Prevalence and Risk Factors
Breathing disorders including sleep apnea appear to have a higher prevalence in people after SCI than those without with some researchers estimating it is present in 60% of motor complete persons with tetraplegia (Prosperio et al. 2015; Chiodo et al. 2016). In general, the studies that examined the prevalence of OSA were limited by small sample sizes and by an experimental design that lacked a non-SCI control group that could be directly compared to the patients with SCI. Both overnight oximetry and full polysomnography (PSG) were used to diagnose disease. The prevalence rate ranged from 9.1-83% (Short et al. 1992; Burns et al. 2000; Burns et al. 2001; Stockhammer et al. 2002; Berlowitz et al. 2005). Obesity was identified as a risk factor for sleep apnea in most studies. The use of muscle relaxants was identified as a potential risk factor for SDB in some but not all studies (Short et al. 1992; Ayas et al. 2001; Burns et al. 2001; Berlowitz et al. 2005).
Discussion
SDB is common in people with SCI; obesity appears to be a consistent risk factor. There are few studies that have assessed the impact of sleep apnea therapy in patients with SCI.
Burns et al. (2005) demonstrated a long-term acceptance rate of CPAP of 63% (20/32) in patients offered CPAP therapy, and Stockhammer et al. (2002) reported that of the study participants that continued with longer-term usage of CPAP (10/16, 62.5%) experienced it as beneficial. Discontinuing use of CPAP was generally attributed to the discomfort of wearing a mask to sleep or feelings of claustrophobia (Burns et al. 2005). A limited number of studies have examined the impact of sleep apnea therapy on health and QOL outcomes in SCI; future investigations should examine these and other questions with larger sample sizes to determine more accurate effects of CPAP therapy.
A few studies with small sample sizes assessed the use of medications in patients with SCI for SDB. Two RCTs (Maresh et al. 2020; Ginter et al. 2020) found that Buspirone or acetazolamide widened the CO2 reserve and hence decreased susceptibility to hypocapnic central apnea more than a placebo. However, both studies also showed limited effects of these medications on other respiratory parameters of SDB. Wijesuriya et al. (2019) also showed no significant differences on components of SDB with the administration of a phenylephrine nasal spray, other than a 72% decrease of nasal resistance. Additional RCTs with groups of at least 20 participants or more will be required to determine if any of these medications can have significant effects on sleep quality, rapid eye movement (REM) sleep time, or if they can make any other improvements on people with SDB.
Conclusion
There is level 1 evidence (from two RCTs: Maresh et al. 2020; Ginter et al. 2020) that medication such as Buspirone or acetazolamide, expands the CO2 reserve and hence decreases susceptibility to hypocapnic central apnea more than a placebo but does not show effects in other respiratory parameters of SDB in people with SCI.
There is level 1 (from one RCT: Wijesuriya et al. 2019) that administration of a phenylephrine nasal spray provides a 72% decrease of nasal resistance without additional effects in other clinical components of SDB in people with SCI.
There is level 4 evidence (from two case series and two pre-post studies: Stockhammer et al. 2002; Burns et al. 2005; Biering-Sørensen et al. 1995; Yang et al. 2014) to support CPAP therapy to treat SDB in people with SCI.
