Diffusion and Carriage of Gases pt1 Flashcards
What is the nomenclature (short hand) for;
- Fractional concentration
- Partial pressure
Fractional pressure = FO₂ (can be expressed as a %)
Partial pressure = PO₂
What is the nomenclature (short hand) for;
- Barometric pressure
(Partial pressure of____ & fractional concentration of___)
- Inspired gases
- Alveolar
- Arterial
- Barometric pressure = Pʙ
- Inspired gases = ɪ
-partial pressure of ɪ
= PɪO₂
The fractional concentration of ɪ
=FɪO₂ - Alveolar = A
PA0₂, FAO₂ - Arterial = a
Pao₂, FaO₂
What is the SI unit of pressure equal to?
SI= kPa (killer pascals)
What is Dalton’s law?
In a mixture of NON-reacting gases the total pressure exerted is equal to the sum of the partial pressures of the individual gases.
For example air is a gas mixture the sum of which is Pʙ, so;
Pʙ = PO₂+PCO₂+*PN₂+PH₂O
How would you work out the partial pressure of any gas in a gas mixture?
Use O₂ in the air as an example
You would need to know the total pressure of the gas mixture which in this example would be = Pʙ.
And the fraction of that gas in the mixture. so in this e.g. The FO₂ of O₂= 21% (because O₂ makes up 21% of our atmosphere)
At sea level Pʙ = 101 kPa
FO₂= 21% or 0.209.
So the dry PO₂ = 0,209 x 101 = 21kPa
What is Henry’s law and what does it mean?
C=KP
where C is the concentration of dissolved gas at equilibrium, P is the partial pressure of the gas, and K is the Henry’s law constant (its about solubility)
This means that:
The more the PO₂ of a gas above a liquid is increased the more gas will dissolve into the liquid. (and vice versa)
What 2 variables affect the pressure of water vapour?
Temperature & Saturation
Saturated water vapour pressure rises with temperature.
%saturation depends on how much water the air has been in contact with.
In the lungs air has already passed over moist surfaces in the body so is 100% saturated
What is the constant water vapour pressure in the lungs?
6.3 kPa
this is due to the constant temp at 37∘C.
How do you calculate the partial pressure of O₂ in the inspired air in our tracheas.
The air inside our lungs is moist air, we need to calculate the dry air. so we need to remove the partial pressure of water vapour. which in the body is 6.3kPa.
So we do the following:
(Pʙ-6.3) x 0.209kPa.
Why cant we directly measure what the partial pressure of O₂ is in our alveoli? aka (PAO₂)
How can we work around that?
This is because CO₂ diffuses into the alveolus to replace O₂ diffusing into the pulmonary capillaries.
So to over come this we do the following equation:
PAO₂ = PIO₂-(PACO₂÷R)
R= CO₂ production ÷ O₂ consumption
(if u don’t understand watch LC from 23mins in)
What is the PO₂, PCO₂ & PH₂O in atmospheric air?
PO₂= 21 PCO₂= 0 PH₂O= Variable
What is the PO₂, PCO₂ & PH₂O in the Trachea?
PO₂= 16 PCO₂= 3.5 PH₂O= Variable
What is the PO₂, PCO₂ & PH₂O in Alveolar gas.
PO₂= 20 PCO₂= 0 PH₂O= 6.3
What is the PO₂, PCO₂ & PH₂O in expired air?
PO₂= 13.5 PCO₂= 5.3 PH₂O= 6.3
What drives the diffusion of O₂ from the alveoli to the capillaries?
The Alveolar PO₂ is higher than the PO₂ in the blood entering the capillary, this partial pressure gradient is what drives the diffusion of O₂.
