| Clinical pressure sore is a disease which has high incidence and is difficult to cure. In order to prevent it we should study its medical principle. Medically, human tissue oxygenation, which includes the weighted average of the blood oxygen saturation and the blood hemoglobin concentration in the microvessels in human tissue, can be monitored mom-invasively, continuously and in real time using near infrared spectroscopy (NIRS). It is significant advantageous comparing with invasive blood gas analysis and monitoring pulse oxygen saturation at finger tip. Pressure sore mostly occur in the sacral area, which should be monitored. We take the sensitivity of rebound ability of the human tissue as the standard to test the deoxygenated hemoglobin concentration, the oxygenated hemoglobin concentration and the blood oxygen saturation of human tissues. To place pressure in the sacral area when people are in the prone position, it is necessary to design a mechanical devise which can place pressures in any direction. Before the pressure is placed, we test the subjects for stated time, then take the pressure over the tissue we are studying after which test the subjects again for the same time using the near infrared spectroscopy and note down the measurements. Compare and analyze the tissue oxygenation saturation of the two states to test the sensitivity of the rebound ability to pressure of the muscle tissues and forecast risk of disease.The main work done in this thesis is as following:(1) The determination of the sensor parameter. In order to monitor the oxygenation of different human tissue, different sensors should be used. We determine the sensor parameters using Monte Carlo simulation. The absorption coefficient and the thickness of each tissue layer are different. The transmission of light in tissue is simulated based on the absorption coefficient and thickness and get the optical coupling parameter.(2) Take experiment on fatigue driving based on NIRS. Monitor the cerebral oxygenation of drivers before and after driving with suitable sensor for cerebral oxygenation. In order to assure the reliability of the measurement, the drivers stay in the same circumstance and physical conditions. The experiments are carried out between 8 and 12 in the morning every day. Determine the response time before the cerebral oxygenation. Take the same procedures after 3 hours simulated driving. According to the analysis of the signals, we find that the cerebral oxygen saturation is effected by long time driving, resulting in fatigue.(3) Assess the effect of the epidermal compression on blood oxygenation in the sacrum tissue. Subjects of elders and persons with spinal cord injury are recruited, setting control group with normal person. In resting conditions, the blood oxygenations in sacrum tissue of all the subjects are monitored for 20 minutes prior and after the loading period. The principle of the NIRS and the oxygenation parameters are introduced.(4) Take spectral analysis of the signal based on wavelet transform. Wavelet transform is a advanced time-frequency domain conversion tool. Signals can be decompounded into multi-scale decomposition with the adjusted scale of wavelet. The changes of the oxygenations in time and frequency domain can be vividly observed through the power spectrum of the characteristic frequencies and the three-dimensional diagram.(5) The establishment of the pressure ulcer risk assessment model. Pressure ulcer risk assessment model is broadly used in the preventions of pressure ulcer. The criteria of the models mostly focus on the subjective judgment of physical conditions instead of objective factors. In this study, the blood oxygenation is chosen as the criteria, which is a innovation in the pressure ulcer assessment area.Experiments are carried out in hospital and houses for the elderly and take data statistics and wavelet transform to the signals using MATLAB7.0 to assure the correctness of this study. |
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