Effects of hemorrhagic hypotension and shock on the central nervous functions: Stretch and crossed extension reflexes

Abstract

As clues to the functional disintegration of the central nervous system in hemorrhagic shock, the ipsilateral quadriceps femoris stretch reflex and the crossed extension reflex were selected for study. Experimental models were 12 intact and 4 decerebrate dogs (by the Sherrington method) and 22 decerebrate cats (10 by the Sherrington method and 12 by the Pollock-Davis method). The stretch reflex was examined in all animals, and the crossed extension reflex was studied in 4 decerebrate dogs and 18 decerebrate cats (8 Sherrington and 10 Pollock-Davis) before, during, and after 2 hours of hemorrhagic hypotension at 30 mm. Hg. The stretch reflex persisted usually for many minutes at the blood pressure of 30 mm. Hg. It recovered after reinfusion of the shed blood unless the animal remained hypotensive. Transient augmentation of the crossed extension reflex occurred occasionally just before depression of this reflex. The crossed extension reflex was deprived of its prolonged tonic contraction by further bleeding. Thereafter, the decerebrate animal's crossed extension reflex was flaccid, resembling that of the spinal animal. Animals are not invariably obedient to Sherrington's principle of double reciprocal innervation in the state of acute hemorrhagic shock. In no case did the crossed extension reflex persist after the stretch reflex was abolished by hemorrhagic shock. After reinfusion of the shed blood, the crossed extension reflex recovered in only 3 (very imperfectly in 2 cats and nearly perfectly in 1 cat) out of 17 animals (2 dogs and 15 cats). It is concluded that the functional integrity of multisynaptic reflex (represented by the crossed extension reflex) is readily impaired by hemorrhagic shock and is hard to restore, while that of the monosynaptic reflex (represented by the stretch reflex) is rather insusceptible to hemorrhagic shock and is easy to restore.