1.1 Characteristics of medical data:
Three basic types of data used for analysis in medical care:
Medical data
Alphanumeric
data
Medical
images
Physiological
signals
Alphanumeric data:
Patients details like demographic data: name, address, ID number, etc. clinical data: results
of lab test, clinical previous encounter details and physicians notes. (It also called as CPR-clinical
patient record). These types of data are generally managed and organized into a database using
advanced software systems.
Medical images:
Medical images include X-ray image, CT-scan, MRI and Ultrasound images etc. Image data
are stored either traditionally like in the form of film or digitally for further analysis /storage.
Physiological signals:
Physiological signals like ECG, EEG, EMG etc. are the essential requirements for diagnostic
and therapeutic purpose.
1.2 Medical Instrumentation system
Patient
Sensors
Processor
Controller
Display
Recorder
Network
The above block diagram concentrates on the acquisition and analysis of physiological signals.
 Physiological signals are acquired form the patients
 Sensors / transducers converts physiological signals into its equivalent electrical signals
 Processors used to process the output form the sensor using signal conditioning operations
like amplification, filtering etc. For further processing real time processors are used.
 Controller: processed signal is used for either for open loop (human intervention) or closed
loop control function (automated intervention).
 Display unit: Usually CRT / analog meters are used for the display of processed data.

Recorders: Graph, chart, magnetic tape, disc etc. are used for processed data storage
 Network: Transmission of processed data is achieved using communications modalities.
The above block diagram can be used to describe the medical instrumentation systems like ICU,
cardiac pacemaker etc.
ICU constitutes several sensors, processors and patient monitoring systems. In case of cardiac
pacemakers sensors are electrodes, the processor is usually a specialized integrated circuit, electrical
stimulator as a closed loop controller.
1.3 Medical care system
Collection
of data
Patient
Analysis of
data
Therapy
Decision
making
 Data collection is the starting point in the health care-CPR
 Analysis of data is achieved using signal conditioning circuits and processors.
 Decision making: Analysed data are used for decision making through medical experts or
intelligent systems.
 Proper decision making leads to correct diagnosis and appropriate therapy
1.5 Physiology of heart
 Heart is a four chambered pump with two atria for collection of blood and two ventricles
for pumping the blood.
 The resting or filling phase of cardiac chamber is called diastole, the contracting or
pumping phase is called systole.
1.5.1 The electrical system of the heart
1.4 Electrocardiogram
The ECG is the electrical manifestation of the contractile activity of the heart and can be recorded
using surface electrodes or chest electrodes.
1.5 Genesis of ECG:
 SA node: is the natural pacemaker, triggers its own train of action potentials. The action
potential of the SA node propagates through the rest of the heart, causing a particular
pattern of excitation and contraction.
 P-wave: Amplitude 0.1-0.2 mV and duration 60 to 80 milliseconds. Caused due to the slow
moving depolarization that is contraction of the atria.
 PQ-segment: 60 to 80 milliseconds after P-wave. This delay is at the AV node. This delay
assists in the completion of transfer of blood from the atria to the ventricles.
 The His bundle, the bundle branches, and Purkinge fibres propagate the stimulus to the
ventricles at a very high rate.
 QRS-complex: Amplitude 1 mV and duration 80 milliseconds. A sharp biphase or triphase
wave due to the stimulus that spreads rapidly from the apex of the heart upwards, causing
rapid depolarization (contraction) of ventricles.
 ST-segments: 100 to 120 milliseconds, segment after QRS. Due to the ventricular muscle
cells possess a relatively long action potential.
 T-wave: Amplitude 0.1 to 0.3 mV and duration 120 to 160 milliseconds. Due to
repolarization (relaxation) of ventricles.
Any disturbance in the regular rhythm of the heart is called arrhythmia.
1.6. Standard limb leads
 Three basic systems are used in cardiology.
Figure. Enthoven’s triangle and the axes of the 6 ECG leads formed by using four limb leads
 Most widely used is 12 lead systems

Lead I , II and III

V1 to V6 chest lead

AVL, AVR, AVF augmented leads
 A combined reference known as Wilson’s central terminal is used with the combination of
chest lead.
 The 6th limb leads i.e. lead I, II, III with AVL, AVR, AVF is given a hypothetical equilateral
triangle formed by the limb lead known as Enthoven’s triangle.
 The heart is assumed to be placed at the centre of the triangle i.e. at the Wilson’s center.
 Six leads measure the projections of 3D cardiac vector on to the axis as shown in the
diagram.
Figure of Enthoven’s triangle.
 Lead I, II, III is the potential difference of limbs as indicated.
 Applying KVL,
II-I-III=0
II=I+III
III=II-I
I=II-III
Most of the machines measures I and II to compute III
1.7 Augmented limb lead
Figures 2.11, 2.22 etc.
The figures show the scheme to produce large amplitude signals. In the case of left arm signals
called AVL is measured using the average of the potentials on the other two limbs as a reference.
From the bottom left loop
iR+iR-II=0
iR=II/2 --------(1)
from the bottom right loop
-iR+III+AVL=0
AVL=iR-III ------(2)
Combining equations 1 and 2 gives AVL=(II/2)-III
=(II-2*III)/2
Substituting II=III+I
AVL=(I-II)/2
Similarly AVR and AVF can be derived.
AVR=(III-II)/2
AVF=(II+III)/2
These are the thevenin’s equivalent voltages for the AVR, AVL and AVF.
Even though measurement of two leads is sufficient to get all the three lead measurements, the
physician still needs the appearance of these three leads to facilitate the diagnosis.
1.8. ECG signal characteristics
Between used for 12lead