Gas Exchange Flashcards
Downhill track of CO2
Tissues(highest), Venous blood, lungs, air (lowest)
Downhill track of O2
Air (highest), lungs, blood, tissues.
Px=Fx(Pb-Ph2o)
Which variables can we control?
Fx = Fraction of gas (100% O2) Pb = Barometric pressure (hyperbaric chamber)
Henry’s Law, what is it?
PP=[dissolved gas]/solubility coefficient
How does hemoglobin alter Henry’s law?
It binds O2, which conjugates O2. This takes it out of solution for more to dissolve. It increases the O2 dissolved in blood.
WHat is more soluble, CO2 or O2?
CO2, and it has a higher solubility coefficient
What is the ideal gas law?
PV=nRT
What are the implications from the ideal gas law?
Respiratory - If P1 is diff from P2, Volume will flow until it is equal
Anesthesia - If drugs are administered through the lungs, (high volume in the lung) partial pressures will equiilbrate
What is fick’s law of diffusion?
DIffusion rates is proportional to the area, inversely proportional to the thickness of membrane
Examples of altered diffusion
Atelectasis, pnemonia, pulmonary edema, pulmonary fibrosis - I think all are dealing with a thicker membrane
What is the PO2 level in the interstitium?
What controls this number?
40mmHg. This is controlled by Blood flow and Tissue Metabolism
Where is the PO2 lost from the blood?
Systemic capillaries
Why is there a quick drop in PO2 levels after the pulmonary capillaries?
Mixture with shunt blood that has not been oxygenated
What three factors rely on each other to control O2 diffusion?
Blood flow, Metabolism, Tissue PO2.
During sleep - metabolism dec, blood flow matches
During exercise - opposite
CO2 diffusion relies on what three principles?
Tissue metabolism, blood flow, PCO2.
Much greater diffusion coefficient, smaller Pressure diff required
When increase in Metabolism, need increased blood flow
How do they measure DIffusion capacity?
Using CO.
Give the patient a known amount and measure how much is in their alveoli after. (sensitive but non specific
O2 gets used by hemoglobbin
CO2 binds Hemoglobin tightly, doesnt get used.
What are cases where Diffusing capacity would decrease?
Thickened or damaged membrane (Emphysema, pulmonary fibrosis, Interstitial lung disease, pulmonary hypertension, chronic pulmonary thromboembolism)d,
Anemia (not enough Hb to bind CO)
What are cases where diffusing capacity would increase?
Polycythemia (increased RBC)
What is the alveolar gas equation and why is it important?
PAO2=FiO2(Pb-Ph2o)-PaCO2/RQ
This tells you a relationship that should exist between inspired O2 and blood CO2. If you measure both and see that it is different, something is wrong.
You can alter FiO2 to treat.
What is the difference between O2 and CO diffusion coefficient?
1.23
DLCO x 1.23 = DLO2
