Question

What would you expect to happen to the lungs if intrapleural pressure were the same as atmospheric pressure?

a) The lungs would collapse.

b) The lungs would expand.

c) The lungs would maintain their normal volume.

Answer 1

a) The lungs would collapse.

Explanation:

At start of inspiration Intraalveolar pressure is -2.5 mmHg. Inrapleural presssure becomes more negative during inspiration and at the end of inspiration it becomes -6 mmHg i.e more negative. During expiration it returns back to -2.5 mmHg.

when itrapleural pressure becomes equal to atmospheric pressure due to injury to the pleura, its pressure becomes positive and hence it cause more expiratory effect leading to the collapse of the lung.

Mechanics of breathing :

Following three types of pressures are observed in breathing mechanics.
1) Intrapleural pressure:
It is the pressure in the space between lungs and chest wall.
Normally it is negative around - 2.5 mmHg at the start of inspiration.

2) Intra alveolar pressure:
It is the pressure inside the alveoli.
It becomes negative during inspiration resulting in sucking of the air in the lungs and become positive during expiration resulting I exhalation of air out.

3) Transpulmonary pressure :
It is the pressure difference between intra alveolar pressure and Intrapleural pressure.

During inspiration :
- Intra alveolar pressure decreases to - 1 mmHg at the end of inspiration.

- Intrapleural pressure reaches - 6 mmHg at the end of inspiration

- Transpulmonary pressure is highest at the end of normal inspiration

- Air flows into the lungs

During Expiration :

- Intra alveolar pressure increases to + 1 mmHg at the end of expiration.

- Intrapleural pressure reaches the Normal value of -2.5 mmHg

- Air flows out of the lung