pk 3 - Lung Mechanics - Surfactant & Resistance

Question 1

The distending pressure is generated by the ……… ……… forces of the lungs and chest wall - and the …….. determines volume at any given distending pressure

Answer 1

elastic recoil

compliance

Question 2

What determines the elastic properties of the lung? x2

Answer 2

• surface tension (65-70%)

- composition of tissues and its shape

Question 3

What determines the compliance of the chest wall?

Answer 3

• inherent rigidity and shape

Question 4

The chest wall compliance depends on rigidity of the thoracic cage and on its shape. This is decreased by conditions such as…

Answer 4

arthritic spondylitis or kyphoscoliosis

spasticity or rigidity of thoracic or abdominal musculature

Question 5

True or False? There are no diseases associated with an increase in chest wall compliance

Answer 5

True

Question 6

Surface tension is a …………… force that must be overcome when the lungs are ……………..

Answer 6

collapsing

inflated

Question 7

Smaller bubbles must have a greater internal pressure to keep them inflated and overcome the surface tension. Why can different size alveoli coexist in the lung? Which Law explains this?

Answer 7

alveoli interdependence, the tendency for one to collapse is prevented by the tendency for others not to collapse
Laplace’s Law

Question 8

What calculations prove that it can’t just be normal interstitial fluid lining the lungs?

Answer 8

calculations using an air interstitial fluid interface in the lungs show a very high surface tensions, reducing compliance significantly and making breathing difficult, if not impossible

Question 9

By how much does surfactant decrease surface tension?

Answer 9

10x

Question 10

What is surfactant made up of?

Answer 10

45% = DPPC (phospholipid)
45% = other phospholipids
10% = proteins, cholesterols and trace amounts of other substances

Question 11

Which compound present in surfactant is responsible for lowering surface tension? By which cells is this secreted?

Answer 11

DPPC

alveolar Type II epithelial cells

Question 12

The presence of a natural surface-acting detergent (…………..) acts to reduce ………….. ………….. and so …………. lung compliance

Answer 12

surfactant
surface tension
compliance

Question 13

What is DPPC?

How does it act?

Answer 13

dipalmitoyl phophatidylcholine
palmitate is hydrophobic, phosphate and choline are hydrophilic.
DPPC molecules line the air liquid interface.
They reduce surface tension by preventing water molecules coming into contact with the air liquid interface

Question 14

As surface area is reduced, the surface tension lowering effects of surfactant …………… .
Area dependent effect - the smaller the radius, the …… the density of DPPC and thus the ……. surface tension lowering effect.
This is the mechanism underlying the ………. observed when lugs are fully inflated and then deflated.

Answer 14

increases

greater
greater

hysteresis

Question 15

What is hysteresis?

Answer 15

If you inflated the lung and measure pressure-volume the curve moves on a different trajectory to when you deflate the lung.

Question 16

Give examples of disease/s that increase lung compliance?

Give examples of disease/s that decrease lung compliance?

Answer 16

emphysema

pulmonary fibrosis, congestion, RDS

Question 17

Infant Respiratory Distress Syndrome:

1. Why does a foetus not require surfactant?
2. At what gestation does surfactant appear?
3. What are the main factors that cause infants to be born with lack of surfactant?
4. What are the consequences of low surfactant?
5. How can lung maturity be assessed in utero?
6. What is the treatment for lack of surfactant, in utero?
7. What can be done to help infants who develop RDS after birth?

Answer 17

1. no air liquid interface
2. from 25-weeks, reaching high cons by 32-36 weeks
3. maternal diabetes mellitus and prematurity
4. low lung compliance, small alveoli collapse, infants become hypoxic, hypercapnic, acidotic and exhausted
5. assay for phosphatidyl cholines
6. give glucocorticoids
7. instill surfactant into trachea

Question 18

What is adult respiratory distress syndrome?

Answer 18

caused by damage to the alveolar-capillary interface and to alveolar Type II cells
associated with a large number of disorders e.g. pneumonia, sepsis, smoking

Question 19

Airflow resistance is defined as…..

Answer 19

the pressure difference required for a given flow

Question 20

What is the most common cause of ventilatory impairment?

Answer 20

increase in airway resistance caused by asthma

Question 21

Extra work is required to overcome resistance. Resistance is made up of two components. What are they?

Answer 21

Airway resistance - resistance to flow by friction in the airways
Viscous resistance - resistance to flow by lung tissue friction

Question 22

Total airflow resistance is normally …… but can be considerably ……… by …………. in airway calibre as described by …………….. Law.

Answer 22

low
increased
reduction
Pouiselle’s

Question 23

Anything that reduces the airway ………. will ………. the work of breathing. this can occur through a variety of means and is either reversible or irreversible. A number of drugs are targeted at the physiological mechanism that control airway …..

Answer 23

diameter
increase
tone

Question 24

Where is the greatest airway resistance found?

Answer 24

In the upper airways

Lowest total cross sectional area

Question 25

What conditions increase upper airway resistance?

Answer 25

intraluminal airway obstruction
aspiration of foreign material
regurgitation of gastric contents or blood
bronchospasm

Question 26

What condition increases lower airway resistance?

Answer 26

COPD

Question 27

What physiological mechanism causes bronchoconstriction?

Answer 27

increase vagal parasympathetic activity, also induces mucus secretion
local chemical mediators e.g. histamines, leukotrienes
decreased airway CO2

Question 28

What causes bronchodilation?

Answer 28

activation of B2 adrenoreceptors by adrenaline or sympathomimetics
non-adrengergic, non cholingergic (NANC) innervation