Introduction

Along with increasing number of computer users in work organizations, upper extremity complaints become more and more common. Research has shown that increased exposure to repetitive keyboard and mouse use increases the risk of musculoskeletal disorders. However, the physiological mechanisms remain unclear. Pathological processes as the rate of the metabolism (energy crisis) can be conceivable as a cause of the symptoms and disability related to intensive computer work ¹ . To date, there are no studies made upon local tissue oxygen (O₂) saturation during computer work in patients suffering from computer related disorders in the upper extremity. In the present study, we examined local tissue oxygen (O₂) saturation in m. trapezius and m. extensor carpi radialis brevis before and during mouse operated computer work in patients suffering from computer related disorders, and looked at relations between oxygen saturation, subjective ratings of pain, symptoms and disability.

Material and method

Four right dominant female patient subjects (PS) aged 27 to 46 recruited through the company health care participated in the study. Their mean height was 166 cm and weight of three PS 55.8 kg (130 kg for the fourth PS). They had one or several diagnoses each, comprising of neck myalgia, diffuse forearm pain and lateral epicondylitis. All of them worked full-time and used computer with keyboard and mouse or mousetrapper device. Three PS used the computer for 7-8 hours per workday. The PS related their disorder to intensive computer work for long hours and high precision demands.

Skin fold thickness was measured with a caliper at m. trapezius (TRAP) and m. extensor carpi radialis (ECRB) on the right side, and ranged from 2-6 mm. The mean skin temperature was 32.2° during rest and 32.7° following work on the ECRB (there was one missing post-value due to technical problems). The local tissue oxygen saturation was measured non-invasively with near-infrared spectroscopy, NIRS (Inspectra, Hutchinson Technology). One NIRS-electrode was placed at TRAP and the other on ECRB, both on the right side. After five minutes of rest, the PS performed a mouse operated computer task for 45 minutes with their right hand. The task consisted of painting squares presented on the screen, by using the mouse. Measurements of oxygen saturation were made throughout the computer work. Furthermore, subjective ratings of tiredness and strain were recorded on a 10 cm long VAS-scale. Symptoms and disability of the hand, arm and shoulder was rated with the DASH questionnaire, which contains the areas activities of daily living (ADL) and work ³. Descriptive statistics of the oxygen saturation comprised average and standard deviation of StO2 values in %. Comparison of the local tissue oxygen was made with the subjective ratings.

Results and discussion

Table 1. Local tissue oxygen (during 5 minutes rest and 45 minutes of computer work) and subjective ratings in PS.

The mean saturation value for ECRB during rest was 52.6 (SD 20.2), work 46.7 (SD 14.7), and for TRAP during rest 58.8 (SD 21.2) and work 61.2 (SD 21.7). Skin fold thickness and skin temperature did not show any obvious interaction with the tissue oxygen values. Neither did comparisons of PS´s subjective ratings of tiredness and strain, symptoms, disability and the oxygen saturation, or severity of ratings and oxygen saturation. This might be due to the small amount of subjects and/or that the subjective ratings were not sensitive enough or do not fully reflect the state of art of computer related disorders from the upper extremity. One of the PS in our study reported intense delayed onset of pain 24 hours after the computer work. It is important to be aware that this can occur. The group of PS in this study had lower mean tissue oxygen saturation than healthy female subjects in another study that used the same device and performed an identical mouse operated computer task². More research is needed for a better understanding of the mechanisms behind upper extremity disorders and the extent to which local tissue oxygen saturation reflects their symptoms and disability.

References

1. Boushel, R.; H., L.; Olesen, J.; Gonzales-Alonzo, J.; Bulow, J.; and Kjaer, M.: Monitoring tissue oxygen availability with near infrared spectroscopy (NIRS) in health and disease. Scand J Med Sci Sports, 11: 213-22, 2001.

2. Heiden, M.; Dahlgren, G.; Lyskov, E.; Crenshaw, A.; and Johansson, H.: Effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense. In Nordiska arbetsmiljömötet. Edited, Nyslott, Finland, 2003.

3. http://iwh.on.ca/dash.html.