The design of an optical fiber pressure transducer for use in the upper airways

The development of an optical fiber transducer for use in biomedical applications has been presented. The design was targeted for use in the upper airways of patients with sleep disorders stemming from partial or total occlusion of the airway. The transducer´s preliminary specification was suited for that of upper airway manometry: a resolution of 10 Pa over the range ±5 kPa, a single transducer being less than 0.94 mm in diameter. Amplitude modulated optical fiber sensors are susceptible to loss due to bending of the fiber core and cladding. The design of the transducer uses a series of three optical fibers, one emitting and two receiving, the combination of the two receiving optical fibers is used to reduce effects of light loss: a bend radius of 50 mm is typical for the insertion into the naso-pharynx. The transducer transduction element is a silicone gel coated with reflective titanium dioxide, the meniscus deforms under pressure and modulates the intensity of light reflected back into the receiving optical fibers. The main disadvantage of optical fiber pressure transducers is their susceptibility to temperature drift. Temperature in the airway rarely changes more than 17°C. The frequency of breathing and the high thermal mass of the catheter means that temperature drift in this application is not significant, and will cause an insignificant error of 12 Pa. The transducer is inexpensive to produce, and may be deemed disposable: approximately $20 in material costs (using current manufacturing techniques this can be halved). The system has the added advantage of being electrically, magnetically, and chemically passive. The potential for miniaturization is limited only by the mechanical strength of the optical fibers as mechanical problems associated with fragile elastic membranes do not apply.