CO2 Effects on Acid-Base Balance in Air Saturation Dives

Blood gas tensions, pH, plasma chloride, sodium and potassium, blood urea, ammonia and amino-acid nitrogen were measured in mature Sprague-Dawley rats at various intervals during and after exposure to pressures equivalent to depth at 50 and 60 feet, lasting for 60 and 35 days, respectively. In both experiments, a consistent decrease in pH values to about 7.30 and a rise in CO2 tensions to 55-60 mm Hg in the arterial blood were found. Plasma bicarbonate was elevated 5-7 mEq and chloride correspondingly decreased. Plasma potassium was consistently increased in both experiments. These findings indicate the existence of a pronounced respiratory acidosis during the saturation dives to 50 and 60 feet. There is no evidence in the literature which would indicate that as individual agents, elevated pressures of nitrogen or oxygen in the ranges observed in these experiments could cause significant acid-base alterations. It must, therefore, be concluded that the increased ambient CO2 levels in conjunction with the effects of increased oxygen and nitrogen is responsible for the observed changes. When compared with data obtained in rats during acute and chronic hypercapnia the observed PaCO2, pH and bicarbonate values correspond to the range of values obtained by exposure to 3 and 5 CO2.