In an normal adult, the ratio of physiological and anatomical dead space is:
**Core Concept**
The question tests the understanding of respiratory physiology, specifically the concepts of anatomical and physiological dead space. Anatomical dead space refers to the volume of the conducting airways, while physiological dead space includes both anatomical dead space and alveoli that are ventilated but not perfused.
**Why the Correct Answer is Right**
The correct answer reflects the normal ratio of anatomical to physiological dead space in an adult. Anatomical dead space is approximately 150 mL, and physiological dead space is about 150 mL (anatomical dead space) + 50-100 mL (alveolar dead space), totaling around 200-250 mL. However, the exact ratio can vary based on the specific volumes, but generally, anatomical dead space is about 70% of the physiological dead space when considering the average values.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it suggests anatomical dead space is significantly larger than physiological dead space, which contradicts the physiological principles.
**Option B:** This option is also incorrect as it overestimates the proportion of anatomical dead space.
**Option D:** This option is incorrect because it implies a much larger anatomical dead space compared to physiological dead space, which is not accurate.
**Clinical Pearl / High-Yield Fact**
Remembering that anatomical dead space is roughly 150 mL in an average adult and that physiological dead space includes both anatomical and alveolar dead space is crucial. This understanding helps in interpreting arterial blood gases and managing respiratory conditions.
**Correct Answer: C. 1:1.35**