Alveolar Gas Exchange Flashcards
Alveolar Ventilation
The volume of air reaching the alveoli per minute
How do you calculate Alveolar Ventilation?
= (Tidal volume - volume of dead space) X frequency
Tidal volume - volume of dead space gives you?
Volume of alveoli
Perfusion
Cardiac output from right ventricle
Average value of perfusion?
5 L/min
Average value of Alveolar Ventilation?
4 L/min
What is the equation (thus the factors) that determine how much CO2 and O2 will cross alveolar barrier?
J = Surface Area X D X (P1-P2)/ Distance
J =
Diffusion rate per minute
– how much gas is exchanged per minute
Diffusion of each gas is _____ from one another
INDEPENDENT
Surface Area and Distance both depend on the structure of the?
Alveolus
What does the Surface Area correspond to?
The NUMBER of alveoli in the lungs
Distance =
Thickness of the Alveolar Membrane
What 4 things does the Alveolar membrane include?
Fluid layer
Alveolar epithelium
Interstitial space
Blood vessel wall
As the Distance increases, what will happen to the Diffusion rate?
DECREASE
As the Distance decreases, what will happen to the Diffusion rate?
INCREASE
As the surface area (number of alveoli) increases, what will happen to the diffusion rate?
INCREASE
As the surface area decreases, what will happen to the diffusion rate?
DECREASE
With Interstitial lung disease, what gets deposited where?
Collagen is deposited in the interstitial space of the alveolar membrane
How does Interstitial lung disease decrease diffusion rate of gases?
It deposits collagen into the interstitial space and thus increases the distance (thickness of alveolar membrane)
D =
Diffusion coefficient for each gas
What 2 things does the Diffusion coefficient for each gas depend on?
- Solubility of gas in water
2. Molecular weight of gas
Which is more soluble, O2 or CO2?
CO2
Is the Diffusion coefficient greater for CO2 or O2?
20 times greater for CO2!!
P1 - P2 =
Pressure gradient across alveolar membrane
At rest, how long does a RBC spend in a pulmonary capillary?
0.75 seconds
How long does oxygen require in a pulmonary capillary to reach equilibrium?
0.25 seconds
At exercise, how long does a RBC spend in a pulmonary capillary?
0.25 seconds
Why will someone with lung disease first notice problems with exertion/exercise?
Oxygen cannot diffuse fast (reach equilibrium) enough to reach equilibrium before the RBC’s leave the pulmonary capillary
- Both for around 0.25 seconds
DLo2
Diffusion capacity of the lung for oxygen
Diffusion capacity of the lung for oxygen
DLo2
What do you use to measure the diffusion capacity of the lung for oxygen (DLo2)?
USE CARBON MONOXIDE
What is the PaCO?
0 - binds to Hb very well
Describe how to measure the diffusion capacity of the lung for oxygen (DLo2)
Have patient inhale one breath with a small amount of carbon monoxide in it
- Take the diffusion capacity of the lung for CO and multiply it by 1.23!!
= diffusion capacity of the lung for O2
How long does CO2 require in a pulmonary capillary to reach equilibrium?
Almost IMMEDIATE
Between CO2 and O2, which has a greater diffusion capacity in the lung?
CO2
What creates surface tension in the lungs?
Air in the alveolus and
Water in the tissues
What is the equation that correlates with surface tension?
Pressure = 2(tension)/radius
In a large alveolus the radius is large, describe the pressure
LOW
In a small alveolus the radius is small, describe the pressure
HIGH
Without surfactant, the HIGH pressure in the small alveolus causes?
Air to be pushed into the larger alveolus and then the small alveolus collapses
Surfactant ____ tension in the small alveoli
DECREASES!
Which form of surfactant is the most important?
SP - B
Describe the equation that correlates with surface tension in the presence of surfactant
Pressure = 2 (LOW tension)/radius == pressure will DECREASE and small alveoli will not collapse
Surfactant decreases the tension in small alveoli. What does this do for the pressure there and the flow of air?
LOWERS the pressure and there is no gradient of flow! (does not get pushed into larger alveoli)
Equation for DLo2 =
1.23 X DLcarbon monoxide
What is a resting DLo2?
21 mL/min/mmHg
