The Pressor Influence of Augmented Breathing

During the course of certain experiments, one of us observed that stimulation of the central end of the divided vagus with a weak current caused in the dog a pronounced rise of pressure, provided that the dog was under artificial respiration just sufficient to cause apnea (figure I, A) . If, however, the nerve was similarly stimulated in an animal breathing naturally a fall of pressure ensued. Occasionally this was the only reaction, but more frequently it was followed by a secondary rise (figure I, B, C, D). Critical examination showed that the pressure in the latter case began to fall at the precise moment when respiration had ceased in passive expiration, a synchronism suggesting that the fall was attributable to the removal of the mechanical respiratory influence which aids in sustaining the blood pressure. Again, it was observed that a prompt recovery to normal or above took place in atropinized dogs, or in those with cut vagi, if the blood pressure was reduced by nitroglycerin or by Meeding to such a degree that hyperpnea followed. On the other hand, under curare and artificial respiration, the recovery from nitroglycerin or hemorrhage was much slower and less complete, the pressure never rising quite to the normal level. The prompt recovery and