Diffusion capacity is the volume of gas diffusing

Options

A. Each second for pressure difference of 100 mm Hg
B. Each minute for pressure difference of 1 mm Hg
C. Each minute for pressure difference of 100 mm Hg
D. Each second for pressure difference of 1 mm Hg

Answer

### Step-by-Step Solution:

1. **Understanding Diffusion Capacity**:
- Diffusion capacity refers to the volume of gas that diffuses across a membrane (like the alveolar-capillary membrane in the lungs) under a specific pressure gradient.

2. **Context of Gaseous Exchange**:
- In the respiratory system, diffusion capacity is crucial for the exchange of oxygen and carbon dioxide. Oxygen is absorbed from the air into the bloodstream, while carbon dioxide is expelled from the blood into the alveoli to be exhaled.

3. **Factors Affecting Diffusion**:
- **Concentration Gradient**: Gases move from areas of higher concentration to areas of lower concentration. The greater the difference in concentration (or partial pressure), the faster the rate of diffusion.
- **Solubility of Gases**: The solubility of the gas affects its diffusion rate. For example, carbon dioxide is 20-25 times more soluble than oxygen, which allows it to diffuse more rapidly.
- **Membrane Thickness**: The thinner the membrane through which gases must diffuse, the higher the rate of diffusion. A thicker membrane will slow down the process.

4. **Definition of Diffusion Capacity**:
- The diffusion capacity is defined as the volume of gas that diffuses across a membrane when there is a pressure difference of 1 mmHg. This is measured per minute.

5. **Conclusion**:
- Therefore, diffusion capacity can be summarized as the volume of gas that diffuses across a membrane per minute when there is a pressure gradient of 1 mmHg.

### Final Answer:
The correct definition of diffusion capacity is the volume of gas diffusing across a membrane per minute under a pressure gradient of 1 mmHg.

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