Pulmonary Gas Exchange Flashcards
Ficks law of diffusion
Physical properties of membrane
Physiochemical properties of gas
PRessure gradient
All effect the diffusion
Thicker = less Area = more
Molecular weight increase - less
More soluble - more
More pressure gradient - increase more (partial pressure of the gas on one side versus the other)
Alveolar capillary membrane
Alveolar epithelium (where surfactant is, etc.)
On capillary side side - alveolar capillary endothelium cells
Basement membrane in between
Solubilities of CO2 vs. O2 and effect
CO2 heavier
CO2 also muh more soluble
Means that CO2 diffuses much easier than O2
Pressure gradient
PO2 venous blood about 40 and alveolar gas about 100
pCO2 is 46 in venous blood to about 40 in alveolar gas
Pressure gradient greater for oxygen
Capillary blood transit
Less than .75 seconds to go through capillary
Time is shortened during exercise so about .25
Normally, saturated with O2 after about .25 seconds
Curve falltened in obstructive lung dz and takes longer to become oxygen saturated…could get hypoxemia during exercise
Capillary reserve time
Amoutn of time it takes between O2 saturation and end of time in the capillary
CO2 transfer along the capillary
Normally takes about .25 seconds
Abnormal would take longer
Exercise still shortens the amount of time
Edema or fibrosis could increase thickness..or emphysema could make abnormal
CO2 almost always gets out during normal resting condition
Diffusion capacity
DL= diffusion rate /(P1-P2)
Rationale for using carbon monoxide for DL, and what are 2 determinants
PCO in the blood is zero
Diffusion pattern of CO is similar to that of O2
Membrane and hemoglobin
How does hemoglobin effect DL?
The rate of reaction with hemoglobin and the blood volume in the alveolar capillaries are both increasing the DL
Hemoglobin is EQUALLY important to the membrane
Things that cause low DL
Increase the thickness
Decrease the SA
Decreased uptake by erythrocytes (anemia)
Ventilation-perfusion mismatch
