Partial Pressure

[kohlerrf]

I am stumped?

We all know that we inspire roughly 79% Nitrogen and 21% oxygen at one atmosphere of 760mm/hg. Leaving water vapor out of the mix for now this brakes down to partial pressures of  600.4 mm/hg of Nitrogen and 159.6 mm/hg Oxygen. In a homeostatic body with a proper pH we normally absorb roughly 5% of that oxygen and none of the nitrogen leaving a "partial pressure" void of 5% which is commonly filled by C02 creating the value  we know as End Tidal CO2.  In addition our O2 sat has risen to 100% because our pH has become more alkolotic causing a left shift in the oxy-hemoglobin curve resulting in greater affinity for hemoglobin to bind with oxygen

The numbers may be a little off here but bear with me.

If CO2 diffuses to fill the void in the partial pressure, in a state of hyperventilation where our CO2 levels drop what files the void to maintain a partial pressure of 760 mm/hg in our exhaled air? Do we just absorb less Oxygen because the Hemi sites are full and we have saturated the plasma?

[Just Plain Ruff]

It's the essential oils that are so popular these days that take the place of the missing stuff.  I should know because I stayed in a holiday inn express last night.  

[ERDoc]

I don't think there is much change in the partial pressures.  You are just unloading more CO2 per minute because of the increased resp rate.  Just to make up some numbers, let's say you get rid of 100gms of CO2 with each breath.  Breathing at 10 times per minute, you are removing 1000gms.  Now, increase your rate to 20 times per minute and you are no getting rid of 2000gms per minute.  Clear as mud?

[Off Label]

On ‎7‎/‎31‎/‎2016 at 7:26 AM, kohlerrf said:

I am stumped?

We all know that we inspire roughly 79% Nitrogen and 21% oxygen at one atmosphere of 760mm/hg. Leaving water vapor out of the mix for now this brakes down to partial pressures of  600.4 mm/hg of Nitrogen and 159.6 mm/hg Oxygen. In a homeostatic body with a proper pH we normally absorb roughly 5% of that oxygen and none of the nitrogen leaving a "partial pressure" void of 5% which is commonly filled by C02 creating the value  we know as End Tidal CO2.  In addition our O2 sat has risen to 100% because our pH has become more alkolotic causing a left shift in the oxy-hemoglobin curve resulting in greater affinity for hemoglobin to bind with oxygen

The numbers may be a little off here but bear with me.

If CO2 diffuses to fill the void in the partial pressure, in a state of hyperventilation where our CO2 levels drop what files the void to maintain a partial pressure of 760 mm/hg in our exhaled air? Do we just absorb less Oxygen because the Hemi sites are full and we have saturated the plasma?

This is a really good question.

I think the answer lies in the increased alveolar ventilation relative to oxygen uptake at the alveoli. If a patient is hyperventilating, by definition it is not for the purposes of increasing oxygen delivery because there isn't an increase in demand. So instead of exhaling the usual (about) 16 % oxygen, he is exhaling something closer to the inhaled 21%.

While more oxygen per minute is reaching the alveoli because of the hyper ventilation, there isn't an increased demand and uptake so there is more left over to be exhaled.