STIMULATION OF EXCITABLE TISSUES - Design and Development of Medical Electronic Instrumentation - page 312

The most common clinical applications of electrical stimulation are:

1. Cardiac pacing . Electrical stimulation of the heart's chambers relieves or eliminates
the symptoms of bradycardia (a heart rate that is too slow). Rhythmic stimulation (pacing)
increases the heart rate to meet the oxygen needs of the body. Cardiac pacing is discussed
in detail in Chapter 8.
2. Cardiac de brillation . High-energy stimulation of the heart (in the form of an elec-

trical shock) interrupts a rapid heart rhythm (tachycardia) so that a more normal rhythm
can be restored. Cardiac de

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brillation is discussed in detail in Chapter 8.
3. Cardiomyoplasty . A skeletal muscle (e.g., the latissimus dorsi, which attaches at one
end to the upper part of the upper arm bone and spreads out like a fan to attach to the spine
and ribs) is dissected free from its normal attachments and then wrapped around the heart. The
muscle is then stimulated to contract in synchronism with the heart. Since skeletal muscle is
prone to fatigue, it must

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fi first be trained by converting its fi fibers to fatigue-resistant type 1 mus-

cle fibers. Training is done with a low stimulation rate with only one pulse in a burst and over

a period of six weeks increasing the repetition rate and the number of pulses in the burst.
4. Electroventilation . Electrical stimulation of the phrenic nerve or the diaphragmatic
muscles is used to support ventilation. Candidates for breathing pacing include patients
who require chronic ventilatory support because of spinal cord injury, decreased day or
night ventilatory drive (e.g., sleep apnea), intractable hiccups (chronic hiccups often lead
to severe weight loss and fatigue and can have fatal consequences), and damaged phrenic
nerve(s). The physiological respiratory function provided by these devices is far superior
to that provided by mechanical ventilators since the air inhaled is drawn into the lungs by
the musculature rather than being forced into the chest under mechanical pressure.
5. Diagnostic stimulation of nerves and muscles . Nerve conduction studies are per-
formed routinely to assess peripheral nerve function. Electrical stimulation is applied to a
nerve and the nearby EMG signal is measured. This is done to determine the speed of trans-
mission along the nerve. It also helps to determine if there is a blockage in the nerve or
where the nerve connects to the muscle. In a similar way, electrical stimuli delivered at the
wrist or behind the knee are used to evoke brain responses to sensory inputs. The
somatosensory-evoked potentials are detected by coherent averaging of the EEG. From
this information, the evaluator may determine whether there is a delay in conduction to the
brain, a blockage at any point, or abnormally low or high activity in the brain. Another
common diagnostic use of nerve stimulation is monitoring the depth of neurological
blocks present in a patient following the administration of muscle relaxant drugs (e.g.,
prior to surgery, and after surgery following the administration of antagonist drugs).
6. Diagnostic stimulation of the brain . Very brief high-voltage pulses or pulse bursts to
stimulate percutaneously human motor cortex, visual cortex, or spinal cord are used for
intraoperative monitoring as well as for diagnosis of neurological diseases.
7. Pain relief . The technique of applying electric currents to the spinal cord or a periph-
eral nerve to relieve pain is known as electroanalgesia . Its use with both permanently
implanted and nonsurgically applied devices is common practice in the treatment of
patients su

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ering from chronic pain.
8. Control of epileptic seizures . Electrical stimulation of the vagus nerve [also known
as vagus nerve stimulation (VNS)] involves periodic mild electrical stimulation of the
vagus nerve in the neck by a surgically implanted device. VNS has been found e

ff

ective in
controlling some epilepsies when antiepileptic drugs have been inadequate, their side
e

ff

ects intolerable, or neurosurgery has not been an option. In some cases VNS has also
been e

ff

ects (e.g., mild tingling sen-
sations and voice hoarseness during stimulation), but unlike many medications, there seem
to be no signi

ff ective in stopping seizures. It carries minimal side e ff

ects to VNS
therapy. VNS is now the second most common treatment for epilepsy in the United States,
and the improvement in seizure control is comparable to that of new antiepileptic drugs.

fi cant intellectual, cognitive, behavioral, or emotional side e ff