US 20100222854 A1
Methods and apparatus are provided for thermally-induced renal neuromodulation. Thermally-induced renal neuromodulation may be achieved via direct and/or via indirect application of thermal energy to heat or cool neural fibers that contribute to renal function, or of vascular structures that feed or perfuse the neural fibers. In some embodiments, parameters of the neural fibers, of non-target tissue, or of the thermal energy delivery element, may be monitored via one or more sensors for controlling the thermally-induced neuromodulation. In some embodiments, protective elements may be provided to reduce a degree of thermal damage induced in the non-target tissues.
31. An apparatus for inhibiting renal nerve activity via an intra-to-extravascular approach, the apparatus comprising:
an intravascular catheter comprising a shaft and a distal section configured for placement within a renal blood vessel proximate to renal nerves; and
a thermal element coupled to the distal section of the shaft,
wherein the thermal element is configured for intravascular delivery and extravascular placement adjacent to renal nerves via an intra-to-extravascular approach, and
wherein the thermal element is configured to thermally inhibit neural signaling along the renal nerves.
32. The apparatus of
33. The apparatus of
34. The apparatus of
35. The apparatus of
36. The apparatus of
37. The apparatus of
38. The apparatus of
39. The apparatus of
40. The apparatus of
41. The apparatus of
42. The apparatus of
43. The apparatus of
44. The apparatus of
45. The apparatus of
46. The apparatus of
47. The apparatus of
48. The apparatus of
49. An apparatus for reducing renal nerve activity via an intra-to-extravascular approach, the apparatus comprising:
an intravascular catheter comprising a shaft and a distal section configured for placement within a renal blood vessel proximate to renal nerves; and
an infusion needle extending from the distal section of the shaft,
wherein the infusion needle is configured for intravascular delivery and extravascular placement adjacent to renal nerves via an intra-to-extravascular approach, and
wherein the infusion needle is configured to inhibit neural signaling along the renal nerves.
50. The apparatus of
51. The apparatus of
The present application claims the benefit of U.S. Provisional Application No. 60/816,999 filed on Jun. 28, 2006. The present application is also a Continuation-In-Part application of co-pending U.S. patent application Ser. No. 10/408,665, filed on Apr. 8, 2003, which claims the benefit of U.S. Provisional Application Nos. (a) 60/370,190, filed on Apr. 8, 2002, (b) 60/415,575, filed on Oct. 3, 2002, and (c) 60/442,970, filed on Jan. 29, 2003. Furthermore, this application is a Continuation-In-Part application of co-pending U.S. patent application Ser. No. 11/189,563, filed on Jul. 25, 2005, which is a Continuation-In-Part application of U.S. patent application Ser. No. 11/129,765, filed on May 13, 2005, which claims the benefit of U.S. Provisional Application Nos. (a) 60/616,254, filed on Oct. 5, 2004, and (b) 60/624,793, filed on Nov. 2, 2004.
All of these applications are incorporated herein by reference in their entireties.
All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.
The present invention relates to methods and apparatus for neuromodulation. More particularly, the present invention relates to methods and apparatus for achieving renal neuromodulation via thermal heating and/or cooling mechanisms.
Congestive Heart Failure (“CHF”) is a condition that occurs when the heart becomes damaged and reduces blood flow to the organs of the body. If blood flow decreases sufficiently, kidney function becomes altered, which results in fluid retention, abnormal hormone secretions and increased constriction of blood vessels. These results increase the workload of the heart and further decrease the capacity of the heart to pump blood through the kidneys and circulatory system.
It is believed that progressively decreasing perfusion of the kidneys is a principal non-cardiac cause perpetuating the downward spiral of CHF. Moreover, the fluid overload and associated clinical symptoms resulting from these physiologic changes result in additional hospital admissions, poor quality of life and additional costs to the health care system.
In addition to their role in the progression of CHF, the kidneys play a significant role in the progression of Chronic Renal Failure (“CRF”), End-Stage Renal Disease (“ESRD”), hypertension (pathologically high blood pressure) and other cardio-renal diseases. The functions of the kidneys can be summarized under three broad categories: filtering blood and excreting waste products generated by the body's metabolism; regulating salt, water, electrolyte and acid-base balance; and secreting hormones to maintain vital organ blood flow. Without properly functioning kidneys, a patient will suffer water retention, reduced urine flow and an accumulation of waste toxins in the blood and body. These conditions result from reduced renal function or renal failure (kidney failure) and are believed to increase the workload of the heart. In a CHF patient, renal failure will cause the heart to further deteriorate as fluids are retained and blood toxins accumulate due to the poorly functioning kidneys.
It has been established in animal models that the heart failure condition results in abnormally high sympathetic activation of the kidneys. An increase in renal sympathetic nerve activity leads to decreased removal of water and sodium from the body, as well as increased renin secretion. Increased renin secretion leads to vasoconstriction of blood vessels supplying the kidneys, which causes decreased renal blood flow. Reduction of sympathetic renal nerve activity, e.g., via denervation, may reverse these processes.
Applicants have previously described methods and apparatus for treating renal disorders by applying a pulsed electric field to neural fibers that contribute to renal function. See, for example, Applicants' co-pending U.S. patent application Ser. Nos. (a) 11/129,765, filed on May 13, 2005, (b) 11/189,563, filed on Jul. 25, 2005, and (c) 11/363,867, filed Feb. 27, 2006, all of which are incorporated herein by reference in their entireties. A pulsed electric field (“PEF”) may initiate renal neuromodulation, e.g., denervation, for example, via irreversible electroporation or via electrofusion. The PEF may be delivered from apparatus positioned intravascularly, extravascularly, intra-to-extravascularly or a combination thereof. Additional methods and apparatus for achieving renal neuromodulation, e.g., via localized drug delivery (such as by a drug pump or infusion catheter) or via use of a stimulation electric field, etc, are described, for example, in co-owned and co-pending U.S. patent application Ser. No. 10/408,665, filed Apr. 8, 2003, and U.S. Pat. No. 6,978,174, both of which are incorporated herein by reference in their entireties.
A potential challenge of using PEF systems for treating renal disorders is to selectively electroporate target cells without affecting other cells. For example, it may be desirable to irreversibly electroporate renal nerve cells that travel along or in proximity to renal vasculature, but it may not be desirable to damage the smooth muscle cells of which the vasculature is composed. As a result, an overly aggressive course of PEF therapy may persistently injure the renal vasculature, but an overly conservative course of PEF therapy may not achieve the desired renal neuromodulation.
Applicants have previously described methods and apparatus for monitoring changes in tissue impedance or conductivity in order to determine the effects of pulsed electric field therapy, e.g., to determine an extent of electroporation and/or its degree of irreversibility. See, for example, Applicant's co-pending U.S. patent application Ser. No. 11/233,814, filed Sep. 23, 2005, which is incorporated herein by reference in its entirety. However, in some patients it may be difficult or impractical to achieve such real-time monitoring when utilizing pulsed electric field neuromodulatory mechanisms. In some patients, this may necessitate re-intervention should it be established after the procedure that a degree of induced neuromodulation was not sufficient to achieve a desired treatment outcome. Thus, it would be desirable to achieve renal neuromodulation via more easily monitored and/or controlled neuromodulatory mechanisms.
Several embodiments of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:
The present invention provides methods and apparatus for renal neuromodulation via thermal heating and/or thermal cooling mechanisms, e.g., to achieve a reduction in renal sympathetic nerve activity. Thermally-induced (via heating and/or cooling) neuromodulation may be achieved via apparatus positioned proximate target neural fibers, for example, positioned within renal vasculature (i.e., positioned intravascularly), positioned extravascularly, positioned intra-to-extravascularly or a combination thereof. Thermal neuromodulation by either heating or cooling may be due to direct effect to, or alteration of, the neural structures that is induced by the thermal stress. Additionally or alternatively, the thermal neuromodulation may at least in part be due to alteration of vascular structures, e.g., arteries, arterioles, capillaries or veins, which perfuse the target neural fibers or surrounding tissue. Furtherstill, the modulation may at least in part be due to electroporation of the target neural fibers or of surrounding tissue.
As used herein, thermal heating mechanisms for neuromodulation include both thermal ablation and non-ablative thermal injury or damage (e.g., via sustained heating or resistive heating). Thermal heating mechanisms may include raising the temperature of target neural fibers above a desired threshold, for example, above a body temperature of about 37° C., e.g., to achieve non-ablative thermal injury, or above a temperature of about 45° C. (e.g., above about 60° C.) to achieve ablative thermal injury.
As used herein, thermal cooling mechanisms for neuromodulation include non-freezing thermal slowing of nerve conduction and/or non-freezing thermal nerve injury, as well as freezing thermal nerve injury. Thermal cooling mechanisms may include reducing the temperature of target neural fibers below a desired threshold, for example, below the body temperature of about 37° C. (e.g., below about 20° C.) to achieve non-freezing thermal injury. Thermal cooling mechanisms also may include reducing the temperature of the target neural fibers below about 0° C., e.g., to achieve freezing thermal injury.
In addition to monitoring or controlling the temperature during thermal neuromodulation, a length of exposure to thermal stimuli may be specified to affect an extent or degree of efficacy of the thermal neuromodulation. The length of exposure to thermal stimuli is longer than instantaneous exposure, such as longer than about 30 seconds, or even longer than 2 minutes. Furthermore, the length of exposure can be less than 10 minutes, though this should in no way be construed as the upper limit of the exposure period. Exposure times measured in hours, days or longer, may be utilized to achieve desired thermal neuromodulation.
When conducting neuromodulation via thermal mechanisms, the temperature threshold discussed previously may be determined as a function of the duration of exposure to thermal stimuli. Additionally or alternatively, the length of exposure may be determined as a function of the desired temperature threshold. These and other parameters may be specified or calculated to achieve and control desired thermal neuromodulation.
In some embodiments, thermally-induced renal neuromodulation may be achieved via direct application of thermal cooling or heating energy to the target neural fibers. For example, a chilled or heated fluid can be applied at least proximate to the target neural fiber, or heated or cooled elements (e.g., a thermoelectric element or a resistive heating element) can be placed in the vicinity of the neural fibers. In other embodiments, thermally-induced renal neuromodulation may be achieved via indirect generation and/or application of the thermal energy to the target neural fibers, such as through application of a ‘thermal’ electric field, of high-intensity focused ultrasound, of laser irradiation, etc., to the target neural fibers. For example, thermally-induced renal neuromodulation may be achieved via delivery of a pulsed or continuous thermal electric field to the target neural fibers, the electric field being of sufficient magnitude and/or duration to thermally induce the neuromodulation in the target fibers (e.g., to heat or thermally ablate or necrose the fibers). Additional and alternative methods and apparatus may be utilized to achieve thermally-induced renal neuromodulation, as described hereinafter.
When utilizing thermal heating mechanisms for thermal neuromodulation, protective cooling elements, such as convective cooling elements, optionally may be utilized to protect smooth muscle cells or other non-target tissue from thermal damage during the thermally-induced renal neuromodulation. Likewise, when utilizing thermal cooling mechanisms, protective heating elements, such as convective heating elements, may be utilized to protect the non-target tissue. When thermal neuromodulation is achieved via thermal energy delivered intravascularly, the non-target tissue may be protected by utilizing blood flow as a conductive and/or convective heat sink that carries away excess thermal energy (hot or cold). For example, when blood flow is not blocked, the circulating blood may provide a relatively constant temperature medium for removing the excess thermal energy from the non-target tissue during the procedure. The non-target tissue additionally or alternatively may be protected by focusing the thermal heating or cooling energy on the target neural fibers such that an intensity of the thermal energy is insufficient to induce the thermal damage in the non-target tissue distant from the target neural fibers.
In some embodiments, methods and apparatus for real-time monitoring of an extent or degree of neuromodulation or denervation (e.g., an extent or degree of thermal damage) in the target neural fibers and/or of thermal damage in the non-target tissue may be provided. Likewise, real-time monitoring of the thermal energy delivery element may be provided. Such methods and apparatus may, for example, comprise a thermocouple or other temperature sensor for measuring the temperature of the monitored tissue or of the thermal energy delivery element. Power or total energy delivered additionally or alternatively may be monitored.
To better understand the structures of devices of the present invention and the methods of using such devices for thermally-induce renal neuromodulation, it is instructive to examine the renal anatomy in humans.
With reference to
The field generator 50 is located external to the patient. The generator, as well as any of the electrode embodiments described herein, may be utilized with any embodiment of the present invention for delivery of a thermal electric field with desired field parameters, e.g., parameters sufficient to thermally or otherwise induce renal neuromodulation in target neural fibers via heating and/or electroporation. It should be understood that electrodes of embodiments described hereinafter may be electrically connected to the generator even though the generator is not explicitly shown or described with each embodiment. Furthermore, the field generator optionally may be positioned internal to the patient. Furtherstill, the field generator may additionally comprise or may be substituted with an alternative thermal energy generator, such as a thermoelectric generator for heating or cooling (e.g., a Peltier device), or a thermal fluid injection system for heating or cooling, etc.
The electrode(s) 212 can be individual electrodes that are electrically independent of each other, a segmented electrode with commonly connected contacts, or a continuous electrode. A segmented electrode may, for example, be formed by providing a slotted tube fitted onto the electrode, or by electrically connecting a series of individual electrodes. Individual electrodes or groups of electrodes 212 may be configured to provide a bipolar signal. The electrodes 212 may be dynamically assignable to facilitate monopolar and/or bipolar energy delivery between any of the electrodes and/or between any of the electrodes and an external ground pad. Such a ground pad may, for example, be attached externally to the patient's skin, e.g., to the patient's leg or flank. In
Referring now to
The positioning element 304 optionally may center or otherwise position the electrodes 306 a and 306 b within a vessel. Additionally, as in
Furthermore, the positioning element 304 optionally may be utilized as a cooling element and/or a heating element. For example, the positioning element 304 may be inflated with a chilled fluid that serves as a heat sink for removing heat from tissue that contacts the element. Conversely, the positioning element 304 optionally may be a heating element by inflating it with a warmed fluid that heats tissue in contact with the element. The thermal fluid optionally may be circulated and/or exchanged within the positioning element 304 to facilitate more efficient conductive and/or convective heat transfer. Thermal fluids also may be used to achieve thermal neuromodulation via thermal cooling or heating mechanisms, as described in greater detail herein below. The positioning element 304 (or any other portion of apparatus 300) additionally or alternatively may comprise one or more sensors for monitoring the process. In one embodiment, the positioning element 304 has a wall-contacting thermocouple 310 (
The electrodes 306 can be individual electrodes (i.e., independent contacts), a segmented electrode with commonly connected contacts, or a single continuous electrode. Furthermore, the electrodes 306 may be configured to provide a bipolar signal, or the electrodes 306 may be used together or individually in conjunction with a separate patient ground pad for monopolar use. As an alternative or in addition to placement of the electrodes 306 along the central shaft of the catheter 302, as in
In use, the catheter 302 may be delivered to the renal artery RA as shown, or it may be delivered to a renal vein or to any other vessel in proximity to neural tissue contributing to renal function, in a low profile delivery configuration through a guide catheter or other device. Alternatively, catheters may be positioned in multiple vessels for thermal renal neuromodulation, e.g., within both the renal artery and the renal vein. Multi-vessel techniques for pulsed electric field renal neuromodulation have been described previously, for example, in Applicant's co-pending U.S. patent application Ser. No. 11/451,728, filed Jul. 12, 2006, which is incorporated herein by reference in its entirety.
Once positioned within the renal vasculature as desired, the optional positioning element 304 may be expanded into contact with an interior wall of the vessel. A thermal electric field then may be generated by the field generator 50, transferred through the catheter 302 to the electrodes 306, and delivered via the electrodes 306 across the wall of the artery. The electric field thermally modulates the activity along neural fibers that contribute to renal function via heating. In several embodiments, the thermal modulation at least partially denervates the kidney innervated by the neural fibers via heating. This may be achieved, for example, via thermal ablation or via non-ablative damage of the target neural fibers. The electric field also may induce electroporation in the neural fibers.
In the embodiment of
Use of the patient's blood as a heat sink is expected to facilitate delivery of longer or higher energy thermal treatments with reduced risk of damage to the non-target tissue, which may enhance the efficacy of the treatment at the target neural fibers. Although the embodiment of
In addition or as an alternative to utilizing the patient's blood as a heat sink, a thermal fluid (hot or cold) may be injected into the vessel to remove excess thermal energy and protect the non-target tissues. The thermal fluid may, for example, be injected through the device catheter or through a guide catheter at a location upstream from an energy delivery element or at other locations relative to the tissue for which protection is sought. Furthermore, this method of using an injected thermal fluid to remove excess thermal energy from non-target tissues to protect the non-target tissues from thermal injury during therapeutic treatment of target tissues may be utilized in body lumens other than blood vessels.
One or more sensors, such as the thermocouple 310 of
As discussed, when utilizing intravascular apparatus to achieve thermal neuromodulation, in addition or as an alternative to central positioning of the electrode(s) within a blood vessel, the electrode(s) optionally may be configured to contact an internal wall of the blood vessel. Wall-contacting electrode(s) may facilitate more efficient transfer of a thermal electric field across the vessel wall to target neural fibers, as compared to centrally-positioned electrode(s). In some embodiments, the wall-contacting electrode(s) may be delivered to the vessel treatment site in a reduced profile configuration, then expanded in vivo to a deployed configuration wherein the electrode(s) contact the vessel wall. In some embodiments, expansion of the electrode(s) is at least partially reversible to facilitate retrieval of the electrode(s) from the patient's vessel.
As seen in
After delivery of the electric field, the electrode 306 a′ may be returned to a reduced profile to facilitate removal of the apparatus 300 from the patient. For example, the positioning element 304 may be collapsed (e.g., deflated), and the electrode 306 a′ may be contracted by withdrawing the catheter 302 within the guide catheter 303. Alternatively, the electrode may be fabricated from a shape-memory material biased to the collapsed configuration, such that the electrode self-collapses upon collapse of the positioning element.
A bipolar electric field may be delivered between the proximal and distal wall-contacting electrodes, or a monopolar electric field may be delivered between the proximal and/or distal electrode(s) and an external ground. Having both the proximal and distal electrodes in contact with the wall of the vessel may facilitate more efficient energy transfer across the wall during delivery of a thermal electric field, as compared to having one or both of the proximal and distal electrodes centered within the vessel.
In addition to extravascular and intravascular systems for thermally-induced renal neuromodulation, intra-to-extravascular systems may be provided. The intra-to-extravascular systems may, for example, have electrode(s) that are delivered to an intravascular position, and then at least partially passed through/across the vessel wall to an extravascular position prior to delivery of a thermal electric field. Intra-to-extravascular positioning of the electrode(s) may place the electrode(s) in closer proximity to target neural fibers for delivery of a thermal electric field, as compared to fully intravascular positioning of the electrode(s). Applicants have previously described intra-to-extravascular pulsed electric field systems, for example, in co-pending U.S. patent application Ser. No. 11/324,188, filed Dec. 29, 2005, which is incorporated herein by reference in its entirety.
With reference to
Catheter 322 comprises an optional expandable positioning element 330, which may comprise an inflatable balloon or an expandable basket or cage. In use, the positioning element 330 may be expanded prior to deployment of the needle electrodes 328 and 329 in order to position or center the catheter 322 within the patient's vessel (e.g., within renal artery RA). Centering the catheter 322 is expected to facilitate delivery of all needle electrodes to desired depths within/external to the patient's vessel (e.g., to deliver all of the needle electrodes approximately to the same depth). In
As illustrated in
The proximal electrodes 328 can be connected to electric field generator 50 as active electrodes, and the distal electrodes 329 can serve as return electrodes. In this manner, the proximal and distal electrodes form bipolar electrode pairs that align the thermal electric field with a longitudinal axis or direction of the patient's vasculature. As will be apparent, the distal electrodes 329 alternatively may comprise the active electrodes and the proximal electrodes 328 may comprise the return electrodes. Furthermore, the proximal and/or the distal electrodes may comprise both active and return electrodes. Furtherstill, the proximal and/or the distal electrodes may be utilized in combination with an external ground for delivery of a monopolar thermal electric field. Any combination of active and distal electrodes may be utilized, as desired.
When the electrodes 328 and 329 are connected to generator 50 and positioned extravascularly, and with the positioning element 330 optionally expanded, delivery of the thermal electric field may proceed to achieve desired renal neuromodulation via heating. The electric field also may induce electroporation. After achievement of the thermally-induced renal neuromodulation, the electrodes may be retracted within the proximal and distal lumens, and the positioning element 330 may be collapsed for retrieval. ITEV system 320 then may be removed from the patient to complete the procedure. Additionally or alternatively, the system may be repositioned to provide therapy at another treatment site, such as to provide bilateral renal neuromodulation.
As discussed previously, cooling elements, such as convective cooling elements, may be utilized to protect non-target tissues like smooth muscle cells from thermal damage during thermally-induced renal neuromodulation via heat generation. Non-target tissues additionally or alternatively may be protected by focusing the thermal energy on the target neural fibers such that an intensity of the thermal energy is insufficient to induce thermal damage in non-target tissues distant from the target neural fibers.
The embodiments of
With reference now to
In addition or as alternative to injection of a thermal fluid to the target neural fibers through infusion needles 328′ and 329′, an alternative neuromodulatory agent, such as a drug or medicament, may be injected to modulate, necrose or otherwise block or reduce transmission along the target neural fibers. Examples of alternative neuromodulatory agents include, but are not limited to, phenol and neurotoxins, such as botulinum toxin. Additional neuromodulatory agents, per se known, will be apparent to those of skill in the art.
An electric current is passed from the power supply to the thermoelectric element, which comprises two different metals (e.g., a p-type and an n-type semiconductor) that are connected to each other at two junctions. The current induces a thermal gradient between the two junctions, such that one junction cools while the other is heated. Reversal of the polarity of the voltage applied across the two junctions reverses the direction of the thermal gradient.
Either the hot side or the cold side of the thermoelectric element faces radially inward in order to heat or cool, respectively, the target neural fibers that travel along the renal artery to achieve thermal renal neuromodulation. Optionally, the radially outward surface of the thermoelectric element may be insulated to reduce a risk of thermal damage to the non-target tissues. The cuff 342 may comprise one or more temperature sensors, such as thermocouples, for monitoring the temperature of the target neural fibers and/or of the non-target tissues.
The pump 352 further comprises one or more thermoelectric or other thermal elements in heat exchange contact with the fluid reservoir for cooling or heating the fluid that is transferred to the cuff to thermally modulate the target neural fibers. The apparatus 350 optionally may have controls for automatic or manual control of fluid heating or cooling, as well as fluid circulation within the cuff. Furthermore, the apparatus may comprise temperature and/or renal sympathetic neural activity monitoring or feedback control. Although the apparatus illustratively is shown unilaterally treating neural fibers innervating a single kidney, it should be understood that bilateral treatment of neural fibers innervating both kidneys alternatively may be provided.
Thermal renal neuromodulation alternatively may be achieved via high-intensity focused ultrasound, either pulsed or continuous. High intensity focused ultrasound also may induce reversible or irreversible electroporation in the target neural fibers. Furthermore, the ultrasound may be delivered over a full 360° (e.g. when delivered intravascularly) or over a radial segment of less than 360° (e.g., when delivered intravascularly, extravascularly, intra-to-extravascularly, or a combination thereof). In
The focal distance may be specified or dynamically variable such that, when positioned within a blood vessel, the ultrasonic wave is focused at a desired depth on target neural fibers outside of the vessel. For example, a family of catheter sizes may be provided to allow for a range of specified focal distances. A dynamically variable focal distance may be achieved, for example, via calibrated expansion of the balloon.
Focusing the ultrasound wave may produce a reverse thermal gradient that protects the non-target tissues and selectively affect the target neural fibers to achieve thermal renal neuromodulation via heating. As a result, the temperature at the vessel wall may be less than the temperature at the target tissue.
The apparatus described above with respect to
As seen in
It is expected that thermally-induced renal neuromodulation, whether delivered extravascularly, intravascularly, intra-to-extravascularly or a combination thereof, may alleviate clinical symptoms of CHF, hypertension, renal disease, myocardial infarction, atrial fibrillation, contrast nephropathy and/or other cardio-renal diseases for a period of months, potentially up to six months or more. This time period may be sufficient to allow the body to heal; for example, this period may reduce the risk of CHF onset after an acute myocardial infarction, thereby alleviating a need for subsequent re-treatment. Alternatively, as symptoms reoccur, or at regularly scheduled intervals, the patient may receive repeat therapy.
Although preferred illustrative variations of the present invention are described above, it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.