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
At constant CO2 production, PACO2 depends on:
Alveolar ventilation
Increased alveolar ventilation = (increased/decreased) PACO2? Why?
Decreased; inspired air dilutes the CO2
Increased CO2 production (increases/decreases) PACO2? Why?
Increases; more CO2 enters alveoli (mass action)
What effect will increased metabolism have on the Valv/PACO2 curve?
Right shift = increased VCO2 will increase respiratory rate/Valv and increase amount of CO2 entering alveoli/PACO2
If CO2 production is constant, what would happen if PACO2 increased from 40 mmHg to 80 mmHg during anesthesia?
Alveolar ventilation would also have to increase 2 fold to compensate
(turn down ventilator)
Alveolar gas equation
PAO2 = PIO2 - PACO2/R
The main drive for ventilation
PaCO2
central chemoreceptors very sensitive to changes in PaCO2
Definition of hyperventilation
Ventilation in excess of that required metabolically
Definition of hypoventilation
Ventilation that is inadequate for metabolic demand
What is hypercapnia? Most common (general) cause?
Increased ARTERIAL CO2
Hypoventilation
What is hypoxemia?
Decreased ARTERIAL O2
What is hypoxia?
Decreased TISSUE O2
What parameter is used to determine the cause of hypoxemia?
A-a gradient
Difference between PAO2 and PaO2
Which can cause the other: hypoxia or hypoxemia?
Hypoxemia can cause hypoxia
Decreased O2 in alveoli can cause decreased O2 utilization
O2 and CO2 transfer is _____-limited. Why?
Perfusion; blood takes 0.75s to traverse pulmonary capillary and only 0.25s to totally equilibrate with alveolar concentrations
___ is a gas that is diffusion-limited. Why?
CO
It is highly soluble so the amount that can diffuse rather than the amount of blood limits gas transfer
If gas is perfusion-limited, how is more O2 able to be delivered to tissue during exercise?
More capillaries open due to increased pulmonary vascular pressures
What is the function of bronchial circulation?
Serves the conducting airways; doesn’t participate in gas exchange
