Which spirometric pattern is typical of interstitial lung disease?

• A. Reduced volumes with increased FEV1/FVC
• B. Obstructive pattern with decreased FEV1
• C. Normal spirometry
• D. Increased FEV1/FVC with increased volumes

Answer: (A)

Interstitial lung disease produces a restrictive pattern on spirometry. The stiff lungs from fibrosis limit expansion, so overall lung volumes drop—FVC and TLC fall. The forceful exhalation in one second (FEV1) decreases too, but not as much as FVC, leaving the FEV1/FVC ratio normal or even increased. That combination—reduced volumes with an increased (or normal) FEV1/FVC ratio—is typical of a restrictive process, which is what interstitial lung disease causes. By contrast, obstructive diseases lower the FEV1 more than FVC, reducing the FEV1/FVC ratio and often increasing volumes due to air trapping; normal spirometry wouldn’t show the reduced volumes seen with ILD.