PLASMA IONIZED MAGNESIUM DURING ACUTE HYPERVENTILATION IN HUMANS

1. Respiratory alkalosis accompanies the clinical syndrome of tetany, precipitates cardiac arrhythmias and predisposes to coronary vasoconst riction. Magnesium plays a critical role in the maintenance of membran e function, and magnesium depletion is often associated with cardiac a rrhythmias or vasoconstriction. 2. As technology for detecting circula ting ionized magnesium (the most interesting form with respect to phys iological and biological properties) is now available in the form of n ew magnesium-selective electrodes, the effect of respiratory alkalosis induced by voluntary overbreathing for 30 min on circulating ionized magnesium was studied in eight healthy subjects. 3. The total plasma m agnesium concentration was not modified by hyperventilation, On the co ntrary, hyperventilation was associated with a significant reduction i n the ionized magnesium concentration of 0.05 (0.02-0.15) mmol/l (medi an and range) and in the free magnesium fraction of 0.06 (0.01-0.19), During hyperventilation the relative intravascular magnesium mass, cal culated from changes in total plasma magnesium concentration and haema tocrit, decreased significantly. 4. It is concluded that acute overbre athing reduces the circulating ionized magnesium concentration and the intravascular magnesium mass, It is therefore conceivable that extrac ellular magnesium deficiency is at least a subsidiary cause of the syn drome of tetany and the cardiac complications that are precipitated by hyperventilation.