In inspiration the intrapleural pressure become: (PGI Dec 2006)
## **Core Concept**
The question tests understanding of the physiological changes in intrapleural pressure during the respiratory cycle, specifically during inspiration. Intrapleural pressure, also known as intrathoracic pressure, is the pressure within the pleural cavity.
## **Why the Correct Answer is Right**
During inspiration, the diaphragm contracts and the rib cage expands. This increase in thoracic volume causes the intrapleural pressure to become more negative (or decrease) compared to atmospheric pressure. This decrease in pressure allows air to flow into the lungs. The correct answer, **C. -0.5 to -1 cm H2O**, reflects this change, indicating that the intrapleural pressure becomes more negative during inspiration to facilitate airflow into the lungs.
## **Why Each Wrong Option is Incorrect**
- **Option A:** . This option suggests that intrapleural pressure becomes positive during inspiration, which is incorrect because a positive pressure would push air out of the lungs, not allow it to enter.
- **Option B:** . This option implies that intrapleural pressure becomes less negative or more positive during inspiration, which does not align with the physiological need for more negative pressure to draw air into the lungs.
- **Option D:** . This option suggests a very slight change towards a more positive or less negative pressure, which does not accurately reflect the significant decrease in pressure needed for inspiration.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that under normal conditions, intrapleural pressure is slightly negative (about -4 mmHg or -0.5 cm H2O) at the end of expiration due to the elastic recoil of the lungs and the outward pull of the chest wall. During inspiration, it becomes even more negative to facilitate lung expansion.
## **Correct Answer:** . -0.5 to -1 cm H2O