Neurotological studies on the role of the sympathetic nervous system in the formation of traumatic vertigo of cervical origin.
To test the validity of the hypothesis that irritation of the cervical sympathetic nerves is a cause of hypertonicity of the cervical soft supporting tissues, especially the deep nuchal muscles, and that this hypertonicity is a cause of traumatic vertigo of cervical origin, we examined 44 vertigo cases with whiplash injury by testing equilibrium function and EMG discharges from the neck before and after administration of drugs affecting the sympathetic receptors. The results obtained were as follows: 1. Administration of iso-proterenol (beta-receptor stimulant) caused a significant increase in the EMG's from the injured neck muscles, in parallel with increased impairment of the righting reflex. The blindfolded vertical writing test showed the appearance or intensification of ataxia or deviation in writing when this drug was given. In contrast, administration of propranolol (beta-receptor depressor) had the opposite effects on the EMG's, the righting reflex and blindfolded vertical writing. Furthermore, the resulting changes in the EMG's and equilibrium functions were parallel with alterations in subjects' complaints, i.e., increase or decrease in neck pain and vertigo. 2. Administration of drugs affecting the alpha receptors, such as noradrenaline (alpha-receptor stimulant) and phentolamine (alpha-receptor depressor) had no appreciable effect on the EMG's, equilibrium function or the subjects' complaints. These results show that in vertigo due to whiplash injury hypertonicity of the cervical erector muscles can be induced sympathetically, and that this hypertonicity is based on over-excitement of beta receptors in the injured neck muscles, which results in vertigo of cervical origin.