ALTERATION OF THE ACTIONS OF VARIOUS RESPIRATORY MODIFIERS BY LOCAL COOLING OF THE FLOOR OF THE FOURTH VENTRICLE

Abstract

Dogs anaesthetized with morphine and urethane were used. The effects of faradic stimulation of the central end of the vagus nerve upon respiration were markedly diminished by local cooling of the floor of the 4th ventricle. If such cooling was severe inflation and deflation of the lungs were without effect on respiration; if the cooling was moderate the effect of inflation was abolished while the effect of deflation was unaffected or enhanced. During severe cooling blocking the vagi was without effect; during slight cooling vagal block caused apneusis. It is suggested that apneusis may result from any procedure which decreases the frequency of impulses arriving at some internuncial neurone in the inspiratory pathway. The resp. accelerating effect of CO2 administration is greatly increased by moderate cooling of the floor of the 4th ventricle. The resp. acceleration resulting from saphenous nerve stimulation is greatly enhanced by such cooling whether moderate or severe. During cooling carbonate injection causes respiratory arrest in inspiration rather than expiration.