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The rapid tilt test has shown that the vertical semicircular canals are in close connexion with the whole postural body musculature. Nystagmus reactions are only a small part of semicircular canal sphere of control.
Further knowledge of the reaction-pattern of the body musculature resulting from the stimulation of each semicircular canal will help in diagnosing a lesion, not only of the individual semicircular canals, but also—even more important—of its intracranial connexions. The few reaction patterns already known, but not recognized as such, namely post-pointing, falling, and head turning, are true compensatory reactions, more easily understood if so considered and grouped with the protective reactions to the tilt tests.
Recognition of the two modes of utricular action is essential to a correct analysis of tilt test reactions. The slow tilt described by Grahe and others, is an excellent test for “first mode” utricular action, but not for “second mode” action or for vertical semicircular canals.
The quick tilt is primarily a test of vertical semicircular canal action, but normally the reaction is complicated by reactions from “second mode” utricular stimulation. If this fact is not taken into account the analysis of a reaction to a quick tilt may be misleading. When performing a quick tilt test, in addition to watching for the absence of the protective reaction (due to loss of one or both labyrinths), the investigator should try to note whether there is a tendency for the patient to be more easily thrown in the direction of the tilt—owing to a lesion of the vertical canals, the utricles being intact (“second mode” utricular action)—or whether there is a tendency for the patient to over-compensate (owing to a lesion of the utricles, the vertical canals being intact).
If, in addition to the usual equilibrial tests, the quick tilt test is used in this way and a careful analysis is made of the reactions of patients with labyrinthine or intracranial lesions, diagnosis of lesions of individual labyrinthine end-organs or of their intracranial connexions may become a routine procedure in the clinic just as it is now possible in the laboratory.