Hypocapnia and electrolyte balance

Hypocapnia (CO2 deficit) has a direct impact on the electrolyte balance of extracellular fluids, including interstitial (fluid that surrounds cells), lymph, cerebrospinal, and blood plasma fluids.   Increased pH (respiratory alkalosis) of interstitial fluids that surround neurons in the brain, for example, leads to exchange of sodium ions (Na+) and potassium ions (K+) for hydrogen ions (H+), which reduces pH toward normal. The result, however, is extracellular sodium deficiency (hyponatremia) and potassium deficiency (hypokalemia), both of which can trigger significant physical symptoms. Sodium deficiency is also the result of chronic hypocapnia, where as a result of CO2 deficit sodium ions are excreted by the kidneys rather than exchanged for hydrogen ions and returned to circulation.

Excessive sodium ions in neurons increase neuronal excitability, contractility, and metabolism. Unfortunately, this increase in metabolism is occurring at a time that neurons can least afford it, at a time of decreased availability of oxygen and glucose.   This decrease is the direct and immediate result of decreased blood flow, vasoconstriction, also the consequence of hypocapnia. Reduced CO2 in blood plasma triggers smooth muscle contraction (vasoconstriction), and reduced CO2 in the in red blood cells (increased pH) inhibits the release of nitric oxide, a potent vasodilator, by hemoglobin.   Reduced CO2 in the red blood cells also increases hemoglobin’s affinity for oxygen (Bohr Effect), thus distributing its oxygen less efficiently to surrounding cells.   This reduces the threshold for anaerobic glycolysis, increasing the likelihood of lactic acidosis in neurons, which may contribute to yet further physical and psychological symptoms and deficits. It also may lead to excitotoxin production and antioxidant depletion.  Click here to learn more about internal respiration (O2 and CO2 distribution).

Hypocapnia also alters the balance of calcium and magnesium in muscles, which increases the likelihood of tetany, spasm, weakness, and fatigue, e.g., carpal tunnel syndrome. This includes skeletal muscles with serious implications for athletes and fitness enthusiasts. And, it includes smooth muscles, where imbalance may exacerbate or trigger migraine, angina, and electrocardiogram abnormalities.

Long-term hypocapnia means chronic CO2 deficit in the kidneys, which results in bicarbonate deficits. This means that bicarbonate ions, crucial to the buffering of metabolic acids, such as lactic acid produced during exercise, are depleted.   The consequences may include (1) compromised physical endurance in sports and fitness enthusiasts, and (2) the appearance of fatigue symptoms associated with chronic stress, where adequate buffering of even small amounts of lactic acid is compromised.   Click here to learn more about chronic hypocapnia and kidney physiology.

Click here to learn more about acid-base balance.