Which of the following volume of capacity of lungs
can't be measured directly by the spirometer?

Options

A. Residual volume
B. Functional residual capacity
C. Total capacity
D. All of these

Answer

To determine which volume or capacity of the lungs cannot be measured directly by a spirometer, we need to analyze the options provided:

1. **Understanding the Spirometer**:
- A spirometer is a device used to measure the volume of air inhaled and exhaled by the lungs. It can measure various lung volumes and capacities, but not all.

2. **Identifying the Options**:
- **Residual Volume (RV)**: This is the volume of air remaining in the lungs after a forceful expiration. It cannot be measured by a spirometer because it represents the air that is always present in the lungs, even after exhalation.
- **Functional Residual Capacity (FRC)**: This is the volume of air remaining in the lungs after a normal expiration. It is a combination of residual volume and expiratory reserve volume. Since it includes residual volume, it also cannot be measured directly by a spirometer.
- **Total Capacity (TC)**: This is the total volume of air the lungs can hold, which includes all volumes (tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume). Since it includes residual volume, it cannot be measured directly by a spirometer either.
- **All of These**: This option suggests that all the previous volumes (RV, FRC, TC) cannot be measured directly by a spirometer.

3. **Conclusion**:
- Since the spirometer cannot measure residual volume, functional residual capacity, or total capacity directly, the correct answer is **"All of These."**

### Steps Summary:
1. Define what a spirometer is and its function.
2. Analyze each option (RV, FRC, TC) to see if they can be measured by a spirometer.
3. Conclude that all the mentioned volumes cannot be measured directly by a spirometer.