Which statement correctly identifies the Deficient physiological zone (10,000-50,000 ft) with the corresponding pressure range?

Which statement correctly identifies the Deficient physiological zone (10,000-50,000 ft) with the corresponding pressure range?

• A. Efficient: 0-10,000 ft; 760-523 mmHg
• B. Deficient: 10,000-50,000 ft; 523-87 mmHg
• C. Space Equivalent: >50,000 ft
• D. Marginal zone: 7,000-12,000 ft; 640-520 mmHg

Answer: (B)

At altitude, atmospheric pressure falls, which lowers the partial pressure of inspired oxygen. To help pilots and students remember how the body handles this, environmental physiology describes zones by altitude and surrounding pressure. The Efficient zone runs from sea level up to about 10,000 feet, with pressures from 760 down to roughly 523 mmHg, where oxygen delivery is generally adequate without extra aid. The Deficient zone spans about 10,000 to 50,000 feet and corresponds to pressures from roughly 523 down to 87 mmHg, where the reduced ambient pressure leads to insufficient oxygen delivery for normal metabolism without supplemental oxygen or pressurization. Above about 50,000 feet is the Space Equivalent, with extremely low pressure, requiring life support systems. A Marginal zone sits around 7,000 to 12,000 feet with pressures roughly 640 to 520 mmHg, representing a transitional range. Therefore, the statement assigning the Deficient zone to 10,000–50,000 feet and 523–87 mmHg is the correct pairing.

At altitude, atmospheric pressure falls, which lowers the partial pressure of inspired oxygen. To help pilots and students remember how the body handles this, environmental physiology describes zones by altitude and surrounding pressure. The Efficient zone runs from sea level up to about 10,000 feet, with pressures from 760 down to roughly 523 mmHg, where oxygen delivery is generally adequate without extra aid. The Deficient zone spans about 10,000 to 50,000 feet and corresponds to pressures from roughly 523 down to 87 mmHg, where the reduced ambient pressure leads to insufficient oxygen delivery for normal metabolism without supplemental oxygen or pressurization. Above about 50,000 feet is the Space Equivalent, with extremely low pressure, requiring life support systems. A Marginal zone sits around 7,000 to 12,000 feet with pressures roughly 640 to 520 mmHg, representing a transitional range. Therefore, the statement assigning the Deficient zone to 10,000–50,000 feet and 523–87 mmHg is the correct pairing.