Lung mechanics and Ventilation

Question 1

What is ventilation?

Answer 1

The process of inspiration and expiration. It is the physical action of breathing and moving air into and out of the lung.

Question 2

What is respiration?

Answer 2

The cellular level of gaseous exchange

Question 3

What is the tidal volume?

Answer 3

Volume of air entering and leaving the lungs in a single breath during quiet inspiration and expiration.

Question 4

What is Boyle’s Law?

Answer 4

Inverse relationship between pressure and volume of a gas

Question 5

Does quiet expiration involve any muscles?

Answer 5

No

All muscles used for inspiration relax and chest has natural passive recall.

Question 6

What ‘keeps’ the lungs against the chest wall?

Answer 6

PLEURAL SEAL
Pleural fluid found between the visceral and parietal pleura (in intrapleural space) forms the pleural seal between lung and thoracic wall.
This means the lungs expand with the thoracic cavity because of the surface tension.

Question 7

What is the resting expiratory level?

Answer 7

This is when the pressures are in equilibrium. It occurs before you inspire just after having expired.

Question 8

Why is the intrapleural pressure always negative?

Answer 8

Elastic recoil of the lungs pulling visceral pleura inwards and chest wall pulling parietal pleura outwards (opposite directions).

Question 9

What happens if the pleural seal is broken?

Answer 9

The negative pressure in the intrapleural space drains air from outside the chest wall into the space, collapsing the lung.

Question 10

What is residual volume?

Answer 10

The volume of air left in the lungs after forced expiration.

Question 11

What accessory muscles are involved in forced inspiration?

Answer 11

Sternacleidomastoid
Scalene muscles
Serratus anterior
Pectoralis major

Question 12

What accessory muscles are involved in forced expiration?

Answer 12

Internal intercostals

Abdominal wall muscles

Question 13

When is forced expiration and inspiration used?

Answer 13

During exercise but also when diseases affect the lungs

Question 14

What is lung compliance?

Answer 14

The “stretchiness” of the lungs.

The higher the compliance, the easier it is to stretch.

Question 15

What is the compliance of the lungs determined by?

Answer 15

Elastic tissue in lung

Surface tension forces of fluid lining alveoli

Question 16

The alveoli surface are lined by fluid, what effect does this have?

Answer 16

This creates surface tension which limits their expansion.

It does this by decreasing compliance which makes it difficult for the alveoli (and therefore the lungs) to expand.

Question 17

What decreases surface tension created by the fluid? How?

Answer 17

Surfactant secreted by type II pneumocutes has detergent properties so, it acts to disrupt the interactions between fluid molecules on the alveoli surface which reduces the surface tension.

Question 18

What type of alveoli are more effective at disrupting surface tension? Why?

Answer 18

Smaller because the surfactant molecules are closer together they they are more effective at disrupting surface tension of fluid.
This means that the force required to expand a small alveoli is less than required to expand a large alveoli.

Question 19

Other than decreasing surface tension, what else does surfactant do?

Answer 19

It prevents small alveoli collapsing into big alveoli by removing the pressure difference.

Question 20

In whom is there no surfactant?

Answer 20

Premature foetus (Inder 25 weeks)
This is known as respiratory distress syndrome.
Give mum steroids to stimulate it.

Question 21

How do the lungs compensate for high individual resistance in small airways?

Answer 21

Parallel arrangement. (think circuits in physics).
This now means there is highest resistance in the upper respiratory tree and lower in the smaller airways (except when they become compressed during forced expiration)

Question 22

How is air drawn into the airways?

Answer 22

Active expansion of the thoracic cavity which lowers pressure, expands the lungs and causes air to move in.

Question 23

How does the volume of the lungs increase?

Answer 23

Flattening the diaphragm

External intercostals draw ribs up and out

Question 24

How does quiet expiration occur?

Answer 24

Air is expelled from the airways passively by relaxing muscles used in inspiration. This reduced the volume of the thoracic cavity and therefore reduces the volume of the lungs.

Question 25

What are the inspiratory / expiratory reserve volumes?

Answer 25

The maximum amount of air you can breath in / out during forced inspiration / expiration.