lung mechanics

Question 1

how do lung volumes change in normal lungs, obstructive lungs and restrictive lungs?

Answer 1

obstructive - the flow of air in and out is obstructed and the lungs are operated at higher volumes

restrictive - inflation and deflation of the lungs is restricted
the lungs are operating at lower volumes

Question 2

causes of restriction?

causes of obstruction?

Answer 2

restriction= lung fibrosis, lung disease, obesity, neuromuscular lung disease 
obstruction= COPD, emphysema, asthma

Question 3

what structures are involved in the mechanics of ventilation?

Answer 3

• chest wall, lungs,

- small pressure changes to either structure initiates as large change in volume

Question 4

how does tidal breathing happen the with alveoli?

Answer 4

• flow changes due to changes we make to the alveolar pressure
• when chest wall rises we create a negative intrapleural pressure so the air flows in
• when the alveoli fill up they return to equilibrium so no pressure difference
• ## At expiration, the chest falls and positive pressure is created which forces the air out

Question 5

** show a graph for tidal breathing with alveoli?

Answer 5

**

Question 6

what are the structural properties of the lung tissue?

Answer 6

• compliance = tendency to distort under pressure

- elastance = tendency to recoil to original shape

Question 7

compare fluid filled lungs to air filled lungs?

Answer 7

• fluid filled lungs are more complaint than air filled lungs
• there is a small amount of water lining the lungs
• the air water interface exhibits surface tension where as the fluid water interface does not exhibit surface tension
• without surfactant the inflation requires much more work

Question 8

*** show a graph comparing volume and pressure in fluid filled lungs and air filled lungs

Question 9

what is surface tension?

Answer 9

the tendency for water molecules to attract

Question 10

why is water tension important in lungs?

Answer 10

♣ The water molecules at the surface have no balancing force on one side which causes a surface tension.
♣ Water molecules are more distributed around the outside.
♣ On the inside, the water attracts to each side which means if the alveoli recoils too much, it will collapse.
♣ With just water, the alveoli could collapse easily with the great inward force but surfactant is secreted to reduce this force and make the alveoli more complaint.

Question 11

what is surfactant produced by?

Answer 11

Produced by TYPE 2 pneumocytes

Question 12

what is surfactant composed of?

Answer 12

-Composed of 80% phospholipid, 10% non-polar lipid and 10% protein.

Question 13

what does surfactant do?

Answer 13

Acts to increase compliance (reduce surface tension), prevent collapse and reduce ‘work of breathing’

Question 14

how does resistance change further down the birfurcations of the lungs?

Answer 14

• you would think that with each generation the resistance would increase but actually the resistance increases because there are so many airways therefore lots of cross sectional area

Question 15

what is conductance ?

Answer 15

this is how well the airways allow the air to pass through

Question 16

how does conductance change with lung

Answer 16

• Conductance steadily increases with increasing lung volume (as resistance decreases – as you breathe in, your airways expand).

Question 17

what is the flow in collapsible tube?

Answer 17

The SMALL airways are not supported by cartilage, only the large airways are

Question 18

what is patency?

Answer 18

whether the airways are open and active and able to conduct air

Question 19

what is the pressure in pre inspiratory lungs?

Answer 19

• the transmural pressure is positive and the airways is patent - this continues throughout inspiration

Question 20

what happens if you do forced expiration?

Answer 20

• ♣ then there is a massive increase in intrapleural pressure from the forces due to the chest muscles and abdominal muscles pleural pressure may exceed internal pressure which may shut the airway.