Gam says that while experimenting on intrathoracic and intra-abdominal
pressures, the blood pressure was observed to fall during vomiting. A
series of experiments were performed to determine the cause of this
fall. In all experiments the blood pressure, the intrathoracic pressure
and the movements of the abdominal wall were recorded. Vomiting was
induced in some cases by means of apomorphin; in others by filling the
stomach with hot salt solution, hot soap suds, copper sulphate solution,
etc. In every case a high negative pressure was observed in the thorax
during the act. The pressure would fluctuate rapidly from zero to
twenty-five or thirty centimeters (water) of negative pressure. The
blood pressure, however, always fell, sometimes to less than half its
former level. The fall in blood pressure was found to be due to a vagus
inhibition of the heart, for on cutting the vagi while the vomiting was
taking place, and while the blood pressure was at its lowest, there was
an immediate increase in heart rate and rise to above the normal in
blood pressure. Furthermore, when the vomiting was induced after the
vagi had been cut, there was a rise instead of a fall in blood
pressure.—_The Journal of the Amer. Med. Asso._