Table 3

Hypothetical combinations of carbon monoxide transfer coefficient (KCO) and single-breath alveolar volume (VA,SB) giving rise to a carbon monoxide transfer factor (TL,CO) of 60% pred at full inflation

V A,SB KCO (TL/VAInterpretation/suggested diagnoses
% pred at actual VA
% reference TLCL BTPS mmol·min−1· kPa−1·L−1 BTPS% pred from reference TLCLoss of units modelLack of expansion model
Without airflow obstruction
352.162.88172134105Acute neuromuscular (lack of alveolar expansion) or (if transient) alveolar haemorrhage (loss of units)
503.092.0212010081Lung resection, collapse, infiltrates (loss of units)
603.71.681008772Diffuse alveolar damage
704.411.41847665Diffuse alveolar damage
855.251.19716963Pulmonary vascular pathology
With airflow obstruction
855.251.1971Emphysema; Churg-Strauss vasculitis
  • TL,CO· of 60% of predicted value (6.23 mmol·min−1·kPa−1) and reference values for KCO and predisease total lung capacity (TLC) derived from equations of Roberts et al. 33 for a male aged 45 yrs and of height 1.75 m

  • see Figure 2b

  • inappropriate as cause of low VA is incomplete gas mixing

  • VA: alveolar volume

  • BTPS: at body pressure and ambient temperature, and saturated with water vapour