NAUI Diving Physics & Physiology 4 — Questions and Answers
Question 1: A diver experiences pain in the ear during descent that stops only when they ascend slightly. What is the most likely cause?
- Outer ear squeeze from a tight hood
- Middle ear barotrauma due to failed equalization (Correct answer)
- Inner ear decompression sickness
- Nitrogen narcosis affecting hearing
Correct answer: Middle ear barotrauma due to failed equalization
Failure to equalize the middle ear during descent causes increasing pressure differential across the eardrum, resulting in pain and potential rupture.
Question 2: Which of the following best describes the term 'residual nitrogen' in dive planning?
- Nitrogen remaining in the tank after a dive
- Excess nitrogen dissolved in tissues from a previous dive (Correct answer)
- Nitrogen that could not be breathed due to depth
- Nitrogen released from tissues during decompression stops
Correct answer: Excess nitrogen dissolved in tissues from a previous dive
Residual nitrogen is the excess dissolved nitrogen that remains in body tissues after a dive that has not yet been eliminated through normal breathing.
Question 3: Hyperventilation before a breath-hold dive is dangerous because it does what?
- Increases blood oxygen to dangerous levels
- Removes CO2, delaying the urge to breathe until hypoxia causes blackout (Correct answer)
- Causes nitrogen to dissolve rapidly into tissue
- Raises blood pressure, risking arterial gas embolism
Correct answer: Removes CO2, delaying the urge to breathe until hypoxia causes blackout
Hyperventilation lowers CO2 levels, which suppresses the breathing reflex, allowing a breath-hold diver to become hypoxic and lose consciousness before feeling the urge to breathe.
Question 4: When using the NAUI dive tables, what does 'surface interval time' (SIT) determine for a repetitive dive?
- The maximum depth allowed on the next dive
- How much residual nitrogen has been eliminated before the next dive (Correct answer)
- The required decompression stop depth
- The total allowable bottom time for the entire dive day
Correct answer: How much residual nitrogen has been eliminated before the next dive
The surface interval allows residual nitrogen to off-gas; the longer the SIT, the lower the repetitive group letter and the more bottom time available on the next dive.
Question 5: What is the effect of increased water density on a diver's buoyancy compared to fresh water?
- Saltwater makes divers less buoyant due to higher resistance
- Saltwater makes divers more buoyant because denser water exerts greater upward force (Correct answer)
- Fresh water and saltwater buoyancy are identical
- Buoyancy is determined only by the diver's weight, not water type
Correct answer: Saltwater makes divers more buoyant because denser water exerts greater upward force
Saltwater (density ~1.025 g/cm³) exerts more upward buoyant force than fresh water (1.0 g/cm³), so divers typically need extra weight when diving in saltwater.
Question 6: Which condition describes a diver who ascends rapidly from a deep dive and develops chest pain, coughing, and shortness of breath?
- Nitrogen narcosis
- Pulmonary over-inflation syndrome (air embolism) (Correct answer)
- Middle ear squeeze
- Carbon monoxide poisoning
Correct answer: Pulmonary over-inflation syndrome (air embolism)
Rapid ascent with breath-holding or airway obstruction can cause lung over-expansion, leading to arterial gas embolism (AGE) with the symptoms described.
Question 7: How does increased depth affect the rate at which a diver's scuba tank is depleted?
- Tank depletion rate stays constant regardless of depth
- Tank depletes slower at depth because pressure compresses the air
- Tank depletes faster because the diver breathes denser, higher-pressure air (Correct answer)
- Tank depletion depends only on the diver's breathing rate, not depth
Correct answer: Tank depletes faster because the diver breathes denser, higher-pressure air
At greater depth, air density increases proportionally with pressure, so each breath consumes more air molecules, depleting the tank proportionally faster.
NAUI Diving Physics & Physiology 4
A diver experiences pain in the ear during descent that stops only when they ascend slightly.
What is the most likely cause?