Lung Function Testing

• Peak flow meter

  • very rapid exhaled 'puff' from full inspiration
  • measures peak expiratory flow rate (PEFR)
  • normal value ~ 500-600 L/min
• Vitalograph

  • sustained forced expiration from full inspiration
  • measures volumes exhaled
  • in total: forced vital capacity (FVC)
  • in first second: forced expiratory volume 1 (FEV1)
• Normal Vitalograph

  A) initial slope = PEFR

  B) FEV1/FVC > 0.75

  C) FVC

  D) FEV1

  E) normal

  
• Spirometer measures continuous trace

  A) normal breathing

  B) full expiration

  C) vital capacity

  D) full inspiration

  E) residual volume

  
• Work of Breathing: 2 factors to overcome

  • resistance
  • ease with which gas flows through conducting airways
  • compliance
  • expandability of lungs and chest wall
• Obstructive disease - narrowing of airways increases resistance
• Obstructive disease e.g. asthma (juvenile)

  A) same volume ultimately reached, but takes longer

  B) normal

  C) obstructive

  
• Obstructive disease e.g. juvenile asthma

  • FVC unchanged
  • FEV1 decreased
  • FEV1/FVC decreased
• Restrictive lung disease decreases compliance
• Restrictive disease e.g. severe pulmonary fibrosis

  A) normal

  B) restrictive

  C) lung cannot expand normally because of restriction

  
• Restrictive disease e.g. severe pulmonary fibrosis

  • FVC decreased
  • FEV1 decreased
  • FEV1/FVC unchanged/increase
• Predicted values for lung function tests vary with:

  • gender
  • height
  • age
• Obstructive = reducing the ability of air to move in/out of the lungs

  • e.g. asthma, COPD, bronchiectasis
• Restrictive = reducing the ability of the lungs to expand

  • e.g. fibrosis (anything ending in ...osis), scoliosis, obesity, myasthenia gravis
• Why do we test lung function?

  • diagnosis
  • monitoring/assessing response to treatment
  • screening e.g. before surgery or before starting a medication that may damage the lungs
• Bronchodilator Testing

  • using spirometry to assess response to a bronchodilator (usually salbutamol)
  • a positive response if FEV1 or FVC increases by >12% and 200ml
• FeNO testing

  • fractional exhaled nitric oxide (FeNO) testing is used in the diagnosis of asthma
  • NO is produced by cells in inflammation
  • patients blow into a machine that measures their FeNO level
  • >40 ppb is considered a positive test
  • smoking can lower a patient's FeNO levels
• Flow Volume Loops

  • assess the flow of air into and out of the lungs using a pnuemotachograph
  • they are often used in the further assessment of obstructive disorders
  • patients are asked to
  • maximally inhale
  • forced expiration as hard and fast as possible (to their residual volume, RV)
  • maximal inhalation as fast as possible (calculating their forced vital capacity, FVC)
• Flow Volume Loops - Normal

  • the flow rate during exhalation sharply increases, before tailing off
  • the volume is recorded along the x-axis
  • during inhalation, the graph is more symmetrical
• Flow Volume Loops - Restrictive

  • how would the graph change for a restrictive condition?
  • the forced vital capacity is reduced, as they are unable to expand their lungs to sufficiently use the space
  • their maximal flow rates may be reduced slightly, especially in mixed disease (e.g. COPD with bronchitis)
• Flow Volume Loops - Fixed Upper Airway Obstruction

  • e.g. tracheal stenosis, tracheal web
  • obstruction during both inspiration and expiration
  • forced vital capacity is unchanged
• Flow Volume Loops - Variable Extrathoracic Obstruction

  • e.g. goitre, anaphylaxis
  • the diameter of the pharynx, larynx and trachea changes very little during inhalation or exhalation
  • therefore, extrathoracic obstructions have a greater effect when the pressure is lower (during inhalation)
• Flow Volume Loops - variable intrathoracic obstruction

  • e.g. foreign body aspiration, endobronchial tumour
  • remember, the bronchi/bronchioles dilate during inhalation and constrict during exhalation
  • therefore, intrathoracic obstructions affect exhalation significantly more than inhalation
• Flow Volume Loops - Lower Airway obstructive

  • e.g. asthma, COPD, bronchiectasis
  • The FVC is largely unchanged
  • Peak expiratory flow rate is reduced
• Diffusing Capacity - DLCO

  • measures ability of lungs to transport inhaled gas from alveoli to pulmonary capillaries
  • patient empties their lungs
  • takes a breath of controlled gas containing 0.3% CO
  • holds breath for 10 seconds
  • exhales
  • exhaled gas analysed for pCO2, compared to the inhaled pCO
• Reduced DLCO (<80% expected)

  • a reduced diffusing capacity is due to conditions which reduce the effective alveolar surface area for gas exchange
  • fibrosis (hinderance in the alveolar wall)
  • pneumonectomy/lobectomy (decreased lung volume)
  • emphysema (decreased alveolar surface area)
  • pulmonary embolus (insufficient blood being pumped into the pulmonary arteries)
  • heart failure (insufficient blood being pumped into the pulmonary arteries)
• Increased DLCO (>120% expected)

  • increased diffusing capacity results from an increase in blood supply to the lungs and impaired exhalation
  • polycythaemia (more erythrocytes able to accept oxygen)
  • exercise (increased pulmonary blood flow)
  • asthma (impaired exhalation and increased recruitment of surrounding capillary beds)
  • obesity (impaired exhalation and increased recruitment of surrounding capillary beds)
  • pulmonary haemorrhage (extra blood in the alveoli that CO can bind to)
• What does a vitalograph measure?

  Volumes exhaled

  • forced vital capacity (FVC)
  • forced expiratory volume 1 (FEV1)
• Forced vital capacity is the maximum volume of air that can be removed from the lungs during forced expiration
• Forced expiratory volume is the volume of gas expelled during specific time intervals of FVC
• How is a vitalograph used?

  • full inspiration, followed by sustained forced expiration
• Vital capacity - total volume of air that can be exhaled after maximal inhalation
• Obstructive lung disease - airways are narrowed, resulting in increased resistance (reduce ability of air to move in and out of lungs)
• Why are children at greater risk from obstructive lung disease?

  • smaller airways
  • higher respiratory rates (main mechanism to compensate for narrowed airways is to increase respiratory rate)
• Restrictive lung disease - reduced lung compliance, leading to reduced lung volume (reduced ability of lungs to expand)
• Obstructive lung conditions

  • chronic obstructive pulmonary disease (COPD)
  • asthma
  • bronchiectasis
  • bronchiolitis
  • upper airway obstruction
• Bronchiectasis - abnormal dilation of the bronchi with accumulation of mucus
• bronchiolitis - inflammation of the bronchioles, usually affecting babies and young children
• Restrictive lung conditions (pulmonary)

  • pulmonary fibrosis
  • pleural thickening
• Restrictive lung conditions (extrapulmonary)

  • obesity
  • scoliosis
  • ankylosing spondylitis
  • pectus excavatum
  • myasthenia gravis