Lung mechanics

Question 1

Describe tidal volume. (2)

Answer 1

“Quiet” inspiration and expiration, volume of air moved involuntarily.

Question 2

Describe quiet inspiration and expiration. (4)

Answer 2

Inspiration - air is drawn in my active but unconscious expansion of the thoracic cavity, which lowers pressure, drawing air in.
Expiration - air is pushed out by the passive relaxation of the thoracic cavity, increasing pressure.

Question 3

Describe Boyle’s law. (2)

Answer 3

There’s an inverse relationship between pressure and volume of gas.

Question 4

Describe the resting expiratory level. (5)

Answer 4

The point immediately after expiration - the point of equilibrium. 
Lungs pull inwards - elastic recoil
Chest wall pulls out - elastic recoil
Diaphragm pulls down - passive stretch 
No chest wall movement.

Question 5

Explain how inspiration and expiration can be seen as a disruption of the equilibrium set up in the resting expiratory level. (4)

Answer 5

Inspiration is active because muscles contract to allow chest wall and diaphragm to overcome the pull of the lung recoil
Expiration is passive because muscles stop contracting so the recoil of the lungs in this expanded state overcomes the pull outwards of the chest wall and diaphragm.

Question 6

Explain how lungs remain patent. (4)

Answer 6

Pressure in the pleural space is always negative compared to the atmospheric pressure because the visceral pleura is constantly being pulled in by the lung recoil, and the parietal pleura is always being pulled out by the recoil of the chest wall.
It is always negative but becomes more negative in inspiration due to the decresed recoil of the chest wall and the increased recoil of the lung.

Question 7

Describe residual volume. (2)

Answer 7

The amount of air left in the lungs that can never be expired.

Question 8

Describe total lung capacity. (2)

Answer 8

All of the air that can possibly fit into a lung at any one time. Includes residual volume.

Question 9

Describe vital capacity. (2)

Answer 9

The maximum that can be breathed out after a big breath in. Total lung capacity - residual volume.

Question 10

Describe inpiratory reserve volume. (2)

Answer 10

Extra amount you can breath in following a normal breath in.

Question 11

Describe functional respiratory capacity.(2)

Answer 11

Amount of air in the lungs following a normal breath out.

Question 12

Describe expiratory reserve volume. (2)

Answer 12

Amount you can breath out following a normal breath out.

Question 13

Describe inspiratory capacity. (2)

Answer 13

Max amount you can breathe in following a normal breath out.

Question 14

Describe the direction of the trace on spirometry (2)

Answer 14

Up is inspiration

Down is expiration

Question 15

Describe the compliance of lungs. (4)

Answer 15

Stretchiness
Higher compliance = easier stretch.
Determined by elastic tissue and surface tension.

Question 16

Describe the roles of surfactant. (7)

Answer 16

Disrupt surface tension - in small alveoli, where the surfactant molecules are closer together, good at reducing surface tension. Less good in larger alveoli because molecules further apart.
This prevents smaller alveoli collapsing into big ones - according to LaPlace, smaller alveoli have higher pressure because their radius is smaller so the recoil of the wall is higher as it’s less stretched. Surfactant reducing surface tension overcomes this.

Question 17

Describe the secretion of surfactant. (6)

Answer 17

Secreted by type 2 pneumocytes.
Develops in foetuses at around 25 weeks so can be a cause of respiratory distress in premies - they can’t inflate their lungs from the collapsed state unless intrathoracic pressure drops really far.
Treat mother with steroids when in labour, give surfactant and give O2.

Question 18

Describe the pattern of resistance to air flow in the lungs. (5)

Answer 18

Highest in the bronchi and trachea (trying to force a thick column of air into a smaller tube)
Lowest in the small airways (air enters the larger alveolar space) unless they collapse in forced expiration because they have no cartilage.

Question 19

Describe how the respiratory tract deals with large particles breathed in. (3)

Answer 19

Deposited in mucus layers in nose and swept by the cilia to the oropharynx where it’s swallowed.

Question 20

Describe how the respiratory tract deals with medium sized particles. (3)

Answer 20

Deposited on mucus layer in trachea, bronchi and bronchioles. Waited up to pharynx by cilia and swallowed.

Question 21

Describe how the respiratory tract deals with small particles. (3)

Answer 21

Carried down to alveoli where they’re engulphed by macrophages and removed via the lymphatic system.

Question 22

Describe radial traction. (3)

Answer 22

The pull of the alveolar walls on bronchioles that prevents collapse of bronchioles during expiration.

Question 23

Describe the relationship between compliance and elastic recoil. (3)

Answer 23

Compliance is proportional to the inverse of elastic recoil.
As compliance increases (as it’s more stretchy) elastic recoil decreases (it is less likely to return to its original shape).

Question 24

Describe the interstitium of the lung. (2)

Answer 24

The space between the alveolar membrane and the capillary that contains elastin, collagen, fibroblasts and proteoglycans.

Question 25

Describe the causes, pathophysiology and symptoms of interstitial lung disease. (6)

Answer 25

Causes: occupational (asbestosis), idiopathic, autoimmune
Occurs when injury is chronic or if the repair process is imperfect; causes interstitium to replace healthy tissue making the lungs stiff (reduced compliance), and have increased recoil. These both decrease volume.