Table 2.

Paediatric OSA upper airway phenotypes by age and neuromotor endotypes. Protective mechanoreceptor and chemoreceptor reflexes ensure appropriate neuromuscular airway tone and ventilatory drive. The former decreases rapidly with the onset of sleep. The latter decreases in response to both hypoxaemia and hypercarbia. However, this results from high airway collapsibility and a blunted ‘airway self-rescue’ arousal threshold and increased instability of ventilatory control (high ‘loop gain’) increasing airway resistance load; sensitivity to oxygen and carbon dioxide is not directly affected. High loop gain refers to an exaggerated cyclical respiratory response to a respiratory disturbance. For example, airway tone and patency cycles between high, unobstructed to low, obstructed because of excessive ventilatory responses to hypo- and hypercarbia, respectively. Obesity may also contribute to blunted ventilatory and arousal responses because of leptin resistance

OSA neuromotor airway endotype	Receptor (location)	OSA phenotypes
		Infant (0–1 yr)	Child (2–8 yrs)	Preteen/teen (9–21 yrs)
Collapsibility (genioglossus)	CO2 (brainstem) Mechano (airway)	High	High	High
Ventilatory drive	O2 (peripheral) CO2 (brainstem)	?	Normal	?
Arousability ‘Airway self-rescue’	O2 (peripheral) CO2 (brainstem) Mechano (airway)	Blunted	Blunted	Blunted to high
Instability of ventilatory control ‘Loop gain’	O2 (peripheral) CO2 (peripheral and brainstem)	High	? High	? High