Gas Transfer FactorDr Rod Taylor

Consultant Respiratory Physician

Transfer Factor of the LungTransfer Factor TLCO

(USA: Diffusing Capacity DLCO)Transfer Coefficient KCO

Measures how well gas is exchanged from

alveolus to haemoglobin.

Carbon Monoxide (CO) isused as a proxy for Oxygen.

Alveolarepithelium

CapillaryBasement membrane

Capillaryendothelium

Red cellmembrane

Intracellularfluid

Alveolarbasement membrane

Capillary

Plasma Interstitial space

Alveolus

Fluid layerwith surfactant

ALVEOLAR-CAPILLARY MEMBRANE

VOLUMES FLOWS

Well matched!

How to do the TestSubject exhales down to RV,and then inhales the test gas

- He and CO in known concentrations

Then holds breath for 10 seconds (!),during which test gas is diluted by RV,

and CO is taken up into the blood.

Measurement of Transfer Factor by single-breath technique

0.3% CO14% He18% O2

Single breath

Spirometer FACOFAHE

CO2 and H2Oabsorption

Analysis ofHe and CO

At start of test Test gas is diluted

What happens during the 10-second breath-hold?

The concentration of Helium goes down, because it is diluted by the RV.

The concentration of CO goes down,because it is similarly diluted by the RV,

and also because it is taken upby haemoglobin in the capillary blood.

Transfer Factor (TL)(ml/minute/kPa)

How much CO was taken up.How long breath was held for.

Average driving pressure.

Alveolar Volume (VA)The volume of lung reachedby the test gas during the

10-second breath-hold.

Transfer Coefficient (KCO)= the Transfer Factor per litre

In other words, the TL per litre of lung that was

reached by the test gas.

KCO = TL divided by VAKCO corrects for maldistribution.

Ventilated and Perfused

Ventilatedand Perfused

Perfused, butnot Ventilated

Ventilatedand Perfused

Transfer Factor (TL) = 50%

Coefficient (KCO) = 100%

Ventilatedand Perfused

Ventilated, butnot Perfused

Transfer Factor (TL) = 50%

Coefficient (KCO) = 100%

Perfused, butnot Ventilated

Ventilated, butnot Perfused

Call Anaesthetistvery quickly indeed

And you’re not coming out until you

do a proper blow!