If the defibrillator described in the passage were fully charged and the entire charge were discharged through a patient in 10 ms, which of the following is closest to the average electrical current that would flow through the paddles?
If the defibrillator described in the passage were fully charged and the entire charge were discharged through a patient in 10 ms, which of the following is closest to the average electrical current that would flow through the paddles?
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Transcribed Image Text:The most common cause of sudden cardiac arrest is ventricular
fibrillation, an event in which the heart loses its electrical coordination.
The only known cure for ventricular fibrillation is early defibrillation: a
carefully timed electrical shock to the myocardium.
The principal component of a defibrillator is a capacitor. It is charged by
placing the switch in Position C in Figure 1.
Rinternal
power supply
3000 V
O B. 15 A
O A. 7.5A
OD. 30 A
O C. 22.5 A
Figure 1 Schematic of a defibrillator
The capacitor consists of a pair of metal plates separated by a
dielectric. During defibrillation the switch is placed in Position D,
discharging the capacitor through paddles pressed against the chest of
the patient. Firm force (~100 N) and a conductive gel pad are used to
improve the electrical contact between each paddle and the patient's
chest.
switch
For successful defibrillation the current delivered must be maintained
for several milliseconds. Because the current in an RC circuit decays
rapidly and exponentially, an inductor is added to the circuit to extend
the duration of current flow.
C
Successful defibrillation also depends on the delivery of electrical
charge to the myocardium. Only a fraction of the total current delivered
by the defibrillator flows through the heart. The rest is dissipated by the
resistance of the skin and the rest of the body. The resistances of the
skin and the thoracic wall act as resistances in series, and the
resistance of the other intrathoracic structures acts as a resistance
parallel with that of the myocardium.
D
If the defibrillator described in the passage were fully charged and the
entire charge were discharged through a patient in 10 ms, which of the
following is closest to the average electrical current that would flow
through the paddles?
capacitor
O A. 3600 V
dielectric
25 microfarad
OB. 3500 V
inductor
O C. 3000 V
OD. 2500 V
100 S2
If both the capacitor and the power supply in Figure 1 are adjustable,
which of the following changes would result in an increase in the
charge on the capacitor?
O A. Decreasing the area of the parallel plates
OB. Decreasing the separation between the parallel plates
O C. Removing the dielectric from the capacitor
OD. Decreasing the voltage of the power supply
If the 25 µF capacitor in the defibrillator in Figure 1 is replaced with a 30
μF capacitor, what new power supply setting would produce the same
amount of charge?
pa
pa
im
pa
Based on the passage, which of the following is closest to the pressure
exerted on the chest by a 10 x 5 cm rectangular paddle during
defibrillation?
(Note: 1 Pa = 1 N/m².)
OA. 5 kPa
OB. 10 kPa
O c. 15 kPa
OD. 20 kPa
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