AASM Membership Sections Newsletter Issue #2
19
history of upper airway surgery (Mwenge 2012). The
multi-contact electrode was implanted on the HGN
trunk. There were 13 patients at baseline a mean BMI
of 30.8±3.4 and mean age of 50.0±10.2. The baseline
AHI was 45.2±17.8 and ODI was 29.2±19.6. After 1
year, the mean AHI declined to 21.0±16.5 (P<.001)
and the ODI from 29.2±19.6 to 15.3±16.2 (P<.001).
One patient was noted to have been implanted with
a morphine pump during the study and developed
predominant central sleep apnea. Ten patients of the
thirteen were considered responders, with AHI reduc-
tion ≥50%. For the responders, after 1 year, the mean
AHI declined 41.3±13.1 to 13.2±5.6 and the ODI
declined from 23.1±10.2 to 7.8±5.3 (P<.001 for both).
The micro-arousal rate declined from 36.8±12.5 to
24.9
±13.7 (P<.001) for the entire group and from
34.8
±6.7 to 20.3±8.1 (P<.001) for the responders. ESS
score declined from 10.8±6.2 to 6.7±5.4 (P=.094).
Serious adverse events reported were one defective
device connector discovered during surgery, three
lead fractures and one IPG replacement for failure.
Seven of ImThera’s patient’s underwent polysom-
nographic testing for two nights after one year of
neurostimulation, with stimulation active one night
and turned off on the other night. The order of on/off
nights was randomly determined. The patients’ mean
baseline AHI was 43±14, and ODI 23±12. After 1
year, with active stimulation, the AHI was 15±5 and
the ODI was 8±3. On the night
without
stimulation,
the AHI and ODI were not significantly different
from the values obtained with stimulation, at 14±8
and 8±5, respectively (D Rodenstein, poster presenta-
tion at ATS, May 21, 2012). This is in contrast with
CPAP, where OSA rapidly recurs in the first night off
therapy (Kohler 2011). Persistence of the therapeutic
effect without stimulation has not been reported with
Apnex Medical’s or Inspire Medical’s devices.
Comments
Studies of the implanted system showed beneficial
effects on airway patency, polysomnographic param-
eters and symptoms. Airflow was markedly increased
and inspiratory flow limitations were resolved in
most patients with acute stimulation (Schwartz
2012).
Using fluoroscopy, investigators noted that
both the retrolingual and the retropalatal airway were
expanded in the saggital plane with stimulation (Go-
ding 2012). Lateral pharyngeal widening and stabili-
zation was also noted to occur (Mwenge 2012), pos-
sibly via the superior constrictor muscle’s attachment
to the tranversalis muscle of the tongue Base (Saigusa
2004).
The AHI and ODI were reduced, albeit not
normalized, and importantly without induction of
arousals from stimulation. The patients tolerated
neurostimulation well and clinically significant im-
provements in quality of life were noted on validated
questionnaire tools. Other than early device or lead
failures and few infections, the therapy appeared safe
in the small population of patients studied.
The incomplete reduction of the AHI in many
patients is suboptimal, especially for those with very
severely elevated AHIs. Nonetheless it represents par-
tial treatment of an otherwise untreated patient, for
the entire duration of the sleep period. Higher BMI
appeared to be associated with less favorable outcome
in Apnex Medical’s and Inspire Medical’s trials while
ImThera Medical has not yet performed the pivotal
study from which BMI relation to outcome can be
studied. The BMI exclusion is problematic as class 2
and 3 obesity is becoming more prevalent and inclu-
sion of this population is desirable. An additional
exclusion parameter for Inspire Medical patients is
concentric (severe) retropalatal collapse on sleep
endoscopy and this may further restrict applicability.
Whether the above will eventually limit utilization of
implantable HGN stimulation technology is un-
known as the technology is in its early phase of study.
Improved outcome could potentially be achieved
by modification of the current schemes for implant-
able hypoglossal neurostimulation. Increased current
may overcome residual obstructions for some devices
Continued >>
Neurostimulation for OSA continued