Body position and caloric nystagmus response.

Abstract

The observation that the caloric nystagmus response is dependent on body position has been repeated in several studies during the course of this century. For many, this position-dependent modulation of the caloric response has been interpreted as evidence in favour of the thermoconvection theory as originally proposed by Bárány. However, the adequacy of this theory has been put into question by recent observations of caloric nystagmus during weightlessness in orbital flight. These zero-g findings clearly demonstrate that any hypothesis based on thermoconvection alone must prove insufficient as a description of the caloric nystagmus response. In the light of these recent findings, it has also become necessary to reconsider the influence of body position on caloric nystagmus intensity and the physiological mechanisms involved. Caloric testing was performed with a group of 30 healthy test subjects. Each person was tested in eight different body positions in the sagittal plane. Caloric nystagmus response was registered by means of horizontal and vertical EOG. The observed modification of the caloric response (SPV) by assumed body position is discussed with reference to associated reports in the literature.