Abstract:

Objective Respiration offers useful information for diagnosis and treatment of respiratory diseases, such as anesthetic sensitivity, sudden infant death syndrome, and obstructive sleep apnea syndrome. In this research, an optical fiber fabric for respiratory monitoring was designed based on the side luminous and photosensitive mechanism of the optical fibers for convenient, real-time and effective monitoring of respiration.

Method The 500 μm-diameter optical fibers were woven into the fabric as warp yarns, and laser marking was performed at the designated positions of the optical fibers to form luminous and photosensitive structures. Displacement in the optical fibers took place due to respiratory movement and the light intensity of photosensitive optical fiber was correspondingly altered, monitering the human respiratory state. The influences of optical fibers marking distance, weft elasticity, optical fibers spacing and optical fibers number on optical fiber respiratory sensing were studied.

Results The effect of photocurrent signal fluctuation was more obvious when the optical fiber marking distance was 1 cm under the same stretching distance (Fig.4(a)). Under the same conditions, the elastic recovery rate decreated from polyester/spandex yarns, nylon-spandex core-spun yarns, high elastic nylon yarns to high elastic polyester yarns, with the elastic recovery rate of polyester/spandex yarns as the highest. When the fabrics were tensile loaded to make the same extension, the light intensity loss (γ) demonstrated an increase in the elastic recovery rate of weft yarns. For optical fiber respiratory sensing fabrics of different elasticities, the spacing between optical fibers for high elastic fabric changed obviously with the same fabric stretching distance, resulting in the largest light intensity attenuation. The nylon-spandex core-spun weft yarn with the highest elastic recovery rate was selected for further study, and its elastic recovery rate was 70%, which facilitated the tensile deformation of the fabric and obained preferable test results.Nylon-spandex core-spun weft yarn with 70% elastic recovery rate was selected for further study. With the increase of optical fiber spacing, the intensity loss increased and then decreased, and the optical fiber spacing of 4 warp yarns was adopted (Fig.4(c)). The intensity loss of fabrics with even optical fibers was lower than that with odd optical fibers (Fig.4(d)). In the former case the light intensity loss (γ) tended to increase with the increase of the number of optical fibers, and in the latter the situation was opposite. The light intensity loss (γ) of 5 optical fibers was as high as 38.61% with a stretch of 2 cm, and the effect was excellent. In summary, optical fiber respiratory sensing fabric was woven with 3 luminous fibers and 2 photosensitive fibers in intervals as warp yarns. The optical fiber spacing adopted 4 warp yarns. The weft yarns employed polyester-spandex core-spun with a high 70% elastic recovery rate, with the fabric warp density of 300 ends/(10 cm). The 4 cm fabric width and 1 cm optical fiber floating was employed with satin weave. The breathing amplitude in the standing was smaller compared to that of the sitting and walking states for the same position, because the human standing caused less body cavity undulation, and the optical fiber spacing change was less obvious (Fig.5).

Conclusion The result shows that the light intensity loss of the optimized sensing fabrics is improved from 13.14% to 38.61%. Hence, it can be concluded that the such made sensing fabrics can monitor the calm respiratory signals in sitting, standing and walking below the sternum of body, and the accuracy of the sensing fabric is high with the error range within 1.2 r/min, which is comparable to the performance of a mask respiratory monitor. The optical fiber respiratory sensing fabrics offer high sensitivity good comfort and can be achieved using the conventional technology, showing potentials for industrialization.

Key words: optical fiber, respiratory monitoring, sensing fabric, luminous and photosensitive structure, woven, wearable