CABT Biomedical Equipment Technology & Function 3 — Questions and Answers
Question 1: During preventive maintenance on a hospital bed, which electrical safety test measures the current that could flow through a patient touching the bed frame and a grounded surface?
- Dielectric strength test
- Chassis leakage current test (Correct answer)
- Ground resistance test
- Insulation resistance test
Correct answer: Chassis leakage current test
Chassis leakage current testing measures current flowing from the equipment chassis to ground, simulating the shock hazard a patient could experience.
Question 2: An anesthesia machine's low-pressure system includes all of the following EXCEPT:
- Flowmeters
- Vaporizer
- Pressure-reducing regulators (Correct answer)
- Breathing circuit
Correct answer: Pressure-reducing regulators
Pressure-reducing regulators are part of the intermediate-pressure system; the low-pressure system begins after the flowmeters and includes the vaporizer and breathing circuit.
Question 3: A transcutaneous electrical nerve stimulator (TENS) unit is contraindicated for placement over which area?
- Lower back for chronic pain
- Carotid sinus area of the neck (Correct answer)
- Knee joint for arthritis
- Shoulder for rotator cuff pain
Correct answer: Carotid sinus area of the neck
TENS electrode placement over the carotid sinus can trigger vagal reflexes, causing bradycardia or hypotension and is therefore strictly contraindicated.
Question 4: In a phototherapy unit used for neonatal jaundice, the therapeutic parameter that should be verified during PM is:
- Output voltage of the ballast
- Irradiance measured in µW/cm²/nm (Correct answer)
- Ambient room temperature under the unit
- Reflective hood surface area
Correct answer: Irradiance measured in µW/cm²/nm
Irradiance (spectral power output) determines the effectiveness of bilirubin photo-isomerization; it must meet clinical thresholds (typically ≥30 µW/cm²/nm) to be therapeutic.
Question 5: Which gas is used as the primary pneumatic drive gas in most hospital ventilators and why?
- Oxygen, because it enriches the delivered FiO2
- Air or oxygen at 50 psi, because it provides consistent driving pressure for bellows or pistons (Correct answer)
- Nitrogen, because it is inert and low-cost
- Helium, because of its low density and reduced work of breathing
Correct answer: Air or oxygen at 50 psi, because it provides consistent driving pressure for bellows or pistons
Hospital ventilators use 50 psi compressed air or oxygen as a pneumatic drive source because this pressure reliably actuates pneumatic valves and drives bellows or pistons.
Question 6: A Doppler ultrasound flow detector operates on the principle that:
- Sound reflects off stationary tissue at a fixed frequency
- Moving red blood cells shift the frequency of reflected ultrasound proportional to their velocity (Correct answer)
- Electrical impedance changes as blood flows through a vessel
- Pressure differentials across a stenosis generate a characteristic waveform
Correct answer: Moving red blood cells shift the frequency of reflected ultrasound proportional to their velocity
The Doppler effect causes the frequency of ultrasound reflected from moving erythrocytes to shift up or down relative to flow direction, allowing velocity calculation.
Question 7: When calibrating an invasive blood pressure transducer, zeroing the transducer at the level of the phlebostatic axis compensates for:
- Electrical offset in the Wheatstone bridge
- Hydrostatic pressure error due to fluid column height (Correct answer)
- Catheter tip resonance artifact
- Damping coefficient variation
Correct answer: Hydrostatic pressure error due to fluid column height
Zeroing at the phlebostatic axis eliminates hydrostatic pressure added by or subtracted from the fluid column between the transducer and the patient's heart.
CABT Biomedical Equipment Technology & Function 3
During preventive maintenance on a hospital bed, which electrical safety test measures the current that could flow through a patient touching the bed frame and a grounded surface?