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:
      1. Gas dilution - use tracer gas
      2. 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
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