Upper airway mechanics in chronic spinal cord injury during sleep.

Sleep-disordered breathing has been shown to be more prevalent in patients with spinal cord injury (SCI) than the general population. The pathogenesis of increased sleep-disordered breathing in individuals with chronic SCI is unknown. The purpose of this study is to determine whether SCI level affects upper airway (UA) collapsibility and neuromuscular compensatory responses to obstruction. Twenty-four participants (8 cervical SCI, 8 thoracic SCI, and 8 controls) were studied. The ventilation, timing, UA resistance, and pharyngeal collapsibility, defined by critical closing pressure, were determined during non-rapid eye movement sleep. Inspiratory duty cycle and minute ventilation were observed in response to increasing severity of UA obstruction. Compared with controls, both cervical and thoracic SCI participants demonstrated elevated passive critical closing pressure (0.5 ± 2.2 and 0.9 ± 2.7 vs. -2.5 ± 1.0 cmH2O, respectively; P = 0.01). No difference in UA resistance was observed between groups. Cervical and thoracic SCI individuals exhibited a similar degree of hypoventilation and dose-dependent increase in inspiratory duty cycle in response to UA obstruction. Passive UA collapsibility is increased in both cervical and thoracic SCI compared with control. The neuromuscular compensatory responses to UA obstruction during sleep are preserved in chronic SCI and are independent of the level of injury.