What is the interpretation and management for a patient with abnormal pulmonary function test results, including decreased Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1)?

Interpretation of Pulmonary Function Test Results

This patient demonstrates a mixed ventilatory defect with evidence of both obstruction and restriction, characterized by reduced FEV1/FVC ratio (75-76%, below the 5th percentile threshold), reduced TLC (84% predicted on the second test), and reduced FVC and FEV1 values. 1

Pattern Recognition and Classification

Primary Abnormality: Mixed Ventilatory Defect

The key diagnostic features are:

• FEV1/FVC ratio of 75-76% falls below the normal threshold (typically <70% or below 5th percentile indicates obstruction) 1
• TLC reduced to 84% predicted (below 5th percentile threshold for restriction) on the second test, though initially normal at 108% 1
• Both FEV1 and FVC are proportionally reduced (68-76% predicted range) 1

A mixed ventilatory defect is characterized by the coexistence of obstruction (low FEV1/FVC) and restriction (low TLC), which is precisely what this patient demonstrates on the second test. 1

Evidence of Air Trapping and Small Airway Disease

Additional concerning features include:

• Elevated RV/TLC ratio (82-88%, above normal limits) indicates air trapping 1, 2
• FEF25-75 values (79-85% predicted) suggest small airway involvement 1, 2
• The pattern of reduced FVC with borderline FEV1/FVC ratio may reflect patchy collapse of small airways early in exhalation 1, 2

Severity Assessment

The severity is classified as moderate based on FEV1 of 68-76% predicted. 1

According to established severity grading:

• Moderate obstruction: FEV1 60-69% predicted 1
• This patient's FEV1 ranges from 68-76%, placing them in the moderate category 1

Temporal Changes Between Tests

Comparing the two test dates reveals:

• TLC declined from 108% to 84% predicted - a significant restrictive component developed 1
• FVC improved from 68% to 76% predicted 1
• FEV1 improved from 69% to 76% predicted 1
• RV/TLC ratio improved from 88% to 82% but remains elevated 1

This pattern suggests evolving disease with development of a restrictive component, though some obstructive parameters improved. 1

Management Recommendations

Immediate Diagnostic Steps

Bronchodilator testing is essential to assess reversibility, as significant improvement (≥12% and ≥200 mL in FEV1 and/or FVC) would indicate reversible airflow obstruction and guide treatment. 1

• Administer salbutamol in four separate 100 mcg doses through a spacer 1
• Reassess lung function after 15 minutes 1
• Even without FEV1/FVC improvement, decreased dyspnea may correlate with improved inspiratory capacity or reduced hyperinflation 1

Additional Testing Required

DLCO measurement is critical for further characterization, as it helps differentiate between parenchymal disease, emphysema, and other causes of mixed defects. 1, 3

• Low DLCO with obstruction suggests emphysema 1
• Low DLCO with restriction suggests interstitial lung disease 3
• DLCO is an important predictor of mortality in both general population and specific disease states 1

Clinical Context Integration

The interpretation must be integrated with clinical history, particularly:

• Smoking history (current or former smoker status) 1
• Occupational exposures 1
• Respiratory symptoms (dyspnea, cough, wheezing) 1
• Chest radiograph findings 1
• Recent hemoglobin values (affects DLCO interpretation) 1

Common Pitfalls to Avoid

Do not rely solely on FEV1/FVC ratio to determine severity - both FEV1 and VC may decline with disease progression, and a ratio of 0.5/1.0 indicates more impairment than 2.0/4.0 despite identical ratios. 1

The lack of bronchodilator response in the laboratory does not preclude clinical response to bronchodilator therapy, so a 1-8 week clinical trial with bronchodilator medication should still be considered. 1

Single-breath VA measurements (from DLCO testing) systematically underestimate TLC and should not be used to diagnose restriction, as they can underestimate TLC by up to 3 L in severe obstruction. 1

Therapeutic Approach

Based on the mixed pattern with air trapping:

• Initiate bronchodilator therapy (long-acting beta-agonists and/or anticholinergics) regardless of acute bronchodilator response 1
• Address the restrictive component based on underlying etiology identified through clinical correlation and DLCO results 3
• Monitor for progression with serial PFTs, as the development of restriction (TLC decline from 108% to 84%) suggests evolving disease 1