Which of the following statements is not correct?

Options

A. An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure
B. Relaxation of the diaphragm and the intercostal muscles increases the thoracic volume and thereby the pulmonary volume.
C. Intrapleural pressure is always less than intrapulmonary pressure
D. We have the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.

Answer

To determine which of the statements is not correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Analyze the First Statement:**
- The first statement claims that an increase in pulmonary volume decreases intrapulmonary pressure to less than atmospheric pressure.
- This statement is correct because when the volume of the lungs increases during inhalation, the pressure inside the lungs (intrapulmonary pressure) decreases below atmospheric pressure, allowing air to flow into the lungs.

2. **Analyze the Second Statement:**
- The second statement states that relaxation of the diaphragm and intercostal muscles increases thoracic volume and thereby increases pulmonary volume.
- This statement is incorrect. When the diaphragm and intercostal muscles relax, the thoracic cavity volume decreases, which leads to a decrease in pulmonary volume. Therefore, this statement is the one that is not correct.

3. **Analyze the Third Statement:**
- The third statement asserts that intrapulmonary pressure is always less than atmospheric pressure.
- This statement is generally true during inhalation when the lungs expand and the pressure drops below atmospheric pressure, allowing air to flow in.

4. **Analyze the Fourth Statement:**
- The fourth statement mentions the ability to increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.
- This statement is correct. Additional muscles can indeed assist in forceful breathing, enhancing both inspiration and expiration.

### Conclusion:
After analyzing all statements, the second statement is the one that is not correct.

**Final Answer:** The second statement is not correct.

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