Respiratory Mechanics

Question 1

what is lung compliance?

Answer 1

the lung’s ability to stretch
- you can test this via an experiment

Question 2

why is the lung compliance curve important?
what does it tell you?

Answer 2

• using the curve you can use volume and pressure changes to determine compliance
• the slope of the curve is used to compare different people, diseases, etc.

Question 3

how does the lung compliance curve appear normally? with other diseases?

Answer 3

Question 4

what factors help describe why lungs collapse/recoil?

Answer 4

elastic forces and surface forces

Question 5

what causes the lungs to recoil?

Answer 5

1. the lung elastic tissue (elastin and collagen)
2. surface forces (i.e. surface tension)

Question 6

what is surface tension and how does it work in the lungs?

Answer 6

= the force generated in the surface of a liquid at a gas-liquid interface; IMF of cohesion
- molecules of a liquid have attractive forces to each other
- at the surface there is not force opposing the surface so there is a net pull down

Question 7

how does surface tension work in the alveoli?

Answer 7

• there is a thin fluid layer covering the alveoli that have air (gas) internally
• this causes uneven forces pulling at the surface resulting in a net force pulling the fluid inwards
• normally a small force but large SA in the lungs thus making surface tension a big deal

Question 8

what is surfactant? what produces it? what does it do?

Answer 8

= a liquid produced by the lung cells
- produced by type II lung cells
- phospholipids (dipalmitoyl phosphatidylcholine)
- reduces surface tension of lung to 1/10 of the expected value and reduces the work needed for ventilation

Question 9

what is the action of surfactant?

Answer 9

the hydrophilic heads of the phospholipids insert themselves between the hydrophilic liquid and the hydrophobic tails prevent the attraction with the molecules and reduces the surface tension forces

Question 10

lung compliance curve

Answer 10

• requires negative pressure to increase the stretch/expand the lungs (when it fills with air)
• if you decrease the pressure in the lungs = increase in the volume of the lungs (expand)

pressure signs are supposed to be opposite of what they are

Question 11

chest wall compliance curve

Answer 11

• requires force to compress (when you exhale)
• if you decrease the pressure inside the chest wall = you increase the stretch/compliance to allow more volume

the signs of the pressure need to be opposite of what they are

Question 12

describe equilibrium in the chest? what kind of forces or activity?

Answer 12

= at functional reserve capacity because the recoil forces are opposing each other
- FRC = the volume that remains at the end of quiet expiration when there is no muscular activity so you are at equilibrium