Phys- Diffusion Flashcards
The volume of oxygen in the lungs that is transported to the blood per unit time is equal to:
The volume of 02 consumption by cells in that same unit of time
The rate of excretion of CO2 is equal to:
The rate of CO2 production by cells
What is the respiratory quotient? Normal value?
CO2 production/O2 consumption
0.8
The respiratory quotients varies with:
What we eat and burn
ex. RQ for carbs is 1, for protein is 0.8; takes more O2 from protein to make one CO2
(T/F): The partial pressure of a gas depends upon the number of molecules in the mixture.
False - pressure exerted by each gas in a mixture is independent (Dalton’s Law)/gas molecules don’t usually interact
Px =
Ptotal*Fx
PIO2 =
(Patm - Pvapor)*FO2
(760-47)*.21 = 150mmHg
Why must we account for water vapor when calculating the pressure of inspired O2?
Dry atmospheric air is humidified in the airway so water vapor “takes up room”, decreasing PIO2
What happens to PIO2 in high altitude? Why?
Decreases; Patm decreases
How do you calculate how much gas is dissolved in a mixture?
Cx = alpha*Px (alpha = solubility)
Normal solubility of O2? CO2?
- 003
0. 07
What is the implication of the different solubilities of O2 and CO2?
CO2 is 20x more soluble than O2, so at any given pressure, diffusion of CO2»_space;» O2
Gas flow =
A/xD(P1-P2)
According to Fick’s Law, how does pulmonary edema cause hypoxemia?
Increased thickness
According to Fick’s Law, how does emphysema cause hypoxemia?
Decreased surface area (obstruction)
Where are the rates of diffusion of CO2 and O2 equal?
Alveoli - since it’s a gas dissolving into a gas, solubility doesn’t matter but the ratio of MW does, which is about the same for both
Where are the rates of diffusion of CO2 and O2 different? How so?
Diffusion of CO2 and O2 between alveoli and pulmonary capillaries - since gas is dissolving into a liquid, solubility is important and CO2 is 20x more soluble than O2 so the rate of diffusion of CO2 from pulm capillaries is about 20x faster
What is the normal PAO2? PACO2?
PAO2 = 105 mmHg PACO2 = 40 mmHg
What is the normal PaO2 in pulmonary vein/systemic arteries? PaCO2?
PaO2 = 100 mmHg PaCO2 = 40 mmHg
What is the normal PaO2 in pulmonary artery/systemic veins? PaCO2?
PaO2 = 40 mmHg PaCO2 = 46 mmHg
What drives the pressure gradient favoring O2 diffusion into cells?
Mitochondria utilize O2 so the PO2 is low in cells
What is the alveolar ventilation equation?
PACO2 = VCO2/Valv
(The alveolar pressure of CO2 is directly proportional to the production of CO2 and inversely proportional to the alveolar ventilation)
Why does alveolar ventilation equation not account for atmospheric CO2 breathed in?
There is virtually no CO2 in inspired air
How do you calculate Palv?
Palv = (TV - Vds) * RR