Biomedical Engineering Reference
In-Depth Information
TABLE 7.10
Typical Parameters Used in Nanosecond Pulse Field Therapy Instruments
Clinical
Method of
Typical
Typical Current
Application
Current Delivery
Waveform
or Voltage
Induction of apoptosis
RF applicator in contact
1 to 10 narrow high-voltage
Su
cient to yield
fi
eld
via nanosecond pulsed
with tumor?
nanosecond-rise-time pulses,
intensities of 50 to
electric
fi
fields (nsPEFs)
10 to 300 ns in duration
300 kV/cm
TABLE 7.11
Typical Parameters Used in Embolic Therapy Instruments
Clinical
Method of
Typical
Typical Current
Application
Current Delivery
Waveform
or Voltage
Detachment of embolic device
Between guide wire (anode) and
Dc delivered until embolic
0.1 to 1 mA with compliance
and initiation of platelet and
gelled surface electrode (cathode);
device separates from
of 10 V
RBC aggregation
typical impedance 1 to 4 k
guide wire
performing a suture ligation of the neck, or wrapping the entire aneurysm. General anes-
thesia, craniotomy, brain retraction, and placement of a clip around the neck of the
aneurysm are required in these surgical procedures. The surgical procedure is often
delayed while waiting for the patient to stabilize, leading to the death of many patients
from the underlying disease or defect prior to surgery.
A minimally invasive alternative to surgery involves reaching the interior of the
aneurysm through a catheter introduced through a remote artery. Once the catheter is posi-
tioned, a long platinum microcoil that is fused to a guide wire is fed into the aneurism.
Detachment of the coil from the guide wire is then achieved by the passage of low-voltage
dc through the guide wire to hydrolyze a sacri
cial link between the guide wire and coil
(Table 7.11). The current along the coil also initiates platelet and RBC aggregation, pro-
moting thrombosis. Within a short period of time after the
fi
filling of the aneurysm with the
embolic coil, a thrombus forms in the aneurysm and is shortly thereafter complemented
with a collagenous material that signi
fi
fi
cantly lessens the potential for aneurysm rupture.
Microcurrent Stimulation and Other Energy Therapies
Microcurrent stimulators have been around since the 1960s. Proponents of the technique
believe that delivering charge-balanced square waves of some 10 to 600
A at frequencies
between 0.5 and 100 Hz across the head “normalizes the activity of the nervous system”
and is thus claimed to treat depression, anxiety, and insomnia. In 1976, when Congress
chartered the FDA with enforcing the Federal Food, Drug, and Cosmetic (FD&C) Act,
these devices were classi
µ
ed as cranial electrotherapy stimulation and their commercial
approval was obtained through a grandfather provision of the FD&C Act. This is why these
devices, although far from being proven e
fi
ff
ective by today's standards, are promoted by
their manufacturers as “FDA Approved.”
The alleged mechanism of operation of these devices certainly groups them along with
the quackery promoted by homeopaths and chiropractors. Just look at what Electromedical
Products International, probably the largest microcurrent stimulator manufacturer, claims
about their devices: [The Alpha-Stim devices are] “based on the concept that the biophysics
underlying the body's biochemistry also plays a signi
cant role in regulating all of life's
processes. . . . Alpha-Stim's proprietary waveform works by moving electrons through the
body and brain at a variety of frequencies, collectively known as harmonic resonance. This
normalizes the electrical activity of the nervous system and brain as measured by an elec-
troencephalogram (EEG).” Controlled studies reported in reputable journals [Tan et al.,
fi
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