Respiratory mechanics of vomiting in decerebrate cats.

MCCARTHY, L. E., AND H. L. BORISON. Respiratory mechanics of vornitiq ilz &cerebrate cats. Am. J. Physiol. 226(3) : 738-743. 1974.-Observations were made on the changes in thoracic venous pressure, abdominal venous pressure, and arterial blood pressure associated with vomiting induced by veratrum alkaloids (50-150 lug; kg, im). Tracheal and intrapleural pressures were also examined for comparison with the vascular indicators. Electromyograms were recorded concurrently from the diaphragm and/or the body wall muscles of the thorax and/or abdomen. Retching was characterized by a growing series of brief negative intrathoracic pressure pulses mirrored by positive pressure pulses in the abdomen. Expulsion then followed as a more sustained abdominal contraction with a sudden reversal of intrathoracic pressure from negative to positive. Remarkably, however, both retching and expulsion were effected by the same set of muscles according to their EMG profiles. Results obtained with spinal cord section at T, and phrenicotomy support the conclusions: I) that the diaphragm, acting in concert with the inspiratory muscles against a closed glottis, is responsible for the negative intrathoracic pressure produced in retching; and 2) that the abdominal musculature is responsible for the positive pressure generated in the abdomen during retching and expulsion, and which in the latter phase is transmitted into the thorax by an upward shift of the diaphragm.