[Respiratory regulation system].

In 1874, Kussmaul described "featiful terminal dyspnea" in a case of severe diabetic coma. Probably, this was the first sign of respiratory regulation for metabolic acidosis. After this first case, about 40 years has been needed to establish the theory of acid-base equiribration, namely Henderson-Hasselbalch's equation. pH = 6.1 + log [HCO3-]/[H2CO3] This equation indicates that plasma pH is determined by the ratio of HCO3 concentration and H2CO3 concentration. Because of linear relationship between H2CO3 and PaCO2, pH depend on the ratio of HCO3- and PaCO2. In the state of metabolic acidosis, increase of [H+] stimulates ventilation and decreases the PaCO2. Inversely, in the state of metabolic alkalosis, increase of PaCO2 occurs. These reactions are called "respiratory compensation" or "respiratory regulation". The respiratory regulation system will not retern pH to normal (7.4), but compensation has some limitation which is shown as "SIGNIFICANCE BAND". In this paper, physiological and clinical importance of respiratory regulation and significance band is discussed.