RELATIONSHIP BETWEEN EXTERNAL AUDITORY CANAL TEMPERATURE AND CALORIC NYSTAGMUS

: The cold-warm caloric test is performed with water irrigation, using a hot temperature of 44 degrees C and a cold temperature of 30 degrees C, which are thermally equidistant from the body temperature 37 degrees C. However, the 30 degrees C irrigation nearly always produces a stronger nystagmic response than that of the 44 degrees C stimulation. The purpose of this study is to investigate the difference in nystagmic response between cold and hot stimulation. The achieved hot (44 degrees C) and cold (30 degrees C) water samples were prepared, and irrigation was with a disposable plastic syringe. Temperature changes in the external auditory canal were monitored by tympanic thermometry during the cold-warm caloric test. Maximal slow phase velocity and the duration of induced nystagmus were recorded on an electro-nystagmograph. The following conclusions were drawn; 1) The average normal external auditory canal temperature was 36.8 degrees C, and there was no side difference between the right and left ears. External canal temperature was higher than that of the axilla. 2) When 20 ml of 30 degrees C water was instilled the temperature change in the external canal was larger than that in response to the 44 degrees C water and the maximal slow phase velocity of nystagmus for cold stimulation was stronger than that for hot. However, the duration of nystagmus for the cold was not significantly longer than that of the hot stimulation.