Hematocrit monitoring in an extracorporeal circulation apparatus is required for detection of adverse events such as hypotension and bleeding. Nevertheless we have researched non-invasive and continuous hematocrit measurements using optical methods, it remains a challenge to measure absolute levels of hematocrit without calibration. The purpose of this study is to develop an optical hematocrit measurement method without calibration, and to confirm the effectiveness in in-vitro blood experiments. We have developed an improvement method for dual wavelength and detector model by maximizing the difference of optical path lengths. Based on the proposed method, a measurement system has been developed. In the basic blood experiment, the correlation of hematocrit and calculated values by the proposed method has been confirmed. Then, we have conducted hematocrit measurement experiments with attachment errors and change of blood flow. The data indicate that the accuracy of the proposed method without calibration has been equivalent to that of an invasive method, which is employed in clinical practice. In conclusion, we have confirmed that the proposed method is effective for non-invasive and continuous hematocrit measurements.
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