Normally only with head movement does fluid
within the inner ear also move informing the brain that a head turn occurred. However if a crystal called an otolith gets
displaced into the semicircular canal of the inner ear, BPPV dizziness occurs. Fluid movement occurs due to the crystal rather
than head turns causing the brain to think movement has occurred even though none has
happened. The Foster Half-Somersault maneuver is performed
to treat this posterior canal BPPV by trying to get the loose crystal out of the canal.
This maneuver is started by kneeling. While kneeling, the head is quickly tipped
upward and back. The somersault position is then assumed with
the chin tucked as far as possible toward the knee. The head is turned about 45° towards the
shoulder, to face the elbow. This position is maintained for 30-60 seconds. While keeping the head turned at 45°, the
head is then raised to be aligned with the back/shoulder. This position is maintained for 30-60 seconds. While keeping the head turned at 45°, the
head is then raised to the fully upright position. At this point, the maneuver is completed and
the patient can sit back up.
So what's going on with these position changes? Essentially the head has moved in such a way
to manipulate the crystal to fall towards ths canal opening. With each position change it takes about 30
to 60 seconds for the crystal to settle into the most dependent position in the canal. If turns are made before the crystal has a
chance to settle, the crystal may fall back the wrong way and the maneuver will fail. It is also important that they head positions
are angled correctly or else the crystal will not settle to the correct position in the
canal and the maneuver will fail.
Also if the position changes are done too
slowly the crystal may not settle quickly enough from lack of momentum and the maneuver
will also fail. Once the Crystal Falls out of the canal, the
dizziness should resolve if due to posterior canal BPPV..