Pulmonary Function Test

See Also

Indications

Asthma Diagnosis and Asthma Management (all cases from age 5 years old and older)
1. (2007) J Allergy Clin Immunol 120(5 suppl): S94-138 [PubMed]
COPD Diagnosis and COPD Management (all cases)
1. Acute decompensation risk increases significantly at FVC <1-1.5 L (esp. with Muscle Weakness, chest wall deformity)
2. Vesbo (2013) Am J Respir Crit Care Med 187(4): 347-65 [PubMed]
Restrictive Lung Disease
Dyspnea Evaluation
Neuromuscular disorders (e.g. Myasthenia Gravis, Guillain Barre Syndrome)

Precautions

Pulmonary Function Tests are primarily indicated for diagnosis of stable patients (not Acute Respiratory Failure)
Vital Capacity and Forced expiratory flow may be used in acute presentations who are alert (esp. to compare to baseline PFTs)
1. FEV1 <1-1.5 L significantly increases the risk of caute Respiratory Failure

Images

Criteria
Adequate test (Minimum of 3 tests)

Full inhalation
Maximal exhalation
No cough or glottic closure (or other artifacts in the flow-volume loop)
Flow-volume loop should reach a baseline plateau at the end of expiration (right side of the loop) prior to inspiratory loop
Adequate test duration (exhale for 6 or more seconds)
No mouth-piece leak
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
Patient Preparation

Stop Bronchodilators before test (Corticosteroids may be continued)
Stop Short-acting Beta Agonists (e.g. Albuterol) 4-6 hours before test
Stop Short-Acting Muscarinic Antagonists (e.g. Ipratropium Bromide) 12 hours before test
Stop long acting beta Agonists (e.g. Salmeterol) 24 hours before test
Stop long acting Muscarinic Antagonists (e.g. Tiotropium or Spiriva) 36 to 48 hours before test
Avoid Tobacco for one before test
Avoid caffeinated coffee in amount >16 oz before test

Protocol
Testing

Pulmonary Function Test (PFT)
1. Adult: 15 minutes
2. Child: 15-30 minutes (age 5 years and older)
Full Pulmonary Function Test (PFT) with pre- and post-Bronchodilator testing
1. Time: 45 minutes
Full Pulmonary Function Test (PFT) and Carbon Monoxide diffusion (DLCO)
1. Time: 60 minutes

Tests
Screening Spirometry Measures

Forced Vital Capacity (FVC)
1. Abnormal
  1. Less than lower limit of normal for adults OR
  2. Less than 80% of predicted for ages 5 to 18 years old
2. Obstructive Lung Disease: Mildly decreased or normal
3. Restrictive Lung Disease: Mildly to severely decreased
4. Calculation
  1. FVC = Race * 1.1 * ((0.0576 * HtCm) - (0.0269 * AgeY) - 4.34)
  2. Where HtCm = Height in cm
  3. Where AgeY = Age in years
  4. Where Race
    1. Caucasian = 1
    2. Black = 0.87
    3. Asian = 0.93
  5. Example: 20 year old white male at height 178 cm, weight 70 kg
    1. FVC (L) = 1.1 * ((0.0576 * 178)-(0.0269*20)-4.34) = 5.9 L
Forced Expiratory Volume in 1 Second (FEV1)
1. Maximal rate of expiration in first 1 second (recorded on spirometer)
  1. Patient inspires to full inspiration (Total Lung Capacity)
  2. Expires towards full expiration (Residual Volume)
2. Interpretation
  1. Obstructive Lung Disease (Asthma, COPD)
    1. Mildly to severely decreased
    2. Airway obstruction slows the maximal rate of expiration, but Lung Volumes are normal (or hyperexpanded)
  2. Restrictive Lung Disease
    1. Moderately to severely decreased
    2. However, low FEV1 is due to low FVC (and FEV1/FVC ratio is normal)
3. Normal FEV1 estimation
  1. FEV1 = Race * 1.08 * ((0.043 * HtCm) - (0.029 * AgeY) - 2.49)
    1. See Legend above (under FVC)
  2. Example: 20 year old white male at height 178 cm, weight 70 kg
    1. FEV1 (L) = 1.08 * ((0.043 * 178)-(0.029*20)-2.49) = 4.95 L
FEV1 to FVC Ratio (Normally over 75%)
1. Not useful if both FEV1 and FVC are normal
2. Obstructive Lung Disease: Moderately to severely decreased
3. Restrictive Lung Disease: Normal or increased
4. COPD Gold criteria define abnormal FEV1/FVC <0.7
5. Interpretation via Lower Limit of Normal (LLN) is preferred and used by ATS/ERS guidelines
  1. Lower limit of normal is <5th percentile for ethnicity and age
  2. Swanney (2008) Thorax 63:1046–51 [PubMed]
6. 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%
7. Calculation
  1. FEV1 to FVC Ratio = 87.2 - (0.18 * AgeY)
Forced Expiratory Small Airway Flow (FEF25-75)
1. Effort Independent
2. More variable than FEV1 or FVC
References
1. Medical Calculator (Merck Manual)
  1. https://www.merckmanuals.com/medical-calculators/PulmonaryPredictM_A.htm
2. Falaschetti (2004) Eur Respir J 23(3):456-63 +PMID: 15065839 [PubMed]

Tests
Complete Lung Volume

See Lung Volumes (includes Tidal Volume, Vital Capacity, Residual Volume and Functional Residual Capacity)
Total Lung Capacity (TLC)
1. Obstructive Lung Disease: Normal or mild change
2. Restrictive Lung Disease: Decreased
Residual Volume (RV)
1. Residual Volume is not directly measured by Spirometry
  1. Functional Residual Capacity (FRC) is measured by plethysmography, gas dilution (e.g. helium) or nitrogen washout
  2. Expiratory Reserve Volume (ERV) is measured
  3. Residual Volume (RV) = FRC - ERV
2. Obstructive Lung Disease: Increased
3. Restrictive Lung Disease: Decreased
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

Diffusing Capacity (DLCO)
1. Reversible Obstructive Lung Disease (Asthma): Normal
2. Irreversible Obstructive Lung Disease (COPD): Low
Inhalation Challenge Test (Methacholine Challenge)
Lung elasticity
Airway resistance
Respiratory Muscle Strength (e.g. Myasthenia Gravis, Guillain Barre, ALS, Ventilator Weaning)
1. Single Breath Counting
2. Negative Inspiratory Flow (NIF) or Maximal Inspiratory Pressure (MIP)
  1. NIF less negative than -20 to -30 cmH2O may predict Respiratory Failure in Myasthenia Gravis
  2. NIF less negative than-25 cmH2O may predict Ventilator Weaning failure
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
Exercise Testing Endpoints
1. Patient uncomfortable and requests to stop
2. Disturbing Physiologic Change
3. Reaching 90% of maximum Heart Rate (age predicted)

Protocol
Approach

Step 1: Determine validity of Pulmonary Function Testing
1. See Criteria above
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)
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
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
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

Technique
1. Patient inspires to full inspiration (Total Lung Capacity)
2. Patient expires to full expiration (Residual Volume) at maximal expiratory force
3. Flow (L/min) is recorded continuously on Y Axis
  1. Normal expiratory flow is rapid at the start in healthy patients (see FEV1)
4. Volume is recorded on X Axis
Obstructive Lung Disease (small airway obstruction of Asthma or COPD)
1. Concave bowing of the the expiratory loop
Restrictive Lung Disease
1. Expiration time is shortened, so the curve appears narrowed on the X-axis
Flattening of the flow volume curve
1. Sub-maximal effort is most common cause
2. High grade upper airway obstruction
  1. Maximal inspiratory flow rate <2 L/s
3. Fixed large airway obstruction (tracheal stenosis, main-stem Bronchus)
  1. Flattening of both the inspiratory and expiratory curves
4. Variable extra-thoracic large airway obstruction
  1. Flattening of the inspiratory curve (e.g. Vocal Cord Dysfunction)
  2. Flattening of the expiratory curve (e.g. tracheal cancer)
    1. Flow is greater during inspiration than expiration
    2. Trachea's posterior membrane billows outward during inspiration (increased flow)
    3. Airway narrows during expiration (pleural pressure > intrathoracic pressure)

Interpretation
Normal

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
Forced Vital Capacity (FVC)
1. Adult: > Lower Limit of Normal (LLN)
2. Ages 5-18 years old: >80% of predicted
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
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

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)
Restrictive Lung Disease - Interstitial Lung Disease (Low Residual Volume, low DLCO)
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. Vital Capacity (VC) and Residual Volume (RV) are typically reduced symmetrically in Interstitial Lung Disease
Restrictive Lung Disease - Neuromuscular Disorders (Normal Residual Volume, normal DLCO)
1. Decreased FVC
2. Normal or increased Residual Volume (RV)
3. Normal DLCO
4. Seen with weak respiratory Muscles
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
Chronic Bronchitis with terminal Bronchiole scarring (Expiratory Airflow Obstruction)
1. Typically seen in combination with Emphysema
2. FEV1 to FVC Ratio <0.7
3. Low flow rates
4. Normal DLCO
Emphysema with destruction of peri-alevolar tissue (Airway Obstruction, Hyperinflation, decreased DLCO)
1. Typically seen in combination with Chronic Bronchitis
2. FEV1 to FVC Ratio <0.7
3. Total Lung Capacity (TLC)>120% of predicted (hyperinflation)
4. Decreased DLCO
Asthma (Airway Obstruction, Hyperinflation, normal DLCO)
1. FEV1 to FVC Ratio <0.7
2. Total Lung Capacity (TLC)>120% of predicted (hyperinflation)
3. Normal DLCO

Precautions

Spirometry is a crude predictor of pre-operative condition
Spirometry is affected by
1. Pneumonia or other acute lung disease
2. Sleep Apnea
3. Anxiety
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)

Resources

Spirometry Normal Calculator (CDC NIOSH)
1. https://www.cdc.gov/niosh/topics/spirometry/refcalculator.html

References

Crapo in Goldman (2000) Cecil Medicine, p. 382-7
Gold in Murray and Nadel (2000) Respiratory, p. 784-90
Barreirdo (2004) Am Fam Physician 69:1107-14 [PubMed]
Johnson (2014) Am Fam Physician 89(5): 359-66 [PubMed]
Langan (2020) Am Fam Physician 101(6): 362-8 [PubMed]
Pellegrino (2005) Eur Resp J 26(5): 948-68 [PubMed]
Salzman (1999) J Respir Dis 20:809-22 [PubMed]