Ventilatory response to fixed acid evaluated by ‘iso-Pco2’ technique

Abstract

In order to avoid changes in a second stimulus to ventilation, i.e. carbon dioxide, while measuring the response to fixed acid, a technique was utilized whereby alveolar carbon dioxide tension (PaCOCO2) could be held constant. This technique includes continuous recording of PaCOCO2 with an infrared type analyzer and addition of sufficient CO2 to the inspired air to keep PaCOCO2 at its control value (near 40 mm Hg). The response of anesthetized dogs to infusion of 0.5 m HCl was measured when the PaCOCO2 was held at the control value and also at various other levels. Other experiments measured the effect of CO2 when it was not allowed to change arterial hydrogen ion concentration [H+]. It was found that both these substances are potent respiratory stimuli and that their effects may be considered essentially separate and additive, as suggested by Gray. The experiments also demonstrated a slightly increased sensitivity to CO2 at increased arterial [H+], but this effect was not found necessary to explain the response to acid. Responses to successive small increments in PaCOCO2 failed to reveal any ‘threshold,’ even with CO2 tensions as low as 15 mm during acidosis. Submitted on December 29, 1958