PFT Interpretation

Patient: 64M, 45-pack-year smoker. Progressive dyspnea × 3 years. PFTs: FEV₁ 42% predicted, FVC 78%, FEV₁/FVC 0.54, DLCO 48%. Post-bronchodilator: FEV₁ improves 6% and 90 mL.

Key findings: Obstructive pattern: FEV₁/FVC < 0.70 (the defining ratio). Low DLCO = emphysema (alveolar destruction). Minimal bronchodilator response (< 12% AND < 200 mL) = COPD, not asthma. GOLD Stage III (severe: FEV₁ 30-49%).

Management:

• LABA/LAMA combination inhaler (first-line for symptomatic COPD GOLD B-E)
• Add ICS only if eosinophils > 300 or frequent exacerbations despite dual bronchodilators
• Smoking cessation (the ONLY intervention proven to slow FEV₁ decline)
• Pulmonary rehab referral (improves exercise capacity, dyspnea, and QOL)
• Annual PFTs to track FEV₁ decline (normal: ~30 mL/yr; COPD smoker: 60-100 mL/yr)

Teaching point: FEV₁/FVC < 0.70 = obstruction. The FEV₁ alone determines severity (GOLD staging). Bronchodilator response distinguishes COPD (minimal) from asthma (significant: ≥ 12% AND ≥ 200 mL). But there is overlap, some patients have both.

Patient: 70F with progressive dyspnea and dry cough × 18 months. Bibasilar velcro crackles. PFTs: FEV₁ 62%, FVC 58%, FEV₁/FVC 0.85 (normal ratio), TLC 65%, DLCO 38%.

Key findings: Restrictive pattern: reduced TLC (< 80%) with preserved or elevated FEV₁/FVC ratio. Very low DLCO = impaired gas exchange (fibrosis thickens alveolar-capillary membrane). HRCT needed to determine cause.

Management:

• HRCT chest, look for UIP pattern (honeycombing, traction bronchiectasis = IPF) vs NSIP pattern (GGO predominant = potentially treatable)
• If UIP pattern: antifibrotic therapy (pirfenidone or nintedanib)
• Serial PFTs q3-6 months, FVC decline > 10% absolute or DLCO decline > 15% = disease progression
• 6-minute walk test (6MWT), desaturation > 4% = significant; supplemental O₂ if SpO₂ < 88%
• Early lung transplant referral if FVC < 80% or DLCO < 40% at diagnosis

Teaching point: FVC is the most important PFT for monitoring ILD progression, a 10% absolute decline in FVC over 6-12 months doubles mortality risk. DLCO is the most sensitive early marker but also declines with anemia and pulmonary HTN.

Patient: 58M with COPD and morbid obesity (BMI 48). PFTs: FEV₁ 45%, FVC 52%, FEV₁/FVC 0.62, TLC 72%, DLCO 55%. Lung volumes show decreased TLC but elevated RV/TLC ratio.

Key findings: Mixed pattern: FEV₁/FVC < 0.70 (obstruction) + TLC < 80% (restriction). Common in COPD + obesity, COPD + ILD overlap, or sarcoidosis. The reduced TLC from obesity masks hyperinflation from COPD.

Management:

• Separate the contributions: body plethysmography (most accurate TLC) + chest imaging to assess parenchyma
• Treat both: bronchodilators for COPD component + weight loss for restrictive component
• Weight loss target: 10% body weight → expect ~5-10% improvement in FVC
• If DLCO disproportionately low for the degree of obstruction: consider concurrent ILD or pulmonary HTN
• ABG if concern for OHS (BMI > 40 + daytime hypercapnia)

Teaching point: A "normal" FEV₁/FVC ratio in a patient with low FVC does NOT rule out obstruction, both FEV₁ and FVC may be proportionally reduced ("pseudo-normalization"). Always check lung volumes (TLC) to confirm true restriction.