This brings the PPCO2 down for half the blood to a level lower than the normal equilibration PP. Remember CO2 is equilibrating OUT of the blood,so this matters. Now half the blood isn't equilibrating with respect to CO2 either but the half that is is equilibrating with twice the volume of air it usually would. So blood 100% sat on one half and 75% sat on the other will be 87.5% sat overall. Now half your blood isn't equilibrating with respect to O2, bringing your O2 sat down to the average between the alveoli. Half your blood isn't participating in exchange at all though (lets say you have pneumonia that fills up half your space). In this case ALL 5L/min of your air is equilibrating with your blood because its only going to the good alveoli. Shunt: Opposite case, now you've got blood flowing where its not wanted. Also why we can do CPR.plenty of O2 left in your breath for a person to absorb. Thus, their body won't blow off anymore CO2, bringing your blood CO2 levels back up and keeping you from passing out from respiratory alkalosis. On a side note, this relates into why people inhale their air when they hyperventilate right? There's plenty of O2 in the air but that air is already equilibrated with respect to CO2. Thus you get hypercarbia but no hypoxemia. Normal air has no CO2, so when that air is equilibrated its done.no more CO2 is gettin in there. Not so with CO2, which is equilibrating the other way. So there's still enough O2 left to saturate that extra blood. Remember that there's still usually a ton of residual O2 left in air you expire.a person can breathe on the air they expire.
Your O2 sat will still be okay because your blood is gonna pull that O2 from the air until it equilibrates. Now all your blood is equilibrating with only half the air volume its used to. Since your blood flow is non existent for half your lung, all that blood has to go past your good alveoli. ALL your alveoli are getting perfused at 5L/min BUT only 2.5L/min are participating in gas exchange, so its basically as if you were inspiring 2.5L/min. Let's say normal ventilation is 5L/min and we'll put none of that in anatomic dead space for simplicity sake. Lets say half your alevoli are dead space because of some type of perfusion interruption. For instance, lets take a simple example.
What this means is that you're only getting half as much air into exchange areas as you usually would. If you want it broken down totally here's my take on it:ĭead Space: Like jdh said, you're reducing your effective minute ventilation. Here's the link to the thread if you want to go there yourself (not much more to be had though).
I'm stealing this from SDN, but it really helped me.
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