Timothy C. Hain, MD Page last modified: April 28, 2013
VEMP testing is a very useful but still rapidly evolving and immature technology. If you are thinking about doing VEMP testing, unless you feel comfortable with electrophysiology, it might be best to wait for a year or two while the market settles down.
If you are in the market for a new device, we think it is best to get a multipurpose machine - can it do ECochG testing ? ABR testing ? Other types of evoked responses such as SSEPs and VEPs ? Does it do OAE's ? Does it interface with NOAH ( a clinical database) ?
If it is an external device, how does it connect to your host computer (USB is best, serial is worst). Is there a possibility of the device supporting an EMG feedback display and normalization of responses to the EMG ? We do not know of any commercial device that can do all of these things, but in a few years, it is likely that this will be the state of the art. A stand-alone "box" should cost about $10,000. Examples of vendors include Bio Logic, GN-otometrics, Nicolet (now Viasys and Teca), and Smart-EP.
We have had considerable experience with the Bio Logic Nav-Pro box. While it works fairly well in routine use, there are a number of problems to watch out for:
Other than the Bio-logic, we have not found any machine that works. This may be due to the lack of any standardization for the intensity (or calibration) of transients sound stimuli such as used for VEMP testing. Here are a few that we have tried or commented on.
We do not know of anyone who uses the GN-otometrics box for VEMP testing.
We have read papers concerning use of the Smart-EP system. We have not used it personally.
We have read several papers in which the Nicolet Spirit as well as the Smart-EP systems were used. The Nicolet Spirit is an old but capable evoked potential system that can be obtained on the used market. The Nicolet Bravo is unable to produce a sound-burst type stimulus, which greatly limits it's utility. The Nicolet Endeavor has the same problem as well as system software that is unable to add together sweeps. We think that Nicolet hardware should be avoided until it is updated or redesigned. Stay away from Nicolet for VEMPs !
The TECA evoked potential system is positioned as an updated Nicolet, and is owned by the same company that bought Nicolet. We DO NOT recommend this piece of equipment for VEMP's.
While it does produce a sound burst type stimulus, the insert transducers are just as poorly designed as the Bio Logic Nav-Pro box. Like the Bio-Logic box, there is no method of calibrating the sound output. The output for the Teca sound is a 5-pin DIN connector, meaning that you cannot use standard earphones (even if you were to manage to calibrate them). The disposable inserts for the Teca box are poorly designed and you must substitute the ordinary foam type disposable inserts to obtain good results. The TECA software, perversely enough, is designed so that it stops after about 200 presentations of high volume sound bursts - -this makes the machine useless for research protocols. To learn to use this machine, the manufacturor suggests that you send someone to a day-long course for an exhorbitant fee. Stay away from TECA for VEMPs!
Be extremely sure that the VEMP machine has a calibrated sound output. Because sound levels are loud, and thresholds are critically dependent on only 10 db steps of loudness, it is critical to be sure that you are getting the right sound volume. A 10 db difference between ears might obliterate a VEMP. While one would think that these devices would be self-calibrating (i.e. have a microphone built into the transducer), peculiarly enough, they don't. Hopefully competition will create some drive to vendors to improve their equipment.
Ask the vendor if their equipment can produce sounds loud enough to produce a reliable VEMP. While the 95 dB maximum produced by the Biologic-Navigator Pro is usually enough, there are sometimes situations where a louder stimulus would be helpful (ask if the equipment can go up to 110 dB). Note that the maximum intensity of the bone vibrator for the Bio-logic is only 60 dB, which is clearly not enough. The sound intensity of these devices seems to vary widely, even though they have the same number (i.e. 95 db). This is an obvious problem.
Exercise due diligence. Ask the company for references -- who is using their equipment already ? Will they talk with you ? What has been their experience ? We have had somewhat bad experiences with several vendors.
Be especially sure to consider the company's technical support. As VEMP testing in general is evolving rapidly right now, it is very likely that you will need technical support. Be very cautious if you cannot reliably reach technical support when you call them, or if technical support is an option that costs more money. Look also to see what the device does "out of the box", and whether or not additional software is needed to do what you want. If you purchase a unit, we also suggest insisting on a 1 month return, should the unit not work out in your environment. Because the technology is evolving rapidly, you may wish to rent or lease equipment rather than buying it outright.