Balance Function
The inner ear contains two organs of balance: the vestibule (which consists of the utricle and saccule) and the semicircular canals. The organs of the vestibule are responsible for the sensation of gravity. The semicircular canals provide information on head rotation.
The vestibule contains fluid and nerve endings. Within the fluid are calcium particles that have a greater density relative to the fluid that they are immersed in. This causes the particles to “fall” because of the effects of gravity. As the head moves the particles exert pressure on the nerve endings, sending signals to the brain about head position relative to gravity.
There are three semicircular canals in each ear: the superior, lateral, and posterior semicircular canals. These are at roughly right angles to each other, each one corresponding to one dimension in three dimensional space. The canals are filled with a fluid called endolymph. As the head turns the endolymph rotates within the canal and stimulates nerve endings within the end of the canal. These nerve endings then send information to the brain about how quickly and in what direction the head is moving. The fluid in the lateral semicircular canal can be artificially stimulated as part of the caloric test of the ENG/VNG test battery in order to help diagnose balance problems.
Benign Paroxysmal Positional Vertigo (BPPV)
Benign paroxysmal positional vertigo (BPPV) is the most common form of peripheral vestibular disorders. It is most commonly characterized by episodic vertigo that is often provoked by specific head movements. BPPV typically occurs spontaneously, but can follow head trauma or labyrinthitis.
In the case of BPPV tiny particles, called otoconia, are floating in the fluid within the canals. When the head is moved it causes the particles to move as well, and stimulate receptor cells inappropriately or disproportionally. This causes vertigo.
Diagnosis is made by provoking and observing an abnormal nystagmus response of the semicircular canals. This can sometimes be done with a simple in test in the office. More complicated cases may require a more technical and diagnostic exam to be performed called an ENG. This test may also be necessary to determine the type of BPPV. Spontaneous remission of BPPV is common, but if it persists treatment is often necessary.
Treatments are safe and simple, and often provide immediate relief of symptoms. There are several simple maneuvers that can be done by your physician in the office to try to reposition those particles. The goal of these maneuvers is to prevent the particles from freely moving within fluid in the canals.