injection of cool or warm water into ear canal produces convection currents in semicircular canals
- if the patient is lying down, and his/her head is tilted back about 60 degrees, the HORIZONTAL semicircular canals will be affected, and will be in a plane that allows easy observation
- COOL WATER IN RIGHT EAR è clockwise current in right semicircular canal è stereocilia deflection to the right (same direction as a head movement to the left) è slow eye movement to the right, followed by rapid eye movement to the left è LEFTBEATING NYSTAGMUS
WARM WATER IN RIGHT EAR è counterclockwise current in right semicircular canal è stereocilia deflection to the left (same direction as a head movement to the right) è slow eye movement to the left, followed by rapid eye movement to the right è RIGHTBEATING NYSTAGMUS
To summarize, in a person with a normally functioning cortex, injection of cool water into the right ear, will produce a LEFTBEATING NYSTAGMUS (COLD=OPPOSITE, WARM=SAME --> COWS). If the patient is COMATOSE, the SACCADE WILL BE ABSENT (the VOR, which operates in the brainstem is still functional and the pursuit will be intact). If the patient is BRAIN DEAD, BOTH the PURSUIT and SACCADE WILL BE ABSENT.
Self learning exercise: be able to describe activity at each stage of the VOR pathway during caloric stimulation