Serial Changes in Tissue Carbon Dioxide Content During Acute Respiratory Acidosis12

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Abstract
Male albino rats (83) were exposed to 24% CO2 in air for periods from 0.5 to 48 hours, and the pH and CO2 content of their blood and tissues was compared with control rats. A profound respiratory acidosis with high plasma CO2 and a plasma pH of 6.92 appeared after 0.5 hours of exposure. This was followed after 7 to 15 hours by a further slow rise in plasma CO2 and a rising pH which reached 7.10 after 48 hours. The total CO2 of muscle and brain rose rapidly but reached a plateau after 5 hours. Rate of rise and the absolute level of tissue CO2 was higher in brain than in muscle. Bone CO2 content in contrast to the other tissues remained fixed or declined slightly even after 48 hours of exposure. It was concluded that the soft tissues rather than the bone formed the site of storage of CO2 under the conditions of these experiments. The bone CO2 may be in equilibrium with the carbonate ion concentration (CO3=) of the extracellular fluid rather than with the alveolar CO2 tension as is the case in the soft tissues. Calculations of intracellular pH and bicarbonate concentration in brain and muscle indicated that a profound acidosis developed rapidly in both these tissues. However, in contrast to plasma no evidence of adaptation with return of pH toward normal was observed up to 48 hours of exposure. Possible implications of such a persistent intracellular acidosis in the syndrome of adaptation to CO2 retention are discussed.

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