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IRM > L06 (pk3) - Surfactant and resistance > Flashcards

L06 (pk3) - Surfactant and resistance Flashcards

1
Q

What is the most freq cause of upper airway resistance

A

Intraluminal airway obstruction

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2
Q

What could cause airway obstruction?

A

Aspiration of foreign material (esp in childrem) or regurgitation of gastric contents or blood

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3
Q

How could airway obstructions be cleared?

A
  • Bronchoscopic removal
  • Heimlich manoeuvre
  • Paroxysm of coughing
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4
Q

Describe how the Heimlich manoeuvre clears obstructions in the airway

A

Forces diaphragm upwards due to sudden sharp movements –> sudden increase in airway pressure distal to the obstruction –> airflow forced out (obstruction with it)

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5
Q

What else could increase airway resistance other than airway obstructions?

A
  • Increased mucus secretion (bronchitis)
  • Bronchospasm (asthma)
  • Oedema
  • In sleep or unconsciousness, severe obstruction may occur from tongue falling back
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6
Q

What is the silent zone in the lungs?

A

The lower airways of the lungs contribute v little to total airway resistance, therefore any disease that progresses/ begins in the lower airways may go undetected until it reaches a profound stage

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7
Q

Despite the little contribution of the lower airways to total R, what is it a prime target for?

A

COPD

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8
Q

What can cause bronchoconstriction?

A
  1. Inc vagal parasympathetic activity
    - There is a 30% vagal tone at rest, when this increases, it causes b. constrict
    - Also inc mucus secretion
  2. Local chemical mediators in response to inflammatory diseases
    - Histamines
    - Leukotrienes
  3. Decreased airway CO2
    - By HYPERventilation
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9
Q

What can cause bronchodilation?

A
  1. Activation of beta 2-adrenoceptors by adrenaline or sympathomimetics (sympathetic activity)
  2. Non-adrenergic, non-cholinergic (NANC innervation)
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10
Q

What is the definition for airway resistance?

A

The pressure difference required for a given flow

- The lower the resistance, the lower the press diff required for a given flow

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11
Q

What is the value of the normal airflow resistance?

A

0.2kPa.L.s^-1

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12
Q

What is dynamic resistance?

A

Extra work required to move air

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13
Q

What is airway resistance and what is its percentage of total resistance?

A
  • Resistance to flow by friction in airways
  • Air molecules rubbing airway sides; causing friction
  • Energy lost in turbulent flow; seen in larger airways
    80-90% of total
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14
Q

What is viscous resistance and what is its percentage of total resistance?

A
  • Resistance to flow by lung tissue friction

10-20% of total

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15
Q

What is the relationship between resistance, pressure and flow?

A

Resistance = (diff in pressure)/ flow

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16
Q

What is Poiseuille’s equation?

A

Flow = (delta P x pi x r^4) / (8 x length x viscosity)

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17
Q

What is the relationship between resistance and radius?

A

R directly prop 1/ r^4

18
Q

After rearranging Poiseuille’s equation and combining the equation for resistance/ flow / press, what is the final equation for airflow resistance?

A

Airflow R = (8 x length x viscosity) / (pi x r^4)

19
Q

Where does most of the airway resistance occur in the lung and why?

A
  • Most R in the larger airways, i.e. trachea and larger bronchi
  • Although INDIVIDUALLY, smaller airways each have a greater R than larger airways, the greater number of smaller airways mean that their total cross sectional area is larger
  • So, the airflow R greatest in larger airways
20
Q

What determines the elastic properties of the lung?

A
  1. Elastic properties of the lung tissue
    - Collagen
    - Elastic fibres
  2. Surface tension forces due to the air-liquid interface
    - Saline filled lungs more compliant than air filled
    - 60-75% of the ELASTIC RECOIL of the lungs caused by surface tension effects
21
Q

What is the distending pressure?

A
  • Essentially intrapleural pressure
  • Generated by elastic recoil forces of the lungs and the chestwall
  • Compliance determines vol for any given distending pressure
22
Q

What is the effect of surface tension on lung compliance?

A

Inc surface tension = decrease lung compliance

- Surface tension forces trying to collapse the surface, therefore lungs working against it

23
Q

What does chestwall compliance depend on?

A

Chestwall compliance depends on the rigidity of thoracic cage and on its shape
- No diseases/ illnesses that can lead to INC CW compliance

24
Q

Which conditions decrease the rigidity of the thoracic cage?

A 
Decreased by: 
- Arthritic spondylitis
- Kyphoscoliosis
- Spasticity or rigidity of thoracic or abdominal muscles
(dec CW compliance makes it more rigid)
25
What is kyphoscoliosis?
- Deformity of spine characterised by abnormal curvature of vertebral column in two planes (coronal and sagittal) - Combination of kyphosis and scoliosis
26
What is arthritic spondylitis?
- Rare type of arthritis - Pain and stiffness in spine - Inflammation in vertebrae - Over time, small bones in vertebrae can fuse tgt, therefore less flexible and can result in hunched forward posture
27
Why does the lung compliance curve flatten out?
Lung reaches its elastic limit at higher lung volumes, therefore leading to plateau of curve
28
What is Laplace's law (for spherical vessels)?
P = 2T / r Where: T = tension P = internal pressure
29
Describe how the wall tension of a spherical bubble arises
Tangenital component, force of the H20 molecules pulling on each other, generates a wall tension (T) that pulls inwards and tends to collapse the bubble --> generates pressure by these collapsing forces
30
What is a common misconception in textbooks explaining the co-existence of alveoli in the lungs?
Using Laplace's law, smaller bubbles must have a greater internal pressure to keep them inflated (assuming T has minimal change) - However, this inc pressure in small alveoli will lead it to collapse
31
Why can alveoli co-exist in the lungs?
Alveolar interdependence - Alveoli are interconnected, therefore the tendency for one alveoli to collapse is prevented by the tendency for other alveoli to not collapse (held open as supported by adjoining alveolar walls) - So, allowing for different sized alveoli
32
Why can it not just be interstitial fluid lining the lungs?
Calculations using air-interstitial fluid interface in lungs results in a V high surface tension --> RED lung compliance significantly --> making breathing impossible (even though it isnt) --> therefore, there is another fluid that is decreasing lung compliance (surfactant)
33
What is surfactant?
A detergent-like substance that acts to greatly lower surface tension in alveoli Lung surfactant reduces surface tension --> inc compliance --> red work of breathing
34
What is surfactant made up of?
1. 35-40% DPPC (a PPL) - MOST IMPORTANT PPL 2. 30-45% other phospholipids 3. 5-10% protein (SP-A, B, C and D) 4. Cholesterols (neutral lipids) and trace amounts of other substances
35
Why is DPPC the most important component of surfactant?
DPPC is responsible for the surface tension lowering effect of surfactant
36
Which cells secrete surfactant?
Alveolar type II epithelial cells
37
What is the typical reduction of surface tension when lung surfactant is introduced?
Surface tension typically reduces by 10x
38
What is the area dependent effect?
The smaller the radius (lower SA), the greater the density of DPPC --> greater surface tension lowering effect
39
What is a difference between surfactant and surfactant?
Surfactant can alter surface tension lowering effect depending on SA - due to density of surfactant molecules to which it is exposed
40
Describe how surfactant reduces surface tension
1. Surfactant lines the air-liquid interface 2. Preventing H2O molecules from reaching the A-L interface (less molecules can get to interface) 3. Surface tension lowering effect is due to the A-L interface 4. Since, H2O molcs are attracted to each other in one direction, it will result in a reduction of collapsing radial forces creating the surface tension skin 5. Therefore, reducing surface tension
41
What is the structure of surfactant?
1. Hydrophobic component (Oily, water insoluble) - Palmitate 2. Hydrophilic component - Phosphate - Choline 3. Glycerol backbone between the hydrophobic and hydrophilic components

IRM (21 decks)

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