Alveolar Ventilation Flashcards
How does gravity affect pleural pressure?
Plueral pressure is more negative at the top of the chest wall where the lung is suspended from the wall
Plueral pressure is less negative at the bottom where gravity is pushing the lung up against the chest wall
This creates a gradient of pleural pressure within the chest wall
What are the two causes for inspired air not being distributed evenly in the lungs?
The gradient in pleural pressure
The non-linear compliance curve of the lungs
How does the distribution of ventilation affect the alveoli?
Alveoli at the bottom of the lung demonstrate the greatest change in volume during inspiration
At the end of expiration these alveoli have the lowest volume because they are subjected to higher pressures than alveoli at the top of the lung
Where is the lung more ventilated?
At the bottom
Why are interstitial lung diseases dangerous with respect to ventilation?
The distribution of the disease is uneven throughout the lung and this creates uneven areas of low compliance
These fibrotic areas are underventilated compared to normal areas of the lung
What is Dalton’s Law of Partial Pressures?
The total pressure of a mixture of gases is the sum of the partial pressures of individual gases
What are the amounts of Oxygen consumption and CO2 production?
Oxygen consumption - 250mL/minute
CO2 production - 200mL/minute
What is the rate of alveolar ventilation?
Volume of air entering the alveoli per minute
Less than total ventilation because it subtracts dead space
Va = Frew (Vt-Vd)
What three things does the rate of alveolar ventilation depend on?
Respiratory rate
Tidal Volume
Dead Space volume
What is anatomical dead space?
Volume of air left in conducting airways
Normal adult = 150mL
What is alveolar dead space?
Volume of air left in unperfused alveoli
Represents a useful measure of lung disease and V/Q mismatch
What is physiological dead space?
Summation of alveolar dead space and anatomical dead space
Measured using the Bohr equation
How does the rate of alveolar ventilation affect the partial pressure of CO2 in the arteries and alveoli?
Assuming CO2 production remains constant…
Hyperventilation - PaCO2 is halved
Hypoventilation - PaCO2 is doubled
What is the relationship between the partial pressures of CO2 and O2?
They are inversely related to each other
The change in PAO2 is approximately the same as the change in PACO2
