Telemetry has essential of human life
Telemetry has become an essential part of human life. It has indispensible uses in all facets of modern world. It plays a vital role in the field of medicine. The various applications of telemetry in this field are monitoring, controlling, counseling and therapy. People in remote areas are mainly the beneficiaries of this emerging phenomenon. It has a great impact on the way medical applications are perceived in the global arena at present. Based on the technology used, it is classified into wired and wireless telemetry.
In wired telemetry, we require specific medium for transfer of data across the distance. Telephone lines and modem are used for this purpose. It is a conventional method of data transmission. But it is obsolete in the case of medical data, mainly in the hospital scenario. The clutter and congestion caused by multiple wires makes the system unmanageable.
In wireless telemetry, which is the current and ongoing trend, we do not use specific media but consider air as the medium of transmission. Emerging technologies such as Bluetooth, HomeRF, 802.11b, HiperLAN, 802.11a, HiperLAN2, Zigbee, 433.92 MHz RF transmission are coming up.
Parameters for differentiating each technology:
- Frequency range,
- Range of transmission ,
- Power consumption and
- Transmission techniques utilized.
1.1.1 Selection of transmission technique:
The transmission technique used in this project is 433.92 MHz RF. The reason for selection of this specific technique is its features. Factors such as cost, performance, size, level of application, flexibility in usage, range of transmission, power consumption were considered for short listing the selection of transmission technique and the best suited one for our needs was chosen.
1.2 Parameter considerations:
In biotelemetry various types of data such as signals, images, reports, and metabolic activity details can be transmitted. The prime importance is given to biological signals which directly indicate the patient condition. Basically we obtain signals of ECG, EEG, PPG, EMG, respiration signals, EOG, ERG, ENG, EGG, pulse, etc. from the patient. They provide information about various physiological functions and related physiological anomalies. Metabolic activity monitoring can be done by using temperature and GSR.
In this project the emphasis is given to primary health monitoring. Hence, we consider ECG and the body temperature as monitored parameters. ECG as such does not give complete information about the patient condition. It has to be further processed to acquire more details. Several abnormal conditions of arrhythmia, like ventricular tachycardia, bradycardia, missed beats, and etc. cannot be identified easily using ECG waveform. Hence heart rate calculation can be done to enable proper acquisition of detail from obtained signal.
Another parameter which is considered quite essential in primary monitoring of health is body temperature. It acts as an indicator for several metabolic processes and helps identify any breach in the pathologic functions of the body. Hypothermia and hyperthermia conditions indicate any basic change in the body activity. Several causes like inflammation, microbial attack, and unbalanced metabolic activity can cause variation in temperature. It also changes in response to external environmental conditions. Extreme cold or hot conditions in the surroundings cause fluctuations in body temperature. Monitoring this parameter aids in understanding the current state of patient health.
Various techniques are used for the monitoring of biophysical parameters. Several of these have been well tried and tested to determine their suitability in possible practical usage.
Sudip Nag and et al. (2006) have developed a wireless e-jacket for the monitoring of biophysical parameters using frequency modulation. The wireless transmission is done using RF transmission of range 2.4 GHz. The particular module has added features of plug-in-port for easy accessibility using USB ports. The smart clothing system was developed with the use of the shelf hardware components for the monitoring of ECG, temperature and movement using accelerometer. The main drawbacks of this module are the absence of provisions for transmission of the available data through the available networks and the increased power consumption of the entire setup.
Veysel Aslantas and et al. (2007) developed a wireless monitoring system using bluetooth transmission technique. The system involved the monitoring of clinical parameters and an alarm system was designed to provide indications for abnormalities in the monitored parameters. The advantages of this design are increased mobility of patients, portable size and the use of integrated technology for development of the device. The device lacks in the flexibility to include more parameters for monitoring as the procedure involved is complicated.
Manish Raghuvanshi (2007) compared the various available wireless transmission techniques and the components involved in the development of the wireless modules, such as microcontroller, memory device, etc. and determined a good combination of the technique and the circuitry. The module developed used Zigbee to transmit and receive room temperature data. The main advantage of the setup was the reduced power consumption and reduced data loss. Though the transmission was proper, the data acquisition was flawed. The data processing technique implemented and the sensor used lacked sensitivity. Also the setup was bulky in size.
Another effort at health monitoring involved the use of Zigbee and mobile phones for the ubiquitous monitoring of the blood glucose level in elderly patients. The transmission technique involved aided in low power and low cost module development. The drawback of this system was the reception of less data values than what was initially sent. The reduced data reception and the reduced device sensitivity caused great reduction in the accuracy of the device functioning.
2.1 Project Innovations:
In this project the transmission is done using RF transmitter of 433.92 MHz. It is rarely used in medical applications but has a good scope in biotelemetry applications. It can be used to provide monitoring systems which are of smaller size, portable and comfortable for the patient to handle. The reduced size enables us to provide a compact solution for the requirements of the consumer. Hence, it is commercially viable and marketable.
3.1ECG and Its Physiological Importance:
Electrocardiogram is a recording of the electrical activity of the heart captured externally using sensors. Electrical impulses present in the heart originate from the sinoatrial node and travel through an intrinsic conducting system to the heart muscle. The impulses generated stimulate the myocardial muscle fibers to contract and thus inducing systole. The electrical waves can be measured using electrodes placed at specific points on the surface of the skin. Electrodes on the different sides of the heart measure the activity of different parts of heart muscle. A typical ECG tracing of cardiac cycle (heartbeat) comprises a P wave, a QRS complex and a T wave.
Heart rate which is expressed in bpm (Beats per Minute) is commonly the ventricular rate. It is the most vital parameter which is monitored to assist in the diagnosis of the health condition of a person.
Normal: The normal heart rate ranges between 60 and 100 bpm.
Bradycardia: This condition occurs when the heart rate falls below 60 bpm. Bradycardia may occur due to secondary to certain illnesses too (such as decrease in thyroid function, particular gastrointestinal disorders, and jaundice) Severe bradycardia (less than 30 beats per minute) can be an emergency situation which may lead to oxygen deprivation in the brain and convulsions. Death may also result unless immediate medical measures are taken to elevate the heart rate.
Fast (tachycardia): This condition occurs when the heart rate exceeds 100 bpm. Sinus tachycardia occurs due to rapid firing of a simple structure called the sinoatrial node (sinus).
Paroxysmal atrial tachycardia (PAT) comprises several bouts of rapid and regular heart beat that originates in the atrium.
Ventricular tachycardia is an abnormal rhythm of the heart which is regular, rapid and originates from an area in the ventricle.
3.2Temperature and its physiological importance:
Normal human body temperature depends upon the place in the body where the measurement is taken, and the time of day and also the activity level of the person. The commonly considered value of average core body temperature, taken internally, is 37.0°C (98.6°F).
Temperature taken from the anus, vagina, or the ear is around 37.6°C (98.6°F)
Oral temperature, taken from the mouth, is around 36.8°C (98.2°F)
Axillary temperature, under the arm, is about 36.4°C (97.6°F)
In order to maintain the homeostasis of the human body it is essential that the human body temperature remains constant. Any abnormal physiological changes in the body causes the body temperature either to increase above or decrease below the normal range thus disturbing the homeostatic condition which at extreme cases may prove to be lethal.
Fever is a common medical phenomenon characterized by an increase of temperature above the normal range due to an increase in the body temperature regulatory set-point. This elevation in the set-point triggers elevated muscle tone with shivering. Hyperpyrexia is a fever with an extreme increase in body temperature which is greater than 41.5°C (106.7°F) or equal to it. Such a rise temperature is treated as a medical emergency as it may point to a serious condition or may lead to significant side effects. The most common cause is a intracranial hemorrhage.
Hyperthermia occurs due to a number of causes including heatstroke, neuroleptic malignant syndrome, malignant hyperthermia, stimulants such as amphetamines and cocaine, idiosyncratic drug reactions, and serotonin syndrome.
Thus continuous monitoring of ECG, heart rate and body temperature helps in the earlier diagnosis of the diseases and thus helps in proving the timely treatment.
4.1ECG AMPLIFIER DESIGN:
The ECG amplifier was designed using the high precision, low noise, instrumentation amplifier, AD624. The salient features high gain accuracy, a very high CMRR of 130 dB at a gain of 500, low gain temperature coefficient and high linearity had made AD624 an ideal choice for design of ECG amplifier. The functional block of AD624 is as below.
The ECG amplifier was designed for a high gain of 1000. The CMMR of the amplifier is 98.3dB. The pin connections of the amplifier is as follows,
The signal from the amplifier was distorted with base line wandering, power line interference and additive noise. Hence a series of active Butterworth filter were designed to remove the signal distortions. The amplified signal was initially filtered using a Band pass filter to remove the base line wandering and higher frequency components. Then the signal is smoothened using a Low pass filter which is followed by a Notch filter to remove the power line interference.
The designed Butterworth filters are 2nd order filters with a 40dB/decade roll off and a phase angle of -90º at the cut off frequency, ωc.
4.1.1 Band Pass Filter Design:
The Band Pass Filter was designed, cascading a high pass filter with a cutoff frequency of 0.5Hz with a low pass filter having a cutoff frequency of 40Hz. Thus the resulting Band Pass filter has a lower cutoff of 0.5 Hz and an upper cutoff of 40Hz and a maximum gain at resonant frequency.
4.1.2 High Pass Filter Design Procedure:
- Cutoff frequency, fc = 0.5Hz
- R1 =(1.414)/(ωc*C) = 45 kΩ
- R2=0.5R1=22.5 kΩ
- Rf=R1=45 kΩ (To reduce the dc offset)
4.1.3 Low Pass Filter Design:
- Cutoff frequency, fc = 40Hz.
- R =(0.707)/(ωc*C1) = 28 kΩ
- Rf=2R=56 kΩ (To reduce the dc offset)
4.1.4 Passive Notch Filter:
The notch filter was designed to filter the 50Hz frequency component.
The amplified signal was then given to LABView for further processing and finding the heart rate. The QRS complex of the ECG signal was extracted using a band pass filter with a centre frequency of 17Hz. The signal was then differentiated and the QRS peaks were detected. The signal was squared to obtain the pulses from which the Heart rate was calculated and displayed.
4.2 Temperature Acquisition:
The surface temperature of the body was acquired using the LM35 precision integrated-circuit temperature sensor, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The accuracy of the sensor is ±0.9 . A voltage change of 10mV from the sensor corresponds to a temperature change of 1ºC. The linear variation of the sensor was verified by tabulating the output voltages from the sensor for the known temperatures. From the calibration table a calibration graph was also plotted which shows the linear working of the LM35 temperature sensor. The calibration table and the calibration graph are a follows
The transmitter section has the major sections of data acquisition, processing and transmitter chip.
The need for a microcontroller arises due to the processing and storage of data involved. The microcontroller aids in digital manipulation of data acquired. It also helps in storage of data in a buffer prior to transmission and collection of data bits in buffer at the receiver end for proper calibration and display. The microcontroller is also required for driving the display device. Based on the requirements of the project the microcontroller was selected.
The microcontroller used for this application is PIC16F877A. The features of this microcontroller are:
- Inbuilt ADC
- 5 ports: A, B, C, D and E
- 1,000,000 erase/write cycle Data EEPROM memory
- 100,000 erase/write cycle Enhanced Flash program memory
- Low-power, high-speed Flash/EEPROM technology
- Wide range of operating voltage (2.0V to 5.5V)
- Industrial and commercial temperature ranges<
- Low-power consumption
The input parameters are provided to the microcontroller using the ports assigned as inputs. For this purpose we use the port A as input and the temperature data acquired from the sensor is given to the pin 2 of the microcontroller (RA0). The analog data given through the input port is then converted into digital format and the digital bits are taken out through the output port, port B. The converted value of 8 bits is delivered throught the 8 pins of port B- RB0 to RB7. This conversion occurs in the transmitter section.
The data from the microcontroller, after conversion, is sent to an encoder. The encoder used for this purpose is HT640. The purpose of the encoder is to convert the parallel data bits to serial and aid in the transmission of the data through the transmitter chip. The data pins (AD10-AD17) of the encoder are connected to the port B output pins and the parallel input data is given to the encoder. Also the encoder is used to differentiate between the tranmitter sections incase of multiple data transmissions or multiple transmitters. This is achieved by using the address pins of the encoder. The address pins (A0-A9) are set as constant high or low bits to provide security during transmission and avoid any discrepencies in the transmission.The transmit enable (TE) pin is kept high to enable the transmission of the serial data from the encoder to the tranmitter chip. The serial data output is obtained through the pin 8 (DOUT).
The transmitter used for this project is the 433.92 MHz RF transmitter chip.
The RF transmitter has 4 pins. They are:
- Data in
The data from the encoder (DOUT) is sent to pin 2 of the transmitter. The modulation technique used in the transmitter is Amplitude Shift Keying(ASK). The amplitude of the carrier signal varies in accordance with the modulating bits to generate the modulated output. The frequency of the carrier used is 433.92 MHz. The data transmission rate is 8kbps.
The antenna used for the purpose can be whip antenna or helical antenna. The modulated signal from the transmitter is sent out via the antenna. Proper type and length must be chosen to avoid noise and provide proper transmission during the data transmission. The antenna is of helical shape and the length is determined based on the wavelength of the signal to be transmitted. It is an omnidirectional antenna and is generally used in most of the mobile applications.
The receiver section is composed of components similar to that of the transmitter section. The major blocks of this section are:
- Display segment
This section is placed in the vicinity of the patient, either in a monitoring station or carried by the caregiver in-charge. The module is made such that it is easy to use and portable. Thus it is suited for the domestic healthcare needs and give more emphasis to home based monitoring.
The receiver section also has an antenna which is similar to that placed in the transmitter block. This antenna is of whip type or helical type with optimal length of 17cm.
The data sent is received via the antenna, pin 8 of the receiver. The data of the antenna pin is the modulated signal. The demodulation of the signal occurs in the receiver and the carrier is separated from the modulating values. Thus the true parameter values are obtained as serial bits in the receiver end. The receiver chip has pins 2, 3 as data and pins 1, 6, 7 as ground. Power supply of 5V is given to pins 4, 5. The demodulated data is taken from pin 2 and given to the decoder as input.
The decoder used for this project is HT 648L. It has pin9 as DIN to give input of serial data from the receiver. The pins 13 to 22 act as address pins. These determine the transmitter that is coupled with the particular receiver. These pins are maintained at a stable state, as high or low, as same as that of the address pins of the encoder. This helps in avoiding improper transmission from other transmitters in the vicinity. The main purpose of the decoder is to convert the serial bits received, to parallel bits, for processing by the microcontroller. The parallel bits taken from pins 1 to 8 and 23 are given to the specific input port of microcontroller.
The microcontroller used here is PIC16F877A. The main purpose of the microcontroller is processing of the received data and enabling its display. The port B of the microcontroller is used to receive the decoder output. This digital data is converted to appropriate parametric value using calibration techniques and microcontroller code. For temperature transmission, the value obtained through transmission is variation in voltage proportional to the change in temperature. Hence, specific coding is done to aid the conversion of voltage to temperature. The controller is also used for driving the display segment, wherein ports C, D and E are used for providing the output values; controlling the display parameters and generating proper delay between subsequent bits along with required repetition respectively. The ports are initialized and the values are continuously updated to keep in track the changes occurring in the patient parameters at the transmitter side.
The display segment has a 16X2 LCD unit. The data for display is taken from appropriate output port of the microcontroller and it is given to the data pins of LCD segment. The data pins D0 to D7 of the LCD are interfaced with the pins C0 to C7 of port C of the microcontroller. The contrast adjustment is done by using a potentiometer connected to pin3 of the display. The required power supply is provided to pin2 and grounding is done using pin1. E0 to E2 of the microcontroller are connected to pins 4, 5 and 6 of the display for performing the functions of register select, read/write and enable. The temperature value when displayed can be either in Fahrenheit or Celsius. The data positioning as well as data representation can be adjusted and manipulated by use of microcontroller code.
We are able to observe that transmission occurs with minimal loss, by use of this module. Data acquisition and transmission is made simpler and cost effective by use of this model. Initial results show that bitwise transmission i.e. serial transmission of acquired data was carried out with zero transmission loss. Noise immunity is also provided for any data transmitted. The temperature values were satisfactorily acquired by means of the specifically used temperature sensor- LM35. Also the transmission provided satisfactory results both in absence and presence of obstacles over a range of around 50 meters.
During acquisition of temperature data, an error of about +/- 5% is observed. The transmission delay is very minute and is not observed very clearly.
The monitoring of functioning of the patient's heart is done by means of continuously observing any variations in the subject's heart rate. The heart rate is monitored at bed side, as a visual and numerical display. Noise elimination and amplification are satisfactory.
Further modifications can be done to accommodate several other parameters that can be monitored sequentially or simultaneously. Also, visual display for observing signals can be added in place of the numeric LCD segment. The monitored value of heart rate can be further processed and transmitted. Several features such as visual alarms, auditory alarms and controlling circuitry for feedback can be added later. This can be further improved to incorporate facilities- Internet, LAN, WBAN, etc.- that help transmit data over wider range. The data can also be stored in databases for future use.