Ventilatory response to alterations of H+ ion concentration in small areas of the ventral medullary surface

Small areas of 3 mm2 on the ventral surface of the medulla oblongata of cats were superfused with buffers of pH 7.0 and 7.8 and an opposite effect of H+ ions was observed, suggesting the existence of two chemosensitive areas.

Abstract

Small areas of 3 mm2 on the ventral surface of the medulla oblongata of cats were superfused with buffers of pH 7.0 and 7.8 while steadily superfusing the surrounding surface with a buffer of pH 7.4. Within a more rostral and a more caudal region of the medullary surface, increases of H+ ion concentration raised the tidal volume. These areas correspond to the regions where under electrical stimulation of the surface increases of tidal volume have been obtained. In an area between the regions an opposite effect of H+ ions was observed. This site corresponds to the area where ventilation can be stopped by cold block and procaine. The data suggest the existence of two chemosensitive areas. The fibers originating there may be bundled in the area in between from where they may enter the depth of the medulla.