Biomedical Engineering Reference
In-Depth Information
or culture media, ions carry the charge from the anode to the cathode. The
movement of ions from anode to cathode is the reason that DC EFs are generally
effective only when the cathode is placed past the injury in the direction of desired
growth. Conversely, if the cathode is placed proximally to the injury, the EF vector
will be against the direction of desired growth, which seems to hinder regenera-
tion (Winter et al. 1981).
DC EFs show similar types of improvements in the regeneration of nerves.
For example, electrodes placed intraluminally in transected rat sciatic nerves
were used to apply a weak-DC EF. After treatment, the regenerated-axonal dis-
tance in the rats sciatic nerve was 69% longer than that of untreated rats (Sisken
1992). However, the age of the treated rat has an effect on the improved rate of
recovery due to DC EF treatment. The application of a DC EF in ten-month-old
rats showed an increase in recovery rate (measured by a behavioral test) of 21%
compared to controls (Pomeranz and Campbell 1993). However, younger rats
(three - months - old) did not have signifi cant improvement in recovery. The unal-
tered recovery rate in younger rates is thought to be due to younger rats having a
better healing ability than older rats: two- to three-months-old rats heal 24%
faster than nine to ten-months-old rats (Campbell and Pomeranz 1993).
18.5.4 Electromagnetic Stimulation
In Vivo
P. Jagadeesh and D. Wilson (Wilson and Jagadeesh 1976) were one of the fi rst
teams to explore the effects of electromagnetic fi elds on nerve regeneration
by stimulating the median-unlar nerves with a radio frequency signal (5-
120 mV/cm
2
) (Wilson and Jagadeesh 1976). Transected median-ulnar nerves were
stimulated for 15 minutes each day for up to 60 days. From observations seen 30
days from the start of treatment, the animals treated with the pulsed electromag-
netic fi eld (PEMF) showed signifi cant restoration of nerve conduction activity
and larger diameter nerve fi bers, compared to untreated rats (Wilson and Jaga-
deesh 1976). Similarly, rats with transected sciatic nerves were completely sub-
jected to PEMF. Treated rats regained motor function in four weeks instead of
untreated rats, which regained motor function in eight weeks (Ito and Bassett
1983). Additionally, sinusoidal electromagnetic fi elds were applied to a crushed
sciatic nerve model with similar results. However, regeneration was attributed to
earlier stages in re-growth of the transected nerve (Sisken 1992).
18.5.5 Therapeutic Electrical Stimulation in the CNS
Jagadeesh and Wilson extended their studies of electrical stimulation from the
PNS to the CNS using cats. Cats were treated with PEMF stimulation after trans-
versely cutting half-way into the spinal cord (hemicordotomy). The PEMF treat-
ment consisted of 50 mW/cm
2
at 400 pulses/second applied 30 minutes each day
for one month. After three months, the spinal cord was dissected, sectioned, and
histologically analyzed. In treated cats, extent of scarring was reduced and neurons
traversed the region of the hemicordotomy (Wilson and Jagadeesh 1976). There-
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