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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
Q

What is kyphoscoliosis?

A
  • Deformity of spine characterised by abnormal curvature of vertebral column in two planes (coronal and sagittal)
  • Combination of kyphosis and scoliosis
26
Q

What is arthritic spondylitis?

A
  • 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
Q

Why does the lung compliance curve flatten out?

A

Lung reaches its elastic limit at higher lung volumes, therefore leading to plateau of curve

28
Q

What is Laplace’s law (for spherical vessels)?

A

P = 2T / r
Where:
T = tension
P = internal pressure

29
Q

Describe how the wall tension of a spherical bubble arises

A

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
Q

What is a common misconception in textbooks explaining the co-existence of alveoli in the lungs?

A

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
Q

Why can alveoli co-exist in the lungs?

A

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
Q

Why can it not just be interstitial fluid lining the lungs?

A

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
Q

What is surfactant?

A

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
Q

What is surfactant made up of?

A
  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
Q

Why is DPPC the most important component of surfactant?

A

DPPC is responsible for the surface tension lowering effect of surfactant

36
Q

Which cells secrete surfactant?

A

Alveolar type II epithelial cells

37
Q

What is the typical reduction of surface tension when lung surfactant is introduced?

A

Surface tension typically reduces by 10x

38
Q

What is the area dependent effect?

A

The smaller the radius (lower SA), the greater the density of DPPC –> greater surface tension lowering effect

39
Q

What is a difference between surfactant and surfactant?

A

Surfactant can alter surface tension lowering effect depending on SA - due to density of surfactant molecules to which it is exposed

40
Q

Describe how surfactant reduces surface tension

A
  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
Q

What is the structure of surfactant?

A
  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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