Timothy C. Hain, MD Page last modified: February 8, 2018
VEMP testing is a very useful but still rapidly evolving and immature technology. In 2018, the market for these devices has "settled down", and there are few vendors of devices that mostly work.
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, Interacoustics, 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 ourselves 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. We have not tried them all however, and it is perfectly possible that several of these work fine. We just don't know.
Here are a few that we have tried or commented on. Note that many of these companies have been bought up by Natus, and the original devices seem to have vanished.
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.