Lung volumes and lung function testing Flashcards
What is lung compliance?
stretchiness of the lungs, ensued by elastic recoil
Which part of the lung is more compliant?
the lung base (larger volume) in comparison to the apex of the lung
therefore has better ventilation
What can cause decreased compliance?
higher pressure - stiffer lung
pulmonary fibrosis, alveolar oedema
What can cause increased compliance?
normal ageing lung
low pressure
What is the total lung compliance dependent on?
- thoracic cage elasticity
2. elasticity of the lungs
What is needed for efficient ventilation?
high lung compliance
low alveolar surface tension due to surfactant
What do lung tests need to assess?
mechanical condition of the lungs - pulmonary fibrosis
resistance of the airways - asthma
diffusion across the alveolar membrane - pulmonary fibrosis
Tests done in the clinic
spirometer: lung volumes
helium dilution or nitrogen washout: functional residual capacity
flow-volume curve or peak flow meter: PEF rate
vitalograph: FEV1 / FVC
Tidal volume (TV)
volume of air entering and leaving the lung with each normal breath
Inspiratory reserve volume (IRV)
extra volume of air inspired above the normal tidal volume
Expiratory reserve volume (ERV)
extra volume of air expired by forceful expiration at the end of normal tidal expiration
Vital capacity (VC)
maximum amount of air expelled from the lungs after first filling the lungs to a maximum then expiring to a maximum
(TV + IRV + ERV)
What measurements can u not make with spirometry?
residual volume
functional residual volume
total lung capacity
Residual volume (RV)
volume of air remaining in the lungs after the most forceful expiration
Functional residual capacity (FRC)
amount of air that remains in the lungs at the end of normal expiration
(ERV + RV)
Total lung capacity (TLC)
maximum volume of air the lungs can hold
VC + RV
What is FVC?
Forced vital capacity
total volume exhaled (normally around 5L)
What is FEV1?
volume expired in the first second
normally >80%
Why is helium used in helium dilution?
not metabolised in the blood and therefore can be tracked
Equation and rearrangement to find FRC using helium dilution
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
Nitrogen washout
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
What is a restrictive deficit?
lung expansion compromised, alterations in lung parenchyma, disease of pleura or chest wall
lungs do not fill to capacity - less full before expiration
Causes of restrictive deficit
pulmonary fibrosis
scoliosis
(not airways)
Effect of restrictive deficit on FVC and FEV1
FVC reduced
FEV1 relatively normal
FEV1/FVC remains relatively normal/increased
What is a obstructuve deficit?
airway obstruction (narrowed), lungs can still fill to capacity resistance increased on expiration
Causes of obstructive deficit
asthma, COPD
Effect of obstructive deficit on FVC and FEV1
FEV1 reduced, FVC relatively normal
low FEV1/FVC
Vitalograph
measures ability to move air out of the lungs (FVC and FEV1)
restrictive - ends lower than normal
obstructive - ends at normal, less steep
Flow-volume curve
expiratory flow rate and expiratory volume measured
Procedure for f-v curve
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
F-v curve annotations
y axis: flow of expiration (L/s)
x axis: volume (L) reverse
Flow volume loops
restrictive - to the right (start with smaller volume)
obstructive - weird shape as smaller airways are affected
How to measure gas transfer?
diffusion conductance
how easily CO/CO2 crosses from alveolar air to blood
inhale and hold breath, calculate before and after
Clinical relevance of gas transfer measurement
fibrosis of lungs - gas diffusion compromised
How to calculate diffusion capacity
lung volume and % of CO/CO2 in alveoli at the beginning and end of breath-hold
