(22) Ventilation/Perfusion (Karius) Flashcards
What is the alveolar gas equation?
What does the alveolar gas equation calculate?
What inspired O2 needs to be to produce a desired alveolar (and therefore arterial) O2 level
Do this example:
What can be deduced from estimating the PAO2 value?
Allows us to calculate the A-a O2 gradient
This is useful number for determining the ‘health’ of the alveoli
What does an increase in the A-a O2 gradient indicate?
Diffusion impairment
(something is wrong with the alveoli)
The alveolar gas equaltion allows us to predict…
The oxygen concentration in the alveoli
(helpful since non-invasive)
What do you need to calculate the A-a O2 gradient?
Alveolar concentration of oxygen
Arterial concentration
What is the normal A-a gradient?
20mmHg
What is the regional blood flow in the lungs?
Regional ventilation in the lungs:
Describe where the intrapleural pressure is highest and lowest
Intrapleural fluid is also acted on by gravity and affects the intrapleural pressure
Apex (less intrapleural fluid) = Intrapleural pressure is more negative (-10 cm H2O)
Base (more intrapleural fluid)= Intrapleural pressure is less negative than you expect (-2 -3 cm H2O)
Describe the relative sizes of the alveoli at the base vs apex of the lung
At Apex: Alveoli are large at rest
At Base: Alveoli are small at rest
Takeaways?
Note the changes in intrapleual pressures in the apex vs the base
Bigger volume change in base
What does (V/Q) ratio stand for?
Ventilation/Perfusion Ratio
What is the average V/Q ratio?
V/Q
4L/min / 5 L/min
0.8
What does a “high” VQ represent?
Ventilation is HIGH relative to perfusion
What does a LOW V/Q represent?
Ventilation low compared to perfusion
Normal V/Q ratio?
0.8
Describe the enviornment you’d expect with a normal V/Q ratio of 0.8
Describe what happens with a LOW V/Q ratio
The airway is blocked by something, but blood continues to arrive at the alveolus
In short time, O2 in that alveolus decreases while CO2 increases.
What happens over time with a LOW V/Q ratio?
What does this represent?
Physiologic shunt
Describe what V/Q inequalities exhist in the regions of the lung:
Zone 1:
Zone 2:
Zone 3:
Zone 1: V/Q is HIGH
Zone 2: V/Q is normal (0.8)
Zone 3: V/Q is LOW
