68
Dorin Panescu
IEEE ENGINEERING IN MEDICINE AND BIOLOGY MAGAZINE NOVEMBER/DECEMBER 2005
Emerging Technologies
vagus nerve stimulation for the treatment of depression
Clinical depression is definedas a psychiatric disordercharacterized by an inabilityto concentrate, insomnia,
loss of appetite, anhedonia, feelings of
extreme sadness, guilt, helplessness and
hopelessness, and thoughts of death [1].
Throughout the course of our lives,
we all experience the blues, or episodes
of unhappiness, sadness, or grief. Most
of us are able to cope with these and
other types of stressful events, and we
return to our normal activities within
several days. But when these feelings of
sadness and other symptoms make it
hard for us to get through the day, and
when the symptoms last for more than a
couple of weeks, we may have what is
called clinical depression [2]. Clinical
depression may be present if the patient
has a depressed mood for at least
two weeks and has at least five of the
following symptoms: feeling sad or
blue, loss of interest or pleasure in usual
activities, significant weight loss or
weight gain, inability to sleep or exces-
sive sleeping, agitation or irritability,
fatigue or loss of energy, feelings of
worthlessness or excessive guilt, and
thoughts of death or suicide [2].
Clinical depression affects about 19
million Americans. It is estimated to
contribute to half of all suicides. About
5–10% of women and 2–5% of men
will experience at least one major
depressive episode during their adult
lives. Depression affects people of all
races, incomes, and ages, but it is 3–5
times more common in the elderly than
in young people [2]. Approximately
5–15% of major depressive episodes
last longer than two years. Up to 1.5%
of the general population suffers chron-
ic or severe depressions. Up to 15% of
all people with severe depression
requiring hospitalization eventually
commit suicide [3]. In 1990, the direct
treatment costs associated with depres-
sion were US$12.4 billion [4].
While the causes of depression are
complex, chemical imbalances in the
brain are believed to contribute to the
onset of the condition. For example,
researchers at the National Institute of
Mental Health (NIMH) and at the
National Heart Lung and Blood
Institute (NHLBI) recently found that a
mutant gene responsible for starving the
brain of serotonin, a neurotransmitter,
was ten times more prevalent in
depressed patients than in control sub-
jects. Patients with the mutation failed
to respond well to the most commonly
prescribed antidepressant drugs, which
work via serotonin, suggesting that the
mutation may underlie a treatment-
resistant subtype of the illness [5].
Certain other factors can modulate the
effects neurotransmitters have on the
patient’s mood. For example, heredity,
personality, medication, substance
abuse, and diet can all play a consider-
able role in the evolution of clinical
depression. For the elderly population,
factors such as co-occurring illnesses,
medication effects, and social isolation
represent incremental risks [2].
Treatments for depression aim at
complete symptom remission and com-
plete restoration of day-to-day function
as well as prevention of relapses (return
of the current episode) and recurrences
(new episodes) [3]. There are currently
three major treatment modalities for
which there is substantial evidence of
effectiveness in the treatment of a major
depressive episode: antidepressant
drugs (ADDs), specific forms of psy-
chotherapy, and electroconvulsive ther-
apy (ECT).
ADDs are the usual first line of treat-
ment for depression. Clinical trials have
demonstrated efficacy for a number of
pharmacologic classes of ADDs.
Commonly, the initial drug selected is a
selective serotonin reuptake inhibitor
(SSRI) such as fluoxetine (Prozac) or
another of the newer ADDs such as
venlafaxine (Effexor) [2], [6]–[7]. Other
drugs, such as tricyclic antidepressants
(TCAs), amitriptyline (Elavil) or trim-
ipramine (Surmontil), for example, are
prescribed when SSRI medication does
not work.
Several forms of psychotherapy are
used to treat depression. There is good
evidence for the efficacy of cognitive
behavior therapy and interpersonal ther-
apy, but these treatments are used less
often than ADDs. Phototherapy is an
additional treatment option that may be
appropriate monotherapy for mild
cases of depression exhibiting a
marked seasonal pattern [3], [7].
Physicians usually reserve ECT for
Fig. 1. The VNS pulse generator and
lead system.
0739-5175/05/$20.00©2005IEEE