DESIGN OF A PHOTOPLETHYSMOGRAPHY BASED PULSE RATE DETECTOR

Transcription

1 DESIGN OF A PHOTOPLETHYSMOGRAPHY BASED PULSE RATE DETECTOR Srijan Banerjee 1, Subhajit Roy 2 1 Department of Electrical Engineering, Siliguri Institute of Technology, 2 Department of Electrical Engineering, Siliguri Institute of Technology, Abstract The proposed device is designed on the principle of Photoplethysmography with infrared LED and photodiode as the basic sensor to sense the pulse beats from the fingertip artery. The pulse signal generated from heart beat is fed to a counter through a timer and relay switching circuit. The counter on receiving signal counts the pulses and gives output digitally. With the device fabricated, some case studies have been made to ensure working of the device and how much the reading obtained from it agrees with the values from a standard monitor. The device is designed to be of low cost by using instruments which are of low cost themselves. Thus it can be used at home by anyone. Also players or athletes can use it at their own convenience to study their physiological conditions. Implementation of various components to design and fabricate the pulse rate detector involves an extensive study on application of instrumentation in biomedical field. Keywords Photoplethysmography, infrared LED I. INTRODUCTION The aim is to design and fabricate low cost, non-invasive pulse rate detector. Pulse rate detection has long been considered to be important in the field of cardiovascular system assessment. Previously, various invasive techniques have been designed to measure pulse rate. But that adds to the discomfort of patient. So, in this case non-invasive methods have proved to be a boon. An approach has been made to design and fabricate a detector that is able to measure the palpation due to flow of blood from fingertip, by a sensor using Photoplethysmography method and correspondingly display output digitally. It is also kept in mind that the device developed is cost effective. Thus with this device fabrication, one is able to study the instrumentation implemented and also further cardiac conditions under different condition can be studied for various person. In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. Pulse is equivalent to measuring the heart rate. The pulse is a decidedly low tech / high yield and antiquated term still useful at the bedside in an age of computational analysis of cardiac performance. However this might not remain same in every individual. Pressure waves generated by the heart in systole moves the arterial walls. Forward movement of blood occurs when the boundaries are pliable and compliant. These properties form enough to create a palpable pressure wave. Pulse rate measurement is one of the very important parameters of the human cardiovascular system. In a way it helps in determining the blood pressure condition of a human also. Pulse rate is also sometimes termed as heart rate. There are various techniques to determine the pulse rate. Numerous methods based on various physical principles were developed to faithfully reproduce the arterial pulse rate. Direct monitoring with an arterial catheter is considered to be the most accurate method but being an invasive procedure it has various disadvantages including patient discomfort, demand of skilled professional and chance of complication. Oscillometric method is a common method to assess automatically in a non-invasive way, but does not provide the wave All Rights Reserved 302

2 II. BLOCK DIAGRAM OF THE DEVICE The block diagram of the optical pulse rate detector is shown in the above figure. The pulse rate is measured from the fingertip. To measure the pulse rate a sensing medium is used. Optical sensor serves that purpose. Infrared (IR) sensor is used as the optical sensor. The technique used is photo plethysmography method. As blood volume through the finger changes with each heartbeat, heart rate can be measured. IR LED and an IR photodiode are placed face to face as in transmission mode. The fingertip is to be placed in between the IR LED and photodiode. The LED and photodiode act as transmitter and receiver combination. Infrared light of wavelength nearly 960nm is emitted from the diode. The diode is connected in forward bias with a current limiting resistor that provides the flow of a regulated current. The value of resistor is chosen so that they produce the maximum amount of light output.ir light falls on the fingertip. Light is absorbed by human soft tissues and thus transmitted to the flowing blood. With change in blood volume due to each heart beat amount of light emitted from diode to the finger is modulated. Thus light is transmitted to photodiode. The intensity of light detected by the photodiode depends on the light modulated by the blood volume. III. DESIGN & FABRICATION A. Design of pulse rate generation All Rights Reserved 303

3 B. Design of Timer & Relay Circuit C. Design of Counter & Display All Rights Reserved 304

4 IV. RESULT & ANALYSIS A. Case 1: To check whether the device is able to detect pulse rate of a person under any condition, pulse rate for 5 different persons where measured using the designed device. Each of the 5 persons where first asked to measure their pulse rate when totally at rest. Next the same people were asked to check for their pulse rate after climbing up and down of 2 floors. The value that was obtained was for 15 seconds. To get the value in bpm the values obtained was multiplied by 4.The result obtained is tabulated below Pulse rate when person under rest (bpm) Pulse rate when person have done some work (bpm) B. Case 2: Pulse rate of five different persons were tested under resting condition once with the fabricated detector and at the same time with a standard pulse rate monitor (BPM-200).The result obtained is shown below from fabricated device (bpm) Pulse rate measured with BPM-200 (bpm) C. Case 3: Pulse rate of five different persons were tested under resting condition once with the fabricated detector and at the same time with the age old method of manual detection still mostly used by doctors and the values are given in the following table; from fabricated device (bpm) with manual method (bpm) All Rights Reserved 305

5 D. Case 4: To check for repeatability of the fabricated device, readings were taken for each of five different persons three times with the same device. The readings are shown in following table. First Time (in bpm) Second Time (in bpm) Third Time (in bpm) V. CONCLUSION Pulse rate detection is a very primary factor in determining a person s health. Various invasive and non-invasive techniques have been utilized in determining pulse rate. But with time non-invasive technique have gained much popularity. Photoplethysmography is a non-invasive method that is incorporated in designing this pulse rate detector. The fabricated pulse rate detector has an optical sensing unit that transmits its electrical output to a digital display unit. The pulse rate detector is of low cost so it can be thought of to be made commercial in future. The readings during case studies are taken for duration of 15 seconds and then multiplied by 4 to get the result in beats per minute(bpm).it is because most doctors prefer taking pulse rate reading for 15 seconds. The design and fabrication of this device involves an extensive study on the application of instrumentation in biomedical science. As biomedical science is developing, hence this work can prove to be a boon in this field. REFERENCES 1. Nitzan, M; Automatic Noninvasive Measurement of Arterial Blood Pressure, IEEE Instrumentation and Measurement magazine, vol. 14, pp , February Roy, R.N; Physiology, Biochemistry, & Biophysics First edition, pp Allen, J; Photoplethysmography and its application in Clinical physiological measurement, Physiological Measurements, vol. 28, 20 th February Zheng, D.C and Zhang, Y.T; A Ring-type Device for the Noninvasive Measurement of Arterial Blood Pressure, Engineering in Medicine and Biology, IEEE 25 th Annual International Conference, vol. 4, pp , September Ibrahim, D; Buruncuk, K; Heart Rate Measurement from the Finger Using a Low-Cost Microcontroller, Near East University, Faculty of Engineering, TRN, Babiker, S.F; Abdel-Khair, L.N; Elbasheer, S.M; Microcontroller Base Heart rate Monitor using Fingertip Sensor University of Khartoum Engineering Journal, vol. 1, pp , October Sur, S and Ghatak, S.K; An Inexpensive Arterial Pressure Wave Sensor and its application in different physiological condition. December, All Rights Reserved 306