CHT CHT Physics & Gas Laws in Hyperbaric Medicine 2 — Questions and Answers
Question 1: Which gas law best explains why middle ear barotrauma occurs during hyperbaric chamber pressurization?
- Henry's Law
- Charles's Law
- Boyle's Law (Correct answer)
- Graham's Law
Correct answer: Boyle's Law
Boyle's Law explains that trapped gas in the middle ear decreases in volume as pressure increases, creating a pressure differential that causes barotrauma if not equalized.
Question 2: The 'oxygen window' in hyperbaric therapy refers to:
- The safe time window for oxygen breathing
- The partial pressure gradient that facilitates inert gas (nitrogen) elimination from tissues (Correct answer)
- The viewing port on a hyperbaric chamber
- The therapeutic range of oxygen concentrations
Correct answer: The partial pressure gradient that facilitates inert gas (nitrogen) elimination from tissues
The oxygen window is the pressure differential created when tissues consume oxygen, replacing it with a gas-free space that accelerates nitrogen elimination without bubble formation.
Question 3: Graham's Law of Diffusion states that lighter gases (lower molecular weight) diffuse:
- More slowly than heavier gases
- At the same rate as heavier gases
- Faster than heavier gases (Correct answer)
- Only under increased pressure
Correct answer: Faster than heavier gases
Graham's Law states diffusion rate is inversely proportional to the square root of molecular weight, so lighter gases like helium diffuse faster than heavier gases like nitrogen.
Question 4: At 3 ATA breathing air (21% O2, 79% N2), the partial pressure of nitrogen is approximately:
- 1800 mmHg (Correct answer)
- 2280 mmHg
- 1520 mmHg
- 760 mmHg
Correct answer: 1800 mmHg
At 3 ATA, total pressure = 3 × 760 = 2280 mmHg; nitrogen partial pressure = 0.79 × 2280 ≈ 1800 mmHg.
Question 5: Charles's Law describes the relationship between gas volume and:
- Pressure at constant temperature
- Temperature at constant pressure (Correct answer)
- Molecular weight and diffusion rate
- Solubility and partial pressure
Correct answer: Temperature at constant pressure
Charles's Law states that at constant pressure, the volume of a gas is directly proportional to its absolute temperature.
Question 6: The partial pressure of oxygen (PO2) at which CNS oxygen toxicity risk significantly increases is above:
- 0.5 ATA
- 1.0 ATA
- 1.6 ATA (Correct answer)
- 3.0 ATA
Correct answer: 1.6 ATA
CNS oxygen toxicity risk increases significantly when PO2 exceeds 1.6 ATA, which is why most therapeutic HBOT protocols are designed to stay at or below this threshold.
CHT CHT Physics & Gas Laws in Hyperbaric Medicine 2
Which gas law best explains why middle ear barotrauma occurs during hyperbaric chamber pressurization?