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.
Copyrighted by
Behavioral Physiology Institute,