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47 Cards in this Set

  • Front
  • Back
What determines movement of gas between gas and liquid phases?
Pressure gradients - whether the gas is in liquid or gas phase.
Equation for partial pressure of a gas in a mixture:
PP= Total Pressure x Fraction
What is the total pressure in a beaker of water at sea level equilibrated with room air?
In this beaker, what are the fractions of
O2= .2093
What law determines solubility of a gas in a liquid?
Henry's law
What is the equation for calculating Concentration of gas in a liquid?
Pressure of gas x Solubility coefficient
What gas has the highest partial pressure?
What gas has the highest solubility coefficient?
What are the concentrations of O2, CO2 AND N2 in a beaker of water?
N2 = .88 mL/100 ml
O2 = .45 ml/100 ml
CO2= .037 ml/100 ml (essentially none)
Where are the pulmonary capillaries?
Embedded in spaces between adjacent alveoli.
Why do pressure gradients determine gas movement?
Because there are difference in kinetic energies; gas moves from regions of high energy to low until equilibrium is reached.
How many structures does O2 have to diffuse through to get from an alveolus to RBC membranes?
What are the seven structures?
1. Water/surfactant in alveoli
2. Alveolar epithelium
3. Epithelial basement membrane
4. Interstial fluid space
5. Capillary basement membrane
6. Capillary endothelium
7. Plasma
Where does edema occur?
At level four - the interstial fluid space.
What are the 2 components of the diffusing capacity of the lung?
1. The part that's due to the diffusion process itself
2. The time required for O2 to react with hemoglobin
What 3 factors are proportional diffusion in the lung?
1. Pressure gradient
2. Area of diffusion
3. Solubility
What 2 factors are inversely proportional to diffusion in the lung?
1. Distance of diffusion
2. Square root of molecular weight of the gas
What gas has a higher solubility, CO2 or O2? By how much?
CO2 - by a factor of 24 it is higher than O2
What are the molecular weights of CO2 and O2?
CO2 = 44
O2 = 32
Which gas is more diffusible? By how much?
CO2 is 20X more diffusable than O2
What factors that determine diffusion can we alter?
-Surface area
How do we increase surface area?
By dilating capillaries and opening or creating new capillaries.
When does capillary dilation occur?
During sustained exercise
How is the diffusing capacity of the lung determined in pulmonary function laboratories?
By using carbon monoxide to measure capillary pressures
Why does CO have to be used?
Because it remains tightly bound to hemoglobin through its capillary transit time, so the capillary pressure is ~0
Why do you want to be able to estimate capillary pressure?
Because it's very difficult to measure, and O2 and CO2 levels vary throughout the capillary.
What has to be measured to study pulmonary diffusing capacity?
-Alveolar CO pressure
-Total CO ventilation
What is the formula for lung diffusing capacity?
Dl = ------
(PC is essentially zero)
How is mean pulmonary capillary pressure of O2 measured?
It can't be! It's calculated.
What is the normal lung diffusing capacity?
25 ml/mm Hg
Do diffusion limitations affect both PaO2 and PaCO2?
What is affected more?
Why is PaO2 affected more by diffusion limitations than PaCO2?
Because diffusion limitations are due primarily to the diffusion process.
What reaches equilibrium faster in pulmonary capillary blood, O2 or CO2? Why?
O2; because CO2 has more complicated chemical reactions.
Approximately how long is one capillary transit time?
.75 sec
How long does it normally take for O2 levels to equilibrate?
About .2 sec
How long does it take for O2 levels to equilibrate
-When Dl is 50%
-When Dl is 25%
50% - takes .3 to .4 sec
25% - takes .6 to .7 sec
How long does it normally take for CO2 levels to equilibrate?
.3-.4 sec
How long does it take for CO2 levels to equilibrate at 25% membrane diffusing capacity?
.6 sec
Capillary transit time during exercise:
.25 sec
How does exercise affect lung-diffusing capacity? How?
It increases it because capillaries that were closed during resting are opened and expanded to increase SA for exchange
How does alveolar hypoxia affect lung diffusing capacity?
It reduces the driving pressure for O2 (pressure gradient) so the time needed for equilibrium is lengthened.
How does emphesyma affect lung diffusing capacity?
Alveoli coalesce so the surface area for diffusion is reduced.
How does pulmonary fibrosis affect lung diffusing capacity?
It increases the distance diffusion has to cross by thickening the alveolar-capillary membranes.
4 types of Pulmonary Fibrosis:
-Farmer's lung disease
-Coal Miners' disease
-Repeated lung inflammation
How does High Altitude effect lung diffusing capacity?
It increases it by stimulating lung growth which increases alveolar-capillary surface area - BUT ONLY IN GROWING CHILDREN
How does O2 move from systemic capillaries to the tissues?
by simple diffusion