Fiber optic sensor for the measurement of respiratory chest circumference changes

A fiber optic sensor for the measurement of the respiratory depth has been developed. The sensor is composed of a bent optic fiber which is connected to an elastic section of a chest belt so that its radius of curvature chang es during respiration due to respiratory chest circumference changes (RCCC) . The measurement of light transmission through the bent fiber provides inf ormation on its changes in curvature since a higher fraction of Light escap es through the core-cladding surface of a fiber bent to a lower radius of c urvature. The sensor can quantitatively measure the RCCC, although in relat ive terms, and it is sensitive enough to detect changes of the chest circum ference due to the heart beat. Measurements of the RCCC were simultaneously performed with photoplethysmography (PPG)-the measurement by light absorpt ion of the cardiac induced blood volume changes in the tissue-and a signifi cant correlation was found between the RCCC and some parameters of the PPG signal. The fiber optic respiratory depth sensor enables a quantitative ass essment of the respiratory induced changes in the cardiovascular parameters , (C) 1999 Society of Photo-Optical Instrumentation Engineers. [S1083-3668( 99)00402-5].