Single Spot Detector for Sleep Apnea Screening

Sleep apneas - i.e. cessation of respiration during sleep of at least 10 s duration - concerns several percent of the adult population, i.e. the order of at least 100.000 persons in a small country like Austria. Corresponding health effects range from reduced quality of sleep to distinct reduction of life expectation. Full assessment is performed in sleep labs the availability of which is strongly restricted as indicated by waiting times of several months. This is due to large costs and high demand on personnel for polysomnography. The alternative is given by portable screening apparatuses. So-called type 4 ones are restricted to single sensors. Thus they are simple to handle, however offering insufficient physiological information. Type 3 apparatuses comprise a minimum of 4 parameters which are being detected with at least as many sensors distributed over the body. For unattended home monitoring this yields problems with respect to instruction of the patient, hook-up, handling, loss of data and quality of sleep. Thus broad screening of potential parts of populaion is impossible, and for 2nd (or even 3rd) world countries unthinkable. The aim of this project is to establish a portable screening system which is restricted to a single, simple to attach, plaster-like detector, thus widely avoiding all above listed disadvantages, but still offering multi-parametric assessment. Based on 20 years prestudy, the location is planned in the region of the large arteria carotis at the neck or the upper thorax region. For this location, already developed sensor concepts promise the possibility to detect both most relevant activities, i.e. the respiratory and the cardiac one. However, a challenge results from the fact that - in contrast to more easy detectable central apneas - obstructive apneas may show local lung activity even though effective air flow does not exist. Usually the flow is detected by means of sensors in the mouth/nose region or indirectly via paradox respiration through an additional abdominal sensor. The aim of project is two avoid such a second sensor spot in the way that the selected spot is utilized excessively for both collection and evaluation of data. For example, it is planned to detect respiration in a synchronous - way by means of an electric, a magnetic and an acoustic sensor principle, and to exploit the total of signal characteristics - e.g. the combinations of harmonic content - in order to distinguish between obstructive and normal respiratory events. As well in a multi- parametric way, attempts will be made to detect the actual sleep time - an important information which usually is not available in the case of home monitoring. A target of project is a low-cost plaster-like detector which shows low mass and dimensions. Apart from using electric field plethysmography, a focus will be put on a magnetic bilayer sensor family which was developed in the EC GROWTH project B-SENS with the applicant as the coordinator. Lowest-cost sensor elements of as little as 100 m thickness promise to detect respiratory and cardiac activities, body position, body movements and temperature - but also flow, respiratory paradoxia, blood pressure variations, REM phases, restless leg syndrome, parameters which here re of mere optional interest since not available at the selected spot. With respect to the planned single spot detector, the main challenge will be to develop specific sensor components which connect the controversial needs of high sensitivity with smallest dimensions, flatness and low mass, on the one hand side, with robustness and reproducible performance independent from anatomical variations, on the other hand side. However, the aims also include a thorough study of consequences of the chosen compromise with respect to the resulting loss of information. In a systematic way, the effect of inclusion of additional parameters - flow, paradoxia, but also oximetry - will be evaluated with respect to sensitivity and specificity. Clinical valiation - as a prerequisite for industrial exploitation - will be subject of a follow-up project. The three years project will be performed in co-operation with the Spanish material research institute CSIC with respect to sensor elements, an Austrian sleep laboratory with respect to system tests and practical assessment, and a sleep lab of Taiwan with respect to broad application.

Sleep apneas - i.e. cessation of respiration of at least 10 s duration - concern several percent of the adult population, i.e. the order of several 100.000 persons in a small country like Austria. Corresponding health effects range from reduced quality of sleep to distinct reduction of life expectation. Full assessment is performed in sleep labs, but their availability is strongly restricted. For unattended home monitoring, screening apparatuses with several detectors are available. However, they yield problems with respect to instruction of the patient, hook-up, handling, loss of data and quality of sleep. Thus broad screening of larger parts of the population is impossible, and for 2nd (or even 3rd) world countries unthinkable. In fact, most concerned persons are not aware about their disease. The aim of project was to establish a portable screening system which is restricted to a single, simple to attach, comfortable detector, thus widely avoiding all above listed disadvantages, but still offering multi-parametric assessment. Extensive comparative optimization studies yielded the region of the upper thorax as the optimum spot. Here, the detection of both respiratory and cardiac activities proved to be most reliable. By means of excessive data processing (e.g. applying artificial neural networks), sufficient physiological data could be reached at this single spot - i.e., not any additional detector components are needed. The target was a low-cost detector which shows low mass and dimensions though containing sensors for acoustics, ECG and electric field plethysmography, magnetic bilayers for cardio-respiratory activities as well as for body motions and position changes. As an initially under-estimated challenge, the sensors should not interact and should not affect the quality of sleep. In an iterative, step-wise way, a variety of initially designed detectors finally yielded flexible and flat plaster-like prototypes, the individual sensors being embedded in clinical silicon material. Selection was performed for optimum performance in lab-tests. For them, three versions of electronic control apparatuses were developed including software packages for the presentation of (i) row data, (ii) filtered physiological activities, (iii) 2 s apnea events (like obstructive snoring) and (iv) obstructive or central apneas. The project also included tests in clinical environments. Here, large difficulties had to be overcome with respect to specific regulations for computer-aided electronic apparatuses. Instead of initially planned tests in Austria and Taiwan, applications for apnea patients were finally performed in a clinic of Lithuania. Apart from problems of integrating the novel method into the existing polysomnography system, the detector showed unexpectedly effective signals in cases of heavy apneas. In special, very pronounced heart rate variations could be revealed in the course of obstructive apnea events. As a final conclusion, the developed detector shows potential to enable broad screening in simple and affordable ways, for the first time. But much closer tests are needed.