CHANGES IN PSYCHOPHYSIOLOGICAL FUNCTIONS DURING NIGHT-SHIFT IN NURSES- INFLUENCE OF CHANGING FROM A FULL-DAY TO A HALF-DAY WORK SHIFT BEFORE NIGHT DUTY

The effects of changing from a full-day to a half-day shift work befor e a night duty shift on physiological and psychological functions duri ng the night shift were investigated in 12 healthy unmarried nurses wo rking on the same ward of a university hospital. Three shift patterns, i.e., a day shift following a day shift, a night shift following a da y shift, and a night shift following a half-day shift, were studied in terms of physical activity level, sympathetic and parasympathetic act ivity levels, cortisol, prolactin, NK cell activity, and changes in mo od states. The change to the half-day shift increased the duration of sleep before night duty by about 86 min and brought wake-up times forw ard by about 1 h, resulting in increases in rest and time before work. In addition, the change was revealed to reduce the influence of rever sed-phase circadian rhythms on autonomic nervous activity during the n ight shift. The score for sleepiness was significantly lower at 0500 h ours following a half-day shift. There were some marginal but not sign ificant differences in the scores reflecting the degree of vigor, tire dness and irritation during the night shift. Although the prolactin co ncentration was significantly decreased at the start of the night shif t after the half-day shift, there was no difference in cortisol concen tration or NK cell activity between the usual night shift after a day shift and the night shift after the half-day shift. The half-day shift was not observed to cause any marked change in the fixed biorhythms o f these nurses. The cortisol and NK cell activity levels were low duri ng the night shift, suggesting that the night shift itself is a high s tress level, which is prejudicial to biodefense.