Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
USB BASED DUAL CHANNEL DATA ACQISITION SYSTEM FOR CAPTURING AND PROCESSING OF PHOTOPLETHESMOGRAPHY AND ELECTROCARDIOGRAPHY SIGNALS Vibhuti Bagga*1, Tanvi Kalra2 , Abhinav3 and Sneh Anand3 1 2 3 Faculty of Science, Jamia Hamdard, New Delhi Department of Biomedical Engineering, Rayat & Bahra Institute of Engineering & BioTechnology, Punjab Centre for Biomedical Engineering, Indian Institute of Technology – Delhi Abstract This paper deals with the development of a USB based dual channel data acquisition system to capture photoplethesmography (PPG) and Electrocardiography (ECG) signals to monitor Pulse Transit Time, Heart Rate Variability and detection of arrhythmias using signal processing algorithm on MATLAB. It can operate with input signal ranging from +/-0.5 V to +/-16V. Using PIC 18F2550 the analog signals were converted to digital value and was plotted using a software was developed on VISUAL BASICS 6.0. Keywords: PPG, ECG, PPT, PIC 18f2550, USB, visual basic 6.0. Introduction Heart rate variability refers to the regulation of the sinoatrial node the natural pacemaker of the heart by the sympathetic and parasympathetic branches of the autonomic nervous system. The beat-to-beat fluctuations in the rhythm of the heart provide an indirect measure of heart health, as defined by the degree of balance in sympathetic and vagus nerve activity. RSA is the natural cycle of arrhythmia that occurs through the influence of breathing on the flow of sympathetic and vagus impulses to the sinoatrial node. HRV is important because it provides a window to observe the heart's ability to respond to normal regulatory impulses that affect its rhythm. Photoplethysmography (PPG) is the electro-optic technique of measuring the cardiovascular pulse wave. This pulse wave is caused by the periodic pulsations of arterial blood volume and is measured by the changing optical absorption which this induces. Pulse Transit Time (PTT) is the time it takes the pulse pressure waveform to propagate through a length of the arterial tree. The pulse pressure waveform results from the ejection of blood from the left ventricle and moves with a velocity much greater than the forward movement of the blood itself. To measure HRV and Pulse transit time ECG and PPG signals need to be measured. The proposed dual channel USB based data acquisition system is capable of acquiring the ECG and PPG signals and plot it on any computer using a user friendly visual basic based plotting software. The small size lends an added advantage of portability. The use of USB 2.0 offers high speed data transfer and plug-n-play capability. METHODOLOGY Parameter measuring module Here a three electrode ECG amplifier is used to measure ECG in lead II configuration. This three leads ECG system includes: 1. 3-Electrode: are placed at Right Arm (RA), Left Arm (LA) & left leg (LL). Hence taking the heart signal from LEAD II of the Einthoven triangle. 2. Pre-amplifier stage: the signal from the RA electrode and LL electrode is buffered & then is pre-amplified (A=5). 3. Differential amplifier: after the amplification, differential output of the signal is taken keeping it in reference with the third electrode (LA). 4. Filter: the signal is then filtered using 2nd order Butterworth band-pass filter allowing the frequency range of 1.2 Hz – 40 Hz to pass. 5. Output stage: the filtered signal is then inverted by putting it on inverting terminal, amplified and output is given with respect to a reference voltage. Acquisition Module: USB At the heart of this acquisition system lies a USB 2.0 compliant PIC 18f2550 microcontroller resulting in a compact unit. The acquisition system is USB driven, which precludes the use of any additional power supply. USB 2.0 with a design data rate of 480 megabits/second [1] facilitates higher speed of data transfer. 18F2550 is capable of executing 12 MIPS, has a 10 bit ADC module with upto 13 – channel multiplexer. It has a wide operating voltage range (2.0V-5.5V). The ECG & PPG signals are transmitted to programmable gain amplifiers well suited to driving ADCs. The gain of the amplifiers can be selected from a range of 1:1-32:1.These programmable gain amplifiers are controlled by the PIC through a simple three wire serial peripheral interface. These amplifiers are designed such that they don’t exhibit phase inversion when input signals exceed the supply voltage. Vref should lie between Vss – Vdd. But these amplifiers accept only positive values which precludes the use of voltage shifting operational amplifier such as LF353 which shifts the input voltage to a 0-5V range. Graphical User Interface The graphical user interface has been developed as a visual basic windows based application. Visual basic offers many features which are useful in designing the graphical plotting software. It reads data from the USB port in bulk and displays it on the monitor. The features include : Two selectable channels No of samples :10-500 selectable time base: 10 us – 1000 ms Data can be stored as a text file and processed as desired. Before acquiring data the acquisition module must be first calibrated also the gain error should be adjusted through the software. The necessary parameters like the channels being used, the number of samples desired, the time base should also be set as per the signal being plotted. The analog input is sampled and digitized by the controllers ADC. A series of commands are given by the software to open the USB lines for reading the digital data and then close data lines once all data has been acquired. All the data so read is stored and displayed together. If needed the signal plotted can be smoothened, averaged and inverted. Discussion The acquisition system and the GUI successfully acquire and plot the ECG signal with clarity and accuracy. This system can be further improved by adding the feature of user selectable acquisition duration so as to display a continuous and dynamic plot as long as the user desires. The various data processing features have to be further added. References 1. VisualECG: a Bluetooth based software for ECG monitoring on personal digital assistants (PDAs) Fernandez, J.; Ruiz, J.; Led, S.; Serrano, L.; Cabeza, R.; Computer Architectures for Machine Perception, 2003 IEEE International Workshop on Digital Object Identifier: 10.1109/ISSMD.2004.1689560 Publication Year: 2004 , Page(s): 57 - 62 2. A fundamental data acquisition saving block Loureiro, C.F.M.; Martins, V.M.G.; Clemencio, F.M.C.; Correia, C.M.B.A.; Nuclear Science Symposium Conference Record, 2005 IEEE Volume: 2 Digital Object Identifier: 10.1109/NSSMIC.2005.1596351 Publication Year: 2005 , Page(s): 685 - 686 3. A preliminary study on the correlation of frequency components between finger PPG and radial arterial BP waveforms Hsin Hsiu; Chia-Liang Hsu; Tsung-Lin Wu; Biomedical and Pharmaceutical Engineering, 2009. ICBPE '09. International Conference on Digital Object Identifier: 10.1109/ICBPE.2009.5384104 Publication Year: 2009 , Page(s): 1 - 4 4. Multichannel Reflective PPG Earpiece Sensor With Passive Motion Cancellation Lei Wang; Lo, B.P.L.; Guang-Zhong Yang; Biomedical Circuits and Systems, IEEE Transactions on Volume: 1 , Issue: 4 Digital Object Identifier: 10.1109/TBCAS.2007.910900 Publication Year: 2007 , Page(s): 235 - 241 5. QT variability and HRV interactions in ECG: quantification and reliability Almeida, R.; Gouveia, S.; Rocha, A.P.; Pueyo, E.; Martinez, J.P.; Laguna, P.; Biomedical Engineering, IEEE Transactions on Volume: 53 , Issue: 7 Digital Object Identifier: 10.1109/TBME.2006.873682 Publication Year: 2006 , Page(s): 1317 - 1329 6. An evaluation of object-based programming with Visual Basic Dukovic, J.M.; Joyce, D.T.; Computers and Communications, 1995. Conference Proceedings of the 1995 IEEE Fourteenth Annual International Phoenix Conference on Digital Object Identifier: 10.1109/PCCC.1995.472470 Publication Year: 1995 , Page(s): 346 - 351 7. Evaluation of arterial compliance on pulse transit time using photoplethysmography Byeong Cheol Choi; Hee Jeong Lee; Soo Young Ye; Dong Keun Jung; Gi Ryon Kim; Kwang Nyon Kim; Gye Rock Jeon; Industrial Electronics Society, 2004. IECON 2004. 30th Annual Conference of IEEE Volume: 3 Digital Object Identifier: 10.1109/IECON.2004.1432329 Publication Year: 2004 , Page(s): 3219 - 3222 Vol. 3