.7 ± 2.7 Kg/m2) in random order. Arteria blood gases were also performed in the morning in 10 of seventeen subjects.

Results: As expected, end-tidal CO₂ during inhalation of 2.5% CO₂ was significantly higher than that during breathing room air (41.4 ± 2.9 mmHg vs 38.3 ± 3.3 mmHg, p<0.001).  Sleep duration during inhalation of 2.5% CO₂ was longer than that during inhalation of room air (411 ± 48 vs 389 ± 51 minutes, p<0.05). The sleep efficacy during inhalation of 2.5% CO₂ also improved significantly (91.8 ± 5.0% vs 87.0± 5.0%, p<0.05).  However, sleep structure including sleep latency, arousal index, respiratory rate, the sensation of breathing difficulty, heart rate and blood pressure between inhalation of 2.5% CO₂ and room air were similar.  

Conclusions: This study shows that inhalation 2.5% CO₂ by using the novel device including an open mask has no obvious side effects in healthy adults.