Gas Diffusion, Transport, and Exchange Flashcards
Central Gas Law
PV=nRT
Pressure (mmHg) Volume (L) = Moles x gas constant x temp
What constants are used for gas phase calculations?
BTPS
Body temp (37C or 310K), Ambient pressure, saturated with water vapor (47mmHg).
What constants are used for gas dissolved in blood?
STPD
Standard Temp (0C or 273K), Standard Pressure (760mmHg), Dry gas
How do pressure and volume of a gas relate?
P1V1=P2V2. During inspiration, there’s increased lung volume, which causes gas pressure to decrease.
How to calculate partial pressure of a dry gas?
Px = Pb x F
Where Pb is barometric pressure and F is fractional concentration
How to calculate partial pressure of humified gas?
Px = (Pb-PH2O) x F
PH2O at 37C is 47 mmHg
True or false?
The sum of partial pressures of all gases in a mixture is the total pressure of the mixture.
True!
What percent of atmospheric air at 760mmHg is Oxygen?
21%
How does high altitude affect PO2 of inspired air?
Decreases PO2 of inspired air due to low barometric pressure.
Concentration of a free dissolved gas equation?
Cx = Px x S. This applies to a dissolved gas that is free in solution.
True or false?
Only a dissolved gas, not a bound gas or chemically modified gas, contributes to its partial pressure.
True
Fick’s Law of Simple Diffusion. Calculate rate of transfer.
Vx = (DAP)/ X
Diffusion coefficient, surface area, pressure gradient, divided by thickness.
What factors affect diffusion coefficient?
Molecular weight and solubility
Difference in diffusion between O2 and CO2
CO2 has a 20X higher D.
How is N2 carried in blood?
Exclusively in dissolved form.
How is O2 carried in the blood?
Mostly (98%) bound to hemoglobin. CO can also bind to hemoglobin.
How is CO2 carried in the blood?
Chemically modified to HCO3-.
Diffusion limited gas exchange
Amount of gas that is transported from alveoli to capillaries is limited by diffusion. This is true for CO, and transport of O2 in emphysema, fibrosis, and exercise.
Perfusion limited gas exchange
The amount of gas transported is based on the blood flow. This is true for O2, CO2. Occurs in the first 1/3 of capillary.
Oxygen binding capacity
1 gram of Hba can bind 1.34 ml O2 when 100% saturated.
Concentration of Hb in blood? How much O2 can it hold?
15 g/dL. Can hold 20.1 mL O2.
How to calculate O2 bound to Hb
Binding Capacity X % Saturation
O2 delivery equation
O2 Delivery = Cardiac Output x (Oxygenated Hb + Dissolved O2)
What causes rightward shifts in the Hb-O2 curve.
Increases in temp, Co2, [H], 2,3 DPG. Causes faster unloading into tissues.
Why is Co dangerous?
Because its affinity for Hb is 250x that of O2.
Conversion of CO2L
Dissolved CO2 in bloodstream. 93% is taken up into RBC’s, 90% is converted to H2CO3 by carbonic anhydrase. H2CO3 dissociates into H+ and HCO3. H+ buffered, HCO3 pushed into plasma via exchange with Cl.
Anion Exchange Protein (3 Band)
Changes HCO3- with Cl- on RBCs.
A-a gradient.
The difference in PO2 of alveolar gas and arterial blood. Normally less than 12 mmHg.
Calculate A-a gradient
A-a = (PiO2 - PACO2/R) - PaO2
Why does A-a gradient change?
If there are shunts or diffusion defects. Anatomic probles.
