Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2001-08-21
2003-03-18
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S051000
Reexamination Certificate
active
06535767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pulsed signal generator for biomedical applications. In particular, the present invention relates to a light-weight, compact pulsed signal generator that produces an output waveform based on at least four timing intervals T
1
-T
4
, more preferably, a waveform based on seven timing intervals T
1
-T
7
.
2. Discussion of Background
Injuries, infections and degenerative conditions are major sources of pain, inconvenience, expense, lost work (and leisure) time and diminished productivity. The problems associated with these conditions grow worse with age, since an injury which would heal quickly in a young, healthy person takes much longer in one who is older, in poor health, or both. In demographically-aging societies such as now seen in most of the industrialized nations, these social and economic impacts will become increasingly magnified over the course of the next several decades.
While it is difficult to estimate the total cost of such conditions—leaving aside their impact on quality of life—the total surely amounts to many billions of dollars per year in the United States alone. For example, between five and ten million United States residents suffer broken bones every year, with many of these cases involving multiple fractures. In a young, healthy patient, many fractures need to be immobilized in a cast for six weeks or more. Even after the cast is removed, the patient's activities are frequently restricted until the healed bone regains its full strength. In the elderly, in persons with poor health or malnutrition, in patients with multiple fractures, or in patients with conditions that impact healing processes, fractures heal more slowly. In some cases, the fractures do not heal at all, resulting in the conditions known as “nonunion” or “nonunion fracture” which sometimes persists for a lifetime.
As a result, an estimated quarter-million person-years of productivity are lost in the United States due to bone fractures alone. Similar statistics can be generated not only for other classes of traumatic injury, but also for chronic conditions such as osteoarthritis, osteoporosis, diabetic and decubitus ulcers, damaged ligaments, tendonitis, and repetitive stress injuries (including the conditions commonly known as “tennis elbow” and carpal tunnel syndrome).
Since the 1960s, it has been increasingly recognized that the human body generates a host of low-level electric signals as a result of injury, stress and other factors; that these signals play a necessary part in healing and disease-recovery processes; and that such processes can be accelerated by providing artificially-generated signals which mimic the body's own in frequency, waveform and strength. Such “mimic” signals can speed the healing of skin and muscle wounds, including chronic ulcers such as those resulting from diabetes; the mending of broken bones, including most nonunion fractures; the regrowth of injured or severed nerves; and the repair of tissues damaged by repetitive motion, as in tendonitis and osteoarthritis. “Mimic” signals can also reduce swelling, inflammation, and especially pain, including chronic pain for which the usual drug-based treatments no longer bring satisfactory relief.
Some of the body's signals, such as the “injury potential” or “current of injury” measured in wounds, are DC (direct current) only, changing slowly with time. It has been found that bone fracture repair and nerve regrowth are typically faster than usual in the vicinity of a negative electrode but slower near a positive one, where in some cases tissue atrophy or necrosis may occur. For this reason, most recent research has focused on higher-frequency, more complex signals often with no net DC component.
While most complex-signal studies to date have been performed on bone fracture healing, the commonality of basic physiological processes in all tissues suggests that the appropriate signals will be effective in accelerating many other healing and disease-recovery processes. Indeed, specific frequency and waveform combinations have been observed to combat osteoarthritis and insomnia, stimulate hair growth, reduce swelling and inflammation, fight localized infection, speed the healing of injured soft tissues including skin, nerves, ligaments and tendons, and relieve pain without the substituted discomfort of TENS (transcutaneous electric nerve stimulation).
FIGS. 1A and 1B
show a schematic view of a waveform
20
which has been found effective in stimulating bone fracture healing, where a line
22
(
FIG. 1A
) represents the waveform on a short time scale, a line
24
(
FIG. 1B
) represents the same waveform on a longer time scale, levels
26
and
28
represent two different characteristic values of voltage or current, and intervals
30
,
32
,
34
and
36
represent the timing between specific transitions. Levels
26
and
28
are selected so that, when averaged over a full cycle of the waveform, there is no net DC component. In real-world applications, waveform
20
is typically modified in that all voltages or currents decay exponentially toward some intermediate level between levels
26
and
28
, with a decay time constant usually on the order of interval
34
. The result is represented by a line
38
(FIG.
1
C).
In a typical commercially-available device for treating fracture nonunions, interval
30
is about 200 &mgr;sec, interval
32
about 30 &mgr;sec, interval
34
about 5 msec, and interval
36
about 60 msec. Alternate repetition of intervals
30
and
32
generates pulse bursts
40
, each of the length of interval
34
, separated by intervals of length
36
in which the signal remains approximately at level
28
. Each waveform
38
thus consists of rectangular waves alternating between levels
26
and
28
at a frequency of about 4400 Hz and a duty cycle of about 85%. The pulse bursts are repeated at a frequency of about 15 Hz and a duty cycle of about 7.5%, alternating with periods of substantially no signal. The timing of such a signal can vary broadly, since the characteristics of signals generated by bone in vivo and in vitro depend on a number of factors, including but not necessarily limited to its type, size and mineral density, and the amount of stress and its rate of application. Hence, osteoblasts are believed to be able to respond to a range of signals which differ somewhat in waveform and frequency content.
However, different tissues may respond differently to markedly different frequencies and waveforms. For example, the waveform of
FIGS. 1A-C
is effective in speeding the healing of a bone fracture but much less so in slowing the progress of osteoporosis. On the other hand, a waveform
50
(
FIG. 2
) consisting of single pulses
52
of polarity
26
lasting approximately 350-400 &mgr;sec each, alternating with intervals
54
of polarity
28
at a frequency of approximately 60-75 Hz, can slow or even reverse osteoporosis but has little effect on fracture repair. Again, the exact waveform and frequency for each application may vary.
The signal intensity may also vary; indeed, more powerful signals often give no more benefit than weaker ones, and sometimes less. This paradoxical relationship is shown schematically in
FIG. 3
, where a line
60
represents the magnitude of the healing effect at various signal intensities. For a typical signal (such as the signal of FIGS.
1
A-C), a peak effectiveness
62
typically falls somewhere between one and ten &mgr;A/cm
2
, and a crossover point
64
at about a hundred times this value. Beyond point
64
, the signal may slow healing or may itself cause further injury. Similar responses are seen in other biological processes that are responsive to electrical stimulation, including cell division, protein and DNA synthesis, gene expression, and intracellular second-messenger concentrations. For example, while conventional TENS can block pain perception with a relatively strong signal, much as a jamming signal blocks radio communication, it can also lead to progr
Reichmanis Maria
Schaetzle Kennedy
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