STUDIES ON THE KNEE JERK

Abstract

In the dog raised and maintained intrapulmonic pressure leads to a sharp drop in the general arterial blood pressure accompanied by a diminution in the knee jerk if the animal is shocked or is under deep anesthesia: or to a pseudo-augmentation of the jerk if the animal is under light anesthesia. The effects of this procedure on the knee jerk are due, for the most part, to changes in circulation through the brain and cord (anemia and asphyxial depression). Some evidence is presented, however, supporting the view that the diminution of the knee jerk, observed during raised intrapulmonic pressure, may be due to reflex inhibitory effect on the knee jerk center as a result of the mechanical stimulation of the sensory fibers of the vagus. The suspended circulation through the cord, during raised and maintained intrapulmonic pressure, results from marked interference with the filling of the heart. The blood, during raised and maintained intrapulmonic pressure, is prevented from reaching the left heart. The giddiness or actual unconsciousness induced in man following powerful compression of the chest, after and during deep maintained inspiration, is attributed essentially to the drop in general arterial blood pressure and the cerebral anemia resulting therefrom. The compensatory after-fling is responsible for the subjective symptoms of nausea, fulness in the head, and general discomfort experienced immediately after release of the raised intrapulmonic pressure.