[Evaluation of the furosemide test using the air caloric stimulator]

Both the furosemide test, and the glycerol test have been reported as being effective for detection of endolymphatic hydrops. In the furosemide test, the caloric test is performed first, and then repeated 40 minutes after i.v. injection of furosemide, 20 mg. The maximum velocities of each caloric nystagmus are compared, so the caloric stimulus conditions must be constant. In the original method, the caloric test is performed by irrigation with 50 ml of water at 30 degrees C or 44 degrees C for 20 seconds. Since it is difficult to accurately maintain the water temperature at a constant level, however, we use the air caloric stimulator NCA-105 (ICS) for the furosemide test. By using this stimulator, we can always perform the caloric test under the same conditions. The conditions of air irrigation in 28 normal subjects were set at 37 +/- 11 degrees C, 61/min, and 60 seconds. These conditions were confirmed in other normal subjects to fairly well correspond to water irrigation (30 degrees C or 44 degrees C, 50 ml, 20 seconds). Next we reassessed the furosemide test by using the air caloric stimulator in normal subjects. As a result, positive effects were observed in 7.4% of the normal subjects. This finding was similar to that reported in the literature (Futaki et al., 1971). The air caloric test is considered to be a more useful examination than the water caloric test because it is less unpleasant for the subject and easily provides the same conditions before and after furosemide administration.