Relationship between acid-base balance and the central respiratory mechanisms

¹ Departments of Anesthesiology and Pharmacology, College of Physicians and Surgeons, Columbia University, and the Anesthesiology Service, The Presbyterian Hospital, New York City

To study the effect of changes in acid-base balance on respiratory patterns, 2-amino-2-hydroxymethyl-1,3-propanediol (THAM, an organic buffer) and sodium bicarbonate (NaHCO₃) were infused into midcollicular decerebrate, pontile, and medullary cats. NaHCO₃ increased the arterial pH, HCO^–₃, and pCO₂. THAM increased the arterial pH and HCO^–₃. The arterial pCO₂ fell initially and then rose gradually with time. In the midcollicular decerebrate preparation with eupnea, NaHCO₃ increased while THAM decreased the rate and amplitude of respiration. In the vagotomized pontile preparation with apneustic breathing, NaHCO₃ accelerated and THAM decelerated the apneustic cycling; neither produced a significant change in amplitude. Larger doses of THAM abolished the apneustic cycling either by producing expiratory apnea or by prolonging the inspiratory phase. In the medullary preparation with periodic breathing, THAM decreased the rate with minimal changes in amplitude. The findings suggest that the respiratory effects of NaHCO₃ and THAM were due to changes in intracellular pH and pCO₂ and that all functional components of the respiratory center are influenced by changes in the acid-base status of the animals. Finally it is pointed out that elucidation of neural respiratory mechanisms requires definition of the acid-base state of the animal.