Untersuchungen zum zentralen chemosensiblen Mechanismus der Atmung

Summary

In cats lightly anesthetized with chloralose-urethane, the respiratory response to changes in the medullary extracellular pH (pH _e ) was studied before and after cervical vagotomy. pH _e was varied by perfusion of the ventral medullary surface with mock CSF of different pH (pH_CSF) and by changes inP _ACO₂; it was calculated from the acid-base parameters of the blood and the mock CSF by means of a mathematical model described by Berndt, Berger, and Mückenhoff (1972).

Results. 1. The hydrogen ion concentration in the CSF does not influence respiration at pH_CSF values below 6.5. 2. An increase of ventilation as a response to increasing extracellular hydrogen ion concentration is only obtained in a pH _e range of about 0.2 pH units, which under the conditions of the present experiments lay between pH _e 7.1 and 7.3, due to the methods of calculation employed. pH _e -values below 7.1 usually caused a decrease in ventilation. 3. Vagotomy influences the response of the tidal volume and the respiratory frequency to changes in pH _e : the tidal volume is increased after vagotomy and the slope of the pH _e -response curve ofV _T is steeper, while the frequency decreases and further diminishes with decreasing pH _e . The average response of ventilation, however, is not significantly altered after vagotomy. This confirms the hypothesis that in the case of the central chemical control of respiration the vagal activity is responsible for the partition of the total response to chemical stimuli into partial responses ofV _T andf rather than for the magnitude of the total ventilatory response.