[Relationship between sleep architecture and severity of obstructive sleep apnea]

To investigate the effect of obstructive sleep apnea (OSA) on different sleep stages, and the relationship between N3 stage of non-rapid eye movement sleep and respiratory abnormal events.

A total of 188 adult patients who underwent overnight polysomnography(PSG)monitoring in Sir Run Run shaw Hospital of Zhejiang University from June 24th to December 26th 2019 were enrolled in the study. OSA patients were classified into 3 groups (mild, moderate and severe) according to the apnea-hypopnea index (AHI). PSG data, AHI and the lowest SPO₂ in each stage of sleep were compared among three groups.

There was no significant difference in total sleep time and sleep efficiency among patients with different severity of OSA (all P>0.05). The proportion of N3 stage in moderate and severe OSA groups were significantly smaller than that in mild OSA group (all P<0.05). The proportion of N3 stage in severe OSA group was also smaller than that in moderate OSA group (P<0.05). In addition, severe OSA group had a longer latency of N3 stage than mild and moderate OSA groups (all P<0.05). The latency of N3 stage in moderate OSA group was longer than that in mild OSA group (P<0.05). The AHI in N3 stage was markedly lower than that in other sleep stages (all P<0.01), regardless of the severity of OSA. Supine AHI in N3 stage in mild and moderate groups was significantly lower than that in N1, N2 and rapid eye movement (REM) stages (all P<0.01). Supine AHI in N3 stage in severe group was also lower than that in N2 and REM stages (P<0.05 or P<0.01). The lowest SPO₂ in N3 stage was significantly higher than that in N1, N2 and REM stages (P<0.05 or P<0.01), regardless of the severity of OSA.

s The proportion of N3 stage is lower in OSA patients, and N3 stage has less sleep respiratory events than non-N3 stages. The results suggest that the increased N3 stage proportion may indicate less severity of OSA.