Patent Description:
Balloon catheters are used for a wide variety of medical applications including angioplasty, stent deployment, embolectomy and balloon occlusion of blood vessels. A standard balloon catheter has a catheter with at least one lumen, a compliant or non-compliant balloon positioned coaxially around and bonded to the catheter at or near its distal tip. At least one of the catheter lumens, the inflation lumen, has at least one orifice positioned within the balloon lumen such that this inflation lumen is in fluid communication with the inside of the balloon. The balloon is deployed by attaching a syringe or other infusion device to the proximal end of the catheter, so that it is in fluid communication with the catheter's inflation lumen, and injecting a volume of fluid (liquid or gas) through the inflation lumen into the balloon, inflating it to a given volume or pressure. The balloon is deflated by withdrawing the fluid from the balloon lumen through the catheter's inflation lumen back into the reservoir of the syringe or other infusion device. The catheter may have additional lumens such as a guidewire lumen to facilitate maneuvering of the catheter within the body, infusion lumens to infuse fluid out the distal tip of the catheter into the patient and monitoring lumens to monitor pressure, temperature or other parameters.

There are applications where it is desirable for the fluid which inflates the balloon to flow continuously into and out of the balloon while maintaining the balloon inflated at the desired volume and pressure. One such application would be thermal ablation balloon catheters which ablate tissue using hyper or hypothermia. Balloon catheters are useful in these applications because they can be designed to conform to the tissue to be ablated once positioned in the appropriate location. Another such application would be a drug delivery balloon catheter where the balloon serves as a reservoir for a drug to be delivered through its permeable wall.

Tissue ablation is performed throughout the body. It is frequently used to destroy abnormal tissue such as malignant tumors (e.g. liver, lung) or other non-malignant tissue (e.g. endometrial, prostatic). It is also frequently used to target structurally normal tissues for a specific therapeutic effect such as cardiac tissue ablation to treat arrhythmias and more recently renal nerve ablation ("renal denervation") to treat refractory hypertension.

Tissue ablation is most commonly performed by applying energy to the target tissue to cause irreversible cellular injury. Common energy sources for tissue ablation include radiofrequency, microwave, laser, ultrasound and cryo. Each source has its own specific characteristics, biophysical mechanism, advantages and disadvantages. All of these modalities, with the exception of cryo, ultimately act by increasing the tissue temperature to cytotoxic levels for a given period of time. Cellular injury is generally reversible below 46C. Although there is some variability in thermal sensitivity among different tissues and cell types, irreversible cellular injury generally occurs after <NUM> minutes at 46C and less than <NUM> minutes at 50C.

Most clinical applications of thermal ablation have involved either large volumes of tissue (e.g. tumor ablation) or at least relatively thick tissues (e.g. cardiac ablation) where complete ablation of the target tissue is necessary for a successful therapeutic effect. Even a small volume of residual viable tissue can lead to clinical failure in the form of recurrent tumor growth, metastases from residual tumor or recurrent arrhythmias from residual pathways. For the ablation to be successful, the cells farthest from the energy source must reach the target cytotoxic temperature. The larger the distance from the energy probe to the border of the target tissue the more challenging the ablation, the more energy needs to be delivered and the higher the temperature near the probe needs to be. For example, RF ablation depends on electrical conductivity to generate heat but creating too much heat near the probe can generate charring which increases impedance and decreases the effective range of the ablation. A wide variety of technologies and techniques have been developed to accommodate the challenges of ablating across a large distances using RF (e.g. multi-electrode probes, cooling, irrigation and complex power algorithms). As a result, these tissue ablation modalities typically require a complex, external console to assure the precise amount of energy is delivered to the tissue to achieve the desired therapeutic effect. Simpler devices which use a "shotgun" approach may be ineffective or downright harmful.

The major limitation of standard balloon catheters in hyperthermic ablation applications is that the surrounding tissue serves as a powerful thermal sink. The temperature in the balloon may equilibrate with the surrounding tissue within a short period of time, shorter than the time necessary to perform the ablation, typically several minutes. For hypothermic (cryo) ablation the fluid temperature can be made so cold using liquid gases (e.g. argon, nitrogen) that the time required for the temperature to equilibrate is longer than the time it takes to ablate the tissue. For hyperthermic ablation, however, the options are more limited since the boiling temperature of most biocompatible fluids are only modestly above the temperature necessary to successfully ablate most tissues. Most tissue ablation is therefore performed using a fixed probe which is inserted into the tissue and attached to an external energy source (e.g. radiofrequency, microwave). The source continuously provides energy to the tissue as the heat dissipates into the surrounding tissue.

<CIT>, <CIT>, <CIT> each disclose a catheter having an inflow lumen and an outflow lumen; a balloon positioned at a distal end of the catheter, the balloon being in fluid communication with the inflow and the outflow lumen; an infusion device in fluid communication with the balloon through the inflow and outflow lumens. During a steady-state of infusion, fluid is circulated into and out of the balloon via the inflow lumen and the outflow lumen in order to keep the balloon volume constant.

In accordance with the present disclosure, a system for balloon inflation, the system comprising a catheter having an inflow lumen and an outflow lumen, a balloon positioned at a distal end of the catheter, the balloon being in fluid communication with the inflow and the outflow lumen, and an infusion device in fluid communication with the balloon through the inflow and outflow lumens. The infusion device is configured for continuously circulating a fluid into and out of the balloon to maintain the balloon at a constant pressure and volume by matching a flow of the fluid into the balloon via the inflow lumen with a flow of the fluid out of the balloon via the outflow lumen in order to keep the balloon volume and pressure constant during an entire infusion. In some embodiments, the infusion device may further comprise a heating mechanism to heat the fluid to generate a heated fluid in order to maintain a constant temperature in the balloon via the heated fluid. In some embodiments the balloon may be is divided by a plurality of septae into multiple compartments, the multiple compartments comprising a mixture of heated compartments and insulating compartments, the heated compartments configured to contain the heated fluid and the insulating compartments configured to contain an insulating fluid. In some embodiments a surface of the balloon overlying one or more of the heated compartments allows heat from the heated fluid to transfer to and ablate a target tissue adjacent to the surface of the one or more heated compartments, and a surface overlying one or more of the insulating compartments prevents heat from transferring to a tissue adjacent to the one or more insulating compartments, thereby protecting the tissue adjacent to the one or more insulating compartments from ablation.

In some embodiments, the infusion device may further comprise a reservoir being configured to hold the fluid, an inflow chamber being in fluid communication with the balloon via the inflow lumen, and an outflow chamber being in fluid communication with the balloon via the outflow lumen. In some embodiments the reservoir may further comprise a piston disposed therein and may be in fluid communication with the balloon such that the reservoir may be configured to inflate the balloon via the inflow lumen. In some embodiments, the reservoir may further comprise a heating mechanism configured to heat the fluid to generate a heated fluid in order to maintain a constant temperature in the balloon via the heated fluid. In some embodiments, the catheter may further comprise a lumen containing a monitoring device for monitoring a location and orientation of the catheter in relation to a target tissue.

In other embodiments in accordance with the present disclosure, a system for ablation of a target tissue comprising a balloon having one or more heated compartments and one or more insulating compartments, a heated fluid contained in the one or more heated compartments, and an insulation fluid contained in the one or more insulating compartments, wherein a distribution of the one or more heated compartments among the one or more insulating compartments is selected to provide a desired ablation pattern at a target tissue. In some embodiments, the one or more heated compartments may comprise an inner balloon, and the one or more insulating compartments may comprise an outer balloon, the inner balloon being configured to contain a heated fluid and to make a point of contact with a portion of the outer balloon in order to deliver heat from the heated fluid to the target tissue adjacent to the point of contact, the outer balloon being configured to contain an insulating fluid and to protect a tissue next to the target tissue from ablation. In some embodiments, the inner balloon may be configured to make more than one point of contact with the outer balloon, the more than points of contact defining an ablation pattern for the target tissue. In some embodiments, the insulating fluid may be a gas.

non-claimed method is disclosed, using a balloon catheter comprising first positioning a catheter at a site of a target tissue for a first process, the catheter comprising a balloon, then inflating the balloon to a first volume and pressure with a fluid, and then continuously circulating the fluid in and out of the balloon at a flow and a rate maintaining the first volume and pressure during the first process. The method may further comprise heating the fluid to generate a heated fluid, and ablating the target tissue with heat from the heated fluid. In some embodiments, in the step of positioning, the balloon may be configured to ablate the target tissue in a desired pattern via the heat from the heated fluid. In some embodiments, the method further comprises monitoring a location and orientation of the balloon relative to the target tissue. The method further comprises terminating the first process by reversing the flow of the fluid. In some embodiments the catheter need not be repositioned, but in some embodiments the method further comprises repositioning the catheter to a different target site for a second process, and inflating the balloon to a second volume and pressure. In some embodiments, in the step of positioning, the balloon catheter may further comprise an infusion device in fluid communication with the balloon catheter. After the positioning step, the method further comprises attaching an infusion device to the catheter, the infusion device configured to be in fluid communication with the catheter.

There are applications where it is desirable for the fluid which inflates the balloon to flow continuously into and out of the balloon while maintaining the balloon inflated at the desired volume and pressure to assure continuous tissue contact. One such application would be thermal ablation balloon catheters which ablate tissue using hyper or hypothermia. In such applications the surrounding tissues serve as a heat sink which rapidly dissipates thermal energy from the balloon. A possible solution to the limitation of balloon catheters equilibrating with their surrounding tissues is to circulate a hot or cold fluid into and out of a balloon while maintaining the balloon at an inflation which is critical to assure tissue contact and thermal transfer into a target tissue. Maintaining such an equilibrium requires continuous flow with precise matching of flow into and out of the balloon. This is not possible with existing syringe-like disposable technologies since it requires continuous flow. Therefore, in accordance with the present disclosure, an embodiment of a system <NUM> with a continuous flow of a fluid into and out of a balloon catheter <NUM> may include at least two devices (see <FIG>), the balloon catheter comprising a catheter <NUM> and a balloon <NUM>, and an infusion device <NUM>. The infusion device <NUM> may continuously drive or recirculate a fluid into and out of a reservoir, through the catheter <NUM>, into and out of the balloon <NUM> while maintaining the balloon <NUM> inflated to a specified volume and pressure. In some embodiments, the fluid may be replenished or replaced for each given cycle. Alternatively, in some embodiments the fluid is recirculated or recycled. In some embodiments, the infusion device <NUM> may first heat the fluid (or liquid) to a target temperature, then continuously drive or recirculate the heated fluid from the reservoir, through the catheter <NUM>, into and out of the balloon <NUM>, and back into the reservoir while also maintaining the balloon <NUM> inflated to a specified volume and pressure.

The balloon catheter <NUM> (<FIG>) is an elongated tube having a proximal <NUM> and distal end <NUM>, with a balloon <NUM> mounted at or near its distal end <NUM>. The balloon <NUM> may be constructed of any compliant, semi-compliant or non-compliant material, typically a plastic such as polyurethane, nylon, polyethylene, PET or PEBAX. The catheter <NUM> may be made of similar materials and comprises at least two or more flow lumens <NUM>-<NUM>, each in fluid communication with the balloon <NUM> through one or more distal orifices. When the system <NUM> is active, one or more inflow lumens <NUM> carries fluid into the balloon <NUM> and one or more outflow lumens <NUM> carries fluid out of the balloon <NUM>. The system <NUM> can be designed so that flow of the fluid can be reversed with each flow lumen <NUM>, <NUM> serving as either inflow <NUM> or outflow <NUM> depending on the direction of flow. In some embodiments, when the flow is reversed, the inflow lumen <NUM> will become the outflow lumen, and the outflow lumen <NUM> will become the inflow lumen. In some embodiments, the catheter <NUM> may contain additional lumens as desired for guidewires, infusion, monitoring, and other functionalities that may be directed via the additional lumens.

In some embodiments, as seen in <FIG> and <FIG>, the one or more inflow lumens <NUM> may carry heated liquid into the balloon <NUM>, and the one or more outflow lumens <NUM> may carry cooled liquid out of the balloon <NUM>, with both sets of lumens configured to operate continuously. A spatial relationship of the lumens <NUM>, <NUM> within the catheter <NUM> may be arranged to minimize a thermal transfer between the inflow and outflow liquid streams, and between these streams and a patient's blood and tissues. The catheter <NUM> may also have additional features to minimize thermal loss such as a thermal insulating material <NUM> or air pockets <NUM> (as seen in <FIG> and <FIG>) surrounding the inflow lumens <NUM>-<NUM>, such that the flow lumens <NUM>, <NUM> are thermally insulated and may have different temperatures (as seen in <FIG>, where the inflow lumen <NUM> carrying heated fluid is at a different temperature than the outflow lumen <NUM>).

Referencing <FIG> and <FIG>, in some embodiments the system <NUM> comprises an infusion device <NUM> having one or more fluids chambers <NUM>-<NUM> serving as fluid reservoirs. In some embodiments, the infusion device <NUM> may be connected to the proximal end <NUM> of the catheter <NUM> so that its fluid chambers <NUM>-<NUM> may be in fluid communication with the inflow and outflow lumens <NUM>, <NUM> of the catheter <NUM> and the balloon <NUM>. Each chamber <NUM>-<NUM> may communicate with the balloon <NUM> through its own lumen. In some embodiments, an inflation chamber <NUM> and inflow chamber <NUM> will each communicate with the balloon <NUM> through the same inflow lumen <NUM> while an outflow chamber <NUM> communicates through the outflow lumen <NUM>. In some embodiments, each chamber <NUM>-<NUM> may have its own separate infusion device (not pictured).

In an embodiment, the fluid chambers <NUM>-<NUM> may include one inflation chamber <NUM>, and two flow chambers <NUM>, <NUM>. The chambers <NUM>-<NUM> are generally elongate structures having proximal <NUM> and distal <NUM> ends, but can be of any shape. For the sake of consistency, the ends will be designated so that the distal end <NUM> of each chamber <NUM>-<NUM> communicates with the proximal end <NUM> of one or more of the catheter lumens <NUM>-<NUM>. The chambers <NUM>-<NUM> generally possess axial symmetry with a cross sectional profile that is most commonly circular but can also be a more complex shape. The chamber walls may include a proximal wall, a distal wall and a contiguous radial wall extending between the proximal and distal wall. The chamber walls may be rigid and may be constructed of any material compatible with the fluid to be infused, including plastic (e.g. polycarbonate, polyethylene, PEEK, ABS, nylon), glass or metal (e.g. stainless steel, aluminum, copper, brass) or some combination thereof.

In some embodiments, the inflation chamber <NUM> may serve as a reservoir for fluid which will be infused through the inflow lumen <NUM> to inflate the balloon <NUM> to a desired pressure and volume. The flow chambers <NUM>, <NUM> may serve as reservoirs for the fluid that will continuously flow through the balloon <NUM> following inflation to maintain the desired therapeutic effect (e.g., constant temperature, drug concentration, etc.). For consistency, the flow chambers <NUM>, <NUM> will be designated based on the direction of fluid flow relative to the balloon <NUM>, not the chamber. Thus, the inflow chamber <NUM> serves as a reservoir from which fluid can be infused into the inflated balloon <NUM>, and the outflow chamber <NUM> may serve as a reservoir to receive fluid that flows out of the inflated balloon <NUM>.

Each chamber <NUM>-<NUM> may have one or more ports <NUM> through which fluid flows into (inlet port) or out of (outlet port) the chamber <NUM>-<NUM>. Each port <NUM> may be associated with a valve <NUM> to control flow through the port <NUM>. Each chamber <NUM>-<NUM> may communicate with the balloon <NUM> through its own lumen. In some embodiments, the infusion device <NUM> may have a heating mechanism <NUM> to heat the liquid in the inflow chamber <NUM>. In some embodiments, the heating mechanism <NUM> may heat the liquid in the inflation chamber <NUM> so that the initial inflation can be performed with heated liquid, and in other embodiments the heating mechanism <NUM> may heat the liquid in the outflow chamber <NUM> provided the system <NUM> has the ability to reverse flow of the fluid and recirculate the fluid.

In some embodiments, as seen in <FIG>, the inflation chamber <NUM> and inflow chambers <NUM> will each communicate with the balloon <NUM> through the same inflow lumen <NUM>, while the outflow chamber <NUM> communicates through the outflow lumen <NUM>. In another embodiment, as seen in <FIG>, the inflation chamber <NUM> may flow into the inflow chamber <NUM>. Each chamber <NUM>-<NUM> may have an infusion mechanism 100a-100c which drives fluid out of or back into the chamber <NUM>-<NUM> and one or more valves <NUM> to control the flow of fluid in and out of the chamber <NUM>-<NUM>.

Referring now to <FIG> and <FIG>, the infusion mechanism of each chamber <NUM>, <NUM> may include a piston <NUM> which controls the volume of fluid in the chamber <NUM>, <NUM> and an associated drive mechanism <NUM>. The piston <NUM> may be a flat, discoid structure with the same cross sectional profile as the chamber <NUM>, <NUM>, and may divide the chamber <NUM>, <NUM> into two sub-chambers, a fluid sub-chamber <NUM> and an air sub-chamber <NUM>. Each sub-chamber <NUM>, <NUM> may have one or more ports <NUM>, <NUM>. The piston <NUM> has two surfaces, orthogonal to the axis of the chamber <NUM>, <NUM>. An internal surface faces inside of the fluid sub-chamber <NUM> and can be exposed to the fluid within it while an external surface may be on an opposite side of the chamber <NUM>, <NUM> and may be exposed to air outside the chamber <NUM>, <NUM>. In certain embodiments, the piston <NUM> may be shared with another chamber so that its external surface can be exposed to fluid in the other chamber, thereby eliminating the air sub-chamber <NUM> altogether. The piston <NUM> moves axially within the chamber <NUM>, <NUM>, decreasing or increasing the fluid sub-chamber's <NUM> volume, driving fluid out of or drawing fluid into the sub chamber <NUM>. In order to form a fluid-tight seal against an inner chamber <NUM>, <NUM> wall, the piston <NUM> may comprise a compliant, rubbery material (e.g., natural rubber, silicone) or a rigid material (e.g., plastic, metal) with a rubbery gasket. In some embodiments, the piston <NUM> may be passive, in other embodiments it may be active. The passive piston <NUM> moves along an axis of the chamber <NUM>, <NUM> as fluid is driven into or out of the fluid sub-chamber <NUM> by the action of another chamber. The active piston may be connected to a drive mechanism <NUM> which exerts a mechanical force on the piston <NUM> and moves it along the axis of the chamber <NUM>, <NUM>.

In some embodiments, once the balloon <NUM> is inflated to the desired volume and pressure, the flow of liquid into and out of the balloon <NUM> is matched to keep the balloon <NUM> volume and pressure constant while continuously replenishing the heated liquid in the balloon <NUM>, while at the same time withdrawing the liquid that is cooled by the patient. In some embodiments, the inflow <NUM> and outflow <NUM> chambers are mechanically linked via their drive mechanisms <NUM> so that each piston <NUM> has a movement that is equal and opposite to the other piston <NUM>. As a result, a total volume of liquid in the inflow <NUM> and outflow <NUM> chambers remains constant throughout the infusion period.

In some embodiments, the inflation <NUM>, inflow <NUM> and outflow <NUM> chambers may be discrete structures, communicating separately with the balloon catheter <NUM> inflow <NUM> and outflow <NUM> lumens. In some embodiments, two or more chambers may be combined into a single structure, sharing their pistons <NUM> and/or drive mechanisms <NUM>. In some embodiments, the infusion device <NUM> may have a shared inflow/outflow chamber facilitating heating of the liquid in both chambers, permitting multiple infusion cycles. Another embodiment may comprise all three chambers in a single structure permitting all chambers, including the inflation chamber, to be heated with a single external heating element which allows the initial balloon <NUM> to be inflated using heated liquid, decreasing the ablation time.

Referring now to <FIG>, in some embodiments the infusion device comprises one or more heating elements <NUM>. The heating element <NUM> may be internal, residing within one or more fluid chambers <NUM>, <NUM>. The internal heating element <NUM> may comprise probes, coils, wire, foil, thin film resistors <NUM> and thick film resistors. If internal heating elements <NUM> are utilized, all or portion of the chamber wall <NUM> may be insulated to minimize ambient heat loss (e.g., by using an insulating jacket <NUM> or by interposing a gas or vacuum <NUM> between an inner <NUM> and an outer chamber wall <NUM>, similar to a thermos).

In some embodiments, referring to FIGS. 4F and <NUM>, the heating element <NUM> may also be external. In some embodiments, the heating element <NUM> may be in contact with the wall of an individual chamber <NUM>, <NUM> or wrapped around one or more chambers. Such a heating element may be a heating jacket <NUM> in contact with at least a portion of the surface area of the chamber <NUM>, <NUM>. In some embodiments, a specific heating element <NUM> within the jacket <NUM> may comprise probes, coils, wire, foil, thin film resistors and thick film resistors. In some embodiments the chamber wall would be designed to maximize thermal transfer, through selection of a chamber wall material and thickness, and/or wrapping or coating the chamber wall with a material of high thermal conductivity. In some embodiments, the chamber <NUM>, <NUM> may have an outer <NUM> and inner wall <NUM> separated by a gas or vacuum <NUM> to minimize ambient heat loss with the external heating residing within a space in contact with the inner wall.

Referring now to <FIG>, in some embodiments the drive mechanism <NUM> (as seen in <FIG>) may be manual, powered by an operator through the manipulation of a mechanical actuator (not pictured), or alternatively, by an autonomous, passive mechanical or active electromechanical source. The drive mechanism <NUM> may extend across the chamber (as seen in <FIG>), be contained entirely within a sub-chamber (as seen in <FIG> and <FIG>) or a portion may extend through an end wall of the sub-chamber (as seen in <FIG> and <FIG>). If a portion of the drive mechanism <NUM> passes through the end wall of the fluid sub-chamber, it must pass through a gasketed port <NUM> to maintain a fluid seal. The drive mechanism <NUM> may be connected to the internal or external surface of the piston <NUM>.

In some embodiments the manual drive mechanism <NUM> may comprise a syringe-like plunger <NUM> (simple, threaded or ratcheted), a cable or cord attached to a crankshaft or knob-driven pulley (simple or ratcheted), a fixed length belt or chain attached to a crankshaft <NUM> or knob-driven pulleys or gears, a lead (translation) screw. In some embodiments, a passive powered drive mechanism is based on a spring (e.g., compression, extension, or rotary drives). In some embodiments, an active powered drive mechanism may be based on an electric motor powering a cable/pulley, belt/chain or lead screw drive mechanism. Referring to <FIG>, the manual drive mechanism <NUM> may include a rigid rod <NUM>, similar to a plunger in a standard syringe, whose proximal end <NUM> has a handle <NUM> which may facilitate axial movement of the rod <NUM> and whose distal end <NUM> is attached to the internal or external surface of the piston <NUM>. In an embodiment where the distal end <NUM> is attached to the external surface (as seen in FIG. 7A) of the piston <NUM>, the drive mechanism <NUM> may function like the plunger in a standard syringe, moving the internal surface against the fluid in the chamber <NUM>, <NUM>. In some embodiments (as seen in <FIG>), the distal end <NUM> is attached to the internal surface of the piston <NUM>, whereby it traverses the fluid chamber <NUM>, <NUM> and exits through a gasketed port <NUM>, moving the interior surface of the piston <NUM> against the fluid chamber <NUM>, <NUM> in a "reverse syringe" fashion. In some embodiments, the operator manually advances or withdraws the rod <NUM>, moving the piston <NUM> in either direction, driving fluid out of or drawing fluid into the chamber <NUM>, <NUM>. The rod <NUM> may have a threaded screw <NUM> or ratcheting mechanism <NUM> (as seen in <FIG>) which allows the piston <NUM> and rod <NUM> to maintain their position under pressure via the use of a ratchet lock <NUM>, crankshaft <NUM> and gear <NUM>.

Referring now to <FIG> and <FIG>, in some embodiments the heating element <NUM> may require some additional electrical circuitry to function. In some embodiments, the electrical circuitry may comprise an electrical power source <NUM>, a control with a temperature sensor <NUM> and a display <NUM> which is configured to indicate that the target temperature has been reached. In some embodiments, the electrical power source <NUM> may comprise a disposable DC battery <NUM>. In some embodiments, the electrical power source <NUM> may comprise AC power (as seen in <FIG>) supplied from a wall outlet <NUM> through a disposable sterilized power cord <NUM> passed off a sterile field. AC power, of course, would be able to provide more power, thereby decreasing the time required to achieve the target temperature and increasing the potential ablation time. The sensor/display <NUM>, <NUM> may be a simple analog thermometer, in contact with the liquid or the chamber wall, without any electrical connection (e.g., a standard mercury or alcohol column or a thermochromatic film commonly used to measure skin temperature). In some embodiments, the sensor <NUM> may comprise an electrical thermocouple in electrical communication with a display <NUM>. Many heating elements have built-in thermocouples. In some embodiments, the display <NUM> may be one or more binary optical indicators (e.g., an LED) that indicate that the temperature is in range. Alternatively, in some embodiments the display <NUM> may be a digital or analog display that shows the actual temperature. In some embodiments, the power source <NUM> may further comprise a manual on/off power switch <NUM>. The operator may manually turn the switch <NUM> on to activate the heating element <NUM> and heat the liquid, and may turn the switch <NUM> off when the target temperature has been reached. Alternatively, the power source <NUM> may be controlled by a knob or pair of up/down buttons <NUM> to set the target temperature. In some embodiments, additional circuitry may be required to create a temperature feedback loop, automatically adjusting power to maintain the target temperature.

Referring now to <FIG>, in some embodiments, the manual drive mechanism <NUM> comprises a cord or cable <NUM> attached to the exterior or interior surface of the piston <NUM> exiting the fluid chamber <NUM>, <NUM> (through a gasketed port <NUM> in the latter case). The operator pulls the cable or cord <NUM>, shortening it, drawing the piston <NUM> towards it and driving fluid out of or drawing fluid into the chamber <NUM>, <NUM>. In some embodiments, the cable or cord <NUM> may be attached to a ratcheting mechanism <NUM> which locks its position as its being withdrawn. In some embodiments, the ratcheting mechanism <NUM> may be reversible. The cable or cord <NUM> may also be engaged onto a pulley <NUM>, which may be fixated on an outside of one end of the chamber <NUM>, <NUM>. The pulley <NUM> may have a crankshaft <NUM> or knob with or without a ratcheting lock mechanism. The operator turns the crankshaft <NUM> or knob, wrapping a length of the cable or cord <NUM> onto the pulley <NUM>, shortening it, while drawing the piston <NUM> towards it and driving fluid out of or drawing fluid into the chamber <NUM>, <NUM>.

Referring now to <FIG>, in some embodiments, the drive mechanism <NUM> may comprise a fixed length belt or chain <NUM>. The belt or chain <NUM> may be attached to the interior surface of the piston <NUM>, exiting the fluid sub-chamber <NUM>, <NUM> and wrapping around the length of the chamber <NUM>, <NUM> through a series of pulleys or gears <NUM>, entering a sub-chamber and attaching to the exterior surface of the piston <NUM>. In some embodiments, one of the pulleys/gears may further comprise a crankshaft or knob <NUM>, with or without a ratcheting lock mechanism. The operator turns the crankshaft or knob <NUM>, moving the belt or chain <NUM> clockwise or counterclockwise, drawing the piston <NUM> towards it and driving fluid out of or drawing fluid into the chamber <NUM>, <NUM>.

Referring now to <FIG>, in some embodiments the manual drive mechanism <NUM> may be a lead (translation) screw <NUM>. The screw <NUM> can be positioned along the long axis of the chamber <NUM>, <NUM> and anchored to one end of the chamber <NUM>, <NUM> while maintaining a freedom of rotation. The screw <NUM> may pass through the other end of the chamber <NUM>, <NUM> through a hole in the piston <NUM> with a matching thread and finally through a hole in the chamber <NUM>, <NUM> which may be gasketed if that portion of the screw <NUM> is in contact with the fluid in the chamber. To prevent the screw <NUM> from spinning, as seen in <FIG>, the piston <NUM> may be axially symmetric or asymmetric (e.g., an ellipse) or there may be one or more guide rails <NUM> to keep the piston <NUM> from rotating. The external end of the screw <NUM> can be attached to a crankshaft or knob <NUM>. In some embodiments, rotating the screw <NUM> advances or withdraws the piston <NUM>, driving fluid from or drawing fluid into the chamber <NUM>, <NUM>.

The infusion device <NUM> may benefit from a passive or active autonomous powered drive mechanism <NUM>, one that acts independent of the operator. Referring now to <FIG>, the passive powered drive mechanism <NUM> may comprise a spring <NUM>. In some embodiments, the spring <NUM> may be a compression spring, which can be positioned outside of the fluid chamber <NUM>, <NUM> so that the spring <NUM> is fully compressed when the chamber <NUM>, <NUM> is full of fluid. When flow is initiated the spring <NUM> exerts a force against the exterior surface of the piston <NUM>, driving fluid out of the chamber <NUM>, <NUM> as it expands. In some embodiments, the compression spring may be positioned in the fluid chamber <NUM>, <NUM>, exerting force against the interior surface of the piston <NUM>, drawing fluid into the chamber <NUM>, <NUM> as it expands. Other types of springs (e.g., extension, rotary) may also be used in additional configuration.

Referring now to <FIG>, in some embodiments the active powered drive mechanism <NUM> may comprise an electric motor <NUM>. In some embodiments, the cable/pulley <NUM> (as seen in <FIG>) or lead screw drive mechanisms <NUM> (as seen in <FIG>) may be connected, directly or through one or more gears <NUM>, to a small electric motor <NUM>, which may be powered by a battery or AC power. In some embodiments, appropriate electrical components and circuitry may include switches or dials to turn the device on/off, adjust flow, temperature, pressure, the volume to be infused, or other parameters may be included as needed.

In some embodiments, referring now to <FIG>, the inflation <NUM>, inflow <NUM> and outflow <NUM> chambers are distinct structures, each with its own piston <NUM>, ports <NUM>, <NUM> and valves (not pictured). The inflow chamber <NUM> comprises at least one outlet port <NUM> and the outflow chamber <NUM> comprises at least one inlet port <NUM>. The inflow chamber <NUM> and outflow chamber <NUM> pistons <NUM> may be mechanically linked by a rigid rod <NUM>, cable <NUM> or belt so that they move in opposite directions relative to their inlet/outlet port <NUM>, <NUM>, wherein the total volume in the two flow chambers <NUM>, <NUM> may be constant and, as a result, the flow out of the outflow chamber <NUM> is the same as the flow back into the inflow chamber <NUM>. These linked pistons <NUM> are controlled by a single inflow/outflow chamber drive mechanism. The inflation chamber <NUM> may have its own piston <NUM> and drive mechanism <NUM>, which may be a manual mechanism. The drive mechanism <NUM> may be a rigid threaded plunger rod <NUM> with an analog or digital pressure gauge which functions just like a pressure syringe commonly used to inflate balloons in interventional procedures. In some embodiments, more complex manual and powered drive mechanisms may be used with the inflation chamber <NUM>. In some embodiments, the inflation chamber <NUM> is activated once at the beginning of a procedure to inflate the balloon <NUM> to the desired volume and pressure, the inflation chamber <NUM> then remains in a fixed position during the infusion and is activated in the reverse direction once at the end of the procedure to deflate the balloon <NUM>.

In some embodiments, the outlet ports <NUM> of the inflation chamber <NUM> and inflow chamber <NUM> can be connected to a three way inflow valve <NUM> which in turn may be connected to the balloon catheter's inflow lumen <NUM> so it is in fluid communication with one or the other fluid chamber <NUM>, <NUM>. The inlet port <NUM> of the outflow chamber <NUM> can be connected to the outflow lumen <NUM> of the balloon catheter <NUM> through a separate outflow valve <NUM>. Once the connections between the infusion device <NUM> and balloon catheter <NUM> are complete, the inflation <NUM> and inflow chambers <NUM> can be filled with fluid, the outflow chamber <NUM> starts empty. The inflow valve <NUM> may be positioned to establish fluid communication between the inflation chamber <NUM> and the balloon <NUM> through the catheter's <NUM> inflow lumen <NUM> while the outflow valve <NUM> may be closed. In other words, in this initial state, neither flow chamber <NUM>, <NUM> is in fluid communication with the balloon <NUM>. The inflation chamber's <NUM> drive mechanism <NUM> is activated, inflating the balloon <NUM> to the desired volume and pressure. The inflow valve <NUM> is then positioned to establish fluid communication between the inflow chamber <NUM> and the balloon <NUM> through the catheter's <NUM> inflow lumen <NUM>. The outflow valve <NUM> is then opened, establishing fluid communication between the outflow chamber <NUM> and the balloon <NUM> through the catheter's <NUM> outflow lumen <NUM>. The infusion can be initiated by activating the inflow <NUM> and outflow <NUM> chamber drive mechanism <NUM> driving their pistons <NUM> in opposite directions, simultaneously driving fluid out of the inflow chamber <NUM> and drawing fluid back into the outflow chamber <NUM> at precisely the same rate, while maintaining balloon <NUM> volume and pressure. Once the infusion is completed, the outflow valve <NUM> is turned off, the inflow valve <NUM> is switched to the inflation chamber <NUM> and the inflation chamber's <NUM> drive mechanism <NUM> is activated in the reverse direction, drawing fluid into this chamber <NUM> from the balloon <NUM> causing it to deflate.

In another embodiment, the outlet port <NUM> of the inflation chamber <NUM> may connect directly to the distal end of the inflow chamber <NUM> while the outlet port <NUM> of the inflow chamber <NUM> may be connected to the inflow lumen <NUM> of the balloon catheter <NUM> through a simple inflow valve (not pictured). When the simple inflow valve is open, both the inflation <NUM> and inflow chambers <NUM> can be in fluid communication with the inflow lumen <NUM> of the balloon <NUM>. The outflow valve <NUM> is initially closed, allowing the drive mechanism <NUM> of the inflation chamber <NUM> to inflate the balloon <NUM> to the desired volume and pressure. Since the inflation <NUM> and inflow <NUM> chambers may be in fluid communication, the inflow chamber's <NUM> piston <NUM> must remain in a fixed position during this period so that the fluid from the inflation chamber <NUM> fills the balloon <NUM> and not the inflow chamber <NUM>. Once the balloon <NUM> inflation is complete and the drive mechanism <NUM> of the inflation chamber <NUM> is deactivated, the outflow valve <NUM> may be opened and the drive mechanism <NUM> of the inflow/outflow chambers <NUM>, <NUM> can be activated to initiate the infusion. The inflation <NUM> and inflow <NUM> chambers remain in fluid communication, so the inflation chamber's <NUM> piston <NUM> must remain in a fixed position during this period so that the fluid from the inflow chamber <NUM> fills the balloon <NUM> and not the inflation chamber <NUM>. When the infusion is complete, the outflow valve <NUM> may be closed and the inflation chamber's <NUM> drive mechanism <NUM> can be activated in the reverse direction deflating the balloon.

Now referencing <FIG>, in some embodiments, the inflation chamber <NUM> remains separate but the inflow and outflow chambers are combined into a single structure <NUM> with a shared piston <NUM>. The piston <NUM> partitions the combined chamber <NUM> into inflow <NUM> and outflow <NUM> chambers. The outlet port <NUM> of the inflow chamber <NUM> and the inlet port <NUM> (see also 1406a and 1406b in <FIG>) of the outflow chamber <NUM> are located on opposite ends of the combined chamber <NUM>. Each port <NUM>, <NUM> has its own valve <NUM>, <NUM>. In some embodiments, as seen in <FIG> both ports <NUM>, <NUM> may be located on one end of the chamber <NUM>, with the outlet port <NUM> communicating directly with the inflow chamber <NUM> and the inlet port <NUM> communicating with the outflow chamber <NUM> through a central (as seen in <FIG>) or eccentric (as seen in <FIG>) outflow channel <NUM> that passes through or adjacent to the piston <NUM> and serves as a rail along which the piston <NUM> rides. The channel <NUM> may terminate close to the proximal end <NUM> of the combined chamber <NUM>, communicating with the outflow chamber <NUM> through an end hole. In some embodiments, the channel may extend all the way through the proximal end <NUM> of the inflow chamber <NUM>, communicating with the outflow chamber <NUM> through one or more side holes located near the proximal end <NUM> of the inflow chamber <NUM>. As the piston <NUM> moves, the volume in the inflow chamber <NUM> decreases by precisely the same amount as the volume in the outflow chamber <NUM> increases. The shared piston <NUM> can be driven by any manual or powered drive mechanisms. Since both sides of the piston <NUM> are in contact with a fluid filled chamber <NUM>, the mechanisms which feature external structures (e.g., rigid rod, cable/cord, lead screw) must have those structures exit the chamber through a gasketed port. A spring drive mechanism <NUM> (as seen in <FIG>), in contrast, can be completely contained within the fluid filled chamber <NUM>.

Now referencing <FIG>, in some embodiments, all three chambers can be part of a single structure <NUM>. The inflow <NUM> and outflow chambers <NUM> share a common piston <NUM> and drive mechanism <NUM> while the outflow chamber <NUM> communicates with its inlet port <NUM> either directly or through a central or eccentric internal channel <NUM> that passes through or adjacent to the piston <NUM> and communicates with the outflow chamber <NUM> through an end or side holes <NUM>. The inflation chamber <NUM> can also be integrated into the structure <NUM>, as a central or eccentric channel with its own piston <NUM>. An inflation channel <NUM> communicates with the inflow chamber <NUM> near its distal end <NUM>, through an end hole or side holes <NUM>. The inflation chamber's <NUM> drive mechanism <NUM> may be a manual mechanism, such as a threaded rigid rod <NUM> that functions like the plunger of a pressure regulated syringe. The inflation chamber <NUM> drive mechanism <NUM> can be activated, inflating the balloon <NUM> to the desired pressure and volume. The outflow chamber <NUM> inlet valve <NUM> may be opened and inflow chamber <NUM> drive mechanism <NUM> is activated, initiating the infusion. The outflow chamber <NUM> inlet valve <NUM> can be closed and the inflation chamber <NUM> drive mechanism <NUM> can be reversed, deflating the balloon <NUM>.

Referring now to <FIG>, in some embodiments a standard elliptical or spherical balloon <NUM> can uniformly transfer heat from the heated liquid <NUM> in the balloon <NUM> to the surrounding tissue. In some embodiments, as seen in <FIG>, the target tissue <NUM> may be relatively symmetric and the balloon <NUM> can be inserted into the middle of the tissue <NUM>. The balloon <NUM> may also be inserted adjacent to the target tissue <NUM> through other normal tissue <NUM>, whereby some normal tissue <NUM> is ablated along with the target tissue <NUM> leading to an ablated tissue lesion <NUM>. In some embodiments, as seen in <FIG>, the balloon <NUM> may be inserted through the lumen <NUM> of a hollow structure such as a blood vessel, airway, bone or gastrointestinal tract. In this case, the inflated balloon <NUM> makes contact with the inner wall of the lumen <NUM>, ablating through the wall <NUM> of the structure and surrounding tissues <NUM> in a uniform fashion.

Now referencing <FIG>, in some embodiments the local anatomy in the vicinity of the target tissue will be much more complex. A center of the target tissue <NUM> may not be directly accessible and the balloon <NUM> will be positioned adjacent to it through other tissue or a hollow structure. There may also be nearby critical structures that need to be protected from thermal damage. The balloon <NUM> may have a more complex structure to add directionality to the flow of heat towards the target tissue <NUM> but not to other tissues or structures. Specifically, when the balloon <NUM> is fully inflated, the heated liquid may be contained in a heated liquid compartment <NUM>, which may be limited to certain portions of the balloon <NUM> that are separated from the others which serve as insulators <NUM>. Such a structure may be used to create a pattern of "hot spots" <NUM> and "cold spots" on the surface of the balloon resulting in a specific ablation pattern <NUM>.

In some embodiments, the heated compartment <NUM> and an insulating substance may be configured such that the heat flows preferentially from the heated liquids into the target tissue <NUM> and not through the insulating portions <NUM> of the balloon <NUM>. Specifically, the volumetric heat capacity and (Cv) and thermal conductivity of the insulating material must be significantly lower than that of the liquid to be heated and the surrounding tissues. Since the water content of most tissues are very high, their thermodynamic properties are similar to water. The insulating material could, for example, a solid with low heat capacity and thermal conductivity such as a compressible foam. In some embodiments, gases may be used as insulators. The volumetric heat capacity of most commonly used gases is approximately <NUM> J m-<NUM>-<NUM> compared to <NUM> J m-<NUM>-<NUM> and <NUM> J m-<NUM>-<NUM> for water and tissues respectively. The thermal conductivity of most commonly used gases is approximately <NUM> W m-<NUM>-<NUM> compared to approximately <NUM> W m-<NUM>-<NUM> for water and most tissues. Because Cv and thermal conductivity are orders of magnitude higher for the liquid in the balloon <NUM> and the surrounding tissues than the gas in the insulating portions <NUM>, the liquid will efficiently transfer its heat through the hot spots to the tissue without significantly heating the gas in the insulating portions allowing the latter to keep the tissues adjacent to them cool until the ablation is complete.

In some embodiments, the balloon has internal septae <NUM> which divide the balloon <NUM> into separate compartments. Heated liquid can be infused into (and recycled through) the heated compartments <NUM>. In some embodiments, a gas (air, carbon dioxide, oxygen or any biocompatible gas) may be used to inflate the insulating compartments <NUM>. The balloon <NUM> surface overlying heated compartments <NUM> serve as "hot spots" <NUM>, allowing heat to transfer to and ablate its adjacent tissue. The balloon <NUM> surface overlying insulated compartments <NUM> serve as "cold spots", preventing heat from transferring to its adjacent tissue, protecting it from ablation.

In reference to <FIG>, <FIG>, and <FIG> in some embodiments, two concentric balloons <NUM>, <NUM> with separate lumens are attached to the distal end <NUM> of the catheter <NUM>. Referencing <FIG>, <FIG> and <FIG>, the inner balloon <NUM> when inflated has a smaller baseline radius than the outer balloon <NUM>. The inner balloon <NUM> may have one or more areas along its length where it protrudes radially to make contact with the inner wall of the outer balloon <NUM> yielding one or more areas of contact <NUM>. The areas of contact <NUM> may be incidental to any relative geometries of the two balloons <NUM>, <NUM>, or the areas of contact <NUM> can be forced by bonding or fusing the balloons <NUM>, <NUM>. The inner balloon <NUM> may be inflated with a circulating heated liquid <NUM> and the outer balloon may be inflated with a gas <NUM>. The areas of contact <NUM> between the inner <NUM> and outer <NUM> balloons become hot spots <NUM> (as seen in <FIG>) or strips <NUM> (as seen in <FIG> and <FIG>) which ablate the tissue <NUM> in matching patterns <NUM>. The rest of the outer balloon <NUM> remains cool because the gas <NUM> within the outer balloon <NUM> insulates the tissue <NUM> from the hot inner balloon <NUM> in much the way a thermos insulates its content from the atmosphere.

In some embodiments, insulating compartments <NUM> may be filled with an appropriate amount of gas <NUM> prior to use of the device. The insulating compartments <NUM> may be pre-filled with gas <NUM> during manufacture and sealed so that only the heated liquid compartments are inflated during the procedure. In some embodiments, in order to maneuver the balloon catheter <NUM> within the patient, the distal tip may be enclosed in a sheath or other delivery mechanism, compressing the pre-filled gas compartments so that a cross sectional profile is acceptable. Once the catheter <NUM> is in position, the distal tip is unsheathed, allowing the gas compartments to expand to their neutral volume. After the ablation is completed and the heated liquid compartments are deflated, the distal tip must be re-sheathed and the gas compartments recompressed to decrease the cross sectional profile prior to repositioning or withdrawing the balloon catheter <NUM>.

Now referring to <FIG>, in some embodiments both the insulating compartments and the heated liquid compartments of the balloon <NUM> are initially empty and communicate with their respective gas and heated liquid inflation lumens. A gas inflation device <NUM> is provided which delivers a volume of the appropriate gas (e.g., air, carbon dioxide, oxygen) through a gas inflation lumen into the insulating gas compartments so that they reach the appropriate volume or pressure. The device <NUM> also allows the insulating gas compartments to be deflated after the ablation is completed prior to withdrawing or repositioning the catheter <NUM>. The gas inflation device <NUM> may be a syringe, with or without a pressure indicator or regulator. Other embodiments of the gas inflation device <NUM> may utilize a cartridge filled with an appropriate gas (e.g., carbon dioxide) or a medical gas line available in an operating or procedure room (e.g., oxygen). The gas inflation device <NUM> may be integrated with the infusion device <NUM>. The insulating gas compartments may contain an effervescent powder such as calcium carbonate. The compartments may then be inflated by infusing a small volume of water into the compartments which reacts with the powder and releases a volume of gas, thereby inflating the compartments.

An embodiment of a method of operating a system in accordance with the present disclosure, as depicted in <FIG>, comprises: setting up the system <NUM>, positioning a catheter <NUM>, inflating a balloon <NUM>, initiating an infusion <NUM>, continuing the infusion <NUM>, and terminating the infusion <NUM>. In some embodiments, referencing <FIG>, setting up <NUM> comprises connecting a distal end <NUM> of an infusion device <NUM> to a proximal end <NUM> of the catheter <NUM> so that its chambers are in fluid communication with inflow <NUM> and outflow <NUM> lumens of the catheter <NUM> and a balloon <NUM>. In some embodiments, an inflation chamber <NUM> and an inflow chamber <NUM> are then filled with the fluid.

In some embodiments, positioning <NUM> comprises inserting a distal end <NUM> of the catheter <NUM> into a patient. In some embodiments, positioning <NUM> further comprises navigating the distal end <NUM> to a desired therapeutic or target location in the patient.

As seen in <FIG> and <FIG>, in some embodiments, inflating <NUM> the balloon <NUM> comprises activating an inflation chamber mechanism <NUM>, which may drive fluid into the inflow lumen <NUM> and inflate the balloon <NUM> (see <FIG>) to a desired volume and pressure. In some embodiments, the method further comprises monitoring inflation of the balloon <NUM>, and monitoring the location and orientation of the balloon <NUM> relative to the target location.

In some embodiments, as seen in <FIG>, initiation of infusion <NUM> may comprise activating the inflow chamber mechanism <NUM> which drives fluid into and draws fluid out of the balloon <NUM> through the inflow <NUM> and outflow <NUM> lumens at the substantially the same rate. As seen in <FIG>, the infusion continues <NUM> by continuously refreshing the fluid within the balloon <NUM> to achieve a desired therapeutic effect while maintaining balloon <NUM> volume and pressure.

As seen in <FIG> and <FIG>, terminating the infusion <NUM> may comprise deactivating the inflow chamber mechanism <NUM>. The balloon <NUM> may be deflated by reversing the inflation chamber mechanism <NUM> to withdraw fluid from the balloon <NUM> back into the inflation chamber <NUM>. The catheter <NUM> can then be withdrawn from the patient or navigated to a new therapeutic location.

In some embodiments, as depicted in <FIG>, a method of inflating a balloon catheter comprises: connecting a balloon catheter to an infusion device and an inflation device <NUM>, filling an inflation chamber and an inflow chamber of the infusion device with a liquid <NUM>, inserting the balloon catheter into a patient and navigating the balloon to a target tissue (or in the vicinity) <NUM>, activating the inflation chamber to fill compartments in the catheter with the liquid until a target pressure and volume are reached <NUM>, activating an infusion mechanism <NUM> of the inflow chamber to drive the liquid from the inflow chamber through an inflation lumen into the balloon while concomitantly drawing the liquid from the balloon through an outflow lumen into an outflow chamber of the infusion device, continuing the infusion <NUM> until a desire effect is achieved, and terminating the infusion <NUM> by deactivating the infusion mechanism. In some embodiments, the inflation device is filled with a gas or connected to a gas line if necessary. In some embodiments, the balloon may be first inflated with the gas by activating a gas inflation device until the target volume or pressure is reached.

Another embodiment of a method of operating a system <NUM> to perform a thermal ablation, as depicted in <FIG>, comprises: setting up the system <NUM>, heating a liquid <NUM>, positioning a catheter <NUM>, inflating a balloon <NUM>, initiating an infusion <NUM>, continuing the infusion <NUM>, and terminating the infusion <NUM>.

In some embodiments, as seen in <FIG>, setting up <NUM> comprises connecting the distal end <NUM> of the infusion device <NUM> to the proximal end <NUM> of the catheter <NUM> so that its chambers are in fluid communication with the inflow <NUM> and outflow <NUM> lumens of the catheter <NUM> and the balloon <NUM>. The inflation <NUM> and inflow chambers <NUM> are then filled with liquid.

Referring now to <FIG>, heating the liquid <NUM> may comprise activating a heating mechanism <NUM>. A liquid in the inflow chamber <NUM>, and optionally in the inflation chamber <NUM>, may then be heated to a target temperature. Positioning <NUM> may, in some embodiments, comprise positioning the distal end <NUM> of the catheter <NUM> into a patient <NUM> and navigating to a target <NUM>. Inflating the balloon <NUM> may comprise activing the inflation chamber mechanism <NUM>, thereby driving liquid into the inflow lumen <NUM> and inflating the balloon <NUM> to the desired volume and pressure. In some embodiments, the balloon <NUM> location and orientation relative to the target <NUM> may be monitored.

In some embodiments, initiating an infusion comprises activating the inflow <NUM> and outflow chamber <NUM> infusion mechanisms which drives heated liquid into and draws cooler liquid out of the balloon <NUM> through the inflow <NUM> and outflow <NUM> lumens at substantially the same rate, maintaining the balloon <NUM> temperature above the target temperature to ablate the target tissue <NUM>. In the continuing step <NUM>, the infusion continues, continuously refreshing the heated liquid within the balloon <NUM>, continuing the ablation process for a designated period of time or until a therapeutic effect is achieved. In some embodiments, the therapeutic effect is ablation, yielding an ablated tissue <NUM>. The infusion can be terminated in the terminating step <NUM> by deactivating the inflow <NUM> and outflow chamber <NUM> infusion mechanisms. The balloon <NUM> may be deflated by reversing the inflation chamber <NUM> mechanism to withdraw liquid from it back into the inflation chamber <NUM>. The catheter <NUM> can then be withdrawn from patient <NUM> or navigated to a new therapeutic location.

An alternative embodiment of a method of operation allows an operator to enhance efficiency of a system while maintaining efficacy of the system. The infusion device <NUM> and balloon catheter <NUM> may be provided separately. Once the inflation <NUM> and inflow chambers <NUM> can be filled, the infusion device <NUM> heats the liquid while the operator positions the balloon catheter <NUM> at the therapeutic target <NUM>. Once the liquid has reached the target temperature and the catheter <NUM> is positioned at the target <NUM>, the infusion device <NUM> and balloon catheter <NUM> are connected. The remainder of the operation proceeds as above with balloon <NUM> inflation followed by continuous infusion followed by balloon <NUM> deflation.

Another embodiment of the method allows multiple infusion cycles by taking advantage of an infusion device <NUM> which allows the inflow <NUM> and outflow chambers <NUM> and lumens <NUM>, <NUM> to be reversed and heats both the inflow <NUM> and outflow chambers <NUM>. The initial steps proceed as above. The infusion device <NUM> is set up, the catheter <NUM> is positioned, the liquid is heated, the balloon <NUM> is inflated and the infusion is initiated. As the infusion is proceeding, the liquid in the outflow chamber <NUM> can be being continuously reheated by the infusion device <NUM>. Once the inflow chamber <NUM> is empty, the operator adjusts the valves <NUM> so that the inflow <NUM> and outflow <NUM> chambers (and their respective balloon lumens) may be switched and reverses the direction of a manual or automatic drive mechanism <NUM> (see <FIG>). Reversing the direction of flow can be accomplished manually (operator adjusts valves <NUM> and reverses the drive mechanism <NUM>) or automatically (device detects completion of infusion and electrically adjusts valves <NUM> and reverses drive mechanism <NUM>). Reversing flow initiates another infusion cycle where the reheated liquid from the original outflow chamber <NUM> (now the inflow chamber) can be infused back though the balloon <NUM> into the original inflow chamber <NUM> (now the outflow chamber). This process can be continued indefinitely over multiple infusion cycles until the ablation has been completed.

In some embodiments the balloon <NUM> may be designed so that it delivers the thermal ablation energy according to a specified pattern. The balloon <NUM> can have a simple or a complex shape and structure to address a specific tissue ablation requirement. The target tissue <NUM> type, location, size, shape and adjacent structures may dictate the ideal balloon <NUM> shape and structure.

In some embodiments, as demonstrated in <FIG>, a method of thermal ablation comprises: connecting a balloon catheter to an infusion device and a gas inflation device <NUM>, filling an inflation chamber and an inflow chamber of the infusion device with a liquid <NUM>, activating a heating mechanism of the infusion device <NUM> and heating a liquid <NUM> in the inflow chamber until a target temperature is achieved, inserting the balloon catheter into a patient and navigating the balloon to a target tissue (or in the vicinity) <NUM>, activating the inflation chamber to fill compartments in the catheter with a heated liquid until a target pressure and volume are reached <NUM>, creating an appropriate pattern of hot and cool spots on a surface of the balloon <NUM>, activating an infusion mechanism <NUM> of the inflow chamber to drive the heated liquid from the inflow chamber through an inflation lumen into the heated compartments while concomitantly drawing a cooled liquid from the compartments through an outflow lumen into an outflow chamber of the infusion device, continuing the infusion until an ablation is confirmed by some measure <NUM>, and terminating the infusion by deactivating the infusion mechanism <NUM>. In some embodiments, the inflation device is filled with a gas or connected to a gas line if necessary. In some embodiments, the insulating compartments are inflated with the gas first by activating a gas inflation device until the target volume or pressure is reached. In some embodiments, the terminating comprising first deflating the heated compartments and then deflating the insulating compartments. In some embodiments, the balloon catheter may be repositioned to a different target tissue or removed from the patient.

A thermal fine element analysis (<FIG> and <FIG>) shows that successful ablation of target tissue requires that the temperature in the inner balloon must be maintained above an ablation temperature. This in turn requires that the heated liquid is continuously recycled through the balloon while maintaining its pressure and volume. A single inflation of a balloon with heated liquid, as seen in <FIG>, will not accomplish the desired effect even if the liquid is heated to a very high temperature. The heat sink effect of the tissue will quickly cool the liquid below the ablation temperature before the balloon heats the tissue, which is shown in <FIG> where over time (as seen between <FIG>) the ablation goes away as the inner balloon cools. Ablating while maintaining the temperature of the liquid in the inner balloon above the ablation temperature quickly heats the tissue adjacent to the "hot spot" leading to a successful ablation, as seen in <FIG>. The continuous flow balloon catheter feature of the device of the current invention allows the liquid in the heated liquid compartments to constantly be replenished with heated liquid, maintaining the liquid temperature while keeping the balloon volume and pressure constant.

Claim 1:
A system for balloon inflation (<NUM>), the system comprising:
a catheter (<NUM>) having an inflow lumen (<NUM>) and an outflow lumen (<NUM>);
a balloon (<NUM>) positioned at a distal end of the catheter, the balloon being in fluid communication with the inflow and the outflow lumen;
an infusion device (<NUM>) in fluid communication with the balloon through the inflow and outflow lumens, the infusion device configured for continuously circulating a fluid into and out of the balloon via the inflow lumen and the outflow lumen at matching flow rates in order to keep the balloon volume and pressure constant during an entire infusion;
wherein the infusion device comprises:
an inflow chamber (<NUM>) being in fluid communication with the balloon via the inflow lumen (<NUM>); and
an outflow chamber (<NUM>) being in fluid communication with the balloon via the outflow lumen (<NUM>)
wherein the inflow chamber (<NUM>) and outflow chamber (<NUM>) each comprise:
a piston (<NUM>), wherein each piston is configured to control the volume of fluid in the respective inflow chamber or outflow chamber; and
an associated drive mechanism (<NUM>);
and wherein the inflow (<NUM>) and outflow (<NUM>) chambers are mechanically linked via their drive mechanisms (<NUM>) so that, once the balloon is inflated, each piston (<NUM>) has a movement that is equal and opposite to the other piston (<NUM>).