BAMS: Respiration (ventilation-perfusion relationships and disorders)

Question 1

what is ventilation?

Answer 1

the process by which air moves in and out of lungs

Question 2

what is perfusion?

Answer 2

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

Question 3

what is a major determinant of normal gas exchange and thus the level of PO2 and PCO2 in blood?

Answer 3

the relationship between ventilation and perfusion (V/Q ratio?

Question 4

what is the distribution of ventilation in lungs?

Answer 4

not uniformly distributed

Question 5

what affects the distribution of ventilation in lungs?

Answer 5

gravity, compliance and resistance

Question 6

how does gravity affect the distribution of ventilation in the lungs?

Answer 6

in upright position, alveoli in apex is more expanded than at base (increased alveolar volume in apex, pleural pressure is more negative at apex than base, and transpulmonary pressure is greater at apex than at base)

gravity pulls lung down and away from chest wall

Question 7

what is compliance (in relation to distribution of ventilation in lungs)?

Answer 7

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

Question 8

what is resistance (in relation to distribution of ventilation in lungs)?

Answer 8

any narrowing or obstruction of the airway

Question 9

what does high compliance mean?

Answer 9

that the lungs and chest wall expand easily

Question 10

what is a common feature in pulmonary conditions?

Answer 10

decreased compliance (lung volume is decreased - more difficult for patients to empty lungs)

Question 11

examples of pulmonary conditions?

Answer 11

tuberculosis (scarring in lung tissue)

edema (lung filled with fluid)

deficiency in surfactant production

emphysema (destruction of elastic fibres)

Question 12

what is a common feature in pulmonary conditions?

Answer 12

increased resistance

Question 13

examples of pulmonary conditions?

Answer 13

asthma

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

Question 14

what are two types of dead space?

Answer 14

anatomical dead space
physiological dead space

Question 15

what is anatomical dead space?

Answer 15

volume of gas during each breath that fills the conducting airways (30%/ 150ml of each breath doesn’t ever reach the lungs)

Question 16

what is physiological dead space?

Answer 16

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

Question 17

which blood circulation is more influenced by gravity - pulmonary or systemic circulation?

Answer 17

pulmonary circulation - low pressure and low resistance system

Question 18

how is the V/Q ratio defined for a single alveolus?

Answer 18

alveolar ventilation divided by capillary flow

Question 19

how is the V/Q ratio defined for a lungs?

Answer 19

total alveolar ventilation divided by cardiac output

Question 20

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

Answer 20

0.8-1.2

(alveolar ventilation ~4-6 L/min)
(pulmonary blood flow ~5L/min)

Question 21

what is the V/Q ratio when ventilation exceeds perfusion? (i.e., when air moving in and out of lungs is more than the process of deoxygenated blood passing through the lung and becoming oxygenated)

Answer 21

V/Q > 1

Question 22

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

Answer 22

V/Q < 1

Question 23

what does mismatching of pulmonary blood flow and ventilation result in?

Answer 23

impaired O2 and CO2 transfer

Question 24

is there apical and basal differences in gas exchange in the lungs?

Answer 24

yes (create avg value for PO2 in circulations)

Question 25

in a 'perfect' model, what is the V/Q ratio?

Answer 25

ventilation = perfusion (V/Q = 1) (alveolar PO2 and arterial PO2 are the same)

Question 26

what is arterial hypoxemia?

Answer 26

arterial PO2 < 80mmHg (normal ~100mmHg)

Question 27

what is hypoxia?

Answer 27

insufficient O2 to carry out metabolic functions - when arterial PO2 < 60mmHg

Question 28

what is hypercapnia?

Answer 28

increase in arterial PCO2 > 40mmHg

Question 29

what is hypocapnia?

Answer 29

decrease in arterial PCO2 < 35mmHg

Question 30

what is an example of a cause for mismatching between ventilation and perfusion?

Answer 30

anatomical shunt physiological shunt

Question 31

what is an anatomical shunt?

Answer 31

malformation/destruction in the anatomy

Question 32

what is a physiological shunt?

Answer 32

when the ventilation to lung units is absent in presence of continuing perfusion (due to a blockage) - so, blood passes through the lungs but that blood doesn't become ventilated

Question 33

what is atelectasis?

Answer 33

obstruction of ventilation due to mucous plug, airway oedema, foreign bodies, or tumors in airways

Question 34

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

Answer 34

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

Question 35

what is COPD?

Answer 35

it is a condition in which airflow is obstructed, due to increases in oedema and mucus

Question 36

what encompasses COPD?

Answer 36

emphysema and chronic bronchitis

Question 37

what is the most frequent cause of COPD?

Answer 37

long-term smoking

Question 38

what are symptoms of COPD?

Answer 38

chronic cough chest tightness shortness of breath increased mucous production

Question 39

what is emphysema?

Answer 39

chronic lung disease that damages the air sacs in the lungs, making it difficult to breath (causes swelling in alveolar sacs)

Question 40

what happens to the lungs in emphysema?

Answer 40

lung lose elasticity, cannot fully expand and contract

Question 41

symptoms of emphysema?

Answer 41

patients can inhale, but exhalation is difficult due to decreased elastic recoil

Question 42

what is chronic bronchitis?

Answer 42

inflammation of bronchi causing mucous production and excessive swelling

Question 43

symptoms of chronic bronchitis?

Answer 43

shortness of breath with mild exertion chest infections more prevalent

Question 44

what does interstitial mean?

Answer 44

relating to spaces between cells, tissues, or organs in the body

Question 45

what is an example of an interstitial lung disease?

Answer 45

pulmonary fibrosis

Question 46

result of tissue in lungs from pulmonary fibrosis?

Answer 46

scarring and thickening of tissue between alveoli

Question 47

cause of pulmonary fibrosis on elasticity of lungs?

Answer 47

decreased elasticity

Question 48

result of pulmonary fibrosis on gas exchange in lungs?

Answer 48

decreased gas exchange

Question 49

what does measuring lung volume using vitalograph/spirogram display on a graph?

Answer 49

volume of gas exhaled against time

Question 50

why are there regional differences in ventilation and perfusion?

Answer 50

because the pulmonary circulation is a low pressure, low resistance system there are differences in ventilation and perfusion, mainly due to gravity but also compliance and resistance have an effect