Biomedical Engineering Reference
In-Depth Information
s
in duration (based on the setting of potentiometer R9) at a frequency of 10 to 100 Hz
(depending on the setting of potentiometer R6). Pulse-rate generator timer IC3 is either
constantly enabled or turned on and of
The circuit of Figure 7.18 drives the output stage to produce output pulses 10 to 300
µ
, depending on the setting of switch SW3. In the
cyclic setting, the burst duration and frequency is de
ff
ned by IC2 to the setting of R8. In
the external mode, the trigger time and duration of the stimulus burst are set to the time
that an external controller (e.g., a microcontroller in a FNS system) energizes the LED in
optocoupler IC1.
There is clinical evidence showing that appropriate electrical stimulation can cause a
denervated muscle to contract, which in turn may help limit edema and venous stasis
within a muscle and therefore delay muscle
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fibrosis. Studies seem
to indicate that proper use of EMS shortens recovery time following denervation.
EMS is not necessarily a benign therapy, however. Some studies indicate that contrac-
tion of a denervated muscle may disrupt regenerating neuromuscular junctions and subse-
quently, delay reinnervation. In addition, denervated muscle is more sensitive to trauma
than is innervated muscle, and electrical stimulation may further traumatize the denervated
muscle. Moreover, prolonged electrical stimulation until reinnervation occurs is often not
worth the costs or time involved.
Television has popularized the cosmetic use of EMS devices. Late-night infomercials
claim that muscle stimulators can help in losing weight and increasing muscle de
fi
fiber degeneration and
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fi
nition
through “no-work” or “passive” exercising. Despite the “guaranteed results” o
ered by
these advertisements, don't count on looking like Venus or Adonis by slapping on some
gelled electrodes to twitch your beer belly. There is no clinical evidence that electrical
muscle stimulation would provide any bene
ff
t toward weight loss and body toning.
In fact, the FDA has seen no evidence that these devices are safe and e
fi
ective for home
use or for applications touted in health spas and beauty salons. FDA considers electrical
muscle stimulation to be misbranded and fraudulent when promoted for weight loss or
body shaping. There are currently no acceptable uses for these devices when labeled for
over-the-counter use. When labeled for medical use by a licensed practitioner, the follow-
ing uses are generally recognized as acceptable:
ff
• Relaxation of muscle spasm
• Prevention or retardation of disuse atrophy
• Muscle reeducation (e.g., rehabilitation of muscle function after a stroke)
• Increasing local blood circulation
• Immediate postsurgical stimulation of calf muscles to prevent venous thrombosis
(formation of blood clots)
• Maintaining or increasing range of motion
The bottom line on the cosmetic use of electrical muscle stimulators: If you want to
look like the models in muscle stimulation commercials, do not buy the stimulator, but do
get on a diet and join a health club.
Transcutaneous Electric Nerve Stimulation
Transcutaneous electrical nerve stimulation (TENS) provides symptomatic relief from
some forms of chronic or acute pain, including postsurgical and posttraumatic pain. TENS
devices require FDA approval as class II medical devices and need physician prescription
to be dispensed to or used on patients. Electrodes are placed at speci
c sites on the body
for treatment with TENS. The current travels through electrodes and into the skin, stimu-
lating nerve pathways to produce a tingling or massaging sensation that reduces the
fi
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