Biomedical Engineering Reference
In-Depth Information
TABLE 7.7
Typical Parameters Used in Chronic Wound Treatment Instruments
a
Clinical
Method of
Typical
Typical Current
Application
Current Delivery
Waveform
or Voltage
Promoting healing
Cathode wrapped in saturated (saline)
Dc applied two or three times per
20 to 100
µ
A with a
of wounds and
gauze and placed directly over
day for 2 hours at a time
compliance of
8V
skin ulcers
the wound site, gelled skin surface
Low-voltage monophasic current
30 to 40 mA with up to
anode placed near the wound
pulses, 50% duty cycle delivered
12-V compliance
at up to 150 Hz
High-voltage monophasic pulses,
100 to 250 V
50% duty cycle delivered at up
to 150 Hz
Biphasic 40-Hz square-wave current
15 to 25 mA with
100-V
compliance
TENS device generating charge-balanced
10 to 50 mA “stimulation”
current-controlled pulses, 0.1 to 0.2 ms
phase with
150-V
duration at 80 to 90 Hz
compliance
Ac magnetic
fi
field applied through
Inductively coupled
fi
field 10 to 150 Hz
Maximum magnetic
fi
eld
coils over wound dressings
burst, 10 to 100 pulses per burst and
amplitude at the wound
a pulse frequency of 2 to 10 kHz
site
50 G to induce an
electrical
fi
field of
0.1 to
0.5 V/m
Nonthermal high-frequency RF
60 to 100
µ
s of high-peak-power RF
Peak pulse power of 200 W
applied with small capacitive
bursts of
27 MHz, repeated at
to 1 kW
“antenna” over wound
80 to 600 Hz
dressings
a
It should be noted that in 1996 the ECRI found no evidence that dc stimulation improves the healing rate of chronic, decubitus, or diabetic ulcers. All other
forms of stimulation seem to improve the normalized healing rate of decubitus ulcers but not of chronic venous or diabetic ulcers.
Electrochemotherapy or Electroporation Therapy
Brief, intense electric pulses have been in use since the 1970s to create temporary pores in
cells without causing permanent damage. This process, known as
electroporation
, happens
when the electrical pulse causes a transmembrane potential of 0.5 to 1.5 V. Under this
eld
intensity, the lipid bilayer of cells is temporarily rearranged, forming aqueous channels in
the cell membrane. These “pores” make the cell membrane permeable to a large variety of
hydrophilic molecules that are otherwise unable to enter into the cell. Once formed, these
pores remain open for a duration of seconds to minutes.
Genetronics, Inc. (San Diego, California) introduced the use of electroporation for in
vivo delivery of high doses of chemotherapeutic drugs to cancerous tumors [Hofmann
et al., 1996] (Table 7.8). Electroporation therapy (EPT) makes it possible to introduce into
cells potent anticancer drugs such as bleomycin, which normally cannot penetrate the
membranes of certain cancer cells. Treatment is carried out by injecting bleomycin directly
into the tumor and applying electroporation pulses through an array of needle electrodes.
The
fi
field strength must be adjusted reasonably accurately so that electroporation of the
cells of the tumor occurs without damage, or at least minimal damage, to any normal or
healthy cells. Treatment with this therapy avoids the toxic e
fi
ects associated with the sys-
temic administration of anticancer agents, making it possible to kill selectively the can-
cerous cells while avoiding surrounding healthy tissue. As such, a patient should require a
much lower dose of chemotherapy than is usually necessary to kill the tumor, drastically
reducing nasty side e
ff
ects such as hair loss, nausea, and vomiting that are associated with
conventional chemotherapy.
ff
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