Nocturnal swallowing and arousal threshold in individuals with chronic spinal cord injury

Respiratory complications are potential causes of death in patients with spinal cord injury (SCI). Nocturnal swallowing could be related to transient arousals and could lead to fragmented sleep in SCI patients. However, the impact of nocturnal swallowing on breathing and sleep physiology in SCI is unknown. The objectives of this study were 1) to determine whether nocturnal swallowing is more common in SCI than in able-bodied (AB) subjects. 2) to determine the role of nocturnal swallowing on arousal threshold (ArTh) in SCI individuals with sleep-disordered breathing (SDB), and 3) to determine the effect of continuous positive airway pressure (CPAP) treatment on nocturnal swallowing. A total of 16 SCI and 13 AB subjects with SDB completed in-laboratory polysomnography with a pharyngeal catheter. A swallowing event (SW) was defined as a positive spike in pharyngeal pressure and was used to calculate the swallow index (SI) defined as a number of SW/total sleep time. Each SW was assessed for a relationship to the sleep stages and respiratory cycle phases, and associated arousals and ArTh were calculated. SI was higher in the SCI group compared with AB subjects during wake and different sleep stages (P < 0.05). SWs were found to be significantly higher in the late expiratory phase in the group with SCI compared with the other respiratory phases and were eliminated by CPAP (P < 0.05). ArTh for the subjects with SCI was significantly lower (P < 0.05) compared with the AB subjects. Nocturnal swallowing is more common in SCI than in AB individuals who have SDB, particularly during the expiratory phase. The ArTh is significantly lower in SCI (indicating increased arousal propensity), which may contribute to the mechanism of sleep disturbances in SCI. NEW & NOTEWORTHY Nocturnal swallowing is common in patients with chronic spinal cord injury (SCI) and is associated with frequent arousals from sleep. The lower arousal threshold during sleep in SCI may contribute to the mechanism of sleep disturbances that are commonly found in cervical and high thoracic SCI. Continuous positive airway pressure may play a therapeutic role in alleviating nocturnal swallowing, which may contribute to reduced risk of aspiration.