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Design & Evaluation of a Low-Cost Android BasedPulse OximeterMalay SoniU.M.ChaskarCollege of Engineering,Pune(COEP)College of Engineering,Pune(COEP)Email:malaysoni18rock@Email: umc.instru@coep.ac.in336677038481000Abstract—The blood oxygen saturation level plays very im-portant role in human health. Lack of oxygen in hemoglobin may cause injurious abnormalities like cyanosis, hypoxemia & their different levels, etc. Blood oxygen saturation level falling below 65% can even cause impaired mental function. Continuous monitoring of oxygen in operation theater for patients having anesthesia injected is required. Pulse oximeter can be used for quick diagnosis of oxygen saturation level. It measures change in blood oxygen level non-invasively. In this paper, android based portable pulse oximeter has been introduced for home based healthcare system. The photoplethysmogram (PPG) is acquired from sensor, given to microcontroller & sent to android based smart phones using Bluetooth technology. The major idea is to make the device portable & cost effective for the development of Healthcare in rural areas.Key words—Pulse oximeter, Home based, Hypoxia, Portable, Android, Cost efficient.I. INTRODUCTIONTelemedicine is field where medicine & engineering collab-orate to produce interdisciplinary systems. Wireless technol-ogy has a big role in Telemedicine. Due to the advancement in wireless connectivity, patient in a remote location can have proper diagnosis through physician sitting over seas. It not only saves time & money but also helps patients in emergency situations where appropriate help is required. Utilizing hand-held devices such as mobile phones for health-related purposes has become widespread & it has been reported to continue to increase [1, 2]. Novel healthcare applications have been devel-oped & it seems there is still incessant need to develop even more of them. In remote healthcare monitoring applications, there is a need of continuous monitoring of vital signs. Due to the growth of mobile devices, embedded systems, cloud computing & data analysis, IoT has become more relevant to the practical world. Internet of Things (IoT) home based healthcare system has been developed rapidly [3, 4]. For medi-cal monitoring & diagnosis biosensors can be easily connected to a remote server via phones or other access points [5, 6]. The data collected from this biosensors should accessible anytime & anywhere, which requires constant network connectivity.In this paper, a system is designed where oxygen saturation in blood is calculated & displayed graphically on mobile application using Bluetooth technology. Oxygen saturation is better known as pulse oximeter. Blood oxygen saturation level (%SPO2) is one of the important vital signs in patient monitor-ing. Due to pollution many breathing disorders are developingFig. 1: System overviewin human body such as asthma. In asthmatic patients oxygen level should be maintained & checked regularly. Even in healthy person due to inhalation of certain gasses like carbon monoxide (CO) can cause decrease in blood oxygen saturation level. Carbon monoxide has adverse effects once combined with hemoglobin it forms carboxyhemoglobin (HbCO) in the blood. Due to HbCO formation hemoglobin is obstructed from releasing oxygen in tissues. All organs require oxygen for metabolism but the brain & heart are particularly sensitive to a lack of oxygen. Shortage of oxygen in the body is called hypoxia. A serious shortage of oxygen for a few minutes is fatal.Another region of interest to monitor %SPO2 is anes-thesia delivery. During anesthesia, patients airways become obstructed, their breathing may become depressed, their cir-culation is affected by blood loss or an abnormal heart rhythm or the anesthetic equipment may develop a problem such as an accidental disconnection or obstruction of the breathing circuit. These components can result in a diminution of oxygen delivery to the tissues which, if not handled correctly, could lead to injury or death. The earlier the anesthesia provider detects a problem, the earlier it can be treated so that no injury can harm to the patient [7]. Moreover, physicians do not recommend patients to undergo surgery & avoid delivery of anesthesia below 90% of SPO2. Another symptom of lack of oxygen is cyanosis. Cyanosis is a bluish color of mucous membranes and/or skin [8]. Patients with blue finger tips or blue lips show low level of oxygen in hemoglobin. Hence, toavoid any such above mentioned abnormalities a regular check & proper steps if required is to be taken. Early detection & early treatment are imperative.Fig. 1 shows the general system overview. As shown in the Fig. 1 the system behaves as the bridge between the patient and hospital situated far from the patient. Signal from patient is given to input side of the system which is having signal conditioning circuitry. Noise free PPG signal is given to microcontroller and finally to smart phone using Bluetooth connectivity. Further data can be transmitted to any hospital wirelessly through Internet.II. SYSTEM ARCHITECTURESystem architecture is divided into two main sub divisions i.e Hardware architecture & Software architecture. Hardware comprises of signal conditioning board, microcontroller & Bluetooth module. The Nellcor DS-100 series pulse oxymeter probe is used in the system as a sensor to acquire the patients’ data[9]. Sensor works on the transmittance principle which consists of two LEDs & a photodetector, which are present on two different sides of probe. Two LEDs are of wavelength 660nm(red) & 940nm(Infrared). Samples cannot be taken at the same time from both the LEDs as there is only one pho-todetector, so Signal from microcontroller is given to switch these LEDs every 1ms. Microcontroller do not provide enough strength to drive LEDs in proper manner therefore LED driver circuit is required which provides sufficient energy to drive the LEDs. Signal conditioning part is required to remove noise & amplify the acquired signal from sensor. MSP430G2553 microcontroller is used for data conversion from analog to digital & data transmission to Bluetooth module.Hardware ArchitectureSignal conditioning unit: As shown in Fig. 2, different filters for different purposes are used along with proper ampli-fication. As the signal form the sensor is in the range of micro-amperes, first stage is to convert current to voltage for further signal conditioning. To remove high frequency noise, low pass filter of cut off frequency 6 Hz is designed. Cut off frequency of passive low pass filter is designed using appropriate valuesof capacitors and resistors. Power-line interference is one of the major noises to be eliminated. To remove this noise passive notch filter of 50 Hz is used. Signal is then filtered with a high pass filter of 0.8 Hz. It removes DC component from the received signal. DC is the unwanted signal which is transmitted through tissues and bones. For calculation purpose of oxygen level in blood, only AC components are required. Hence this high pass filter is used to pass AC components which indicates signal transmitted through atrial blood which is the region of interest. Last stage of signal conditioning is of amplification. To adjust the amplitude of photoplethysmogram an active amplifier with variable gain is designed. This noise free and amplified signal is fed to microcontroller.2) Microcontroller: In this system MSP430G2553 micro-controller is used. It is a 16-bit ultra-low power microcontrollerFig. 2: Block diagram of Signal conditioning222250-11963400031369017018000Fig. 3: Visualization Routine of the Android Applicationby Texas Instruments & is based on RISC architecture. It op-erates on low voltage ranges, ranging from 1.8V to 3.6V. The ADC10 module is a high performance 10-bit analog-to-digital converter embedded on the microcontroller (MSP430G2553), is used to convert the SPO2 signal coming from the front end circuit in digital form.To calculate %SPO2, we have developed an alogorithm which detects the change in peak to peak voltage level of PPG and measures the percentage in proportion to the change in voltage level. The calculated information is then transfered to UART module for serial communication & wireless trans-mission.3) Bluetooth: Bluetooth module is used for wireless trans-mission of SPO2 signals to any Bluetooth supported devices. It gives easy wireless connectivity & works on 3.3V dc voltage which is easily available from microcontroller. The module is cost effective & very simple to use for serial communication.B. Software ArchitectureThe software part consist of the development of java based android application. The microcontroller transmits the sampled PPG signal serially to Bluetooth module which communicates with the android application. The overview of the android application is shown in Fig. 3. This application has four major functions viz. monitor, record, store & transmit the data through E-mail for further analysis.In Fig. 4, layout of the developed android application is shown. Fig. 4(a) shows the home screen of the application which is having functions like Connect, Options, Guide & Credits. To pair with the available bluetooth ’Connect’ option is given through which we want to communicate. ’Options’121031068580000Fig. 4: (a) Home screen of application, (b) Bluetooth scan, (c) Result on application, (d) E-mail layoutfunction has some facilities like to change language, profile settings etc. To make use of this device as home-based healthcare system, we have introduced an option known as ’Guide’ to understand the procedure for accurate measure-ments without any physician’s help. Next Fig. 4(b) shows all the available bluetooth devices & one can easily connect to the system. Fig. 4(c) shows the main screen of the application which will show the graph of PPG once connected with the patient and will give the value in percentage as well. This screen is also having the option to save the data or send it through E-mail to anywhere across the globe for further diagnosis. Fig. 4(d) shows the layout of E-mail.III. RESULTSIn order to test the system & verify it’s results, it has been calibrated using patient simulator manufactured by FLUKE. It is a standard simulator used globally by many medical devices for calibration purpose. One of the advantages of using simulator is that a wide range of oxygen level (30%-100%) can be given as input to system for calibration.Fig. 5 shows plotting of PPG and it’s equivalent %SPO2 on android application. There is also a provision for abnormal condition i.e if blood oxygen saturation level falls below 90% alarm blows. This condition of abnormality has been tested & verified with the help of FLUKE simulator. Table. 1 shows the comparison of the functionality between the designed system and standard EASY CARE fingertip Pulse Oximeter where FLUKE simulator is used as reference.Fig. 5: Results on application588010-356425500FLUKE patient simu-Designed SystemEASY CARE finger-latortip Pulse Oximeter1009999999998989897979796969695959494908989858484808279Table.1 %SpO2 comparison between the designed system and the market product with FLUKE as referenceIV. CONCLUSIONThe system collects, records & sends the PPG signal. Designed system provides facility to monitor the waveforms & also check for abnormalities present if any. The idea behind this developed system is to monitor real time oxygen level in blood without visiting to hospitals. It is not only used for urban areas but also for rural health development. No device can clearly replace doctors but as a part of engineering, we can make efforts to process, examine & display real time signals which can help doctors to cure if found abnormal. Such interdisciplinary innovation combining engineering & medicine is a need of hour.For the advancement of this project, system can be im-plemented as a wearable device for 24 hours monitoring & notice the slightest change in oxygen level. The results show accurate graph of PPG & also indicates abnormal oxygen level in blood with alarm notification hence, making the device more compact & handy is our next step in pulse oximeter.ACKNOWLEDGMENTWe are also thankful to the Department of instrumentation & Control, College of Engineering, Pune (COEP) for providing us all the necessary components and support.REFERENCESRosser, Benjamin A., and Christopher Eccleston. ”Smartphone applica-tions for pain management.” Journal of telemedicine and telecare 17.6 (2011): 308-312.Chan, Marie, et al. ”Smart wearable systems: Current status and future challenges.” Artificial intelligence in medicine 56.3 (2012): 137-156.Suraki, Mohsen Yaghoubi, and Mohsen Jahanshahi. ”Internet of Things and its Benefits to Improve Service Delivery in Public Health Approach.” International Conference on Application of Information and Communi-cation Technologies, Azerbaijan, Baku. 2013.Tarouco, Liane Margarida Rockenbach, et al. ”Internet of Things in healthcare: Interoperatibility and security issues.” Communications (ICC), 2012 IEEE International Conference on. IEEE, 2012.Xue, Fei, et al. ”Healthcare delivery with IP-based sensor networks.” Biomedical and Health Informatics (BHI), 2012 IEEE-EMBS Interna-tional Conference on. IEEE, 2012.Wallace, Sean, Marcia Clark, and Jonathan White. ”It’s on my iPhone: attitudes to the use of mobile computing devices in medical education, a mixed-methods study.” BMJ open 2.4 (2012): e001099.Tavakoli, Maziar, Lorenzo Turicchia, and Rahul Sarpeshkar. ”An ultra-low-power pulse oximeter implemented with an energy-efficient tran-simpedance amplifier.” Biomedical Circuits and Systems, IEEE Trans-actions on 4.1 (2010): 27-38.Walker, Henry Kenneth, Wilbur Dallas Hall, and John Willis Hurst. Chest Roentgenography for Cardiovascular Evaluation–Clinical Methods: The History, Physical, and Laboratory Examinations. Butterworths, 1990.Lopez, Santiago, and R. T. A. C. Americas. ”Pulse oximeter fundamentals and design.” Free-scale Semiconductor, Inc., application note document number: AN4327 Rev 1.09 (2011).Rostami, Mariam, and Amin Janghorbani. ”Design and implementation of telemedicine system for Spo2 monitoring.” Electrical Engineering (ICEE), 2014 22nd Iranian Conference on. IEEE, 2014. ................
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