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SGUL - Physiology 1 > Mechanics of Breathing > Flashcards

Mechanics of Breathing Flashcards

1
Q

Why is the fall in alveolar pressure large enough to be observed?

A

Delay in pressure change as it takes time for the air to move

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2
Q

What does impaired airway function lead to?

A

Insufficient ventilation

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3
Q

What does the rate of airflow depend on?

A

Pressure gradient and level of airway resistance

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4
Q

What happens to resistance as airway radius decreases?

A

Greater resistance to airflow

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5
Q

What is airway resistance increased by?

A

Turbulent airflow

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6
Q

What is patency?

A

State of being open

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7
Q

What can cause airway obstruction?

A

Loss of airway patency due to degradation of structure

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8
Q

What maintains patency in a healthy alveoli?

A

Elastin in surrounding alveoli

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9
Q

What happens to the alveoli in COPD?

A

Reduction in radial traction, so the bronchioles collapse

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10
Q

What does lung compliance quantise?

A

The relationship between the level of expansive force applied to the lung and the resulting change in lung volume

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11
Q

What is transpulmonary pressure?

A

The level of force acting to expand the lung

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12
Q

What is transpulmonary pressure made up of?

A

Alveolar pressure - intrapleural pressure

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13
Q

How is lung compliance calculated?

A

Dividing a change in lung volume by the associated change in pressure

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14
Q

What is compliance expressed as on a graph of lung volume against transpulmonary pressure?

A

Gradient

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15
Q

On a graph of lung volume against transpulmonary pressure, what does it mean if the curve is steeper?

A

Greater lung compliance

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16
Q

What does it mean if there’s a greater lung compliance?

A

Easier to inflate lung
- Less elastic recoil
- Less force required to inflate

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17
Q

What does a low lung compliance mean?

A

It’s harder to inflate the lung
- More elastic recoil
- More force required to inflate

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18
Q

What factors affect lung compliance?

A

Chest wall mechanics
Alveolar surface tension
Elastin fibres (density)

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19
Q

What diseases affect chest wall mechanics?

A
  • Scoliosis
  • Muscular dystrophy
  • Obesity
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20
Q

What disease affects the alveolar surface tension?

A

Neonatal respiratory distress syndrome

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21
Q

What diseases affect the elastin fibre density?

A

Fibrosis (increases density - decreases compliance)
COPD (decreases density)

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22
Q

What is the effect of air-liquid interfaces?

A
  • A bubble is formed of water molecules and air in the alveoli through a water-air interface
  • Surface tension is created due to H-bonds between the water molecules pulling them together
  • This exerts a collapsing force towards the centre of the bubble/alveoli. Lungs become stiffer
  • In order to expand the alveoli we must overcome these forces along with other factors
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23
Q

Why are alveoli lined with fluid?

A

Enable gas exchange

24
Q

What does Laplace’s law describe?

A

The pressure generated by the surface tension within a given area

25
Q

What would happen if two different sized alveoli were connected via airways and what is this force overcome by?

A
  • Pressure gradients being created between the alveoli, resulting in smaller alveoli emptying into larger ones
  • Overcome by pulmonary surfactants
26
Q

What is a pulmonary surfactant?

A

Mixture of different phospholipids and phospholipoproteins

27
Q

What are pulmonary surfactants secreted by?

A

Type 2 pneumocytes

28
Q

What do pulmonary surfactants do?

A
  • Reduce surface tension using ampipathic molecules to disrupt H-bonds (so lungs expand easier)
  • Equalise pressure and volume across varying alveoli
29
Q

What happens to the concentration of pulmonary surfactant as the alveoli expand and why does it happen?

A
  • Decreases, which increase surface tension
  • Set amount of surfactant in each alveoli
30
Q

What does surfactant mean for the distribution of air in the alveoli?

A

Larger alveoli collapse into smaller alveoli

31
Q

How does surfactant prevent alveolar oedema?

A
  • Surface tension produced at the air-liquid interface reduces hydrostatic pressure. It is then pulled out of the surrounding capillaries into the alveoli
32
Q

What is neonatal respiratory distress syndrome caused by?

A

Insufficient production of pulmonary surfactant

33
Q

What is the pathway of neonatal respiratory distress syndrome?

A
  • insufficient surfactant production
  • stiff lungs, alveolar collapse, oedema
  • respiratory failure
  • hypoxia
34
Q

What are the causes of death for neonatal respiratory distress syndrome?

A

Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary and cerebral haemorrhage

35
Q

Describe the different sub-divisions of the lungs.

A
  • Trachea
  • Primary bronchi
  • Smaller bronchi
  • Bronchioles
  • Alveoli
36
Q

How do the airways change as they get closer to the alveoli?

A

Air passes down a series of increasingly narrow and numerous airways

37
Q

What is Ohm’s Law?

A

Airflow (V) = ΔPressure (P)/ Resistance (R)

38
Q

Using Ohm’s Law, suggest how airflow can be increased?

A

Increasing ΔP and decreasing R

39
Q

What is the Hagen-Poiseuille Law?

A

Resistance (R) ∝ 1/(r)^4

40
Q

What can be inferred from the Hagen-Poiseuille Law?

A

As the radius of an airway decreases, the resistance increases which in turn causes the airflow to decrease dramatically

41
Q

What is laminar flow?

A

When air flows in one plane and in one uniform direction

42
Q

What is turbulent flow?

A
  • Air flow becomes multi-directional and doesn’t move in an efficient manner
  • Caused by obstruction in airways causing the pattern of flow to change from laminar to turbulent or around branching of airways
43
Q

Define lung compliance.

A

Stiffness of the lung

44
Q

What is Laplace’s law of pressure?

A
  • Pressure (P) = 2Surface Tension (T)/radius of bubble/alveoli (r)
  • If T is constant then P∝ 1/r
  • The smaller the alveoli the larger the pressure/collapsing force generated
45
Q

How can insufficient surfactant production be treated?

A
  • Supplying mothers carrying babies with maternal glucocorticoid which increases the development of cells in the lungs
  • Artificial surfactant supplementation to infants
46
Q

What is the difference between static and dynamic compliance?

A
  • Static compliance is the measurement taken whilst there is no airflow.
  • Dynamic compliance is the measurements taken during the movement of air.
47
Q

How can the level of airway obstruction be investigated?

A

Using a spirometry graph demonstrating forced vital capacity (FVC) and forced expiratory volume in one-second (FEV1) values.

48
Q

If a lung condition is obstructive, what can be observed about the FEV1/FVC ratio?

A

FEV1/FVC <70% (for example, asthma, with increased resistance)

49
Q

If a lung condition is restrictive, what can be observed about the FEV1/FVC ratio?

A

FEV1/FVC >80% (for example, fibrosis, with decreased compliance)

50
Q

How is resistance generated in the airways?

A

As air passes through airways, it generates resistance as it comes into contact with the airway surface.

51
Q

Why is an increase in lung compliance bad?

A
  • Easy to expand the lungs but they cannot recoil
52
Q

What happens with an increased concentration of surfactant molecules?

A
  • The surface tension decreases as water molecules do not have space to bond.
53
Q

What happens with a decreased concentration of surfactant molecules?

A
  • Surface tension increases as water molecules are free to bond.
54
Q

What happens when the lumen diameter increases?

A
  • Increase in luminal area
  • Decrease in resistance
  • Increase in flow
55
Q

What happens when the lumen diameter decreases?

A
  • Decrease in luminal area
  • Increase in resistance
  • Decrease in flow
56
Q

Name some factors that will decrease lumen diameter

A
  • Contraction of airway smooth muscle,
  • Excessive mucus secretion
  • Oedema
  • Loss of patency

SGUL - Physiology 1 (68 decks)

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