On the tonus of the vaso-motor center in shock

Abstract

The experiments here reported were designed to show if possible whether the vaso-motor center is paralyzed or shows evidence of any considerable degree of tonus during surgical shock.

White rabbits were used. One superior cervical sympathetic ganglion was removed and the auricularis magnus nerve on the same side cut. The connections of the blood vessels of the denervated ear with the vaso-motor center were therefore severed. 1 Twenty-four hours or more later the animal was etherized and shock induced by opening wide the abdomen, manipulating the abdominal viscera, and by applying cold water. When the blood pressure had fallen to a low level, e. g., 19 to 25 or 30 mm. Hg., the normal ear, that is, the ear still connected with the vaso-motor center was practically always blanched and bloodless. Even with this low blood pressure, however, the vessels of the denervated ear, contained in most cases, definitely though, as would be expected with low blood pressure, slightly more blood than the normal ear. If at this stage a clamp was applied to the abdominal aorta just below the diaphragm the blood pressure in the anterior portion of the body usually rose quickly to a relatively high level, for example, from 18 mm. Hg. before clamping to 75 or 85 mm. Hg. afterward. With this rise in blood pressure there developed a striking contrast in the appearance of the two ears. The vessels of the denervated ear become gorged with blood, while the vessels of the normal ear in almost every case remained practically maximally constricted. If the connection of the vessels of the normal ear with the vaso-motor center was severed, either by cutting the nerves, destroying their conductivity by the local application of ether, or by freezing the nerves with ethyl chloride, the vessels of the normal ear also became widely dilated.