# Question about hyperventilation

#### misterwiggles

2+ Year Member
If a person is hyperventilating, the blood has:

A) increased saturation of hemoglobin with O2.

B) a higher level of CO2.

C) a higher pH level.

D) an increase in carbonic acid.

Every time I look back at old notes it all says that hyperventilation causes an high pp. CO2 and thus increase in [H+] which means lower pH. I choose B, but the answer is C. C is completely contradictory to my notes so I thought I'd ask you guys to help explain why it's right! HELP

#### FutureMrDr

2+ Year Member
When you hyperventilate you are losing a ton of CO2 so Le Chatelier's principle tells us that the body will try to compensate for the deficit by shifting the bicarbonate buffer system to the left.

For reference, the bicarbonate system looks something like this:
CO2 + H20 <-> H2CO3 <-> H(+) + HCO3(-)

When that system moves to the left (in response to low CO2) the concentration of H+ decreases and we know that there is an inverse relationship between H+ and pH.

tl;dr: Hyperventalation = Low CO2 levels = Leftward Bicarb buffer system shift = decreased H+/Carbonic Acid = higher pH levels = C.

Last edited:

#### popopopop

7+ Year Member
This question is tricky at first because of the wording. You probably picked B because you're thinking a person is hyperventilating to correct a high blood CO2 level. However, the question already explicitly stated the person is hyperventilating (so you start from there, don't assume acidotic blood), thus, his pH will be corrected towards a higher pH.

T

#### torontopharm

My thought process is that, when you're hyperventilating you have a lot of O2 going to the red blood cells, and a lot of CO2 going in the opposite direction to your alveoli. You have a high Pp of CO2 in your lungs initially but as we exhale the CO2 out, both blood and alveolar Pp CO2 decrease, the equilibrium shifts left and we get high blood pH.

Someone correct me if i'm wrong!

#### tenblackalps

2+ Year Member
Faster breathing rate = blowing off more CO2

CO2 acidifies blood via bicarbonate exchange.

Therefore hyperventilation = less CO2 = less acidic blood = higher blood pH

#### SteyrFWB

2+ Year Member
From a simpleton anesthesiologist point of view about CO2.

You hyperventilate, you bring down your CO2. You bring down CO2, you have cerebral vasoconstriction, less blood to brain, you feel you want to faint.

For this question, decrease CO2, use that simple pH is proportional to HCO3/ CO2 equation, pH will go up. So you hyperventilate, CO2 goes down, you have respiratory alkalosis (pH goes up).

So answer is respiratory alkalosis ( higher pH).

Hyperventilation has not much to do with oxygen level. You are still breathing the SAME oxygen concentration. Hyperventilation does not increase your oxygen level.

Hyperventilation will decrease your respiratory drive. If you hyperventilate, you can hold your breath much longer, your urge to breath will be less.

So if you are a world champion diver, you hyperventilate before diving. You go down, you have no urge to breath. You can stay down longer. Great ? right? Wrong ! You die.

You have no urge to breath, your oxygen level is now decreasing. Once your oxygen saturation gets below 60%, you just pass out under water. You still have no urge to breath. You die under water.

Last edited:

#### EverStriving

This is a very poorly worded question because it uses comparatives without stating the reference point. If 'higher pH' means higher than before the patient started hyperventilating, then yes that's the answer.

But if 'higher pH' means higher than normal, then we have no way of knowing whether that's true because we don't know the cause of the hyperventilation. If the hyperventilation is caused by acidosis, then we also need to know if the body is fully compensating.

Fortunately, the other three answer choices will never be true, so you know the answer is C.

OP

#### misterwiggles

2+ Year Member
So hyperventilation is low CO2, high pH?
I realize some of you shed light on the fact that this was worded weird because it depends on the reference point. But if someone could just give me a straight out like hyperventilation is ____ so I know for sure what happens because I don't want to mix it up from now. Thank you to everyone that responded

OP

#### misterwiggles

2+ Year Member
I might also shed light on this fact. If in fact this is an increase in pH, wouldn't A also be true because of Bohr shift?

#### EverStriving

A would not be true because normal breathing is already capable of fully saturating hemoglobin. Hyperventilation can't increase saturation past 100%. Hyperventilation does cause increased loss of CO2 from the lungs, which shifts the carbonic acid-CO2 equilibrium away from carbonic acid by le chatelier's principle. Therefore hyperventilation both decreases [CO2] and increases pH.

6

#### 691622

hemoglobin gains affinity to oxygen, look at the shift in the graph, it makes sense. When you hyperventilate you lose CO2, pH rises, and your body wants less oxygen. So hemoglobin gains affinity to oxygen in order to keep it from going to the tissues, but this is not called saturation since you are still breathing the same room air.

nothing can really be said to make it as simple as "hyperventilation is _____" you just have to understand it.