Shift work is considered a risk factor for health problems due to the continuous desynchronization and resynchronization of circadian rhythms. This study used heart rate measurement during sleep to determine whether shift work, and different length of this work, affects nonlinear aspects of cardiovascular dynamics, indicators of the autonomous nervous system, in healthy shift workers. The study included 48 healthy, premenopausal, female participants (nurses) divided in two groups of equal age and length of service. One group worked in a three-shift rotation system and the other (control) worked only the day shift. Cardiac activity (R-R intervals) was monitored continuously during sleep using the Data Logging System. Cardiac activity was recorded in both day and shift workers at night after the second consecutive day shift. Results showed that shift workers with up to 10 years of service had higher values of correlation dimension than the equivalent group of day workers but shift workers with more than 10 years of service had lower values of correlation dimension than comparable groups of day workers. All shift workers, regardless of length of service, had significantly higher indices of determinism than day workers, but the index of determinism slightly enlarges with increased years of services. Generally, it seems that shift work has a negative impact on cardiovascular dynamics from the very beginning, and nonlinear parameters of cardiovascular dynamics can be potential predictors of future health problems.

shift work, cardiovascular dynamics, R-R interval, index of determinism, correlation dimension