Resp. 3 - Diffusion and V-Q Relations Flashcards
Dyuring diffusion, what goes into ther alveoli and out of them?
CO2 coming out of blood, into alveoli 9expired through lungs) and O2 diffuses form alveoli into blood.
• CO2 is 20X more soluble then O2. Therfore
diffusion constant for CO2 is greater then O2.
If we have a solution in which Po2 and PCO2 are the same, the conc. Of CO2 would be a lot higher.
Ficks law
How gas gets through BBB. Diffuses through respiratory membrane (thin).
Vgas=A/T D(P1-P2)
- VGAS direct with A, D, and diff in P
Diffusion constant is
Solubility / M.W
Partial pressure in atmosphere
Nitrogen 78.5%
Oxygen 20.93%
H2O 0.5%
Carbon Dioxide 0.04%
Partial pressure in alveoli
Nitrogen 74.9%
Oxygen 13.7%
H2O 5.2%
Carbon Dioxide 6.2%
• The percentages of gases change as we go into the lungs, because the lungs have
metabolic processes, and so CO2 goes form negligible to significant, as as out bodies are warm, H2O increases a lot too. So N2 and O2 decrease.
Because of normal shunts, the amount of O2 in
arterial blood is always < theoretical maximum because of the little bit of CO2 that goes back to the left side of the heart
PO2 and PCO2 (mmHg)
Atmosphere
PO2: 160
PCO2: 0.3
PO2 and PCO2 (mmHg)
Alveolar air
PO2: 100
PCO2: 40
PO2 and PCO2 (mmHg)
Pulmonary veins
PO2: 100
PCO2:40
PO2 and PCO2 (mmHg)
Systemic arteries
PO2: 100
PCO2: 40
PO2 and PCO2 (mmHg)
Cells
PO2: <40
PCO2: >46
PO2 and PCO2 (mmHg)
Systemic veins
PO2: 40
PCO2: 46
PO2 and PCO2 (mmHg)
Pulmonary arteries
PO2: 40
PCO2: 46
What are the pressure gradients found for O2 and CO2
Two gradients,
1) between systemic capillaries & cells
2) alveoli and pulmonary capillaries
CO2 is 6mmHg
O2 is 60mmHg
• The reason why O2 require 60mmHg to get it into the cells and CO2 only require 6mmHg to get it into the blood is because of
Fiks law, the diffusion constant term, and the solubility of CO2 is 20X more then O2
An increase in altitude leads to a
Decrease in:
- atmospheric pressure
- PO2 in air
- PO2 in alveoli
- PO2 in arterial blood
Limitation:
This means that equilibration does not occur between the PO2 in the pulmonary capillary blood and alveolar gas.
Kind of limitations
Perfusion and diffusion limitation
Something that causes a perfusion limitation (example)
if there’s a reduction in blood flow to the lungs causing the partial pressure of O2 leaving the lungs to be less then the partial pressure going into the aveoli, its perfusion.
At rest,
an increase in diffusion would cause ?
A decrease in diffusion would cause?
No limitation
No limitation
During exercise,
An increase in blood flow would cause?
A decrease in diffusion AND increase in blood flow would cause?
- no limitation
- DIFFUSION LIMITATION
At high altitude,
A decrease in diffusion would cause ?
A diffusion limitation.
What is the concentration gradient for CO2 going into the alveoli.
6 mmHg
Between PvCO2 (46) and PaCO2 (40)
During the diffusion of CO2,
A decrease in diffusion would cause?
An increase in blood flow would cause?
A decrease in diffusion AND an increase in blood flow causes?
No limitation
No limitation
LIMITATION
Regional differences in ventilation due to gravity and posture:
- ventilation not equal throughout the lungs, due to gravity and posture.
- Lying down, highest ventilation is at the back of the lungs.
Regional differences in Plp:
• Plp is more (-) at top of lungs.
• Plp pressure generated by the balance between elastic recoil of the lung and the elastic chest wall.
• Weight of lungs is affected by gravity
At the start of inspiration, aveoli at bottom of lung are more deflated
At the start of inspiration, aveoli at bottom of lung are more deflated cuz of
Ptp that generated lung V is influenced by Plp. During inflation aveoli in bottom of lung do the best since lil changes in Plp = large changes in lung V.
Where is airflow / ventilation the greatest in the lungs ?
At the bottom due to gravity
What is the ventilation perfusion ratio
Ventilation(airflow) / blood flow (V/Q)
Ratio between ventilation (O2 into alveoli & CO2 out) and perfusion (O2 out of alveoli and CO2 in).
The ventilation perfusion ratio
- More ventilation =
- More perfusion =
- More ventilation = PO2 and PCO2 in alveoli similar to atmosphere P.
- More perfusion = PO2 and PCO2 in alveoli similar to mixed venous blood.
Why is the ventilation perfusion ratio increase exponentially?
• this is cuz blood flow decreases at a greater rate, so the denominator decreases faster then airflow. Resulting in VQ ratio that exponentially increases.
why is the VQ ratio less then 1 at the beginning?
• This is cuz you have more blood flow (more gravity dependant) at the bottom of the lung then you would airflow (denominator is greater then numerator)
DEADSPACE unit
- Lots of ventilation, but no perfusion (possibly due to blood clot)
- PO2 in alveoli will INC in the alveoli and PCO2 will DEC since there’s no gas exchange b/w alveoli and capillaries.
- Doesn’t contribute to gas exchange.
Shunt Unit
- Caused by airway obstruction = collapsed bronchi and bronchioles
- No gas exchange
- Blood that passes through this system is determined by a shunt (doesn’t get oxygenated)
Silent unit
- no blood flow or ventilation
- hypoxic vasoconstriction occurs in blood vessel heading to the aveoli whose airflow has been reduced, this is in response to reduced airflow to aveoli. This then moved more blood towards aerated units, so its a GOOD THING!
Ventilation-Perfusion Inequality
- this means that ventilation and blood flow are
mismatched in various regions of the lung with the result that all gas transfer becomes inefficient.
Is the ventilation and perfusion unit form throughout the lungs?
No
- Ventilation and perfusion are both greater at the bottom of the lungs (perfusion more so)
• compared to the top of the lung
decrease from the bottom of the lungs to the top of the lungs
