| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 97 === Pressure ulcers are common in elderly or bed-ridden patients. They are caused by compression of soft tissue and capillary deformation, which will lead to decreased capillary blood flow, hypoxia and soft tissue necrosis in the long term. The treatment of pressure ulcers is cumbersome, time-consuming and costly. Pressure ulcers often accompany complications, which increases the mortality rate. The pressure between body and mattress is one of the main causes for pressure ulcers. Therefore it is important for clinical nurses to assess the mechanical properties of the mattress.
The current pressure test system of mattress normally is operated by a professional technician and is inconvenient for a nursing staff to measure the mattress pressure at any time. Therefore, the purpose of this study is to develop an easy-operated instrumentation which is capable of analyzing the material properties of mattress by measuring the load and deformation. In addition, the simulations were carried out by using the finite element analysis on sacrum, where pressure ulcers happen most often. By means of comparing analysis results with experimental data, the relation between pressure and deformation can be obtained and the tolerance time of soft tissue can be determined as the reference to the nursing staff for caring.
In the study, the designed instrumentation was utilized to measure the material property of commonly medical mattress by the fixed weight and a specific spring elongation operated by hand, respectively. The experimental results showed that the Young's modulus is less in the permanent deformation area of the mattress and may prone to the mattress bottoming out and contact with the hard bed board below the mattress, increase the interface pressure. The testing results by the fixed weight and a specific elongation by hand were similar and they show that the design of this study can be operated by either ways. The result of finite element analysis shows that the maximum equivalent stress occurred at the outer edge of sacrum, and closer to the bone the greater tress occurred. Except for the region of the inferior sacrum, the stress will be larger when soft tissue contact with harder mattress.
Analyze the results of experiment and finite element, and then define the relationship between the parameters of measurement and the tolerance time of soft tissue. As an example of the test mattress in this study, the tolerance time is about 3-4 hours, so this study suggests that time interval should be less than three hours for a nursing staff to turn the bed-ridden patients over. The current nursing staff turn the patients over once every 2 hours, and this interval is within the proposed time of this study, so the results of this study is reasonable.
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