31 mechanisms of hypoxia Flashcards
what determines PaO2?
ventilation and perfusion
What is FiO2?
the fraction of inspired air that is O2. (21%)
How do you calculate PAO2?
PAO2=FiO2 x (barometric pressure - H2O pressure) - PCO2 pressure/R
P(baro)=751 in Iowa city
P(H2O)=47
P(CO2)=40
What is PAO2 in Iowa city?
98mmHg
This is only important because he uses it all the time and its easier to remember it than calculate it
In the lungs, is oxygen perfusion limited or diffusion limited?
Perfusion limited. It is not diffusion limited because any O2 that can get into the alveoli can easily pass through the thin membranes to get into the blood.
What is the A-a gradient?
The difference between PAo2 and PaO2.
A-a gradient=(PAO2 - PaO2)
This number should be near zero because it is measuring diffusion and this is not normally a problem.
All Alveoli are not ideal (the same) in the lungs. Why?
Blood flow is not homogeneous
Ventilation is not homogeneous
What is the west three-zone model?
A model describing the blood flow patterns in the lungs. It shows that the bases receive the majority of the blood while the apex receive the least. This is mainly due to gravity.
LOOK AT THIS IN THE NOTES!
what happens when (Palveolar>Ppulmonary artery>Ppulmonary vein)?
There is no flow because the capillaries are collapsed. This is what happens in the apex of the lung. [Zone 1]
what happens when (Ppulmonary artery>Ppulmonary vein>Palveolar)?
capillaries are fully open and perfusing well because they are not collapsed like in the apex.
[Zone 3]
Transpulmonary pressure under normal physiological conditions is always positive/negative?
Positive.
Transpulmonary pressure= alveolar pressure - pleural pressure.
How would you describe the PO2 and PCO2 at the apices or the lungs?
At the apices, the alveoli are usually overinflated and have more ventilation than perfusion can keep up with. Therefore, you would see a higher than average PO2, and a lower than average PCO2.
why is V/Q mismatch so bad?
1) Low V/Q has low PAO2, leaving the blood with a low PaO2.
2) High V/Q has high PAO2, leaving the blood with a high PaO2
3) When you mix these 2 (High and low) PaO2, the result is not an average of PaO2 but a value closer to the lower PaO2.
[Key: High V/Q units cant compensate]
What is one of the major reasons why your oxygen concentration in you blood (SpO2) is not 100%?
The blood that has dumped oxygen to the bronchioles is released into the pulmonary veins which are already oxygenated. (This also makes it so the A-a gradient is larger then 0)
What percent of cardiac output goes to bronchial circulation?
about 1%
what are the normal BP values for systemic and pulmonary circulation?
systemic= 120/80
pulmonary=24/9
Under normal conditions, what percent of blood flows to normal V/Q matched areas? Low V/Q areas? High V/Q areas?
90% of blood flows to normal V/Q areas
5% of blood flows to Low V/Q areas
5% of blood flows to High V/q areas
what does the body do to the low V/q areas since they do so much harm?
The body chokes them off. This happens when the pulmonary arteries are exposed to low PAO2 areas.
[this is opposite to other areas of the body]
How does the body deal with over ventilated alveoli?
Over ventilated alveoli have lower PACO2 so the body can constrict the bronchial smooth muscle sending the oxygen to other areas that need it.
What would a V/Q ratio of 50 mean? When would you see this?
It would mean that there is 50x more ventilation than perfusion going on.
You could see it with severely diseased lungs that cause diffusion to be significantly reduced.
What has a worse effect of blood oxygen, Low V/Q or a shunt?
Shunt. A shunt is like an ultra low V/Q mismatch because nothing is being exchanged, but be careful because this is not exactly true.
They tend to occur in different areas of the lung, and their response to oxygen is different.
Why is the shunt worse than the V/Q mismatch?
A shunt will not respond to higher oxygen levels very well because PaO2 will only rise minimally.
V/Q mismatch will respond to higher oxygen levels pretty well and many times bring oxygen saturation up to 100%
what would be a reason for a shunt in the lungs?
1) Congenital heart disease
2) alveolar filling with blood/fluid
3) alveolar collapse
