Yes, the proton acceptor is CO2 gas dissolved in the blood, at certain partial pressure, determined by the breathing rate. Deoxygenated hemoglobin is also a proton acceptor. There are other serum proteins that form an acid/base equilibrium as well, to affect total blood pH. The carotid process, a bundle of chemoreceptors surrounding the carotid artery in your neck, "tastes" if you will, the pH of your blood, and alters your breathing rate, to remove or add more CO2 in you blood, to affect pH. I'm thinking, it will be hard to overcome all these factors and change blood pH.