Respiration: V, Q and respiratory disorders

Question 1

Ventilation definition

Answer 1

process by which air moves in and out of lungs

Question 2

Perfusion definition

Answer 2

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

Question 3

What is the V/Q ratio?

Answer 3

the relationship between ventilation and perfusion (blood flow) which is a major determinant of gas exchange and therefore pO2 and pCO2 in blood.

Question 4

Why is ventilation not uniformly distributed in the lungs?

Answer 4

due to gravity

Question 5

What factors affect ventilation?

Answer 5

gravity, resistance, compliance

Question 6

When upright, where is alveolar volume the greatest?

Answer 6

Alveoli in apex more expanded - gravity pulls lung wall down so Ppl is more negative at the apex than the base so PL (transpulmonary) is greater at the apex

Question 7

Compliance definition

Answer 7

how much effort is required to stretch the lungs and chest wall (high compliance means easily expandable)

Question 8

What does resistance refer to?

Answer 8

any narrowing or obstruction of airway

Question 9

How does a decreased compliance affect lung volumes?

Answer 9

decreases lung volume

Question 10

How does an increased resistance affect lung volume?

Answer 10

decreased rate of filling (volume change) and slight decrease in volume overall.

Question 11

Which pulmonary conditions is decreased compliance a common feature of?

Answer 11

tuberculosis (scarring in lung tissue), oedema (fluid-filled lung), deficiency in surfactant production, emphysema (destruction of elastic fibres)

Question 12

Which pulmonary conditions is increased resistance a common feature of?

Answer 12

asthma, COPD (emphysema, chronic bronchitis) due to obstruction/collapsed airways

Question 13

What are the 2 types of dead space?

Answer 13

anatomical and physiological dead space

Question 14

What is anatomical dead space?

Answer 14

volume of gas in each breath that fills conducting airways (150ml / 30% of each breath)

Question 15

What is physiological dead space?

Answer 15

total volume of gas in each breath that does not participate in gas exchange e.g. alveoli that are perfused but not ventilated (?)

Question 16

What are the 2 blood circulations of the lung?

Answer 16

pulmonary and bronchial circulations

Question 17

Function of pulmonary circulation

Answer 17

transports deoxygenated blood from the heart to the lungs and oxygenated blood back to heart

Question 18

Function of bronchial circulation

Answer 18

supplies oxygenated blood to lung parenchyma

Question 19

Why is the pulmonary circulation influenced by gravity more than the systemic circulation?

Answer 19

pulmonary circulation is low pressure and low resistance

Question 20

How is pulmonary blood flow distributed when upright?

Answer 20

greater flow to base than apex (gravity) - arterial and venous pressures vary. Influences V/Q ratio

Question 21

What structures can a V/Q ratio be defined for?

Answer 21

single alveolus, group of alveoli, entire lung

Question 22

How is the V/Q ratio defined for an alveolus?

Answer 22

alveolar ventilation divided by capillary flow

Question 23

How is the V/Q ratio defined for the entire lung?

Answer 23

total alveolar ventilation divided by cardiac output

Question 24

What is alveolar ventilation in healthy individuals?

Answer 24

4-6 L/min

Question 25

What is pulmonary blood flow (perfusion) in healthy individuals?

Answer 25

5 L/min

Question 26

What is the V/Q for lungs in healthy individuals?

Answer 26

0.8 - 1.2 (4-6 / 5)

Question 27

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

Answer 27

V/Q > 1

Question 28

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

Answer 28

V/Q < 1

Question 29

What is the consequence of mismatched pulmonary blood flow and ventilation?

Answer 29

impaired O2 and CO2 transfer

Question 30

Why are there apical and basal differences in gas exchange?

Answer 30

gravity - pulls lung wall downwards, so Ppl is more negative at apex resulting in increased PL so there is increased alveolar volume in apex.

Question 31

What would be the ideal V/Q ratio?

Answer 31

V/Q = 1 (inspired gas and cardiac output shared equally between alveoli so alveolar pO2 and arterial pO2 same)

Question 32

What is arterial hypoxemia?

Answer 32

arterial pO2 < 80 mmHg (normal is 100)

Question 33

Hypoxia definition

Answer 33

insufficient O2 to carry out metabolic functions - arterial pO2 < 60 mmHg

Question 34

Hypercapnia definition

Answer 34

increase in arterial pCO2 > 40 mmHg

Question 35

Hypocapnia definition

Answer 35

decrease in arterial pCO2 < 35 mmHg

Question 36

What are the 2 types of shunts that can impact the V/Q ratio?

Answer 36

anatomical shunt or physiological shunt

Question 37

What is an anatomical shunt?

Answer 37

an anatomical malformation resulting in mixed venous blood 'shunted' directly into arterial blood

Question 38

What is the anatomical shunt in the case of lungs?

Answer 38

mixed pulmonary artery blood shunted into pulmonary veins

Question 39

What aspects of the V/Q ratio is altered in an anatomical shunt?

Answer 39

perfusion (distribution of blood flow changed, but same alveolar ventilation)

Question 40

What is meant by a right to left shunt?

Answer 40

deoxygenated blood is shunted into oxygenated blood

Question 41

Where do most anatomical shunts occur?

Answer 41

heart (septal defects) - blood from RA/RV crosses septum to LA/LV (right to left shunt)

Question 42

Consequence of anatomical shunts

Answer 42

varying degrees of hypoxemia (pO2 depends on size of shunt). pCO2 unaffected

Question 43

Why do anatomical shunts not affect pCO2?

Answer 43

Central chemoreceptors highly sensitive to CO2 changes and will increase ventilation to decrease pCO2

Question 44

What is a physiological shunt in lungs?

Answer 44

absent ventilation to lungs (due to atelectasis) but continued perfusion

Question 45

What aspect of the V/Q ratio is affected by a physiological shunt?

Answer 45

alveolar ventilation (blood flow distribution is the same)

Question 46

What is the V/Q ration of a non-ventilated alveolus?

Answer 46

V/Q = 0

Question 47

What is the effect of a physiological shunt?

Answer 47

blood perfusing non-ventilated alveolus continues to be mixed venous and mixes with arterial blood causing varying hypoxemia

Question 48

Atelectasis definition

Answer 48

obstruction of ventilation due to mucous plugs, airway oedema, foreign bodies, tumours in airways

Question 49

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

Answer 49

V-Q mismatching - some alveoli V/Q > 1, some V/Q < 1 which results in varying alveolar and capillary gas contents

Question 50

Example of respiratory disorders

Answer 50

Chronic obstructive pulmonary disease (COPD), emphysema, chronic bronchitis, pulmonary fibrosis

Question 51

What is COPD?

Answer 51

Chronic obstructive pulmonary disease - condition encompassing emphysema and chronic bronchitis which obstructs airflow

Question 52

What is the most frequent cause of COPD?

Answer 52

long term smoking

Question 53

Symptoms of chronic obstructive pulmonary disease

Answer 53

chronic cough, chest tightness, shortness of breath, increased mucous production

Question 54

What is emphysema?

Answer 54

swelling/overinflation in alveoli

Question 55

What is the consequence of emphysema?

Answer 55

lungs loose elasticity and cannot fully expand and contract. Patients able to inhale but exhalation difficult due to decreased elastic recoil. (ventilation reduced)

Question 56

What is chronic bronchitis?

Answer 56

inflammation of bronchi causing mucous production and excessive swelling

Question 57

Symptoms of chronic bronchitis

Answer 57

shortness of breath with mild exertion, chest infections more prevalent

Question 58

What is pulmonary fibrosis?

Answer 58

type of interstitial lung disease where there is scarring (fibrosis) and thickening of tissue between alveoli.

Question 59

Consequence of pulmonary fibrosis

Answer 59

decreased elasticity and decreased gas exchange (greater diffusion distance)

Question 60

How can lung volumes be measured?

Answer 60

vitalograph / spirogram (volume of gas exhaled vs time)

Question 61

What is FVC/FEV?

Answer 61

Force vital capacity / forced expiratory volume - volume that can be breathed out at maximal speed following full inspiration

Question 62

What is FEV1?

Answer 62

forced expiratory volume in one second - volume breathed out in the first second at maximum speed following full inspiration

Question 63

What is a healthy FEV1/FVC ratio?

Answer 63

FEV1/FVC > 70% (70% of lung volume expired in one second)

Question 64

What instruction would you give the patient to measure their FEV1/FVC ratio?

Answer 64

take a big inspiration and then exhale as fast as possible

Question 65

Examples of obstructive lung disease

Answer 65

emphysema, asthma, pulmonary oedema

Question 66

What is the FEV1/FVC ratio in patients with obstructive pulmonary disease?

Answer 66

FEV1/FVC < 70% (expire more slowly and overall volume expired is lower)

Question 67

Examples of restrictive lung diseases

Answer 67

pulmonary fibrosis, neuromuscular diseases, respiratory distress syndrome

Question 68

What is the FEV1/FVC ratio in patients with restrictive pulmonary disease?

Answer 68

FEV1/FVC > 70% (able to expired 70% of lung volume in one second but FVC is smaller (80% or less of healthy individual))

Question 69

What is RQ?

Answer 69

respiratory quotient - ratio of amount of CO2 produced by metabolism to amount of O2 consumed

Question 70

What is tidal volume?

Answer 70

volume of gas inspired/expired during one respiratory cycle

Question 71

What is vital capacity?

Answer 71

volume which can be breathed out after a full inspiration