THE EFFECT OF CARBON DIOXIDE, HYPERVENTILATION, AND ANOXEMIA ON THE KNEE JERK

Abstract

The effects on the knee jerk of increasing and of decreasing the CO2 tension and of lowering the O tension in the blood were studied in spinal and normal dogs. Increased CO2 tension in the blood decrease''d the reflex in dogs with intact spinal cord, while in the spinal animal there was frequently an initial stage of augmentation, followed by a depression. Evidence indicated that inhibitory impulses from the higher centers play an important part in the early depressant effect in animals with the spinal cord intact. Hyperventilation primarily augments the knee jerk, but rigidity may mask the effect, or impulses from the higher centers may counter-balance it. The effect of anoxia is predominantly depressant, but in about 4 of the cases studied a brief period of augmentation of the knee jerk was noted. The results indicate that the spinal centers are affected qualitatively, like the respiratory center, by an increase in CO2 and by anoxia, but are in no way commensurate quantitatively; also that acid-base changes in the blood play no important role in accounting for the variability of spinal reflexes within physiological limits.