Interactive model of subsidiary behaviors, work performance and autonomic nerve activity during visual display terminal work.

OBJECTIVES: The aims of the study were to investigate the systematic classification of subsidiary behaviors during visual display terminal (VDT) work and discuss the interpretation of these behaviors through an interactive model of subsidiary behaviors, work performance and autonomic nerve activity. METHODS: Twelve university students were instructed to perform continuous 120-min English transcription tasks in a sedentary posture. Data on subsidiary behaviors, work performance (mean keystroke and mean error rates), and autonomic nervous system balance (log-transformed low frequency (LF) / high frequency (HF) ratio) were recorded every 5 min during VDT work. RESULTS: The subsidiary behaviors were categorized into 3 qualitatively independent factors: distractive behaviors against monotony (DBM), sleepiness-related behaviors (SRB), and habitual behaviors (HB). A cross-correlation analysis indicated that an increase of DBM, which is considered as a sign of workers' attempt to escape from monotonous task operations, was related to a decline in performance. A decrease in the LF/HF ratio was followed by SRB after 5 min passed (r=-0.57, p<0.05), eventually leading to a restriction of the deterioration in performance. An increase of DBM was predictive of an increase in errors (r=0.54, p<0.05), and a significant negative correlation (r=-0.46, p<0.05) between HB and autonomic nerve activity at 10 min after the appearance of HB was observed. CONCLUSION: It emerged from the results that the factor structure of subsidiary behaviors consists of 3 mutually independent factors. The interactive model suggests that subsidiary behaviors are possibly precursory signs of errors and changes in autonomic nervous system balance.

Characterizing recovery of sleep after four successive night shifts.

The purpose of this study was to characterize the recovery pattern of sleep following simulated, four successive night shifts in ten healthy men (22.9 + or - 3.2 yr). Poor sleep was defined as sleep efficiency of 80% or lower as determined actigraphically. The results showed that four (rapid, slow, pseudo, and incomplete) patterns of sleep recovery were observed over three recovery sleep periods. The rapid and slow recovery pattern represented immediate and slow return to baseline level prior to the nightshifts, respectively. The pseudo recovery pattern demonstrated poor sleep at the 3rd recovery sleep period, despite transient recovery at the 2nd sleep period. The incomplete recovery pattern was characterized by consistently poorer sleep during the entire recovery period. The correlation analysis indicated that sleep habits (bed time and variation of wake time) prior to the experiment were significantly related to the recovery patterns, rather than performance and alertness during the night shifts.

Effects of adjustable sit-stand VDT workstations on workers' musculoskeletal discomfort, alertness and performance.

Adjustable sit-stand workstations, which are designed to allow workers to sit and stand autonomously while working, were examined to identify the effects on workers' musculoskeletal discomfort, alertness and performance. Twenty-four healthy subjects participated in the study. The subjects were required to do an English transcription task for 150 min under the following conditions: 1) sitting at standard workstations (Standard), 2) sitting on a chair with the work surface elevated to standing position (High-chair) and 3) a combination of 10-min sitting and 5-min standing with the same setting as that in the high-chair condition (Sit-stand). The subjective musculoskeletal discomfort scores indicated that High-chair and Sit-stand resulted in relatively higher discomfort levels than the Standard condition. Although the ratio between low-frequency (0.04-0.15 Hz) and high-frequency (0.15-0.4 Hz) components of heart rate variability (LF/HF ratio) in Sit-stand was higher than that in other conditions, there were no significant differences in subjective sleepiness among the three conditions. As for work performance, there was a tendency to be steadily high under the Sit-stand condition compared with other conditions, but not a significant difference. This study revealed that although the use of sit-stand workstations can contribute to keeping workers' arousal level steady, it has an adverse effect in light of musculoskeletal discomfort.

[Characteristic patterns of fatigue feelings on four simulated consecutive night shifts by "Jikaku-sho shirabe"].

The aim of the present study was to reveal characteristic patterns of fatigue feelings on consecutive night shifts by a questionnaire for work-related fatigue feelings "Jikaku-sho shirabe". Ten healthy males (Mean +/- SD: 22.9 +/- 3.2 years old) participated in the experiment. Participants were required to attend the laboratory for nine consecutive nights under the following conditions: adaptation sleep (0:00-7:00), simulated day shift (10:00-18:00), baseline sleep (0:00-7:00), directly followed by four simulated night shifts (22:00-9:00) and the subsequent daytime sleep (12:00-18:00), three recovery nights (0:00-7:00) and two simulated day shifts (10:00-18:00). During each simulated shift, participants were required to complete an English transcription task (30 min), a performance test battery (20 min) and break (10 min) every hour. Fatigue feelings were evaluated by "Jikaku-sho shirabe", which was proposed by the Industrial Fatigue Research Committee of the Japan Occupational Health in 2002. This questionnaire consists of 25 subjective fatigue symptom items that are categorized into 5 factors: feeling of drowsiness (Factor I), feeling of instability (Factor II), feeling of uneasiness (Factor III), feeling of local pain or dullness (Factor IV), and feeling of eyestrain (Factor V). For each item, respondents are requested to estimate the intensity of the feelings as "Disagree at all," "Agree scarcely," "Agree slightly," "Agree considerably," and "Agree strongly." These five intensities were assigned scores of 1 to 5 points, respectively. Hierarchical cluster analysis suggested that there might be at least three variation patterns of fatigue feelings on the consecutive night shifts (i.e. Clusters A, B and C). On the basis of subjective fatigue symptom items of each cluster, the patterns in Clusters A, B and C might reflect the loads of the reticular activating system, musculoskeletal and central nervous systems, and limbic system, respectively. For Clusters A and C, significant improvements were observed with the increase of the number of night shifts (F(11,99)=3.07, p<0.01, F(11,99)=3.37, p<0.01, respectively). On the other hand, Cluster B deteriorated with the progress of the simulated night shifts. Taken together, we suggest that the characteristic patterns of fatigue feelings on consecutive night shifts might represent dissociation among the feelings induced by several loads.

High-amplitude QRS complex in the electrocardiograms of normotensive people and risk of subsequent hypertension.

BACKGROUND: Left ventricular hypertrophy sometimes develops in normotensive people with a genetic background for hypertension. The aim of this case-control study was to test the hypothesis that a high-amplitude QRS complex (high-QRS) is indicative of risk of eventual hypertension. METHODS: We reviewed medical charts that included blood pressure data obtained every 6 months from 7011 Japanese workers. The cases were all of 24 normotensive people showing an electrocardiogram with SV1+RV5>4.0 mV (high-QRS). The 24 controls chosen presented normal electrocardiograms and were matched for blood pressure, body mass index, age, gender, glycated hemoglobin A1c fraction, and parental occurrence of hypertension. The incidence of hypertension and change in blood pressure during a 5-year study period were compared in the two groups. RESULTS: The cases were more likely than the controls to have a parent with hypertension (18/24 [75.0%] and 686/5704 [12.0%], respectively; P<0.01, odds ratio=21.8 [95% CI: 8.6-55.2]). At the end of the study period, hypertension was more frequent (18/24 [75.0%] and 3/24 [12.5%], respectively; P<0.01, odds ratio=21.0 [95% CI; 4.6-96.2]) and both systolic and diastolic blood pressures were higher (149.0+/-17.1 mmHg vs. 139+/-17.1 mmHg, P<0.01; and 89.5+/-9.2 mmHg vs. 81.7+/-11.5 mmHg, P=0.01, respectively) in the cases than in the controls. CONCLUSIONS: High-QRS may be indicative of risk of eventual hypertension, and may therefore be useful for screening purposes.

Elevated white blood cell count as a risk factor of coronary artery disease: inconsistency between forms of the disease.

White blood cells (WBC) destabilize coronary artery plaques and an elevated WBC count is a risk factor of coronary artery disease (CAD). Nevertheless, the differences between the forms of CAD in the relationship with WBC count remain to be elucidated. To study these differences, we reviewed the health-checkup records from 1994 to 1999 for 6021 Japanese post office workers without any cardiovascular abnormalities. Baseline WBC counts of patients with acute coronary syndrome (ACS) were significantly higher than those of subjects free from coronary artery discase (mean +/- SD = 9210 +/- 2703/microL vs 6205 +/- 1635/microL, P<0.001), while the patients with stable angina pectoris (sAP) (6233 +/- 1528/microL) were similar to subjects without coronary artery disease in baseline WBC counts. Hypertension at the baseline was related to sAP (relative risk [95% CI] = 61.78 [17.29 to 78.66]) but not to ACS. Conversely, hypercholesterolemia and cigarette smoking were risk factors for ACS (relative risk [95% CI] = 11.48 [2.39 to 18.03] and 10.04 [3.00 to 12.12], respectively) but not for sAP. Multivariate logistic regression analysis found only WBC count (1000/microL) discriminated between ACS and sAP (P=0.038, odds ratio 2.049 [1.042-4.016]). We conclude that an elevated WBC count may be a risk factor of ACS but not sAP, and this finding is consistent with previous reports demonstrating the effects of WBCs in the destabilization of coronary artery plaques.