A new fibre optic sensor for respiratory monitoring

A new fibre optic plethysmograph has been designed to monitor respiration non invasively. The device incorporates the idea of using thoracic and abdominal belts similar to conventional inductance plethysmography but uses an optical fibre woven into the belts rather than the usual coiled wire. The fibre optic belts incorporate a loop design in the fibre and rely on "macrobending" losses from laser light transmitted down the fibre when the bend radius of the loop changes during respiration. Changes in lung volume are monitored by analysing the relatively large resultant changes in light transmitted through the fibre. The output from the light detector has been interfaced to a computer containing a data acquisition card and the resultant intensity trace is monitored in real time using a virtual instrument created using LabVIEW graphical programming. Preliminary results suggest a highly sensitive system capable of detecting small changes in lung volume using a technique which is not susceptible to electrical noise and which is electrically safe.