scotsman9
07-06-2005, 02:49 AM
Hi All,
A few months ago I wrote about the seminar with Prof Halmagyi from RPA on diagnoses of peripheral dizzy disorders. I have since found an article that discusses further the utilty of the caloric and Head Impulse Test and explains why the caloric does not always work and why the head impulse test should also be used in diagnosis. Just like we can lose certain frequencies in hearing we can also have frequency-specific functional deficits in the semicircular canals (SCC).
Clinical tests of unilateral vestibular dysfunction.
G. MICHAEL HALMAGYI M.D., F.R.A.C.P.
The Journal of Laryngology & Otology
Aug 2004, 118:589–600
The caloric test is still the basis of all vestibular testing. The advantages are that it is relatively simple and widely available and therefore the results it produces should be reproducible within, and perhaps between, laboratories. However, because of theoretical problems and practical limitations, this is not generally so. The caloric test measures only lateral SCC function and only at low frequency; it does not produce absolute values – normal nystagmus slow-phase velocity can vary from eight to 80 deg/s; the stimulus persists between irrigations and this can confound the whole test.
In the horizontal head impulse test, the examiner turns the patient’s head as rapidly as possible about 15 degrees to one side and observes the ability of the patient to keep the eyes fixated on a distant target.
The findings suggest that SCC pathology just like cochlear (hearing) pathology can produce frequency-specific functional deficits: whereas impulsive testing represents a 4–5 Hz stimulus, the dominant frequency of the caloric test is around 0.025 Hz.
Scott :cool:
A few months ago I wrote about the seminar with Prof Halmagyi from RPA on diagnoses of peripheral dizzy disorders. I have since found an article that discusses further the utilty of the caloric and Head Impulse Test and explains why the caloric does not always work and why the head impulse test should also be used in diagnosis. Just like we can lose certain frequencies in hearing we can also have frequency-specific functional deficits in the semicircular canals (SCC).
Clinical tests of unilateral vestibular dysfunction.
G. MICHAEL HALMAGYI M.D., F.R.A.C.P.
The Journal of Laryngology & Otology
Aug 2004, 118:589–600
The caloric test is still the basis of all vestibular testing. The advantages are that it is relatively simple and widely available and therefore the results it produces should be reproducible within, and perhaps between, laboratories. However, because of theoretical problems and practical limitations, this is not generally so. The caloric test measures only lateral SCC function and only at low frequency; it does not produce absolute values – normal nystagmus slow-phase velocity can vary from eight to 80 deg/s; the stimulus persists between irrigations and this can confound the whole test.
In the horizontal head impulse test, the examiner turns the patient’s head as rapidly as possible about 15 degrees to one side and observes the ability of the patient to keep the eyes fixated on a distant target.
The findings suggest that SCC pathology just like cochlear (hearing) pathology can produce frequency-specific functional deficits: whereas impulsive testing represents a 4–5 Hz stimulus, the dominant frequency of the caloric test is around 0.025 Hz.
Scott :cool: