Lab

Pulmonary Function Test

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Pulmonary Function Test, Spirometry, PFT

  • Criteria
  • Adequate test (Minimum of 3 tests)
  1. Full inhalation
  2. Maximal exhalation
  3. No cough or glottic closure (or other artifacts in the flow-volume loop)
  4. Flow-volume loop should reach a baseline plateau at the end of expiration (right side of the loop) prior to inspiratory loop
  5. Adequate test duration (exhale for 6 or more seconds)
  6. No mouth-piece leak
  7. Variation between two best effort tests are within 5%
    1. Difference between 2 largest FVC <0.2 L
    2. Difference between 2 largest FEV1 <0.2 L
  • Protocol
  1. Pulmonary Function Test (PFT)
    1. Adult: 15 minutes
    2. Child: 15-30 minutes (age 5 years and older)
  2. Full Pulmonary Function Test (PFT) with pre- and post-Bronchodilator testing
    1. Time: 45 minutes
  3. Full Pulmonary Function Test (PFT) and Carbon Monoxide diffusion (DLCO)
    1. Time: 60 minutes
  • Tests
  • Screening Spirometry Measures
  1. Forced Vital Capacity (FVC)
    1. Obstructive lung: Mildly Decreased or normal
    2. Restrictive lung: Mildly to severely decreased
  2. Forced Expiratory Volume in 1 second (FEV1)
    1. Obstructive lung: Mildly to severely decreased
    2. Restrictive lung: Moderately to severely decreased
  3. FEV1 to FVC Ratio (Normally over 75%)
    1. Not useful if both FEV1 and FVC are normal
    2. Obstructive lung: Moderately to severely decreased
    3. Restrictive lung: Normal or increased
    4. Interpretation via Lower Limit of Normal (LLN) is preferred
      1. Swanney (2008) Thorax 63:1046–51 [PubMed]
    5. Normal ranges vary by age
      1. Age 8 to 19 years: FEV1/FVC 85%
      2. Age 20 to 39 years: FEV1/FVC 80%
      3. Age 40 to 59 years: FEV1/FVC 75%
      4. Age 60 to 80 years: FEV1/FVC 70%
  4. Forced Expiratory Small Airway Flow (FEF25-75)
    1. Effort Independent
    2. More variable than FEV1 or FVC
  1. Total Lung Capacity (TLC)
    1. Obstructive Lung Disease: Normal or mild change
    2. Restrictive Lung Disease: Decreased
  2. Residual Volume (RV)
    1. Obstructive Lung Disease: Increased
    2. Restrictive Lung Disease: Decreased
  3. Maximal voluntary ventilation (MMV)
    1. Technique
      1. Patient breathes hard and fast for 12 seconds
      2. Calculate liters per minute by extrapolating
    2. Interpretation
      1. Normal: MMV = FEV1 x 40
      2. Low MMV
        1. FEV1 and FVC reduced: Restrictive Lung Disease
        2. FEV1 and FVC normal
          1. Inadequate effort or neuromuscular disease
          2. Severe airway disorder
  • Tests
  • Additional
  1. Diffusing Capacity (DLCO)
    1. Reversible Obstructive Lung Disease (Asthma): Normal
    2. Irreversible Obstructive Lung Disease (COPD): Low
  2. Inhalation Challenge Test (Methacholine Challenge)
  3. Bronchodilator response (Significant values)
    1. Response suggests reversible component
    2. FVC or FEV1 improves by 12 to 15% over baseline
    3. FVC or FEV1 increases by at least 200 ml
    4. FEF25-75 improves by 15 to 25% over baseline
  4. Exercise Testing Endpoints
    1. Patient uncomfortable and requests to stop
    2. Disturbing Physiologic Change
      1. Hypoxemia
      2. Hypotension
      3. Arrhythmia
    3. Reaching 90% of maximum Heart Rate (age predicted)
  • Protocol
  • Approach
  1. Step 1: Determine validity of Pulmonary Function Testing
    1. See Criteria above
  2. Step 2: Evaluate FEV1 to FVC Ratio
    1. FEV1 to FVC Ratio <0.7 (or <LLN or for children<85% of predicted)
      1. Go to Step 4 (Obstructive Lung Disease evaluation)
    2. FEV1 to FVC Ratio Normal
      1. Go to Step 3 (Restrictive Lung Disease evaluation)
  3. Step 3: Restrictive Lung Disease Evaluation (FEV1 to FVC Normal)
    1. Forced Vital Capacity (FVC) < LLN (or for age 5 to 18 years old, <80% of predicted)
      1. Consistent with Restrictive Lung Disease
      2. Perform complete Pulmonary Function Tests with DLCO
      3. Consider Restrictive Lung Disease differential diagnosis
    2. Forced Vital Capacity (FVC) Normal
      1. No Restrictive Lung Disease
      2. Consider further Asthma Evaluation if high level of suspicion
        1. Inhalation Challenge Test (e.g. Methacholine Challenge) or
        2. Exercise Spirometry
  4. Step 4: Obstructive Lung Disease Evaluation (FEV1 to FVC Low)
    1. Forced Vital Capacity (FVC) Normal
      1. Consistent with Obstructive Lung Disease
      2. Bronchodilator response with FEV1 or FVC increased >12% at any age (or >200 ml in adults)
        1. Consistent with reversible Obstructive Lung Disease (Asthma)
      3. Inadequate Bronchodilator response
        1. Consistent with irreversible Obstructive Lung Disease (COPD)
    2. Forced Vital Capacity (FVC) < LLN (or for age 5 to 18 years old, <80% of predicted)
      1. Consistent with mixed obstructive-Restrictive Lung Disease
      2. Go to Step 5
  5. Step 5: Mixed Obstructive-Restrictive Lung Disease (FEV1 to FVC Low and FVC decreased)
    1. Consistent with Mixed Obstructive Lung Disease - Restrictive Lung Disease
    2. Assess Bronchodilator response
      1. FVC increases >80% of predicted in children (or >LLN in adults) with Bronchodilator
        1. Suspect COPD with pure Obstructive Lung Disease and air trapping
      2. FVC with inadequate Bronchodilator response
        1. Evaluate and treat as Restrictive Lung Disease
        2. Perform complete Pulmonary Function Tests with DLCO
        3. Consider Restrictive Lung Disease differential diagnosis
  • Interpretation
  • Flow Volume Loop
  1. Obstructive Lung Disease (small airway obstruction of Asthma or COPD)
    1. Concave bowing of the the expiratory loop
  2. Restrictive Lung Disease
    1. Expiration time is shortened, so the curve appears narrowed on the X-axis
  3. Flattening of the flow volume curve
    1. Sub-maximal effort is most common cause
    2. Fixed large airway obstruction (trachea, main-stem Bronchus)
      1. Flattening of both the inspiratory and expiratory curves
    3. Variable extra-thoracic large airway obstruction (e.g. Vocal Cord Dysfunction)
      1. Flattening of the inspiratory curve
  • Interpretation
  • Normal
  1. Forced Expiratory Volume in one second (FEV1)
    1. Normal
      1. FEV1 >80% of predicted
    2. Mild Obstructive Lung Disease
      1. FEV1 70-80% of predicted
    3. Moderate Obstructive Lung Disease
      1. FEV1 50-70% of predicted
    4. Severe Obstructive Lung Disease
      1. FEV1 <50% of predicted
  2. Forced Vital Capacity (FVC)
    1. Adult: > Lower Limit of Normal (LLN)
    2. Ages 5-18 years old: >80% of predicted
  3. FEV1 to FVC Ratio
    1. Adult GOLD Criteria: >0.7
    2. Adult ATS Criteria: > Lower Limit of Normal (LLN)
    3. Ages 5-18 years old: >85% of predicted
  4. Lower Limit if Normal (LLN) - Used in ATS Guidelines
    1. Based on Third National Health and Nutrition Examination Survey (NHANES III) PFT data
    2. Calculated the lowest 5% (fifth percentile) cut-offs for FEV1 to FVC, FVC and FEV1
    3. Replaces GOLD Criteria which are less accurate
      1. Miss up to 50% of young adults with Obstructive Lung Disease and
      2. Overdiagnose Obstructive Lung Disease in healthy non-smokers
    4. Recently manufactured PFT software calculates the LLN based on patient age, gender and height
    5. Online calculator
      1. http://hankconsulting.com/RefCal.html
  • Interpretation
  • Abnormal
  1. Obstructive Lung Disease
    1. FEV1 to FVC Ratio <0.7 (or <LLN or for children<85% of predicted) AND
    2. Normal FVC or FVC response to Bronchodilator
    3. Reversible Obstructive Lung Disease (Asthma) criteria
      1. Bronchodilator response with FEV1 or FVC increased >12% at any age (or >200 ml in adults)
  2. Restrictive Lung Disease
    1. FEV1 to FVC Ratio >0.7 (or >LLN or for children>85% of predicted) AND
    2. FVC < LLN (or for age 5 to 18 years old, <80% of predicted)
  3. Mixed Obstructive-Restrictive Lung Disease
    1. Criteria
      1. FEV1 to FVC Ratio <0.7 (or <LLN or for children<85% of predicted) AND
      2. Low FVC
    2. Approach: Bronchodilator response
      1. FVC increases >80% of predicted in children (or >LLN in adults) with Bronchodilator
        1. Suspect COPD with pure Obstructive Lung Disease and air trapping
      2. FVC with inadequate Bronchodilator response
        1. Evaluate and treat as Restrictive Lung Disease
  • Precautions
  1. Spirometry is crude predictor pre-operative condition
  2. Spirometry affected by
    1. Pneumonia or other acute lung disease
    2. Sleep Apnea
    3. Anxiety
  3. Lung Volumes vary by ethnicity
    1. Lung Volume is lower in Black, Asian and Native American
    2. These groups have 8% lower Lung Volumes than whites (on average)