CIRCADIAN HEART-RATE-VARIABILITY RHYTHM IN SHIFT WORKERS

The objective of this study was to assess the influence of day-night c ycle and sleep-awake period on the circadian pattern of heart rate var iability (HRV). Twelve male oil refinery security shift workers, aged 39 +/- 7 years, were studied with 24-hour Holter monitor recordings du ring morning and night work periods. Hourly HRV parameters in the time and frequency domains were evaluated. For both shifts, all HRV parame ters during awake or work periods were found nor to be statistically d ifferent. In both day and night work shifts, the very low frequency an d high-frequency components of HRV and the proportion of differences i n successive R-R intervals greater than 50 ms increased during the sle ep period, while the low frequency/high frequency ratio decreased. The low-frequency component in absolute units and the SD of the R-R inter val did not show any variation in either shifts for the different peri ods. These results suggest that the circadian pattern of HRV seems to be predominantly related to sleep (supine) and wakefulness (standing) and remains independent of night-day cycle.