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respiratory mechanisms Flashcards

1
Q

airflow in tube definition

A

the movement of air in a tube where there is a difference of pressures between the ends

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2
Q

what does the pressure difference depend upon?

A

the rate and pattern of airflow

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3
Q

two basic types of airflow

A

laminar flow and turbulent flow

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4
Q

laminar flow definition

A

when the stream lines are parallel to the sides of the tube and is found at low flow rates

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5
Q

flow rate definition

A

the volume/mass of a gas/liquid that moves per unit time

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6
Q

what does Poiseuille’s law state?

A

that flow is related to viscosity, the pressure gradient, length and radius of the tube

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7
Q

flow rate equation

A

Pᴨr^4/8nl

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8
Q

resistance equation

A

8nl/ᴨr^4

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9
Q

what is flow rate proportional to?

A

the pressure gradient

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10
Q

why is the tube radius critical?

A

halving the radius can increase the resistance by x16

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11
Q

what happens when flow rate is increased?

A

the unsteadiness of the laminar flow increases, stream lines separate from the tube walls and local eddies (swirling and reverse currents) form at branches

forms a transitional flow

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12
Q

turbulent flow definition

A

when complete disorganisation of the stream lines is seen at high flow rates

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13
Q

what affects the turbulent flow?

A

viscosity of gas becomes unimportant, however an increase in gas density matters and affects the pressure gradient

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14
Q

what determines whether air flow is turbulent or laminar?

A

Reynolds number

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15
Q

How is Reynold’s number calculated?

A

2rvd/n

r= radius

v= average velocity

d= density

n= viscosity

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16
Q

when does turbulence occur?

A

Re>2000

17
Q

Explain types of flow in the lungs

A

mainly laminar flow

but the lungs highly complicated branching pattern means that there may be eddies and that the flow is non steady,

complete laminar flow only occurs in the terminal bronchioles

true turbulence may occur in the trachea during exercise, when velocity/flow rate is high

18
Q

what causes wheezing?

A

occurs during the expiratory phase of respiration due to an obstruction that produces turbulent air flow

19
Q

what does the resistance determine?

A

the rate of laminar flow down a pressure gradient?

20
Q

causes of airway resistance

A
  • decrease in lung volume increase airway resistance
  • upper most parts of the bronchial tree, as in total these have less divisions and thus a smaller radius than the total branches further down. Although the smallest bronchioles have the smallest radius, the very large cross sectional area compensates for this
  • segmental bronchi are the site of maximal resistance- 1/3 of total resistance arises from the nose, pharynx and larynx
21
Q

what reduces the resistance caused by the nose, pharynx and larynx?

A

mouth breathing

22
Q

what is the silent zone?

A

peripheral airways that contribute very little to resistance, therefore airway disease that begins here is unlikely to produce a difference in resistance that could be detected

23
Q

what does anaphylaxis cause?

A

bronchiolar contraction that increases airway resistance by reducing the radius

decreases in lung volume compress the airways and increase resistance further

24
Q

what is radial traction?

A

a force that keeps airways open during lung expansion and volume increases

25
Q

sympathetic control of resistance explained

A

B2 adrenergic receptor agonists cause bronchodilation, reducing resistance, such as adrenaline and salbutamol

can be used as treatments for asthma and COPD

26
Q

parasympathetic control of resistance explained

A

M2 GPCR, where ACh acts and causes bronchocontriction

anticholinergic agents used in COPD

27
Q

how is airway resistance measured?

A

subject sealed in plethysmograph

breathes through a pneumotachograph to measure flow

when they breathe, the alveolar pressure falls and the pressure in the box rises

alveolar pressure can then be estimated by P1V1=P2V2

28
Q

peak expiratory flow definition

A

the maximum air flow during forced expiration beginning with the lungs fully inflated

29
Q

what happens to the peak expiratory flow in asthma patients?

A

lower, due to high resistance

30
Q

what happens to the peak expiratory flow in emphysema?

A

low lung elasticity, resulting in poor airway support, easy collapse and thus reduced peak expiratory flow

31
Q

what limits the peak expiratory flow rate?

A

the person’s maximum rate of expiration is limited by the compression of the airways by intrathoracic pressure

forced expiration intrapleural pressure exceeds airway pressure so the airways would collapse due to the greater positive pressure outside than inside

32
Q

FEV1 definition

A

the volume of air exhaled in the first second

33
Q

how is peak expiratory flow measured?

A

spirometry

34
Q

is FEV1 different to forced vital capacity?

A

yes it is less, however not that much less as the majority of air is expired in the first second

35
Q

what happens to FEV1 and FVC in restrictive diseases?

A

both are reduced

36
Q

what happens to FEV1 and FVC in obstructive diseases?

A

both reduced but FEV a lot more than FVC

37
Q

Obstructive disease definition + examples

A

respiratory disease characterised by airway obstruction

asthma, COPD, chronic bronchitis

38
Q

restrictive disease definition + examples

A

extra pulmonary, pleural or parenchyma respiratory diseases that restrict lung expansion, resulting in a decreased lung volume

decreased force vital capacity as physically cannot inhale more and thus expel more

pulmonary fibrosis

39
Q

what diseases affect airway resistance

A

COPD, asthma, emphysema and chronic bronchitis

Lungs (10 decks)

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