Ventilation - Perfusion Relationship (Part 2) Flashcards
What does the Alveolar Gas Equation allow you to calculate?
The oxygen concentration in the alveoli
Once you know the oxygen concentration in the alveoli, (and you know the oxygen concentration in the arteries), what can you calculate?
A - a oxygen gradient
What does the A - a oxygen gradient determine?
The health of the alveoli
Normally, the A - a oxygen gradient should be around what value?
20 mm Hg
What is the Alveolar Gas Equation?
PAo2 = PIo2 - (Paco2/RQ)
What is PAo2?
Oxygen concentration in the alveoli
What is PIo2?
Partial pressure of oxygen in inspired air
What must the PIo2 account for?
Water vapor
What is the equation to calculate PIo2?
(760 - 47) X oxygen%
Normal water vapor value?
47
Normal oxygen percentage of inspired air?
21%
What is RQ?
Respiratory Quotient
What is a normal value of RQ?
0.8
What is the equation for RQ?
Volume of CO2 produced/Volume of O2 consumed
If you are breathing room air, what is the equation for PIo2?
(760 - 47) X 21%
What is the equation for A - a oxygen gradient?
PAo2 - Pa02
If there is an increase in the A - a oxygen gradient, what does this mean?
There is a diffusion impairment at the alveoli
>20mmHg
What is a normal value for Intrapleural Pressure?
- 5 mmHg
At the apex of the lung, what is the amount of Intrapleural Fluid?
LOW
- due to gravity
At the apex of the lung, what is the level of the Intrapleural Pressure?
LOWER - MORE Negative
At the apex of the lung, what are the sizes of the alveoli?
LARGER
Since the alveoli are larger at the apex of the lung, with inspiration, can they grow much in size?
No
At the base of the lung, what is the amount of Intrapleural Fluid?
HIGH
- due to gravity it pools there
At the base of the lung, what is the level of the Intrapleural Pressure?
HIGHER - LESS negative
At the base of the lung, what are the sizes of the alveoli?
SMALL
Since the alveoli are smaller at the base of the lung, with inspiration, can they grow much in size?
YES
Where are alveoli the largest?
Apex of the lung
Where are alveoli the smallest?
Base of the lung
What is a V/Q ratio?
Ventilation/Perfusion ratio
What is a normal V/Q?
0.8
High V/Q means?
Ventilation is HIGH compared to a normal perfusion
Low V/Q means?
Ventilation is LOW compared to a normal perfusion
With a Low V/Q, what happens with time?
Low ventilation - the alveoli will equilibriate with the blood due to no oxygen coming into the lungs
= PO2 = 40; PCO2 = 45;
NO GAS EXCHANGE WILL OCCUR
With a Low V/Q, what do you expect the Pa of O2 and CO2 to be in arterial blood?
PaO2 = 40mmHg (low) PaCO2 = 45mmHg (high)
With a High V/Q, what happens with time?
Low perfusion (blood flow) - the alveoli will equilibriate with the atmosphere due to no exchange occurring with blood = PO2 = 150; PCO2 = 1 Little effects on the blood since there isn't much arriving there
With a High V/Q, what do you expect the Pa of O2 and CO2 to be in the little arterial blood that does arrive there?
PaO2 = 150mmHg (high) PaCO2 = 1mmHg (low)
What downstream effects does a High V/Q have on a normal alvelous?
It will turn it into a LOW V/Q situation by increasing the blood flow (perfusion) to that area
The apex of the lung has a ____ V/Q
HIGH
The middle of the lung has a ____ V/Q
Normal - 0.8
The base of the lung has a ____ V/Q
LOW
