Restrictive Lung Disease Pattern
This spirometry demonstrates a restrictive pattern with FEV1 68% predicted, FVC 63% predicted, and a preserved FEV1/FVC ratio of 89%, indicating moderate severity restriction that requires total lung capacity (TLC) measurement for confirmation and further evaluation to identify the underlying cause. 1
Pattern Recognition
The elevated FEV1/FVC ratio of 89% is well above the lower limit of normal (typically <70% or below the 5th percentile indicates obstruction), definitively ruling out obstructive lung disease. 1, 2 The proportional reduction in both FEV1 and FVC with a preserved ratio is the hallmark spirometric pattern suggesting restrictive impairment. 1, 3
However, spirometry alone cannot confirm true restriction - only 58% of patients with this classic spirometric restrictive pattern (low FVC with normal/elevated FEV1/FVC ratio) actually have confirmed restriction on lung volume measurements. 4 The positive predictive value is only 41% when considering all patients with low FVC, regardless of the ratio. 4
Severity Classification
Based on the FEV1 of 68% predicted, this represents moderate severity impairment. 1 The European Respiratory Society classification defines:
- Mild: >70% predicted
- Moderate: 60-69% predicted
- Moderately severe: 50-59% predicted
- Severe: 35-49% predicted
- Very severe: <35% predicted 1
This moderate impairment level is associated with increased respiratory complaints, reduced ability to work and function in daily life, and carries prognostic significance for both respiratory and cardiovascular morbidity and mortality. 1
Essential Next Steps
Measure TLC immediately to confirm true restrictive lung disease. 1, 2, 4 A TLC below the 5th percentile of predicted confirms restriction. 1, 2 Without TLC measurement, you cannot distinguish between:
- True parenchymal restriction (interstitial lung disease, chest wall disorders, neuromuscular disease)
- Submaximal effort during testing
- Early mixed disease patterns 1, 4
Measure diffusing capacity for carbon monoxide (DLCO) as it helps differentiate causes of restriction and is an important predictor of mortality in both general populations and specific disease states. 1
Differential Diagnosis Considerations
With confirmed restriction (TLC <5th percentile), consider:
Parenchymal causes:
- Interstitial lung diseases (idiopathic pulmonary fibrosis, sarcoidosis, hypersensitivity pneumonitis)
- Post-infectious or inflammatory scarring 1
Extrapulmonary causes:
- Chest wall disorders (kyphoscoliosis, obesity)
- Neuromuscular diseases (note: VC may show only small decrements even with severe respiratory involvement in rapidly progressive neuromuscular disease)
- Pleural disease 1
Critical Pitfalls to Avoid
Do not diagnose restrictive lung disease based on spirometry alone. The FVC reduction could represent poor effort, early obstruction with air trapping, or other non-restrictive causes. 1, 4
Do not use FEV1/FVC ratio to determine severity - both values decline together in restriction, and a ratio of 0.5/1.0 indicates more impairment than 2.0/4.0 despite identical ratios. 1 Severity classification is based solely on FEV1 % predicted. 1
Be cautious if TLC is at the lower limit of normal in patients with conditions expected to cause restriction (e.g., post-lung resection) - the restrictive defect may be difficult to prove if TLC remains above the 5th percentile despite clinical disease. 1
Additional Testing Based on Clinical Context
Consider bronchodilator testing if there is any clinical suspicion of coexisting airway disease, though the elevated FEV1/FVC ratio makes pure obstruction unlikely. 2, 3 A positive bronchodilator response (≥12% and ≥200mL improvement in FEV1 or FVC in adults) would suggest a reversible component. 2, 3
Assess respiratory muscle strength if neuromuscular disease is suspected, as VC may be only slightly impaired despite severe respiratory compromise in certain neuromuscular conditions. 1