0021 Altered Association Between Sleep Duration and Nocturnal Heart Rate Variability in Shift Workers

Introduction Shift work disrupts sleep and circadian rhythm, potentially impairing cardiac autonomic regulation. This study aimed to examine whether the relationship between sleep or circadian rhythm parameters and nocturnal heart rate variability (HRV) differs between shift workers (SW) and non-shift workers (controls), and to explore sleep pattern indices within the SW group that are associated with altered autonomic activity reflected in nocturnal HRV. Methods Fifty-four SW and 41 controls underwent nocturnal polysomnography (PSG), sleep-wake assessment including sleep diary and actigraphy. Two-week actigraphy and sleep diary recordings were used to derive sleep and circadian rhythm parameters. In addition, self-report questionnaires on psychiatric symptoms were completed. Moderation analyses were performed to test whether shift-work status modulated associations between N2 HRV indices and sleep or circadian measures. Subsequent factor analyses in SW group examined associations between sleep diary-derived sleep pattern indices (e.g., total sleep time (TST) variability, bout/TST) and N2 HRV. Results No significant differences were observed in N2 HRV indices between shift workers and controls. Shift work significantly moderated the relationship between actigraphy-derive TST and normalized LF, normalized HF, and Ln-LF/HF (all ps < 0.001, pFDRs < 0.001). However, it did not moderate significantly the relationship between circadian measures and HRV parameters. Within the SW group, high bout/TST ratio based on sleep diary was associated with increased pNN50 (p = 0.014). Conclusion The findings suggest that prolonged or segmented sleep in shift workers may reflect compensatory rather than restorative sleep, accompanied by heightened sympathetic activation and reduced HRV stability during N2 sleep. Although it should be interpreted cautiously, HRV in shift workers may be related to sleep deprivation rather than circadian disturbances. A comprehensive assessment of sleep quantity and quality may therefore be crucial for identifying and preventing autonomic dysregulation in shift workers. Support (if any) This work was supported by the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIT) (no. NRF-2022R1A2C1008209)