LOW-POWER TELEMETRY SYSTEM USING SC VOLTAGE-TO-FREQUENCY CONVERTER

J.B. BEGUERET, F. RODES, M. ZHANG and J.P. DOM
Laboratoire IXL - ENSERB - Université Bordeaux I
351 cours de la Libération
33405 TALENCE - FRANCE

INTRODUCTION - The design constraints of an intracorporal telemetry system are a minimum size, a minimum power consumption and a maximum noise rejection. This paper presents a new strain gage telemetry system based on an optimized switched-capacitor (SC) voltage-to-frequency converter, which is well suited for long term monitoring of orthopedic implants used for the treatment of bone fractures.

METHODS - The improvement of the noise rejection is performed with the use of a voltage-to-frequency converter which integrates the input signal. The SC technique minimizes the size circuitry, integrating the precision integrator time constant into the ASIC chip. The topology of this system is the following : the strain gage is included into a Wheaststone bridge which generates an input signal V_IN and a reference voltage V_REF. These bridge output voltages are applied to a SC integrator and then coded with a pulse position modulation (PPM). This PPM coded signal modulates a 180 MHz radiofrequency transmitter. The conversion principle is performed with two successive integrations of V_IN and V_REF. The originality of this system is to realize, at the receiver end, the ratio between this two integration times. Then the transfer function only depends of the strain gage resistance. Indeed no external components are needed. Furthermore, this transfer function is independent of the supply voltage, which is very attractive for intracorporal circuit where very often the supply voltage can fluctuate.

RESULTS - We realized an ASIC chip in a 2 µm BiCMOS technology and an hybrid circuit measuring 16 x 12 mm². The overall circuit has been successfully tested and the measurements mainly exhibit a 0.1% accuracy, a 12 mW power consumption under 4 V, a low drift characteristic and zero off-chip component.

DISCUSSION - We successfully designed and tested an intracorporal telemetry system dedicated for long term monitoring of stainless steel orthopedic implants. The retained topology proved to be an optimized version in terms of size minimization, low power consumption and input noise rejection. Therefore, this PPM converter can find applications in other low power telemetry systems.

A LOW-POWER DATA ACQUISITION IC FOR A MICROTRANSPONDER SYSTEM

M. Oberle¹, Q. Huang¹, P. A. Neukomm^2
1Integrated Systems Laboratory, ETH Zurich
²Laboratory of Electrical Engineering Design, ETH Zurich
Gloriastr. 35, CH-8092 Zurich

INTRODUCTION An implantable, fully-integrated, single-chip, one-channel microtransponder system for low-power biomedical data acquisition applications is reported. The energy and communication is provided using passive telemetry by absorption modulation. The microtransponder is part of an monitoring system which also includes an adapter unit and a standard stationary unit. The monitoring system allows long term recording of external blood pressure sensor signals. The microtransponder system is integrated in standard 3 m m high-voltage BiCMOS process.

METHOD The microtransponder incorporates a RF/DC converter for power conversion and data communication, a low drop-out, low-power 3V / 200 m A voltage regulator and a low-power data acquisition circuitry.

The blood pressure is measured through an external semiconductor strain gauge bridge. The resulting electrical signal is sampled, amplified and filtered by the analog part of the data acquisition circuit. Finally, it is transformed into a digital word through an integrated 9 bit dual-slope A/D converter. The output is a bit-serial pulse train transmitted through the RF/DC converter. A complete conversion cycle for one word is 10 ms long.

The digitized sensor data will be transmitted using a passive RF telemetry link by modulating the bit-serial pulse train onto a 40.68 Mhz RF carrier with a data rate of 1kBaud.

To reduce the average power consumption, a clock frequency of 1kHz and a duty cycle of 1:100 has been chosen for the sampling of the sensor signal. Amplification is achieved by a fully-differential switched-capacitor instrumentation amplifier, followed by a fully-differential switched-capacitor lowpass 50 Hz notch filter. Employing correlated-double sampling technique allows excellent DC offset and 1/f-noise reduction.

The clock signals for the switched capacitor circuitry will be generated by an internal 100 kHz clock oscillator. The overall power consumption of the data acquisition circuit is less than 400 m W.

RESULTS The switched-capacitor readout-amplifier of the data acquisition circuit has already been integrated and successfully tested. The amplifier features are listed in the following table. The complete microtransponder system is in fabrication. Final test results will be reported at the symposium.

Test results of the switched-capacitor readout-amplifier

PHILOSOPHY OF MICROWATT CHEST TO POCKET TELEMETRY AND UNDERWATER ELECTROMAGNETIC WAVE TRANSMISSION

Yasuhito Takeuchi
GE-Yokogawa Medical Systems, Ltd.
Hino 191 Japan
takeuchi@us.geyms.med.ge.com

INTRODUCTION A truely wireless signal acquisition and transmission system using microwatt coin-size transmitter taped on to the patient skin, is studied. It has no wire from patient body surface to recording or transpoding device loated in his/her inner pocket of clothing. Design examples and experiences in real world usage, are presented.

METHODS A 5SFr coin size plastic container carries all necessay electronics for 1ch. ECG acquisition and transmission. Lithium coin battery and 433MHz "NBFM FM" single transistor SAW controlled oscillator and LiMnO2 coin battery are also included. It basically aims sealed-off, water-tight, one-time use design for patient own management. Its battery retention time clears 24 hours continuous operation, aerial power is 50 to 100 microwatt level, the electrode leads are used also for antenna. Aerial signal reachs to about 3 to 5 meter distance in office and home environments, to a professional communication receiver. This coverage is quite sufficient to reach to recording or memory device stored in patient clothing pocket, or handbag, or portmanteau. Application includes 24h holter monitoring with patient own management under completely unrestricted, clothing closed as usual, data acquisitions.

RESULTS One of most danger-full spot for heart, in Japanese lifestyle, other than daily work, travel and sports, etc., is the dipping into Japanese style bath, and out. The device, on patient chest, nearly 50cm underneath the water surface, survived and has kept signal continuity for almost all cases. In-water transmission of 433MHz aerial signal was also very clearly seen, and utilized by underwater antenna to form in-water/in-air diversity reception. This style of diversity is crucial for signal continuity in this case. This is reasonable since because flesh (tapped) water for bathing is just a dielectric material, even in this fequency, than sea water being always so lossy media unapplicable for electromagnetic wave propagation. Using another version of this device where aerial frequency and power (in-water) being 100MHz and 1mW, more than 10 meter distance subsurface transmission was obtained with diagnostic quality of output signal, in a swimming pool.

CONCLUSION Chest to pocket telemetry is applicable philosophy for truely wire-less, unconstrained, live study of biological signal. In-water/in-air diversity reception is also crucial, if taking account of bathing and swimming.

HARDWARE CONSIDERATIONS IN TELEMETRIC MONITORING OF PHYSIOLOGICAL VARIABLES

B.R.Hayes-Gill, J.Taylor, A.Hendroff, J.Ashley, J.A.Crowe, and C.J.Paull
Department of Electrical and Electronic Engineering,
University of Nottingham, University Park, Nottingham, UK, NG7 2RD
Email: brhg@eee.nott.ac.uk

INTRODUCTION The choice of hardware for a wireless application depends upon: data rate; local processing requirements; transmission range; protocol; cost; and size. The design of high frequency RF transmitters is not only a specialist task but necessitates license applications. Hence off the shelf, license exempt, RF units are a more efficient choice in terms of time and expense. This paper discusses the restrictions placed on the choice of hardware for three wireless physiological monitoring applications.

METHODS The first application is to provide a multi-user, leadless, intrapartum monitor utilising a 418MHz transceiver. Simultaneous patient monitoring requires data compression and a reliable protocol. A microcontroller was chosen due to its high processing capability, reprogrammable nature and available C compiler. Data integrity is essential and so the RF units must have transmit and receive for data acknowledgment.

The experiences gained from this project led to the application of telemetry to temperature monitoring of multiple sites on the body during surgery. In this case the data rate is low and minimal processing is required. However, the transducers must be small and hence a custom IC integrating an on-chip, low frequency, short range, license free transmitter is planned which will greatly reduce size and cost. A local receiver unit, positioned within 1.5m, will collect data from all sites and retransmit to a base station via a 418MHz transmitter.

The final application is the monitoring of heart rate, speed, stride length and respiration of free running horses. A central unit on the horse, again controlled by a microcontroller, collects all data. Footfall data is passed to this unit via a 418MHz transmitter attached to the horse’s leg. All data is then transmitted via a 458MHz long range (4km) transceiver to a base station.

RESULTS Block diagrams, power requirements and real time physiological data of all three applications will be presented.

DISCUSSION The choice of hardware for a wireless application depends upon: data rate; local processing; transmission range; protocol; cost; and size. Alternative hardware solutions are presented one of which uses a microcontroller and the other a custom IC.

A CROSS-BAND UHF TRANSPONDER FOR SHORT-RANGE PHYSIOLOGICAL SIGNAL ACQUISITION

G C Crumley and N E Evans
N Ireland Bioengineering Centre & School of Electrical and Electronic Engineering
University of Ulster, Shore Road, Newtownabbey, Co Antrim, N Ireland, UK, BT37 0QB

DISCUSSION The hardware described represents a minimum-power solution to transponder design in a part of the RF spectrum where advantage can be taken of inherently low levels of man-made noise, wide channelling and potentially higher antenna efficiencies.

TECHNIQUES FOR THE LABORATORY CONSTRUCTION OF MINIATURE HYBRID-CIRCUITS: A 350-MG ECG-TRANSMITTER

YORK WINTER
Erlangen University, Institute of Zoology II
Staudtstrasse 5, 91058 Erlangen, Germany,
ywinter@biologie.uni-erlangen.deSession

INTRODUCTION: Telemetric methods are necessary for the investigation of small (<15g) flying animals in a wind-tunnel to minimize any disturbances of flight aerodynamics or kinematics by the measuring devices. The small transmitter size required here cannot be achieved with standard SMD (surface mount device) -components. I therefore developed a method for the laboratory construction of hybrid-circuits, i.e. for the connection of passive electronic components (resistors and capaci-tors) with unencapsulated ('naked') semiconductor chips, which are only 2% in volume of the SMD-package type.

METHODS: Transmission of the ECG-signal is done here by conventional pulse-frequency modulation using a biopotential amplifier which modulates an asymmetric subcarrier oscillator which in turn pulses a UHF-oscillator transmitting from its coil. Passive components (resistors, capacitors) were used in sizes from 1.0 x 0.75 down to 0.25 x 0.25 mm. To obtain 'naked' semiconduc-tor chips, standard SMD-components were decapsulated by immersing them within a teflon-gaze net into boiling, fumic nictric acid (99.9% HNO3). This treatment leaves the gold bonding wires intact. The printed circuit board was etched from a laminate of 25 m m Polimid film with double sided 18 m m copper sheets (Pyralux LF-8515R, Du Pont) by using a conventional photo-chemical method. The components were mounted onto the circuit board under a stereomicroscope by soldering (resistors and capacitors) or glueing with silver-filled conduc-tive epoxy glue (semiconductor bond wires). The epoxy glue was applied with the help of a micromanipulator after it was either filled into a glass electrode of the type used for intra-cellular recordings or placed as a small droplet onto the tip of a 100 m m stainless steel needle (minuten pin).

CIRCUIT SIZE AND PERFORMANCE: The final circuitboard with 22 components including a dual Op-Amp (TLC 25L2 C) and three transistors was 5.8 mm in diameter and 750 m m high. The complete transmitter weighed 350 mg including electrodes, transmitting coil, outer case and a 190 mg 1.55 volt silver oxide battery (no. 317; 9 mAh). The biocompatible coating for the implant specimen of this transmitter weighed an additional 100 mg. Average power consumption was 15 m A at a subcarrier oscillation frequency of 300 Hz. A battery lasted for about 3 weeks. The transmission range was between 2 and 5 m.

DISCUSSION: With the techniques described here it is possible to assemble very small electronic hybrid-circuits with the tools available in a standard biological laboratory. This was used here for the construction of an ECG-transmitter for a 10 g mammal. With a potential sampling rate of up to several kHz this same transmitter is usable for a variety of purposes from ECG to neurophysiology in small animals.

DESIGN OF CIRCULAR AND SOLENOID COILS
FOR MAXIMUM MUTUAL INDUCTANCE

Sérgio Francisco Pichorim & Paulo José Abatti
CPGEI / CEFET-PR - Paraná Federal Center of Technological Education
Av. Sete de Setembro, 3165 CEP : 80230-901 - Curitiba - Paraná - Brazil

INTRODUCTION Practical biotelemetry system design commonly requires the determination of optimal size of the coils involved on power and/or information transmission. In principle, coils optimal size can be determinated using the Neumann mutual inductance general formula. However, the latter involves elliptic integrals [1], from which solutions are usually obtained using tabulated or graphical values [2]. The aim of this work is to present the derivation of mutual inductance simplified equations, useful to compute optimal size of circular-circular and circular-solenoid (including solenoid with ferrite core) pair of coils.

(1) (2)

METHODS Calculating the magnetic flux density (B) due to a current in primary coil using Biot-Savart law, and assuming that r²>>a² (where, r is the distance between primary coil center and secundary coil, and a is the primary coil radius), it is possible to obtain simplified equations of mutual inductance (M) between two circular coils (eq. 1), and between a solenoid and circular coil (eq. 2). In these equations n₁ and n₂ are the coils' number of turns, D distance between them, b radius of secundary circular coil, L solenoid length, and gm a constant related to solenoid core (gm=1 for air). Since eq. 1 and 2 do not employ elliptic integrals, the secundary coil radius (b), yielding maximum mutual inductance, can be calculated for a given set of geometrical parameters (a, D or L).

RESULTS The proposed equations have been compared with the general equations and measured values, giving results with negligible errors for D/a>10. Calculations using eq. 1 and 2, for D/a=5, yield results with errors less than 4%. For D/a<5, these equations cannot be considered useful to calculate the maximum mutual inductance.

CONCLUSIONS Observing that most biotelemetry systems use weakly coupled coils, i.e. the coils are within the above conditions (D/a>5), the authors believe that simplified equations are useful for optimal coil design.
[1] - Soma, M., Galbraith, D. C. & White, R. L., "Radio frequency coils in implantable devices: misalignment analysis and design procedure". IEEE Trans. Biom. Eng., 34, 276-282, 1987.
[2] - Terman, F. E., "Radio engineering handbook". McGraw-Hill, New York, 1943.

MULTICHANNEL MICROCONTROLLER-BASED REPEATER
TELEMETRY SYSTEM WITH DIGITAL RADIO DATA LINK

Franz Schober ¹⁾, Gerhard Fluch ¹⁾, Ralf Boegel ^2)
1) Research Institute of Wildlife Ecology, Vienna Veterinary University,
Savoyenstrasse 1, A-1160 Vienna, Austria
²⁾ Berchtesgaden National Park, Doktorberg 6, D-83471 Berchtesgaden, Germany

INTRODUCTION For an ecophysiological study on free-ranging Griffon Vultures (Gyps fulvus) a multichannel telemetry system has been developed, which has to fulfil the requirements for long-range transmission and long-term application and should be compatible to commercially available tracking receivers and data logging equipment.

METHODS The radio frequency parts of the design are based on a former design of a repeater system for heart rate and body temperature. The system has to meet the following requirements: i) capability to measure heart rate, body temperature, ambient temperature and air pressure/altitude; ii) applicability under wildlife conditions which require long range (about 5 km), long life, minimum impact on the animals (minimum weight, optimal sociability), and iii) adaptability to other applications (animal species, physical and physiological parameters). In contrast to common wildlife systems the solution could be found in integrating microcontrollers in both the implant and the repeater (PIC16LCxx low power and low voltage family). Heart rate (by QRS detection of an ECG signal) is counted in the implant and transmitted (100 kHz) together with body temperature (using the AD-conversion capability of the microcontroller, accuracy 0.1 °C) as binary numbers to the repeater using pulse modulation with a serial data transmission protocol. In the repeater air pressure and ambient temperature are measured also by AD-conversion. The 4 parameters are transmitted consecutively by pulse-interval modulation (0.5 to 1.5 sec) at 150 MHz. The pulse-duration is changed for identification of the 4 parameters (10, 15, 20 and 25 msec).

RESULTS The implant package is designed for intraabdominal implantation and weighs 45 g. Two ECG electrode leads each 8 cm in length are attached. The repeater device is formed to be carried as a back-pack and has 120 g in weight with an output power of 8 dBm (6 mW). The operating life of the batteries is 2 years. With the implant this could only be achieved by using a very power-saving digital data link to the repeater and by switching off all power-consuming parts of the electronic when they are not in use.

DISCUSSION Prototypes of this system were tested under laboratory conditions up to now. Until the beginning of this symposium tests on animals will be carried out.

Session 2 - 1

ENHANCEMENT OF INFRARED BIOTELEMETRY FOR MONITORING AMBULATORY PATIENTS OVER WIDE AREAS

Ante Santic, Faculty of Electrical Engineering and Computing, Zagreb, Croatia
Michael R. Neuman, Case Western Reserve University, Cleveland, USA
Vedran Bilas, Faculty of Electrical Engineering and Computing, Zagreb, Croatia

INTRODUCTION A limitation of infrared (IR) telemetry is that its range is usually confined to a small space such as a room, and shadows and non-reflecting surfaces require that multiple receivers be used for reliable operation. The goal of this work was to optimise infrared diffuse telemetry by determining the most efficient pulse transmission and extending the area over which the patient can freely move. This system is applied in the rehabilitation of patients with lower extremity injury.

METHODS A biotelemetry system for measuring forces on the feet and crutches or cane as a patient walks has been developed. Capacitive transducers sense up to six different forces on the legs while crutches or cane have a transducer based on IR radiation. Information was transmitted using time-division multiplexing and pulse position modulation. Pulse durations were 5m s, and the eight channels were sampled at 8x200=1600Hz. This keeps transmitter input power at 160mW, so that a small 9V rechargeable battery ( Varta, 110mAh) can be used for 4 hours of continuous operation. The whole transmitting system including the sensors requires twice as much energy and uses two additional 9V batteries. A personal computer with A/D performs signal processing and displays the 8 channels of data. A unique aspect of the system design is the use of multiple receiving units to include larger areas. This means that several rooms as well as halls or staircases can be covered. This is possible because transmitted pulses received simultaneously by receivers that are within range can be summed, and the noise from the other receivers can be muted. This improves transmission reliability by increasing the signal-to-noise ratio when the transmitter is not close to any receiver. Automatic gain control circuits at each receiver help to compress signal dynamic range especially when the transmitter is close to a receiver.

RESULTS The system has performed reliably in interior areas as large as 10 x 10 m and in up to 3 different rooms simultaneously. As many as 10 receivers have been used with the system at one time.

DISCUSSION The advantages of IR telemetry of simplicity and reliability over short ranges have been extended using multiple receivers with intelligent signal summing. There is no theoretical limit to the number of receivers that can be used in such a system, so it should be possible to extend the range to be even greater than reported. The utility of the system in the rehabilitation clinic has been demonstrated.

Session 2 - 2

APPLICATION OF SPREAD SPECTRUM TECHNIQUE FOR MULTICHANNEL TRANSMISSION IN OPTICAL TELEMETRY

Koichi Shimizu, Nobuyuki Toya and Katsuyuki Yamamoto
Department of Bioengineering, Graduate School of Engineering,
Hokkaido University, Sapporo, 060, Japan

INTRODUCTION With the recent increase of medical equipment in an ICU and an operating room, their systematization has been required. However, the confusion of electric wires and tubes around a patient has to be avoided, and wireless transmission is preferable. Considering the EMC problems in a hospital, we have developed a data-transmission technique using an indirect scattered light. As a multiplexing technique for the multichannel transmission, the spread spectrum (SS) technique was applied.

METHOD Fig.1 illustrates the developed system. It is designed for the sampled and digitized medical data, such as an ECG, medical images and control signals for medical equipment. In the transmitter, the data is pre-modulated first, and then multiplied with a pseudo-noise (PN) signal for the SS modulation. The modulated signal is emitted in the air from an array of LED's. The indirect light reaches the receiver after the multiple reflections at a ceiling, a floor and walls. The signal received by a Si-PIN photodiode is demodulated by a SAW device using the same PN signal as used in the transmitter.

RESULTS To examine the feasibility of this technique, we have developed the fundamental part of the wireless data-transmission system. An experimental system was manufactured which consisted of two transmitters and one receiver. Using this system, the fundamental characteristics of this technique were investigated. Although there were some points to be improved, the feasibility of this technique was verified.

Session 3 - 1

Biotelemetry for space life sciences research

Chris Somps and John Hines
Sensors 2000! Program
NASA-Ames Research Center, Mail Stop 213-2
Moffett Field, CA 94035-1000

    The space life sciences research community needs physical, chemical, and biological sensors and associated instrumentation to monitor physiologic adaptation to the space flight environment. Cardiovascular deconditioning, bone demineralization, skeletal muscle atrophy, and vestibular disturbances are just a few of the physiologic changes which occur during space flight and which are the focus of current scientific inquiry. Because crew time is limited, automated data acquisition, processing, and storage are required, and since animal models are group-housed to conserve volume and mass, wireless data systems are clearly preferred. In response to these needs, NASA’s Sensors 2000! (S2K!) program is developing radio frequency biotelemetry systems for automated physiologic monitoring of animal models in space.

    The S2K! program collaborates with academia, industry, and other government agencies in the development of a variety of wireless telemetry systems, subsystems, and components. Collaborations take the form of codevelopment partnerships, grants, cooperative ventures, and contracted vendor efforts. Development phases include definition of need and constraints, preliminary design and prototyping of novel or advanced concepts, further development and testing of promising technologies, and finally integration and flight. Technologies are also evaluated for application to ground-based biomedical research and clinical monitoring needs.

    Areas of current focus include the development of miniaturized, implantable chemical sensors, development and evaluation of pulse-encoded biotelemeters including pulse interval and pulse code modulation systems, evaluation of commercial off-the-shelf low-power microcontrollers and DSP processors for use in encoding and decoding circuits, and the establishment of standardized, miniaturized biotelemetry building blocks, e.g., signal conditioning blocks, controller blocks, data buses, and transmitter circuits. We are also working on a novel slot antenna design for use in metal wire-mesh animal enclosures. As an example of a project in its final phases, a biotelemetry system for monitoring circadian rhythms in rodent heart rate and body temperature is currently undergoing final test and evaluation in preparation for an upcoming Space Shuttle mission.

    The goal of these S2K! efforts is to identify, develop, and apply new and emerging technologies for application to wireless telemetric monitoring of space flight research subjects. This will facilitate the acquisition of data critical to understanding physiologic adaptation to the space flight environment and thus further NASA’s commitment to future human exploration and development of space. In addition, spin-offs of these technology development efforts are finding application in biomedical research and clinical monitoring environments.

Session 3 - 2

MICROFABRICATED MINIATURE CHEMICAL SENSORS

M. R. Neuman*, R. P. Buck**, V. V. Cosofret**, E. Lindner***, M. Erdosy**,
C. R. Edwards*, R. A. Lucic***, C. Xu**, and S. Marzouk**
NSF Engineering Research Center for Emerging Cardiovascular Technologies and University Sensors Consortium

INTRODUCTION Biomedical sensors serve as the interface between physiologic systems and electronic instrumentation such as biotelemetry devices. These sensors must provide an accurate measurement of physiologic variables if the telemetry system is to be useful for physiologic monitoring. Sensors must also be reproducibly and economically produced for practical application. This presentation describes sensors and technologies for producing them to achieve these goals.

METHODS Miniature ion-selective electrodes and enzyme-mediated amperometric sensors have been developed and fabricated using thin- and thick-film microfabrication techniques. Sensor structures with sensitive surfaces with areas as small as a fraction of a square millimeter are constructed from layers of conductors, insulators, electrolyte-containing hydrogels, and ion-selective membranes on polyimide or ceramic substrates. The fundamental design consists of a well 0.5 to 3.0 mm in diameter with one to three electrodes at its base. The well can be from 10 to 150 m m in depth and is formed by depositing thick-film insulators such as glazes or photopolymerized polyimide on the substrate. The well pattern is defined by thick-film printing or photolithography. Silver/silver chloride, gold, or platinum electrodes and lead wires are formed on the substrate using the same technologies. Sensor inner solutions are formed using poly-(hydroxyethyl methacrylate) containing ions and where appropriate enzymes that is deposited in a methanol solution using a precision solution dispenser and xyx-positioner. Chemically or physically selective membranes cover the well to complete the sensor. Ion-selective sensors for H⁺, K⁺, Na⁺, Ca⁺⁺, and Cl^- have been fabricated. Enzyme-mediated sensors have an additional layer of inner solution and membrane and have been fabricated for lactate, glucose, creatinine, creatine, and putrescene. Sensors have been made in the form of single sensor devices or multisensor arrays of the same or different sensors.

RESULTS Sensors have been fabricated and found to have close to theoretical characteristics. Devices have been batch-fabricated with yields ranging from 62 - 100%. Biological application by collaborators has demonstrated that some sensors can be used reliably in acute animal experiments.

DISCUSSION The use of microfabrication processes enables batches of sensors to be fabricated in one manufacturing process. This can lead to devices with reproducible characteristics that can ultimately be produced at a relatively low per unit cost.

* Case Western Reserve University, Cleveland, OH USA
** University of North Carolina, Chapel Hill, NC USA
*** Duke University, Durham, NC, USA

Session 3 - 3

MICROFABRICATED VARIABLE CAPACITANCE FORCE SENSORS

C. Cristalli*, C.R. Edwards and M.R. Neuman
Case Western Reserve University, Cleveland, OH, USA
* Instrumentation Laboratory, Milano , Italy

INTRODUCTION Variable capacitance force sensors have been designed employing a compliant dielectric structure using thick- and thin- film technology. The resulting thin sensor can be used in many applications including electronic force measurement instrumentation and biotelemetry devices. Different geometries have been developed for a variety of applications utilizing single and multielement devices.

METHODS The sensing element consists of a parallel plate capacitor with a compliant, elastic dielectric material. As a force normal to the plates is applied, their separation decreases and the capacitance increases. The sensors consist of thin, gold films on flexible polyimide substrates that serve as the plates. These are separated by narrow strips of silicone elastomer deposited on top of each plate using thick-film techniques. Sensor capacitance is measured by sampling the voltage at the end of a fixed charge pulse applied to the structure at regular intervals. Stray capacitance effects are minimized by locating an isolation amplifier or multiplexer-amplifier on or near the sensor. Fabricated sensor structures include: (1) a single element 10 mm diameter sensor, (2) a linear array of eight 7 mm square elements, and (3) an 8x8 square array of 2 mm square elements. Sensors were tested and calibrated element by element using a special test fixture that applied weights of differing mass over the active surface area of that element. They were characterized in terms of sensitivity, stability, reproducibility, response time, hysteresis and temperature stability. Special circuits or algorithms were developed to minimize crosstalk in multielement arrays and to determine total force over the array.

RESULTS Single element sensors had a range of 0 - 10 N, and multielement sensors had a range of 0 - 5 N for each element. All sensor systems were linear over this range, although hysteresis was present. The sensitivity and baseline capacitance from one sensor to the next could vary because the thick-film process does not have tight tolerance on dielectric film thickness. Sensors have been applied to measure grasping force, contact force for limb length measurement, and to determine interfacial pressure distributions between a sphygmomanometer cuff and the arm.

DISCUSSION An advantage of using microfabrication film technology in constructing these sensors is that very thin structures can be built. This makes it possible to intersperse the sensor between a sphygmomanometer cuff and the arm or a finger tip and the object being grasped with only minimal effect on the system due to the presence of the sensor. The use of polyimide substrates allows the sensors to be flexible although sensor flexure results in a shift in baseline force. The use of microfabrication technology opens the possibility to economically batch fabricate these devices.

Session 3 - 4

Effect of rat subcutaneous tissue on a polymeric membrane ph sensor

Somps, C.J., Madou, M.J., and Hines, J.W.
SENSORS 2000! Program
NASA-Ames Research Center, Mail Stop 213-2
Moffett Field, CA 94035-1000

INTRODUCTION The space life sciences research community needs physical, chemical, and biological sensors and associated instrumentation to monitor physiologic adaptation to the space flight environment. Since crew time is limited, automated data acquisition, processing, and storage are required, and wireless systems are clearly preferred. In response to these needs, NASA’s Sensors 2000! (S2K!) program is developing wireless telemetry systems for physiologic monitoring in animal models. In many cases, implanted sensors, in direct contact with biologic tissue, are the only way to acquire the needed information. However the performance of chronically implanted sensors, especially chemical and biological sensors, is not well understood.

METHODS To determine if sensors based on ion selective, polymeric membranes retain their sensing properties following chronic exposure to a physiologic environment, miniaturized pH sensors were implanted chronically in the subcutaneous tissue of alert rats. Sensors were constructed from a medical-grade PVC tubing (0.07" O.D.) and a sensing membrane cast over the end of the tubing which incorporated a plasticized, PVC support matrix doped with an H⁺ ionophore (tri-n-dodecylamine). Sensor performance, including stability, sensitivity, and response time were measured on the bench following as much as 28 days of implantation and compared to pre-implant values. Sensor stability and sensitivity were also measured in vivo for implant times up to 8 days. In vivo measurements of sensor sensitivity were made in rats subjected to elevated CO₂ levels.

RESULTS We found that our polymeric membrane pH sensors showed little change in sensitivity, selectivity, and response time following up to 28 days of implantation. The only significant change observed was a drift in the response baseline, which diminished to less than 0.03 pH units/day for implant times beyond 4 days. Similar drift was observed with direct measurements from implanted sensors. We also found that sensor sensitivity determined in vivo showed a close correlation with values obtained on the bench, at least over most of an 8 day implant period.

DISCUSSION Our data suggest that chemical sensors based on ion selective, polymeric membranes are not significantly altered by a subcutaneous tissue environment. We further conclude that, at least in the case of pH, these sensors can chronically measure changes in the ionic activity of local tissue that is reflective of physiologically relevant systemic changes. NASA’s S2K! program is integrating these sensors with a fully implantable wireless telemetry system for chronic monitoring of pH and other chemical parameters. This unique capability will have exciting space and ground-based medical and research applications.

Session 3 - 5

INJECTABLE PASSIVE RESONANT CIRCUIT
FOR PRESSURE BIOTELEMETRY

Paulo José Abatti, Sérgio Francisco Pichorim & Thorsten Enders
CPGEI / CEFET-PR - Paraná Federal Center of Technological Education
Av. Sete de Setembro, 3165 CEP : 80230-901 - Curitiba - Paraná - Brazil

INTRODUCTION This works describes the design and preliminary results in vitro of an injectable passive resonant circuit useful to monitor body internal pressure (in the muscle, brain or blood vessels).

METHODS The injectable resonant circuit, composed of a 68µH inductor, a 4.7nF capacitor (frequency @ 280kHz) and a moveable ferrite core, is encapsuleted in a glass tube (diameter of 1.5 mm and length of 10 mm). The inductor is constructed using a ferrite core (diameter of 0.75mm, length of 5.5 mm, µ=2000), and a 43 AWG wire (135 turns). The moveable core (0.9 x 0.9 mm) has its relative position (inside the glass tube) proportional to the external pressure, changing total inductance and, consequently, the circuit resonant frequency. The circuit resonant frequency is measured using three external coils (one primary excitation coil, located between two other receiving coil). The receiving coils are carefully constructed so that the direct influence of the primary on them is minimized. Thus, applying a trapezoidal current signal in primary coil, the internal circuit is excited during current changing period, and then set free to oscillate when current is constant. These oscillations are then received externaly, and after amplifying and filtering, the signal is processed to determinate its frequency, and therefore, the pressure value.

The receiving frequency measurement has been realized using an A/D-converter based on Schmitt-Trigger, a high frequency oscillator and counter circuits. Because of the noise due to practical problems of compensation, windows of time to get the right position of the natural oscillation has been used. A squarewave oscillator with a frequency of 44 MHz and six 4-bit-counters measure the width of the impulses, which is related to the resonance frequency of the implanted circuit. Multiplexers transfer these informations to a computer to calculate and display the transmitted values.

RESULTS The injectable circuit has shown a sensitivity of 16.6 kHz per millimeter of ferrite core movement, presenting for a specific membrane (air volume of 6.6 mm³), a final sensitivity of 880Hz/10mmHg. Preliminary receiver tests demonstrated that average measurement of frequency (ten measurements) yielded in a stable value (S.D. of 0.5 %).

DISCUSSION & CONCLUSIONS A injectable passive resonant circuit for pressure biotelemetry has been presented and its characteristics discussed. Preliminary results has shown that the system is able to monitor body internal localized pressure.

Session 3 - 6

STUDIES ON BIO-SENSING MICROSYSTEMS FOR HEALTH CARE

Eiji Takeda, Takashi Handa, Shuichi Shoji, Akihiko Uchiyama
Waseda Univ. Dep. of Electrical and Communication Engineering
3-4-1 Ohkubo, Shinjuku-ward, Tokyo, JAPAN 169

INTRODUCTION A Micro-Capsule (MC) for measuring pressure, temperature, and pH in digestive tract, and a very low-powered consumption wireless ECG (Electrical Cardio Gram) sensing system is studied in order to realize real time monitoring for health care.

MICRO-CAPSULE The capsule including a glass pH sensor, a transmitter and a button battery was already presented.^* To achieve miniaturization for this capsule, we applied micro-machining to fabricate a silicon based multi-sensor of pressure, temperature, pH. A piezo resistive diaphragm pressure sensor (1.8 x 1.8 mm²), a p-n junction temperature sensor (0.5 x 1 mm²), and a Si₃N₄ gate pH ISFET (0.2 x 0.6 mm²) are fabricated on a 4.2 x 2.8 x 0.2 mm³ silicon wafer as shown in Fig.1.

ECG SYSTEM The schematic of an ECG monitoring system is shown in Fig.2. The ECG detector/transmitter, located on the chest, has three detection electrodes (R,L,RF), and an electrode for signal transmission (T). The detected ECG is amplified and modulated, then applied between electrodes T and RF. The signal is turned into AC micro current and can be transmitted through the body. It is then detected by the relay transmitter placed on the wrist that has three detection electrodes. The power necessary for this transmission is only 8µW (400mV_RMS x 20µA_RMS), and can be driven by a very small battery. This concept is useful for multi-monitoring of health parameters because each detector part should not have its own RF transmitter so as to minimize the electromagnetic noise problems and to achieve low power consumption.

^*K. Saito, A. Uchiyama, et. al. 12^th Int. Symp. Biotelemetry, pp415-419, 1992

Session 4 - 1

TELEMONITORING OF INTRACARDIAC ELECTROGRAMS

H. Hutten, G. Schreier, P. Kastner, M. Schaldach*
Institute of Biomedical Engineering, Technical University Graz (Austria)
*Institute of Biomedical Engineering, University Erlangen-Nürnberg (Germany)

INTRODUCTION: Telemonitoring of intracardiac electrograms is a promising new approach for rejection monitoring after heart transplantation, but also for diagnostic purposes and drug therapy management.

METHODS: The recent development of advanced pacemaker technology with extended bandwidth telemetry feature in combination with with fractally coated electrodes renders possible the monitoring of intracardiac electrograms from the spontaneously beating and the paced heart. The pacemaker telemetry bandwidth covers the range 0.3 - 200 Hz and can be utilized with polarization-artefact free electrodes. The recorded electrograms contain relevant information concerning all influences on membrane permeability and excitability (e.g. activity of the autonomous nervous system, electrolyte concentrations, hormons, drugs). Depending on the type of employed electrode and the site of measurement, the recorded electrograms monitor either the behaviour of only few cells (i.e. monophasic action potentials) or a global view on the process of excitation spreading (e.g. unipolar measurement using an epimyocardially fixed electrode against the pacemaker housing). After transmission to an extracorporeal data acquisition station the electrograms can be further processed employing averaging, feature extraction etc.

RESULTS: The first applied method for routinely telemonitoring intracardiac electrograms has been established during the last 5 years for the computerized monitoring of acute rejection after heart transplantation. The electrograms are recorded in five centers worldwide with more than 110 patients and transmitted via internet from the local data acquisition station to the central computer in Graz using either the FTP protocol or e-mail. The electrograms are evaluated with regard to rejection or infection diagnosis. After signal processing the hospital receives a record that supports further decisions in therapy management. More then 10.000 transmissions have been performed without any serious problems.

DISCUSSION: Intramyocardial electrograms contain useful information for diagnostic or therapeutical purposes. Signal processing can be performed in specialized centers.

Session 4 - 2

A EUROPEAN NEUROLOGICAL NETWORK USING TELEMATICS

T. Penzel, R. Conradt, C. Guilleminault^*, K. Kesper, T. Paiva^**, J.H. Peter
Medizinische Poliklinik of Philipps-University, Baldingerstrasse, D-35033 Marburg
^* Hospital Santa Maria, P-1600 Lisboa, Portugal
^** Stanford sleep disorders center, Palo Alto, Calif. USA

INTRODUCTION Sleep disorders and headache are common symptoms caused often by chronic disorders. A diagnosis of these chronic disorders requires well equipped laboratories and trained physicians. Epilepsy is less prevalent but diagnostics need special training in Neurophysiology. Today differential diagnosis and a problem oriented therapy of these disorders is possible. The main problem is the limited availability of diagnostic systems and of appropriate medical knowledge. Telemedicine can help by setting up a network of diagnostic laboratories linked with general practitioners to achieve an early diagnosis and thereby an adequate therapy throughout cities and rural areas.

METHODS A central server accessible by 34 expert centres was installed in Marburg using existing Internet connections. Expert systems to support medical decisions are developed on the basis of the database. The communication network is extended to connect remote locations such as the Azores. Remote monitoring devices which can be connected to telephone lines are used by general practitioners for diagnostic long-term recording of sleep disorders and EEG. Tutorial material is developed with TOOLBOOK software tools to train physicians in the diagnosis of these chronic disorders.

RESULTS The database server installed at the university Marburg (ppsl01.hrz.uni-marburg.de) is connected with the internal hospital network via a firewall computer. As selected polygraphic recordings and the tutorial software is collected there, the tutorial system can be accessed on-line by centres with reasonable network transmission speed. The tutorial system supports interactive training. It is built on an underlying knowledgebase and database collected by the centres working in the network. The database contains case reports with diagnoses, therapies and questionnaires concerning symptoms as well as biosignals and video clips recorded in sleep- and EEG laboratories. The database forms the basis for a new digital atlas of polysomnographic recordings. A first atlas was distributed on CD-ROM and is available through WWW. Typical biosignal patterns of sleep disorders are kept there. As we use a standard format for biosignals the exchange of signal data is as easy as the exchange of digital text, graphics and video.

CONCLUSION The European neurological network is used to create interactive educational material for sleep disorders, headache and epilepsy. A common database of biosignals and case reports is built. The network enhances the exchange of multimedia patient records among specialised centres and interested physicians. Centres can use X25 and ATM connections whereas general practitioners can use ISDN connections.

Supported by the European Commission DG XIII, grant no. HC1014

Session 4 - 3

TECHNOLOGIES AND DEVICES FOR THE TELEMONITORING OF BIOMEDICAL SIGNALS: AN INTEGRATED APPROACH

Franchi D, Palagi G, Bedini R, Ripoli A and Belardinelli A.
CNR Institute of Clinical Physiology,
Via P. Savi 8, 56100 Pisa, Italy.

Telemedicine is the delivery of care to patients anywhere in the world by combining communications technologies with medical expertise. This is an emerging field that could have a revolutionary impact on health management. The main goal of this approach, namely to improve access to high quality medical care at affordable cost, can be pursued by means of an effective integration of Hospital and Home Care. In this work we report about a developed system for the home and hospital monitoring and surveillance of patients. The subject is equipped with a palmtop datalogger based on a 16 bit RISC, C native, processor. The device, provided with 8 analogic channels for the acquisition of physiological parameters such as electrocardiogram, blood pressure etc., is connected by telephone with a central specialistic station; the connection between the device and the public telephone line is accomplished by a modem, embedded in the telephone plug, communicating with the patient terminal through an IR link. The communication between the patient and the hospital is managed by a reliable developed protocol; the linkage may be previously programmed or accomplished on request both by the central station or the patient or the device itself. The computing power of the used processor makes possible to place a local intelligence, for on-line analysis, directly in the patient terminal. As an example we have developed a programme for the analysis of the RR variability of the electrocardiogram, in such a way that alarms and special connections procedures are activated by pre-selected threshold values and computed parameters of the processed signal.

Session 4 - 4

Monitoring of physiological key functions of free moving patients via mobile phones

Rolf Weiß, Anita Jain, Gerhard Mutz & Egon Stephan
Psychological Department, Cologne University
Herbert-Lewin-Straße 2, 50996 Köln, Germany

INTRODUCTION We will introduce a system consisting of various commercially available devices to monitor and automatically report critical states of free moving patients.

METHODS A small ambulatory monitoring device was equipped with special software to control a mobile phone via a serial link. A 8-channel digital recorder is used to measure and store the physiological signals, evaluate them by special purpose software, control the mobile phone and send a message to a hospital or doctor. If a critical state is detected in the patient, the mobile phone is automatically activated and a short message is transmitted to the doctor's phone specifying the patient's name, history, medication, actual physiological status (e.g. heart rate, oxygen saturation, temperature, body position, and an actual diagnosis like tachyarrhtmia, hypoxämia, ictus or status febrilis) and - if necessary - patient’s location (together with a GPS device). The message can be received by almost every GSM cellular phone even while talking to another participant. In case of emergency the doctor can then access raw data (e.g. the ECG) via the graphical display of a small, handheld computer or a normal, stationary computer or fax. The kind of signal measured and the sensors used can be changed according to the field of application.

APPLICATIONS The system is advantageous for any patient who does not need constant care, but regular supervision of critical functions. Such patients are often very restricted in their daily life because they are not released from the hospital or have to visit their doctors very often for control. Example applications are post-infarct patients (monitoring of ECG), pregnant women with certain risk factors (monitoring of labour contractions), babies at risk for sudden infant death or elderly people in a labile health state.

DISCUSSION This kind of telemetric monitoring can provide a better quality of life to patients who otherwise would be very restricted in their normal life and secures at the same time uninterrupted medical supervision.

Session 4 - 5

DEVELOPMENT OF BIOTELEMETRY SYSTEM FOR ADVANCED EMERGENCY CARE IN AMBULANCE

Koichi Shimizu, Seiji Matsuda, Isao Saito, Katsuyuki Yamamoto and Takeshi Hatsuda*
Graduate School of Engineering, Hokkaido University, Sapporo, 060, Japan
* Hokkaido Institute of Technology, Sapporo, 006, Japan

INTRODUCTION In the medical emergency out of a hospital, the patient has to be diagnosed properly and transported to an appropriate medical institution as quick as possible. To improve the lifesaving rate in emergency medicine, there has been a strong demand for the medical care in a moving vehicle such as and ambulance and passenger vehicles. In Japan, the licensed paramedic is legally requested to get a concrete instruction from a medical doctor to conduct advanced lifesaving operations. To answer this demand, we have applied a biotelemetry technique with the recent technology to the emergency radio communication system.

METHOD Fig.1 illustrates the principle of this technique. The appearance of the patient is caught with a CCD camera. Color still pictures are transmitted and each scene is renewed every 20-80 seconds. The vital sign, such as an ECG and a blood oxygen level are sampled, digitized and multiplexed in a personal computer. They are fed to the transmitter through a modem. The signals are transmitted to a central fire station using an emergency radio link or a mobile telephone network. At the fire station, the wireless communication channel is connected to a wire telephone line. In the hospital, a medical doctor can grasp the situation with the color image and monitor the vital signs of the patient in a real time. With these information, the doctor sends the necessary instructions to a paramedic through a vocal communication channel.

RESULTS In the experiment in the moving ambulance, the feasibility of this technique was verified. In the regular condition of the communication link, the stability of signal transmission was reasonably well. The fidelity of the transmitted signal was satisfactory for the use of an emergency medicine.

Session 4 - 6

MULTIPARAMETRIC TELEMETRIC ASSISTANCE OF THE ELDERLY

Bedini R, Palagi G, Belardinelli A, Ripoli A, Franchi D, Deganello P ++, Macellari V +.
CNR Institute of Clinical Physiology, Via P. Savi 8, 56100, Pisa, Italy.
+ Istituto Superiore di Sanità, Rome, Italy.
++ ISIA, Firenze.

The available telematics technologies allow the development of telemetric surveillance systems, increasing the quality of the life of people and reducing the costs for the Health System, bringing the care from the hospital to the patient home. The increasing ageing of the world population has focused the attention on the elderly problems. Instability and fallings represent for elderly an high risk of functional losses. The detection of the original disturbances causing the fall is not generally easy, depending on both the multi-pathologic status and on the eventually associated cognitive deficit, often presented by this kind of subjects. In order to obtain a clear picture of physio-pathologic status of the elderly, eventually driving a correct rehabiltation training, we developed a telemetric system for the elderly affected by motor disability. The system

is composed by a terminal, really "worn" by the patient, constituted by a microprocessor-based datalogger, connected and on-line and/or off-line controlled by a central specialistic station. The connection is accomplished by telephone line and GSM; assuring the maximum diffusion and expandability of the service. Particularly, GSM technology allows three basic operations: the telemonitoring of all the necessary biosignals (electrocardigram included), because of the intrinsic channel bandwidth and noise figure; the home surveillance of the subject.

To investigate the postural and the cardiovascular conditions of the patient, the telemetric system may acquire the accelerations of arms and legs, the angles between body segments, the electrocardiogram and the blood oxygen saturation. The oxygen saturation is acquired by means of an ad hoc developed system.

Particular attention has been paid for the development of an "easy-portable" patient terminal, bearing in mind the necessity of a true friendly interaction between device and aged carrier.

Session 5 - 1

THE FUTURE OF TELEMETRY IN CLINICAL MEDICINE

T. Penzel
Medizinische Poliklinik of Philipps-University, Baldingerstrasse, D-35033 Marburg

Telemetry in clinical medicine is well established in some specific applications. The well known field of application is ECG using RF telemetry within a hospital. There are some applications which use infrared telemetry for the transmission of different signals within short distances to free the patient from wires within a room, as it is used in sleep medicine and chronobiology research. This enhancement in patient comfort requires additional technical equipment and therefore is not very common. Another field of application is stimulation and the control of stimulators for nerves and muscles. A number of applications are found in this field, mainly in rehabilitation medicine. The introduction of new devices for neurostimulation reveals the importance of recording signals through conventional telemetry. A new stimulator recently introduced allows hypoglossal nerve stimulation in patients with obstructive sleep apnea to overcome the collapse of the upper airways during sleep. A pressure transducer is implanted in the manibrium of the patient to sense the negative intrathoracic pressure changes created during inspiratory efforts. This signal is analyzed and during the period of inspiration a pulse train of impulses is sent to an electrode connected to the hypoglossal nerve. This results in a protrusion of the tongue and thereby opens the upper airways leading to efficient breathing in this particular disorder. Telemetry is used to record the signals of respiration and to adapt the algorithm in the implanted pacemaker to the specific needs of the patient during the initial phase of treatment.

Beside these classical fields of telemetry the area of ambulatory monitoring and the new field of telemedicine applications are evolving rapidly taking advantage of improved technologies such as miniaturisation and reduction in power consumption. Nowadays many biological signals can be recorded using very small portable equipement and the load to carry for a patient does not exceed the weight of a cassette recorder. High capacity digital storage allows a high precision of recordings and preserves all signal characteristics if time and amplitude resolution were choosen apropriate.

The new field of telemedicine makes use of digital communication transmission. Theirby it is possible to equipe remote health care centers with simple recording equipment. The recorded biosignals such as ECG, EEG or even images can be transmitted using telephone networks to specialized centers for expert interpretation. This approach will be used increasingly, as no longer technology is the most expensive part but the medical experts expertise becomes more expensive in relation and is less available.

In conclusion, the field of clinical telemetry is moving from conventional applications, such as signal transmission, which is in common use in wildlife telemetry, towards ambulatory recording applications and systems which support telemedicine technologies. These new technologies support remote monitoring as well as remote control if desired.

Session 5 - 2

ALGORITHMS FOR THE EVALUATION OF SLEEP-WAKE RHYTHM: A COMPARISON OF DATA FROM TELEMETRY AND ROUTINE POLYSOMNOGRAPHY WITH ACTIMETRY

Ralf Trippe*, Geert Mayer**
*Dept. of Psychology University of Marburg, **Hephata Klinik
*Marburg, ** Schwalmstadt-Treysa, Germany

INRODUCTION Sleep-wake discrimination by actimetry (with AMI actometer) and polysomnography corresponded in 78% in pts. with insomnia and 92% in pts. with apnea. We were interested in quality of results recorded with ZAK actometer, telemetry and application of two algorithms for sleep-wake discrimination of actimetry.

METHODS We investigated 14 patients with sleep apnea and 14 with narcolepsy. All subjects had 24 hour polysomnography (9 channels), half of which was performed with telemetry TEL (Biotel 88, Glonner/München), the other with a stationary system STAT (Glonner/Neurosys). Maximum amplification was 0.2 mV/cm for TEL and 0.1 mV/cmfor STAT. During the 24 hour recording the patients were wearing two actometers (AMI, ZAK) on the wrist of the dominant hand. Sleep-wake discrimination was analysed with algorithms by Webster and Sadeh&Lavie and both methods compared with each other. Sleep-wake from STAT/TELE was defined as one state for each minute (0=sleep, 1=wake, 9=not definable). The data of both actometers was evaluated with each algorithm separately, creating four sleep-wake diagrams. Each of the four diagrams was compared with the STAT/TELE diagrams and correspondence was calculated.

RESULTS The following table shows correspondence in percent between sleep-wake scoring of actimetry with two algorithms and with TEL/STAT for both patient groups

Combination of AMI and Webster algorithm corresponded best with sleep-wake data gained by STAT and TEL. Correspondence with TEL is markedly worse than with STAT except for the aforementioned combination. Sleep-wake discrimination from TEL and STAT differ. These effects were highly significant in multivariate ANOVA (p>0.05). There was no significant difference between the patient groups.

DISCUSSION TEL are worse than STAT recordings for sleep-wake discrimination due to artifacts caused by external interference and analogue transmission.

Session 5 - 3

FEASIBILITY OF NON-LABORATORY ELECTROPHYSIOLOGICAL RECORDING OF SMALL VIGILANCE FLUCTUATIONS

Regina Conradt, Ulrich Brandenburg, Thomas Penzel, Jörg Hermann Peter
Schlafmedizinisches Labor, Innere Medizin der Universität Marburg, Germany

INTRODUCTION Daytime Sleepiness and impaired vigilance are among the most important symptoms of Obstructive Sleep Apnea (OSA). Nasal CPAP is a common therapy for OSA. Polygraphy, including electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) is considered to be one of the most reliable methods of assessing whether a person is alert, drowsy or sleepy. The sleep stage classification of Rechtschaffen and Kales is almost exclusively used for sleep stage scoring. It does not provide substages for the description of drowsiness with rapid electrophysiological changes. Moreover, the epoch length of 30 sec which is used for whole- night records is too long for the description of short micro-sleep episodes or fast vigilance fluctuations. When dealing with electrophysiologic activity with regard to vigilance and reactivity, not only more vigilance substages (here 10) and shorter scoring epochs are useful but also an adaptive segmentation. That means, when a change takes place at the electrophysiological activity the current epoch is ended and a new one started.

METHOD In 6 patients diagnosed with OSA vigilance was tested using a 90 minute, four choice reaction time test (RTT) before and with nCPAP-therapy. Reaction times (RT), electrophysiological signals (4 EEGs, 2 EOGs, EMG chin and ECG) and oronasal airflow were recorded digitally by EMBLATN (Flaga hf. Medical Devices, Island), an ambulatory data recorder and stored on a Power Macintosh 7200. Each of the available 16 channels has the same physical properties and the configuration can be altered to meet different data acquisition requirements for different signals and sensors. The gain of the amplifier is kept at a low value while the necessary accuracy is digitally achieved. All the 16 analog inputs are simultaneously sampled and depend on the input signal sampling rates of 200Hz (ECG), 100Hz (EEG, EOG, EMG), 10 Hz (Airflow, RT-signal), or 50, 20 and 1 Hz are possible. All data were recorded in real time, and were continuously stored in a data file on computer. For ambulatory monitoring, a PCMCIA slot for PC Cards in EMBLATN is available. Rechargeable Lithium-Ion batteries give a recording time of around 24 hours, varying somewhat depending on the sampling rate and number of channels being recorded.

RESULTS With nCPAP therapy the mean RT decreased significantly to 1.03 (SD±0.44) sec compared to the pretreatment reaction time of 2.30(±0.30) sec. In contrast, each patient showed a marked increased vigilance with nCPAP therapy compared to the pretreatment investigation. Percentages of drowsy substages decreased from 41.5 (33.4) % in the pretreatment group to 8.76 (±21.43) % with nCPAP therapy.

CONCLUSION Ambulatory monitoring systems with electrophysiological parameter become more importance. The systems have to be easy to handle and the quality of recording must be of a high standard. This study shows the feasibility of recording very small vigilance fluctuations which need high recording quality for every electrophysiological signal. Our study suggests that the EMBLA would be a useful tool and its advantages include a lower cost of recording and more patients` comfort.

Session 5 - 4

HIGH QUALITY AMBULATORY SLEEP MONITORING

WITH ON-LINE SUPERVISION

Anita Jain, Rolf Weiß, Leonie Fricke, Mario Köhn, Marie-Luise Krohm, Andrea Steinhausen, Gerhard Mutz & Egon Stephan
Psychological Department, Cologne University
Herbert-Lewin-Straße 2, 50996 Köln, Germany

INTRODUCTION As beds in sleep laboratories are scarce and costly, other methods for high quality sleep recordings are needed. An alternative to time consuming and costly laboratory research is ambulatory monitoring, especially if an expert has online access to current data from any place.

METHODS A small, high quality 24 channel digital recorder (Koelner Vitaport System, device type 2) was developed in order to measure all variables relevant to normal and pathological sleep as well as additional physiological signals and environmental conditions (light, temperature). Our standard setting, that can be changed according to demands, consists of two channels of EOG, EMG, three EEGs, excursion of thorax and abdomen, airflow, O2-Saturation, ECG, puls wave, skin conductance, skin temperature, leg movement, body position, snoring sound and ambient light.

Digital data is stored on a 170 MB hard disk on the device and power is supplied by batteries, thus allowing for unrestricted movement of patients or subjects. The device can also be connected via a high speed modem and a normal telephone line by ISDN or the Internet with TCP/IP to the hospital, doctor's room or research laboratory. By this means, constant or occasional high resolution online supervision of signal quality and the patient's state is possible by an expert from any place.

In order to compare sleep under natural and laboratory conditions, polysomnographic recordings were carried out with this setting in 12 students on two consecutive nights in the laboratory and two nights at their homes.

RESULTS The measurement device was well tolerated by the subjects and high quality signals could be obtained under laboratory as well as under ambulatory conditions. Subjects could even remove recording equipment by themselves in the morning.

DISCUSSION The device offers cost effective means for high quality polysomnography in research as well as in the clinical field, because constant supervision during the night is not needed and no special room is required. The sleep of people, who would not visit a sleep laboratory, can be assessed. The possibility to connect the ambulatory device via the telephone line to the investigator ensures supervision when needed.

Session 5 - 5

LUNG VENTILATION TELEMETRY USING A BIOIMPEDANCE METHOD

V. M Bolshov, V. I. Lebedev*, and. N. N. Tratkevich**
"Medas" Medical-Engineering Center (Moscow, Russia);
*Biotelemetry Laboratory (Kislovodsk, Russia);
**"Pulsar" Medical-Engineering Center (Saint Petersburg , Russia)

METHOD. Lung ventilation parameters are usually measured by pneumotachometry or spirometry. However, these methods are not suitable for those situations when the patients under examination are in the state of long-time motor activity. Much has been done to solve this problem through an electrical impedance pneumography method, without any noticeable success, though.

The paper puts forward a pneumographic method which uses sets of electric lung impedance measurement and anthropometric data to establish a correct relation between these data and ventilation parameters. A telemetric system has been developed based on this approach.

The patient-borne compact unit converts the thorax impedance parameter between the measuring electrodes to an electric signal which is transmitted to a receiver by means of a frequency-pulse modulation technique.

At the receiver output the signal is processed by a computer which solves the following multiple regression equation:

                    V = D Z(23.176 - 0.103P - 0.059M + 0.053B), where

V is the lung ventilation volume (l);
D Z is the pneumographic curve impedance swing (Ohm);
P is the height of the patient (cm);
M is the weight of the patient;
B is the age of the patient (years).

RESULTS. The studies were made on three groups of patients, a total of 56 persons (32 male and 24 female). The first group consisted of healthy people (30 persons), the second had obstructive lung ventilation disturbances, and the third one were patients with restrictive or combination impairments.

The mean error in lung ventilation examinations in all the groups did not exceed 5.7% to suggest the validity of the principle thus established, as expressed by the above equation.

DISCUSSION. If some restrictions are imposed on the patients' motor activity, the method described above ensures lung ventilation parameters measurement to an accuracy suitable for the clinical practice.