Mental work-load has increased with technical innovation, while manual work-load has decreased. As a result, eye fatigue has become one of the complaints in the modern working environment. Heretofore, the evaluation of visual work-load was based mainly on observation of the refractive power and accommodative function of the eyes. The purpose of this study is to assess, through observation of eye movement, the work-load created by eye-tracking tasks.
The subjects were required to track, only by eye movement, a target oscillating between a distance of 35 cm in the horizontal or vertical direction for seven minutes. Mispursuit of the target, blinking and heart rate were recorded during the period of the experiment. The subjects were given eye-tracking tasks under nine conditions comprising angles 20°, 40° and 60° in the respective moving widths and 0.1 Hz, 0.3 Hz and 0.5 Hz in the moving frequency of the target. Four healthy male volunteers participated in the eye-tracking experiments involving the horizontally moving target and five healthy male volunteers participated in those involving the vertically moving target.
The task load condition of visual angle of 20° with target frequency of 0.1 Hz was employed as standard. The relative velocity of the target and the velocity of eye movement were obtained using various combinations of visual angles and target frequencies.
The following results were obtained:
1) The frequency of mispursuits increased significantly with the increase of relative target velocity. The degree of increase of mispursuit was especially remarkable at relative target velocities exceeding 1.0 Hz or at eye movement velocities exceeding 40°/s.
2) The frequency of repeated blinks decreased significantly under the task load condition of eye movement velocities exceeding 24°/s.
3) No significant changes in heart rate or sinus arrhythmia were observed with increase of relative target velocity.

View full abstract

In 1950-1960, a cohort of dust-exposed workers and a cohort of multiple matched unexposed subjects was set up from the files of preventive medical checkups performed in 1, 089 Viennese plants. Male workers with a history of long-term exposure to nonfibrous particulates in different industries (metal, ceramics, brick, glass, stone etc.) aged ≥40, and male workers without dust exposure (matched for residency, start of observation, age, and smoking) were followed up to 1980 or death (48, 960 person yr). By life table methods, dust-exposed workers compared to unexposed workers showed a reduced survival of age 60 (p<0.0001), due to lung cancer (123 exposed, 87 controls, p=0.001), stomach cancer (48/27, p=0.003), silicosis (40/0), emphysema, bronchitis and asthma (41/23, p=0.007). No difference in mortality from cardiovascular diseases was observed (p>0.50). We concluded that heavy and long term exposure to respirable particulates is related to increased lung cancer mortality after age 60. A comparison of 2, 212 deaths among Austrian silicotics, with deaths in the corresponding population showed a relation between lung cancer and silicosis (p<0.001), fairly independent of age and time-period. The estimated relative lung cancer risk of Austrian silicotics in the period 1955-79 averaged 1.41 (95% confidence 1.21-1.64).

View full abstract

The relationship between decrease in cerebral arousal level and sleep stage pattern was examined when a cycle of 22 h-wake and 8 h-sleep was repeated four times. The subjects of the experiment were six healthy male university students.
The results of the experiment showed that the period between the time when the average score of Stanford Sleepiness Scale (SSS) reached point four (a little foggy) and the rising time was gradually decreased by repetition of the 22 h-wake and 8 h-sleep cycle. It was also found that the average score for the 6th experimental day after the third cycle was significantly increased, compared with that for the 1st 22 h waking period. These results show that the cerebral arousal level, which was indicated on the scores of SSS, was gradually decreased under the present experimental wake-sleep condition. The day-to-day variation of critical fusion frequency showed a tendency similar to that of SSS, demonstrating a gradual decrease in arousal level.
On the other hand, stage 4 sleep (S4) was significantly increased during sleep after the 1st 22 h waking period, compared with baseline sleep after 16 h waking time. However, a significant increase in S4 was not seen during the sleeping periods in the second to the fourth cycles of 22 h-wake and 8 h-sleep, compared with that during the sleep after the 1st 22 h waking period.
These results suggest that, with respect to the 1st cycle of 22 h-wake and 8 h-sleep, the increase in S4 was related to the decreased level of arousal which was caused by a long prior wakefulness of 22 h. However, our results also suggest that a further decrease in arousal level due to the repetitive cycles did not increase the amount of S4.

View full abstract

The present experiment was conducted under the assumption that exposure conditions (time of exposure, concentration of exposed substances and working intensity) should be taken into account in estimating the level of invasion of injurious substances into the human body.
Experiments were carried out on rats under various exposure conditions of toluene and the toluene concentration in the blood was monitored for the estimation of its intake.
The results were as follows;
1. It was confirmed that toluene concentration in blood increased and plateau-time was delayed in proportion to increase in exposure concentration.
2. Light exercise (5.0, 7.0 m/min) increased toluene concentration in blood and it was proportioned to intensity of physical exercise.
3. Light daily exercise (2.7 m/min) for six days increased toluene concentration in blood gradually day after day when compared to exposure without exercise, though the exposure conditions were the same every day.
It is thus considered that physical exercise is one of the very important factors in estimation of exposure.

View full abstract

Mutagenicity of seven aromatic amines, two heterocyclic amines, two azo compounds and one polycyclic aromatic hydrocarbon was examined with a fluctuation test modified by Gatehouse. The test was performed by using Salmonella typhimurium TA98 in the presence of liver and bladder S9 from PCB pretreated rats.
Seven out of 12 compounds showed mutagenic activities with liver S9 and seven with bladder S9. Benzidine, 3-methylcholanthrene and 2-acetylaminofluorene showed a negative response with bladder S9 but a positive response with liver S9. The mutagenicity of the seven compounds observed with bladder S9 had a lorwer sensitivity than with liver S9. 3-Amino-1, 4-dimethyl-5H-pyrido [4, 3-b] indole and 3-amino-1-methyl-5H-pyrido [4, 3-b] indole showed mutagenic activity at lower concentrations than the other compounds which showed mutagenic activity either with bladder S9 or liver S9. Mutagenicity of 3-methylcholanthrene was observed at high concentration only in the presence of liver S9.
The findings from the present study suggested that aromatic amines, heterocyclic amines and polycyclic aromatic hydrocarbons were more likely to be activated to strong mutagens with liver S9 than with bladder S9.

View full abstract

To investigate the relationship between vibration hazards and blood viscosity, vibration exposure experiments were conducted. The rat's hind limbs were continuously exposed to local vibration (60 Hz, 5 G) for 4 h. The exposed group showed a slightly lower blood viscosity and plasma fibrinogen in the blood obtained immediately after exposure when compared with the control group. However, in the blood obtained 18 h after exposure, there was no significant difference in the levels of whole blood viscosity and plasma fibrinogen between the exposed group and the control group. Hematocrit was not affected by this exposure. These results indicate that the decrease in the levels of whole blood viscosity induced by local vibration exposure is transient and that some relationship exists between changes of whole blood viscosity and those of plasma fibrinogen.

View full abstract