30. Ventilation/Perfusion Relationship Flashcards Preview

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Flashcards in 30. Ventilation/Perfusion Relationship Deck (18)
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1
Q

What is the % oxygen in inspired, expired and alveolar air?

A

21
16
14

2
Q

What is the % carbon dioxide in inspired, expired and alveolar air?

A

0
4
6

3
Q

What is the % nitrogen in inspired, expired and alveolar air?

A

79
80
80

4
Q

What is the PO2 in inspired, expired and alveolar air?

A

150
120
100

5
Q

What is the PCO2 in inspired, expired and alveolar air?

A

0
30
40

6
Q

How is the partial pressure found?

A

Take atmospheric pressure (760) and take away vapour pressure (47)
Then multiply by the percentage the gas takes up

7
Q

Why is the PO2 in pulmonary veins slightly higher than arteries?

A

Blood supply to the lungs themselves (ie bronchial and thebesian veins) rejoin into arteries

8
Q

How can arterial blood gas be measured?

A

Arterial blood sample
Blood gas analyser
Resulting graph is a capnogram

9
Q

What factors affect diffusion?

A

Pressure difference
Surface area
Distance the gas has to travel

10
Q

What is the diffusing capacity?

A

Rate of transfer of gas from lung to blood/partial pressure difference
Measure of a patient’s ability to diffuse passively

11
Q

Why is CO used to find the partial pressure difference?

A

Binds to haemoglobin so effectively that the partial pressure difference is equal to the alveolar PCO

12
Q

In what cases would the diffusing capacity be reduced?

A

Lung fibrosis
Pneumonia
Oedema
Emphysema

13
Q

What is the alveolar gas equation?

A

PAO2= PiO2-PaO2/R

14
Q

What is the closing volume?

A

Volume at which airways start collapsing

Higher intrapleural pressure at base will cause it to collapse first

15
Q

Why is there high nitrogen after closing volume?

A

Air coming out is preferentially from apex

Has more nitrogen because inspiration went primarily to base

16
Q

What is wasted ventilation?

A
Increased V/Q ratio
Higher alveolar dead space
Respiratory muscles are carrying out useless work
No gas exchange
Embolism, emphysema
17
Q

What is shunting?

A

Decreased V/Q ratio
Deoxygenated blood bypasses exchange area and rejoins left heart
Arterial hypoxia
COPD, asthma, bronchitis

18
Q

What causes hypoxic pulmonary vasoconstriction?

A

Low PAO2 or high PACO2 causes relaxation of airway smooth muscle
Constriction of pulmonary arterioles- directs oxygen elsewhere