Diffusion Flashcards
Ficks law states that transfer of a gas
directly prop to tissue area
inversely prop to thickness
Co2 diffuses how many times than Oxygen
20 times
because it has higher solubility
diffusion constant
prop to gas solubility
inv prop to square root of its molecular weight
Uptake of carbon monoxide along pulmonary capillary is
diffusion limited
*no increase in partial pressure
CO is not dissolved
Nitrous oxide uptake is
Perfusion limited
partial pressure rises rapidly
depends on the blood flow
as oxygen enters the capillary, it already reaches
4 tenths of alveolar value (partial pressure)
PO2 reaches alveolar gas when RBC is about __________ of the way along the capillary
1/3 (0.25 secs)
*perfusion limited
during severe exercise, time available for oxygenation is reduced to
0.25 secs
due to increase pulmonary blood flow
diffusion is challenged by
exercise
high altitue (alveolar hypoxia)
thickening of blood gas barrier
normal diffusing capacity
25 ml/min/mmhG
Conditions with decreased diffusing capacity
Thickened barrier: pulmonary edema, pulmonary fibrosis, sarcoidosis, scleroderm
decreased surface area: emphysema, tumors, low cardiac output, low pulmonary capillary blood volume
decreased uptake by erythrocytes: anemia, low pulmonary capillary blood volume
VQ mismatch
diffusing capacity for CO is
volume of CO transferred over alveolar partial pressure
when does diffusing capacity increase?
during exercise
(recruitment and distention of pulmo capillaries)
Uptake of oxygen (or O2) occurs in 2 stages
diffusion of oxygen through Blood gas barrier
reaction of oxygen with hgb
Reaction rate of oxygen and carbon monoxide with hemogblobin
