Biomedical Engineering Reference
In-Depth Information
FIGURE 6-25
Vibrant Soundbridge
device. (a) Cross
section showing
installation. (b) Photo
of FMT. [Adapted
from (Shohet 2008).]
attached to the long process of the incus, and the magnet is aligned with the long axis of
the stapes, which causes it to vibrate along that axis.
One of the disadvantages of this device is that the confined space of the middle ear
restricts the dimensions and crucial mass of the transducer, limiting the vibratory power
output.
The phase III FDA trial was completed in 2000, and results from the 53 patients
submitted to the FDA were published in 2002. The device was safe, with no notable change
in preoperative and postoperative bone thresholds. Additionally, functional gain and word-
recognition scores were improved with the Vibrant device compared with the patients'
conventional hearing aids. Self-assessment indicated that 94% of the patients believed
that the overall sound quality of the device was better than that of their conventional
hearing aid.
As of 2007, the use of the Soundbridge has been expanded. It was successfully im-
planted on the round window membrane in patients with aural atresia and mixed hearing
losses. It has also been applied to the incus in a more traditional configuration in patients
with otosclerosis.
The audio processor has evolved from the original, analog Vibrant P unit to a digital,
three-channel Vibrant D unit to the current digital, eight-channel Vibrant Signia unit.
The Signia device modestly increases functional gain and speech-in-noise understanding
results compared with the Vibrant D device (Shohet, 2008).
WORKED EXAMPLE
A VORP that is 2 mm long and 1.5 mm in diameter contains an outer coil that uses the finest
commercially available insulated copper wire, AWG-60 (American Wire Gauge), with a bare
copper diameter of 0.00786 mm and a final diameter of 0.01mm with insulation. The cross
sectional area of the copper is
A
10
−
11
200 turns can be
accommodated along the 2 mm length of the VORP, with a total wire length,
l
(m), of
=
4
.
85
×
m
2
. A total of
N
=
10
−
3
l
=
N
π
d
=
200
×
π
×
1
.
5
×
=
0
.
942 m
