What is the most appropriate description of a normal forced expiratory volume (FEV) to forced vital capacity (FVC) ratio with a reduced forced vital capacity (FVC) on office spirometry?

Spirometry Pattern: Normal FEV1/FVC with Reduced FVC

This pattern most frequently indicates poor patient effort (incomplete inhalation or exhalation) and should prompt repeat testing with careful coaching before considering any pathological diagnosis. 1

Primary Interpretation

When both FEV1 and FVC are decreased but the FEV1/FVC ratio remains normal, the European Respiratory Society guidelines emphasize that special attention must be paid to this pattern because it has multiple possible explanations 1:

Most Common Cause: Technical/Effort Issues

• Failure to inhale or exhale completely is the most frequent explanation 1
• This is a submaximal effort problem, not true lung disease
• Action required: Repeat spirometry with proper coaching and technique

Less Common Pathological Causes

If the patient demonstrates maximal, sustained effort, consider:

1. Peripheral airflow obstruction with early airway collapse 1

   • Patchy collapse of small airways early in exhalation
   • Flow-volume curve may appear concave at end of maneuver
   • TLC typically normal, but RV ordinarily increased
   • Consider bronchodilator trial - significant improvement (≥12% and ≥200 mL in adults) suggests reversible obstruction 1

2. Very slow flow preventing complete exhalation 1

   • Patient cannot exhale long enough to reach residual volume
   • Flow-volume curve shows concave pattern toward end
   • TLC will be normal, FEF75 will be low
   • Measuring slow VC (inspiratory or expiratory) may give more accurate FEV1/VC ratio 1

Critical Distinction: This is NOT Restriction

A reduced FVC with normal FEV1/FVC ratio does NOT prove restrictive lung disease. 1 The guidelines are explicit:

• True restriction requires TLC below the 5th percentile 1
• Reduced VC alone is associated with low TLC only about 50% of the time 1
• The pattern may be "suggestive" of restriction when FEV1/FVC is increased (>85-90%) with convex flow-volume curve, but this still requires TLC measurement for confirmation 1

Recommended Clinical Algorithm

1. First: Verify test quality and patient effort

   • Review flow-volume curves for submaximal effort
   • Repeat spirometry with careful coaching

2. If pattern persists with good effort:

   • Perform bronchodilator testing
   • Improvement of ≥12% and ≥200 mL (adults) suggests reversible obstruction 1

3. If no bronchodilator response:

   • Measure lung volumes (TLC, RV) to differentiate:
     • Normal TLC with increased RV = peripheral airflow obstruction 1
     • Low TLC = true restriction 1
     • Normal TLC and RV = likely technical issue

4. Consider measuring slow VC (inspiratory or expiratory) for more accurate assessment 1

Common Pitfalls to Avoid

• Do not diagnose restriction based on spirometry alone - this is a critical error emphasized repeatedly in the guidelines 1
• Do not use single-breath TLC estimates (like VA from DLCO) to diagnose restriction - these systematically underestimate TLC 1
• Do not overlook poor technique - this is the most common explanation and should be excluded first 1

Special Considerations

The guidelines note two unusual scenarios with this pattern:

• Pneumothorax or noncommunicating bullae: Normal FEV1/VC and plethysmographic TLC, but low FEV1 and VC 1
• In these cases, gas dilution TLC will be falsely low 1