Editor’s Note: While Alan Desmond is away, we are pleased to have Guest Blogger Don Worthington, PhD. His blogs are compilations of Frequently Asked Questions and Answers from his extensive experience in teaching about vestibular measurement issues.
The bithermal caloric test was first described by Fitzgerald and Hallpike in 1942, and the current standard for caloric testing has evolved from their original work. The caloric is the most important, although most difficult to perform, and most time-consuming test in the ENG/VNG battery. The first post in the series addressed Question 1: “What are the advantages/disadvantages of air vs water calorics?” Last week’s post went over Questions 2 through 5.
Q6. What is the rationale for using only 2 temperatures for caloric testing and why the specific temperatures that are recommended?
The convection theory of caloric stimulation was proposed by Dr. Robert Barany who received a Nobel Prize in 1914 for his work on the vestibular system. The key principle of the caloric test is the convection current created by changing the temperature of the endolymph in the horizontal semi-circular canal.
During a warm irrigation, the introduction of warm air or water heats the ear canal and middle ear. This temperature change (or heat) is transmitted to the horizontal semi-circular canal and to the vestibule through air in the middle ear space. The endolymph closest to the canal wall is heated, causing it to become less dense. The heated endolymph rises and is replaced by denser/cooler endolymph, which is then heated and rises in the semicircular canal. The endolymph moves in the direction of the utricle, which in turn, deflects the cupula in the same direction. This deflection of the cupula toward the utricle (uticulopetal endolymph flow) bends the stereocilia towards the kinocilia resulting in increased neural firing of the primary vestibular afferent nerve.
Thus, warm water/air irrigation causes an excitatory response in the horizontal semi-circular canal, so that nystagmus beats towards the ear that is stimulated. Warm water/air in the left ear causes left beating nystagmus, and warm water/air in the right ear causes right beating nystagmus. Cool water/air irrigation produces the opposite effect. The effect of heating and/or cooling may not always be equal.
Q7. When is the addition of ice water caloric indicated?
Ice water stimulation would be indicated when there is no response to either cool or warm water/air stimulation for one ear or both, and computerized rotation is not available. Ice water is a very intense stimulation, and if used with normals will really induce nausea and vomiting.
The level of the noise in air calorics is certainly loud enough to cause damage if the patient were exposed to it for a sufficient length of time. However, stimulation time is two minutes per ear. I am not aware of any studies that have actually looked at possible noise induced loss from air caloric stimulation.
Q9. Will CT scans show canalithiasis or cupulolithiasis.
No, not at this time. Several centers have tried to see if they can identify otoliths that have been displaced, but as yet cannot detect that small of particle. Even if they could, it would not necessarily be better for the patient. The particles, if out of place, would still have to be repositioned. Our diagnostic procedures and treatment are still much cheaper than CT scans.
Q10. Some ENT’s recommend CT vs ENG/VNG because of the vertigo the patient may experience with ENG/VNG. Which is best?
Actually, there are ENT’s that recommend MRI’s rather than an ENG/VNG. However, both CT and MRI they are tests of structure, and the ENG/VNG is a test of function. The MRI will show if there is a significant space occupying lesion. Most vestibular problems are not caused by space occupying lesions. So they still don’t have information about what problems the patient is having. Don’t get me wrong, there is need for all tests, CT, MRI, and ENG/VNG. Physicians, audiologists and others just need to know how to use them and when to use them.
Q11. How often do patients with BPPV have vertiginous symptoms?
When BPPV is present, essentially 100% of patients will have vertiginous symptoms. Different patients have different perceptions of what is happening and most patients have real nausea and many experience vomiting as well.
Don W. Worthington, PhD (Northwestern University) started his career in private practice before entering the military and serving at Walter Reed General Hospital where he was Director of the Army Audiology and Speech Center, and Audiology Consultant to the Army Surgeon General. In 1975 he became Director of Audiology & Speech Pathology at Boys Town National Research Hospital. Dr. Worthington held positions in the AAS, AAA, ASHA, and consulted to the FDA and VA. He founded and directed the Center for Hearing and Balance Disorders (Salt Lake City) in 1993. He has numerous publications and has received a number of honors and awards.