Pulmonary Function Assessment

Introduction to Spirometry

• Most reference equations consider values between 80-120% of predicted as within normal range for FEV1%, according to the European Respiratory Society guidelines 1

Factors Influencing Spirometry Results

• Superior lung function may be seen in athletes or individuals with excellent respiratory health, with FEV1% values often exceeding 100% 1
• Reference equation mismatch can occur when the reference equations used are not optimal for the specific population being tested, although this is not always the case 1

Interpreting Spirometry Results in Clinical Context

• A normal FEV1% with decreased FEV1/FVC ratio may indicate early or mild obstructive airway disease, even when asymptomatic, and should be evaluated further 1
• The American Thoracic Society recommends checking the FEV1/FVC ratio to confirm excellent lung function, and considering bronchodilator testing if obstructive indices are present 1
• The European Respiratory Society guidelines define obstruction as FEV1/VC ratio below the 5th percentile of the normal distribution (lower limit of normal) 2
• Using a fixed ratio of 0.70 can lead to false-positive diagnoses of obstruction in older adults and false-negative diagnoses in younger adults, as stated by the European Respiratory Society 3
• The GOLD Science Committee recommends using post-bronchodilator FEV1/FVC <0.7 to confirm COPD diagnosis 4

Pitfalls in Spirometry Interpretation

• Assuming normal lung function solely based on FEV1% > 100 can lead to missed diagnoses of early obstructive disease, and the FEV1/FVC ratio should always be checked as well 1
• Overlooking the possibility of incomplete exhalation during spirometry, which can falsely normalize the FEV1/FVC ratio, is a critical error, as noted by the European Respiratory Society 2
• Failing to recognize that a normal FEV1 doesn't exclude obstructive disease is a common mistake, according to the European Respiratory Journal 5

Additional Testing and Considerations

• Lung volume measurements may help distinguish between true obstruction and other causes, as recommended by the European Respiratory Society 2
• Measuring slow vital capacity (SVC) instead of FVC may better detect airflow obstruction in patients with small airways disease, as recommended by the European Respiratory Society guidelines 4
• Measuring total lung capacity (TLC) helps distinguish between true restriction and air trapping from obstruction when spirometry shows reduced FVC and FEV1 with normal ratio, according to the European Respiratory Society guidelines 2
• Significant reversibility (increase in FEV1 ≥12% and ≥200mL) suggests asthma or asthma-COPD overlap, according to the European Respiratory Society guidelines 2

Classification of COPD Severity

• COPD severity can be classified based on FEV1 percentage predicted, with Moderate COPD (FEV1 50-69% predicted) and Severe COPD (FEV1 <50% predicted), as stated by the European Respiratory Society guidelines 6
• The following table summarizes the classification of COPD severity based on FEV1 percentage predicted:

Management of Obstructive Airway Disease

• Initial therapy for obstructive airway disease may include a short-acting beta-agonist (SABA) as needed for symptoms, and consideration of inhaled corticosteroid (ICS) if symptoms are persistent, as suggested by 3
• Step-up therapy may involve ICS + long-acting beta-agonist (LABA) combination, and for mild to moderate COPD, a long-acting bronchodilator (LABA or LAMA) may be used, with consideration of combination therapy (LABA + LAMA) if exacerbations or persistent symptoms occur 3, 7
• The European Respiratory Society guidelines recommend considering combination therapy, such as LABA + LAMA, if exacerbations continue despite monotherapy, or adding inhaled corticosteroid (ICS) if the patient has ≥2 exacerbations per year or shows features of asthma-COPD overlap 4

Additional Considerations in Management

• Lung volume measurements to assess for hyperinflation, and diffusing capacity to evaluate for emphysema, may be considered if clinical suspicion remains high despite borderline spirometry 2, 4
• Comorbidities, such as cardiovascular disease and sleep apnea, should be assessed as they may contribute to symptoms 3
• Overlooking volume responses, such as FVC improvement, may lead to underestimation of bronchodilator efficacy, especially in patients with more severe disease, as warned by the European Respiratory Society guidelines 4
• Not measuring lung volumes, such as TLC, can lead to misdiagnosis of restrictive lung disease instead of obstructive lung disease, as cautioned by the European Respiratory Society guidelines 2