First understand the following equation :
CO2 + H2O <-- --> H2CO3 <----> H+ + HCO3-
where CO2 is the dissolved CO2 in the plasma, which diffuses into RBCs where it reacts with H2O in the presence of carbonic anhydrase
Enzyme found in our body tissues including in the red blood cells catalyze the hydration reaction—
carbonic anhydrase is an important enzyme for this. Our carbon dioxide that enters our red blood cells enters our carbonic anhydrase and combines carbon dioxide with water to form carbonic acid. It dissolves quickly into bicarbonate and proton. This reaction that is catalyzed is reversible. In regions in our body where we have high pressure of carbon dioxide, that carbon dioxide diffuses based on concentration gradient. When blood gets transported to lungs and alveoli, we have a region of low carbon dioxide concentration. This reaction shifts towards the left, bringing up carbon dioxide that is going to diffuse into alveoli and then we expire and we remove that carbon dioxide from our body.
What happens to plasma pH during hyperventilation to high altitude?
When there is hyperventilation, you blow off more CO2. Because there is decreased carbon dioxide concentration in your body, you are shifting reaction to the left in order to increase carbon dioxide levels. To do that, your hydrogen ion concentration is dropping.
How does this hyper-ventilatory affect unloading of O2 at the cells?
Is decreased. As reaction shifts to the left to make more Co2, you are consuming H+ ions. The hydration reaction is up here and it is reversible. As we consume hydrogen ions, our pH values become more alkaline. As our pH becomes more alkaline, we are going to shift our oxygen dissociation curve towards the left. When you shift it to the left, hemoglobin has a HIGHER binding affinity for oxygen. So when affinity for hemoglobin is very high to oxygen, it doesn’t want to let go of oxygen to the body tissues. So unloading of oxygen at the tissues is decreased.