Gas Transfer Factor Dr Rod Taylor Consultant Respiratory Physician

Transfer Factor of the Lung Transfer Factor T L CO (USA: Diffusing Capacity D L CO) Transfer Coefficient KCO

Measures how well gas is exchanged from alveolus to haemoglobin. Carbon Monoxide (CO) is used as a proxy for Oxygen.

Alveolar epithelium Capillary Basement membrane Capillary endothelium Red cell membrane Intracellular fluid Alveolar basement membrane Capillary Plasma Interstitial space Alveolus Fluid layer with surfactant ALVEOLAR-CAPILLARY MEMBRANE

VOLUMES FLOWS

Well matched!

How to do the Test Subject 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% CO 14% He 18% O 2 Single breath Spirometer F A CO F A HE CO 2 and H 2 O absorption Analysis of He 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 up by haemoglobin in the capillary blood.

Transfer Factor (T L ) (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 reached by the test gas during the 10-second breath-hold.

Transfer Coefficient (KCO) per litre = the Transfer Factor per litre In other words, the T L per litre of lung that was reached by the test gas. KCO = T L divided by VA KCO corrects for maldistribution.

Ventilated and Perfused Ventilated and Perfused

Perfused, but not Ventilated Ventilated and Perfused Transfer Factor (T L ) = 50% Coefficient (KCO) = 100%

Ventilated and Perfused Ventilated, but not Perfused Transfer Factor (T L ) = 50% Coefficient (KCO) = 100%

Perfused, but not Ventilated Ventilated, but not Perfused Call Anaesthetist very quickly indeed

And you’re not coming out until you do a proper blow!