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Respiratory physiology > airway resistance / obstruction > Flashcards

airway resistance / obstruction Flashcards

1
Q

what is the pressure gradient in the respiratory system?

A
  • the difference in pressure of the alveoli and the atmospheric pressure
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2
Q

what equation is relavent to the pressure gradient?

A

pressure gradient = resistance x flow

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3
Q

therefore, if the pressure gradient P= R x F, what is the resistance equal to (as an equation)?

A
  • R= delta P divided by flow
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4
Q

what is a low airflow rate called?

A
  • laminar flow - ie the air flow runs parallel through the airway
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5
Q

what are higher airflow rates called ?

A

turbulent flow

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6
Q

what 3 main factors determine airway resistance?

A
  1. air viscosity - if it increases, resistance increases
  2. airway length - longer airways have higher airway resistance
  3. radius - the largest effect
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7
Q

what effect does a decreased radius have on the resistance of the airway?

A
  • a decreased radius causes an increase in resistance
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8
Q

what effect does an increased radius have on the resistance of an airway?

A
  • it lowers the resistance
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9
Q

what does poiseuilles law state?

A
  • states that the flow of fluids is related to a number of factors including viscosity (n), radius (r), the pressure gradient (P) and the length (l)
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10
Q

at resting rate, what is the flow rate like in normal lungs?

A

predominantly laminar flow

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11
Q

what is the flow rate like in normal lungs during exercise?

A
  • transitional flow ie
  • laminar flow in small airways
  • turbulent flow in certain regions such as branch points and large airways
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12
Q

what 2 factors affect the probability of a turbulent flow rate occuring?

A
  • increasin radius
  • increasing velocity
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13
Q

how does the resistance change along the airway?

A

from the trachea- lower resistance - down to the alveoli - higher resistance

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14
Q

what are the major sites of resistance in the respiratory system?

A
  • larger airways and medium sized bronchioles
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15
Q

what structures of the respiratory system contribute little to total resistance?

A
  • small bronchioles down to terminal bronchioles
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16
Q

why does the **total airway resistance decline with increasing lung volume?

A
  • because the airways distend as the lungs inflate and wider airways have less resistance
17
Q

how does bronchilar diameter change with decreasing or increasing lung volume?

A
  • bronchial diameter increases with increasing lung volume
  • bronchiolar diameter decreases with decreasing lung volume
18
Q

what type of tissue specifically regulates bronchial smooth muscle?

A
  • airway smooth muscle - regulates airway diameter by bronchoconstriction and bronchodilation
19
Q

Describe the autonomic effects on smooth muscle in the airways

ie what effect do they have - constriction or dilation and what happens to the airway diameter and resistance

A
  • parasympathetic stimulation causes bronchoconstriction - reducing airway diameter and increasing airway resistance
  • sympathetic stimulation causes bronchodilation of smooth muscle which increases the airway diameter and decreaes airway resistance
20
Q

what is dynamic compression of the airways?

A
  • occurs when the** intrapleural pressure equals or exceeds the alveolar pressure **which causes dynamic collapsing of the lung
  • it is termed dynamic as the given **transpulmonary pressure **(pressure between alveoli and intrapleural) **varies **based on different factors
21
Q

in what type of situations can dynamic compression of airways occur?

A
  • forced expiration - when the intrapleural pressure is greater than the ATM pressure
  • also seen in diseases like COPD- wheezing sound during expiration
22
Q

why are the airways compressed during forced expiration?

A
  • as the intraplueral pressure is highly positive
  • this positive pressure is exerted on all the airway regions and airway begins to collapse
23
Q

what is the equal pressure point and what happens above this point??

A
  • the point at which the pressure inside the airway equals the pressure outside (intrapleural pressure)
  • above this point, there is a tendancy for airway collapse
24
Q

Describe factors (seen in diseases) that enhance dynamic airway collapse

A
  • increased small airway resistance - eg in asthma and chronic bronchitis
  • increased compliance- eg in emphysema
25
Q

what effect does an increased compliance (eg during emphysema) have on inspiration and expiration?

A
  • during inspiration, the lung is much easier to inflate and dynamic collapse is not a problem here
  • during expiration - there is dynamic airway collapse - as it causes a forced expiration - using the muscles which creates a positive pressure and collapse
26
Q

what is chronic bronchitis histoogically associated with?

A
  • thickening of the airway wall with encroachment into the lumen
27
Q

how does chronic bronchitis affect the radius and resistance of the airway?

A

as chronic bronchitis is associated with thickening of the airway wall, there is a reduced lumen radius and increased resistance

28
Q

why does asthma cause increased airway resistance?

A
  • as there is excessive bronchial smooth muscle contraction
29
Q

how can we test for increased airway resistance?

A

doing clinical pulmonary function tests - checking forced vital capacity (FVC - sum of lung volumes) and FEV1(forced expiration volume)

30
Q

what are obstructive diseased characterised by & give a clinical example?

A
  • airway obstruction / narrowing
  • difficulty expiring air
  • eg COPD and asthma
31
Q

what are restrictive diseases characterised by & give a clinical example?

A
  • reduced compliance ie ability to expand lungs
  • ie difficulty to get air into the lungs
  • eg pulmonary fibrosis
32
Q

how if FVC, FEV1 and FEV1/FVC affected by obstrutive lung disease?

ie are they reduced / normal etc

A
  • FVC - same or can be slightly reduced
  • FEV1 - reduced
  • FEV1/FVC - reduced
33
Q

how is FVC, FEV1 and FEV1/FVC affected by restructive lung diseases?

ie are they reduced or normal

A
  • FVC - reduced
  • FEV1- reduced
  • FEV1/FVC - normal

Respiratory physiology (17 decks)

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