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BDS1 BAMS: Respiratory System > Ventilation and Perfusion > Flashcards

Ventilation and Perfusion Flashcards

1
Q

What is ventilation?

A

The process by which air moves in and out of lungs

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2
Q

What is perfusion?

A

Process by which deoxygenated blood passes through the lung and becomes oxygenated

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3
Q

What does the ventilation/perfusion relationship (V/Q ratio) determine?

A

Normal gas exchange and thus the level of PO2 and PCO2 in the blood

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4
Q

What happens is V/Q is mismatched?

A

Indicates a respiratory disorder

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5
Q

Why is ventilation not uniformly distributed throughout the lungs?

A

Gravity, compliance and resistance

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6
Q

Describe the alveoli in apex when in an upright position

A

The alveoli in apex are more expanded in an upright position (gravity)

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7
Q

What effect does gravity have on the lungs and chest wall?

A

Pulls the lungs downwards and away from the chest wall

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8
Q

What is pleural pressure?

A

Pressure in the pleural space - always negative because lung is always pulling inwards and chest wall pulling outwards

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9
Q

Pleural pressure is more negative at which part of the lung?

A

The apex of the lung

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10
Q

Transpulmonary pressure is greater at which part of the lung?

A

The apex of the lung

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11
Q

What is compliance?

A

Compliance refers to how much effort is required to stretch the lungs and chest wall

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12
Q

What does high compliance mean in terms of the lungs and chest wall?

A

High compliance means that the lungs and chest wall expand easily

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13
Q

When might decreased compliance occur?

A

Pulmonary conditions:

1) Scarring in lung tissue (tuberculosis)
2) Lung filled with fluid (oedema)
3) Deficiency in surfactant produced
4) Destruction of elastic fibres (emphysema)

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14
Q

What is resistance?

A

Any narrowing or obstruction of the airway that might reduce airflow

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15
Q

Describe the resistance in large diameter airways

A

Decreased resistance

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16
Q

When might increased resistance occur?

A

Pulmonary conditions:

1) Asthma
2) COPD (emphysema, chronic bronchitis) due to obstruction or collapse or airways

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17
Q

What is COPD?

A

Chronic Obstructive Pulmonary Disease

Includes emphysema and chronic bronchitis

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18
Q

What are the 2 types of dead space?

A

1) Anatomical dead space

2) Physiological dead space

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19
Q

What is anatomical dead space?

A

Volume of gas during each breath that fills the conducting airways

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20
Q

What is physiological dead space?

A

Total volume of gas in each breath that does not participate in gas exchange e.g. alveoli that are ventilated but NOT perfused

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21
Q

Why is surfactant important?

A
  • Reduces surface tension/friction between pleural layers

- Important in maintaining elasticity of lungs

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22
Q

The lung has 2 separate blood supplies. What are they?

A

1) Pulmonary circulation

2) Bronchial circulation

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23
Q

Describe the pulmonary circulation

A

Brings deoxygenated blood from the heart to lung and oxygenated blood from the lung to the heart

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24
Q

Describe the bronchial circulation

A

Brings oxygenated blood from heart to lung parenchyma

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25
Q

Describe the differences between the pulmonary circulation and systemic circulation

A

1) Systemic circulation = high pressure (120/80 mm Hg). Pulmonary circulation = low pressure (24/9 mmHg)
2) Systemic circulation = high resistance. Pulmonary circulation = low resistance.
3) Systemic circulation = smooth muscle in vessels. Pulmonary circulation = wider vessels with less smooth muscle

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26
Q

Pulmonary circulation is a ___ pressure and ___ resistance system

A

Low pressure

Low resistance

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27
Q

Which of the following 2 circulations is more influenced by gravity: pulmonary circulation or systemic circulation

A

Pulmonary circulation

28
Q

When upright, which part of the lungs receive greater blood flow?

A

The base (gravity)

29
Q

What is the V/Q ratio?

A

The ratio of ventilation to blood flow

Ratio can be defined for a single alveolus, a group of alveoli or entire lung

30
Q

Describe the V/Q ratio for a single alveolus

A

Ratio defined as alveolar ventilation divided by capillary flow

31
Q

Describe the V/Q ratio for a lung

A

Ratio defined as total alveolar ventilation divided by cardiac output

32
Q

What is the V/Q ratio for a healthy individual?

A

0.8-1.2

33
Q

What are the typical values for alveolar ventilation and perfusion in a healthy individual?

A

Alveolar ventilation = ~4-6L/min

Pulmonary blood flow = ~5L/min

34
Q

What is the V/Q ratio when ventilation exceeds perfusion?

A

V/Q > 1

35
Q

What is the V/Q ratio when perfusion exceeds ventilation

A

V/Q < 1

36
Q

What happens when ventilation and perfusion are mismatched?

A

Impaired O2 and CO2 transfer

Indicates a respiratory disorder

37
Q

What is arterial hypoxemia defined as?

A

Arterial PO2 < 80 mmHg (normal ~100 mmHg)

38
Q

What is hypoxia?

A

Insufficient oxygen to carry out metabolic functions - when arterial PO2 < 60 mmHg

39
Q

What is hypercapnia?

A

Increase in arterial PCO2 > 40 mmHg

40
Q

What is hypocapnia?

A

Decrease in arterial PCO2 < 35 mm Hg

41
Q

What is the most common cause of arterial hypoxemia in patients with respiratory disorders?

A

V/Q mismatching
Some alveoli: V/Q > 1
Other alveoli: V/Q <1
Results in varying alveolar and capillary gas contents

42
Q

What is an anatomical shunt? (that can underlie V/Q mismatching)

A

Extra vessel that results in mixing of oxygenated and deoxygenated blood
e.g. mixed venous blood shunted directly into arterial blood

43
Q

Where do most anatomical shunts occur?

A

In the heart - e.g. blood from right atrium or ventricle crosses septum to left atrium or ventricle

44
Q

What does an anatomical shunt result in?

A

Results in varying degrees of hypoxemia

45
Q

In the case of an anatomical shunt, why is PCO2 not increased?

A

Central chemoreceptors are very sensitive to CO2 changes - leads to increased ventilation - leads to reduction in PCO2

46
Q

What is a physiological shunt?

A

Ventilation to lungs units is absent with continuing perfusion (venous admixture)

47
Q

What is the V/Q ratio when there is a physiological shunt present?

A

V/Q = 0

48
Q

What is atelectasis?

A

Obstruction of ventilation due to mucous plug, airway oedema, foreign bodies, tumours in airway
Results in absence of gas exchange (absence of ventilation)

49
Q

When might the V/Q relationship be 0?

A
  • When ventilation to a region is 0 (physiological shunt)
  • e.g. child inhaling a peanut
  • Blocks airway
  • Ventilation redistributed to other alveoli -elevated V/Q in other regions
50
Q

What might be the cause of a low V/Q relationship (<0.8)?

A
  • Asthma
  • Chronic bronchitis
  • Low ventilation, high perfusion
51
Q

What would cause a V/Q relationship of ∞?

A
  • When perfusion goes to 0/absence of perfusion i.e. no blood flow
  • Physiological dead space
  • e.g. pulmonary embolism
  • blood diverted to other capillaries - low V/Q in other regions
52
Q

What might cause a high V/Q relationship?

A
  • Emphysema: disrupted gas exchange
  • Pulmonary fibrosis: decreased gas exchange
  • High ventilation, low perfusion
53
Q

What is chronic obstructive pulmonary disease (COPD)?

A
  • Condition in which airflow is obstructed

- COPD encompasses emphysema and chronic bronchitis

54
Q

What is the most frequent cause of COPD?

A

Long term smoking

55
Q

What are the symptoms of COPD?

A
  • Chronic cough
  • Chest tightness
  • Shortness of breath
  • Increased mucous production
56
Q

What is emphysema?

A
  • Lung condition
  • Structures in alveoli over-inflated
  • Lungs lose elasticity, cannot expand and contract
  • Patients can inhale but exhalation is difficult due to decreased elastic recoil
57
Q

What is chronic bronchitis?

A
  • Inflammation of bronchi causing mucous production and excessive swelling
  • Shortness of breath with mild exertion
  • Chest infections more prevalent
58
Q

What is pulmonary fibrosis?

A
  • A type of interstitial lung disease
  • Scarring and thickening of tissue
  • Decreased elasticity
  • Decreased gas exchange
59
Q

What is the FEV1/FVC ratio in healthy individuals?

A

> 70%

i.e. >70% of lung volume expired in 1 second

60
Q

Describe the FEV1/FVC ratio in patients with restrictive lung disease e.g. pulmonary fibrosis, neuromuscular diseases, respiratory distress syndrome

A

FEV1/FVC ratio >70%

BUT lung volume (FVC) smaller, <80% of a healthy individual

61
Q

Describe the FEV1/FVC ratio in patients with obstructive lung disease e.g. emphysema, asthma, pulmonary oedema

A

FEV1/FVC ratio <70%

Less than 70% of lung volume expired in 1 second

62
Q

What is the term for the total volume of gas in each breath that does not participate in gas exchange

A

Physiological dead space

63
Q

Regional differences in ventilation and perfusion are largely due to what?

A

Gravity

64
Q

What is the typical V/Q ratio in a healthy lung?

A

0.8

65
Q

When does V/Q ratio exceed 1?

A

When ventilation exceeds perfusion

66
Q

When is the V/Q ratio <1?

A

When perfusion exceeds ventilation

BDS1 BAMS: Respiratory System (8 decks)

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