Session 2 - part II Flashcards
What is the partial pressure of O2 in alveolar air?
13.3 KPa (Atmospheric is 21 KPa)
What is the partial pressure of CO2 in alveolar air?
5.3 KPa (Atmospheric is tiny <1)
What is the partial pressure of O2 and CO2 in venous blood?
6.0 KPa O2 & 6.5 KPa CO2 (at rest)
These values vary with different levels of metabolism
What causes O2 to diffuse into the blood?
The partial pressure of O2 in the alveolar gas is greater than the partial pressure of O2 in the returning blood.
What causes CO2 to diffuse into the alveoli?
The partial pressure of CO2 in the alveolar gas is lower than the partial pressure of CO2 in the returning blood.
What does diffusion of gases depend on?
Area
Gradients
Dsitance
What does resistance to diffusion depend on?
Nature of the barrier
Nature of the gas
How does the barrier effect gas exchange in the alveoli?
The gas has to diffuse through other gases and the alveolar wall which has; Simple squamous epithelium Tissue fluid Simple squamous of the vessel Plasma Membrane of the red blood cell
Diffusion of gases through gases is inversely proportional to what?
Molecular weight
Which molecule is heavier out of CO2 & O2?
CO2 is heavier
Which molecule is more soluble out of CO2 & O2?
CO2
What gas transports the fastest?
CO2 so exchange of O2 is always limiting
How thick is the barrier for oxygen transport in the alveoli?
0.6 micro meters
How can you determine the gas composition in the alveoli?
Take a sample from an artery in the wrist, the partial pressures will be the same here as in the alveoli
Define ventilation
Expansion of the lungs which increases the volume of the respiratory bronchioles and alveolar ducts so air can flow down the airways to them.
Which parts of the airways can/cannot expand?
Can - Respiratory bronchioles, alveolar ducts
Cannot - Rest of respiratory system
How can you measure the ventilation?
A spirometer - Patient breathes from a closed chamber (Pressure held constant) over water whose volume changes with ventilation
Define Tidal volume
Volume in and out of the same airways with each breath
Define Inspiratory reserve volume
The extra volume that can be breathed in over the Tidal volume at rest
Define Expiratory reserve volume
The extra volume that can be breathed out over the Tidal volume at rest
Define Residual volume
The volume left in the lungs at maximum expiration.
How do you measure Residual volume?
Using Helium dilution, not a spirometer
Why do lung capacities not vary?
They’re measured from fixed points in the breathing cycle, so better clinically as they are always the same as always taken at the same point.
Define Vital capacity
Maximum inpsiration to maximum expiration.
The biggest breath that can be taken and is often effected in disease
Usually 5L
Define Inspiratory capacity
The biggest breath that can be taken from resting expiratory level
Usually 3L
Define Functional residual capacity
Volume of air in the lungs at resting expiratory level.
Usually 2L
Expiratory reserve + Residual volume
Define Ventilation rate
Amount of air moved in and out of a space per minute. It is the product of volume moved per breath and respiratory rate
Define Pulmonary ventilation rate
Tidal volume x Respiratory rate
What is Dead space?
Due to the air entering and leaving the system via the same airways, the last air stays in the airways and is the first air out. Therefore it never reaches the alveoli and is wasted.
What is the alveolar ventilation rate?
The amount that reaches the alveoli
Dead space is taken into account
Define Serial dead space
The volume of the airways
Measured using a nitrogen washout
Usually 0.15L
Define Distributive dead space
Parts of the lung which are not airways, but don’t support gas exchange due to being dead, damaged or having poor perfusion.
What is Physiological dead space?
Distributive dead space + Serial dead space
Usually 0.17L
How do you calculate dead space ventilation rate?
Dead space volume x Respiratory rate (number of breaths per min)
What type of breathing is most work, but gets most air to the alveoli?
Deep breathing
What is the standard Tidal volume?
0.5L
What is Pulmonary ventilation rate?
Tidal Volume x Respiratory Rate
What is the standard Inspiratory volume?
2.5L
What is the standard Residual volume?
0.8L
What is the standard Expiratory volume?
1.5L
What is the standard Functional residual capacity?
2.3L
What is the standard Inspiratory capacity?
3.0L
What is the standard Vital capacity?
5.0L
What is the standard Lung capacity?
5.8L
