DLCO: The diffusing capacity of the lung for carbon monoxide, also known as

TLCO : Transfer factor of the lung for carbon monoxide.

Used to determine transfer of gas from the distal airspaces-alveoli into the pulmonary capillaries.



  • V(.) = uptake of CO in ml of CO at STPD conditions/min
  • PACO2 is the average partial pressure of CO in alveoli
  • PC(-)CO is the average partial pressure of CO in the pulmonary capillary plasma.

(Hb) has a very high affinity for CO (200 times > then 02).

Partial Pressure of CO in plasma (PC(-)) =0 when COHb is low

As a result, DLCO=V(.)CO/PACO

Increases in DLCO occur in:

  • Pulmonary hemorrhage
  • Polycythemia
  • Exercise
  • Diseases with increased blood flow
  • Asthma

Decreases in DLCO occur in:

  • Cardiovascular diseases
  • Emphysema
  • Parenchymal lung disease (Fibrosis)
  • Anemia
  • CRF


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