“We have specifically dealt with the topics of respiratory frequency and respiratory depth as well as heart rate and pulse oximetry“


Fiber Optic Sensor Technology is geared towards opening up new possibilities in medical measurement- and testing technology.

COMPAMED.de spoke with Director and Professor of Engineering Doctor Werner Daum, Division Measurement-and Testing Technology and Sensory Technology at BAM, about current, sensory research projects, how they are applicable and what other applications can be implemented in the future.


COMPAMED.de: Professor Daum, in several projects you have developed sensors that are used to, for instance, monitor the respiration of patients. What problems and tasks needed to be solved by the Federal Institute for Materials Research and Testing?

Werner Daum: We have concentrated on the development of so-called sensitive, technical textiles for applications in Geotechnology for quite some time. Two functions are combined in such textiles: mechanical properties to reinforce dikes for example and sensory properties for the early detection of dike instabilities for instance. After we received a request on whether we could also develop sensitive textiles for medical diagnostics purposes, we integrated fiber optical sensors among other things for the measured variables temperature and strain in normal textiles. In the OFSETH project, which is supported by the 6th EU framework program, we designed special textiles, with which narcotized or sedated patients can be monitored during magnetic resonance tomography scans.

COMPAMED.de: On which technology are these developed sensors based?

Daum: The fiber optic sensors are based on optical waveguides, as known from communications technology. We can insert special structures, for instance so-called diffraction grating, into these optical fibers made of glass or plastic, or we can chemically modify them to measure different physical or chemical variables.

COMPAMED.de: How are vital parameters being measured in the “intelligent T-Shirt“?

Daum: For this development, the focus was on measuring vital parameters in the respiratory area, meaning the respiratory frequency or heart rate or also the respiratory depth. Polymer optical fibers or optical glass fibers are incorporated into an elastic textile either using conventional textile manufacturing techniques or simply by stitching them onto the surface. Inside the optical fiber is a diffraction grating, which acts like an optical filter. The spacing between the grating lines defines a specific wavelength of light, which gets reflected through the fibers on the grating if white light passes through. If the patient now takes a deep breath, the ribcage expands and the elastic textile is being stretched accordingly. The strain in turn gets transferred to the optical fiber with the diffraction grating. The grating is being stretched and the distance between the grating lines changes. This causes for the wavelength, which is filtered out from the light that’s passing through the fiber, to be shifted. The degree of wavelength shift then provides information on the expansion of the ribcage. In this way, we can for instance determine respiratory depth, the difference between inspiration and expiration in the chest measurement.

 
 

The foundation of sensitive textiles is always a textile, in which an
optical fiber made of glass or plastic is integrated; © Centexbel/
Belgium

 
 

COMPAMED.de: Besides respiration of a patient, what else can you measure and test with these techniques?

Daum: Our developments within the realms of the European OFSETH-project were targeted towards the topics of respiratory frequency- and depth as well as heart rate and pulse oximetry, this meaning the assessment of arterial oxygen saturation by measuring the light absorption during transillumination of the skin. By now there are other developments that are commercially available, for example temperature- and blood pressure measurement using fiber optic sensors. Another diagnostic method on the basis of fiber optic sensors, the analysis of breathing gas, is in the research stage.

COMPAMED.de: What materials are used in the construction of this technology?

Daum: To develop sensitive textiles, we use normal clothing textiles as well as also special textiles for technical applications. The latter for example come from the geotextile area. The foundation is always a textile, in which we can integrate an optical fiber made of glass or plastic. We call the combination of textile and fiber ”sensitive technical textile“. The characteristics of the textile are determined by the specific application. In the field of geotechnology we deal with robust and resistant materials, which for instance can resist strong tension loads. For medical applications it is important, that textiles are comfortable, elastic, sturdy and easy to put on and meet clinical requirements.

 
 


COMPAMED.de: In which medical areas is this special sensor technology meant to be used or is it already implemented?

Daum: Fiber optic sensor technology has two significant advantages. Fiber optic sensors are small and compact and have a diameter of about 100 to 250 micrometers (µm). This enables measurement in places that are very tight and difficult to access. For the medical area of application it is important, that they are unsusceptible against electromagnetic fields and resistant to ionizing, medical radiation. They are absolutely metal-free and in terms of different measurements they possess a high measuring sensitivity. In computer tomography, magnetic resonance tomography or other image-guided x-ray procedures, metallic sensors and wires could possibly interfere. In magnetic resonance tomography (MRT) the use of metallic sensors and wires is strictly not possible. In this area, fiber optic sensor technology opens up new possibilities for monitoring a patient during an MRT examination or to measure diagnostically relevant parameters like for example in the area of respiration.

COMPAMED.de: What developments will be able to build on this technology in the future?

Daum: In the future, applications won’t just encompass the hospital area. Long term monitoring of patients in nursing homes or at home using sensitive clothing or bed linens is also conceivable. There is one application that we might like to research soon. This application is about the early detection of hypoglycemia, which can be crucial for survival especially at nights during your sleep. Hypoglycemia is mostly accompanied by excessive sweating. Fiber optical sensors near the skin, for instance integrated into the bed linens, can detect this state early through moisture measurement. Interesting is also one application, which we are researching in the “i-Protect“ research project, supported by the 7th EU framework program: the integration of fiber optic sensor technology in protective clothing like the gear that must be worn by medical staff, firemen or rescue workers during chemical accidents. It is also essential in this case, to monitor vital basic functions during the deployment.

The interview was conducted by Diana Posth and translated by Elena O’Meara.
COMPAMED.de