TABLE 8

Summary of types of spirometrically defined and lung volume defined ventilatory impairments

Ventilatory impairmentsPatterns
Obstruction

  • FEV1/FVC <5th percentile

  • Decrease in flow at low lung volume may reflect small airway disease in individuals [100, 101, 108]

  • Concomitant decrease in FEV1 and FVC most commonly due to poor effort but may reflect airflow obstruction or a restrictive pattern; recommend lung volumes

  • Measurement of absolute lung volumes may assist in diagnosis and assessment of hyperinflation [108]

  • Measurement of airflow resistance may assist in diagnosis [139]

Restriction

  • TLC <5th percentile

  • Reduced FVC does not prove restrictive impairment but may be suggestive of restriction when FEV1/FVC is normal or increased

  • Low TLC from single-breath test not reliable, especially with low FEV1/FVC [125]

  • A normal FVC usually excludes restriction [153]

Mixed

  • FEV1/FVC and TLC both <5th percentile

FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity.