Download Examples of electric stimulators - O6U E

Therapeutic equipment I
Lecture (5)
Electric stimulator
• A wide variety of electric stimulators is used in
patient care and research.
• They range from very low current such as the
cardiac pacemaker, to high current single
pulse stimulator such as defibrillators.
Examples of electric stimulators
• Cardiac pacemaker
• Bladder stimulator
• Muscle stimulator
• defibrillators
Cardiac pacemaker
• The cardiac pacemaker is an electric
stimulator that produces periodic electric
pulses that are conducted to electrodes
located on the surface of the heart
(epicardium), within the heart muscle ( the
myocardium), or within the cavity of the heart
or the lining of the heart (endocardium).
• The stimulus that conducted to the heart
causes it to contract, this effect can be used in
disease states in which the heart is not
stimulated at a proper rate on its own.
• The principal pathologic conditions in which
cardiac pacemakers are applied are known as
heart block.
Types of cardiac pacemaker
• 1.
Asynchronous/Fixed
Rate.
• 2. Synchronous/Demand.
• 3. Single/Dual Chamber
Sequential (A & V).
• 4.Programmable/nonprogrammable.
Asynchronous pacemaker
• Power supply: provide the energy required for
the operation of the pacemaker.
• Lithium-iodine cell is the current standard battery
• Advantages:
(1) Long life – 4 to 10 years
(2) Output voltage decreases gradually with time
making sudden battery failure unlikely
• The oscillator establishes the pulse rate for the
pacemaker, this in turn, control the pulse
output circuit that provide the stimulating
pulse to the heart.
• This pulse is conducted along lead wires to the
cardiac electrodes.
• Another component of the overall construction
that is the package itself.
• The package should be compatible and well
tolerated by the body.
• It must provide the necessary protection to the
circuit components, where the body is a corrosive
environment, so the package must be designed to
operate well in this environment, while occupying
minimal volume and mass.
• Titanium and stainless steel are frequently used
for the package.
• Timing circuit: The asynchronous pacemaker
represents the simplest kind of pacemaker,
because it provides a train of stimulus pulses
at a constant rate regardless of the
functioning of the heart.
• A free running oscillator is all that is required
for the timing pulse in such a system.
• Output circuit: The pulse output circuit produces
the actual electric stimulus that is applied to the
heart.
• At each trigger from the timing circuit, the output
circuit generates an electric stimulus pulse that
has been optimized for stimulating the
myocardium through the electrode system.
• Constant voltage or constant current amplitude
pulses are the two usual types of stimuli
produced by the output circuit.
• Constant voltage amplitude pulses are typically in
the range of 5.0 to 5.5V with a duration of 500 to
600 micro-sec.
• Constant current amplitude pulses are typically in
a range of 8 to 10 mA with pulse duration ranging
from 1.0 to 1.2 mS.
• Rates for asynchronous pacemaker range from 70
to 90 beats per min. whereas pacemakers that
are not fixed rate typically achieve rates ranging
from 60 to 150 beats per min.
Implantation procedure
• The procedure is usually done
under local anaesthesia
• The pulse generator
implanted under the skin
is
• The leads are inserted using
x-ray control, via a vein found
in this area, and positioned in
the appropriate right sided
heart chamber
• The leads are tested before
the pulse generator is
attached