Caloric testing by continuous automatic alternating irrigation.

Quantitative caloric test results show a high variability. They were described as questionable by Frenzel (1955) and a review of the test was recommended by Hood (1973). Thus, we developed a new method: continuous automatic alternating irrigation. An irrigator is connected to two water-baths of 30 degrees C and 44 degrees C. A time-relays switches over from one bath to the other every 60 s. The continuous, but alternating, irrigations produce subsequently alternating exponential temperature waves in the temporal bone. The mathematical model shows a quasi-periodicity and sufficient symmetry of the alternating thermal gradient across the canal, except for the first stimulus. After 11 irrigations of 60 s, a short (20 s) "washout" irrigation terminates the sequence. By the five repetitions of each stimulus and the additional possibility of correlating the response to the paper-marked stimulus periodicity the judgement is far more reliable and therefore, in doubtful cases, despite the five-fold data, quicker. The technical device is simple enough for routine use and inexpensive. The results of the caloric test are now much more clear-cut and the correlation to a known clinical pathology is remarkably high.