Caloric testing has been a standard part of the test battery for dizziness and vertigo for more than fifty years. Although newer technology and techniques are gradually making us less dependent on the information produced by caloric testing, it still remains a commonly performed procedure.
Here is a simple explanation of the test: the ear canal is irrigated with air or water that is a few degrees warmer or cooler than body temperature. This warms up or cools down the inner ear fluid, causing it to expand or contract, essentially causing movement in one ear, while the non-test ear senses no movement. This conflict between the two ears results in nystagmus (involuntary eye movements) in healthy ears which can be measured to determine if both ears are responding normally and equally.
So, the obvious question? Who thought of that? How did someone determine that irrigating an ear canal could provide information about dizziness and vertigo?
The originator of caloric testing is Dr. Robert Barany, who won the Nobel Prize for Physiology or Medicine in 1914 for his research. His Nobel Prize acceptance speech describes the process of accidental discovery, but also demonstrates how much one can learn if they are paying attention.
Here is Dr. Barany:
As a young otologist I worked in Professor Politzer’s Clinic in Vienna. Among my patients there were many who required syringing of the ears. A number of them complained afterwards of vertigo. Obviously I examined their eyes and I noticed in doing this that there was nystagmus in a certain direction. I made a note of this. After a time, when I had collected about twenty of these observations, I compared them one with another and was amazed always to find the same note. I then realized that some general principle must be implied, but at the time I did not understand it. Chance came to my aid. One of my patients, whose ears I was syringing, said to me: “Doctor, I only get giddy when the water is not warm enough. When I do my own ears at home and use warm enough water I never get giddy.” I then called the nurse and asked her to get me warmer water for the syringe. She maintained that it was already warm enough. I replied that if the patient found it too cold we should conform to his wish. The next time she brought me very hot water in the bowl. When I syringed the patient’s ear he shouted: “But Doctor, this water is much too hot and now I am giddy again.” I quickly observed his eyes and noticed that the nystagmus was in an exactly opposite direction from the previous one when cold water had been used. It came to me then in a flash that obviously the temperature of the water was responsible for the nystagmus. From this I immediately drew certain conclusions. If the temperature of the water was really responsible, then water at exactly body temperature should cause neither nystagmus nor vertigo. An experiment confirmed this conclusion. Furthermore, I said to myself, if it is the temperature of the water, nystagmus must be caused in normal cases also and not only in cases of suppurating ears. This I was also able to prove.
To view the entire Nobel lecture click here.
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