Download electro myogram

The electro myogram (EMG):
The electrical signals from muscles .
EMG electrodes :
Record the electrical activity of the muscle .
1. Surface electrode :
attached to the skin and measures the signals from
many motor unit (Muscle ).
2. Concentric needle electrode :
3. inserted under the skin and measures single motor
unit activity .
The electrocardiogram :
The electrical signals from the heart .
The human heart :
- The rhythmical action of the heart is controlled by
an electrical signal initiated by spontaneous
stimulation of special muscle cells located in the
right atrium .
- SA node ( pacemaker ) sinoatrial node 72 times /
min .  electrical signal from SA node  initiates
the depolarization of the nerves and muscles of both
atria  countrad and pump blood into ventricles 
repolazation of the atria follows . The signal theu
passes into atrioventricular (AV) node , which
initiates the depolarization of the both ventricles 
pump the blood into pulmonary and general
circulations .
- The action potential in the wall of the heart . The
action potential moving down the wall of the heart ,
some of the ion current , indicated by the circles ,
passes through the torso( electrical conductor)
indicated by the resistor in fig (1) .
The potential on the chest wall is due to current
flow through the resistance of the torso .
- The relationship between the pumping action of the
heart and the electrical potentials on the skin .
This relation comes from fig (1) and :- The potential distribution for the entire heart when
the ventricles are one half depolarized is shown by
the equipotential lines in fig (2) .
- The potential on the surface of the body depend
upon the location of the electrodes .
- The form of the potential lines is the same as that
obtained form an electric dipole .
- The equipotential lines in the heart's cycle can also
be represented by electric dipoles .
- The dipoles for different moments in the cycle
would differ in the size and orientation .
- The electrical ( Cardiac ) potential on the body's
surface is the instantaneous projection of the electric
dipole vector in a particular direction .
- As , vector changes with time , fig (3) shows an
electric dipole vector along with the three
electrocardiographic body planes .
1. frontal planes .
2. Transverse plane
3. Sagittal plane .
The measuring electrode :
The surface electrode : The surface electrodes for
obtaining the ECG in frontal plane .
A. The three limb leads : Fig (4) :
1. Lead I :
Measurment5 of potential between
RA & LA
(RA = right arm , LA = Left arm)
2. Lead II :
measurement of potential between
RA & LL
LL = Left Leg
3. Lead III
measurement of potential between LA & LL
Fig. (4) electrical connections for Lead I , II , III the
usual polarities of the recording instrument are indicated
for each lead .
Lead I , II , III are called standard limb leads the
potential between two gives the relative amplitude and
direction of the electric dipole vector in the frontal plane.
B. Three augmented lead configurations :
Three leads in frontal plane :
1. a VR Lead , one side of the recorder is connected to
RA and the other side is connected to the center of
two resistor connected to LL and LA . Fig (5).
2. a VL lead , the recorders is attached to the LA and
the resistors are connected to RA & LL .
3. a VF lead , the recorder is attached to the LL
electrode and the resistors are connected to RA &
LA .
The surface electrode for obtaining ECG in
transverse plane :Six transverse plane ECGS ( V1,V2 , V3 , V4 , V5 ,
V6 ) , the negative terminal of the ECG recorder is
attached to an indifferent electrode at the center point of
three resistors connected to RA , LL and LA and the
other electrode is moved across the chest wall to the six
different positions .
The typical ECG from lead II position :
Cardiologist , who can determine the patterns of the
(ECG) signals are normal or arrhthmias .
- The arrhythmias  rhythm disturbances exist in the
ECG signals [ heart block ].
- ECG is monitored and displayed on the CRT of an
oscilloscope .
- Typical ECG from Lead II
P= represens the atrial depolarization and contraction .
QRS – complex wave , the ventricular depolarization .
S-T : ventricular contraction .
T = The ventricular repolarization .
Heart rate :
The reciprocal of interval time between two R-wave
in the ECG signals .
If R1 at t1 = 0.5 sec
Ra at t2 = 1.5 sec.
t = t2 – t1 = 1.0 (S) Sec
H. rate =1 / Δt = 1 / 1sec = 60 beats / min .
Normal heart  SA node  76 beat /min.
If SA node signed is not conducted into the
ventricle , then a pulse from AV node will control the H.
beat at frequency of 30 to 50 beats/min .
Abnormal heart :
Using artificial pacemaker .
The Ein thoven triangle :
- If the heart is changing its state of polarization ,
then at each instant in time the sume of all of the
currents can be represented by a single dipole vector
through the center of the heart .
- Consider an instant in which the heart is
depolarizing the muscle fibers are contracting .
- Schematic of electric dipole vector projected on the
frontal plane , the three electrodes ( KA , LA and
LL) can be thought of as the points of a triangle ,
the Enithoven triangle .
- Einthoven triangle showing the projection of an
instantaneous heart dipole vector on the three legs
of an equilateral triangle .
From this triangle :
1. The potential in Lead I proportional  to the
projection of dipole vector on the line RA – LA .
2. The potential in Lead II  to the projection of the
electric dipole vector on the line RA –LL .
3. The potential in Lead III  to the projection of the
dipole vector on the line LA – LL .
- These are induced electric field due to the dipole ,
and the voltmeter connected between the head and
tail of any of the projections on the triangle legs
will indicate a potential difference .
- Voltmeters in I and III are connected with negative
and positive terminal together .
- The connections of II are reversed with the – Ve
terminal of II connected to –Ve terminal of I and
the +Ve of II connected to +Ve of III.
- If RA is –Ve with respect to the LL  VII is +Ve .
- If LA is the +Ve with respect to the LL  VIII is
+Ve .
- From the triangle :
VI = VL - VR
VII = VR – VF , VIII = VF - VL
Where VL = potential at left area .
VR = potential at right area .
VF = potential at LL (foot ).
Since I , II and III connect points on an equi
potential surface their sum must be zero .
I + II + III = zero
= (VL – VR) + (VR – VF) + (VF – VL) = 0
II = I + III [ because of the reversal of the leads of
voltmeter II].