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YEAR 2: Respiratory Disease (MGEM2013 UNUK) (SPR1 23-24) > Respiratory Failure and VQ matching: Part II > Flashcards

Respiratory Failure and VQ matching: Part II Flashcards

1
Q

Ventilation-Perfusion VQ matching

what is the most common cause of hypoxia in respiratory diseases and respiratory failure

A

Ventilation (V) and Perfusion (Q) mismatching of alveolar capillaries

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2
Q

ventilation-perfusion VQ matching

what 2 things does correlating alveolar ventilation and perfusion do?

think gases

A

it maximises gas exchange and efficiency.

ideally should be 1:1

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3
Q

ventilation-perfusion VQ matching

how do you calculation VQ ratio

A

Ventilation (V) divided by Perfusion (Q)

  • VQ ratio = V/Q
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4
Q

VQ mismatching

what does VQ mismatching increase

think space

A

increases alveolar dead space (space not used for gas exchange)

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5
Q

VQ mismatching

what are 3 causes of VQ mismatching

Think:

  • oxygen
  • circulation
  • dysfunctions
A
  • lack of inspiring oxygen
  • lack of circulation/blood flow (shunts)
  • respiratory dysfunctions
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6
Q

VQ mismatching

what is the consequence of VQ mismatching regarding oxygen saturation and what does this lead to?

think:

  • alveoli
  • systemic circulation
A
  • there will be a much lower oxygen saturation in blood leaving the alveoli
  • will lead to hypoxaemia when they mix with the systemic circulation
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7
Q

how come Type 1 respiratory failure always occur before type 2 respiratory failure and explain why?

A

this is because you get hypoxia before hypercapnia, due to the limited solubility of Oxygen

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8
Q

what are 6 diseases/disorders that commonly cause V/Q mismatches?

Think:
- C
- a
- e
- p
- p
- p

A
  • Covid
  • acute asthma
  • exacerbation COPD
  • pneumonia
  • pulmonary oedema
  • pulmonary embolism
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9
Q

Regulation of V/Q

what is the relationship between resistance and radius (Poiseullle’s Law)

A

resistance to flow is inversely proportional to the radius^4

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10
Q

regulation of V/Q

what do medium-sized bronchioles provide most resistance for and what do arterioles provide the most resistance for

A

Medium-sized Bronchioles:
- most resistance to airflow

Arterioles:
- most resistance to perfusion

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11
Q

regulation of V/Q

what are the 2 equations of Poiseulle’s law

A

resistance = 8nl / πr^4

Where:
- n = viscocity
- l = length of tube
- r = radius

OR

Q = ΔP/R

Where:

  • Q = flow
  • ΔP = change in pressure
  • R = resistance
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12
Q

VQ matching - continuous local changes

what do the bronchioles do in response to raised PaCO2 (hypercapnia) and why

A
  • bronchioles dilate in response to increased PaCO2
  • does this to improve airflow so CO2 has more space to be eliminated
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13
Q

VQ matching - continuous local changes

what do pulmonary arterioles do in response to low PaO2 (hypoxia) and why

A
  • pulmonary arterioles constrict in response to hypoxia
  • does this to reduce flow and redirect blood to better perfused areas
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14
Q

state what would happen in these vessels if O2 decreases or increases and describe in one sentence the relationship between the 2 vessels:

- Pulmonary arterioles

- systemic arterioles

A

Oxygen decrease:

  • pulmonary arterioles: vasoconstrict
  • systemic arterioles: vasodilate

this is vice versa for an oxygen increase

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15
Q

Ventialtion and perfusion

what causes ventilation and perfusion to not be uniform throughout the lungs and what is also NOT uniform as a result

A
  • Gravity
  • as a result, VQ (V/Q ratio) is also not uniform
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16
Q

perfusion but not ventilation and ventilation but no perfusion

what is perfusion but no ventilation called and what is the V/Q ratio for this

A
  • called a “shunt”
  • V/Q = 0 as “V” has a value of 0
17
Q

perfusion but not ventilation and ventilation but no perfusion

what is ventilation but no perfusion called and what is the V/Q ratio for this

A
  • called “dead space”
  • V/Q is infinity as “Q” is 0, and anything divided by 0 is infinity
18
Q

Gravity and compliance

why does pulmonary ventilation increase from the apex of the lung compared to the base

A

because of gravity and compliance

19
Q

Gravity and compliance

outline 2 reasons as to why lots of gas exchange occur at the base of the lungs

think:

  • intrapleural pressure
  • alveoli and compliance
A
  1. intrapleural pressure is less negative towards the base of lungs
  2. Alveoli at the base are highly compliant so can accommodate more easily
20
Q

where is intrapleural pressure more negative in the lungs?

A

intrapleural pressure is more negative at the apex.

21
Q

pulmonary blood flow

describe and explain the different pressures in Zone I of the lungs (the apex), state what this leads to

think:

  • alveolar pressure
  • blood vessels
A

Alveolar pressure is greater than both local pulmonary arterial and venous pressures in zone 1.

This is because the blood vessels are compressed by the high alveolar pressure and there is only intermittent flow if Pa increases during the breathing cycle

  • this leads to little blood flow at the lung apex

Pressure hierachy: P.alv > P.a > P.v

22
Q

outline a size hierachy of partial pressures between the alveoli (Palv/PA) , arteries (Pa) and veins (Pv) in zone I of the lungs (the apex)

A

Pressure hierachy: P.alv > P.a > P.v

23
Q

pulmonary blood flow

what can the normal pressure gradient form arteries to veins be disrupted by in Zone II of the lungs?

A

can be disrupted by intermittnet high alveolar pressures

24
Q

outline a size hierachy of partial pressures between the alveoli (Palv/PA) , arteries (Pa) and veins (Pv) in zone II of the lungs (the midsection)

A

Pressure hierachy: Pa > Palv > Pv

25
Q

what does flow depend on in zone II (the midsection) of the lungs and what is it independent of?

A

dependent on:
- the difference between pulmonary arterial pressure and alveolar pressure

independent of:
- venous pressure

26
Q

pulmonary blood flow

what is the pressure gradient like between arteries and veins in zone III (the base) of the lungs?

A
  • normal pressure gradient from arteries to veins
27
Q

how is perfusion ensured in zone III (the base) of the lungs?

A

pulmonary artery pressure is greater than venous pressure and alveolar pressure ensuring perfusion

28
Q

outline a size hierachy of partial pressures between the alveoli (Palv/PA) , arteries (Pa) and veins (Pv) in zone III of the lungs (the midsection)

A

Pressure hierachy: Pa > Pv > Palv

29
Q

what happens to ventilation and perfusion between the base and the apex when a patient is in the supine (lying down) position

A

it equals out, so the base perfusion is no longer much greater than the apex

30
Q

What receptors are involved in vasoconstriction and vasodilation in the arterioles?

A

a1 and a2 receptors

YEAR 2: Respiratory Disease (MGEM2013 UNUK) (SPR1 23-24) (39 decks)

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