What tests are included in a disability evaluation for pulmonary impairment?

Comprehensive Tests for Pulmonary Impairment Disability Evaluation

A comprehensive pulmonary disability evaluation must include spirometry (pre- and post-bronchodilator), lung volume measurements, diffusing capacity, and exercise testing as the core components to accurately assess the degree of respiratory impairment. 1

Core Pulmonary Function Tests

Spirometry

• Pre- and post-bronchodilator testing to measure:
  • Forced Expiratory Volume in 1 second (FEV₁)
  • Forced Vital Capacity (FVC)
  • FEV₁/FVC ratio
  • Flow-volume curves to assess for concavity indicating obstruction 1

Lung Volumes

• Measurement by either:
  • Body plethysmography (preferred in obstructive disease due to air trapping)
  • Helium dilution technique
• Key parameters:
  • Total Lung Capacity (TLC)
  • Residual Volume (RV)
  • Functional Residual Capacity (FRC) 1

Gas Exchange Assessment

• Diffusing capacity (DLCO) - critical for evaluating parenchymal disease and emphysema
• Arterial blood gas analysis - to assess:
  • PaO₂ (arterial oxygen tension)
  • Alveolar-arterial oxygen gradient
  • PaCO₂ (for evaluation of ventilatory control) 1

Exercise Testing

Exercise testing is particularly valuable for disability evaluation as it directly measures work capacity and functional limitation:

Field Walking Tests

• 6-Minute Walk Test (6MWT)

  • Most established field test
  • Requires 30-meter walking course
  • Measures distance walked in 6 minutes
  • Reflects daily living activities better than laboratory tests 1

• Shuttle Walk Tests

  • Incremental Shuttle Walk Test (ISWT) - maximal exercise capacity
  • Endurance Shuttle Walk Test (ESWT) - endurance capacity
  • Performed over 10-meter course with external pacing 1

Cardiopulmonary Exercise Testing (CPET)

• Gold standard for comprehensive assessment of exercise limitation
• Equipment options:
  • Cycle ergometer (safer, easier for blood gas collection)
  • Treadmill (achieves higher VO₂ max, more reflective of daily activities) 1
• Measurements:
  • Maximum oxygen consumption (VO₂ max)
  • Ventilatory threshold
  • Breathing reserve
  • Oxygen saturation during exercise
  • Exercise-induced bronchospasm 1

Additional Specialized Tests

Respiratory Muscle Function

• Maximum Inspiratory and Expiratory Pressures (MIP/MEP)
  • Evaluates respiratory muscle strength
  • Particularly important in neuromuscular disorders or advanced disease 1

Cough Effectiveness

• Peak Cough Flow (PCF)
  • Assesses ability to clear secretions
  • Critical value: < 270 L/min indicates ineffective cough 1

Maximal Voluntary Ventilation (MVV)

• Measures maximum sustainable ventilation over 12-15 seconds
• Useful in identifying:
  • Neuromuscular disorders
  • Upper airway obstruction
  • Estimating breathing reserve during exercise 1

Imaging Studies

• Chest radiography - to assess anatomical restriction and signs of chronic lung disease
• High-Resolution Computed Tomography (HRCT) - when parenchymal disease is suspected 1

Severity Classification

Severity of impairment is typically classified based on FEV₁ % predicted:

• Mild: >70%
• Moderate: 60-69%
• Moderately severe: 50-59%
• Severe: 35-49%
• Very severe: <35% 1

Important Considerations

1. Interpretation pitfalls: When using multiple tests, the likelihood of at least one abnormal result increases (10% with 3 parameters, 24% with 14 parameters) even in healthy individuals 1

2. Test selection: Choose tests based on suspected pathophysiology:

   • Obstructive disease: Focus on FEV₁, FEV₁/FVC, lung volumes, bronchodilator response
   • Restrictive disease: Focus on TLC, vital capacity, diffusing capacity
   • Exercise limitation: Include exercise testing when symptoms exceed resting pulmonary function abnormalities 1

3. Reference values: Use appropriate reference equations accounting for age, height, sex, and ethnicity; consider arm span measurements in patients with skeletal abnormalities 1

4. Quality control: Ensure tests meet ATS/ERS standards for acceptability and reproducibility to provide valid results for disability determination 1

By systematically applying these tests, clinicians can objectively quantify pulmonary impairment, which forms the foundation for disability evaluation and determination of functional limitations in daily activities.