biomedical instrumentation - description

Biomedical Engineering

1. Electrocardiogram

3. Anatomy and function of heart
•Systole (1,1,1,1,1
•Diastole (1,1,1,1,1
•Specialized conduction system of heart (1,
•SA node (1,1,1,1
•AV node (1,
•Purkinje (1,1
•Anastomosing
•Intercalated disk
•Myofibrils (1
•Functional syncytium
•-85mV
•150V/s
•200ms to 300ms (1,
•Electrical systole (1,
•Electrical diastole (1,
•Isochronous excitation
•Myocardium (1,1,1
•Endocardium (1,1

4. Anatomy and function of heart

6. Electrical activity from various regions of the heart

7. Activation of human heart

8. Electrical conduction of the heart
•https://www.youtube.com/watch?v=fZT9vlbL2uA
•https://www.youtube.com/watch?v=v3b-YhZmQu8
•https://www.youtube.com/watch?v=kwLbSx9BNbU&t=
73s
•https://www.youtube.com/watch?v=MTqzDu_YL24

9. Cardiac Generator

10. Cardiac vector
•Dipole – a vector of magnitude M, directed from negative charge to positive charge-
cardiac vector
•Combination of several electrodes through a resistive network - lead
If a2 is perpendicular to M, then the component of a2 along the direction of M is zero
•We need two leads with different lead vectors, both of which lie in the same plane as a1 and
a2 we can describe M

11. Einthoven triangle - Bipolar and Unipolar
KVL for three leads
I – II + III = 0

12. ElectroCardioGram

13. ECG WAVEFORM

14. Einthoven and first ECG

15. Einthoven Triangle

16. Types of Leads
•Coronal plane (Limb Leads)
–Bipolar limb leads
•Lead I
•Lead II
•Lead III
–Unipolar leads or augmented limb leads
•aVR
•aVF
•aVL
–Unipolar Chest leads
•V1 – V6

20. Unipolar chest leads - V1 — V6 (Chest Leads)

21. Measurements
Detection criterion for QRS is based upon QRS height,
QRS duration, QRS offset, QRS polarity and R-to-R
interval

22. Block diagram
•The paper recording speed is 25 mm/s
•The sensitivity of an electrocardiograph is typically set at 10 mm/mV

23. Biopotential amplifiers
To increase the amplitude of a weak electric signal of biological origin
The basic requirements that a biopotential amplifier has to
satisfy are:
• The physiological process to be monitored should not be influenced in any
way by the amplifier
• The measured signal should not be distorted.
• The amplifier should provide the best possible separation of signal and
interferences
• Amplifier has to offer protection of the patient from any hazard of electrical
shock
• Amplifier itself has to be protected against damages that might result from
high input voltages as they occur during the application of defibrillators or
electrosurgical instrumentation

24. Biopotential Amplifiers
Typical bio-amp requirements
•High input impedance - greater than 10 M ohms
•Safety: protect the organism being studied
•careful design to prevent electrical shocks
•Isolation and protection circuitry to limit the current through the electrode
to safe level
•Output impedance of the amplifier should be low to drive any external load
with minimal distortion
•Biopotential are typically less than a millivolt (1 mV)
•Most biopotential amplifiers are differential
•Gain greater than 1000
•Signals are recorded using a bipolar electrodes
•High common mode rejection ratio
•Rapid calibration of the amplifier in laboratory conditions
•Adjustable gains

25. Isolated amplifier
•Filter usually has a cut off frequency higher than 10 kHz.
•Isolation of the patient circuit is obtained using a low capacitance transformer
whose primary winding is driven from a 100 kHz oscillator.
•The transformer secondary is used to obtain an isolated power supply of ±6V

26. • Patient’s right leg tied to the output of an auxiliary amp
• Common mode voltage on body sensed by averaging resistors, Ra’s, fed back to right leg
• Provide negative feedback to reduce common mode voltage
• If high voltage appears between the patient and the ground, the auxiliary amplifier
effectively un-grounds the patient to stop the current flow
Driven Right leg circuit

27. 12-Lead system

28. Cardiac arrhythmias
•Ecotopic beats – other than SA node
•Idioventricular rhythm – independent
ventricle (30 to 45bpm)
• First-degree heart block – His bundle
not completely interrupted (P-R
prolonged)
• Second-degree heart block – 2:1 or
3:1 block
•Wenckebach period (prolonged P-R
interval, where next beat might be
absent)
•Ischemic – deficient blood supply

30. Vector cardiograph
•Vectorcardiography is the technique of analyzing the electrical
activity of the heart by obtaining ECG’s along three axes at right
angles to one another and displaying any two of these ECGs as a
vector dis axesplay on an X-Y oscilloscope.
•Vectorcardiogram displays the electrical events simultaneously in
two perpendicular.
•This gives a vectorial representation of the distribution of electrical
potentials generated by the heart, and produces loop type patterns
on the CRT screen
•Direction of depolarization and repolarization of the atria and the
ventricles.

31. •Each vectorcardiogram exhibits three loops, showing the vector
orientation of the P wave, the QRS axis and the T wave.
•Because of the high amplitude associated with QRS, loops from the
QRS complex predominate.
•An increase in horizontal and vertical deflection sensitivities is
normally required to adequately display the loops resulting from the
P wave and T wave.
•Atrial and ventricular hypertrophy, myocardial infarction, multiple
infarctions in the presence of fascicular and bundle branch blocks