T2 L5: Lung Function Tests

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Zey

Cards (31)

What does spirometry do?
facilitates the measurement of airflow and lung volumes
it is:
uncomplicated
affordable
reliable
What are the 2 spirometry methods?
Bellows spirometer: measures volume in a calibrated chamber
Pneumotachograph: measures proportional pressure gradient over a defined resistance, which can be used to calculate flow according to Ohm's law
What is TV (tidal volume)?
volume of air that leaves lungs during normal breathing
What is FRC (functional residual volume)?
volume of gas within the lungs at the end of normal expiration
What is TLC (total lung capacity)?
volume of gas in the lungs after a full inspiration
What is RV (residual volume)?
volume of gas in the lungs after a full expiration
What is VC (vital capacity)?
volume of air expelled by a full expiration from a position of full inspiration
What does a flow-volume loop show?
how flow changes with volume
What is VC and how is it measured?
maximal amount of air that can be exhaled when blowing out at a steady rate
measured with spirometry
individual takes a full slow inspiration and blows steadily for as long as possible until no more air is left
nose clip to prevent air leaks from nose due to low flow
How is IC (inspiratory capacity)measured?
performed by taking a fast breath in after breathing all the way out
What is lung volume measurement?
offers additional information to spirometry to aid diagnosis
used to confirm restrictive lung disease
expensive equipment
two established methods:
Gas dilution - use tracer gas
Body plethysmography - body box with either constant volume or constant pressure principle
What happens to TLC (lung vol. at maximal inspiration) in obstructive and restrictive lung disease?
obstructive: increases (secondary to hyperinflation)
restrictive: decreases
What happens to RV during obstructive and restrictive lung disease?
obstructive: increases
restrictive: decreases
What happens to the RV/TLC ration during hyperinflation?
it increases
how is FRC measured?
helium dilution method
spirometry indications
o Assessment of respiratory symptoms
o Follow up of pulmonary disease
o Monitoring of disease progress
o Pre-operative assessment
spirometry: absolute contradictions
pulmonary TB
spirometry: relative contraindication
o Pneumothorax (6-weeks prior)
o Aneurism
o Embolism
o Recent surgery (4-weeks)
o Recent MI/unstable CV status (4-weeks)
o Recent haemoptysis
o Acutely unwell
what is used for reference equations in spirometry
the global lung function initiative (GLI)
GLI allows for standardised reports
Include largest samples of healthy individuals and represent a single standard to compare observed measurements applicable across all ages
Issues with GLI equations
o Does not include data from all populations of the world
o Does not explicitly consider the factors that may contribute to the observed differences in lung function between populations
o only Four populations
spirometry patterns
obstructive: FEV1/FVC <0.7
restrictive: FEV1/FVC >0.7
normal spirometry 
.
what does this spirometry show?
fixed airflow obstruction
What are the gas transfer measure?
Transfer factor for carbon monoxide (TLCO) - the amount of CO gas that diffuses through the alveolo-capillary membrane
Single breath method - easy to perform and readily available; but motivating paitents can be a disadvantage
VA - ventilated volume
how much alveoli volume is available for gas exchange
KCO
rate-constant amount of gas-exchanged between the alveolar space and red blood cells relative to the ventilated volume (TLCO/VA)
what does reduced TLCO and KCO suggest?
diffusion disorder (i.e. pulmonary fibrosis)
what does isolated reduced TLCO and normal KCO suggest?
result of reduced lung volume (i.e. post-pneumonectomy)
Reduced Hb will result in a reduction of CO uptake falsely indicating a diffusion disorder
intepretation strageies