NAUI Diving Physics & Physiology — Questions and Answers

Question 1: What happens to air volume in the lungs as a diver ascends?

Air volume decreases.
Air volume remains the same.
Air volume increases (Correct answer)
Air volume is unaffected by pressure.

Correct answer: Air volume increases

As a diver ascends, the ambient water pressure decreases. According to Boyle's Law, as pressure decreases, the volume of a gas increases, assuming constant temperature. Therefore, the air in a diver's lungs will expand significantly as they rise towards the surface, necessitating continuous exhalation.

Question 2: Which gas law best explains the risk of lung overexpansion during ascent?

Dalton’s Law
Boyle’s Law (Correct answer)
Henry’s Law
Charles’s Law

Correct answer: Boyle’s Law

Boyle's Law states that for a fixed amount of gas at constant temperature, pressure and volume are inversely proportional. As a diver ascends, the external pressure decreases, causing the air in their lungs to expand. If a diver holds their breath, this expansion can lead to severe lung over-expansion injuries.

Question 3: Why is nitrogen narcosis a concern for deep divers?

It increases oxygen intake.
It causes hypothermia.
It impairs cognitive function (Correct answer)
It improves reaction time.

Correct answer: It impairs cognitive function

Nitrogen narcosis is caused by the increased partial pressure of nitrogen at depth, which acts as an anesthetic on the central nervous system. This impairment can lead to symptoms like confusion, poor judgment, euphoria, and reduced motor skills. For deep divers, these cognitive effects can significantly compromise safety and decision-making abilities.

Question 4: Which condition results from rapid ascent without proper decompression?

Oxygen toxicity
Nitrogen narcosis
Decompression sickness (Correct answer)
Carbon monoxide poisoning

Correct answer: Decompression sickness

Decompression sickness (DCS), or 'the bends,' occurs when a diver ascends too quickly, causing dissolved nitrogen in the body's tissues to form bubbles. These bubbles can block blood flow, damage tissues, and cause a range of symptoms from joint pain to paralysis or even death. Proper ascent rates and decompression stops are crucial to prevent DCS.

Question 5: What physiological effect can occur when diving below 100 feet?

Improved vision
Decreased oxygen consumption
Increased metabolism
Greater risk of narcosis and toxicity (Correct answer)

Correct answer: Greater risk of narcosis and toxicity

As divers go deeper, the partial pressures of gases in their breathing mixture increase. This elevated pressure increases the risk of nitrogen narcosis, which impairs judgment, and oxygen toxicity, which can lead to seizures. Both conditions become more pronounced and dangerous at depths below 100 feet, requiring careful gas management.

Question 6: What does Henry’s Law state about gases in liquid?

Gases contract when cooled.
Gases expand with temperature.
Gases dissolve in liquid based on pressure (Correct answer)
Gas solubility is unrelated to pressure.

Correct answer: Gases dissolve in liquid based on pressure

Henry’s Law states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. In diving, this means that as a diver descends and ambient pressure increases, more nitrogen dissolves into their blood and tissues. Conversely, during ascent, as pressure decreases, nitrogen comes out of solution.

Question 7: What is the primary concern of oxygen toxicity in diving?

Muscle cramps
Mild dizziness
Seizures (Correct answer)
Dehydration

Correct answer: Seizures

Oxygen toxicity, specifically Central Nervous System (CNS) oxygen toxicity, is a severe risk when breathing high partial pressures of oxygen at depth. Its most dangerous manifestation is a sudden, uncontrolled seizure, which can lead to loss of regulator, drowning, or other serious accidents underwater. Divers must manage their oxygen exposure carefully to avoid this.

Question 8: How does water pressure affect a diver’s body?

It has no impact.
It decreases metabolism.
It compresses air spaces and increases nitrogen absorption (Correct answer)
It reduces heart rate permanently.

Correct answer: It compresses air spaces and increases nitrogen absorption

Water pressure increases significantly with depth, affecting a diver's body in several ways. It compresses air-filled spaces like ears, sinuses, and lungs, requiring equalization to prevent barotrauma. Additionally, according to Henry's Law, the increased pressure causes more inert gases, primarily nitrogen, to dissolve into the body's tissues, which is a key factor in decompression sickness.

Question 9: What is barotrauma in diving?

Heatstroke during dives
Tissue damage due to pressure differences (Correct answer)
Overhydration
Dehydration

Correct answer: Tissue damage due to pressure differences

Barotrauma refers to physical damage to body tissues caused by a difference in pressure between an air space inside the body and the surrounding fluid or gas. In diving, this commonly affects the ears, sinuses, lungs, or mask space if pressure is not properly equalized during descent or ascent. It can range from mild discomfort to severe injury.

NAUI Diving Physics & Physiology

What happens to air volume in the lungs as a diver ascends?