Asphyxia of the Spinal Cord of the Cat

Abstract

The effect of the onset of asphyxia of the spinal cord has been investigated frequently. Usually a period of increased reflex excitability during the development of asphyxia has been described. In a series of experiments we studied the recovery of reflex activity after various periods of asphyxia. The cord was asphyxiated by bringing it under a pressure higher than that of the blood, thus excluding the blood supply. The spinal cord was ligated in the lower thoracic region 5 days previous to the planned experiment, without opening the dura. A cannula was brought in the subdural cavity of the lower part of the cord, which was separated from the rest of the central nervous system by the ligature. Deoxygenated physiological solution was then forced into the cavity under a pressure of 23-25 cm of mercury. The cord was kept under pressure for periods varying between 25 and 75 minutes. The animals were observed up to 3 weeks afterwards.

After 75 minutes of asphyxia no reflex activity returned; after 25 minutes of asphyxia all the reflexes of the hind limb and the tail returned within 2 hours, and these reflexes resembled those in the normal animal except that their excitability was increased. As the time of asphyxia was lengthened in 10 minute increments more and more reflexes did not return. First the skin reflexes were lost, then the tendon reflexes, and finally tone. The excitability of the tendon reflexes when their return was observed was usually much higher than normal. The tone in the extensor muscles of the legs was greatly enhanced in many cases, even in some instances to such a degree that it resembled rigor mortis. This tone could continue for days or even weeks; it was proven to be reflex in origin because transection of the dorsal roots of the lumbo-sacral cord caused its disappearance.