Respiratory Mechanics

Question 1

Relationship between pressure and volume at low lung volumes?

Answer 1

At low lung volumes, it takes a fairly big pressure change to make a small increase in volume

Question 2

What happens once there is some air in the lungs?

Answer 2

Once there is some air in the lungs, a little pressure change produces a large volume change-in other words, it becomes easy to stretch the lungs

Question 3

When the lung gets close to the TLC?

Answer 3

It again becomes difficult to inflate-so a large pressure change produces a small change in volume

Question 4

Compliance of the lungs

• What is it?
• How is it measured?

Answer 4

• Measure of the “stretchability” of the lungs

- (change in volume)/(change in pressure)

Question 5

When is compliance highest?

Answer 5

• The compliance of the lungs is highest in the normal breathing range
• Don’t have to work particularly hard to get a decent Vt

Question 6

What happens to compliance at either extreme (too small or too large)?

Answer 6

Compliance is low-have to work harder to inflate the lungs at low or high volumes

Question 7

Thought question

• What is the compliance of the lungs for the first breath?
• How hard does the baby have to work?

Answer 7

• Prior to the first breath, lung volume is very low, compliance is low, and the effort to breath is high
• With successive breaths, the baby’s lungs inflate and become more compliant, so work decreases

Question 8

Describe the pressure-volume curve of the normal lung and explain the differences observed in inspiration versus expiration
-Respiratory mechanics: pressure and volume relationships

Answer 8

• Something really interesting happens when we allow our lung model to “exhale”-The lung doesn’t deflate the same way it inflated
• Even better, if we inflate the lungs with saline (rather than air), the whole shape changes and the lung mostly deflates the same way it inflated

Question 9

Why is surfactant important?

Answer 9

Alleviates surface tension-reduces tension in the smallest alveoli more than in larger alveoli

Question 10

The difference in the inspiratory and expiratory lines on the graph is mostly due to?

Answer 10

the presence of surfactant

Question 11

Hysteresis

Answer 11

difference between inspiration and expiration

Question 12

It is believed that the hysteresis is due to?

Answer 12

the molecules of surfactant moving one direction during inspiration but coming back a different way

• surfactant is not evenly distributed on the alveolar surface
• small droplets randomly positioned
• if the alveolar volume is small, the droplets are close together and pull apart during inspiration/fuse during expiration

Question 13

The slight hysteresis of the saline filled curve is due to?

Answer 13

the resistance of the tissue sliding over one another

Question 14

Define compliance

-equation?

Answer 14

change in volume/change in pressure

Question 15

What does low compliance mean?

Answer 15

Low stretchability; hard to inflate

(high compliance is the opposite)

Question 16

Compare and contrast the compliance of the lung vs. the rib cage vs. the intact system

• Be able to draw the figure!
• Lungs?

Answer 16

Lungs have lots of elastic fibers so they “want” to get smaller (minimal volume)

Question 17

Rib cage

Answer 17

Due to joint arrangement in body wants to get larger

Question 18

Intact system

Answer 18

The elastic recoil of the lungs and the rib cage exactly counter each other at FRC

Question 19

What happens in a pneumothorax?

Answer 19

The lungs get smaller and the rib cage gets larger

Question 20

Airway resistance equation

Answer 20

R=(8(viscosity)(tube length))/r^4

Question 21

Contraction of bronchial (airway) smooth muscle changes the radius of the airway and therefore?

Answer 21

changes the resistance

Question 22

Forced expiratory volume

Answer 22

• Very helpful in identifying changes in the pulmonary mechanics
• Both the FEV itself (total volume out) and how fast the air can be moved out of the lungs is important

Question 23

FEV1

Answer 23

The amount of air that can be exhaled in the first second is used as one measure of pulmonary function

Question 24

FEV1:FVC

-normal?

Answer 24

about 80% of the FVC is exhaled in the first second of expiration

Question 25

FVC, FEV1, and FEV1:FVC in patients with obstructive disease

-2 obstructive diseases?

Answer 25

• 2 obstructive diseases-asthma and emphysema
• It takes far longer to get air out of the lungs
• The FVC is reduced because the air is trapped
• FEV1 is even more reduced
• FEV1:FVC is below 70%

Question 26

FVC, FEV1, and FEV1:FVC in patients with restrictive disease

-Restrictive disease?

Answer 26

• Interstitial fibrosis
• FVC and FEV1 are both reduced due to inability of the lungs to expand
• FEV1:FVC ratio is higher than normal (>90%) because the elastic recoil of the lungs forces the air out more rapidly

Question 27

Describe the control of airway resistance

Answer 27

Via the smooth muscle and ANS

Question 28

Define interdependence

Answer 28

• The structural stability of the small airways and alveoli depends on all the connecting airways alveoli
• The elastic recoil in one alveolus is countered by the elastic recoil of an alveolus with shared walls

Question 29

Describe how interdependence influences airway resistance

Answer 29

-If you lose the alveolar walls (due to age, smoking, etc) remaining alveoli can collapse during expiration

Question 30

Describe the work of breathing and how it influences normal respiratory processes

Answer 30

• Work is done to overcome the elastic recoil (emphysema) of the lungs or resistance to airflow
• The elastic recoil is the greater effort (bigger area of the curve)

Question 31

Describe the factors that alter the work of breathing

Answer 31

?

Question 32

What happens to air flow as intrapleural pressure becomes more negative?

Answer 32

Air flows into the lungs