U.S. patent application number 13/400460 was filed with the patent office on 2012-06-14 for method for fractional skin treatment.
Invention is credited to Yossef Ori Adanny, Baruch Levine, Genady Nahshon, Avner Rosenberg.
Application Number | 20120150168 13/400460 |
Document ID | / |
Family ID | 43465802 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120150168 |
Kind Code |
A1 |
Adanny; Yossef Ori ; et
al. |
June 14, 2012 |
METHOD FOR FRACTIONAL SKIN TREATMENT
Abstract
A method for cosmetic RF skin treatment where the RF energy
supply is isolated from the patient treated, such that in course of
treatment no undesired current flows through the subject body. The
method includes RF energy to the skin using an applicator with a
tip populated by at least one voltage to skin delivering element
and an isolating transformer located proximate to the tip to reduce
ground currents through parasitic capacitance. The impedance of the
skin is monitored during an RF treatment pulse, and operating a
controller to control the delivery of an amount of energy to the
skin, the amount sufficient to cause a desired skin effect. The
pulse energy is increased if the skin impedance is lower than a
predetermined impedance threshold; cutting off RF energy supply if
the skin impedance is below a predetermined skin impedance value;
and preventing pain by cutting-off RF pulses above a predetermined
skin impedance value.
Inventors: |
Adanny; Yossef Ori; (Mitzpe,
IL) ; Nahshon; Genady; (Binyamina, IL) ;
Levine; Baruch; (Afula, IL) ; Rosenberg; Avner;
(US) |
Family ID: |
43465802 |
Appl. No.: |
13/400460 |
Filed: |
February 20, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12505576 |
Jul 20, 2009 |
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13400460 |
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Current U.S.
Class: |
606/33 |
Current CPC
Class: |
A61B 2018/00452
20130101; A61B 2018/0047 20130101; A61B 18/1233 20130101; A61B
2018/00642 20130101; A61N 1/0476 20130101; A61B 2018/165 20130101;
A61B 2018/00827 20130101; A61B 18/18 20130101; A61B 2018/162
20130101; A61B 2018/0016 20130101; A61N 5/00 20130101; A61B
2018/00702 20130101; A61B 2018/00577 20130101; A61B 18/14 20130101;
A61B 2018/00875 20130101; A61B 2018/1467 20130101; A61B 2018/00589
20130101 |
Class at
Publication: |
606/33 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. A method for fractional RF skin treatment, said method
comprising: applying to the skin an applicator including a tip
populated by at least one voltage to skin delivering element and an
isolating transformer located proximate to the tip to reduce ground
currents through parasitic capacitance; monitoring the skin
impedance during an RF treatment pulse, and operating a controller
to control the delivery of an amount of energy to the skin, the
amount sufficient to cause a desired skin effect; and increasing
the pulse energy if the skin impedance is lower than a
predetermined impedance threshold; excluding inefficient RF pulses
by cutting off RF energy supply if the skin impedance is below a
predetermined skin impedance value; and preventing pain by
cutting-off RF pulses above a predetermined skin impedance
value.
2. The method according to claim 1 further comprising notifying the
operator on the need to clean the tip when the value of skin
impedance is increasing.
3. The method according to claim 1 further comprising notifying the
operator on the low value of skin resistance and the need to dry
out the skin.
4. The method according to claim 1 further comprising filtering out
the low frequency currents generated by plasma formed at the
voltage to skin delivering elements in course of applicator
operation.
5. The method according to claim 4 wherein capacitors serially
connected with a tip populated by at least one voltage to skin
delivering element and an isolating transformer are filtering out
the low frequency currents produced by the plasma formed at the
voltage to skin delivering elements.
6. The method according to claim 1 further comprising a current
limiter operative to set a maximum to current which flows into the
skin and direct the current to an energy absorbing element.
7. The method according to claim 6 wherein the current limiter
protects the subject from electric shock and skin burn.
Description
CROSS-REFERENCE TO RELATED REFERENCES
[0001] This application a divisional application of the
non-provisional patent application that was filed in the United
States Patent Office on Jul. 20, 2009 and assigned Ser. No.
12/505,576, which application is related to the United States
Application Publication No. 2006/0047281 and the U.S. patent
application having the Ser. No. of 12/324,932, all of the
afore-mentioned documents are incorporated herein by reference.
TECHNOLOGY FIELD
[0002] The method and apparatus generally relate to skin treatment
procedures and in particular to cosmetic skin resurfacing and
rejuvenation procedures.
BACKGROUND
[0003] Fractional skin resurfacing or rejuvenation is a recently
developed skin ablative technology. There are two types of devices
used to ablate the skin: laser based devices and RF based devices.
Both types of these devices ablate a pattern of extremely small
diameter shallow holes or zones. The holes are microscopically
small treatment zones surrounded by untreated skin areas. The
treatment results in a very rapid healing or recovery and skin
resurfacing of the treated. In the healing process of the treated
zones, a layer of new skin appears, restoring a fresh, youthful
complexion.
[0004] The pattern of small holes is typically produced by an X-Y
scanning laser beam or by application of RF energy or voltage. The
laser is focused on the skin and usually operates in pulse mode
ablating micron size holes in the skin.
[0005] RF based fractional skin treatment produces a scanning
pattern of micron size holes in the skin a similar to laser.
Typically, the energy is delivered to the skin by an applicator
equipped by a tip having a plurality of voltage to skin
applying/delivering elements or contact elements arranged in a
matrix or in an array. The voltage to skin applying elements are
placed in contact with the segment of the skin to be treated and
driven by a source of suitable power and frequency RF energy.
Application of a high voltage RF pulse to the electrodes ablates
the skin under the respective electrode forming a small hole.
[0006] In some instances application of laser or RF voltage pulses
causes discomfort and even pain to the treated subject, although
the experience based on the individual and as such, the pain
sensation may be different from subject to subject. In other
instances there may be a difference in the size of micro holes
formed by the applicator at the same treatment session. Healing of
larger size holes may take a longer period of time than the healing
process for smaller size holes and in some instances, the larger
holes may tend to result in causing damage to the skin rather than
producing the desired skin effect.
[0007] In order to soften the discomfort and lessen the pain and
other side effects associated with the fractional treatment,
practitioners have started using topically applied lidocaine cream
or even oral sedation.
[0008] Fractional skin treatment is applicable in the correction of
almost all cosmetic skin defects such as signs of aging, wrinkles,
discolorations, acne scars, tatoo removal, and other skin defects.
The cost of the RF based products is lower than that of the
products operating with laser radiation and they will most probably
become widely used if the discomfort and occasional pain associated
with their use could be eliminated.
[0009] US Patent Application Publication No. 2006/0047281 and U.S.
patent application Ser. No. 12/324,932 to the same assignee
disclose RF based products such as eMatrix.TM. suitable for
fractional skin treatment.
GLOSSARY
[0010] In the context of the present disclosure "RF voltage" and
"RF energy" are used interchangeably and have the same meaning. The
mathematical relationship between these two parameters is well
known and knowledge of one of them allows easy determination of the
other.
[0011] In the context of the present disclosure "skin resistance"
and "skin impedance" are used interchangeably and have the same
meaning. The mathematical relation between these two parameters is
well known and knowledge of one of them allows easy determination
of the other.
[0012] The term "desired skin effect" as used in the present
disclosure means a result of RF energy application, which may be
wrinkle removal, hair removal, collagen shrinking or destruction,
skin rejuvenation, and other cosmetic and skin treatments.
[0013] The term "plateau" of a function is a part of its domain
where the function has constant value.
BRIEF SUMMARY
[0014] An apparatus for cosmetic RF skin treatment where the RF
energy supply is isolated from the subject treated, such that in
course of treatment no undesired current flows through the subject
body. The apparatus includes an applicator with a tip that is
populated by a plurality of voltage applying dome shaped elements
protruding from the tip surface and organized in one common cluster
and a cluster of electrodes bounding the dome shaped elements and
having an area larger than the dome shaped elements have. The
apparatus applies voltage to the elements with a magnitude
sufficient to cause a desired skin effect. A current limiter limits
the RF induced current thereby preventing skin damage. The
apparatus continuously senses the treated skin segment impedance
and varies the RF energy at a low skin impedance and/or stops the
pulse in cases of too low or too high skin impedance.
BRIEF DESCRIPTION OF THE FIGURES
[0015] FIGS. 1A and 1B, collectively referred to as FIG. 1, are
schematic illustrations of a prior art RF applicator tip for
fractional skin treatment.
[0016] FIG. 2 is a schematic illustration of a prior art RF voltage
supplying circuit for driving the RF applicator tip for fractional
skin treatment.
[0017] FIGS. 3A through 3C are schematic illustrations of an
equivalent electric circuit of the tip for fractional skin
treatment.
[0018] FIG. 4 is a schematic illustration of an exemplary
embodiment of the present tip for fractional skin treatment driving
circuit.
[0019] FIG. 5 is a schematic illustration of another exemplary
embodiment of the present tip for fractional skin treatment driving
circuit.
[0020] FIG. 6 is a schematic illustration of skin resistance
variation under the application of an RF energy pulse.
[0021] FIG. 7 is a schematic illustration of an exemplary
embodiment of the present tip for fractional skin treatment control
circuit.
[0022] FIG. 8 is a schematic illustration of an exemplary
embodiment of the present RF applicator tip for fractional skin
treatment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0023] The principles and execution of the method and the apparatus
may be better understood with reference to the drawings and the
accompanying description of the non-limiting, exemplary
embodiments, shown in the Figures.
[0024] Reference is made to FIG. 1, which is a schematic
illustration of a prior art RF applicator tip for fractional skin
treatment disclosed in the U.S. patent application Ser. No.
12/324,932 to the same assignee. A carrier 100 on which voltage to
skin delivering elements or contact elements are formed may be a
flexible or rigid article made of a polyimide film or similar
material, with an exemplary thickness range of 0.5 mil to 6 mil
(12.5 micron to 150 micron). The term "carrier" in the context of
the present disclosure means a substrate having an array of voltage
to skin application elements, a two dimensional array or matrix of
voltage to skin application elements. Substrate 104 has on one of
its surfaces 112 an array or matrix of miniature (microscopic),
discrete, voltage to skin application elements 116 protruding from
surface 112 and terminated by dome type shapes 120. A pattern of
conductors 124 and 128 shown in broken lines arranged on the back
or second side of substrate 104 enables addressing of all elements
116, a cluster of elements 116, or each of elements 116
individually. Carrier 100, having formed on it, the voltage to skin
delivering elements is configured to allow quick attachment to an
applicator and will be termed in the present document as a "tip" or
an "applicator tip." An arrangement of RF contacts enabling
connection to a source of radio frequency voltage is provided by
forming on the back side of the carrier 104 contact points or
strips 108 communicating with respective contact arrangements made
in substrate 104. Voltage to skin delivering elements 116 are
arranged in a symmetric pattern with all even rows 124 connected to
one of the RF supply contact strips or ports 124 and all uneven
rows 128 connected to another or second contact strip or RF supply
port 128.
[0025] FIG. 2 is a schematic illustration of a prior art RF voltage
supplying circuit for driving the RF applicator tip for fractional
skin treatment. A source of RF voltage 200 may be located in stand
alone housing 204. Alternatively, the source of the RF voltage may
be located in the applicator case 208 shown in broken lines. The
source provides RF voltage to applicator tip 212, and in particular
to voltage to skin delivering elements 216 through a shielded
harness 220. Shield 224 is schematically shown in broken and doted
lines. The length of the harness 220 is selected to enable
convenient caregiver operation and may be oneto two meters long,
for example. There exists a certain parasitic capacitance 232 and
236 between the shield 224 and each of the RF current conducting
lines 240 and 244. The treated subject has also certain capacitance
248. For skin treatment, tip 212 is placed in contact with a
segment of the skin 228 to be treated. As a result of uneven
contact of the voltage to skin delivering elements 216 organized
into even 124 and uneven 128 rows or clusters with segment of the
skin 228 to be treated, an undesired RF current path 252 may be
formed. This current passes through the subject 228 and may cause a
painful sensation and even an electric shock to the subject.
[0026] FIG. 3 is a schematic illustration of an equivalent electric
circuit of the tip for fractional skin treatment 212 being in
contact with the treated segment of the skin. FIG. 3A schematically
shows the tip 212 with all contact elements 330 located in uneven
rows 1, 3, 5, and 7 of the tip 212 collectively marked as 302 and
shown as connected to a first RF port of RF voltage source 306 and
all contact elements located in even rows 2, 4, 6, and 8
collectively marked as 310 and shown as connected to a second RF
port of RF voltage source 306. All of the contact elements are in
contact with the upper skin layer 320 for example, stratum corneum
which has a relatively low conductivity, where numeral 324 marks
dermis layer and even deeper skin layers that have a relatively
high, as compared to stratum corneum, conductivity.
[0027] Referring to FIG. 3B, the electrical channel from each
contact element through the low conductance skin layer is
represented as a resistor (for the simplicity of the explanation
channel capacitance is neglected). The high conductivity dermis is
represented as a common resistor Rs. Further equivalent electric
scheme simplification is shown in FIG. 3C, where all uneven
resistors have been replaced by an equivalent resistor Ru and even
rows resistors by Re. Typically, each of the individual contact
element resistors is 50K-100K Ohms, therefore Ru and Re are about
2K Ohms each, whereas Rs is an order of magnitude smaller, about
200 Ohms and it can be neglected for the purpose of the
discussion.
[0028] Because not all of the voltage to skin delivering elements
or contact elements 330 (FIG. 3A) may be properly attached to the
skin and some of them may bear some dirt and other residuals from
the previous treatment, and different skin segments may have
different resistance, there is a difference in the resistance to
current passing through each of the contact elements and
accordingly through the clusters (even or uneven clusters) they
form. If the RF voltage or energy flows into any of the Ru or Re
resistors, it increases its resistance it generates a positive
feedback under which the larger resistor gets more energy than the
smaller one, its resistance increases more rapidly, therefore it
gets even more energy, and so on. The end result is that the one of
Ru or Re clusters, which had initially greater value finally takes
most of the energy and leaves a different imprint on the skin (for
example, only contact elements located in even or uneven rows may
leave an imprint). This reduces the efficacy of the treatment and
generates undesired skin effects, excessive pain, and even electric
shock.
[0029] In order to resolve this problem, as disclosed in the U.S.
patent application Ser. No. 12/324,932 assigned to the same
assignee, it is possible to address individually each contact
element or pin and connect it to the source of voltage through a
large impedance, which can be a resistor, a small capacitor, a
large inductor, or a combinations of all of them. This would
stabilize the RF induced current to each individual channel
reducing the "competition" between the contact elements and
clusters of contact elements. For sterilization and hygiene
purposes use of disposable tips is preferred to the use of reusable
tips. Addressing of each individual contact element however,
complicates and increases manufacturing cost of such tips.
[0030] Another way to equalize the resistance or impedance of each
contact element and reduce the pain sensation and potential
electric shocks to the treated subject is to bring the skin by some
initial treatment to an optimal and more uniform resistance value,
which for example may be about 3000 Ohms There will always be
however, segments of skin where the resistance is low and any
slight sweating may drive the skin to lower impedances.
[0031] FIG. 4 is a schematic illustration of an exemplary
embodiment of the present tip driving circuit. The embodiment of
FIG. 4 eliminates or at least, greatly reduces the pain sensation
and electric shock that could affect the treated subject. A low
capacitance for example, 4 pF to 10 pF isolating transformer 404 is
located in close proximity to the tip 212 with the voltage to skin
delivering elements 216. In the course of operation, transformer
404 reduces or completely eliminates currents flowing through the
subject body due to parasitic capacitances 408 and 412 formed by
the subject skin 320, 324 and the ground and between the shield 224
and each of the RF conducting lines 420 and 424. A controller 432
governing operation of all of the apparatus devices may be located
in housing 204. Controller 432 may have a processor, a memory, and
other devices necessary for controlling the treatment process.
[0032] FIG. 5 is a schematic illustration of an additional
exemplary embodiment of the present tip 212 driving circuit that
eliminates, or greatly reduces, pain sensation and electric shock
that could affect the treated subject. In addition to the low
capacitance transformer 404 one or more capacitors 502 and 504
located in the current path and connected in series to the
electrodes 216 form a high pass filter. In the course of apparatus
operation, the high pass filter filters out the low frequency
currents, to which the sensitivity of the treated subject is high,
generated by plasma formed at the voltage to skin delivering
elements 216 being in contact with the skin 320, 324 and flowing
through the subject body in course of the apparatus/applicator
operation. (reference can be made to Guidelines for Limiting
Exposure to Time-Varying Electric, Magnetic, and Electromagnetic
Fields up to 300 GHz; International Commission on Non-Ionizing
Radiation Protection, Page 10.
[0033] Electrical resistance of skindiffers from subject to subject
and complicates proper RF energy value selection and application of
the RF energy for cosmetic skin treatment. Further to this,
resistance of the subject may vary under application of RF energy.
FIG. 6 is a schematic illustration of skin resistance variation
under the application of RF energy in a pulse mode. Lines 602 and
606 mark different skin behavior under an RF energy pulse and lines
610 and 614 mark the upper and lower skin resistance or impedance
values that result in a desired skin effect, although because of
the large variability of the treated subjects skin properties,
there may be a need to set experimentally other values matching a
particular subject properties. The length of the pulse, as will be
explained later, may vary from few milliseconds to hundreds of
milliseconds or even seconds.
[0034] In order to establish proper treatment parameters prior to
the treatment, a system operator or user can calibrate the
apparatus and operational treatment parameters derived as a result
of the calibration are loaded into a look-up-table (LUT) that may
be stored in the memory of the controller 432. For the purpose of
calibration, a known variable resistance modeling the subject and
the tip behavior is connected instead of a subject to the RF
voltage supply. In one of the calibrations, a current flowing in
the circuit at different RF voltages and different resistance value
is recorded and in another calibration the RF energy applied to the
variable resistance, modeling different skin impedance is
recorded.
[0035] When skin is wet its resistance is low and with the
application of the RF energy it continues to fall (line 606).
Without being bound by a specific theory it is believed that most
of the RF energy applied to the skin is initially wasted to dry the
skin and when the skin under the influence of RF energy becomes
dry, the skin resistance begins growing to higher values.
Resistance increase is believed to be connected with vaporization,
accompanied or followed by tissue ablation. It is considered a good
treatment (desired skin effect) when ablation is created in the
tissue below the electrodes.
[0036] It has been experimentally established that treatment
resulting in a desired skin effect takes place when the resistance
of the subject's skin is between Rlow and Rhigh, where the specific
values depend on the number of electrodes in the tip and their
arrangement and on the skin properties. For a typical tip shown in
FIG. 1, with 64 electrodes and a diameter of 250 .mu.m each, Rlow
is about 1500 Ohms and Rhigh is about 4000 Ohms For the
asymmetrical tip of FIG. 8, Rlow is about 600 Ohms and Rhigh is
about 1600 Ohms When the skin resistance (or impedance) falls below
the lower limit, most of the RF energy applied to the skin is
wasted on drying the skin and not on causing the desired skin
effect. Generally, the upper skin resistance limit is in the
vicinity of the stratum corneum resistance with the lower limit
corresponding to wet skin. When the skin resistance is within the
indicated resistance limits, as shown by broken lines 610 and 614,
application of RF to the skin through the voltage to skin
delivering elements results in a desired skin effect. Continuous or
pseudo continuous monitoring of the skin impedance during the RF
pulse enables control of the energy delivered to skin. For example,
when the resistance falls below the pre-set threshold of e.g. 600
Ohms, the time of the RF pulse may be increased by the control,
until the control unit identifies or detects the beginning of an
increase in the resistance. From the time that the beginning of the
resistance increase is detected, the amount of energy delivered is
either fixed or it takes into consideration the energy delivered up
to that point, thereby allowing or ensuring the proper skin effect.
It is also possible to cut off the RF pulses when the skin
impedance is below a pre-set impedance or resistance value and
notify operator, to exclude inefficient pulses. Another possibility
is to notifying the operator on the low value of skin resistance
and the need to dry out the skin. It is also possible to set the
apparatus to deliver a pre-set amount of energy to the skin.
[0037] It is possible to generalize the skin behavior under an RF
pulse into at least two typical cases, although a mixture of these
cases and other skin behavior may be present: a) skin resistance
remains high through all of the RF pulse application time and b)
skin resistance drops down below the lower resistance limit and
after it reaches (the function reaches) a plateau it begins to
rise. Accordingly, by monitoring the current flowing in the voltage
to skin delivering elements circuit, it is possible to set proper
treatment parameters resulting in a desired skin effect and not
causing adverse side effects such as pain, burnings and other. It
was found that resistances above Rhigh correspond to dirty tip
and/or are caused by improper attachment of the tip to the skin. In
both cases, the pulses may cause undesired pain. In order to reduce
the pain, current limiter 704 (FIG. 7) or a control system
immediately cuts the pulse when the resistance is above a certain
pre-set threshold. The control will notify the operator to check
proper attachment of the tip to skin and/or clean the tip.
[0038] FIG. 7 is a schematic illustration of another exemplary
embodiment of the present tip for fractional skin treatment driving
circuit that eliminates pain sensation and electric shock that
could affect the treated subject. A sensing element 700 senses the
current flowing in the immediate to the tip for fractional skin
treatment circuit. The sensing and sampling may be continuous or
performed at very short time intervals, for example every few tens
of a microsecond. A fast response RF induced current limiter 704 in
course of operation sets a maximum to the current which flows into
the skin. Immediately, with the current increase above a pre-set
value, it operates a fast switch 708 that closes the circuit
directing the current to an energy absorbing element 712, which
dissipates the excessive energy as heat. The RF energy absorbing
element 712 may be packaged or even be a part of current limiter
704. The switch may be a bi-polar transistor, a MOSFET switch, an
IGBT switch or any other fast switch. If the switch is operated in
the analogue regime, it can stabilize the current to the pre-set
maximum value or below that value. The energy absorbing element 712
may be a bank of resistors, bridge of diodes or similar devices.
This protects the subject from electric shock, skin burn, and other
potential treatment side effects.
[0039] FIG. 1 illustrates a prior art tip, which is basically a
symmetrical tip including even and uneven arrays of electrodes.
FIG. 8 is a schematic illustration of an exemplary embodiment of
the present RF applicator tip for fractional skin treatment that
eliminates or significantly reduces the "competition" between the
tip electrodes. Although the tip 800 is for a bi-polar treatment,
it is an asymmetrical tip. Tip 800 has one or more (a cluster)
large "ground" electrodes 804 located in the peripheral area of
substrate 808 and connected to one RF output port. All of the
miniature discrete, voltage to skin application elements 812
protruding from the substrate surface and terminated by dome type
shapes are connected together to the other port of the RF output
transformer. The particular tip has 64 elements, although other
designs with different number of elements are possible. The further
advantage of this solution is that the resistance variations may be
more obvious since there is no competition between the electrodes
located in the even and uneven contact strips, thus preventing the
undesired partial imprint on the skin and the accompanied pain. The
area of the voltage to skin application elements 804 is
substantially larger than the area of the terminated by dome type
shapes elements 812. Tip 800 possesses a mechanism 820 enabling
quick removal and attachment of the tip to the applicator and RF
voltage connection elements (not shown).
[0040] The electric scheme and the tip structure disclosed above
eliminate electrical shock feeling, reduce or eliminate the pain
associated with the treatment and increase the treatment efficacy.
The isolating transformer is located very close to the application
tip to reduce ground currents through parasitic capacitance. Series
capacitors located in the path to the electrodes filter out low
frequency currents which are produced by plasma formed at the
electrodes and fast current limiter sets a maximum to the current
which flows into the skin.
[0041] Typical operating parameters of the apparatus are:
[0042] Voltage on high impedance load: 850 Vp-p
[0043] 5 Current: 50-400 mA
[0044] Pulse length: 10-150 msec
[0045] Energy per pulse (Actual energy delivered to the skin):
0.5-4 J, more typical 1-2 J.
[0046] Frequency of the RF: 1 MHz, although 100 kHz up to 10 MHz
may be considered.
[0047] Typical control parameters for the asymmetrical tip, 64
pins, 250 microns each:
[0048] High resistance limit for cutting of pulses for pain
reduction: >1600 Ohms (for 64 pins asymmetrical tip)
[0049] Low resistance limit for cutting low efficiency pulses:
<200 Ohms (for 64 pins asymmetrical tip)
[0050] Range of resistance where control adds energy to dry the
skin: 200-600 Ohms (for 64 pins asymmetrical tip)
* * * * *