Biosignal Analysis Part 2
ECE 4923: Mar 14, 2022 (Lec 15)
Last Updated: Mar 13, 2022
Administrative Matters
• Assignment 1 – Due March 25, 2022 (5 pm)
• Lab 3 – Mar 21, 2022
- CircuitLab – registration
• Quiz 2 – Date (Mar 23?) and Syllabus?
• Seminar presentations
- Mar 25 to April 11
- Any no-go days for your team?
• Assignment 2 – will be open this Friday (Mar 18)
2
Quick Recap
• MES> MUAPT> SFAPT
• Innervation point or innervation
zone?
• EMG amplitude measurement –
MAV, RMS
3
Outline (Mar 14, 2022)
• ECG
• Review of Mechanical and electrical
activity
• Clinical ECG- Standard lead configurations
• Diagnosis with ECG
• EEG
•
•
Frequency bands
Diagnosis – Useful indicators and sleep
patterns
• EMG
• Generation of muscle force
• Muscle Force Twitch
• Force and MES estimation of force
4
Autonomic Nerve
Amplitude (mV)
Electrocardiography (ECG)
1
0.5
0
-0.5
1
2
Time (sec)
3
ECG
References:
Chapter 5- Richard Normann, Principles of Bioinstrumentation,
https://ecgwaves.com/topic/ekg-ecg-leads-electrodes-systems-limb-chest-precordial/
5
Let’s recall (1)
• ECG = surface level measurement of the electrical activity of cardiac
muscles.
• Also known as EKG
• Cardiac electrogram – when electrodes are placed on or in the heart
to measure the electrical activity.
• Self excitation property (don’t need a nerve to initiate the firing)
• The muscle fibres fire more or less synchronously
6
Let’s recall (2) – Mechanical activity
Image Source: Saladin, Anatomy and Physiology : Unity of Form and Function, McGraw Hill Publication, 2017
7
Let’s recall (3) – Electrical activity
• Pacemaker cells:
- Those groups of cells that have the ability to pace the heart.
- 3 such groups
- SA node, AV node, Bundle of His & Purkinjee fibres
• Diastole and systole phases (the rest and the active phase)
8
Let’s recall (4) –
Electrical Activity
• Rest phase – atria fill with
blood. There is no electrical
activity.
• 2) The SA node depolarizes
spontaneously, and waves of
depolarization move from the SA
node across the atria – causing a
mechanical contraction pushing the
blood into the ventricles
9
Let’s recall (5) –
Electrical Activity
3) AV node then delays the
depolarization spread to ensure
that the ventricles are filled
4) Purkinjee fibres conduct the
depolarization wave very rapidly –
causing the ventricles to contract
from the bottom upwards.
(Ventricular depolarization)
5) Ventricles repolarize (T wave)
and return to the rest phase.
10
GENERATION OF ECG
Amplitude (mV)
FORMATION OF THE ECG SIGNAL
1
0.5
0
-0.5
1
2
Time (sec)
3
Sources: adapted from Bioelectromagnetism - Principles and Applications of Bioelectric and Biomagnetic Fields by Malmivuo and Plonsey, Oxford University Press, 1995.
11
Clinical Electrocardiography
• Clinicians observe the shape, duration, amplitude, etc of the ECG as
compared to the normal ECG to detect diseases.
• But these parameters all depend on the electrode configuration used
in the measurement. So standard “lead” configurations are used.
• ECG lead – is a graphical description of the electrical activity and is
computed by analysing electrical currents detected by several
electrodes.
12
Standard 12 Lead configuration
• 12 lead display – has 12
curves derived from 10
electrodes that are placed
on standard location.
• 6 leads come from 4
electrodes placed on
the limbs.
• 6 leads come from the
6 electrodes placed on
the chest.
13
Limb Leads
• All the limb leads use the
electrode on the RL to be the
ground electrode.
• Standard electrode leads are
(1) RA – LA
(2) RA – LL
(3) LA - LL
14
Augmented
Limb leads
• Augmented limb leads use stand
limb electrode configuration, but
the electrodes are connected
through resistors to a common
node.
• This decreases the noise level
and increases the size of the
apparent signal.
Image source: https://ecgwaves.com/topic/ekg-ecg-leads-electrodes-systems-limb-chest-precordial/
15
Einthoven's Triangle (1)
• Leads I, II and III form the
original leads constructed by
Wilhelm Einthoven.
• Their spatial orientation forms a
triangle in the chest.
16
Einthoven's Triangle (2)
• Based on Kirchoff’s current law:
𝐿𝑒𝑎𝑑 𝐼 + 𝐿𝑒𝑎𝑑 𝐼𝐼𝐼 = 𝐿𝑒𝑎𝑑 𝐼𝐼
• So we only need information
from two leads to calculate the
exact appearance of the
remaining lead.
17
Einthoven's Triangle (3) – Augmented Leads
𝐿𝑒𝑎𝑑 𝐼 − 𝐿𝑒𝑎𝑑 𝐼𝐼𝐼
𝑎𝑉𝐿 =
2
𝐿𝑒𝑎𝑑 𝐼 + 𝐿𝑒𝑎𝑑 𝐼𝐼
𝑎𝑉𝑅 = −
2
𝐿𝑒𝑎𝑑 𝐼𝐼 + 𝐿𝑒𝑎𝑑 𝐼𝐼𝐼
𝑎𝑉𝐹 =
2
18
Chest Leads
19
Presentation of ECG
20
ECG signal processing specs
• Bandwidth: 0.1 – 100 Hz
• Gains: between 100 to 5000 (usually much smaller than EMG as the
signal is larger)
• CMRR: 100 dB or above
• Input resistance: >100 MΩ
21
Diagnosis with ECG (1)
Hate Rate: 60-100bpm
1 p-wave for each QRS-complex (0.06-0.1 sec)
Normal ECG
Sinus Brachacardia
Sinus Tachacardia
HR<60-100bpm
HR>60-100bpm
Source: figures extracted from http://courses.cs.washington.edu/courses/cse466/13au/pdfs/lectures/ECG_filtering.pdf 2015
Asystole
22
Diagnosis with ECG (2)
Abnormal Ventricular Conditions
Abnormal Atrial Conditions
Ventricular Tachycardia
Atrial Flutter
Sawtooth appearance resulting from
a focused irritation in atria causing
too many but regular P-waves
Regular plateaued appearance
resulting from a focused
irritation in the ventricles
Atrial Fibrillation
Ventricular Fibrillation
chaotic appearance within irregular QRScomplexes resulting from a unfocused
irritation causing fibrillatory atrial
reaction
Chaotic appearance void of QRScomplex resulting from unfocused
irritation in the ventricles causing
fibrillatory ventricular reaction
Source: figures extracted from http://courses.cs.washington.edu/courses/cse466/13au/pdfs/lectures/ECG_filtering.pdf 2015
23
Markers for a Myocardial Infarction
(Aka Heart Attack)
• ECG measurements can carry
tell-tale signs that a heart attack
has taken place, even if the
patients themselves didn’t
notice it.
• The ST segment acts as a marker.
24
Source: figures extracted from immflife.com/Heat-attack.html