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Asthma > Lung volumes and lung function testing > Flashcards

Lung volumes and lung function testing Flashcards

1
Q

What is lung compliance?

A

stretchiness of the lungs, ensued by elastic recoil

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2
Q

Which part of the lung is more compliant?

A

the lung base (larger volume) in comparison to the apex of the lung
therefore has better ventilation

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3
Q

What can cause decreased compliance?

A

higher pressure - stiffer lung

pulmonary fibrosis, alveolar oedema

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4
Q

What can cause increased compliance?

A

normal ageing lung

low pressure

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5
Q

What is the total lung compliance dependent on?

A
  1. thoracic cage elasticity

2. elasticity of the lungs

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6
Q

What is needed for efficient ventilation?

A

high lung compliance

low alveolar surface tension due to surfactant

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7
Q

What do lung tests need to assess?

A

mechanical condition of the lungs - pulmonary fibrosis
resistance of the airways - asthma
diffusion across the alveolar membrane - pulmonary fibrosis

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8
Q

Tests done in the clinic

A

spirometer: lung volumes
helium dilution or nitrogen washout: functional residual capacity
flow-volume curve or peak flow meter: PEF rate
vitalograph: FEV1 / FVC

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9
Q

Tidal volume (TV)

A

volume of air entering and leaving the lung with each normal breath

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10
Q

Inspiratory reserve volume (IRV)

A

extra volume of air inspired above the normal tidal volume

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11
Q

Expiratory reserve volume (ERV)

A

extra volume of air expired by forceful expiration at the end of normal tidal expiration

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12
Q

Vital capacity (VC)

A

maximum amount of air expelled from the lungs after first filling the lungs to a maximum then expiring to a maximum
(TV + IRV + ERV)

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13
Q

What measurements can u not make with spirometry?

A

residual volume
functional residual volume
total lung capacity

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14
Q

Residual volume (RV)

A

volume of air remaining in the lungs after the most forceful expiration

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15
Q

Functional residual capacity (FRC)

A

amount of air that remains in the lungs at the end of normal expiration
(ERV + RV)

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16
Q

Total lung capacity (TLC)

A

maximum volume of air the lungs can hold

VC + RV

17
Q

What is FVC?

A

Forced vital capacity

total volume exhaled (normally around 5L)

18
Q

What is FEV1?

A

volume expired in the first second

normally >80%

19
Q

Why is helium used in helium dilution?

A

not metabolised in the blood and therefore can be tracked

20
Q

Equation and rearrangement to find FRC using helium dilution

A

C1 x V1 = C2 x (V1 + V2)
V2 = V1 x C1 - C2 / C2

C1 and V1 is conc/vol of helium before equilibrium
C2 is conc of helium after equilibrium
V2 is unknown vol of air in lungs

21
Q

Nitrogen washout

A

mixed air inspired
100% oxygen inspired
expires into spirometer system with N2 meter
repeated until N2 in lungs replaced with O2
FRC calculated from exhaled N2 and estimated alveolar N2

22
Q

What is a restrictive deficit?

A

lung expansion compromised, alterations in lung parenchyma, disease of pleura or chest wall
lungs do not fill to capacity - less full before expiration

23
Q

Causes of restrictive deficit

A

pulmonary fibrosis
scoliosis
(not airways)

24
Q

Effect of restrictive deficit on FVC and FEV1

A

FVC reduced
FEV1 relatively normal
FEV1/FVC remains relatively normal/increased

25
Q

What is a obstructuve deficit?

A 
airway obstruction (narrowed), lungs can still fill to capacity
resistance increased on expiration
26
Q

Causes of obstructive deficit

A

asthma, COPD

27
Q

Effect of obstructive deficit on FVC and FEV1

A

FEV1 reduced, FVC relatively normal

low FEV1/FVC

28
Q

Vitalograph

A

measures ability to move air out of the lungs (FVC and FEV1)
restrictive - ends lower than normal
obstructive - ends at normal, less steep

29
Q

Flow-volume curve

A

expiratory flow rate and expiratory volume measured

30
Q

Procedure for f-v curve

A

deep breath in - TLC , deep and fast breath out - RV
TLC - PEF: effort dependent, increase in effort will increase flow rate
PEF - RV: effort independent, increase in effort won’t increase flow rate

31
Q

F-v curve annotations

A

y axis: flow of expiration (L/s)

x axis: volume (L) reverse

32
Q

Flow volume loops

A

restrictive - to the right (start with smaller volume)

obstructive - weird shape as smaller airways are affected

33
Q

How to measure gas transfer?

A

diffusion conductance
how easily CO/CO2 crosses from alveolar air to blood
inhale and hold breath, calculate before and after

34
Q

Clinical relevance of gas transfer measurement

A

fibrosis of lungs - gas diffusion compromised

35
Q

How to calculate diffusion capacity

A

lung volume and % of CO/CO2 in alveoli at the beginning and end of breath-hold

Asthma (6 decks)

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