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gas exchange and lung function testing Flashcards

1
Q

what features maximise gas transport in the lungs

A
  • Large exchange area
  • A thin diffusion membrane
  • A low partial pressure difference
  • A high permeability coefficient.
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2
Q

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

A

100mmHg

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3
Q

what can cause reduced surface area of the alveoli?

A

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

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4
Q

what can cause increased thickness of the alveolar membrane?

A

pulmonary fibrosis, alveolar proteinosis, and acute lung injury

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5
Q

what can cause reduced oxygen concentration?

A

high altitude

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6
Q

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

A

lung disease

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7
Q

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

A

ventilation perfusion mismatch

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8
Q

what is the normal value for apical alveolar gas?

A

135mmHg

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9
Q

what is the normal value for basal alveolar gas?

A

92mmHg

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10
Q

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

A

bc the blood leaving the apical alveoli are fully saturated

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11
Q

how do the lungs adjust CO2 excretion?

A

changing the breathing rate

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12
Q

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

A

intrapleural fluid cohesiveness (surface tension)

negative intrapleural pressure

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13
Q

explain the surface tension on the surface of the lungs

A

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

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14
Q

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

A

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

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15
Q

what are the two layers of the pleura?

A

parietal pleura - covers the lungs

visceral pleura - attached to the thoracic wall

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16
Q

what type of membrane is the pleura?

A

serous membrane

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17
Q

where do the two layers of the pleura fuse?

A

at the hilum

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18
Q

what is Boyle’s Law?

A

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

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19
Q

what does Poiseuille’s law state?

A

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

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20
Q

how can Boyle’s Law be applied to inspiration?

A

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

21
Q

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

A

about 1mmHg

22
Q

how does the elastic recoil during expiration affect pressure?

A

causes pressure in the lungs to rise

23
Q

what 2 factors cause the lungs to recoil during expiration?

A

elastic connective tissue in the lungs

alveolar surface tension

24
Q

what is alveolar surface tension?

A

the attraction between water molecules at the water-air interface

25
Q

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

A

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

26
Q

what does Laplace’s law state about smaller alveoli?

A

have a higher tendency to collapse during expiration

27
Q

why are collapsed alveoli hard to reinflate?

A

walls tend to stick together

28
Q

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

A

types A, B, C and D

29
Q

what do surfactants containing lipoprotein B and C do?

A

reduces surface tension and ensure proper lung function

30
Q

what do surfactants containing lipoproteins A and D do?

A

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

31
Q

what is surfactant D deficiency a risk for?

A

pulmonary tuberculosis

32
Q

why is there no mucus in alveoli?

A

would impair gas exchange

33
Q

how are pathogens in the alveoli dealt with?

A

macrophages that can move around the alveoli and phagocytose invading bacteria

34
Q

what causes respiratory distress syndrome of newborns?

A

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

35
Q

how does respiratory distress syndrome present?

A

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

36
Q

what is the purpose of spirometry?

A

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

37
Q

how is total lung capacity measured?

A

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

38
Q

why is helium used to measure TLC?

A

isn’t absorbed into the blood

39
Q

what is the equation for calculating TLC?

A

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
40
Q

what does peak flow rate assess?

A

airway resistance

41
Q

what conditions is peak flow used for?

A

obstructive lung diseases such as asthma and COPD

42
Q

how is peak flow rate measured?

A

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

43
Q

what factors cause peak flow rate to vary?

A

age, height and gender

44
Q

how is ventilation/perfusion measured?

A

analysed with isotope scanning

45
Q

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

A

hypoxaemia

46
Q

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

A

comparing alveolar oxygen levels with arterial levels

47
Q

how can alveolar oxygen partial pressures be measured?

A

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

48
Q

how can arterial oxygen partial pressure be measured?

A

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

c (25 decks)

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