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[Interpreting carbon monoxide transfer coefficient: significance and difficulties]
S Guillot1, J Beillot, C Meunier
1Service d'Explorations Fonctionnelles, CHU de Rennes, Rennes, France.
Introduction:
Interpreting measurements of carbon monoxide can be problematic.
State Of The Art:
The transfer factor (TLCO) is usually calculated by multiplying the decrease in alveolar CO concentration between the beginning and the end of a 10 second breath hold (KCO) by the alveolar volume (VA). Thus a reduced TLCO may occur due to either a low KCO, a reduced VA, or a combination of both.
Perspectives:
A careful examination of KCO and VA will usually suggest a specific explanation for a reduction in TLCO. In restrictive lung diseases from extrapulmonary origin, TLCO is low but TLCO/VA [[/INF 120% of the reference values. In interstitial lung disease, the value of TLCO/VA depends on whether the loss of lung units is diffuse or not, and probably also on the status of the microcirculation. In airflow obstruction, a low VA is caused by uneven distribution of inspired He/CO mixture within the breath-hold time.
Conclusions:
The transfer factor for carbon monoxide is best interpreted in terms of its components, alveolar volume and carbon monoxide transfer coefficient.
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