Development of a Digital Auscultation Device for real time Murmur Detection
Tanvi Kalra*1, Abhinav2 and Sneh Anand2
1 Department of Biomedical Engineering, Rayat & Bahra Institute of Engineering & Bio-Technology, Punjab
2 Centre for Biomedical Engineering, Indian Institute of Technology – Delhi
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ABSTRACT
This paper deals with the development of a digital auscultation device using a second order butterworth filter to reduce the ambient noise. The system was developed by modifying a traditional stethoscope, an electret microphone and an amplifier circuit. Using audacity software the signal was plotted in real time for detection of murmurs. This low cost system developed provides improved diagnosis of heart sounds (lubb-dup i.e.S1, S2). The system is powered using batteries and hence makes it portable.
Keywords: Digital Auscultation Device, murmur detection, heart sound.
INTRODUCTION
Detection of subtle heart sounds requires a lot of training and doctor learn it over years of practice. Moreover the ambient noise in the hospital results in doctors missing on those few subtle sounds of the heart. For a reliable diagnosis, a portable digital auscultation device has been developed which not only amplifies the heart signal for clear audibility but also removes out ambient noise using second order butterworth filter with frequency range (50-600Hz) for diaphragm mode.
The data is also plotted on a computer in real time for visual interpretation of the signals and visualising and comparing the signals with the previous values. Offline signal processing can also help provide an insight to the signal captured using the device.
METHODOLOGY
For the development of this system integration of the traditional stethoscope, an electret microphone, an amplifier circuit, second order band pass filter and audacity software. Figure 1 shows block diagram of the developed system.
1. Electret microphone – the signal from the stethoscope was picked up through the microphone. The frequency response of the microphone is 30 Hz - 10 KHz.
Figure 1: block diagram of the digital auscultation device
Figure 2: (a) – traditional stethoscope, (b) – hardware circuit, (c) – compatible earphones, (d) – connecting cable, (e) – plotted heart sounds.
2. Amplifier circuit – linear op-amps has been used and the gain of 20 is set to amplify the signal in the pre-amplifier stage.
3. Buffers – buffers are used in between for removing the loading effects.
4. Filters – second order butterworth band pass filter was designed keeping the frequency range from 50 Hz – 600 Hz i.e. the range for diaphragm mode
5. Output – potentiometers are used for volume control and gain control in the respective jack.
· Jack 1 – Audible signal (through earphones)
· Jack 2 – Plotted signal (connector wire to the computer)
6. Software – the software used for the plotting of the signal is AUDACITY that is compatible with the developed system.
Figure 3: heart sounds of healthy and unhealthy subjects
RESULTS AND DISCUSSION
The system developed shows promising results and has proved to be a beneficial device for cardiologists and for various other clinical assessments. An effort is in progress to make the system automated for murmur detection. Figure 3 shows the plot of heart sounds of different subjects.
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