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. Considerable research was carried out to determine what temperatures were needed to try to obtain equal responses to both cool and warm stimulation in the same ear of the same patient. These studies also studied the flow rate and length of stimulation to maximize the response. While these studies with normals tried to equalize the temperature needed for equal response, clinical experience soon shows that not all patients have equal responses for cool irrigations and for warm irrigations. The premise requiring two temperatures is still valid. That way, it takes into account differences in excitatory responses versus inhibitory responses (warm vs cool), and also takes into account differences any spontaneous/positional nystagmus (right beating vs left beating) might have on the responses. If only one temperature was used, one could make a number of mistakes diagnostically. Jongkees’ (1964) formula takes these factors into account.
1. What are the advantages/disadvantages of air vs water calorics? Your preference and why?
Water Caloric Irrigator
Over the years the water caloric stimulus has been considered the most reliable stimulus. Dr. David Cyr performed a comparison study between the three methods (Air, Water, and Closed Loop). His findings showed better test retest reliability within the same subjects with water than with either of the other methods. The important components of the water irrigation system are:
- A pair of reservoirs to hold the water at appropriate temperatures (with a carefully calibrated thermostat for temperature control).
- A calibrated delivery system to deliver the proper amount of water to the ear. The hose and delivery handle should be a constant recycle type so there is little or no variation in the temperature from the tank to the tip.
- A timing system to control the duration of water flow.
If these components are in place, the delivered stimulus is the same temperature and duration for each presentation.
The disadvantages of water irrigation are:
- it can be somewhat messy and you need a sanitary way to dispose of the water.
- Water irrigation is contraindicated for some middle ear pathologies such as a tympanic membrane perforation.
- The water must be distilled or de-ionized in most areas of the world, or it will form calcification on the heating coils and ruin the pump system.
Air Caloric Irrigator
The air irrigators have been improved and do eliminate some of the disadvantages of water calorics. You don’t have to worry about drenching the patient. They can be used safely with TM perforations, but be cautious in your analysis of the data, as air blowing on a moist middle ear can result in the opposite effect. That is, warm air can result in cooling. The transfer of thermal energy between air and tissue is less efficient than between water and tissue and therefore a greater quantity of air and more extreme temperatures are needed to generate the same caloric stimulus. The standard air caloric stimulus is 8 liters of air at 24 degrees C and 50 degrees C over a 60 second period. Remember, this is 6 degrees cooler and 6 degrees warmer than with water.
The disadvantages of Air irrigation are:
- As mentioned, sometimes warm air irrigation can produce a cooling effect by evaporation if there is a perforation and “wet” ear. In this case the direction of nystagmus will be opposite the direction expected.
- Coats, 1976, Cyr, 1988, found air responses had significantly greater test-retest variability than water calorics. Ford and Stockwell (1978) however, found no significant difference in responses if care was taken so that the irrigator tip was directly aimed at the tympanic membrane. Basically, the irrigator tip placement may be more critical with air caloric irrigation than with water caloric irrigation. In my experience, more patients find the air stimulation to be more uncomfortable than the water.
Closed Loop Caloric Irrigator
The closed loop (Brookler Grams) irrigator is a form of water caloric. To my knowledge, this system is no longer being manufactured. With this system, water is circulated in a balloon inserted in the external auditory canal. The system continuously exchanges the water in the balloon with fresh temperature controlled water. The standard stimulus is a 30 second irrigation at 28 degrees C and 44 degrees C. Cyr (1980) reported that the closed loop irrigator yielded response intensities and reliabilities that are comparable to those produced by the traditional water system. Advantages of the closed loop system are:
- It is less messy.
- Iit can be used with tympanic membrane perforations.
- Patients prefer closed loop system.
- Risk of eardrum perforation if the balloon should burst.
- If there is a crooked canal, or a narrow canal, it is difficult to get the balloon to go up against the tympanic membrane. In our experience, we did have several balloons rupture or burst.
In summary, any system can be used if you are aware of the pitfalls or disadvantages of the system you use. At the present time for the majority of the patients, we prefer the Water Irrigation System. We feel that with a clear external canal, irregardless of the shape, we get the most consistent response and as Karlsen (1992) demonstrated, the most robust caloric response.
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.