New Approaches for Continuous Non Invasive Blood Pressure Monitoring Petr Zurek, Martin Cerny, Michal Prauzek, Ondrej Krejcar, and Marek Penhaker VSB – Technical University Ostrava, Faculty of Electrical Engineering and Computer Science, Biomedical Engineering Laboratory, Ostrava, Czech Republic
Abstract— The article is focused on two new approaches for non invasive blood pressure monitoring. There are discussed and in tested two possibilities for this measurement. The first one is system with NIR CCD camera (Near Infra Red), which measure the wide changes of the blood vessels and the second one is system, which measure the pulse transmit time (PTT). The results from laboratory test are discussed in this article too.
special high power Infra Led Diodes, two power converters, USB digitizer with 10 bits RGB A/D converter and measurement device (PDA or desktop station) (Fig 2). Camera is applied to patients hand with opposite applied three high power Led Diodes, which screen the patients hand with infra red light. Both these elements are powered by special developed power converters with high power.
Keywords— Continuous Blood Pressure, Non Invasive Measurement, NIR Camera, Pulse Transmit Time.
I. INTRODUCTION By the help of hemoglobin (in blood) is possible to take a pictures or video sequences of bloodstream from hands where the vessels are dark and the rest of scene is brighter. Such images are possible to get by NIR CCD camera which is a standard small size color PAL camera with a spectrum of sensing near infra red. Firstly the video sequence is obtained throw the camera to a mobile device (PDA, MDA, XDA), standard PC or notebook PC. These stations are used to analyze a video sequence and detect a heart rate and a blood pressure. Video signal from camera to client stations is transferred wirelessly by WiFi standard (802.11b,g). Due to a limited performance of mobile devices the blood pressure is not visualized, but only an actual number is displayed to user. The second chance, how to measure the continuous cuff less, noninvasive blood pressure is to detect this value from the information about pulse transmit time (PTT). The PTT is time which informs us, how fast the volume change (wave) is expanding in the blood vessels (Fig. 1). This time will be change with the blood pressure change too. Theoretically when the blood pressure will be growing, the PPT will be shorter respectively. Of course there are some others variables, which can affect the PTT (elasticity of vessels etc.). A. NIR CCD System Measurement scheme consist of one NIR CCD camera with two circles of small power Infra Led Diodes, three
Fig. 1
Pulse transmit time derivated from ECG and PPG (photopletysmography on finger) signals
II. DEVELOPED SYSTEMS Measurement schema continues from camera wirelessly throw WiFi network to special USB digitizer which is equipped by high speed 10 bits RGB A/D converter. Finally the desktop station is placed at the end of measurement schema or the mobile device is used. The most power PDA HTC Touch HD is actually used in tests with sufficient results. During our project the software to analyze and measure the vessels width was created in Microsoft Visual Studio 2005.
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Table 1 Test with classical blood pressure device and our measurement solution. Value are in [mm Hg]
Fig. 2
Vessel selection for realize width measurement
Software has a two function modes: First case is Image Enhance, from menu Mode. This mode is for creating of image adjustment sequence to measure a vessels width. This solution was selected to offer a maximal variability for input image source. Our application has embedded a many of different adjustment filter to offer a large variability to user for creation an own convolution filter which is able to store in program. By this our software is possible to use as an simple image editor. Second mode - Vein Measure allow to user setup and run a multiple image adjustment and vessels width measurement by selected process. In this mode is important to select a part of image to realize a vessels width measure. This is due to a fact that more than one vessel is exist on image. Resulting width is displayed to output window and stored in database file for future use. Experiments Our first tests were executed on a group of five university students. The aim of test results was expected as a percentage of successful rates of blood pressure diagnosis and quality of measurement in compare to classical blood pressure devices. We start every test with measurement of blood pressure on classical blood pressure device to get a starting value of blood pressure. This start value is an input value for our noninvasive blood pressure software. After a successful synchronization of starting value, the continual blood pressure measurement was realized for a period of 10 minutes (This time is a minimum period between two measurements on classical blood pressure device). After 10 minutes period the second – final comparative measurement was executed and the results was recorded. All these results are summarized in [Table 1].
Persone no.
Start pressure
continuous measurement time from start [min] 0 5 10
Final Pressure
1 2 3 4 5
86 75 82 78 67
86 75 82 78 67
82 74 76 82 75
84 73 80 80 71
83 72 79 81 72
Behind the Scenes – Code Implementation Our software uses standard .Net Framework libraries like System.Drawing.Imaging, System.IO and System.Text.RegularExpressions. Software is developed in Microsoft Visual Studio. The most important part of software is image processing. Working with pixels is possible by SetPixel and GetPixel methods. Unfortunately these methods are very slow and we suggest using a direct memory access by help of unsafe code. To access bitmap pixels is necessary to lock them in memory by LockBits method. This method expect as argument a class instance Rectangle – bitmap part for locking and System.Drawing.Imaging.ImageLockMode enumeration type. The last argument is System.Drawing.Imaging.PixelFormat enumeration type which defines a color depth of bitmap. Vessel width measure is realized by simple function which counts pixels white color on given y-axis. For required accuracy of width the rotation of image is needed. The vessel must be a vertically to direction of measurement. This is done automatically by Get_angle(Bitmap b) which compute a angel of slope against to y-axis. Next function rotateImage(Bitmap b, float angle) realize the turning of image as it is needed. A. PTT System For the research in this area we developed the special measurement system. This system is unique at that, that it can measure different biosignals in one time synchronous. This system consists of the basic sensors for measure biosignals. These sensors are connected to the biosignal amplifier (g.tec - BSAmp). This amplifier is connected to A/D convertor (NI- DAQpad 6052), which is connected wia FireWire with PC. For our research we measure the main biosignals as ECG (g.tec - ECGbox), photoplethysmography (g.tec – g.Pulse). Other measured biosignals are capacity wave (piezosensor ADInstrument MTL1010 and special measuring system with bhv5355) and breathing curve (ADInstrutments - pneumotrace). The last but not least biosignal is continuous invasive blood pressure. This system is prepared for measuring the continuous invasive blood pressure – we are prepared to connect this system with the
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Nihon Kohde monitor. This is very important signal, which we can measure synchronous with other biosignals. Then we can really exactly compare our intended blood pressure (compute with PTT using) and real blood pressure in the time. The most emphasis was take to testing and verification of the alternate synchronization of all sensors and measuring. Software for the synchronious measuring of differerent biosignals, which we use for computing the pulse transmit time and other value for blood pressure computing, was made in the Matlab software. The big emphasis was take on possibility to set the parameters of the signal processing, as sample rate, possibility to set the filtration parameters for each channel separately. This is very important, because each channel process different biosignal, which has different frequency parameters. That is why we must set each channel separately based on processing signal. Emphasis was taken on the lucidity and simplicity of user interface too. At once was designed algorithm for the detecting the important parts (points) of the biosignals and determination of their together correlation in the time. For the detection of the important points we used and tested the derivation principle, or the wave transformations. All this measuring system is in the testing process just now. We are preparing this system for the quality measuring of biosignals. Than we can determine exact blood pressure.
III. DISCUSSION Noninvasive cuff less continuous blood pressure measurement will be very useful. For example for monitoring blood pressure of the peoples, who has some problems with heart or arterial system (hypertension, people after heart attack). In this time this people use standard blood pressure monitor – they have cuff on their arm, which is filling with air with adjusted delay. It can be very uncomfortable especially during the night. Also it is not really continuous measurement. If we replace this with some other system, which will be with passive sensors, it will be more comfortable for the patient and also for the doctors. Also it can be use in homecare systems for old peoples, or for peoples with some handicap, where we need to monitor their life functions. Indeed we can employ system for blood pressure monitoring with for example ECG and actimetry monitoring for peoples, who are working in dangerous environment (fire brigade, soldiers). System could detect some changes in health of this people and precede weightier problems.
Fig. 3
User inerface of system for measuring different biosignals
IV. CONCLUSION The largest software part for NIR CCD is tuned and program is well functioned. Unfortunately the visualization and measure part would be more extend on practical needs and performance possibilities. The mobile devices like PDA withhold such possibilities so they exist only in limited version in compare to desktop client version. These limitations are not found as a majority problem and our solution is possible to use. Our first tests results are very good and give to us a positive feedback for future works. The PPT system is testing process and tuning process just now. In the near future we would like to measure first official data – in the main the data with the synchronous invasive blood pressure. Then we can find out mutual biosignals coherence and define finally algorithm between biosignals parameters (PTT) and blood pressure. This solution can be very useful for investigation, where we need not only the blood pressure, but also ECG or some other biosignal, because we have not too measure the blood pressure separately, but we could compute it from other these biosignals. Of course after testing and tuning this system we will develop small mobile system, which will be able to measure the biosignal, analyze them, compute the blood pressure and save this information, or send it to some wireless docking, or supervisory station. In near future we plan to use our solution in cryogenic room where temperature is going down by -142OC. In such
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cases is continuous blood pressure very important for physicians and other medical staffs.
ACKNOWLEDGMENT The work and the contribution were supported by the project Grant Agency of Czech Republic – GAČR 102/08/1429 “Safety and security of networked embedded system applications”. Also supported by the Ministry of Education of the Czech Republic under Project 1M0567.
REFERENCES 1. Krejcar, O., Fojcik, P.(2008) Biotelemetric system architecture for patients and physicians – solutions not only for homecare, In Portable 2008, 2nd IEEE International Interdisciplinary Conference on Portable Information Devices, Ga-Pa, Germany 2. Cerny M., Penhaker M. (2008) Biotelemetry In conference proceedings 14th Nordic-Baltic Conference an Biomedical Engineering and Medical Physics, JUN 16-20, 2008 Riga, LATVIA, Volume: 20 Pages: 405-408 Published: 2008, ISSN: 1680-0737, ISBN: 978-3-54069366-6 3. Černý, M. (2009) Movement Monitoring in the HomeCare System . In IFMBE proceddings. Ed. Dossel-Schleger, Berlin:Springer, 2009, issue. 25, ISBN 978-3-642-03897-6; ISSN 1680-07
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4. Krejcar, O., (2006) “PDPT framework - Building information system with wireless connected mobile devices”, In Icinco 2006, 3rd International Conference on Informatics in Control, Automation and Robotics, Insticc Press, Setubal, Portugal, pp. 162-167 5. Krejcar, O., Janckulik, D., Motalova, L., (2009) “Complex Biomedical System with Mobile Clients”. In The World Congress on Medical Physics and Biomedical Engineering 2009, WC 2009, September 0712, 2009 Munich, Germany. IFMBE Proceedings, Vol. 25/5. O. Dössel, W. C. Schlegel, (Eds.). Springer, Heidelberg. 6. Penhaker, M., Cerny, M., Martinak, L., Spisak, J., Valkova, A., (2006) “HomeCare - Smart embedded biotelemetry system”, In World Congress on Medical Physics and Biomedical Engineering, Vol 14, PTS 16, Aug 27-Sep 01, pp. 711-714, Seoul, South Korea 7. Penhaker M., Cerny M., Martinak L., et al. HomeCare (2006) - Smart embedded biotelemetry systém In Book Series IFMBE proceedings World Congress on Medical Physics and Biomedical Engineering, AUG 27-SEP 01, Seoul, SOUTH KOREA, Volume: 14 Pages: 711714, 2007, ISSN: 1680-0737, ISBN: 978-3-540-36839-7 8. Peterek, T., Žůrek, P., Augustynek, M., Penhaker, M. (2009) Global courseware for visualization and processing biosignals, In World Congress 2009. Sept 7. – 12. in Munich, ISBN 978-3-642-03897-6, ISSN 1680-0737 Author: Institute: Street: City: Country: Email:
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Petr Zurek VSB – Technical University of Ostrava 17. listopadu 15 Ostrava Czech Republic
[email protected]
