Studies of Calcium and Inorganic Phosphorus Levels in Plasma and Erythrocytes During Acute and Chronic Hypercapnia

To ascertain the effects of acute and chronic hypercapnia on blood levels of calcium Ca and inorganic phosphorus Pi, guinea pigs were exposed to 1, 3, and 15 CO2 for various periods up to seven days. Plasma and RBC Ca and Pi and serum ionized Ca were determined. Blood from submariners exposed to up to 1 CO2 for three weeks, followed by one-week recovery, was analyzed for plasma electrolytes and RBC Ca. The serum ionized Ca of guinea pigs during acute exposure to each concentration of CO2 shows a pH dependent inverse relationship. During chronic hypercapnia, increase in total plasma Ca and decrease in Pi in those animals exposed to 3 and 15 CO2 suggests increased parathyroid function. In those guinea pigs exposed to 1 CO2, a depressed total plasma Ca in the presence of increased serum ionized Ca is interpreted as a possible functional hypoparathyroidism. In the submariners exposed to up to 1 CO2, both total plasma Ca and Pi tended to decrease although the changes did not become significant. RBC Ca, however, increased gradually and became significant after three weeks exposure. This finding suggests inhibition of active transport andor increase in RBC permeability to Ca. After one-week recovery in air, the RBC Ca had returned to control levels.