Midori Sotoyama

Adjustments of posture and viewing parameters of the eye to changes in the screen height of the visual display terminal

To understand the motions caused by the interaction among the different body parts, adjustments of both eye position and body posture to screen height settings of 80, 90, 100, 110 and 120 cm were determined in 10 subjects. The subjects engaged in a non-keyboard, interactive computer game requiring constant visual monitoring. Changes in body positions were determined by video image analysis for the posture parameters and by video frame analysis for the eye parameters. Analysis of variance and correlation analysis showed that neck angle, thoracic bending and vertical eye position were significantly affected by changes in the screen height of the VDT. The study of the interrelationship of eye position and body posture suggested that changes in body positions served to complement the eye position in attaining a better view of the visual target. Viewing angle was observed to be decided mainly by inclination of the neck and the eye. Thoracic bending was also noted to contribute in setting the viewing angle, although to a lesser extent. On the other hand, viewing distance and trunk inclination showed significant correlation.

Analysis of ocular surface area for comfortable VDT workstation layout

This paper proposes a comfortable visual display terminal (VDT) workstation layout based on an analysis of ocular surface area (OSA). A large OSA induces eye irritation and eye fatigue because the eye surface is highly sensitive to various stimuli. The authors considered that OSA must be one of the useful indices of visual ergonomics and applied it to evaluate VDT workstation layout. Each subject was asked to perform a word processing task using four different VDT workstation layouts. It was found that the main factor affecting OSA was not cathode ray tube (CRT) height itself but the distance between the CRT and keyboard. Thus the following workstation layout is recommended to realize comfortable VDT operation: (1) the desk height should be adjusted to the users height; and (2) the CRT display should be set closer to the keyboard to provide a smaller OSA.

Work schedule differences in sleep problems of nursing home caregivers

Nursing home caregivers (n=775; 604 women; mean age 33.6 years) were studied to examine how work schedules affect their sleep. The shift group (n=536) worked under a rotating two-shift system (n=365), a rotating three-shift system (n=66), or other types of shifts (n=78). The non-shift group included 222 caregivers. Participants completed a questionnaire about working conditions, sleep problems, health, lifestyle, and demographic factors. The two-shift caregivers reported the highest levels of difficulty initiating sleep (DIS, 37.6%), insomnia symptoms (43.0%), and poor quality of sleep (24.9%) among the groups. Adjusted odds ratios for these problems were significantly greater for the two-shift caregivers than for non-shift counterparts: DIS (odds ratio 2.86, 95% confidence interval 1.57-5.20), insomnia symptoms (2.33, 1.36-4.02), and poor sleep quality (2.15, 1.09-4.22). Our data suggest that working under a rotating two-shift system, which has a longer night shift, is associated with an elevated risk of sleep problems for nursing home caregivers.

Effects of the liquid crystal display tilt angle of a notebook computer on posture, muscle activities and somatic complaints

Abstract More con strained posture and higher neck muscle activities have been reported among users of notebook computers than those of desktop computers. Complaints of eye and musculoskeletal d iscomfort as well as di fficulty of keying were greater during work with notebook computers. These reports ascribed the findings to the differences in the size of desktops and notebooks. Another ergonomic aspect of the notebook computer distinct from the CRT is its angle-dependent luminance contrast. The present study investigated the effects of liquid crystal display (LCD) tilt angle of a notebook computer on posture, muscle activities and somatic complaints in 10 subjects. At the tilt angle of 100°, the subjects were noted to have relatively less neck flexion. The static neck extensor muscle activity was also lowest at this tilt angle. Nonetheless, the complaint survey revealed higher rates of discomfort while viewing and using the LCD set at the tilt angle of 100°. The findings of this study strongly suggested that the ergonomic features and problems attributable to notebook computers are distinct from the desktop computers. The points of interest raised in this paper should be considered when contemplating the use of notebook computers. Relevance to industry The use of notebook computers has increased steadily over the last 5 years , especially in Japan. Few authors have ventured to study the problems associated with these smaller computers . The results and suggestions of this stu dy may contribute to improve the design of notebook computers and the workstations .

Musculoskeletal pain and night-shift naps in nursing home care workers

BACKGROUND Care workers in nursing homes are at high risk of developing musculoskeletal disorders (MSDs). Many care workers work in shifts, which may compromise both the quality of care they give and their working life. Taking a nap during night shifts has been proposed to ameliorate shift work-related problems, but its relationship with MSDs is not clear. AIMS To explore how MSD pain differs according to frequency of night-shift naps. METHODS A questionnaire study was conducted on 111 care workers at three nursing homes. Of 98 respondents, data from 66 shift workers (54 women) were analysed. Data on self-rated pain in multiple sites (neck, shoulder, arm, leg and low back), naps during night shifts and relevant variables were collected. Participants were categorized into three groups on the basis of frequency of night-shift naps taken during the previous month: non-nappers, <50% nappers and >or =50% nappers. RESULTS Pain at all sites, with the exception of low back pain, differed significantly among the three groups. Pain scores were lowest at the arm and leg for the > or =50% nappers. Neck and shoulder pain was lower for the > or =50% nappers and the non-nappers compared to the <50% nappers. CONCLUSIONS Reduced pain in the arm and leg was associated with taking a nap at least once every two night shifts among the nursing home care workers. No association was found between low back pain and night-shift naps in this sample.

Electroencephalographic and autonomic responses to trichloroethylene inhalation in freely moving rats

Effects of trichloroethylene (TRI) on the central nervous system (CNS) and autonomic functions were examined by means of continuous polygraphic measurements of electroencephalogram (EEG), electromyogram (EMG) and electrocardiogram (ECG) in electrode-implanted and freely moving rats, while they were exposed via inhalation to TRI vapor of 300, 1000 or 3000 ppm for 8 h/day or 6000 ppm for 4 h/day on 3 consecutive days. The exposures to 3000 and 6000 ppm produced abnormal EEG activity and incapacitation of postural maintenance during the exposure period, while the post-exposure period was characterized by decreased waking (W) time, lowered heart rate (HR) and increased numbers of bradyarrhythmic episodes after recovery from anesthesia. The exposure to 1000 ppm decreased W time without the appearance of anesthesia. The exposure to 300 ppm did not produce any observable effects except the lowered HR, which occurred during the post-exposure period. The relationships between internal doses of TRI and its metabolites and these TRI-induced pathophysiological responses were determined by blood and brain analyses of TRI, trichloroethanol and trichloroacetic acid in the TRI-exposed rats. Recordings of respiratory chest wall movement revealed that the number of TRI-induced bradyarrhythmias accompanying apnea during paradoxical sleep (PS) increased significantly after cessation of exposure to 6000 ppm TRI. This suggests that TRI-induced hypoxemia due to apnea during PS triggers bradyarrhythmogenesis through increased cardiac vagal efferent tone.

Correlation analysis between visual acuity and sitting postural parameters of young students

The relationship between failing eyesight and the sitting posture of young students while studying was studied quantitatively. Among the 19 students who participated in this study, 9 were classified as emmetropic and 10 were myopic. The mean age was 13.2 +/- 2.2 (mean +/- standard deviation) years. Viewing distance, neck angle, viewing angle, vertical gaze direction, and ocular surface area while studying were measured from the lateral and frontal view images of video recordings of the posture. Viewing distance, accommodative power, neck angle, viewing angle, near point, and log transformed visual acuity showed significant differences between these two groups (p < 0.001). Viewing distance of myopes (15.0 +/- 1.9 cm) (mean +/- standard desviation) is shorter than that of emmetropes (30.2 +/- 4.1 cm). Accommodative power of myopes was lower than that of emmetropes. Correlation analysis revealed that the viewing distance of students significantly correlates to neck angle, viewing angle, accommodative power, near point, and visual acuity (p < 0.01). It can be surmised that the failing eyesight of young students results from postural problems such as shortness of viewing distance and increased neck flexion.

Research Activities on the Ergonomics of Computers in Schools in Japan

Recently, Japanese government took positive steps financially to introduce computers into schools and to promote the use of the internet in school environments. A proactive approach must be taken to eliminate the foreseeable ergonomic problems from the use of these new technologies. The Japan Ergonomics Society (JES) has had discussions on the topics concerned. The postural and visual characteristics of young students, ergonomic improvements of workstations for the school children, operating conditions of PCs in junior-high schools, questionnaire surveys on the ergonomic aspects of computers in schools were discussed in the JES symposium held in 1999. In conclusion, the introduction of computers in schools should be given more careful consideration and the development of ergonomic guidelines for the use of computers in schools should address the prevailing social needs.

Positive emotion inducement modulates cardiovascular responses caused by mental work

BackgroundPositive emotion is considered as an important factor related to health-relevant biological processes, including cardiovascular responses. To explore the possibility of using positive emotion as a tool to manage cardiovascular response of white-collar workers, we examined the influence on cardiovascular response of positive emotion inducement before a mental work.MethodSeventeen healthy males participated and performed a 10-min, PC-based Stroop color word task as their mental work. Before the task, 60 pleasant pictures chosen from the International Affective Picture System were presented in a random order under a positive emotion inducement condition while a gray screen was presented under a control condition. A 30-min relaxation period after completing the task was provided to examine the aftereffects of positive emotion inducement. Throughout these periods, systolic and diastolic blood pressure, mean arterial blood pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance were measured continuously.ResultsBlood pressure and total peripheral resistance were lower during the picture presentation period under the positive emotion inducement period compared to the control condition. All indices did not differ during the color word task period. During the relaxation period after the task, however, blood pressure and total peripheral resistance were lower under the positive emotion inducement condition compared to the control condition.ConclusionPositive emotion inducement before a mental work beneficially modulates cardiovascular responses, suggesting that positive emotion inducement may be a useful tool to manage the cardiovascular response to mental work.

White-collar workers’ hemodynamic responses during working hours

In the present study, two investigations were conducted at a communication center, to examine white-collar workers’ hemodynamic responses during working hours. In investigation I, hemodynamic responses were measured on a working day; and in investigation II, cardiovascular responses were verified on both working and non-working days. In investigation I, blood pressure, cardiac output, heart rate, stroke volume, and total peripheral resistance were measured in 15 workers during working hours (from 9:00 am to 18:00 pm) on one working day. Another 40 workers from the same workplace participated in investigation II, in which blood pressure and heart rate were measured between the time workers arose in the morning until they went to bed on 5 working days and 2 non-working days. The results showed that blood pressure increased and remained at the same level during working hours. The underlying hemodynamics of maintaining blood pressure, however, changed between the morning and the afternoon on working days. Cardiac responses increased in the afternoon, suggesting that cardiac burdens increase in the afternoon on working days. The present study suggested that taking underlying hemodynamic response into consideration is important for managing the work-related cardiovascular burden of white-collar workers.