The pacemaker is a very important structure which functions in producing a rhythmic pattern of action potentials for the generation of a uniform contraction within the heart. Myocardial cells are connected by gap junctions which easily permit action potentials to spread and are thus useful in spreading a signal. There are conducting cells within the heart which are excellent at excitating and conducting system.
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| Figure 18-14 from Rhoades and Pflanzer. | |
| >100 msec delay between atrial muscle depolarization and ventricle muscle depolarization |
system 2 pacemakers show depol.
why construct pacemaker
Pacemaker power consumption
Example: A cardiac pacemaker delivers 5-V pulses of 2 ms duration to bipolar electrodes, which can be approximated as being a 2 k-ohm resistive load. The mean pulse rate of the pacemaker is 70 per minute. The pulses represent 25% of the energy consumed by the pacemaker. The pacemaker is powered by two lithium cells connected in series to give a voltage of 5.6 V. As the designer of this circuit, you are called on to specify a battery capable of operating the pacemaker for 10 years. What is the minimal acceptable capacity for each cell?
ANSWER: The energy per stimulus pulse will be
The number of pulses in 10 years (including 2 leap years) will be
Thus the total energy in these pulses will be
The energy supplied by the battery must be four times as great:
If for the sake of argument (because it would be unwise to draw such a large
current from these cells due to polarization and source resistance effects),
we draw a current of 1 A from the battery, it would be supplying a power of
5.6 W. The period of time over which this power would have to be supplied to
give an energy Eb would then be
Thus the battery capacity must be at least 1.83 A*h, or rounding off, 2 A*h, to operate this pacemaker.
From Medical Instrumentation 2nd Edition, 1995.
