MANUAL PHYSIOLOGY PRACTICAL - Repository:The Medical ...

FM/UOJ
Experiment C1
ELECTROCARDIOGRAM
Electrical activities in excitable tissues results in fluctuation in the charges
between different parts of the tissues. These charges cause feeble electrical fields in the
body. When many cells generate electrical fields at the same time in an organized
manner, electrodes placed on the surface of the body will be to pick up the net changes
in the electrical field. These changes when amplified and fed to appropriate recorder, a
meaningful picture is obtained. In this way activities of the skeletal muscles could be
recorded as electromyogram and that of the heart as electrocardiogram activities in the
nerves produce feeble electrical fields and very sensitive instrument are needed to
record their activities.
The electrodes for recording electrocardiogram are of two types. One set is
fitted to the limbs which connect the trunk to the machine at the points of Eintovan’s
triangle. These electrodes record the changes in the electrical field in the sagittal plane
and help to provide zero potential for the unipolar leads. The other is a chest electrode,
which can be moved along the chest and helps to record the changes in the cross
sectional plane.
Instrument:
Electrocardiograph
Demonstration:
Fitting the electrodes
The subject lies comfortably in a bed. The subject is instructed to lie still and to
make no muscular movements. The limb electrodes are wetted by saline for better
contact with skin and secured in place by a rubber strap at the fore arms and legs above
muscle belly. If the skin is hairy the place may have to be shaved to ensure god contact.
The chest electrode is secured to the appropriate place by creating vacuum around the
electrode. When all leads are connected to the electrocardiograph according to the color
code, the necessary connections can be obtained by positioning the appropriate knob.
Recording
The standard setting of the electrocardiograph is to give 10 mm deflection for 1
mV and the paper movement of 25 mm per second. The machine is switched on and
about five beats are recorded with the knob at lead I. Then the knob is turned to lead II.
Lead III, aVR, ave & aVL. The knob is then turned to V which stands for chest leads,
and the chest electrode is placed at the appropriate places on the chest to record V1 to
V6 the tracing is removed and the leads are disconnected.
The biopack system is used to demonstration
Circulation
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