| MadSci Network: Medicine |
Hi Kuan -
Respiratory alkalosis generally happens after *hyperventilating* for a while - you exhale more CO2 than the body can produce to maintain the normal concentration of CO2 in the blood. Why this happens involves an interesting look at some of the chemical reactions that take place in the blood.
Carbon dioxide is an acid anhydride of carbonic acid - H2CO3. Add water to it ("hydrate it..") and you get:
CO2 + H2O <--> H2CO3
In the blood you also have the following equilibrium reaction:
H2CO3 <--> H+ + HCO3
Note the production of H+/protons which
help buffer the blood to keep it in its normal pH range of 7.35 - 7.45.
Normal blood is not neutral 7. Proteins and other factors in the
blood give it the slightly 'basic' pH. In fact if your pH dropped to 7,
you'd become quite delirious! The same happens if the pH rises significantly
above the normal range. Young children who hyperventilate ultimately save
themselves when they pass out - at which point respiration returns to
involuntary control, CO2 levels increase, and little Bobby wakes up
slightly groggy, but ready to go at it again...
In the equilibrium reactions below, CO2 and H2O are constanly formed into H2CO3 which is also being broken down into CO2 + H2O, and H+ + HCO3-. The system is fully reversible (part of the definition of being at "equilibrium").
CO2 + H2O <--> H2CO3 <--> H+ HCO3-
By removing CO2 from the system, you convert more H2CO3 into CO2 + H2O,
and more H+ HCO3- into H2CO3, etc.. The equilibrium reactions shift
from the right side to the left. This effect demonstrates Le Chatelier's
Principle. If an equilibirum system is disturbed, the system
attempts to adjust itself to overcome the disturbance. In this case hyperventilation
removes CO2 from the blood. The blood responds by generating more CO2
from the breakdown of carbonic acid. This response is faster than altering
the body's metabolic rate, which is how we usually generate CO2.
So to become alkalotic, you need to exhale more CO2 than your body can readily produce via normal metabolism. If the person talking for a long time were inhaling and exhaling very rapidly, it is possible they could become alkalotic. If anything, I think people are more likely to hold their breath when talking rapidly which leads to the opposite effect -- acidosis, as the amount of CO2 in the blood would increase. I'll leave it to you to figure out how the increase would drop the pH of the blood...
-Lynn Bry
MD/PhD Student, Washington University Med School
Try the links in the MadSci Library for more information on Medicine.