| VDT (Visual Display Terminal) has become ubiquitous in various fields. However, while bringing numerous benefits, this technology is accompanied by work-related health disorders, including visual fatigue, musculoskeletal discomfort, and mental fatigue, which are collectively referred to as VDT Syndrome or Computer Vision Syndrome in medical science. In this paper, I intend to propose an objective and real-time detection method for evaluating VDT visual fatigue.Pulse signals are a kind of physiological signals containing abundant human physiological and pathology information which reflects various physical and physiological changes in subsystems of human body. It may be desirable that analysis of these pulse signals can help us obtain information which will reveal the health condition. In this thesis, simple and easily used photoelectric finger pulse sensor is applied to making a real-time analysis on finger pulse wave signals in order to obtain the objective parameters used as the diagnosis and evaluation of VDT. Meanwhile, we apply photoplethysmography (PPG) to fatigue detection, which is a method of low computational complexity and good performance and is expected to be used in real-time inspection of the visual fatigue of VDT workers.This paper analyzes problems existing in studies about VDT visual fatigue based on researches at home and abroad and confirms the feasibility of carrying out VDT visual fatigue research through studying physiological signals, providing a real-time and objective detection method for evaluating VDT visual fatigue which is expected to be adopted in clinical healthcare.This paper also gives a brief summary of reasons for and influencing factors in VDT visual fatigue from the perspective of Physiology and Ergonomics. Meanwhile, basic information about pulse signals is introduced, and the paper provides a theoretical confirmation of the connection between pulse signal and visual fatigue, demonstrating the feasibility of this subject.We design an electrophysiological data acquisition system and the VDT visual fatigue experiments. According to the brief introduction to VDT visual fatigue, we know that there are lots of factors influencing VDT visual fatigue; therefore, in designing VDT visual fatigue experiments, we try to reduce or remove factors that may disturb the experiments. The fatigue assessment questionnaire and critical flicker fusion frequency (CFF) counter have both shown that all subjects participating in VDT experiments experience visual fatigue.Pulse signals are processed. In pre-processing signals, simple integer coefficient filters are adopted. This filter not only works effectively in real time but also has low computational complexity and is expected to be implemented in hardware. Simple integer coefficient filter meets our requirements ideally. The pulse signals are analyzed both in time domain and frequency domain, and physiological features like waveform height and magnitude spectrum peaks are obtained. The results have shown that the peak-to-trough amplitudes and magnitude spectrum peaks all significantly decrease in visual fatigue (P<0.001) and classification accuracy reaches 94.59%. There is also remarkable decrease in body temperature (P<0.01). All the above information indicates that the strength of pulse signals decrease after visual fatigue. Based on pulse-to-pulse interval, we analyze the Poincare plot and find that there are no significant changes in the SD1 and SD2. However, the SD1/SD2 have obviously decreased after fatigue compared to that before fatigue (P<0.05). |
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