L09: Alveolar Gases And Diffusion Flashcards
What is Pa
Partial pressure of arterial
What is PA
Alveolar partial pressure
What is the PA(o2)
13
What is the PA(co2)
5
What is Pv
Venous partial pressure
What is Pv(o2)
5
What is Pv(co2)
6
What is pa(o2)
13
What is pa(co2)
5
Which process increases PA(co2)
Metabolism
What decreases PA(CO2)
Ventilation
What is ventilation
Breathing out
What is hyperpnoea
When there is an increase in metabolism, ventilation increases to MATCH it
When does hyperpnoea occur
During exercise
What is hyperventilation
When there is an increase in ventilation above the requirement of metabolism
What factor do we need for diffusion to occur
Partial pressure gradient
What are the 3 layers of the alveolar capillary membrane
Alveolar epithelium
Basal lamina
Capillary endothelium
What does the grahams law state
Diffusion of gases is dependent on partial pressure gradient and bigger molecules diffuse slower
Does oxygen or carbon dioxide diffuse slower
Carbon dioxide
Why does carbon dioxide diffuse slower than oxygen
Carbon dioxide has a higher molecular weight than oxygen
Does carbon dioxide or oxygen more soluble in liquid
Carbon dioxide
Which gas will show a diffusion limitation
Oxygen
What can diffusion limitation of oxygen result in
Hypoxia (low oxygen)
What does Henry’s law state
The concentration of gas in liquid is equal to to the partial pressure times solubility coefficient
In general what does diffusion of a gas into blood depend on
Concentration gradient
What is partial pressure gradient of a gas dependent on
Solubility Chemical combination (form a molecule with haem)
What does it mean to have a diffusion limited gas
Gas has high solubility and high chemical combination (binds readily with haemoglobin)
What does it mean to have a perfussion limited gas
Gas has a low solubility and no chemical combination
Name an example of a diffusion limited gas
Carbon monoxide
Name an example of a perfusion limited gas
Oxygen
Carbon dioxide
What are the 2 main ways of a reduced pulmonary diffusing capacity
Reducing surface area
Increasing diffusion path length
How can you reduce surface area
Loss of lung tissue
Airway obstruction
Capillary obstruction
Ventilation/perfusion mismatch
How can you increase the diffusion path length
Thickened alveolar capillary membrane
Accumulation of lung fluid
Increased intracapillary distance
When can you get a thickened alveolar capillary membrane
Fibrosis
When can you get an increased intracapillary distance
Low haemoglobin
If carbon monoxide is diffusion limited what will happen to the other carbon monoxide in the atmosphere
It will move into the lung and never reaches equilibrium
How can you increase a perfusion limited gas into the body
Increase the blood flow
How can you increase a diffusion limited gas into the body
Increase the alveolar partial pressure of that gas
What is a pulmonary diffusing capacity
The ability to diffuse gases across the lungs
What is flow of a gas across a diffusion barrier proportional to
Diffusibility of a gas
Area
Partial pressure gradient
Thickness (inversely proportional)
What gas do we use to measure the diffusion constant
Carbon monoxide
After calculating the diffusion constant with carbon monoxide how do we convert it to a value representing oxygen
Use a conversion factor of 1.25
When might we use diffusion constant
When there is a problem with the way the oxygen moves in the lungs and NOT ventilation
