Def: insufficient minute ventilation during sleep, reduced breathing with reduced gas exchange
BMI ≥30, awake PaCO2 ≥45 mmHg, other causes excluded
Causes prolonged nocturnal O2 desaturation and elevated CO2
Increased risk of pulmonary HTN and consequent HF
AASM scoring (either):
a. PaCO2 or surrogate >55 mmHg for ≥10 min
b. PaCO2 rise ≥10 mmHg vs awake supine to >50 mmHg for ≥10 min
Causes
1. Increased load on respiratory muscle pump, e.g. OHS
2. Increased airway resistance, e.g. COPD
3. Diminished respiratory muscle pump capacity: myopathies, dystrophies, myasthenia gravis, spinal cord injury, stroke
4. Inability to sustain neural respiratory drive in sleep, e.g. Ondine’s curse (CCHS), stroke
Modifying factors
Supine: abdominal pressure splints diaphragm and adds threshold load on inspiratory muscles
Lateral or prone sleep generally reduces SDB impact
REM: atonia of all skeletal muscles except diaphragm and extraocular muscles
Pts who rely on accessory muscles can develop significant REM hypoventilation
Treatment: NIV with bilevel pressure support often needed for adequate nocturnal ventilation
- Oxford Handbook of Sleep Medicine 2022