There are patients with floating dizziness who do not show abnormalities in current vertigo balance tests. We developed a clinical examination to quantify gravity perception as a first step to test our hypothesis that a gravity perception disturbance is the cause of floating dizziness. The gravity sensitivity can be measured accurately by adding the head tilting condition to the original subjective visual vertical (SVV) test. We named this test the Head Tilt SVV (HT-SVV). The most important measurement item in HT-SVV is head tilt perception gain (HTPG). HT-SVV measurements in 329 healthy subjects yielded an average value and standard deviation of 1.02±0.12 and a reference value of 0.80-1.25 for HTPG, and a difference between the left and right HTPG of 4.7±3.7%, i.e.,<10.0%. We could not detect age-related changes in gravitational sensitivity by the original SVV, but found that HTPG, determined by HT-SVV, increased with age. A significantly higher rate of subjective dizziness was noted in patients who tested positive in the HT-SVV than in those who tested negative among patients who developed floating dizziness after BPPV. We would like to clarify the clinical significance of the test method and establish the concept of gravitational susceptibility disorder, although a number of relevant issues still remain to be clarified.
