Shiftwork makes the necessity for the equal reliable and effective operator work at different times of day or night in contrast to the circadian variation of functions’ activity that is imposed from outside and strengthened by experience. Operators in a balanced state are able to smooth away the incoming influences and maintain the performance at the due level. When the functional state deteriorates an operator can not resist the incoming circadian influences that results in pronounced fluctuations of mental performance. In this sense the significance of circadian variations in mental performance can serve as an integral criterion of the functional state of shiftworkers. The purpose of this study was to reveal and analyse the significant circadian fluctuations of the operator mental performance in shift rotation.

Eleven control room operators of a heat power plant (healthy men aged 28-53 with up to 19 years of work experience who worked in three 8-hours shifts) have been examined periodically over one year using a computer based system of performance testing [1]. At the end of the 1^st hour of a work shift each operator was given 30 logic-combinatorial tasks on the PC screen (every next task being given after the previous task being solved). The task was to arrange 4 random numbers from 0 to 9 in order to create an increasing row, mentally rearranging the numbers for one position at a time. The response was the number of changes made; it was given by operator’s pressing the corresponding PC key. The speed and quality of tasks solution were registered automatically. The test took about 3-5 minutes. Every test procedure was evaluated by calculation of 4 characteristics of Time of Task Solution (TTS) distribution - mean, deviation, asymmetry, excess - and a number of mistakes made (NM). The inter-shift differences in TTS and NM were analysed for a year as a whole and also 3 time points of a year: at the beginning (after vacation), in the middle and at the end (on the eve of vacation) of the individual work year according to the results of five tests on each shift (night, morning and evening) at each time point of a year. N = 5 tests * 3 shifts * 3 year periods * 11 subjects = 495 subject-shift tests. Interrelationship of the alterations of characteristics of performance rate and quality during a year at the night, morning and evening shifts; variability of performance rate and quality (multi-day alterations and inter-shift amplitude of variations) were analyzed as well. The Student t-assessment of statistical reliability of differences and correlative analysis were used with a p-value of 0.05. The results obtained for a year as a whole and 3 time points of a year were compared.

Two operators showed inter-shift differences in mental performance for a whole year epoch of analysis (df=28, p<0.05). Operator A (aged 31y with 1y experience) showed inversion of TTS inter-shift changes regarding the group tendency, the least TTS variability and the highest linear correlation of TTS and NM -- all over the group, that can be connected with body (over)tension. Operator B (aged 53y with 19y experience) showed TTS changes conformity to the group tendency, the most TTS variability all over the group and the absence of linear correlation of TTS and NM, that can be caused with decentralisation of regulatory interrelationship in the body, as a result of (chronic) fatigue. Two operators showed inter-shift differences (df=8, p<0.05) in mental performance at the beginning of individual work year, four operators revealed that in the middle of a year, six operators -- at the end of a year, owing to development of unfavourable changes in the functional state. Operator A showed inter-shift changes in mental performance for a year analyse epoch also all 3 time points of a year. Operator B showed inter-shift changes for a year analysis epoch and did not show that for any 3 time points of a year. Six operators manifested inter-shift changes in mental performance at one or two time points during a year.

Computer-assisted analysis of inter-shift differences in mental performance can allow both to reveal operators who need prophylactic or rehabilitative measures and to ascertain the type of unfavourable changes in their body functional state for correction of these ones in due manner and time. This could help to maintain good health of shiftworkers and prolong their professional activity.

References

1. Karpenko, A.V.; Burov, A.Yu.; Bobko, N.A.; Grigorus, A.G. (1987). Individual automatized assessment of operators’ work capacity at large technological enterprises using ASM calculation technique. Gigiyena Truda i Professionalnye Zabolevaniya, 1, 5-8.