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Prepared by: Guided by: Priyanka Dhar Mr. Sarosh Dastoor B.E IV E&C(8th Sem) Roll No: 41

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A Seminar Report on

Wireless Biotelemetry

Prepared by : Priyanka Dhar

Roll No. : 41

Class : B.E.IV (Electronics & Communication

Engineering.)

Semester : 8th Semester

Year : 2006-2007

Guided by : Mr. Sarosh Dastoor

Department of

Electronics & Communication Engineering. Sarvajanik College of Engineering & Technology Dr R.K. Desai Road, Athwalines, Surat - 395001,

India

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Sarvajanik College of Engineering & Technology

Dr R.K. Desai Road, Athwalines, Surat - 395001,

India.

Department of

Electronics& Communication Engineering.

CERTIFICATE

This is to certify that the Seminar report entitled _____Wireless

Biotelemetry is prepared & presented by Ms._Priyanka Dhar

Class Roll No. __41____ of final year (B.E.IV) Electronics &

Communication Engineering during year 2006-2007. Her work is

satisfactory. Signature of Guide Head of Department Electronics Engineering Signature of Jury Members

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INDEX Sr. No

TOPIC Page No

1 Acknowledgement���������������������� I

2 Abstract�������������������������� II

3 List of figures�����������������������.. III 4 Chapter 1: Introduction 1

1.1 History 2 1.2 Physiological Parameters 3 5 Chapter 2: Types of Biotelemetry Systems 5

2.1 Single Channel Telemetry System 5 2.1.1 ECG Telemetry System 5

2.2 Temperature Telemetry System 7 2.3 Multi-channel Telemetry System 8

2.3.1 Obstetrical Telemetry System 9 2.3.2 Telemetry In Operating Rooms 9

2.3.3 Sports Physiology Studies Through Telemetry 10 6 Chapter 3: Wireless Radio Frequency (RF) telemetry 11

3.1 Choice of Radio Carrier Frequency 11 3.2 Spread-Spectrum Technology 12 3.3 Channel-Hopping 12 3.4 Error-Correction & Re-Transmission 12

3.5 Line-Of-Sight 12 3.6 Antennas & Cable 13

7 Chapter 4: Operation 14 4.1 Components 16

4.2 Mobile Unit 16 4.3 Modulation Systems 16 4.3.1 Frequency Modulation 17 4.3.2 Pulse Width Modulation 17 4.4 Working Principle 18 8 Chapter 5: Implantable Units 20 9 Chapter 6: Applications 25

6.1 Equipments Used in Biotelemetry 25 6.2 Applications of telemetry in patient care 25 6.3 Monitoring physiological functions of mammals 28 6.4 Implantable Biotelemetry System for Preterm Labor and Foetal Monitoring

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10 Chapter 7: Benefits 30 11 Chapter 8: Limitations 31 12 Chapter 9: Conclusion 32 13 Chapter 10: Bibliography IV

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ACKNOWLEDGEMENT

It gives me great pleasure to thank Mr. Sarosh Dastoor, my seminar guide, who helped me in successful completion of the report. I would also like to thank my father for having helped me and supported me as and when required My very special thanks to our Department In charge Prof. Mehul Raval for motivating me in choosing a good topic and for being a constant support .

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ABSTRACT

With miniaturization and technical advancements in electronics and communications field, we are now in a position to safely monitor, diagnose and treat various intricate ailments in patients with relative ease. This has made complex surgeries simple, easy and efficient.

Wireless communications have enabled development of monitoring devices that can be made available for general use by individuals/patients and caregivers. New methods for short-range wireless communications not encumbered by radio spectrum restrictions (e.g., ultra-wideband) will enable applications of wireless monitoring without interference in ambulatory subjects, in home care, and in hospitals.

Wireless biomonitoring, first used in human beings for featal heart-rate monitoring has now become a technology for remote sensing of patients' activity, blood pulse pressure, oxygen saturation, internal pressures, orthopaedic device loading, and gastrointestinal endoscopy. Biotelemetry provides a wireless link between the subject and the remote site where the recording, signal processing, and displaying functions are performed. Rather than using a traditional radio transceiver, which can only broadcast over a limited range, now-a-days the readily available cell phones are used to transmit biological data by creating a link between the subject and a computer receiving the signal via a landline phone.

Wireless telemetry of bioelectric signals, specifically neural recordings, is desirable in many research and clinical applications. These include, but are not limited to telemetry and recording of neural activity in laboratory animals, telemetry of EEG, telemetry of short-term implanted electrode arrays for epilepsy medical diagnosis, functional electrical stimulation (FES) systems, and implantable neuroprosthetic devices for sensory and command control.

This study will focus on Wireless telemetry in general and also details of Wireless biotelemetry specifically.

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List of Figures

Figure No. Title of Figure Page No

Fig: 1.1 ECG measurement using immersion electrodes. 3 Fig: 2.1.1.1 Block diagram of a single channel telemetry system. 5 Fig: 2.1.1.2 Block Diagram of ECG Telemetry Transmitter 6 Fig: 2.1.1.3 Block diagram of high frequency section of ECG telemetry

receiver. 6

Fig: 2.1.1.4 Schematic diagram of ECG demodulation and �inoperate� circuits in ECG telemetry receiver

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Fig:2.2.1 Circuit diagram of a temperature telemetry system. 7 Fig: 2.3.1 Schematic diagram of FM-FM modulated radio telemetry

transmitter for ECG and respiration activity simultaneously. 8

Fig:2.3.1.1 Telemetry receiving system for monitoring foetal heart rate and urine contractions in use .

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Fig: 2.3.4 A three channel telemetry system to monitor the physiological data of a sprinter.

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Fig . 4.1 Patient data monitor 15 Fig.4.3.1 Biotelemetry mobile unit 16 Fig. 5.1 Different Telemetry Components 20 Fig. 5.2 Single channel implantable transmitter for blood pressure. 21 Fig. 5.3 Transducer implanted in the aorta 21 Fig. 5.4 Cut-away single channel temperature transmitter. 22 Fig.5.5 Complete implantable telemetry system. 23 Fig. 5.6 Cut-away multi-channel telemetry system 23 Fig.5.7 Jacket for partially implanted telemetry system. 24 Fig.6.2.1.1 ECG Telemetry transmitter: (a)Hewlett-Packard type 78100A in

hospital use. (b)Electrode placement for telemetered ECG 26

Fig.6.2.2.1 Emergency medical care system, portable transmitter nit. 27 Fig.6.2.3 Emergency medical care system, transmitter unit in use. 28 Fig.6.2.4 Emergency medical care system, hospital console. 28

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1. Introduction

Biotelemetry is defined as a means of transmitting biomedical or physiological data from a remote location (e.g., astronauts in space) to a location that has the capability to interpret the data and affect decision making (e.g. ground controllers at Mission Control Center). Biotelemetry is a vital constituent in the field of medical sciences. It entails remote measurement of biological parameters. Mode of transmission of physiological data from point of generation to the point of reception can take many forms. Use of wires to transmit data may be eliminated by wireless technology. Biotelemetry, using wireless diagnosis, can monitor electronically the symptoms and movements of patients.

This development has opened up avenues for medical diagnosis and treatment. It enables monitoring of activity levels in patients suffering from heart trouble, asthma, pain, Alzheimer�s disease, mood disorders, cardiovascular problems, accidents, etc. A patient�s response and reaction to drugs can be investigated for treatment.

Radio-telemetry transmits biological data using various radio transmission techniques. No wires are required to be attached to the patient�s body. The patient just carries a bracelet-sized transmitter that enables monitoring of the patient�s symptoms.

Literally, biotelemetry is the measurement of biological parameters over a

distance. The means of transmitting the data from the point of generation to the point of reception can take many forms. Perhaps the simplest application of the principle of biotelemetry is the stethoscope, whereby heartbeats are amplified acoustically and transmitted through a hollow tube system to be picked up by the ear of the physician for interpretation. A major advantage of modern telemetry is the elimination of the use of wires.

The use of telemetry methods for sending signals from a living organism over some distance to a receiver. Usually, biotelemetry is used for gathering data about the physiology, behavior, or location of the organism. Generally, the signals are carried by radio, light, or sound waves. Consequently, biotelemetry implies the absence of wires between the subject and receiver.

Generally, biotelemetry techniques are necessary in situations when wires running from a subject to a recorder would inhibit the subject's activity; when the proximity of an investigator to a subject might alter the subject's behavior; and when the movements of the subject and the duration of the monitoring make it impractical for the investigator to remain within sight of the subject. Biotelemetry is widely used in medical fields to monitor patients and research subjects, and now even to operate devices such as drug delivery systems and prosthetics. Sensors and transmitters placed on or implanted in animals are used to study physiology and behavior in the laboratory and to study the movements, behavior, and physiology of wildlife species in their natural environments.

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Biotelemetry is an important technique for biomedical research and clinical medicine. Perhaps cardiovascular research and treatment have benefited the most from biotelemetry. Heart rate, blood flow, and blood pressure can be measured in ambulatory subjects and transmitted to a remote receiver-recorder. Telemetry also has been used to obtain data about local oxygen pressure on the surface of organs (for example, liver and myocardium) and for studies of capillary exchange (that is, oxygen supply and discharge). Biomedical research with telemetry includes measuring cardiovascular performance during the weightlessness of space flight and portable monitoring of radioactive indicators as they are dispersed through the body by the blood vessels.

Telemetry has been applied widely to animal research, for example, to record electroencephalograms, heart rates, heart muscle contractions, and respiration, even from sleeping mammals and birds. Telemetry and video recording have been combined in research of the relationships between neural and cardiac activity and behavior.

There are usually two concerns associated with the use of biotelemetry: the distance over which the signal can be received, and the size of the transmitter package. Often, both of these concerns depend on the power source for the transmitter. Integrated circuits and surface mount technology allow production of very small electronic circuitry in transmitters, making batteries the largest part of the transmitter package.

1.1 History Of Biotelemetry

In the early days of human space flight, NASA utilized biotelemetry to provide biomedical data from orbiting astronauts to medical personnel at the NASA Johnson Space Center (Manned Space Flight enter in the early 1960's). Biomedical data transmitted to Earth from space included astronaut's heart rate, body temperature, ECG, oxygen (O2) and carbon dioxide (CO2) concentration. Further research and technology from NASA was instrumental in driving both telemetry and telemedicine into civil health care.

Distance medicine has been around for most of this century. In the early days, doctors treated patients in remote locations via wireless radio and by sending diagnostic samples through the mail. Today, communication is done digitally, and it's called biotelemetry. On an extended space flight, the need to consult, diagnose and deliver effective medical care when the doctor is far away from the patients is crucial. Scientists are developing hardware and software to facilitate this process. Whether it's a case of analyzing blood samples for medical diagnosis when a problem occurs during a three-year voyage to Mars or installing a microchip inside the body to measure vital signs, biotelemetry is revolutionizing medical care in space.

Historically, Linthoven, the originator of the electrocardiogram, as a means of analysis of the electrical activity of the heart, transmitted electrocardiograms from a hospital to his laboratory many miles away as early s 1903. The rather crude immersion electrodes

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Fig: 1.1 ECG measurement using immersion electrodes. Original Cambridge electrocardiograph (1912) built for Sir Thomas Lewis. [2] (see above picture), were connected to a remote galvanometer directly by telephone lines. The telephone lines in this instance were merely used as conductors for the current produced by the biopotentials. 1.2 Physiological and Technology Parameters

Any quantity that can be measured in the biomedical field is adaptable to

biotelemetry. The measurements are divided into two categories: bioelectrical and physiological variables. Bioelectrical variables include measurements like ECG, EMG, and EEG. Signals are obtained directly in the electric form. Physiological variables such as temperature, blood pressure, blood flow, etc require some excitation or external electrical parameters. Transducers are used for the conversion of physiological parameters into an electrical signal. Parameters are measured as the variations of resistance, capacitance, or inductance. Variations can be calibrated to represent pressure, temperature, or blood flow. Base signal is modulated for transmission. And finally, this signal is detected (demodulated) and converted back to its original form.

PCM technology offers significant advantages in the application of telemetry to medical and physiological studies. The requirements for less complicated handling, standardized system layout, improvement of weight, size and power supply by commercial battery modules, as well as different wireless data links are met better by a PCM encoder which was specially developed for physiological applications. The advantages of PCM are illustrated by relating the experimental requirements to technical specifications for the elements of a telemetry link. 1. Temperature by rectal or oral thermistor. 2. Respiration by impedance pneumograph. 3. Electrocardiograms by surface electrodes. 4. Indirect blood pressure by contact microphone and cuff.

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As the technology progressed, it became apparent that literally any quantity that could be measured was adaptable to biotelemetry. Just as with hardwire systems, measurements can be applied to two categories: 1. Bioelectrical variables, such as ECG, EMG, and EEG. 2. Physiological variables that require transducers, such as blood pressure, gastrointestinal pressure, blood flow, and temperatures.

With the first category, a signal is obtained directly in electrical form, whereas the second category requires a type of excitation, for the physiological parameters are eventually measured as variations of resistance, inductance, or capacitance. The differential signals obtained from these variations can be calibrated to represent pressure, flow, temperature, and so on, since some physical relationships exist.

In a typical system, the appropriate analog signal (voltage, current, etc.) is converted into a form or code capable of being transmitted. Currently, the most widespread use of biotelemetry for bioelectric potential is in the transmission of the electrocardiogram.

One example of ECG telemetry is the transmission of electrocardiograms from an

ambulance or site of an emergency to a hospital. Telemetry is also being used for transmission of the electroencephalogram. Most applications have been involved with experimental animals for research purposes. Telemetry of EEG signals has also been used in studies of mentally disturbed children. The third type of bioelectric signal that can be telemetered is the electromyogram. Telemetry can also be used in transmitting stimulus signals to a patient or subject. For example, it is well known that an electrical impulse can trigger the firing of nerves. Another example is the use of telemetry in the treatment of �dropfoot,� which is one of the most common disabilities resulting from stroke. A method for correcting �dropfoot� by transmitting a signal implanted electronic stimulator has been used successfully at Rancho Los Amigos Hospital in Los Angeles.

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2. Types of Biotelemetry Systems

2.1 Single channel telemetry systems A majority of the situations requiring monitoring of the patients by wireless

telemetry, parameter which is most commonly studied is the electrocardiogram. It is a known that display of the ECG and cardiac rate gives sufficient information on the loading of the cardio vascular system of the active subjects. Therefore, we shall first deal with a single channel telemetry system suitable for transmission of electrocardiogram. 2.1.1 ECG Telemetry System

Figure below shows the block diagram of a single channel telemetry system suitable for transmission of electrocardiogram. The Telemetry Transmitter which consists of ECG amplifier, sub-carrier oscillator and a UHF transmitter along with dry cell batteries. Telemetry Receiver, consisting of a high frequency unit and a demodulator, to which an electrocardiograph can be connected to record, a cardioscope to display and a magnetic tape recorder to store ECG. A. heart rate meter with an alarm facility can be provided to monitor continuously beat-to-beat heart rate of the subject Fig: 2.1.1.1 Block diagram of a single channel telemetry system. [1]

Some ECG telemetry systems operate in the 450�470MHz band, which is well-suited for transmission- within a hospital and has the advantage of having a large number of channels available.

Tape Recorder

Graphic Recorder

Transmitter RF Amplifier

Subcarrier Modulator Demodulator

Heart rate monitor ECG Amplifier

Battery Cardioscope

ECG Electrodes

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Transmitter A block diagram of the transmitter is shown in Fig. 2.1.1.2. The ECG signal, picked up by three fluid column electrodes attached to the patient�s chest is amplified and used to frequency modulate a 1 kHz sub-carrier that in turn frequency-modulates the UHF carrier The resulting signal is radiated by one of the electrode leads (RL) which serves as the antenna. The input circuitry is protected against large, amplitude pulses that may result during defibrillation.

Fig: 2.1.1.2 Block Diagram of ECG Telemetry Transmitter [1]

Receiver The receiver uses an omnidirectional receiving antenna which is a quarter-wave monopole, mounted vertically over the ground plane of the receiver top cover. This arrangement works well to pick up the randomly polarized signals transmitted by moving patients. The receiver comprises an RF amplifier which provides a low noise figure, RF filtering and image frequency rejection.

Fig: 2.1.1.3 Block diagram of high frequency section of ECG telemetry receiver. [1] The 1 kHz subcarrier is demodulated to convert frequency-to-voltage to recover the original ECG waveform.

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Fig: 2.1.1.4 Schematic diagram of ECG demodulation and �inoperate� circuits in ECG telemetry receiver [1] 2.2 Temperature telemetry system

Systems for the transmission of alternating potentials representing such

parameters as ECG, EEG and EMG are relatively easy to construct. Telemetry system �which are sufficiently stable to telemetry direct current outputs from temperature, pressure or other similar transducers continuously for long periods resent greater design problems. In such cases, the information is conveyed as a modulation of the mark/space ratio of a square wave. Heal (1974) described a temperature telemetry system based on this principle and

Fig:2.2.1 Circuit diagram of a temperature telemetry system.[1] the circuit is shown in Fig.2.2.1 The system is particularly well suited for use in medical and biological research.

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On the receiver side, a vertical dipole aerial is used which feeds an FM tuner, and whose output, a 200Hz square wave, drives the demodulator. In the demodulator, the square wave is amplified, positive dc restored and fed to a meter where it is integrated by the mechanical inertia of the meter movement. Alternatively, it is filtered with simple RC filter to eliminate high ripple content and obtain a smooth record on paper. 2.3 Multi channel wireless telemetry systems

Medical measuring problems often involve the simultaneous transmission of several parameters. For this type of application, multi-channel telemetry system is employed. Multi-channel telemetry is particularly useful in athletic training programs as it offers the possibility of surveying simultaneously several physiological parameters of the person monitored.

With appropriate preamplifiers, the multi-channel systems permit the transmission of the following parameters simultaneously depending upon the number of channels required, ECG and heart rate, respiration rate, temperature, intravascular and intra-cardiac blood pressure.

In multichannel telemetry, the number of subcarriers used are the same as the

number of signals to be transmitted. Each channel therefore has its own modulator. The RF unit�the same for all channels-converts the mixed frequencies into the transmission band. Similarly, the receiver unit contains the RF unit and one demodulator for each channel.

Pulse width modulation is better suited for multichannel biotelemetry systems.

Such systems are insensitive to carrier frequency shifts and have high noise immunity. FM-FM system for similar use, though may have low power consumption and high base line stability, they are more complicated and turn out to be more expensive. They can be troubled by interference.

Fig: 2.3.1 Schematic diagram of FM-FM modulated radio telemetry transmitter for ECG and respiration activity simultaneously.[1]

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2.3.1 Obstetrical Telemetry System There has been a great deal of interest to provide greater freedom of movement to

patients during labour while the patient is continuously monitored through a wireless link. Thus, from a central location, it is possible to maintain a continuous surveillance of cardiotocogram records for several ambulatory patients. In the delivery room, telemetry reduces the encumbering instrumentation, cables at the bedside. Moreover, when an emergency occurs, there is no loss of monitoring in the vital minutes during patient transfer.

The patient carries a small pocket-sized transmitter which is designed to pick up

signals for foetal heart rate and uterine activity. The foetal heart rate is derived from Foetal ECG which is obtained via a scalp electrode attached to the foetus after the mother�s membranes are ruptured. Uterine activity is measured via an intra-uterine pressure transducer. If only foetal ECG is measured, the patient herself can indicate uterine activity or foetal movement by using a handheld pushbutton.

The receiver located away from the patient, is connected to a conventional

cardiotocograph. If the patient exceeds the effective transmission range or the electrode has a poor contact, it is appropriately transmitted for corrective action.

Fig:2.3.1.1 Telemetry receiving system for monitoring foetal heart rate and urine contractions in use .[1] 2.3.2 Telemetry in Operating Rooms

The use of telemetry in operating rooms seems to be particularly attractive as it offers a means of achieving a high degree of patient safety from electric shock as well as elimination of the hanging inter-connecting patient leads which are necessary in direct-wired equipment. Normally. there are several parameters which are of interest in surgical patient monitoring, most common being ECG, blood pressure, peripheral pulse and EEG.

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Basically, the signal encoding is based upon frequency modulation of 4

subcarriers centred at 2.2, 3.5, 5.0 and 7.5 kHz, respectively. The system is designed to give a bandwidth of dc to 100 Hz at the 3 dB point and the discriminator provides 1.0 V dc output for a 10% shift.. The transmitted signals are tuned by a FM tuner whose output is fed into a fourth-channel discriminator which separates the sub- carriers through filtering and demodulates each using a phase-locked loop. The demodulated signals are displayed on an oscilloscope. 2.3.3 Sports Physiology Studies through Telemetry

Monitoring of pulmonary ventilation, heart rate and respiration rate is necessary for a study of energy expenditure during physical work, particularly for sports such as squash, handball, tennis and track, etc. The transmitter uses pulse duration modulation, i.e., each channel is sampled sequentially and a pulse is generated, the width of which is proportional to the amplitude of the corresponding signal. At the end of a frame, a synchronisation gap is inserted to ensure that the receiving system locks correctly onto the signal. Each channel is sampled 200 times a second. With each clock pulse, the counter advances one step, making the gates to open sequentially. At the opening of a particular gate, the corresponding physiological signal gets through to a comparator where it is compared with the ramp. As soon as the ramp voltage exceeds the signal voltage, the comparator changes state. Thus, the time required for the comparator to change state would depend upon the amplitude of the signal. The counter and gates serve as multiplexer.

Fig: 2.3.4 A three channel telemetry system to monitor the physiological data of a sprinter.[1]

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3. Wireless Radio Frequency (RF) telemetry

Wireless Radio Frequency (RF) telemetry offers a great advantage over other telemetry methods by making use of a cheap and easily accessible transmission medium - AIR. When properly installed, wireless systems are very reliable and require little, if any maintenance. Using a license-free RF band eliminates the need for obtaining a site license from the FCC.

2.4GHz RF Band is License Free Reliable Spread-Spectrum Radios Channel-Hopping Algorithm Error Correction Protocol Automatic Re-Transmission on Error

3.1 Choice of Radio Carrier Frequency

In every country there are regulations restricting frequency and bandwidth to be used for medical telemetry. Therefore, the permission to operate a particular telemetry system needs to be obtained from the postal department of the country concerned. The radio frequencies normally used for medical telemetry purposes are of the order of 37, 102, 153, 159, 220, 450 MHz. Transmitter is typically of 50mW at 50Ohms which can give a transmission range of about 1.5 KM in the open flat country.

Radiowaves can travel through most non-conducting materials such as air wood,

and plaster with relative ease, However, they are hindered, blocked or reflected by most conductive materials and by concrete because of the presence of reinforced steel.

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Therefore, transmission may be lost or result in poor quality when a patient with a telemetry transmitter moves in an environment with a concrete wall or behind a structural column.

3.2 Spread-Spectrum Technology

Spread-Spectrum Technology uses more than one frequency to transmit data. The radios choose from over 500 channels between 2.4000GHz and 2.4835GHz. This RF band has been set aside specifically for the licensefree operation of spread-spectrum radios.

3.3 Channel-Hopping

Spread-spectrum radios use channel-hopping technology to make use of the many available channels. Radios will use one channel for only ¼ of a second before jumping to another channel. This ensures that no one channel is ever occupied by one radio preventing another from using the channel. Each radio may use a different channel-hop-table thus allowing many radios to share the same RF band without interfering with one another. If two foreign radios should happen to make use of the same channel, a collision will be detected by both radios and they will each move onto a different channel and re-send their data. 3.4 Error-Correction & Re-Transmission

The radios use a comprehensive error checking algorithm to ensure that the transmitted data is indeed correct. If incorrect data was received, the receiver will instruct the sender to re-send the data until it has been received correctly. Since all data is transmitted in digital form there is no degradation in analog values when signal strength decreases. Forward error correction algorithms �repair� any questionable data on the fly. 3.5 Line of Site Dependence of Wireless Telemetry

As with any Radio Frequency (RF) system, the radio waves propagate best through the air. Obstruction such as buildings, walls, hills, trees etc. pose a potential hindrance to radio wave propagation (imagine your car radio going silent inside a tunnel). The ideal system is one where all radio antennas are in direct line-of-sight with one another. Although, radio waves may reflect off hard surfaces and find an alternate path that is not line-of-sight.

Fig.3.5.1 [10]

In the ideal system setup, both antennas can see each other without any obstructions. This yields the greatest transmission distance and the most reliable signal conditions. This is called line-of-sight transmission.

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Fig. 3.5.2 [10]

Fig. 3.5.3 [10] 3.6 Antennas & Cables used

One of the most important components of any RF system is the antenna. This is where the radio waves are sent on their way to the other radio. There are many different types of antennas for different applications. Ideally antennas are located outdoors and typically on a mast that clears all surrounding obstructions. Besides transmitting the radio waves, antennas can also act as �radio wave amplifiers�. The cable that connects the antenna with the radio is equally important. Unfortunately, all cable poses a �resistance� to the RF signal thereby limiting the amount of signal being transmitted by the antenna. Using low-loss coaxial cable and keeping this cable length short are two important considerations.

If there is a large physical obstruction between the two antennas, the radio waves will be blocked. No transmission is possible in this case.

In many cases where there is no direct line-of-sight path between antennas, the RF signal may still get through by �bouncing� off buildings or other solid structures. Signal strength must be taken into consideration here to determine if there is enough signal available for reliable transmission.

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3.6.1 Omni-Directional Antenna

3.6.2 Panel Antenna

3.6.3 YAGI Antenna

Fig. 3.6.3 3.6.4 Antenna Polarization

All antennas have a direction of polarization. This means that radio waves leaving an antenna are �oriented� by the polarization of the antenna. Radio waves can only be received by an antenna of equal polarization. Directional antennas have a polarization marking (vertical or horizontal) and a direction arrow to indicate which way is UP. Omni-directional antennas can be mounted in any orientation so long as ALL antennas in the system are mounted the same way.

An Omni-Directional antenna is a non-directional antenna. It radiates equal amounts of radio wave energy in a spherical pattern. Higher gain antennas radiate in a 360° pattern that is flattened on top and bottom and looks more like a donut. These antennas are ideal for a host site that has several remote sites located in various directions.

A panel antenna is a directional antenna that �focuses� the radio wave energy into a beam which is aimed out the front of the antenna. Panel antennas have a high gain for greater distance transmissions and are great for a point-to-point RF system.

A Yagi antenna is a highly directional antenna that produces a very narrow beam of radio waves. These antennas provide the greatest distance transmission and obstruction penetration . Because of the narrow RF beam they are more difficult to align.

Fig 3.6.4

Fig. 3.6.1

Fig.3.6.2

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4. Operation

Current radio monitoring systems keep thousands of patients under surveillance, with limited scope. Biotelemetry systems consist of transmitter, simple telephone modem, and central receiving station.

Central receiving station tunes into a transmitter, whose size may range from a bracelet to a small pocket transistor. This tracking system can be used within the hospital premises. Each patient is equipped with a pager sized personal monitoring as well as alarm system. When the patient wearing the transmitter device�attached to his wrist, chest, waist, etc-�leaves a specified range, periodic RF signals are sent to the modem. The modem sends out an alert signal to both the patient and to the central monitoring station. When the patient�s health condition becomes worse, emergency signals are transmitted.

The mobile unit attached to the patient has an output of nearly 1W. Location of the patient is derived from time- of-arrival calculations. The system uses spread spectrum techniques operating in the RF band of 902-928 MHz to transmit signals of the patient�s condition along with whereabouts. A network of receivers scattered throughout the specified area picks up the signals with health condition of patient. Location is displayed on a map at a central facility in the hospital treatment centre.

Fig . 4.1 Patient data monitor

Tracking is done by a spread spectrum system, using triangulation technique based on time of arrival at various receivers, to locate the patient. This triangulation technology is applied to locate the origins of all emergency signals sent and users with personal two-way digital wireless communication devices.

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4.1 Components A basic biotelemetry system consists of.- besides a transmitter, simple modem,

and a central receiving station � the basic circuits like oscillators, amplifiers, power supply, etc, usually present in a communication system. The earliest (1952) biotelemetry transmitter was the �Endo radio-sonde.� This pressure-sensing device was a �radio pill,� winch had a volume less than 1 cm3 and could be swallowed by the patient. As it passed through the gastro-intestinal tract, it measured the pressure at various points it encountered. Such radio pills are available to measure temperature, pH, and enzyme activity also. 4.2 Mobile unit

A mobile unit attached to the patient consists of a transmitter and a receiver. (Refer to Fig.4.3.1) Bioelectrical signals are obtained directly from the patient while physiological variables like temperature, pressure, or other parameters from the patient are converted into electrical form using appropriate transducers. Signal conditioning circuit is used to amplify, modulate and process the input received. It combines or relates the output of two or more transducers. Even though the input it receives is an electrical signal, signal conditioning circuit produces an output to satisfy the function and prepares signals suitable for transmission. The physiological signal modulates a low-frequency carrier, called a subcarrier, often in the audio-frequency range. The subcarrier in turn modulates the RF signal to be propagated and sent to the antenna. 4.3 Modulation Systems

The modulation systems used in wireless telemetry for transmitting biomedical signals makes use of two modulators .This means that a comparatively lower freq. subcarrier is employed in addition to the VHF which finally transmits the signal from the transmitter. The principle of double modulation gives better interference free performance in transmission and reception of low frequency biological signals. The submodulator can be a FM (freq modulation) system or PWM (Pulse Width modulation) system, whereas the final modulator is practically always FM system.

Fig.4.3.1: Biotelemetry mobile unit [3]

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If several physiological signals are to be transmitted simultaneously, each signal

is placed on a subcarrier of a different frequency and all subcarriers are combined to simultaneously modulate the RF carrier. This process of transmitting many channels of data on a single RF carrier, called frequency multiplexing, is more efficient. The sub-carrier is modulated either by AM (amplitude modulation) or FM (frequency modulation). For reducing noise interference, FM is frequently used. The method of modulating sub-carrier, followed by modulating the RF carrier, is termed as AM/FM or FM/FM depending sub-carriers are frequency- modulated and the 1W carrier amplitude- modulated, the method is designated as FM / AM. If both the subcarriers and the RF carrier are frequency-modulated, it is designated as FM / FM.

4.3.1 Frequency Modulation:

In freq modulation, intelligence is transmitted by varying the instantaneous freq in accordance with the signal to be modulated on the wave, while keeping the amplitude of the carrier wave constant. The rate at which the instantaneous freq varies is the modulating frequency. The magnitude to which the carrier frequency varies away from the center freq is called �Freq Deviation� and is proportional to the amplitude of the modulating signal. Usually, an FM signal is produced by controlling the freq of an oscillator by the

Amplitude of the modulating voltage. For example The frequency of oscillation in most oscillators depends on a particular value of capacitance. If the modulation signal can be applied in such a way that it changes value of capacitance, frequency of oscillation will change in accordance with the amplitude of the modulating signal. 4.3.2 Pulse Width Modulation

Pulse width modulation method offers the advantage that it is less perceptive to distortion and noise. Fig.4.3.2 shows a typical pulse width modulator. In practice the negative edge of the square wave is varied in rhythm with the ECG signal. Therefore, only this edge contains information of interest. The ratio P : Q (see Fig.4.3.2.2) represents the momentary amplitude of the ECG. Fig.4.3.2.1: Pulse width modulator.[1]

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Pulses generated by astable multivibrator (symmetrical 1000Hz)

Fig. 4.3.2.2: Variation of pulse width with amplitude of the input signal.[1]

The amplitude or even the frequency variation of the the P: Q ratio and consequently on the ECG signal. The signal output from this modulator is fed to a normal speech transmitter, usually via an attenuator, to make it suitable to the input level of the transmitter.

Modulation schemes are used depending not only on the noise interference, but

also on size of the unit, its complexity, location, and other operational aspects. The receiver circuit uses RF tuner to select the transmitted frequency of the base station. The signal is demodulated though demodulator and sent to the processor. The processor enables necessary action depending on the command given to it from the base station. Both transmitter and receiver circuits function as a modem. Control feedback incorporates a control system to enable automatic control of the stimulus, the transducers, or any other part of the instrument system. Tins system comprises a loop in which output from the signal conditioning equipment or signal received is used to control the operation of the system. 4.4 Working Principle

To illustrate the basic principles involved in telemetry, a simple system is described. The stages of a typical biotelemetry system can be broken down into functional blocks, as shown in the Fig.4.4.1 for transmitter and Fig.4.4.2 for the receiver. Physiological signals are obtained from the subject by means of appropriate transducers. The signal is then passed through a stage of amplification and processing circuits that include generation of a sub carrier and a modulation stage for transmission.

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Fig.4.4.1: Block Diagram of a Biotelemetry Transmitter [2]

The receiver (Fig.4.4.2) consists of a tuner to select the transmitting frequency, a demodulator to separate the signal from the carrier wave, and a means of displaying or recording the signal..

Fig.4.4.2:Receiver-storage-display unit [2]

It receives the multiplexed RF carrier emitted by the patient�s transmitter, as shown in Fig .4.4.2. The tuner has a tuning circuit. When the circuit is tuned to receive signals, the appropriate signal is selected and the unwanted signals are rejected. The multiplexed RF carrier is demodulated to recover the individual sub-carriers. Sub-carriers are then demodulated to reproduce original physiological signals emitted by the patient. A recorder records physiological signals for future reference. Signals can be stored on any secondary media like tape, magnetic discs etc. Display system used can be CRT or computer monitor, chart etc.

Tuner

Tape Recorder

Demodulator Chart Recorder or Oscilloscope

Direct biopotential

Subject

Exciter

Amplifier

Processor

Modulator

Carrier

Transducer

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5. Implantable units

Fig. 5.1: Different Telemetry Components

It was mentioned previously that sometimes it is desirable to implant the

telemetry transmitter or receiver subcutaneously. The implanted transmitter is especially useful in animal studies, where the equipment must be protected from the animal. The implanted receiver has been used with patients for stimulation of nerves.The life of the unit depends on how long the battery can supply the necessary current.

A partial implant is a good example of a system used for the monitoring of the

electroencephalogram where the electrodes have been implanted into the brain and the telemetry unit is implanted within and on top of the skull. This type of unit needs a protective helmet. The use of implantable units also restricts the distance of transmission of the signal. The body fluids and the skin greatly attenuate the signal and because the unit must be small to be implanted, therefore has little power, the range of signal is quite restricted, often to just a few feet. This disadvantage has been overcome by picking up the signal with a nearby antenna and retransmitting it. However, with the plastic potting compounds and plastic materials available today, encapsulation is easily possible. Silicon encapsulation is commonly used.

Mercury and silver-oxide primary batteries have been used extensively and, more

recently, lithium batteries have found many applications. For field work with free-roaming animals, the power requirements are quite different from those needed in a

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closed laboratory cage. Requirements range from an electrical capacity of 20 mA-hr to 1000 mA-hr.

Fig. 5.2: Single channel implantable transmitter for blood pressure. [2] In simple terms the complete implantable telemetry transmitter system consists of

the transducer(s), the leads from the transducer(s) to the transmitter, the transmitter unit itself, and the power source. The transducers are implanted surgically in the position required for a particular measurement, such as in the aorta or other artery for blood pressure. Fig.5.3 shows a typical pressure transducer implantation in a dog. The transmitters and power units have to be placed in a suitable body cavity close to the under surface of the skin and situated so that they give no physical or psychological disturbance to the animal. An antenna loop is also part of the transmitter.

Fig. 5.3 Transducer implanted in the aorta [2] A basic unit is shown in Figure 5.1. This is a single-channel blood pressure

transmitter. The module at the top contains the signal conditioning circuitry and RF

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transmitter. The second module contains a 200-mA-hour lithium power source and a 1.7-MHz RF switch for turning the system on and off remotely.

Fig. 5.4: Cut-away single channel temperature transmitter. [2]

Fig. 5.4 is a cutaway view of a single-channel temperature transmitter. A 1.35-V

battery is contained inside the antenna loop at the top. Besides, one of the three hybrid packages is shown open. Fig. 5.5 shows array of all parts of the complete system. The top unit in the figure is the, 6 Telemetry Demodulator. It has six main channels and is designed to work with the 88 to 108-MHz receiver shown immediately below it. The receiver is modified to accept both continuous FM and pulsed-RF-mode telemetry signals. An inductive power control wand for turning the implant on and off is shown on the bottom right side. Below the wand there is an external recharging transmitter.

A cutaway view of an inductively-powered multichannel telemetry system is shown in Fig.5.6. Sensor leads and compensation components are shown on the right. Power and antenna leads are shown on the left. I the center, one of three hybrid packets is shown open. It contains six sensor input amplifiers, an eight-channel multiplexer, an analog-to-PWM converted and a 1O-kHz clock and binary counter. Finally, there are systems with only partial implantations. Refer again to Fig.5.3, a pressure transducer is shown implanted in the aorta of a dog. In that particular system, the lead from the transducer brought Out through the dog�s back and connected to a telemetry transducer external to the body of the dog. This type of preparation is achieved b having the dog wear a jacket. Prior to surgery, dogs are trained to wear jackets continuously so that they get used to them. After the surgical it plantation of the transducer and after the chest wall is healed, the jacket put back on the dog. It is made of strong nylon mesh so that it is comfortable and permits air circulation, but cannot easily be bitten into by the dog. The lead that comes out of the dog�s back from the transducer is plugged into an external telemetry transmitter which is kept in a pocket of the jacket. The transmitter can be removed when not in use. Another pocket, on the opposite side of the jacket, is available for other equipment.

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Fig.5.5: Complete implantable telemetry system. [2]

Fig. 5.6: Cut-away multi-channel telemetry system [2].

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For example, in an experiment concerned with the effect of the hormone, norepinephrine, on blood pressure, a small chemical pump was placed in the other pocket to inject norepinephrine into the blood stream at various rates. The effect on the blood pressure of the dog was observed and recorded by the use of the telemetry system. The system is the same as that shown in Fig.5.2 A photograph of a dog wearing a jacket with the telemetry transmitter in the pocket is shown in Fig.5.5.

Fig.5.7: Jacket for partially implanted telemetry system. [2]

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6. Applications

There are many instances in which it is necessary to monitor physiological events from a distance. Typical applications include the following: 1. Radio-frequency transmissions for monitoring astronauts in space. 2. Patient monitoring where freedom of movement is desired, such as in obtaining an exercise electrocardiogram. In this instance, the requirement of trailing wires is both cumbersome and dangerous. 3. Patient monitoring in an ambulance and in other locations away from the hospital. 4. Collection of medical data from a home or office. 5. Research on unrestrained, unanesthetized animals in their natural habitat. 6. Use of telephone links for transmission of electrocardiograms or other medical data. 7. Special internal techniques, such as tracing acidity or pressure through the gastrointestinal tract. 8. Isolation of an electrically susceptible patient (see Chapter 16) from power-line- operated ECG equipment to protect him from accidental shock. These applications have indicated the need for systems that can adapt existing methods of measuring physiological �variables to a method of transmission of resulting data. This is the branch of biomedical instrumentation known as biomedical telemetry or biotelemetry. 6.1 Equipments Used in Biotelemetry Some of the equipments used for the applications of biotelemetry are:

a.) Imagers: Xray, MRI, Ultrasound b.) Sensors, transmitters: surgical instruments, analyzers c.)Microsatellites: multipurpose, regional coverage, steerable beams

6.2 Applications of telemetry in patient care

There are a limited number of situations in which telemetry is practical in the diagnosis and treatment of hospital patients. Most involve measurement of the electrocardiogram. Some common applications are described below. 6.2.1. Telemetry of ECGs from Extended Coronary Care patients

Cardiac patients must often be observed for rhythm disturbances for a period of time following intensive coronary care. Such patients are generally allowed a certain amount of mobility. To make monitoring possible, some hospitals have extended coronary-care units equipped with patient-monitoring systems that include telemetry. In this arrangement, each patient has FCC electrodes taped securely to his chest. The electrodes are connected to a small transmitter unit that also contains the signal-conditioning equipment.

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Fig.6.2.1.1: ECG Telemetry transmitter: (a)Hewlett-Packard type 78100A in hospital use.

(b)Electrode placement for telemetered ECG [2]

The transmitter unit is fastened to a special belt worn around the patient�s waist. Fig. 6.1 shows typical units. Batteries for powering the signal- conditioning equipment and

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transmitter are also included in the transmitter package. These batteries must be replaced periodically. A telemetry receiver for each monitored patient is usually included as part of the monitoring system. The output of each receiver is connected to one of the ECG channels of the patient monitor. A potential problem in the use of telemetry with free-roaming patients concerns being able to locate a patient in case his alarm should sound. Telemetry equipment has no provision for indicating the location of a transmitter. 6.2.2 Telemetry for ECG Measurements During Exercise

For certain cardiac abnormalities, such as ischemic coronary artery disease, diagnostic procedures require measurement of the electrocardiogram while the patient is exercising, usually on a treadmill or a set of steps. Although such measurements can be made with direct-wire connections from the patient to nearby instrumentation, the connecting cables are frequently in the way and may interfere with the performance of the patient. For this reason, telemetry is often used in conjunction with exercise FCC measurements. Two-way voice transmission is normally used in conjunction with the telemetry to Facilitate identification of the telemetered information and to provide instructions for treatment. Through the use of such equipment, ECGs can be interpreted and treatment begun before the patient arrives at the hospital.

One type of system in use is illustrated in Fig.6.2.2.1, 2, 3. The coronary

observation display console on the receiving end of the system in the hospital is illustrated in Fig.6.2.2.4.

The portable unit carried in the ambulance or paramedic vehicle has a nominal

output of 12 W RF. It can transmit on any different channels. These are the eight approved MED frequencies ant EMS or public safety dispatch channels. The Federal Communication Commission (FCC) has set up rules and regulations concerning the �Special Emergency Radio Service� (see the Bibliography) in which MED frequencies are defined.

Fig.6.2.2.1: Emergency medical care system, portable transmitter nit.[2]

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Fig.6.2.3: Emergency medical care system, transmitter unit in use.[2]

Fig.6.2.4: Emergency medical care system, hospital console.[2]

6.3 Monitoring physiological functions of mammals

The Biotelemetry System monitors physiological functions of mammals onboard the Spacelab. Each unit can monitor one animal for one to four physiological parameters. It consists of three basic parts: A) the implantable sensor and transmitter within the animal; B) the antenna/receiving system C) the data-handling system onboard the Spacelab.

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Fig.6.3 Block diagram representation

Sensor data are telemetered to antennae within selected rodent cages and primate

cages. A pulse interval modulated FM radio signal is received from each animal cage being monitored. The animal ECG rate is up to 320 samples/second. Data can be stored or down linked to Earth by radio transmission in real time or near-real time. . 6.4 Implantable Biotelemetry System for Preterm Labor and Foetal Monitoring

Foetal Treatment Center (FTC) at UC San Francisco has developed a revolutionary surgical procedure to treat foetuses suffering from diaphragmatic hernia, a condition in which a hole in the diaphragm allows internal organs to shift from the abdominal cavity into the chest cavity. The FTC first used traditional hysterotomy surgery to correct this anomaly. They recently developed a minimally invasive procedure using endoscopic techniques, called "FETENDO." Accurate monitoring of uterine contractions in the postoperative period is critical to develop medications that can inhibit the progression of preterm labor.

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7. Benefits of Biotelemetry

Scientists foresees a revolution in global health care delivery through the application of telecommunications, computer, and microelectronic and nanoelectronic technologies to support revolutionary improvements in such delivery. NASA promotes, develops and uses advanced technologies to deliver health care that benefits space flight and enhances health care for everyone.

That development continues. Researchers are working on biotelemetry applications that support U.S. astronauts aboard the Russian Mir space station and the ISS. NASA also has used its expertise in telemedicine and telecommunications to provide assistance to disaster-stricken areas of the world and to aid in the application of space-based technologies to terrestrial medical care. 7.1 Futuristic approach

The existing worldwide wireless infrastructure could be a spring-board for the development of system-level architecture for vital transmission from patients and also for detecting their position. It wou1d include cellular telephony, two-way paging, and data packet networks. RE monitoring device can be as small as a bracelet or about the size of pager- The second-generation units would comprise small computers, exchanging data packets using radio communications with a central database system. . Computerised database systems would control communication with the transmitters and maintain pertinent information about the patients being tracked. The transmitter would be equipped with a broad-based tool for monitoring vital signals as pulse rate and blood pressure. A hypothetical third-generation system, as soon as it detects even paltry malfunction, would send to the patient an audible alarm or other warning signal.

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8. Limitations

The system has inherent limitations. Movement of patient is restricted. If the patient goes beyond the range of system, his ECG cannot be monitored. Research is in progress for upgrades. Practical systems are being developed to build on existing technology and public infrastructure.

A consortium of private companies, national laboratories, universities, and end- users such as hospitals, healthcare centers, non-profit organisations, etc would be the best to explore the alternatives. The consortium could study the feasibility of such systems, communication and interface standards, methods of improving the communication infrastructure in the locale, and human aspects such as which types of patients would be candidates for these systems. Legal changes, ethics, social impacts and safeguards, etc are the other issues to be considered. Economic considerations such as cost to the society in comparison with outlays for the existing system, size of the market, number of patients qualifying as system users, etc need to be examined. A demonstration system could be developed and tried out on patients.

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9. Conclusion

Use of biotelemetric techniques in medical science will bring out a sea-change with improvements in patient care and treatment. Since the technology uses the existing communication infrastructure, it is easy to realise and implement biotelemetry without much effort and cost.

Biotelemetry will enable patients to move and perform their daily chores without any worry or mental stress of the unpredictable attack due to their body disorders. Patients who need continuous monitoring can wear a biotelemetry device which sends the vita signals to the base (hospital). There is a need to create interest in this field and initiate research activities.

Another imp area of biotelemetry is conservation of rear species of birds and animals. There living condition, mortality rate n movements can be remotely monitored for appropriate conservation steps. This can also help in understanding the behavior of certain birds, animals, aquatic animals for the benefit of the mankind.

This technique can open new vistas for development of new techniques and understanding for the good of human kind. Nanotechnology is becoming increasingly supportive in biotelemetry especially because of large strides made in nanotechnology in recent times

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Bibliography

1. Mr R S Khandpur- Handbook of BMI, Third edition. 2. M/S Leslie Cromwell, Weibell and Pfeiffer-Biomedical Instrumentation and

measurements, Second edition. 3. Electronics for you � March 2000 4. www.biotelemetry.com 5. The national academics press

http://books.nap.edu/openbook.php?record_id=6066&page=12 6. NCBI-Pubmed.com http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7047072&dopt=Citation 7. Biomedical Instrumentation And Measurements by Cromwell 8. M. Steyaert, S. Gogaert, T. Van Nuland, and W. Sansen, �A low-power portable telemetry system for eight-channel EMG measurements,� in

Proc. Annu. Int. IEEE-EMBS Conf., vol. 13, 1991, pp. 1711�1712. 9. hthtetry.html http://www.datafilter.com/mc/sensors2000biotelem 10. http://www.hq.nasa.gov/office/olmsa/aeromed/index.html 11. http://www.paho.org/english/DPImag/Number5/article2.htm

13. www.biomedical-engineering-online.com/ articles/browse.asp