Phys: Test 3: Lecture 2. Mechanics Of Breathing

Front 1

• Describe what is meant by the lung and chest wall being „elastic‟ structures.

Back 1

o Elastic=resists deformation
 Not easy to stretch it
 Can maintain its original shape

Front 2

• List the muscles that are involved in inspiration in order of importance. Explain why inspiratory muscle contraction produces inspiration.

Back 2

o 1. Diaphragm
 When it contracts, it flattens pushing the margins of the ribs (the chest wall) out
• This increases the volume of the chest cavity
o 2. External intercostals
 Raise the rib
• Increases the volume of the chest cavity
o 3. Accessory muscles
 Scalene
 Sternocliedomasto

Front 3

• List the muscles that are involved in expiration in order of importance.

Back 3

o During quiet breathing
 Relax the inspiratory muscles
 So the lung and chest wall elasticity causes the expiration
o Can be assisted by
 Abdominal muscles
• Increases intra abdominal pressure, pushing the diaphragm back up again
 Internal intercostals
• Lower the ribs
o Lower the chest cavity volume

Front 4

• Explain why the lung typically expands with the chest wall.

Back 4

o There is cohesion between the lung and the chest wall
 This is done by intrapleural fluid (analogous to glass slides, with liquid inbetween)
o Chest wall wants to move outward
o Lungs want to collapse
o This creates a negative pressure in the intraplueral fluid

Front 5

What is the FRC?

Back 5

 Equilibrium of lung in the chest wall
 This is where the pressures are equal and opposite (lung wanting to collapse versus chest wanting to expand)

Front 6

• Explain the movement of lung and chest wall in a pneumothorax.

Back 6

o Get air in the intrapleural space
 Removes negative pressure
• Separates lung and chest wall
o Lungs collapse inward, chest wall moves outward

Front 7

o Transpulmonary pressure

Back 7

 Net pressure acting to distend the lung and the chest wall

Front 8

o TLC

Back 8

total lung capacity

Front 9

o RV

Back 9

 Residual volume
 Minimum volume of the lungs

Front 10

when the distending pressure is zero what does the volume of the chest wall and lungs equal?

Back 10

FRC

Front 11

What is intrapleural pressure at rest? inspiration?

Back 11

rest: -5
insp: -8

Front 12

• Explain the sequence of events resulting in lung inflation

Back 12

expand chest wall
increase volume in chest cavity
reduce pressure in lungs
alveolar pressure becomes less than atmospheric pressure
air moves into lung until the pressure is equal to atmospheric again

Front 13

explain the sequence of events resulting in deflation

Back 13

decrease chest wall
compress gas in lung
increase alveolar pressure greater than atmospheric
gas pushed out of lung

Front 14

during normal inspiration what is the pleural pressure (positive or negative)

Back 14

negative

Front 15

• Explain why measuring lung volumes and capacities can be diagnostic of disease.

Back 15

o Want to know how easy it is for the lungs to inflate/deflate
o If the lungs are too stretchy
 They are very easy to inflate, but the lose their elastic recoil
• So they don’t deflate very easy
o When the lungs are stiff
 It is hard to inflate
 Easy to deflate

Front 16

• Name the lung volumes/capacities that cannot be measured by spirometry.

Back 16

TLC, RV, FRC

Front 17

• Define compliance

Back 17

o Compliance=Change in volume over change in pressure
o Lung compliane is a measure of stiffness that reflexts the extent of elastic recoil

Front 18

• List one disease in which there is increased lung compliance and two conditions where compliance is decreased. Relate these changes in compliance to changes in lung elastic tissue content.

Back 18

o Emphysema
 Increased compliance
 Easy to inflate, less elastic recoil, hard to deflate
 Decreased elasticity
o Fibrosis and Alveolar edema
 Reduced compliance
 Harder to inflate, more elastic recoil, easy to deflate

Front 19

• Describe the changes in lung volumes, FRC, and RV expected with increases and decreases in lung compliance.

Back 19

o With fibrosis
 Lung volume decreased, harder to inflate the lungs (Decreased TLC, FRC, and RV)
o With Emphysema
 Lung volume increased, easier to inflate the lungs (increased TLC, FRC, RV)

Front 20

• What 3 things are lung compliance controlled by?

Back 20

o Elastic tissue (elastin/collagen)
o Surface tension (liquid lining of alveoli)
o Ease of rib movement

Front 21

• Explain why surface tension in the alveoli contributes to lung compliance.

Back 21

o Acts to decrease the surface area of the alveoli
o Harder to inflate the alveoli
o Removal of surface tension makes lungs easier to inflate (increases compliance)

Front 22

• Define „atelectasis‟ and explain how it can be produced by surface tension.

Back 22

o Alveolar collapse
o P=2T/r
o The larger the sphere, the lower the pressure produced by surface tension
o When you have small and large alveoli interconnected
 The small has more surface tension
• The pressure difference causes the small one to collapse
o Then the connected one inflates

Front 23

P=
(consider surface tension)

Back 23

2T/r

Front 24

• Describe the source, chemical nature and effects of surfactant in the lung. Predict the effects of loss of surfactant on lung function.

Back 24

o Type II alveolar cell makes surfactant
 Has hydrophobic regions
• Hydrophobic tail, hydrophilic head inserts in liquid lining
o As the surface area is reduced, the surfactant molecules are pushed together and they repel each other
 This opposes the surface tension
o They reduce surface tension, particularly at low lung volumes

Front 25

• What are the 3 actions of surfactant?

Back 25

o Increases compliance (by reducing surface tension)
o Promote alveolar stability (stops collapse)
o Keeps lungs dry

Front 26

how does surface tension decrease compliance (mechanism)

Back 26

attractive force btw liquid molecules make its surface area as small as possible
-this creates internal pressure by squeezing on the air molecules inside the sphere

Front 27

how does surfactant work to keep the lungs dry?

Back 27

normally surface tension will have a suction effect on a capillary trying to pull water out of it
surfactant lowers this suction of water by decreasing surface tension