gas exchange and lung function testing

Question 1

what features maximise gas transport in the lungs

Answer 1

• Large exchange area
• A thin diffusion membrane
• A low partial pressure difference
• A high permeability coefficient.

Question 2

what is the average partial pressure of oxygen in the alveolar gas?

Answer 2

100mmHg

Question 3

what can cause reduced surface area of the alveoli?

Answer 3

pneumonectomy, lobectomy or reduced ventilation from airway obstruction or reduced effective area with emphysema or increased dead space

Question 4

what can cause increased thickness of the alveolar membrane?

Answer 4

pulmonary fibrosis, alveolar proteinosis, and acute lung injury

Question 5

what can cause reduced oxygen concentration?

Answer 5

high altitude

Question 6

what can cause inadequate time for gas transfer in the alveoli?

Answer 6

lung disease

Question 7

why do the lung apices have a high partial pressure of oxygen than the bases?

Answer 7

ventilation perfusion mismatch

Question 8

what is the normal value for apical alveolar gas?

Answer 8

135mmHg

Question 9

what is the normal value for basal alveolar gas?

Answer 9

92mmHg

Question 10

why does the blood in the apices have a higher partial pressure?

Answer 10

bc the blood leaving the apical alveoli are fully saturated

Question 11

how do the lungs adjust CO2 excretion?

Answer 11

changing the breathing rate

Question 12

what are the two important forces holding lungs to the thoracic wall?

Answer 12

intrapleural fluid cohesiveness (surface tension)

negative intrapleural pressure

Question 13

explain the surface tension on the surface of the lungs

Answer 13

water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart

Question 14

explain how the negative intrapleural pressure holds the lungs to the thoracic wall

Answer 14

sub-atmospheric intrapleural pressure creates a pressure gradient between the lung wall and the chest wall. This holds the outer surface of the lung against the inner surface of the thorax

Question 15

what are the two layers of the pleura?

Answer 15

parietal pleura - covers the lungs

visceral pleura - attached to the thoracic wall

Question 16

what type of membrane is the pleura?

Answer 16

serous membrane

Question 17

where do the two layers of the pleura fuse?

Answer 17

at the hilum

Question 18

what is Boyle’s Law?

Answer 18

if the volume of a gas is made to increase the pressure exerted by the gas decreases

Question 19

what does Poiseuille’s law state?

Answer 19

as the diameter increases, the flow of gas into the alveoli increases as the fourth power of the radius of the alveolar ducts and respiratory bronchioles

Question 20

how can Boyle’s Law be applied to inspiration?

Answer 20

During inspiration the increase in the size of the lungs makes the intra-alveolar pressure fall

Question 21

what is the decrease in pressure in the lungs during inspiration?

Answer 21

about 1mmHg

Question 22

how does the elastic recoil during expiration affect pressure?

Answer 22

causes pressure in the lungs to rise

Question 23

what 2 factors cause the lungs to recoil during expiration?

Answer 23

elastic connective tissue in the lungs

alveolar surface tension

Question 24

what is alveolar surface tension?

Answer 24

the attraction between water molecules at the water-air interface

Question 25

what would happen to the alveoli if they didn't have surfactant?

Answer 25

the surface tension would make the alveoli completely collapse during expiration as they have no connective tissue to hold them open

Question 26

what does Laplace's law state about smaller alveoli?

Answer 26

have a higher tendency to collapse during expiration

Question 27

why are collapsed alveoli hard to reinflate?

Answer 27

walls tend to stick together

Question 28

what are the lipoproteins which can make different forms of surfactants?

Answer 28

types A, B, C and D

Question 29

what do surfactants containing lipoprotein B and C do?

Answer 29

reduces surface tension and ensure proper lung function

Question 30

what do surfactants containing lipoproteins A and D do?

Answer 30

coat bacteria and viruses and help the immune system deal with them

Question 31

what is surfactant D deficiency a risk for?

Answer 31

pulmonary tuberculosis

Question 32

why is there no mucus in alveoli?

Answer 32

would impair gas exchange

Question 33

how are pathogens in the alveoli dealt with?

Answer 33

macrophages that can move around the alveoli and phagocytose invading bacteria

Question 34

what causes respiratory distress syndrome of newborns?

Answer 34

premature babies may not have enough pulmonary surfactants bc foetal lungs cant synthesise surfactant until late in pregnancy

Question 35

how does respiratory distress syndrome present?

Answer 35

lungs are hard to inflate and some alveoli may fail to open at all during inspiration baby has to make strenuous effort to breath in and overcome high surface tension

Question 36

what is the purpose of spirometry?

Answer 36

assess prognosis of respiratory disease, assess severity, effect of treatment etc

Question 37

how is total lung capacity measured?

Answer 37

inspiration of a fixed volume of gas such as helium rebreathing it so its evenly distributed in the lungs total lung capacity can be measured by measure volume of helium in expired gas

Question 38

why is helium used to measure TLC?

Answer 38

isn't absorbed into the blood

Question 39

what is the equation for calculating TLC?

Answer 39

V2 = (C1 x V1)/C2 ``` V2 = TLC C1 = conc of helium in the inspired gas C2 = conc of helium in the rebreathed gas V1 = volume of inspired gas ```

Question 40

what does peak flow rate assess?

Answer 40

airway resistance

Question 41

what conditions is peak flow used for?

Answer 41

obstructive lung diseases such as asthma and COPD

Question 42

how is peak flow rate measured?

Answer 42

measured by the patient taking a full inspiration and then giving a short sharp blow into the peak flow meter The BEST of three attempts is usually taken

Question 43

what factors cause peak flow rate to vary?

Answer 43

age, height and gender

Question 44

how is ventilation/perfusion measured?

Answer 44

analysed with isotope scanning

Question 45

what can reduced ventilation and normal perfusion in pneumonia lead to?

Answer 45

hypoxaemia

Question 46

how can efficiency of oxygen transport across the alveolar membrane be measured?

Answer 46

comparing alveolar oxygen levels with arterial levels

Question 47

how can alveolar oxygen partial pressures be measured?

Answer 47

analysis of the last portion of expired gas with an oxygen meter - will have the same composition as alveolar gas

Question 48

how can arterial oxygen partial pressure be measured?

Answer 48

with a pulse oximeter which measure saturation of Hb with oxygen --> related to partial pressure using the curve