Lecture 3

Question 1

Electrical hazards

Answer 1

• Current causes phycological effect
• can cause 3 effects
  1. Electrical stimulation of excitable tissue (muscle or nerve)
  2. Resistive heating tissue
  3. Electrical burns or tissue damage

Question 2

Macroshock

Answer 2

When electrical current is applied to two points on the body,

If the current stays within one limb the risk of heart fibrillation is low, even with high current.

The skin naturally resists electricity (like insulation), with resistance ranging from 15,000 ohms to 1 million ohms per cm².

This resistance drops if the skin is damaged

Question 3

Microshock

Answer 3

If a device (like pacemaker ) touches the heart and is insulated everywhere else, it can directly deliver current to the heart.

Even very small currents can cause ventricular fibrillation (a deadly heart rhythm).

To prevent this, the safety limit for microshock (tiny currents affecting the heart) is 10 microamps (μA).

Question 4

Macroshock Hazards Protection

Answer 4

Ground fault + short circuit to metal chassis:

Not grounded chassis → Dangerous

Grounded chassis → Safe

Ground-Fault Circuit Interrupters (GFCIs):

Found in homes, they cut power if a ground fault over 6 mA is detected.
Not used in patient-care areas

Question 5

Microshock hazard protection

Answer 5

Microshock risks come from:

Leakage currents in electrical equipment (safety limit: 10 μA).

Voltage differences between grounded metal surfaces.
How leakage current flows:

Through the ground wire → Safe

Through a patient touching metal equipment while having a grounded catheter → Dangerous.

Through a patient touching the ground while having a catheter → Dangerous.

Microshock can happen if current flows into or out of the heart’s electrical connection.

Question 6

What can be used to protect patients from
microshock?

Answer 6

Electrical isolation using isolation amplifiers
.
Works by break direct electrical contact between input and output signals.

They use separate power sources and grounds on both sides of the isolation barrier.

They consist of:
An instrumentation amplifier at the input ,
A unity-gain isolation stage

They have very high resistance across the isolation barrier, preventing dangerous current flow.

Question 7

FDA Device Classification

Answer 7

Question 8

Medical Device Pathway to US FDA Approval

Answer 8