PADI Dive Physiology and Health 3 — Questions and Answers
Question 1: Oxygen toxicity affecting the central nervous system (CNS) is most likely at partial pressures above:
- 0.21 ATA
- 1.0 ATA
- 1.6 ATA (Correct answer)
- 2.0 ATA
Correct answer: 1.6 ATA
CNS oxygen toxicity risk increases significantly when the partial pressure of oxygen exceeds 1.6 ATA, which can cause convulsions.
Question 2: A diver using enriched air nitrox must calculate the maximum operating depth (MOD) to avoid:
- Nitrogen narcosis
- CNS oxygen toxicity (Correct answer)
- Carbon monoxide poisoning
- Hypercapnia
Correct answer: CNS oxygen toxicity
Higher oxygen fractions in nitrox reach the 1.6 ATA oxygen partial pressure limit at shallower depths, so MOD must be calculated.
Question 3: Which symptom is a warning sign of CNS oxygen toxicity that a diver should recognize?
- Slow heart rate
- Visual disturbances or tunnel vision (Correct answer)
- Increased buoyancy
- Decreased breathing rate
Correct answer: Visual disturbances or tunnel vision
Visual disturbances are among the early CNS oxygen toxicity warning signs remembered by the acronym VENTID-C.
Question 4: Pulmonary oxygen toxicity (the Lorrain Smith effect) results from:
- A single breath of high-pO2 gas
- Prolonged exposure to elevated oxygen partial pressures (Correct answer)
- Rapid descent on oxygen-enriched mixtures
- Breathing pure oxygen at surface only
Correct answer: Prolonged exposure to elevated oxygen partial pressures
Pulmonary oxygen toxicity develops with extended exposure to elevated oxygen and causes lung irritation and reduced vital capacity.
Question 5: Carbon dioxide buildup (hypercapnia) in a diver most commonly results from:
- Breathing too slowly or skip breathing (Correct answer)
- Ascending too rapidly
- Using a full wetsuit
- Diving in cold water
Correct answer: Breathing too slowly or skip breathing
Skip breathing reduces ventilation efficiency, causing CO2 to accumulate in the lungs and bloodstream.
Question 6: Which condition describes insufficient oxygen delivery to body tissues, potentially causing unconsciousness?
- Hypercapnia
- Hypoxia (Correct answer)
- Barotrauma
- Embolism
Correct answer: Hypoxia
Hypoxia is a deficiency of oxygen reaching the tissues, which can lead to blackout, especially in breath-hold diving.
Question 7: A freediver who hyperventilates before a breath-hold dive risks:
- Nitrogen narcosis
- Shallow-water blackout due to hypoxia (Correct answer)
- Increased buoyancy
- Pulmonary barotrauma
Correct answer: Shallow-water blackout due to hypoxia
Hyperventilation lowers CO2 without raising O2, suppressing the urge to breathe and leading to hypoxic blackout before CO2 triggers surfacing.
PADI Dive Physiology and Health 3
Oxygen toxicity affecting the central nervous system (CNS) is most likely at partial pressures above: