A new approach to ballistocardiographic measurements using fibre Bragg grating-based sensors

A method for acquiring a ballistocardiographic (BCG) signal from the feet of a standing person and the back of a sitting or lying patient is described. The measurements are carried out using in-house constructed fibre-optic sensors interrogated with a commercially available system. The sensor head consists of a fibre Bragg grating (FBG) attached to an elastic board that is placed between the monitored person's body and a soft surface, enabling the board to deform in an unobstructed way. The body's movements, including the BCG component, exert pressure on the board and make it deform along with the attached FBG. The changes to the Bragg wavelength are proportional to the body's movement and a BCG signal can be extracted from the obtained recording. The measuring capabilities of the sensors were evaluated by comparing the heart rate (obtained on the basis of the BCG signal) with the reference signal registered by an ECG recorder. An RMS value of the relative error is below 1.8% and statistical analyses show a satisfactory reconstruction of measurements. Tests carried out in the MRI environment proved the method to be immune to strong electromagnetic fields. The presence of the sensor in an MRI scanner does not affect the quality of imaging.