Static Mechanics of Breathing

Question 1

What are the static mechanics of breathing?

Answer 1

mechanical properties of the lung that influence gas flow but which are independent of volume change

Question 2

What are the static properties of the lung?

Answer 2

elasticity
compliance
surface tension

Question 3

What does the pleural sac do?

Answer 3

links elastic forces in the chest wall and lung

Question 4

What happens when you apply muscular effort to change the chest cavity volume?

Answer 4

the link means that the lung volume changes and the intra-alveolar pressure changes

Question 5

How much pleural fluid is usually circulating?

Answer 5

15ml

Question 6

What does elastin in the alveoli cause?

Answer 6

inward collapsing forces - elastic recoil

Question 7

What opposes the elastic recoil?

Answer 7

the opposing outward expanding elastic recoil of the ribs

Question 8

What does the balance of the ribs and recoil cause?

Answer 8

a sub-atmospheric intrapleural pressure

Question 9

What kind of pressure keeps the lung inflated?

Answer 9

-ve pressure

positive causes lung to collapse

Question 10

What happens during inhalation?

Answer 10

Ppl decreases pulling Palv down and air into the lung

Question 11

What causes Palv to restabalise?

Answer 11

Lung volume increasing

Question 12

What causes exhalation?

Answer 12

Ppl increases causing Palv to increase and thus exhale

Question 13

What is the equation for compliance?

Answer 13

C=Delta V/Delta P

Question 14

What is significant about a lung with high compliance?

Answer 14

it is easily distended

Question 15

What is significant about a lung with low compliance?

Answer 15

it is difficult to distend

Question 16

What does lung compliance vary inversely with?

Answer 16

lung elasticity

Question 17

What is a normal compliance?

Answer 17

0.2L/cmH2O

Question 18

What is a high compliance and what disease might it come with?

Answer 18

0.4L/cmH2O

emphysema

Question 19

What is a low compliance and what is a typical disease with this?

Answer 19

0.1L/cmH2O

fibrosis

Question 20

What is pulmonary compliance and elastic recoil produced by?

Answer 20

Elastin connective fibres

Alveolar surface tension

Question 21

What does the surface tension do?

Answer 21

tries to collapse the lung

Question 22

What causes surface tension?

Answer 22

molecules at the surface trying to have more interactions

Question 23

What is the effect of greater surface tension on compliance?

Answer 23

less compliant

Question 24

What is the effect of surface tension in the alveolus?

Answer 24

resists stretch
tends to become smaller
tends to recoil after stretch

Question 25

What is hysteresis?

Answer 25

the difference between inflation and deflation because a greater Ptp is required to open the airway

Question 26

What is significant about smaller alveoli?

Answer 26

they have a much higher surface tension which would mean a variation in alveolar size would cause collapsing

Question 27

What does pulmonary surfactant do?

Answer 27

stabalises the alveolar structure by reducing the surface tension

Question 28

How does pulmonary surfactant reduce the surface tension?

Answer 28

decreasing the density of water molecules at the air-water interface

Question 29

What is pulmonary surfactant made of?

Answer 29

dipalmitoyl phosphatidyl choline packaged around surfactant proteins

Question 30

Which cells secrete pulmonary surfactant?

Answer 30

type II alveolar epithelial cells

Question 31

What is the effect of pulmonary surfactant?

Answer 31

prevents collaps of alveoli during lung expansion | reduces pressure required to inflate lungs

Question 32

What happens in a rapidly expanding alveolus?

Answer 32

increase in size reduces density of surfactant molecules allowing surface tension and elastic recoil to brake the expansion

Question 33

What happens to surfactant when r falls?

Answer 33

surfactant molecules crowd together stabalising the alveolus

Question 34

What is Laplaces law?

Answer 34

P = 2xsurface tension/radius of bubble