Photonics textiles eyed for pulse oximetry
Nancy D. Lamontagne
Several companies have integrated fiber optics into clothing, but right now these photonic textiles are used mainly to provide “hip” light-up outfits. From a medical perspective, fiber optics integrated into clothing could allow convenient sensing of physiological parameters.
Such sensing typically requires that optical fibers not only emit light but also detect light that is reflected and/or transmitted. Although light emission from photonic textiles has been well studied, detection has not. Thus, researchers from Empa, Laboratory for Protection and Physiology, in Gallen and from University Hospital Zurich, both in Switzerland, set out to study how well fibers integrated into clothing could detect reflected light.
Although there are many sensing applications that could be possible with photonic textiles, the researchers chose to study pulse oximetry. The technique, which monitors arterial oxygenation, is used extensively in hospital settings from intensive care to recovery rooms. Currently, pulse oximeters come in the form of a plastic device that is clipped onto a patient’s toe or finger. The device uses two wavelengths to measure the light absorption of oxy- and deoxyhemoglobin.
To use photonic clothing for pulse oximetry, the researchers studied how well the textiles could couple reflected light into the optical fiber. Most fiber-sensing applications involve the end of the fiber being placed on the sensing area; however, with fiber incorporated into cloth, the fiber is parallel to the sensing area.
Figure 1. Optical fibers embroidered onto cloth coupled reflected light better than woven samples did. Shown here are “soutage” embroidery (left) and “schiffli” embroidery (right). Images reprinted with permission of Optics Express.
The researchers, led by Markus Rothmaier, compared plastic optical fibers that either were interconnected with polyester in a woven pattern or embroidered onto a woven polyester substrate. The embroidery patterns included “soutage,” in which optical fiber is on one side of the woven substrate and held in place with retention stitches (Figure 1, left), and “schiffli,” in which the optical fiber is guided to a place of interest on one side of the weave, then crossed to the opposite side and back (Figure 1, right). Schiffli embroidery produces random loops in the optical fiber and uses retention stitches on both sides of the substrate.
Measurements showed that woven samples could not couple enough light into the fibers unless they were modified in some way, such as roughening the fiber surface. The embroidered samples, however, were better at coupling the light, with the Schiffli embroidery technique and the addition of a rear alumina reflector performing the best.
Figure 2. The researchers incorporated photonic textiles into a glove to create a pulse oximeter. The sequence shown is for fingers that were closed, then opened, then closed again (as pictured at the top). SpO2 = arterial oxygen saturation; ADC = analog/digital counts.
The researchers also integrated two optical fiber emitters and one optical fiber detector into the tip of a finger of a cotton glove and measured oxygen saturation (Figure 2).
They concluded that textile-based oximetry is feasible, and they plan to further improve the detection efficiency of photonic textiles as well as to develop whole sensors based on the technology.
Optics Express, Aug. 19, 2008, pp. 12,973-12,986.
- Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
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