In general, blood flow to the brain reduces proportionately to each reduction in carbon dioxide. A study by Dr. Daniel M. Gibbs, which was published in the American Journal of Psychiatry to assess arterial constriction induced by excessive breathing, found that the diameter of blood vessels reduced in some individuals by as much as 50 percent. Based on the formula πr2, which measures the area of a circle, blood flow decreases by a factor of four. This shows you how radically overbreathing can affect your blood flow.
