1. Authors: Noor Mohammed Dr. M.Z. Hossain Dr. Sumon Saha
11th International Conference on Mechanical Engineering, 2015
Indigenous Development of Auscultatory Method Based Semi Automatic Blood Pressure Monitor
Authors:
Noor Mohammed
Dr. M.Z. Hossain
Dr. Sumon Saha

2. Blood Pressure
The term ‘blood pressure’ refers the arterial blood pressure exerted by the circulating blood upon the walls of blood vessels.
In human body, arterial blood pressure is pulsatile in nature.
During each heartbeat, blood pressure varies between maximum (systolic) and minimum(diastolic) value
11th International Conference on Mechanical Engineering, 2015

3. Blood Pressure
11th International Conference on Mechanical Engineering, 2015

4. Blood Pressure Measurement
Place of measurement: Brachial artery at left upper arm.
Measurement Methods: a) Invasive
b) Non invasive
Non Invasive Methods:
Two popular techniques.
Auscultatory method
Oscillometric method
11th International Conference on Mechanical Engineering, 2015

5. Auscultatory Method
The auscultatory method involves the use of inflatable arm cuff with a stethoscope to listen the Korotkoff sound (a special tapping sound having five phases but not the sounds of heartbeat) during the blood pressure measurement.
11th International Conference on Mechanical Engineering, 2015

6. Auscultatory Method
11th International Conference on Mechanical Engineering, 2015

7. The Proposed BP Monitor
The proposed method is the modified electronic version of the mechanical Auscultatory method.
Device architecture: Divided into two parts
Digital Stethoscope: To listen K-sound
Control and Processing Unit:
11th International Conference on Mechanical Engineering, 2015

8. Measurement Algorithm

9. Control and Processing Unit
The BP Monitor
Control and Processing Unit
Pumping Unit
Power supply
Digital Stethoscope
11th International Conference on Mechanical Engineering, 2015

10. Stethoscope Performance Analysis
Stethoscope circuit output:
Fig.1: Input recorded K- sound
Fig.2: Amplified and Filtered Signal
11th International Conference on Mechanical Engineering, 2015

11. Pressure Sensor Calibration
Sensor Model:
MPXV 5050GP
Fig.3: Calibration curve for the pressure sensor
Calibration result:
Best fitted correlation: E=0.012P+0.196
Sensitivity, S= mv/kPa
11th International Conference on Mechanical Engineering, 2015

12. Result Analysis
Higher error in systolic pressure reading relative to diastolic pressure readings.
Fig.4: Comparison between the standard device value and the designed device value.
11th International Conference on Mechanical Engineering, 2015

13. Limitations of the device
Shows error in detecting the starting phase and the ending phase of K-sound during the measurement which can be evidenced from the errors in the measured pressure readings. This results from the less sensitivity of the microphone to the low sound pressure level(SPL).
The sensor requires periodic calibration as the calibration changes after a certain period of time.
Amplification of the noise hence deteriorates the signal to noise ratio(SNR).
11th International Conference on Mechanical Engineering, 2015

14. Recommendations & Future Scope
A capacitive microphone can be used instead of condenser microphone for better pickup of the low decibel sounds.
A higher order filter is required to improve the signal to noise ratio.
Instead of using single ended amplifier, we can use differential amplifier to remove the common noise results from the 50Hz interference.
A proper shielding is required for the digital stethoscope circuit.
11th International Conference on Mechanical Engineering, 2015

15. A better visualization of the whole method
Fig.5: The pressure graph and the K-sound graph during the measurement (captured using LabTutor data acquisition device). Here Bp reading is 123/78 mm HgP.
11th International Conference on Mechanical Engineering, 2015

16. THANKS QUSETIONS? THE END
11th International Conference on Mechanical Engineering, 2015