Anatomy of chest wall and mechanics of breathing

Question 1

Describe the anatomy of the pleural sac

Answer 1

The visceral pleura membrane coats the outer surface of the lung
The parietal pleural membrane coats the inner surface of the ribs
Pleural fluid lies between the membranes
Lungs are effectively stuck to the movements of the rib cage

Question 2

What is Pneumothorax?

Answer 2

At rest: the lung and rib cage are coupled, elastic recoil of the chest wall pulls it outwards, while the lung is pulled inwards
If the rib cage is penetrated by a knife, air moves inwards, uncouples the lung and rib cage and lung collapses

Question 3

What muscles are used during inspiration?

Answer 3

External intercostal muscles, sternocleidomastoids, scalene and the diaphragm

Question 4

What muscles are used during expiration?

Answer 4

Expiration is passive at rest, uses internal intercostal muscles and abdominal muscles during severe respiratory load

Question 5

Describe inspiration

Answer 5

The diaphragm contracts (pulls downwards to abdomen), which increases thoracic volume, decreases pressure and forces gas into the lungs.

Question 6

Describe expiration

Answer 6

The diaphragm relaxes (into thorax), which decreases thoracic volume, increases pressure and forces air out of the lungs

Question 7

Describe the pathophysiology of asthma

Answer 7

Asthma - over reactive constriction of bronchial smooth muscle - increasing resistance and making expiration difficult.

Question 8

What is Intra-thoracic (Alveolar) Pressure (PA)?

Answer 8

Pressure inside the thoracic cavity (in the lungs), may be -ve or +ve compared to atmospheric pressure

Question 9

What is Intra-pleural Pressure (Pip)?

Answer 9

Pressure inside the pleural cavity - always -ve

Question 10

What is Transpulmonary pressure (PT)?

Answer 10

The difference between the alveolar pressure and intra-pleural pressure - always +ve