Spirometry

1. See Also
   1. Lung Volumes
   2. Diffusing Capacity
   3. Inhalation Challenge Test
2. 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. Forced Expiratory Small Airway Flow (FEF25-75)
      1. Effort Independent
      2. More variable than FEV1 or FVC
3. Interpretation: General
   1. Normal
      1. FEV1 to FVC Ratio >0.7
      2. FEV1 >80%
      3. FVC >80%
   2. Obstructive Lung Disease: FEV1 to FVC Ratio <0.7
      1. Assess Severity
         1. FEV1 over 80%: Normal
         2. FEV1 over 60%: Mild obstructive lung disease
         3. FEV1 over 40-50%: Moderate obstructive lung disease
         4. FEV1 under 40%: Severe obstructive lung disease
      2. Assess Bronchodilator response
         1. See additional testing below
         2. Distinguish reversible from irreversible disease
            1. Asthma
            2. COPD
   3. Restrictive Lung Disease: FEV1 to FVC Ratio >0.7
      1. Assess Severity
         1. FVC over 80%: Normal
         2. FVC over 60%: Mild restrictive lung disease
         3. FVC over 40-50%: Moderate restrictive lung disease
         4. FVC under 50%: Severe restrictive lung disease
      2. Additional testing
         1. Diffusing lung capacity for carbon monoxide (DLCO)
         2. DLCO to alveolar volume ratio
         3. Expiratory Reserve Volume
4. Interpretation: Flow Volume Loop
   1. Obstructive lung disease (small airway obstruction of Asthma or COPD)
      1. Concave bowing of the the expiratory loop
   2. Fixed large airway obstruction (trachea, main-stem Bronchus)
      1. Flattening of both the inspiratory and expiratory curves
   3. Restrictive lung disease
      1. Expiration time is shortened, so the curve appears narrowed on the X-axis
   4. Variable extra-thoracic large airway obstruction (e.g. Vocal Cord Dysfunction)
      1. Flattening of the inspiratory curve
5. Tests: Complete Lung Volume
   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
6. 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)
7. Criteria: Adequate test (Minimum of 3 tests)
   1. Full inhalation
   2. Maximal exhalation
   3. No cough or glottic closure
   4. Adequate test duration (exhale for 6 or more seconds)
   5. No mouth-piece leak
   6. Variation between two best tests is within 5%
      1. Difference between 2 largest FVC <0.2 L
      2. Difference between 2 largest FEV1 <0.2 L
8. Disadvantages
   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 lower in Black, Asian and Native American
      2. These groups have 8% lower Lung Volumes than whites
9. References
   1. Crapo in Goldman (2000) Cecil Medicine, p. 382-7
   2. Gold in Murray and Nadel (2000) Respiratory, p. 784-90
   3. Barreirdo (2004) Am Fam Physician 69:1107-14
   4. Salzman (1999) J Respir Dis 20:809-22