Fibre-Optic Interferometry as a Means for the First Heart Sound Detection

摘要

Ambient-assisted living, in particular for the elderly and people with disabilities, call for sensors being capable of detecting several vital sign at a time. We introduce a new healthcare monitoring technology based on fibre-optic interferometry which detects sub-micron changes of optical fibre length. The human heart activity causes fibre-optic changes of a few microns. These can be extracted by analysing the acquired intereferometric signal. We applied modified continuous wavelet transform whose multiresolution properties can sort out different signal components. Our main finding is that Morlet-wavelet-based transform of fibre-optic interferometric signal can detect the first heart sound with considerable reliability. To confirm the locations of extracted signal components are representative, we compute their delays after referential R waves and compare their inter-beat intervals to referential RR intervals. Estimated delays of 48.91±21.48 ms fall within the expected physiological limits for the first heart sound. Also the inter-beat intervals are aligned with high precision, yielding P_(90) error below 10%.