Gas Transfer Flashcards
(21 cards)
What is transfer factor
Rate of transfer of gas gas between alveoli and erythrocytes in the capillaries
What is gas transfer
Transfer of O2 from inspired air to circulation
Why use carbon monoxide for gas transfer test
Similar properties to O2
Technically easier to use
Not already present in lungs
What is KCO?
Transfer coefficient
Rate of disappearance of CO from alveolar gas during 10s breath hold
What is VA?
Alveolar volume
Lung volume seen by inhaled CO during the measurement
What is TLCO also known as DLCO
Carbon monoxide transfer factor
Ability of lungs to transfer gas across into bloodstream
Calculation for TLCO
KCO X VA
Gas transfer test procedure
Tidal breathing
Big breath in
Blow out to RV
followed by controlled breath in to TLC in 2-4 seconds
During insp pt receives gas containing CO and methane
TLCO and KCO plateau at 90% VC which is aim of the inhale
Pt holds breath for 10 seconds allowing diffusion
Normal exp to empty
What does the tracer gas do?
Provide estimate of alveolar vol
Dilution effect on CO
Can measure concentration on inhalation and exhalation to determine vol involved in gas exchange
Why is methane used for tracer gas?
Does not diffuse into bloodstream
It’s an inert gas
Gas transfer reproducibility?
X2 technically acceptable
Max 5 efforts
TLCO within 0.67mmol/min/kPa
KCO within 0.10mmol/min/kPa/L
VA within 5%
5 or more decrease transfer factor
Causes of decreased TLCO or KCO
(Decreased gas transfer)
COPD
Fibrosis
Pulmonary vascular disease
Causes of increased TLCO or KCO
Asthma (as blood more readily available)
Extra pulmonary restriction as lots of blood supply meeting ventilated areas of lung, but TLCO is normal or reduced due to decreased VA
Gas transfer results for Emphysema
Decreased TLCO and KCO
As diffusion distance increases and surface area for gas exchange decreases
Gas transfer results in asthma
TLCO may be increased or decreased
KCO increases
Reason not known
Likely due to hyperaemia of airways and greater perfusion of lung apices in asthma
What is measured in spirometry
FEV1
FVC
FEV1/FVC %
What is measured in static lung vols
TLC
FRC
RV
What is measured in gas transfer
TLCO
VA
KCO
Gas exchange examples in restrictive disease extrapulmomary restriction
Decreased TLCO
Increased KCO
E.g in PH pressure and flow around lung is high so KCO increase however gas exchange is impaired so TLCO decreased
Intra pulmonary restriction (fibrosis) gas exchange results
Decreased TLCO and KCO
