lecture 16 Flashcards
Exam 3 content
Does venous blood have more or less bicarb than arterial blood?
Less bicarb
what is the total CO2 content per dL of arterial blood if PCO2 is 40mmHg?
48mL of CO2/ dL of blood
What is the total CO2 content per dL of venous blood if PCO2 is 40mmHg?
52.5 mL of CO2/ dL of blood
The difference between the CO2 content in venous blood and arterial blood corresponds to what?
52.5mL - 48mL = 4.5mL corresponds to the amount of CO2 dropped off at the lungs
Recall that 5mL of O2 is picked up by the lungs
Deoxyhemoglobin is different from oxyhemoglobin with regards to CO2 transport how? What is the name for this?
There is more room for CO2 to bind in deoxyhemoglobin than oxyhemoglobin.
This is called the Haldane Effect.
Deoxyhemoglobin is more willing to accept a proton than oxyhemoglobin, what does that make deoxyhemoglobin?
a weak acid (a good buffer!)
How long does it take for gas exchange to occur in the pulmonary capillaries?
It takes 0.25 sec under normal conditions
How long does the blood hang out in the pulmonary capillary of the alveolus?
about 0.75 sec under resting conditions
If we increase our CO, what happens to the blood in the pulmonary capillary? Does this pose a problem for gas exchange?
blood speeds up d/t high CO and the blood only hangs out in the pulmonary capillary for 0.25 sec. This isn’t a problem for gas exchange unless the person has unhealthy lungs.
What gas equilibrates between the pulmonary capillary blood and the alveolus faster than oxygen? Why?
nitrous oxide, because it is less soluble than oxygen (onsets and offsets quickly)
What gas is used as a diagnostic gas to mirror oxygen in measuring the diffusing capacity of the lungs?
carbon monoxide
What is a perfusion-limited gas?
A gas that has equilibration between the air in the alveolus and the blood in the pulmonary capillary –> oxygen (oxygen absorption depends on how much blood is moving through the lungs)
What is a diffusion-limited gas?
No equilibration between the pulmonary capillary blood and the alveolar air. Oxygen absorption is limited by the rate of diffusion.
Give an example of a diffusion-limited gas…
CO
Example of perfusion-limited gasses…
N2O and O2
According to Fick’s Law what is directly proportional to how fast gas can move across a barrier?
surface area, diffusivity, and delta P
What is diffusivity?
D ~ solubility / square root (molecular weight)
According to Fick’s Law what is inversely proportional to how fast gas can move across a barrier?
thickness of the barrier
How much more soluble is CO2 than O2? Which gas diffuses faster?
CO2 is 24x more soluble than O2, so even though it is larger than O2 it will diffuse faster (it’s diffusivity is 20x O2)
What is a normal V/Q ratio in a healthy person?
4200/5000mL (0.8)
If your patient has a V/Q ratio greater than 0.9, what does this indicate?
a perfusion problem (increased alveolar dead space)
If your patient has a V/Q ratio less than 0.8, what does this indicate?
a ventilation problem (shunting)
The V/Q ratio is higher at the____ of the lung.
The V/Q ratio is lower at the_____ of the lung.
Where is there more O2 coming from? CO2 from?
Higher V/Q: apex (top) (more O2 and less CO2)
Lower V/Q: base (more CO2 and less O2)
What happens to V/Q when you give someone anesthesia? How can you overcome this?
atelectasis occurs, and small airways collapse. Give PEEP!
