U.S. patent number 3,651,813 [Application Number 04/870,399] was granted by the patent office on 1972-03-28 for cryosurgical delivery and application of liquefied gas coolant.
This patent grant is currently assigned to Brymill Corp.. Invention is credited to Michael D. Bryne.
United States Patent |
3,651,813 |
Bryne |
March 28, 1972 |
CRYOSURGICAL DELIVERY AND APPLICATION OF LIQUEFIED GAS COOLANT
Abstract
A self-contained, mobile, compact, untethered cryosurgical
instrument is provided in which liquefied gas coolant in a
container with heat conducting walls is pressurized by ambient
temperature for delivery to a lesion to be necrotized. The coolant
is discharged in a controlled spray in one embodiment; the delivery
tube includes a vent tube coaxially spaced therefrom in other
embodiments. Freezing to tissue is overcome with "Teflon"
coatings.
Inventors: |
Bryne; Michael D. (Vernon,
CT) |
Assignee: |
Brymill Corp. (Vernon,
CT)
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Family
ID: |
25355300 |
Appl.
No.: |
04/870,399 |
Filed: |
October 8, 1969 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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683351 |
Nov 15, 1967 |
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Current U.S.
Class: |
128/200.14;
606/22 |
Current CPC
Class: |
A61B
18/0218 (20130101) |
Current International
Class: |
A61B
18/00 (20060101); A61B 18/02 (20060101); A61b
017/36 (); A61m 011/04 () |
Field of
Search: |
;128/303.1,173R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Marshall, Principles and Practice of Operative Dentistry, J. B.
Lippincott Co., Philadelphia, 1901, pp. 578-581 .
Zacarian, S. A. Cryosurgery in Dermatology. In International
Surgery, Vol. 47, No. 6, June 1967, pp. 528-534.
|
Primary Examiner: Pace; Channing L.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a division of my copending application Ser. No.
683,351, filed on Nov. 15, 1967.
Claims
Having thus described typical embodiments of the invention, that
which I claim as new and desire to secure by Letters Patent of the
United States is:
1. A cryosurgical instrument adapted for use in the freezing of
tissue, comprising:
a nozzle; and
a source of pressurized liquified cryogenic gas coolant having a
boiling point of less than -100.degree. C. including means for
delivering said coolant in substantially liquid phase to said
nozzle at a pressure relating inversely to the internal diameter of
said nozzle to provide a spray of the coolant emerging from said
nozzle in substantially the form of atomized liquid.
2. A cryosurgical instrument according to claim 1 wherein:
said coolant comprises nitrogen; and
the pressure (p) of said source is related to the diameter (d) of
said nozzle, in mils, by p = P- 17.6 (Log.sub.10 d-1.6) for values
of P between 1 psi and 9 psi above atmospheric pressure.
3. A cryosurgical instrument according to claim 1 wherein:
said coolant comprises nitrogen; and
the pressure of said source bears a relationship to the diameter of
said nozzle included in the range of relationships substantially
within the vertically hatched portion of FIG. 8.
4. A cryosurgical instrument according to claim 1 wherein:
said coolant comprises nitrogen; and
the pressure of said source bears a relationship to the diameter of
said nozzle included in the range of relationships substantially
within the horizontally hatched portion of FIG. 8.
5. A cryosurgical instrument adapted for use with liquid nitrogen
and capable of delivering nitrogen in substantially the form of
atomized liquid, comprising: a nozzle; and means for delivering
nitrogen in substantially liquid form to said nozzle, said means
delivering nitrogen to said nozzle at a pressure related to the
internal diameter of said nozzle to provide a spray of nitrogen
emerging from said nozzle in substantially the form of atomized
liquid.
6. A cryosurgical instrument according to claim 5 wherein:
the internal diameter of said nozzle is between 50 mils and 8 mils;
and
said means is adapted to deliver nitrogen to said nozzle at a
pressure of from 1 psi to 30 psi above atmospheric.
7. A cryosurgical instrument according to claim 6 wherein:
said means delivers nitrogen to said nozzle at a pressure related
to said diameter to provide a spray of nitrogen emerging from said
nozzle in substantially the form of atomized liquid.
8. A cryosurgical instrument according to claim 5 wherein:
said means is adapted to deliver nitrogen at a pressure (p), in psi
above atmospheric pressure, related to the diameter (d), in mils,
of said nozzle by p = P- 17.6 (Log.sub.10 d- 1.6) for values of P
between one psi and nine psi above atmospheric pressure.
9. A cryosurgical instrument according to claim 5 wherein:
said means is adapted to deliver nitrogen to said nozzle at a
pressure (p) of from 1 psi to 30 psi above atmospheric; and
the internal diameter (d) of said nozzle, in mils, is given by d =
40 .times. 10.sup.-.sup.0.06 (p - P) for values of P between 1 psi
and 9 psi.
10. A cryosurgical instrument according to claim 5 wherein:
said means is adapted to deliver nitrogen to said nozzle at a
pressure which bears a relationship to the internal diameter of
said nozzle included in the range of relationships substantially
within the vertically hatched portion of FIG. 8.
11. A cryosurgical instrument according to claim 5 wherein:
said means is adapted to deliver nitrogen to said nozzle at a
pressure which bears a relationship to the internal diameter of
said nozzle included in the range of relationships substantially
within the horizontally hatched portion of FIG. 8.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to cryosurgery, and more particularly to the
delivery and application of liquefied gas coolant to living tissue
in order to necrotize the same.
2. Description of the Prior Art
It has long been known in the prior art to use liquefied gas (such
as helium, nitrogen, oxygen, air, freon, zenon, carbon dioxide,
etc.) to freeze healthy or diseased tissue, and thereby necrotize
the tissue. For instance, one well-known use of liquefied gas in
cryosurgery is the removal of lesions, both on the skin or
internally. Usually, the object is to remove the lesion by
destroying the tissue; in other cases, the object is the
destruction of the tissue while maintaining adjacent portions of
the tissue structure in place, such as in the walls of vital
organs. As used herein, lesion means both diseased and healthy
tissue which is to be frozen; the destruction of lesions includes
removal of healthy tissue for cosmetic purposes, and killing of
tissues as a complementary modality to surgical procedures.
Heretofore, the liquefied gas has been delivered through an
insulated tube to an applicator. The delivery of the liquid to the
applicator has been accomplished by using pressure within the
reservoir containing the liquid to force the liquid out of the
reservoir. The creation of pressure within the reservoir has been
achieved in several different ways. A first and perhaps most widely
used method of creating pressure in a liquefied gas container is to
place an electric heater within the reservoir of the liquid,
thereby raising the temperature of the liquid to its boiling point
so that a gas pressure is created. The liquefied gas, as it
vaporizes, creates sufficient pressure to force the liquid out of
the reservoir. A different type device utilizes external gas
pressure (such as a separate tank of compressed dry air, or other
suitable source of compressed gas) to force the liquefied gas
coolant out of the reservoir.
All of the before described devices require connections either to a
source of fluid pressure or to electrical energy, or on the other
hand, are bulky due to the need of a heat exchanger or batteries.
Additionally, the need for adjunct equipment makes such devices
expensive, complex and cumbersome. Such devices are not well
adapted to portable office use for small dermatological
applications, nor for certain internal applications which involve
small spaces or tortuous routes. Furthermore, cumbersome devices of
the type described tend to absorb too much space in already
overcrowded operating rooms.
Another characteristic of previously known cryosurgical devices is
the need to have a long delivery tube which must be insulated in
order to achieve an adequate percentage of liquid nitrogen
delivered to the application-end (the distal end) of the device.
The insulated delivery tubes which have been found to be practical
in the prior art usually comprise coaxial evacuated Bellows-type
tubing, which is usually comprised of stainless steel. Therefore,
these tubes are quite stiff and offer substantial resistance in
mobility to the surgeon using the device. It can readily be
understood that it is essential that the surgeon be able to
position the device very accurately in order to freeze the selected
area without freezing adjacent areas. For instance, a lesion on an
eyelid presents a near probability of doing great damage to the eye
unless precision application is possible. Therefore, the
positioning of the equipment relative to the patient is critical.
Moreover, many lesions are of a very complex shape, and must be
addressed from different angles in order to adequately treat all of
the portions thereof. Furthermore, anatomical irregularities of the
body relative to the positioning of the lesion make mobility of
instrumentation critical. It is therefore apparent that the stiff
delivery tubes known to the prior art hinder the surgical usage of
the equipment, and render it difficult to provide adequate lesion
removal. Certain other devices have attempted to overcome stiffness
by using flexible plastic tubing; however, at temperatures capable
of freezing human tissue, these devices become stiffer than the
evacuated metallic types, and are therefore relatively useless.
So great is the problem with insulated delivery tubes that various
devices have been composed for overcoming the need for such
delivery tubes. One such device provides liquid nitrogen in a probe
handle, and utilizes an external source of compressed gas which
will not freeze much above liquid nitrogen temperature to be cooled
by the nitrogen and mixed with nitrogen gas so as to provide a cold
gas application to the tube and applicator tip which is cooled
sufficiently so that when the applicator tip is applied to a
lesion, it will freeze it. However this device, though providing a
flexible tube, is nonetheless tethered and the device itself is so
large, relative to the amount of nitrogen in it, that its
application is limited to the removal of extremely small lesions.
Furthermore, the device is so complex as to render it extremely
difficult to construct, and it may also have a tendency for
unreliable operation.
A different problem in the cryosurgical freezing of tissue is a
need for good heat exchange. Most devices known to the prior art
utilize liquid nitrogen to cool a probe, and the probe in turn is
applied to the lesion. This has taken a variety of forms, and in
the more sophisticated cryosurgical apparatus known to the prior
art, the probe applicator tip is sprayed with liquid nitrogen fed
through the inner tube of a coaxial tube assembly, the outer tube
venting the nitrogen gas away from the area of the applicator
tip.
A severe limitation on devices of the prior art is that the heat
removing applicator has been rigid and unable to conform to the
contours of living tissue. Additionally, the amount of liquid
coolant required to cool an applicator is so great that large
lesions could not be accommodated except with huge, cumbersome
apparatus. Further, large lesions require numerous applications of
prior art devices in order to cover the area with an adequate
degree of freezing. Thus, the prior art is inadequate in terms of
application means and techniques in cryosurgery.
The coaxial systems of the prior art including liquid feed, gas
vent lines and vacuum insulation are impossible to manufacture
below a given size. As the diameter of the coaxial tubing is
reduced, the ability to destroy tissue is markedly decreased.
Therefore, such devices are extremely limited in the nature and
size of lesions that can be removed thereby. It is therefore
apparent that the use of probe-type cryosurgical instruments known
to the prior art is severely limited in cases where the tissue that
is to be destroyed is enclosed within a body cavity, such as the
larynx, pharynx, bladders, bronchi or other locales where the
cryosurgical instrument must be used in conjunction with other
instrumentation, such as a laryngoscope, a broncoscope, or a
cystoscope.
A related problem is the need to provide electrical heating to the
probe tip in any case where wet tissue (which includes most
nondermatological applications of the device) is being frozen. This
is required because the probe tip actually freezes to the tissue
due to the formation of ice at the surface of the tissue which is
being destroyed. In order to remove the device from the tissue it
is necessary to melt the ice which binds the device to the tissue.
Therefore, such devices require not only a coaxial combined feed
and vent tube assembly, but also require the presence of an
electrical heater and the electrical conducting lines in the probe
tip itself. This not only further complicates the apparatus, but
requires an increase in size such that all of the problems
described hereinbefore are further compounded.
SUMMARY OF THE INVENTION
Objects of the invention include:
Application of substantially liquid, nonsplashing liquefied gas
coolant to living tissue for the necrotization thereof;
Provision of means for confining to a localized area, liquefied gas
coolant in the application thereof to living tissue;
Provision of cryosurgical applicators capable of insertion into,
and routing adjacent to, living tissue without the freezing of or
adherence to the tissue;
Cryosurgical destruction of wet tissue without the freezing of
instruments thereto;
Provision of a cryosurgical instrument capable of implementation
with application tubes as small as 10 thousandths of an inch in
diameter.
In accordance with the present invention, there is provided a
cryosurgical application and delivery instrument having a coating
of nonsticking fluorocarbon, such as "Teflon," which substantially
eliminates sticking of the instrument to tissue with which it comes
in contact.
In accordance further with the present invention, liquefied gas
coolant is delivered in the liquid phase to a nozzle, the diameter
of which is chosen in conjunction with the pressure of the
liquefied gas coolant source so as to atomize the coolant as it
leaves the nozzle, the coolant therefrom partially vaporizing so
that it neither splashes nor obscures the field of application by
over vaporization. A further aspect of the invention is that by
delivering liquid, rather than vapor, to the lesion, a much greater
depth and area of freezing can be achieved, and a given amount of
freezing takes less time while still maintaining precise control of
the affected tissue.
The forgoing and other objects, features and advantages of the
present invention will become more apparent in the light of the
following detailed description of preferred embodiments thereof as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially sectioned, broken away side elevation view of
one embodiment of the present invention adapted for unvented
application of cryosurgical coolant;
FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1;
FIG. 3 is a partially sectioned, broken away side elevation view of
another embodiment of the present invention including venting of
vapor from the coolant application area;
FIG. 4 is a top plan view of the embodiment OF FIG. 3;
FIG. 5 is a partially broken away end elevation view of the
embodiment of FIGS. 3 and 4;
FIG. 6 is a partial sectioned elevation view of the detail of
coaxial delivery and vent tubes in accordance with the present
invention;
FIG. 7 is a pictorial illustration of the application of atomized
coolant utilizing the embodiment of FIGS. 1 and 2;
FIG. 8 is a chart illustrating the ranges of pressures which will
deliver liquid nitrogen coolant with neither spurting nor splashing
for various sized nozzles;
FIG. 9 is a sectioned elevation view of an applicator tip known to
the art;
and FIG. 10 is a side elevation illustrating coating of the
delivery tube.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, one embodiment of a cryosurgical liquefied gas
coolant delivery and application system in accordance with the
present invention comprises a container 20 within which the
liquefied gas coolant is placed. The container 20 is threaded (22)
so as to releasably engage a cover assembly 24, which has matching
threads. A delivery tube 26, fitted through a hole 27 in the cover
assembly 24, has a bend 28 therein so as to provide an external,
substantially horizontal portion 32. At the external end of the
tube 26 there is a fitting 34, which may comprise any suitable
compression or flared fitting known to the art, a number of which
are commercially available. This fitting may have any suitable
application means 36 attached thereto; in accordance with one
aspect of the present invention, the application means 36 comprises
a nozzle formed by drilling a suitable hole (as described with
respect to FIGS. 7 and 8 hereinafter) in a blind cap or plug, to
provide a controlled spray.
The cover assembly 24 has a pressure control vent hole 38 therein,
which provides gaseous communication with a passage 40 in a handle
assembly 42. The handle assembly 42 is affixed to the cover
assembly 24 by any suitable means such as screws 44 (see also FIG.
2). The passage 40 joins and is axially aligned with a further
passage of a larger diameter 46. Within the passage 46 is a passage
closure means 48 which may comprise a cylindrical barrel portion 50
being conical at one end 52, and having a cap portion 54 at the
other end. The closure means 48 may be resiliently urged to the
left in FIG. 1 by any suitable means such as a spring 56, one end
of which is inserted in a hole 58 within the closure means 48. The
other end of the spring 56 may be fastened to the handle assembly
42 by a screw 60. With the closure withdrawn to the left (as seen
in FIG. 1), the passage 46 is in communication with a passage 62
which passes any gas therein out of a port 64 to atmosphere.
In operation, the container 20 is filled with liquefied gas
coolant, such as liquid nitrogen, to a suitable level. The
container 20 may consist of metal or glass, or other suitable
material capable of conducting heat from ambient atmosphere to the
liquid therein. This causes some of the liquid to boil, resulting
in the generation of gas. So long as the closure means 48 is left
in its rest position (to the left, as shown in FIG. 1), the gas is
vented to atmosphere through the passages 40, 46, 62. However, when
delivery of coolant to tissue is desired, the nozzle 36 may be
directed by the surgeon (holding the instrument by the main shank
portion 65 of the handle assembly 42) toward the tissue, and the
surgeon may push the closure means 48 (to the right in FIG. 1),
thus causing the conical end 52 to sealably engage a chamfered
surface 66 at the intersection of the passages 40, 46, 62. It has
been found that relatively light force applied by the surgeon's
thumb to the button end 54 of the closure means 48 will positively
block the vent passages 40, 46, so that pressure will build up
within the container 20. This pressure forces liquid coolant into
the delivery tube 26 and through the nozzle 36.
In order to prevent the loss of pressure within the container 20,
and to prevent vapor from escaping about the cap and handle
assemblies 24, 42, suitable seals are provided. A gasket 68 (FIGS.
1 and 2) provides a seal between the container 20 and the cap
assembly 24. The gasket 68 may be fitted tightly into the cap
assembly 24 as is well known in the art. It may be of any suitable
material, depending on the temperature of the liquid coolant
chosen; cotton, cork and other natural products (except rubber) as
well as silicon rubber and "Teflon" are suitable materials even at
liquid nitrogen temperatures.
The delivery tube 26 is preferably welded to the hole 17 so as to
seal the joint as well as to give structural support to the tube
26. However, other modes of attachment and sealing may be
utilized.
To provide a seal at the joinder 70 of the handle assembly 42 with
the cap assembly 24, some modicum of sealant is required. For
instance, a thin sheet of "Teflon," coated on each side with
silicon (vacuum) grease, works quite well. Other means may be used
to suit any design criteria in accordance with the skill of the
art.
The embodiment of the invention thus described with respect to
FIGS. 1 and 2 comprises a completely self-contained, untethered
cryosurgical instrument. It can be directed toward a field of
application from many angles without requiring repositioning of the
subject, or the rolling around the room of a console (as is true of
prior devices). It can, by suitable choice of length of delivery
tube 32, be used to reach into small cavities, or by bending the
delivery tube 32 (which is not possible with prior devices), be
used to reach around corners or traverse tortuous routes.
A second embodiment of the present invention is adapted for use
where venting of coolant vapor from the point of application is
required. As seen in FIGS. 3-5, this is identical to the embodiment
of FIGS. 1 and 2 except that a vent tube 100 is provided coaxially
with and externally of the delivery tube portion 32. The vent tube
100 may be press-fit into a passage 102 in the handle assembly 42,
with an extension 104 of the passage 102 venting the tube 100 to
atmosphere through the main shank portion 65 of the handle assembly
42. Note that the vent passages 62 (FIGS. 1 and 2) and 104 (FIGS.
3-5) vent cold vapor away from the treatment area, and downwardly
so as not to injure the patient, nor to injure nor obscure the
vision of the surgeon.
The delivery tube 26 may be assembled to the vent tube 100 by
slotting the vent tube 100 at the bottom thereof to the left of the
delivery tube portion 30 (as seen in FIG. 3). The tube 100 may
thereafter be welded shut, or may remain slotted, since the tube 26
and the handle assembly 42 are sealed with respect to the cap
assembly 24, and no leakage will take place therebetween, as
described hereinbefore with respect to FIGS. 1 and 2.
The apparatus of FIGS. 3-6 may have a fitting 110 thereon so as to
permit connecting chambers of the type described and claimed in my
prior copending application, Ser. No. 886,260, filed Dec. 18, 1969,
entitled CRYOGENIC APPLICATION CHAMBERS AND METHODS, attached
thereto, or regular applicator tips 112 known to the prior art, of
the type illustrated briefly in FIG. 9 may be threaded thereon. On
the other hand, the invention may also be practiced by fastening
any suitable application means to either or both of the tubes 32,
100, in any suitable way, or by forming the end of tube 100 in a
suitable fashion as an applicator. The pertinent fact is that the
invention may use a non-vented spray, or vented application of
various types.
As seen in FIG. 6, very small coaxial tubes may be spaced from one
another, according to the invention, by a thin thread or filament
108 wound about the inner tube 32. The thread or filament may be
stranded, or may be a monofilament. It may be of any suitable
material such as cotton (or other natural fiber) or suitable
plastic or fluorocarbon. A poor heat conductor is preferably
selected. This allows very close tolerances while maintaining
independent spacing of the two tubes.
Referring now to FIGS. 7 and 8, the spraying of atomized coolant
directly on a lesion is illustrated. This is quite advantageous
when a large area is to be treated due to the high rate of heat
exchange and the mobility of the application. It is also quite
advantageous in treating lesions of irregular shape. One problem
with this type of application which is overcome by the present
invention is that splashing of the coolant can result in freezing
of tissue other than that which it is desired to treat. Even if
tissue surrounding the lesion is protected with cloth or other
covering, a severely cold coolant (such as liquid nitrogen) may
penetrate the covering as a liquid, or heat transfer may take place
through a non-permeable covering. Additionally, splashing results
in a dense and opaque spray or vapor which interferes with the
surgeon's vision of the field of application. On the other hand, if
the coolant leaves the nozzle as a vapor, it does not have a high
cooling capacity, since it is at a temperature higher than the
liquid phase which may exist at temperatures as low as -196.degree.
C. Additionally, the vapor phase does not absorb the heat of
transfer as does the liquid when being vaporized by the heat of the
tissue. Therefore, a very significant degradation of freezing
capacity results when the coolant is ejected primarily as a vapor.
Moreover, if the spray falls between liquid and vapor, spurting of
liquid between periods of vapor may result. This makes it difficult
for the surgeon to judge the isotherm profile achieved during an
application period, and is otherwise difficult and less comfortable
to work with.
These difficulties are overcome by maintaining substantially a
liquid coolant at the nozzle, and by a proper relationship between
the size of the nozzle and the pressure of the coolant. Of course,
unless ideal insulation is used along the delivery tube, some heat
will be absorbed by the coolant as it traverses the tube, and
therefore some of the coolant will vaporize before it reaches the
nozzle. However, by choice of delivery systems, the coolant
delivered to a nozzle can be substantially in the liquid phase (90
percent liquid, for instance).
Referring to FIG. 8, for liquid nitrogen, it has been found that
coolant pressures between 3 pounds and about 15 pounds are
preferred. With coolant pressures in this range, nozzles between
about 15 mils (0.015 inches) and 40 mils give best results in the
relationship set forth in the horizontally hatched (doubly hatched)
area of FIG. 8. For instance, with a 30 mil nozzle, the pressure
should preferably be between slightly over 5 psi and 10 psi (above
atmosphere). If a 9 psi system is being used, then a nozzle size
between about 17 mils and 35 mils should preferably be chosen.
However, the invention may also be practiced to advantage, under
some conditions, utilizing a combination of nozzle size and
pressure which may fall slightly outside of the horizontally
hatched area in FIG. 8. In other words, combinations of pressure
and nozzle size which fall within the vertically hatched area of
FIG. 8 may be advantageous. This depends, at least in part, on the
particular delivery system being utilized. Nonetheless, the
pressures and ranges set forth in the double hatched area
(horizontally hatched area) of FIG. 8 are preferred since these
will provide a proper spray without spurting or splashing. Choice
of too high a pressure for a given size nozzle results in
splashing; too low a pressure results in eratic spurting of
coolant. Similarly, too large a nozzle for a given pressure results
in splashing and too small a nozzle results in spurting. Proper
choice of pressure and nozzle gives a really wet spray which is
soft (it will not splash) and which is uniform and steady (without
spurting). It should be understood that practice of this aspect of
the invention is predicated on there being a flow of significant
liquid, rather than vapor, through the selected nozzle.
As before described, if the coolant is delivered to the nozzle in a
highly vaporized fashion, then the pressure/nozzle characteristics
described hereinbefore and shown in FIG. 8 do not apply.
Additionally, since there is a higher vaporization of the coolant
when a system is first turned on and the walls of the delivery tube
are relatively warm, the optimum adjustment for any given
application will vary somewhat between the time that the system is
started and the time that it establishes a relatively uniform rate
of vaporization of liquid being passed through the delivery tube to
the application area. In other words, when the system is first
started up, more pressure for a given size nozzle or a larger
nozzle for a given pressure may be most advantageous. As the system
cools down, however, so that a very high percentage of liquid is
being delivered to the nozzle, then smaller diameter nozzle and/or
a lower pressure may be utilized. In fact, best results are
achieved by running the system for a short period of time prior to
commencing the application of coolant to tissue, so that the
preferred conditions of the present invention may obtain during the
application of coolant to the tissue as a result of having a
relatively uniform flow of substantially liquid coolant to the
nozzle, with the nozzle and pressure chosen in accordance with the
relationship herein so as to provide a suitable spray in accordance
with the present invention.
A spray obtained by matching of a nozzle to a suitable pressure in
accordance with the present invention permits uniform application
of large amounts of liquid directly to the tissue. This in turn
avoids problems of matching the contour of the tissue being frozen,
and allows freezing of deep and/or wide areas.
The preferred relationship between the pressure of coolant and the
size of the nozzle, for liquid nitrogen, can be expressed
mathematically.
Taking:
d = the diameter of the nozzle in mils;
p = the pressure in the coolant delivery system in psi above
atmospheric;
and P = a constant, such that 3 .ltoreq. P.ltoreq. 8;
then:
d = 40 .times. 10.sup.-.sup.0 06 (p.sup.-P)
or p = P - 17.6(Log.sub.10 d - 1.6)
Thus, given either a diameter or a pressure, one may mathematically
determine a preferred pressure or diameter, respectively, by
selecting a value of P between 3 and 8 and obtaining a result in
accordance with the appropriate relationship expressed above. To
find a range of values, the relationship may be calculated twice,
once for the value of P = 3 and once for the value of P = 8 in the
above expressions. It should be noted that selecting a value of 3
defines the lower left curved portion of the single-hatched,
preferred area of FIG. 8, whereas selecting a value of 8 in either
equation will define the upper right curved portion of the
single-hatched, preferred area of FIG. 8.
I have found that cryosurgical instrumentation frequently sticks to
adjacent tissue with which it comes in contact during an operation.
To overcome this, the various parts which are likely to come into
contact with the body of a patient may be covered or coated with a
non-sticking fluorocarbon, such as "Teflon." As seen in FIGS. 9 and
10, this may comprise a sheath 120 slipped over a portion of the
instrument (such as tube portion 32), or it may comprise a coating
113 applied by any suitable one of a number of techniques known to
the prior art to a portion of the instrument (such as an applicator
112). By this feature of the invention, wet tissue may freeze, but
it will not stick to the fluorocarbon.
Although the invention has been shown and described with respect to
preferred embodiments thereof, it should be understood by those
skilled in the art that the foregoing and other changes and
omissions in the form and detail thereof may be made therein
without departing from the spirit and scope of the invention.
* * * * *