Which of the following is listed as a cause of hypoxia in divers?

• A. Hyperventilation before breath holds
• B. Inadequate hydration
• C. Exposure to high pressure only
• D. Eating before diving

Answer: (A)

The key idea here is how breath-hold diving can become hypoxic. When you hyperventilate before holding your breath, you blow off a lot of carbon dioxide, causing hypocapnia. Since the body's main drive to breathe is governed by CO2 levels, this reduces the urge to breathe and lets you hold your breath longer. But the oxygen you’ve inhaled at the start is being used while you’re underwater, so the blood and tissues can become low on oxygen before you feel the need to surface. That mismatch between a delayed urge to breathe and ongoing oxygen consumption is what can lead to hypoxic blackout underwater.

The other options don’t directly cause a drop in oxygen delivery during a breath-hold. Inadequate hydration doesn’t produce hypoxia by itself; exposure to high pressure can cause other issues like nitrogen narcosis or oxygen toxicity depending on the gas mix, not a straightforward hypoxia from lack of oxygen, and eating before diving can cause gastric problems but not a dangerous fall in tissue oxygen.