Catheter steerable by directional jets with remotely controlled closures

A catheter is provided with a directional steering capability by one or more jets ejecting fluid from the distal end of the catheter in a radial direction which causes the catheter tip to bend in the opposite direction by reaction force. Actuation of the jet is controlled by a closure valve at the jet orifice, the closure valve being driven by a signal transmitted from the proximal end of the catheter. Preferred signals are either fluid pressure signals or electrical signals.

This invention lies in the field of medical catheters and relates in 
particular to means for steering catheters to direct their distal tips 
into branched or convoluted bodily passages. 
BACKGROUND OF THE INVENTION 
Catheters are widely used in medical procedures, since they provide access 
to internal bodily passages and cavities for both diagnostic and 
therapeutic purposes without surgery. Catheters have proved valuable over 
the years for use in regions of the body such as the heart and coronary 
arteries, the brain, and the genito-urinary tract. 
A critical procedure associated with the use of medical catheters is the 
insertion of the catheter into the body and the placement of the catheter 
tip at the appropriate location. Precise placement of the catheter tip is 
often critical to the success of the function the catheter is intended to 
perform, since the function must often be directed to a highly localized 
region of internal tissue while avoiding areas which are immediately 
adjacent. In addition, bodily passages are often of a very small diameter, 
and the interior wall of the passage is often delicate and susceptible to 
puncture. Steering capability is important, for example, in cardiovascular 
surgery when catheters are used as an alternative to bypass surgery to 
selectively remove plaque from arteries. The use of a catheter in these 
procedures offers significant benefits in terms of lower cost and lower 
risk. Steering capability is of particular importance in procedures 
involving peripheral arteries where plaque or thrombi are to be removed. 
In obstetrics and gynecology, catheters can be used in conjunction with 
dilatation and curettage procedures for the selective removal of excessive 
tissue and cyst growth, and directional control is important here as well. 
The same is true for the use of catheters for the delivery of 
site-specific treatments for ovarian cancer. Directional control is also 
important in urology procedures involving catheters. Examples of such 
procedures are the selective removal of prostate cancer and the treatment 
of urinary tract blockages infections. In certain oncology procedures, 
accurately guided catheters can be used for the selective removal of 
malignant tissue without affecting critical healthy tissue located nearby, 
and for improved biopsy methods, where it is important to reduce the 
incidence of trauma in healthy tissue. In neurosurgery, catheters can be 
used for the removal of intracranial hematomas and similar procedures, and 
precise directional control of the catheters is critical. In radiology, 
close directional control provides imaging and mapping catheters with 
active stabilization within the cardiac chamber. In internal body 
procedures in general, guided catheters are useful for such procedures as 
fluid aspiration to relieve abscesses and localized drug delivery. Other 
procedures and applications where steering capability is important will be 
readily apparent to the experienced medical practitioner. 
Steering mechanisms have been devised for directing the distal tip of the 
catheter in a desired direction by remote control from the proximal end. 
One such mechanism includes a series of wires running the length of the 
catheter body on either side of its central axis and terminating in shims 
or thin strips at the distal end of the catheter. The operator steers the 
catheter by applying tension to one shim relative to the other, thereby 
causing the distal end to curve in the direction of the wire to which 
tension has been applied. The wires and the mechanism at the proximal end 
for selectively applying tension are unwieldy, however, and susceptible to 
breakage. Furthermore, they offer limited directional choice without 
twisting the entire catheter to achieve angular adjustments relative to 
the catheter axis. 
Guidewires are widely used to assist in the placement of catheters in 
locations which are particularly difficult to reach. A guidewire is 
typically of very narrow diameter to fit within the lumen of a catheter. 
This permits the operator to slide the catheter over the guidewire after 
first directing the guidewire to the appropriate location. It also permits 
the operator to remove one catheter and replace it with another without 
removing the guidewire and hence without the cumbersome procedure of 
independently relocating the catheter tip to the region of interest. The 
steering of a guidewire is generally accomplished by constructing the 
guidewire to include a slight curvature at its distal tip, the tip being 
resilient in construction to resume the curvature when relaxed. This 
enables the operator to direct the guidewire tip laterally into branches 
of the vessel. To do this, however, the operator must rotate the guidewire 
from the proximal end so that the tip curves in the desired direction. 
SUMMARY OF THE INVENTION 
The present invention resides in a catheter with a steering capability 
which significantly reduces or eliminates the difficulties enumerated 
above, as well as other difficulties associated with catheter steering 
mechanisms of the prior art. Steering is accomplished by one or more jets 
of fluid at the catheter tip, directed radially outward and causing the 
catheter tip to move in an opposite direction due to the reaction force. 
Preferably, a plurality of jets are included, formed by a series of ports 
distributed around the circumference of the catheter. The bending of the 
catheter tip in any particular direction is achieved by selecting a jet to 
emerge from the opposing side of the catheter to the exclusion of the 
remaining jets. Further directional control can be achieved by using two 
or more adjacent jets so that the reaction force is opposite to the 
combined vector of the jets. 
Fluid is supplied to all of the jets through a single lumen which extends 
the full distance to the catheter's distal end to communicate directly 
with each of the ports. The ports are individually and independently 
opened and closed by closures which are operated by signals transmitted 
from the proximal end of the catheter. The signals to operate the closures 
is transmitted to each closure independently of the remaining closures. 
The signals may be any of various types, the two most prominent being 
pressure signals and electrical signals. Closures actuated by pressure 
signals include pivoting closures and sliding closures, where pressure 
differentials govern the position of the pivot or of the sliding member. 
The same types of closures, and particularly sliding closures, may be 
actuated by electrical signals, by means analogous to electrically 
operated valves. 
For embodiments in which the closures are operated by pressure signals, 
fluid pressure is transmitted to each closure independently of the 
remaining closures and of the fluid to the lumen supplying the jets 
themselves. In some of the preferred embodiments of the invention, the 
closures are operated by levers, and the fluid pressure which drives each 
closure imposes a pressure differential across the lever. The opening and 
closing of the closure is thus controlled by the imposition and direction 
of the pressure differential. The levers are part of the closure structure 
and are likewise located at the distal end of the catheter. Independent 
transmission of fluid pressure to each lever is achieved by individual 
lumens traveling the length of the catheter, each of these lumens being 
independent of the lumen supplying the jets. To distinguish among the 
various lumens, the term "primary lumen" is used in this specification to 
refer to the lumen supplying the jets, while the term "secondary lumens" 
is used to refer to the lumens supplying the fluid pressure which controls 
the closures. 
The actuation of any single jet, and the selection among the various 
directional jets when a plurality of jets is present, is thus achieved by 
closures positioned at the sites of the jets themselves, i.e. , at the 
distal end of the catheter, while the operation of these closures is 
achieved by remote control from the proximal end of the catheter. This 
offers a number of advantages to the operation and effectiveness of the 
directional control. For example, closures arranged and operating in this 
manner permit a quick response to signals from the proximal end of the 
catheter for changes of direction. Furthermore, the use of a single lumen 
supplying all of the jets rather than a series of lumens to supply each 
jet. individually permits one to use a jet supply lumen of a larger 
diameter without increasing the outer diameter of the catheter. With a 
larger diameter lumen, any frictional loss of jet fluid as the fluid flows 
the length of the catheter is substantially reduced. Still further, the 
control of the closures through secondary lumens which are separate from 
the primary lumen used for the jet supply permits the closures to be 
operated by pneumatic pressure, which can be transmitted more quickly and 
modulated with a faster response than liquid pressure as is preferably 
used in the jets themselves. 
In embodiments of the invention that entail the use of pneumatic or other 
fluid pressure to actuate the closures, the supply of the fluid pressure 
to the individual closures on a selective basis is achieved by a series of 
valves which are operatively connected to the secondary lumens at the 
proximal end the catheter. The valves are individually controlled in any 
of a variety of ways known to those skilled in the art, and their 
selection may be conveniently governed by a manually or electronically 
operated directional selector. 
The term "fluid" is used herein to include both gases and liquids. One or 
the other will be preferred in specific applications, depending on the 
region of the body into which the catheter is to be directed. 
The term "catheter" is used herein to include both functional catheters and 
guidewires. The invention thus extends to guidewires whose sole purpose is 
to be directed to a particular situs in a bodily vessel and once at that 
situs to serve as a guide for insertion of a functional catheter to the 
same situs. The invention likewise extends to functional catheters 
themselves which may be used without a separate guidewire, the functional 
catheters containing any of a variety of functional elements for either 
diagnostic or therapeutic purposes. The catheters of this invention may 
thus contain additional lumens serving functions unrelated to the 
directional jets, or additional transmitting elements for transmitting 
signals such as optical or electronic signals from the distal end of the 
catheter to the proximal end, or both lumens and transmitting elements. 
Additional features and advantages of the invention will be apparent from 
the description which follows.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
While the invention is broad in scope and defined as indicated above by 
certain parameters each of which entails a range of variations, the 
invention is best understood by detailed descriptions of specific 
examples. Five such examples are shown in the drawings. 
The first example is depicted in FIGS. 1 and 2. FIG. 1 shows the distal end 
of the catheter in this example is shown in disassembled and exploded 
form. The catheter body is formed in three parts--an elongate shaft 11 
which comprises the bulk of the catheter, a ring 12 which abuts the 
elongate shaft at the distal end of the shaft, and a sleeve 13 which 
encircles both the end of the shaft 11 and the ring 12, securing the ring 
to the shaft. Construction of the catheter in three parts promotes ease of 
manufacture, and permits a high degree of precision in the formation of 
the lumens, ports and closures, as discussed below, on a miniature scale. 
The distal end 14 of the shaft 11 shows the arrangement of the lumens, each 
of which extends the full length of the shaft. The primary lumen 15 is 
coaxial with the shaft, i.e., it shares a common central axis with the 
shaft. The primary lumen 15 has the largest cross-sectional area of all 
lumens in the shaft. The secondary lumens 16 in this example are four in 
number, distributed around the periphery of the primary lumen and equally 
spaced. Each of these secondary lumens is of considerably smaller 
cross-sectional area than the primary lumen. 
The cross-sectional geometries of the lumens are not critical and may vary. 
The primary lumen preferably has a circular cross section for purposes of 
maximizing the ratio of cross section to perimeter length and thereby 
minimizing the shear force on fluid passing through the lumen. This will 
minimize the pressure loss of the fluid along the length of the catheter, 
since the fluid will typically be a liquid such as saline. The secondary 
lumens will function effectively with a flattened or oblong cross section, 
which will permit them to transmit pressure adequately while still leaving 
a large segment of the catheter cross section for the primary lumen. Since 
the pressure transmission fluid in the secondary lumens remains 
substantially static regardless of the pressure, there is less of a 
concern in regard to fluid friction and pressure loss than in the primary 
lumen. 
The number of secondary lumens and their arrangement around the primary 
lumen, and consequently the number and arrangement of jets at the distal 
end of the catheter, as described below, may vary. The catheter will 
function in accordance with the invention with as few as one secondary 
lumen and associated jet. Such a jet would produce a reaction force in one 
direction only. Changes of direction are then accomplished by rotating the 
catheter from its proximal end. In most applications, however, best 
results will be obtained with a total of 3 to 12 secondary lumens and 
associated jets, spaced at substantially regular intervals. In preferred 
constructions, the lumens and jets will number from 4 to 8. The lumens may 
be spaced apart from each other at regular intervals, or combined in pairs 
which are spaced apart at regular intervals, or other similar 
arrangements. The arrangement, in any event, will be one which permits a 
selection of any single jet or pair of adjacent jets to produce a reaction 
force in any desired direction without rotation of the catheter. 
The ring 12 contains the lateral apertures which form the jets, as well as 
the closures which open and close the jets. These elements and their 
operation are best seen in the enlarged section of the ring as shown in 
FIG. 2. The central opening 21 of the ring is aligned with and open to the 
primary lumen 15 of the catheter shaft. The outer wall 22 of the ring 
contains the apertures 23 which form the jets, ejecting fluid radially 
outward. The sleeve 13 which fits over the ring and the catheter shaft 
(FIG. 1) contains further apertures 25 which are aligned with the 
apertures 23 in the ring when the parts are assembled. In the embodiment 
shown in these drawings, the ring apertures 23 are four in number, as are 
the sleeve apertures 25, one corresponding to each of the secondary 
lumens. Also in this embodiment, the ring apertures 23 are rectangular 
slits which open on one face of the ring (in this case the distal face 
27). 
One closure 28 is associated with each ring aperture, and as shown in FIG. 
2, the closures are separated by partitions 29. Each closure is formed as 
a lever 30 with a fulcrum 31 at one end and a stopper 32 at the other. 
Pivoting of the lever occurs about a pivot axis which passes through the 
fulcrum 31 in the direction perpendicular to the plane of the Figure and 
thereby parallel to the longitudinal axis of the catheter. The stopper 32 
is aligned with the ring aperture 23 and is shaped to seal off the 
aperture when lowered into it. Attached to the lever at a location between 
its two ends is a hook 33 which is received in a recess 34 within which 
the hook travels back and forth in approximately the radial direction of 
the ring as the lever pivots. In its raised position (the position shown 
in the drawing), the hook 33 engages a complementary hook 35 which extends 
inward from the outer wall 22 of the ring and serves as a stop for the 
range of motion of the mobile hook 33. The complementary contacting 
surfaces of these hooks also serve as a seal against the passage of fluid 
when the hooks are engaged. 
The portion of the lever extending from the fulcrum 31 to the hook 33 
together with the facing portion of the outer wail 22 of the ring form an 
enclosure 36. When the parts are assembled, the enclosure 36 is enclosed 
at its proximal end by the distal end 14 of the catheter shaft 11 (see 
FIG. 1), and at its distal end by a shoulder 37 at the distal end of the 
sleeve. Each of these enclosures 36 is in axial alignment with one of the 
secondary lumens 16, whose opening is shown in dashed outline in FIG. 2. 
When the pressure in the secondary lumen 16 exceeds the pressure in the 
primary lumen 21 to cause a pressure differential across the lever 30, the 
enclosure expands until the hooks 33, 35 engage, and the lever is pushed 
outward toward the center of the ring. This movement of the lever in turn 
unseats the stopper 32 from the aperture 23. When the pressure in the 
secondary lumen is released, the lever returns to its original position, 
reseating the stopper against the aperture. The direction of motion of the 
lever and hence the stopper is indicated by the arrows 39, 40. 
Return of the stopper to the seated position against the aperture may be 
achieved by a reverse pressure differential created by lowering the 
pressure in the secondary lumen below that in the primary lumen. 
Alternatively, the material of construction of the lever 30 and/or its 
shape and that of the fulcrum may be selected or designed to cause the 
lever to return to the closed position upon the relaxation of forces in 
contact with it. The stopper would thus automatically reseat upon 
relaxation of the pressure in the secondary lumen. The ability to reseat 
independently may be enhanced if the contacting hooks 33, 35 permit a slow 
leakage of the pressurization fluid past them, thereby releasing the 
pressure in the enclosure 36 when the supply pressure is removed. 
When the stopper 31 is seated against the aperture in this example, the 
seating is enhanced by angled lateral surfaces 38 on the stopper. These 
angled surfaces amplify changes in the width of the opening relative to 
the lowering or raising of the stopper. 
The closures 28 shown in FIGS. 1 and 2 thus act in response to pressure 
signals transmitted through the secondary lumens 16, the pressure signals 
being periods of high or low pressures relative to the pressure of the jet 
fluid in the primary lumen 15, the periods being of controlled duration. A 
high pressure in one secondary lumen will unseat the stopper 32 and turn 
on the associated jet, whereas a low pressure will close the stopper and 
turn off the jet. The independent transmission of these pressure signals 
permits independent operation of the closures, and jets are emitted 
selectively as desired to achieve the directional steering of the catheter 
tip by reaction force. 
In the embodiment shown in FIG. 2, the lever 30 and the connecting fulcrum 
31 where the lever is joined to the outer wall 22 of the ting is 
preferably constructed and shaped such that the stopper 32 is seated in 
the aperture 23 in the absence of a pressure differential. This is a 
"normally-closed" closure. For normally-closed closures in general, 
positive pressure signals are needed to activated the respective jets. As 
an alternative to the structure shown in FIGS. 1 and 2, the fulcrum of the 
closure (and hence its point of attachment to the ting 22) may be situated 
in the center of the lever, with the enclosure 36 on one side and the 
stopper 32 on the other. A positive pressure in the secondary lumen 16 
will then close the stopper rather than open it, and the closure will be 
"normally-open" rather than "normally-closed." 
Further alternatives are those in which the lever 30 is positioned further 
toward the outer wall 22 of the ting, placing the enclosure 36 between the 
secondary lumen 16 and the outer wall 22. This will require an additional 
partition along the inside rim of the ring to complete the enclosure. Here 
as well, the fulcrum will either be at the center of the lever or at one 
end. Alternatives to the use of a lever, although still operating in 
response to pressure signals transmitted along the length of the catheter, 
may also be devised. The stopper may for example be an inflatable bladder 
positioned to close the aperture only when inflated. Still further 
constructions and arrangements utilizing the underlying concepts of this 
invention will be apparent to those skilled in the art. 
The ring 12 with its lateral apertures and closures can be manufactured in 
a variety of ways. Micromachining methods such as those used in the 
fabrication of semiconductor chips are particularly useful. Examples are: 
(1) Laser micromachining of a blank disk to form the various openings and 
contours by etching or ablation; 
(2) Thick film deposition, i.e., the deposition of multiple layers of 
particles on a substrate through a mask, using the process of physical 
vapor deposition, followed by removal of the layers from the substrate and 
the mask; 
(3) Chemical vapor deposition over a substrate, again through a mask; 
(4) Ion vapor deposition, again through a mask; and 
(5) Metal plating, using selective buildup methods. A variety of substrates 
may be used for the deposition and plating procedures. A preferred 
substrate is silicon. 
In certain embodiments of the invention, the catheter contains functional 
elements either for the transmission of diagnostics and sensor signals 
from the distal end to the proximal end of the catheter, or for performing 
a therapeutic function at the distal end, or both. The functional element 
may be mounted on an axial shaft 41 as shown in FIG. 3, passing through 
the primary lumen 15, or it may itself be a separate lumen 42 as shown in 
FIG. 4, either coaxial with or offset from the primary lumen 15. For 
signal transmitting purposes, the functional element may be a radiopaque 
marker, a fluoroscopic contrast agent retained in a reservoir such as a 
microballoon, an optical fiber, or an ultrasonic transducer. For 
therapeutic purposes, the functional element may be a cutting blade, an 
abrading element such as a grinding burr, a laser ablation element, an 
angioplasty balloon or simply a lumen for delivering a therapeutic fluid 
which may be either a drug or an abrading solution or slurry. Other 
possibilities will be readily apparent to those skilled in the art. 
FIGS. 5 and 6 represent an embodiment of the invention which is similar in 
certain ways to the embodiment shown in FIGS. 1 and 2, but differs in the 
direction of rotation of the strip containing the lever and closure. 
The catheter 51 has a central passage or primary lumen 52 enclosed at the 
distal end by a ring 53. Each jet is formed by a pair of radially aligned 
apertures 54, 55 on either side of a chamber 56 formed within the wall of 
the ring 53. Inside the chamber is a lever arm 57 adjoined to the internal 
walls of the chamber by pivot posts 58, 59, which permit rotation of the 
lever arm about an axis directed radially relative to the catheter. 
As shown in FIG. 6, the lever arm pivots between two positions, one shown 
in solid lines in which one end 60 of the lever arm (the stopper end) lies 
between the two apertures 54, 55 and thereby shuts off the jet emerging 
through those apertures, and the other shown in dashed lines in which the 
stopper end 60 is clear of the two apertures, causing the jet to flow 
outward from the primary lumen 52. The range of movement of the lever arm 
57 is restricted by blocking posts 61, 62. The position of the lever arm 
is governed by pressurized fluid fed to the chamber 56 at either side of 
the pivot axis by lumens 63, 64. By using separate supplies of pressurized 
fluid for each side of the lever arm, this construction does not rely on 
the pressure in the primary lumen 52 to maintain the arm in any one 
position. The individual supplies may be regulated such that the apertures 
are either normally-open or normally-closed. 
FIG. 7 illustrates an embodiment which does not utilize levers, but instead 
utilizes axially movable rods or pistons 71. The pistons reside in lumens 
72 in which they are sufficiently loose to permit them to move back and 
forth axially. They may be forced forward by fluid pressure in the lumens 
or by electromagnetic means such as by the use of coils 73 serving as 
miniature solenoid valves. Alternatively, the coils may be used to retract 
the pistons until fluid pressure forces them forward. In FIG. 7, the 
lowermost piston is shown in an extended position while the remaining 
three pistons are in a retracted position. 
When in the extended position, the pistons 71 cover apertures 74 in the 
distal ring 75 of the catheter. Stops 76 at the distal terminus of the 
ring limit the range of motion of the pistons and retain them in the 
catheter. Pistons which are retracted are clear of the apertures, thereby 
permitting jets to emerge through those apertures. 
A system for operating a steerable catheter in accordance with this 
invention and for supplying all necessary fluids is shown in FIG. 8. The 
catheter 81 has distal 82 and proximal 83 ends, and contains four 
secondary lumens, thereby supplying four jets 84. Although four secondary 
lumens are included in this drawing, this number is used for illustrative 
purposes only. The actual number may be other than four, depending on the 
type of closure and its operation, as well as the number of jets, as 
explained above. 
Four supply conduits 85 are connected to the proximal end of the catheter, 
one such conduit feeding each of the four secondary lumens. Pressurized 
gas or liquid for use in these conduits originates from a common source 
86, which may be a reservoir with a downstream pump, a pressurized 
container, or any other means of supply appropriate for the desired 
pressure. The pressurized gas or liquid passes through a safety regulator 
87 which protects the system from overpressurized fluid. From the 
regulator, the fluid passes through a manifold 88, then to a series of 
four valves 89 arranged in series, one of these valves per supply conduit 
85. 
The valves are individually controlled by control signals from a computer 
91 of conventional programming for catheter operation. The valves 89 are 
normally open in this particular embodiment, and close upon receiving 
pulse-modulated signals from the computer. Referring to the embodiment of 
FIGS. 1 and 2 as an example, closure of any single valve results in 
opening of the corresponding jet closure 28 at the distal end of the 
catheter, and ejection of fluid from the jet. 
The fluid for the jets themselves is supplied by a separate fluid source 
92, which again may be a reservoir with a downstream pump, a pressurized 
container, or any other means of supply appropriate for the desired 
pressure. For this source as well, a safety regulator 93 protects the 
system from overpressurization. 
The four valves 89 may be solenoid valves, pressure-operated valves or any 
other type of valve controllable by control signals from a computer. The 
valves preferably have a high frequency response to cause them to open and 
close rapidly in response to the control signals. 
In one application of the system shown in FIG. 8, the computer 91 emits 
control signals to the valves 89 based on information from a sensor 
affixed to the catheter 81 near its distal end. The sensor may be an 
ultrasonic transducer, an optical fiber, or any other of the variety of 
known means for collecting information at the distal end of the catheter 
and transmitting it to the proximal end. The information from the sensor 
is transmitted backward through the catheter through an imaging system 94 
and from there to the computer 91. When the catheter is positioned in a 
blood vessel, for example, signals from the sensor are processed by the 
imaging system 94 to generate a virtual map, or two-dimensional or 
three-dimensional image of the interior of the vessel and the position of 
the catheter inside the vessel. The information produced by the imaging 
system may for example be a tabulation of distances from the catheter to 
the vessel wall as a function of radial angle. Alternatively, the 
information may be a video image of the vessel surrounding the catheter. 
The information generated by the imaging system 94 can be used by the 
operator to direct the catheter tip along a desired path through manual 
operator input. To accomplish this, the operator uses a manual control 
device 95 such as a joystick, a mouse, a touch-sensitive display panel, or 
any other known type of directional control device. Signals from the 
control device 95 will be transmitted to the computer which will then 
calculate the appropriate sequence of control pulses and transmit them to 
the valves 89 according to the calculated sequence. 
This is but one of a variety of ways in which a computer system such as 
that shown in FIG. 8 can be used. The system may also be used to direct 
the catheter along a predetermined path, with the computer programmed 
accordingly prior to the insertion of the catheter. A further use would be 
to integrate the system with therapeutic action such as cutting, abrasion 
or ablation. For this use, the therapeutic element will be incorporated 
into the catheter construction as described above and functioning of the 
element will be controlled by an external control unit 96. The physician 
will designate undesirable tissue or the presence of an undesired deposit 
on an image generated by the imaging system. The computer is then 
programmed to generate a series of cutting or ablation paths until the 
specified tissue or deposit is destroyed or removed. 
The foregoing is offered primarily for purposes of illustration. It will be 
readily apparent to those skilled in the art that the components of the 
system, their configuration, arrangement and operation can be further 
modified or substituted in various ways without departing from the spirit 
and scope of the invention.