Effect of Large Doses of Head Irradiation in Dogs

¹ From the Department of Physiology, Columbia University College of Physicians and Surgeons, New York City

Dogs in which the head was x-irradiated with 23,500 r survived from 14 to 28 hours. The chief neurological signs were disturbance of equilibrium and extensor rigidity. Throughout the whole postirradiation course, the blood volume showed very little change. Arterial pressure, heart rate and respiratory rate remained essentially unchanged until about 1 hour before death. The carotid sinus reflex did not change until 30–60 minutes before death, but then deteriorated rapidly. Generally, the respiratory response to cyanide injection was still present after the disappearance of the carotid sinus reflex. At the terminal stage, the pressor response of the medullary vasomotor center to electrical stimulation decreased in parallel to that of the carotid sinus reflex. The vital centers in the medulla oblongata are directly damaged by large doses of x-irradiation. The failure of respiration is the cause of death.