From the Guidelines
Blowing off CO2 increases blood pH by reducing the amount of carbonic acid in the bloodstream, thereby decreasing the concentration of hydrogen ions and making the blood less acidic. This process is based on the principle that acidity in any fluid, including blood, is determined by the concentration of hydrogen ions [H+], which is normally regulated between 35 and 45 nmol/L, as defined in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. The normal pH range of the blood in humans is between 7.35 and 7.45 units, and acidosis is defined as a pH<7.35 ([H+]>45 nmol/L) while alkalosis is defined as a pH>7.45 ([H+]<35 nmol/L) 1.
When you hyperventilate or breathe rapidly and deeply, you exhale more carbon dioxide than normal, which directly affects the carbonic acid-bicarbonate buffer system in your blood. Carbon dioxide combines with water in the blood to form carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-). By eliminating more CO2 through rapid breathing, you decrease the formation of carbonic acid, which means fewer hydrogen ions are released into the bloodstream. Since pH is a measure of hydrogen ion concentration (with fewer H+ ions indicating higher pH), this reduction in hydrogen ions makes the blood less acidic and more alkaline.
Key points to consider:
- The reduction of CO2 in the blood leads to a decrease in carbonic acid formation
- This decrease in carbonic acid formation results in fewer hydrogen ions being released into the bloodstream
- With fewer hydrogen ions, the blood pH increases, making it more alkaline
- This process can lead to respiratory alkalosis, which may cause symptoms such as lightheadedness, tingling in the extremities, and muscle spasms due to abnormally high blood pH.
From the Research
Mechanism of Blood pH Increase
Blowing off CO2 increases blood pH through the following mechanisms:
- Reduction of carbonic acid (H2CO3) in the blood, which is formed by the reaction of CO2 and water (H2O) 2
- Decrease in hydrogen ion (H+) concentration, leading to an increase in blood pH 2
- Activation of the bicarbonate/carbon dioxide buffer system, which plays a pivotal role in maintaining acid-base homeostasis 3
Effects of Hyperventilation
Hyperventilation, which is characterized by breathing in excess of the metabolic needs of the body, eliminates more carbon dioxide than is produced, resulting in:
- Respiratory alkalosis 2
- Elevated blood pH 2
- Low Pa,CO2 (partial pressure of carbon dioxide in arterial blood) 2
Relationship Between CO2 and Blood pH
The relationship between CO2 and blood pH is complex and involves various physiological mechanisms, including: