Influence of Installing Method on Pulse Wave Signal in Blood Pressure Prediction by FBG Sensor

Vital signs such as pulse and blood pressure change greatly due to mental factors. Therefore, it is desired to continuously measure unconsciously. However, the oscillometric method which measures using the cuff pressure is generally used for blood pressure measurement, and continuous measurement is impossible. In addition, the measuring instrument is large and difficult to measure under unconsciousness. Therefore, we are conducting research to measure vital signs such as pulse and blood pressure continuously and noninvasively using Fiber Bragg Grating (FBG) sensor. The FBG sensor is created by irradiating the core of the optical fiber with ultraviolet rays to form a diffraction grating. FBG sensor is able to measure the pulse wave signal since the FBG sensor is distortion sensor. In this paper, we confirmed that the pulse wave signal changes with FBG sensor installing method. By pressing the FBG sensor against the skin using a clip, the S / N ratio of the pulse wave signal is improved about nine times. However, it is suggested that it is difficult to measure the reflected wave component of the blood flow caused by blood vessel branching and capillary resistance when the blood vessel is greatly deformed, which has an adverse effect on construction of calibration curve for blood pressure prediction. Therefore, pulse wave measurement is performed using a clip that minimized blood vessel deformation, and blood pressure is predicted. As a result, the correlation coefficient at the time of constructing the calibration curve is improved from 0.48 to 0.88 at the maximum. From these facts, it was found that when blood pressure prediction is performed using the pulse wave signal measured by the FBG sensor, it is necessary to measure pulse wave without losing the reflected wave component.