"We have developed a new type of vibrating device called B250 that is placed behind the ear of the patient during the test," says Bo Håkansson, a professor in the research group 'Biomedical Signals and Systems' at Chalmers.
“The vibrating device is small and compact in size and optimised to provide an adequate sound level for triggering the reflex at frequencies as low as 250 Hz, which we have found to be optimal for VEMP stimulation. Previously, no vibrating device has been available that was directly adapted for this type of test of the balance system.”
In bone conduction transmission, sound waves are transformed into vibrations through the skull, stimulating the cochlea within the ear, in the same way as when sound waves normally go through the ear canal, the eardrum and the middle ear. This can be used in various technologies, and Bo Håkansson has over 40 years of experience in this field – he has previously developed hearing aids using this technology.
Dizziness a common problem in older patients
Every other person over 65 year suffer from dizziness, but the causes can be difficult to diagnose for several reasons. In 50 precent of those cases, dizziness is due to problems in the vestibular system. But today's VEMP methods have major shortcomings and can cause hearing loss and discomfort for patients. The VEMP test uses very high sound levels and can in fact cause permanent hearing damage itself. And, if the patient already suffers from certain types of hearing loss, it can sometimes be impossible to draw any conclusions from the test.
" The previous test was like a machine gun going off next to the ear – with this bone-conduction method it will be much more comfortable. The sound levels to which patients are exposed can be minimised. The test can be performed at 40 decibels lower than today's method, which uses air-conducted sounds through headphones. This eliminates the risk that the test itself could cause hearing damage,” says researcher Karl-Johan Fredén Jansson, who made all the measurements in the project.
“The benefits also include safer testing for children, and that patients with impaired hearing function due to chronic ear infections or congenital malformations in the ear canal and middle ear can still be diagnosed for the origin of their dizziness,” says Bo Håkansson.
A prototype of the vibrating device was first developed by the researchers in 2018, and it has now been tested and developed in several patient studies that have been published internationally, both with healthy individuals to obtain normal data, and in patients suffering from various types of dizziness. The device is compatible with standardised equipment for balance diagnostics in healthcare, which makes it easy to use. In addition to the benefits for patients, the cost of the new technology is also judged to be lower than the corresponding equipment used today, and discussions are ongoing with companies wishing to commercialise the technology.
B250 can also detect tumors
A research group in Germany hopes to be able to use the technology in patients with a benign tumor on the balance organ (Vestibular Schwannom). With B250, you can detect the tumor at an early stage. At Karolinska Institutet, B250 is used to develop a method and with the help of vibrations on the ankle, be able to diagnose patients with so-called "skylight syndrome" who suffer from dizziness problems caused by a hole in the upper arch of the balance organ.
More about Diagnostics for Dizziness
A common method of diagnosing the cause of dizziness is a VEMP test – Vestibular Evoked Myogenic Potentials. The test uses sound stimulation to evoke a muscle contraction in the neck and eye muscles, triggered by a reflex from the vestibular system – the system that is responsible for our sense of balance. The muscular response is measured and provides information on whether the disorders responsible for the patient’s dizziness are in the vestibular system, or in its pathways to the brain.
In a traditional vestibular investigation, two variants of VEMP tests are used today: air transmitted sound through headphones or bone conducted sounds via a vibrating device attached to the head. When air transmitted sounds are used, high sound levels are required, which is uncomfortable for the patient and risks hearing damage. For bone conducted sound, the sound levels are lower, but the equipment currently available on the market is large and cumbersome, and therefore difficult to use. The new method uses new transducer technology, is smaller in size and generates bone conducted sound at a lower frequency than has been possible before (around 250 Hz). At this level, the muscle reflexes are more efficiently evoked.
The muscle contractions in both the neck and the eye muscles are measured using fairly standardised equipment, so it should be easy to start incorporating it into healthcare systems.
"In the long term, we hope to offer an alternative for bone-guided stimulation of the balance organ in VEMP measurements and especially on improving the diagnosis of dizziness problems in patients who also suffer from conduction obstruction, says Sabine Reinfeldt, Associate Professor at Chalmers Department of Electrical Engineering.
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For more information contact
Professor in Biomedical Engineering, Department of Electrical Engineering +46-(0)31-772 18 07, firstname.lastname@example.org
Karl-Johan Fredén Jansson
Researcher, Department of Electrical Engineering , +46- (0)31-772 17 83, email@example.com