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BDS1 Respiratory System > Ventilation (V), Perfusion (Q) and the V/Q Relationship > Flashcards

Ventilation (V), Perfusion (Q) and the V/Q Relationship Flashcards

1
Q

What is ventilation?

A

Process by which air moves in and out of the 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

A major determinant of normal gas exchange and thus the level of PO2 and PCO2 in blood is the relationship between ventilation and perfusion. What is this relationship called?

A

The V/Q ratio

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4
Q

Ventilation is not uniformly distributed in the lung. What is one of the main reasons for this?

A

Gravity

  • In an upright position, alveoli in the apex are more expanded than at the base
  • Gravity pulls the lung down and away from the chest wall so:
  • Pleural pressure is more negative at the apex than the base
  • Transpulmonary pressure is greater at the apex than at the base
  • Increased alveolar volume in apex
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5
Q

In addition to gravity what 2 other factors affect the distribution of ventilation?

A
  • Compliance

- Resistance

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6
Q

What does compliance refer to in relation to the lungs?

A
  • How much effort is required to stretch the lungs and chest wall
  • High compliance means that the lungs and chest wall will expand easily
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7
Q

Decreased compliance is a common feature in pulmonary conditions, due to what 4 conditions/changes of the lung?

A

1, Scarring in lung tissue (TB)

  1. Lung filled with fluid (oedema)
  2. Deficiency in surfactant production
  3. Destruction of elastic fibres (emphysema)
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8
Q

What does resistance refer to in relation to the lungs?

A

Any narrowing or obstruction of the airway that may reduce airflow
- Large diameter airways have decreased resistance

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9
Q

Increased resistance is a common feature in pulmonary conditions, what are these conditions?

A
  1. Asthma

2. COPD (emphysema, chronic bronchitis) due to obstruction or collapse of airways

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10
Q

What is the definition of dead space?

A

The volume of gas not participating in gas exchange

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11
Q

What are the 2 different types of dead space?

A
  • Anatomical dead space

- Physiological dead space

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12
Q

What is anatomical dead space?

A

Volume of gas during each breath that fills the conducting airways

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13
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 perfused but not ventilated

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14
Q

How should anatomical and physiological dead space compare in a healthy individual?

A

The should be around the same

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15
Q

What is the pulmonary circulation of the lung?

A
  • Brings deoxygenated blood from the heart to the lung and oxygenated blood from the lung to the heart
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16
Q

What is the bronchial circulation of the lung?

A
  • Brings oxygenated blood to the lung parenchyma
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17
Q

What are the characteristics of systemic circulation in terms of pressure and resistance?

A
  • High pressure - 120/80mmHg
  • High resistance (used to control distribution of blood)
  • Smooth muscles in vessels
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18
Q

What are the characteristic of pulmonary circulation in terms of pressure and resistance?

A
  • Low pressure - 24/9 mmHg
  • Low resistance
  • Wider vessels with less smooth muscle
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19
Q

How can the V/Q ratio be defined for a single alveolus?

A

Ratio defined as alveolar ventilation divided by capillary flow

20
Q

How can the V/Q ratio be defined for the entire lung?

A

Ratio defined as total alveolar ventilation divided by cardiac output

21
Q

For a healthy individual what is the V/Q of the lung?

A

0.8-1.2

22
Q

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

A

> 1

23
Q

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

A

> 1

24
Q

In a ‘perfect model’ where inspired gas and cardiac output is shared equally so alveolar PO2 and arterial PCO2 are the same, what would the V/Q ratio be?

A

1

25
Q

What is the arterial PO2 in arterial hypoxemia?

A

<80mmHg (whereas normal is around 100mmHg)

26
Q

What is the arterial PO2 in hypoxia?

A
  • When insufficient O2 to carry out metabolic functions, so arterial PO2 <60mmHg (this is the level in which peripheral chemoreceptors start to kick in to increase ventilation)
27
Q

What is the arterial PCO2 in hypercapnia?

A

Increase in arterial PCO2 > 40mmHg

28
Q

What is arterial PCO2 in hypocapnia?

A

Decrease in arterial PCO2 < 35mmHg

29
Q

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

A

V-Q mismatching

- Results in varying alveolar and capillary gas contents

30
Q

What is an anatomical shunt?

A

When mixed venous blood is shunted directly into arterial blood which lowers the levels of oxygen in the blood

  • The alveolar ventilation is the same, but distribution of blood flow is changed
  • A ‘right to left shunt’ means blood that is being shunted is deoxygenated
31
Q

Where do most anatomical shunts occur?

A

Mainly within the heart - blood from the right atrium or ventricle crosses septum to left atrium or ventricle: right to left shunt
- Results in varying degrees of hypoxemia

32
Q

What is a physiological shunt?

A

Air is no longer getting to an alveoli, but blood perfusion and gas exchange is still occurring (still get gas exchange occurring initially however there is a build up of CO2 and a low level of O2 which causes gas exchange to stop occurring)
- So V/Q=0

33
Q

What is atelectasis?

A

An obstruction of ventilation due to mucous plugs, airway oedema, foreign bodies and tumours in the airways which causes the collapse of the lung tissue

34
Q

What is happening when V/Q=0 for an area of the lung?

A
  • Ventilation to a region is 0
  • Airway is blocked
  • Ventilation redistributed to other alveoli - elevated V/q in other regions
35
Q

What conditions are associated with a low V/Q?

A
  • Asthma

- Chronic bronchitis

36
Q

What is happening when V/Q= infinity for an area in the lung?

A
  • No blood flow; perfusion to a region is 0
  • Physiological dead space e.g. pulmonary embolism
  • Blood diverted to other capillaries - low V/Q in other regions
37
Q

What conditions are associated with a high V/Q?

A
  • Emphysema - disrupted gas exchange

- Pulmonary fibrosis - decreased gas exchange

38
Q

What is chronic obstructive pulmonary disease (COPD)?

A
  • A condition in which airflow is obstructed

- It encompasses emphysema and chronic bronchitis

39
Q

What is a frequent cause of COPD?

A

Long term smoking

40
Q

What are the symptoms and signs of COPD?

A
  • Chronic cough
  • Chest tightness
  • Shortness of breath
  • Increased mucous production
41
Q

What is emphysema?

A
  • Structures in the alveoli are over inflated
  • Lungs loose their elasticity and cannot fully expand and contract
  • Patients can inhale but exhalation is difficult due to decreased elastic recoil?
42
Q

What is chronic bronchitis?

A
  • Inflammation of bronchi causing mucous production and excessive swelling
  • Shortness of breath with mild exertion
  • Chest infections are more prevalent
43
Q

What is pulmonary fibrosis?

A
  • A type of interstitial lung disease
  • Scarring and thickening of tissue
  • Decreased elasticity
  • Decreased gas exchange
44
Q

What is forced vital capacity?

A

The maximal volume of gas that can be exhaled from a full inhalation by exhaling as forcefully and rapidly as possible

45
Q

What is the forced expiratory volume of the lungs in 1 second?

A

The maximal volume of gas that can be exhaled in 1 second from a full inhalation

46
Q

In healthy individuals, what should the FEV1/FVC ratio be?

A

> 70%

- In other words 70% of the lung volume should be expired in 1 second

47
Q

How many breaths should a healthy individual take per minute?

A

around 12-15

BDS1 Respiratory System (8 decks)

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