25- PFTs

• Indications of Pulmonary Function Tests (PFTs)

  • 45 years old or older smokers or ex-smokers
  • Prolonged or excessive cough or sputum production
  • History of exposure to lung irritation
  • To assess disease severity with progression in: COPD, BA, CF, ILD, sarcoidosis, CHF, Pul HTN, congenital heart disease, Neurological disorders: ALS, GB, MS, MG
  • To detect pulmonary disease in patients presenting with chest pain, cough, orthopnea, dyspnea, wheeze, phlegm, cyanosis, clubbing, reduced BS, chest wall problem, abnormal ABG or CXR
  • For preoperative risk stratification
  • Evaluating disability and impairment

  
• Technique for PFTs

  1. Breathe in & out several times (Normal breaths and deep breaths several times)

  2. Breathe in as deeply as you can

  3. Place mouth completely around mouthpiece, blow out as fast and quick as possible for at least 6 seconds

  4. Repeat the whole test 3 times to ensure the results are reproducible and accurate
• FVC (Forced Vital Capacity)

  Maximum amount of air a person can exhale, usually measured in 6 seconds
• FVC % Predicted Values

  • 80-120% of predicted is normal
  • <35% = very severe reduction
  • <50% = severe reduction
  • 50-70% = moderate reduction
  • 70-80% = mild reduction
• FEV1 (Forced Expiratory Volume in 1 second)


  Part of FVC. Amount you can exhale in the 1st second
• FEV1/FVC Ratio


  Percentage of FVC that can be expired in 1 second
• Predicted


  The value given by the machine based on age, gender, height, weight
• Actual

  The value the patient actually scores
• % Predicted


  (Actual/Predicted) is used to decide if the score is Normal or Reduced
• Interpreting PFT Results

  #1: Look at the FEV1/FVC ratio

  If the % predicted is <80% → obstructive pattern

  If the % predicted is normal or high → normal or restrictive pattern (differentiate by FEV1 and FVC values)

  #2: Look at FEV1 and FVC

  If the % predicted for both is normal → normal

  If the % predicted for both is low → restrictive pattern → determine if due to pulmonary vs extrapulmonary disease by DLCO
• DLCO (Diffusing Capacity of the Lungs for Carbon Monoxide)

  The patient inhales trace amount of CO, CO traverses the alveolar bed much faster & therefore most of the CO inhaled must be absorbed. Low absorption indicates pulmonary scarring/fibrosis (ex: ILD)

  If DLCO is low: pulmonary cause (ILD)

  If DLCO is normal: extrapulmonary cause (neuromuscular)

  
• Pure Obstructive Pattern

  Low FEV1/FVC, low FEV1, normal or slightly low FVC
• Bronchodilator Challenge


  Done if obstructive pattern is found

  If obstruction is reversible after bronchodilator (i.e. FEV1 increase by 12% and FEV1 or FVC by 200ml -both needed) → reversible airway obstruction → asthma (although some pts with COPD may have a degree of reversibility)
• Methacholine Challenge Test

  Done if asthma is suspected but all other test (PFTs, ABG, CXR) are normal, or if occupational/exercise-induced asthma is suspected

  Patient inhales methacholine (bronchoconstrictor). A positive test is 20% decrease in FEV1 with the use of methacholine.
• Flow-volume loops