Can you interpret Pulmonary Function Test (PFT) results?

From the Guidelines

I can interpret pulmonary function testing (PFT) as it's a valuable tool for assessing lung function, with the most recent and highest quality study 1 providing guidance on standardized reporting and interpretation. PFT interpretation requires analyzing several key measurements including spirometry (FEV1, FVC, FEV1/FVC ratio), lung volumes, and diffusion capacity. Normal values are based on age, height, sex, and ethnicity. Obstructive patterns show reduced FEV1/FVC ratios (<0.7) with decreased airflow, typical in asthma and COPD. Restrictive patterns show proportionally reduced FEV1 and FVC but normal or increased FEV1/FVC ratios, seen in pulmonary fibrosis or chest wall disorders. Mixed patterns show elements of both. Bronchodilator response testing helps determine if airflow limitation is reversible, with improvement of ≥12% and ≥200mL in FEV1 considered significant. Diffusion capacity (DLCO) measures gas exchange efficiency, with reductions suggesting conditions like emphysema or pulmonary vascular disease. Proper interpretation requires considering clinical context, symptoms, and sometimes additional tests like chest imaging or exercise testing for comprehensive evaluation, as recommended by the American Thoracic Society technical statement 1. Some key points to consider when interpreting PFTs include:

• Only reporting validated parameters, such as FVC, FEV1, and FEV1/FVC, as recommended by 1
• Using a standardized format for reporting PFT results, including the normal limit(s) of each test value and the measured value before reference values, ranges, or normal limits, as suggested by 1
• Considering the displacement of the result from a predicted value in standard deviation units (z-score) to help understand abnormality, as recommended by 1
• Including clinical application and only displaying information with validated parameters, as recommended by 1.

From the FDA Drug Label

The primary endpoints were change from baseline in FEV1 AUC0-3hr and trough FEV1 after 24 weeks of treatment. Results from Trial 2 are shown in Figure 1 FEV1 profile for STIOLTO RESPIMAT, tiotropium 5 mcg and olodaterol 5 mcg over a 24-hour dosing interval after 24 weeks (12 hr PFT subset from Trial 2) In controlled 12-week studies in patients with bronchospasm associated with chronic obstructive pulmonary disease (chronic bronchitis and emphysema) significant improvements in pulmonary function (FEV1 increases of 15% or more) occurred within 15 to 30 minutes, reached a peak in 1 to 2 hours, and persisted for periods of 4 to 5 hours in the majority of patients, with about 25% to 38% of the patients demonstrating increases of 15% or more for at least 7 to 8 hours.

Interpretation of PFT Testing:

• FEV1 (Forced Expiratory Volume in 1 second): measures the volume of air exhaled in the first second of a forced exhalation.
• FEV1 AUC0-3hr: measures the area under the curve of FEV1 over a 3-hour period.
• Trough FEV1: measures the lowest FEV1 value after treatment.
• FVC (Forced Vital Capacity): measures the total volume of air exhaled during a forced exhalation. The provided drug labels 2 and 3 describe the results of clinical trials evaluating the effectiveness of tiotropium and ipratropium in patients with COPD, including improvements in FEV1 and FVC. However, they do not provide a direct interpretation of PFT testing results.

From the Research

Interpretation of PFT Testing

Pulmonary function testing (PFT) serves many purposes in clinical practice, and its interpretation depends on the clinical context, with multiple challenges influencing the results 4. The goal of PFT interpretation is to distinguish normal from abnormal, which is affected by the selection of reference standards and the choice of cut-off values.

Challenges in PFT Interpretation

There are several challenges in interpreting PFT results, including:

• The selection of reference standards 4
• The choice of cut-off values 4
• Controversies regarding PFT analysis, which may lead to important differences in interpretation 4
• The need for a comprehensive approach, including consideration of the clinical context, laboratory methodology, and reference standards 4

PFT Interpretive Strategies

The American Thoracic Society/European Respiratory Society guidelines for interpreting PFTs lack recommendations for the best reference equations for lung volumes and diffusing capacity of the lung for carbon monoxide (D(LCO)), and lack reference equations for non-whites 5. The pre-test probability of lung disease should be determined using a short questionnaire, and the "nonspecific pattern" occurs in about 15% of patients referred to a PFT lab 5.

Indications for PFT Testing

PFT testing is indicated in various clinical scenarios, including:

• To determine the pathophysiology present in the patient with cardiopulmonary disease 6
• Before certain types of surgery, to assess pulmonary function and determine if there are any contraindications 6
• In the diagnosis and management of chronic obstructive pulmonary disease (COPD) 7

Safety of PFT Testing

PFT testing is generally safe, with a low risk of adverse events 8. The most common adverse events are cardiopulmonary, with syncope being the most frequently occurring 8. The risk of hospital admission or emergency department attendance is low, and there is no reported PFT-associated mortality 8.