Ambulatory Monitoring System - IJETT-International Journal of ...

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International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013elderly, pregnant and obese subjects (provided the correctsize cuff is used). Ambulatory BP monitoring is safe and isnot usually associated with complications. Occasionallyedema or petechiae of the upper arm or bruising under theinflating cuff may occur. Modern ABP devices are quiet,lightweight and easy to wear, but inflation of the cuff maycause some transient discomfort, particularly in people withhypertension or when multiple readings are triggered due toerrors in measurement. Ambulatory BP measurementsduring the night may disturb sleep; potentially requiringretesting if there are poor nocturnal BP measurements. [8]Ambulatory BP monitoring provides a more reliablemeasure of a patient’s BP than isolated clinic measures andis not subject to the ‘white-coat effect’, which canoverestimate BP, particularly in susceptible patients, Whileclinic measurement of BP is useful for screening, and in themanagement of suspected and true hypertension.Ambulatory BP and home BP measurements addconsiderably to the accurate diagnosis of hypertension andthe provision of optimal care. Recent recommendationsfrom expert groups such as the United Kingdom’s NationalInstitute for Health and Clinical Excellence stronglyadvocate wider use of ABP monitoring in the diagnosis andmanagement of hypertension. [8]II.WIRELESS TRANSMISSION METHODMany of the wireless monitoring system currently beingproduced use Bluetooth networking systems, which is thefirst task group of the IEEE 802.15. There are threeadvantages to using Bluetooth over other low-power PLANsystems:1. High frequency-to-noise ratio (up to -104dB receiversensitivities, and transmission strengths of 23dBm or more)2. Capable of high data rates, theoretically up to 2.1 Mbit/s(Bluetooth 2.0)3. Bluetooth technology is present in many cellular phones,PDAs, and notebook computers, making any Bluetoothenableddevice very technologically compatibleBluetooth is also a very mature technology, with a multitudeof chipsets available from many vendors and well-exploredtransmission and encryption software. However, it sharesthe downsides of all PLAN systems, which include shortrangeeffectiveness and weakness towards interference, as itshares the 2.4GHz band with the higher-power 802.11WLAN traffic. Bluetooth also possess a number ofadditional disadvantages specific towards our needs. First,Bluetooth transceiver chips are somewhat high-power forthis application; up to 190ma during transmission19, andeven with a low duty cycle, current draw is still higher thanwould be preferred. Second, the protocol stack for Bluetoothtransmission is much larger than that of other PLANsystems, and therefore demands a microcontroller withgreater memory20.Besides Bluetooth, there are other wireless variants withinthe 802.15 specification that are very applicable to smallarea,low-bandwidth uses such as patient monitoring. TheIEEE 802.15.4 task group focuses on low-bit-rate WPAN,with peak speeds of 100-250 kbps. ZigBee provides anupper-level specification for the 802.15.4 standard, which istargeted towards Wireless Personal-Area Network. Typicaltransmission distance is only a few meters for these LANs.Applications needing long battery life, secure networking,and a low data rate. The advantages to using a ZigBee-basedwireless transmitter include:1. Very long battery life, with average current draws in the30mA range for Tx. This current draw is low enough to lastalmost 100hrs on a single AA battery.2. Secure data transfer, with 128-bit encryption3. Simple, integrated architecture using the ZigBeespecification4. ZigBee-compliant hardware is very inexpensive. Anentire transceiver solution at quantities of 1000 can cost lessthan US$5.Although ZigBee lacks the throughput of even Bluetooth,which is a low-data specification, it certainly has a highenough data rate for an uncomplicated sensor reading; infact, target applications for ZigBee include wireless sensorsand monitors, such as water or gas metering, or medicalmonitoring, in this case. Also, ZigBee is well suited toReduced Function Device (RFD) networking, in a simplestar-style network opposed to the mesh or cluster-treenetwork topologies. This is ideal for a group of sensortransmittercommunicating with a single receiver, as in ourapplication.Figure 11: ZigBee network topologiesISSN: 2231-5381 http://www.ijettjournal.org Page 2833
International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013III. FINAL AMBULATORY MONITOR DESIGNEwalls begin to vibrate or oscillate as the blood flowsturbulently through the partially occluded artery and thesevibrations will be sensed in the transducer systemmonitoring cuff pressure. As the pressure in the cuff furtherdecrease, the oscillations increase to maximum amplitudeand then decrease until the cuff fully deflates and blood flowreturns to normal. Oscillometric pulses generated in the cuffduring inflation or deflation. Blood pressure values aredetermined by oscillometric pulse index. These values arefurther passes to microcontroller for wireless transmission.Temperature is sensed by a thermistor having a resistance of100ohm (at 20’C) placed in emitter of transistor. Changes inresistance of the thermistor with changes in temperature aremeasured in a bridge circuit and indicated on a led. Themeasuring range is 30-42’C.The real time samples are also send via transreceiver chipCC2530-CC2519 to PC. A separate PC GUI displays thesesamples a graphic trace.B. Wireless Module InterfaceA. Circuit implementationFigure 1 depicts the system block diagram. ECG sensorconsists of mainly parts are.The first is instrumentation amplifier with high CMRR(Common Mode Rejection Ration) to remove the noiseinduced from body and amplify the difference between rightand left body parts. The left and right thumbs are input assignal detection of ECG. The analog amplified ECG voltageis fed to processor to pass through digital FIR filters. Highpass and low pass filters are implemented to get ECG signalof proper range. The processor converts these signals toanalog output in serial format and pulse output. The serialdata is 1 byte every 5 mili-second. Each byte can be from 0-255 indicating an analog value of the signal. The pulseoutput is also fed to onboard LED to indicate the heart beatand same is output through optocoupler. Board uses twooptocoupler to isolate the board from external voltages sinceany little noise from external source can be amplified asnoise. So to get clean ECG signal the board is operated from3V battery isolated from external supplies.For Heart Beat, output is calculated from the analog outputby monitoring the analog waveform and when it detects apeak(R wave) in last 100 samples average value then the onboard LED is made on and same pulse output is madethrough optocoupler. This pulse output signal can directly befed to microcontroller pins.For Blood pressure, the automated oscillometric method ofnon-invasive blood pressure measurement has used. Thecuff of monitor is placed on wrist. An occluding cuffdeflates from a level above the systolic pressure, the arteryTo make the application wireless, the MSP430 needs tointerface to some of the existing transceivers. As discussedpreviously, an on-board option has been provided tointerface with the wireless world via the pin headerssupporting the CC11xx, CC2500, CC2420, CC2430 EMKboards and the eZ430-RF2500T target. These devices arelow-cost, single chip transceivers equipped with serialinterfaces that can be used to directly communicate with theMSP430. The transceiver modules CC11xx, CC2500,CC2420, CC2430 EMK and eZ430-RF2500T target boardsare connected to the USART/SPI pins of theMSP430FG437.The eZ430-RF2500T target is also connected to theUSART/UART pins of the MSP430FG437. The UART Txand Rx lines are routed directly to the eZ430-RF 6-pinheader and via jumpers to the USB circuitry.C. LabVIEW Ambulatory Monitor GUIA customized LabVIEW GUI application has beendeveloped to display the signal samples on the PC. There isno need to install LabVIEW to run the Ambulatory GUIapplication. The users only need the LabVIEW Run-TimeEngine or the stand-alone executable to run the AmbulatoryGUI on a PC.LabVIEW stand-alone applications include executable filesthat are distributed to users. However, these executablesproduced by the application builder (in LabVIEW) are nottruly standalone in that they also require that the LabVIEWrun-time engine to be installed on the target computer onwhich users run the application. Therefore, the user requiresthe LabVIEW run-time engine to run the stand-aloneexecutable. The LabVIEW run-time engine helps load andrun LabVIEW VI. This GUI application is different from theISSN: 2231-5381 http://www.ijettjournal.org Page 2834
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