A volume-dependent apneic threshold during NREM sleep in the dog

Area of Science:

• Respiratory Physiology
• Sleep Medicine

Background:

• Central apnea frequently follows hyperpnea induced by airway occlusion during non-rapid-eye-movement (NREM) sleep.
• Understanding the mechanisms behind post-occlusion central apnea is crucial for sleep disorder research.

Purpose of the Study:

• To determine the specific causes of central apnea following airway occlusion during NREM sleep.
• To investigate the roles of tidal volume, arousal, and hypocapnia in post-occlusion central apnea.

Main Methods:

• Measurement of ventilation and end-tidal gases in three dogs during NREM sleep.
• Analysis of 214 trials involving 15-20 second tracheal occlusions.
• Assessment of physiological responses including inspiratory effort, tidal volume, and electroencephalogram activity.

Main Results:

• Central apnea occurred in 62% of occlusion trials, with expiratory durations 3-15 times normal.
• A volume-dependent apneic threshold was identified; tidal volumes exceeding three times eupneic levels were necessary for apnea.
• Transient electroencephalogram arousal augmented tidal volume, prolonging apneas, but was not essential for their occurrence.
• Significant hypocapnia occurred post-occlusion but showed weak correlation with apnea length.
• Vagal blockade reduced hyperventilation and expiratory duration prolongation after occlusion.

Conclusions:

• Tidal volumes significantly exceeding eupneic levels are required to induce central apnea after airway occlusion in NREM sleep.
• Transient arousal at occlusion release exacerbates central apnea by increasing tidal volume.
• Hypocapnia contributes minimally to the central apnea observed after airway occlusion during NREM sleep.