Preliminary communication
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An Internet-based blood pressure monitoring system for patients Ishak Bin Aris*, A A E Wagie*, Norman Bin Mariun* and A B E Jammal{ *Department of Electrical and Electronic Engineering, University Putra Malaysia; { Faculty of Medicine and Health Sciences, University Putra Malaysia, Selangor, Malaysia
Summary We developed a personal blood pressure monitoring system for patients with hypertension or hypotension. The system can be used to measure a patient’s blood pressure at home and to transmit the data automatically to a hospital database via the Internet. The accuracy of blood pressure readings using the system was assessed by comparison with readings from a standard digital sphygmomanometer in four subjects. The measurement error for the systolic readings was 1.7–2.7% and for the diastolic readings 2.7–3.2%. The system therefore appears to be a promising means of assessing blood pressure remotely.
Introduction
............................................................................... Telemedicine enables the electronic transfer of medical data (e.g. images, sounds, text) by one of several means, such as the Internet, an intranet, satellite links or the telephone network. The Internet represents an almost ubiquitous communications system and recent advances in Web-browser technology have made it a major communications tool. For example, the World Wide Web can now be used as a telemedicine communications channel1 . With it, a computer running standard, low-cost applications can send and receive medical information from almost anywhere in the world2 . Hypertension and hypotension are common diseases in Malaysia, as elsewhere. If not treated, they predispose the patient to more serious conditions, such as heart disease and stroke. Regular blood pressure monitoring at home can be helpful in the management of these diseases. The data can be used to evaluate the patient’s condition and to indicate the need for treatment. Systolic blood pressure is the peak pressure while the heart is contracting. The diastolic reading
Accepted 24 September 2000 Correspondence: Dr Ishak Bin Aris, Department of Electrical and Electronic Engineering, Faculty of Engineering, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia (Fax: +603 8948 8939; Email:
[email protected])
Journal of Telemedicine and Telecare 2001; 7: 51–53
represents the blood pressure when the heart is resting between beats. For example, 122/76 mmHg indicates that the systolic reading is 122 mmHg (162 hPa) and the diastolic reading is 76 mmHg (101 hPa). A blood pressure reading of less than 140/90 is considered normal for adults, while anything above this is high3,4. A number of surgical (invasive) and non-surgical (non-invasive) methods can be used to measure blood pressure, with various degrees of accuracy and suitability for the clinical situation. The invasive catheterization technique is not suitable for measuring blood pressure generally5 and non-invasive methods are normally preferred4,6–9. We have therefore developed an Internet-based blood pressure monitoring system for measuring patients’ blood pressure regularly at home.
Methods
............................................................................... The system consisted of both hardware and software components. Blood pressure was measured with an automatic sphygmomanometer. An eight-bit serial interfacing card was developed to link the output of the blood pressure monitoring device with a PC. As shown in Fig 1, the hardware parts of the interfacing card included an analogue/digital (A/D) converter (ADC0804), a universal asynchronous receiver transmitter (CDP6402), a clock generator (74HC4060)
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Internet-based blood pressure monitoring
Fig 1 Block diagram of the serial interface card.
and an RS232 converter (MAX232). Only three lines were required for data transfer. The first line received data, the second line transmitted data and the third was a common line. The crystal used in the card operated at 2.4576 MHz. The clock generator was used to provide 2400 bit/s and 9600 bit/s baud rates. The latter was used to synchronize the data transfer in both the hardware and software. The 2400 bit/s rate was used to trigger the A/D converter as the start signal.
Website The system homepage, with both text and graphics, was created using HTML (Fig 2). It had eight links information on diseases related to blood pressure, the patient’s background/medical history, blood pressure data, diagnosis, questions and answers, system manual, patient’s opinions and background of the designers. Details of the patient’s name, number, age, date, blood pressure reading and diagnosis were recorded in the system.
Fig 2 The system homepage.
Procedure The system was tested on four subjects aged 24–30 years. All patients gave informed consent. The patient measured his/her blood pressure at home using the automatic sphygmomanometer. The measurements were taken during the day at room temperature, with the subject seated on a chair with legs and ankles uncrossed, and back supported, as shown in Fig 3. The method of measurement was:
Fig 3 A subject measuring his blood pressure.
to be slipped under. The bottom edge of the cuff was 2.5 cm above the elbow.
(1) the patient rested for 3–5 min before measurement; (2) the arm was placed on a table at the same level as the heart; (3) the cuff was wrapped around the bare upper arm, fitting snugly with just enough room for a fingertip
The cuff was then inflated automatically to occlude the brachial artery and the pressure slowly released the system recorded the pressure automatically and
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displayed it at all times. The blood pressure signal was displayed as a waveform on the PC screen and transferred to the hospital database via the Internet. The measurements from the Internet-based system were compared with those from a digital blood pressure device (HEM-704C, Omron, Tokyo, Japan).
Results
............................................................................... Fig 4 shows a blood pressure reading of 140/70 mmHg from one of the subjects using the system. Fig 5 shows a blood pressure reading of 115/65 mmHg from a different subject. From Table 1, it can be observed that the measurement error for the systolic readings of the four subjects was 1.7–2.7%, while for the diastolic readings it was 2.7–3.2%.
Fig 4 Blood pressure reading of 140/70 mmHg from one of the subjects.
Discussion
............................................................................... The comparison results show that the computed error when using the proposed system lay within the range of the standard error of the HEM-704C Omron blood pressure monitor, which was used as the reference10 . The system was easy to operate and offered userfriendly features such as pop-up menus and a graphical user interface. The system is therefore likely to be a convenient tool for regular blood pressure monitoring at home.
Acknowledgement: We thank University Putra Malaysia for providing nancial support to this project.
References 1 Nagata H, Mizushima H. A remote collaboration system for telemedicine using the Internet. Journal of Telemedicine and Telecare 1998;4:89–94 2 Barrett JE, Brecht RM. Historical context of telemedicine. In: Viegas SF, Dunn K, eds. Telemedicine: Practising in the Information Age. New York: Lippincott-Raven, 1998: 9–15 3 American Heart Association. Fighting heart disease and stroke. High blood pressure. http://www.americanheart.org 4 Drzewiecki GM, Hood R, Apple H. Theory of the oscillometric maximum and the systolic and diastolic detection ratios. Annals of Biomedical Engineering 1994;22:88–96 5 Geddes J, Voels M, Combs C, Reiner D. Characterisation of the oscillometric method for indirect blood pressure. Annals of Biomedical Engineering 1983;10:271–80 6 Webster JG. Medical Instrumentation Application and Design. 3rd edn. New York: Wiley, 1998
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Fig 5 Blood pressure reading of 115/65 mmHg from a different subject.
Table 1 Blood pressure readings from the reference sphygmomanometer and the system’s monitoring screen Subject’s age (years)
Reference reading (mmHg)
Monitor screen reading (mmHg)
Systolic/diastolic measurement error (%)
30 29 27 24
143/72 117/67 113/62 109/62
140/70 115/65 110/60 107/60
2.1/2.7 1.7/2.9 2.7/3.2 1.8/3.2
7 Drzewiecki G. Noninvasive assessment of arterial blood pressure and mechanics. In: Bronzino J, ed. Biomedical Engineering Handbook. Hartford, CN: IEEE Press, 1989: 65–98 8 Drzewiecki G, Pilla JJ. Noninvasive measurement of the human brachial artery pressure–area relation in collapse and hypertension. Annals of Biomedical Engineering 1998;26:965–74 9 Bondmass M, Bolger N, Castro G, Avitall B. The effect of home monitoring and telemanagement on blood pressure control among African Americans. Telemedicine Journal 2000;6:15–23 10 Omron Corporation. Automatic Blood Pressure Monitor: Instruction Manual HEM704C. Tokyo, 1998
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