Patent Publication Number: US-2020284471-A1

Title: Fluid Heating Apparatuses, Systems, and Methods

Description:
This application is a divisional of U.S. application Ser. No. 15/869,656 filed on Jan. 12, 2018, which is a continuation of U.S. application Ser. No. 14/115,807 filed on Nov. 5, 2013, which is a national stage entry of International Application No. PCT/US2012/037854, filed on May 14, 2012, which claims the benefit of U.S. Provisional Application No. 61/485,340, filed on May 12, 2011. The entire contents of each of the above applications is expressly incorporated by references herein. 
    
    
     FIELD 
     The disclosed subject matter involves medical electrical (ME) equipment in the form of fluid heating or warming apparatuses and systems and methods thereof. 
     BACKGROUND 
     Prevention and protection against electrical shock or leakage currents is a significant consideration in the design of medical electrical equipment. Leakage currents for medical electrical equipment may be defined by the path current takes and can include earth leakage current, enclosure leakage current (or touch current), patient leakage current, patient auxiliary leakage current, and mains voltage to applied part leakage current. 
     Most medical electrical equipment or devices have contact with a device operator, a patient, or both. Though leakage currents typically are small, the amount of current required to produce adverse physiological effects on a human body is also small, so such leakage currents must be limited to safe values by the design of medical electrical equipment. Accordingly, medical electrical devices must be designed to pass certain tests to ensure that excessive leakage current does not dissipate from the mains, the device enclosure, or applied parts to and through a human body. Portions of Standard ANSI/AAMI/IEC 60601, for instance, address safety requirements for medical electrical equipment. 
     Medical electrical equipment has a designated class and type, with categorization into class being based on the form of protection used against electrical shock or leakage current and type designation being defined by the degree of protection from electrical shock or leakage current. 
     Class I medical electrical equipment has a protective earth connection. The primary means of protection for Class I medical electrical equipment is the insulation between “live” parts and exposed conductive parts, such as a metallic enclosure. Supplemental protection is provided by the protective earth connection. Fault or leakage current can flow from the mains to earth via the protective earth conductive connection, which causes a protective device (e.g., a circuit breaker or a fuse) to disconnect the medical electrical equipment from the supply. Note, of course, that not all medical electrical equipment having a protective earth connection necessarily is classified as Class I medical electrical equipment. 
     Class II medical electrical equipment, on the other hand, does not have a protective earth, and protection against electrical shock is provided by reinforced insulation or double insulation. For double insulation, primary protection is provided by a first layer of insulation (including air) and secondary protection is provided by a second insulation layer. Leakage current can flow from Class II medical electrical equipment. 
     Different types of medical electrical equipment include B, BF, and CF and each type can afford a different degree of protection against electrical shock or leakage current. Generally speaking, B is for medical electrical equipment providing a particular degree of protection against electrical shock, particularly regarding allowable leakage currents and reliability of the protective earth connection (if present). BF is as type B, but with isolated or floating (F-type) applied part or parts. CF provides a higher degree of protection against electrical shock than BF, particularly with regard to allowable leakage currents and has floating applied parts. For instance, a Class II CF type medical electrical equipment applied part may be required to be designed to allow leakage current of less than 10 μA. Incidentally, an applied part may be defined as a part of the medical electrical equipment which in normal use necessarily comes into physical contact with the patient for the equipment to perform its function or can be brought into contact with the patient or needs to be touched by the patient. 
     Leakage current can result due to capacitance between the AC supply and the patient. A low dielectric constant, low surface area, and large spacing are common design requirements for minimizing the flow of leakage current. 
     SUMMARY 
     The Summary describes and identifies features of some embodiments. It is presented as a convenient summary of some embodiments, but not all. Further the Summary does not necessarily identify critical or essential features of the embodiments, inventions, or claims. 
     Fluid heaters or warmers and systems and methods thereof according to embodiments can be used with intravenous (IV) therapies including blood transfusions (e.g., blood normal electrolyte) and fluid infusions (e.g., saline, electrolyte solutions, medicines, specialty pharmaceuticals, lethal injections, etc.). 
     Included among embodiments described herein are groundless, extracorporeal, in-line fluid heating or warming apparatuses (and systems and methods thereof) characterized by substantially no leakage current or low leakage current, for instance to satisfy existing, contemplated, or future medical standard(s) for acceptable leakage current. Thus, fluid heating apparatuses according to embodiments of the disclosed subject matter either do not substantially induce or otherwise leak current into the fluid flowing through the fluid heater, or only leak or induce an acceptable amount of current into the fluid flowing through the fluid heater. Accordingly, substantially no or an acceptable amount of current may reach a patient intravenously connected to the fluid path heated by a fluid heater according to embodiments of the disclosed subject matter. 
     In addition to having low or substantially no leakage current, embodiments of the disclosed subject matter can quickly and evenly heat or warm a fluid flowing therethrough at acceptable or optimal application-specific flow rates (e.g., transfusion and infusion flow rates). Real-time temperature sensing also may be implemented for adjusting temperature and/or to monitor fluid or heater temperature against predetermined maximum and minimum temperature values. Optionally the maximum and minimum temperature values may be electronically set or reset by an operator of the fluid heating apparatus. 
     Fluid heating apparatuses according to embodiments described herein each can be configured as a standalone device, with its own control system, to be used with any suitable fluid processing system. Or, fluid heating apparatuses according to embodiments can be a component of a specific fluid processing system, such as a dialysis machine or system. In the latter case, the fluid heating apparatus may not have its own control system and can thereby be controlled by a controller of the specific fluid processing system, or, a controller of the specific fluid processing system can operate in a master-slave relationship with a controller of the fluid heating apparatus. 
     According to embodiments, the disclosed subject matter includes any systems and/or methods configured to implement any of the apparatuses described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will hereinafter be described in detail below with reference to the accompanying drawings, wherein like reference numerals represent like elements. The accompanying drawings have not necessarily been drawn to scale. Any values dimensions illustrated in the accompanying graphs and figures are for illustration purposes only and may not represent actual or preferred values or dimensions. Where applicable, some features may not be illustrated to assist in the description of underlying features. 
         FIG. 1A  illustrates a cross-sectional rear view of a fluid heating apparatus according to an embodiment of the disclosed subject matter. 
         FIG. 1B  illustrates an overhead view of the fluid heating apparatus of  FIG. 1A . 
         FIG. 2A  illustrates a cross section view of another embodiment of a fluid heating apparatus according to the disclosed subject matter. 
         FIG. 2B  illustrates a cross section view of a variation of the fluid heating apparatus of  FIG. 2A . 
         FIG. 3A  is an illustration of a cross section view of another embodiment of a fluid heating apparatus according to the disclosed subject matter. 
         FIG. 3B  is an illustration of a cross section view of yet another embodiment of a fluid heating apparatus according to the disclosed subject matter. 
         FIG. 4A  illustrates a cross section of a fluid heating apparatus according to another embodiment of the disclosed subject matter. 
         FIG. 4B  illustrates an overhead view of a fluid heating apparatus according to another embodiment of the disclosed subject matter. 
         FIG. 4C  illustrates a cross section view of a fluid heating apparatus according to another embodiment of the disclosed subject matter. 
         FIG. 4D  illustrates a cross section view of a variation of the fluid heating apparatus of  FIG. 4C . 
         FIG. 5A  illustrates a cross section view of yet another embodiment of a fluid heating apparatus according to the disclosed subject matter. 
         FIG. 5B  illustrates a side view of the fluid heater according to  FIG. 7A . 
         FIG. 6A  is an overhead view of a side-by-side multi-channel fluid heating apparatus according to embodiments of the disclosed subject matter. 
         FIG. 6B  is a side view of an over/under multi-channel fluid heating apparatus according to embodiments of the disclosed subject matter. 
         FIG. 6C  is an illustration of an overhead view of a fluid heating apparatus with a channel having a bifurcated portion according to embodiments of the disclosed subject matter. 
         FIG. 6D  is a side view of a fluid heating apparatus having a non-uniform fluid channel. 
         FIG. 7A  illustrates a side view of a fluid heating apparatus with an attachment according to embodiments of the disclosed subject matter. 
         FIG. 7B  illustrates a side view of the fluid heating apparatus of  FIG. 5A  with another attachment according to embodiments of the disclosed subject matter. 
         FIG. 8  shows a system having the fluid heating apparatus of  FIGS. 1A and 1B  as a component according to embodiments of the disclosed subject matter. 
         FIGS. 9A-9E  illustrate examples of control circuitry to control fluid heating apparatuses according to embodiments of the disclosed subject matter. 
         FIG. 9F  shows a current command signal output of the circuitry of  FIG. 9E . 
         FIG. 10A  illustrates embodiments of the disclosed subject matter. 
         FIG. 10B  illustrates embodiments of the disclosed subject matter. 
         FIG. 11  illustrates a method according to embodiments of the disclosed subject matter. 
         FIG. 12  is a heating apparatus according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments in which the disclosed subject matter may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the disclosed subject matter. However, it will be apparent to those skilled in the art that the disclosed subject matter may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the disclosed subject matter. 
     Included among embodiments described herein are fluid heating or warming apparatuses (and systems and methods thereof) characterized by substantially no leakage current or low leakage current, while at the same time sufficiently heating a fluid flowing therethrough to a desired temperature at a given flow rate. Generally speaking, the configuration of fluid heating apparatuses according to embodiments of the disclosed subject matter can have a structure and be operative to provide for heat from one or more heating elements to be distributed to a relatively large surface area for heat transfer to a fluid flowing through a fluid channel or channels of the fluid heating apparatus. Additionally, embodiments of the invention can also include heating elements for heating bags, for instance, providing heat to a relatively large plate or plates. 
     The fluid can be heated from an initial temperature to a predetermined temperature or temperature range. Moreover, the heat output from the heating element(s) can be maintained so as to uniformly heat fluid flowing through a fluid channel of the fluid heating apparatus. For instance, fluid heating apparatuses according to embodiments of the disclosed subject matter can heat a fluid from 15° C. to 40° C. flowing at a flow rate of 300 ml/min and providing leakage current of less than 10 μA. As another example, fluid can be heated to about 38° C. through about 43° C. at a flow rate of up to 500 ml/min. Heating to the aforementioned temperatures or temperature ranges is not intended to limit the temperature or temperature ranges to which fluid(s) can be heated according to embodiments of the invention. For example, temperatures much higher than the foregoing temperatures or temperature ranges can be achieved, for example, temperatures above the boiling point of water. Fluid temperature can be maintained at any of the aforementioned temperatures or temperature ranges. Additionally, the desired maximum temperature can be set to the aforementioned temperature, the aforementioned temperature range, or a specific temperature in the temperature range. Embodiments of the disclosed subject matter also can warm a product (e.g., blood) from 10° C. at flow rates from 10 to 300 ml/min to a temperature in the range of 35° C. to 40° C. Fluids having flow rates of over 500 ml/min can also be heated. Moreover, heating to temperatures or temperature ranges above 43° C. also can be attained. Higher pressures and bubbles can also be accommodated for or otherwise heated and handled. 
       FIGS. 1A and 1B  show a fluid heating apparatus  100  according to embodiments of the disclosed subject matter. Fluid flow direction is into the page for  FIG. 1A  and upward in  FIG. 1B , as indicated by the up-going arrow F. 
     Fluid heating apparatus  100  includes a fluid channel  102 , a fluid channel interface  104  partially surrounding the fluid channel  102 , heat spreaders  106  adjacent the fluid channel interface  104 , a first heating element  108   a , a second heating element  108   b , and a seal  110 . Fluid heating apparatus  100  also can include a temperature sensor  112 . Not shown in  FIGS. 1A and 1B , and as will be discussed later, fluid heating apparatus  100  can be electrically coupled to a controller, and the controller can receive feedback signals from temperature sensor  112  and provide control signals to a driver to control operation of the fluid heating apparatus  100 , for example, to control operation of the heating element(s), such as on/off operation, the amount of heat output by the heating element(s), ramp up heating time, etc. 
     Fluid channel  102  generally may be narrow to maximize velocity and minimize volume throughput of a fluid flowing through the fluid channel. In the embodiment shown in  FIGS. 1A and 1B , the fluid channel  102  may be formed by fluid channel interface  104  and seal  110 . Not explicitly shown, optionally, the fluid channel  102  can be sized as shown in  FIG. 1A  for the entire length of the fluid heating apparatus  100 , or, alternatively, it can be sized as shown in  FIG. 1A  for only a portion of the length of the fluid heating channel (e.g., only at the middle, only the ends, or only one end of the fluid heating apparatus). Thus, in various embodiments, fluid channel  102  may be of a same size and shape through the length of the fluid heating apparatus  100 , and in alternative embodiments the fluid channel  102  can vary in size and shape along the length of the fluid heating apparatus  100 . 
     Both fluid channel interface  104  and seal  110  can be non-fouling, as these components will be in contact with fluids that are to enter a patient, for example. Non-fouling characteristics of the fluid channel interface  104  and the seal  110  can also prolong the life of the fluid channel  102  or the fluid heating apparatus itself and/or it may make the fluid heating apparatus  100  easier to clean. For instance, the fluid channel interface  104  may be a copper plate having a surface treatment thereon, such as a nickel and gold multi-layer plate, film, or laminate. Fluid channel interface  104  and seal  110  can be sealingly coupled together by any suitable means, such as an adhesive, fusing, etc. 
     Incidentally, optionally, fluid heating apparatuses (including fluid heating apparatus  100 ) according to embodiments of the disclosed subject matter can have a fluid channel that is configured for bidirectional fluid flow. Alternatively, fluid heating apparatuses according to embodiments of the disclosed subject matter may have a fluid channel configured for unidirectional fluid flow. Thus, in the latter case, indicia, such as positioning of temperature sensor  120  and/or markings may indicate direction of flow and thus instruct an operator or technician, for instance, as to proper orientation for connecting the fluid heating apparatus to attachments, such as fluid flow lines into and out of the fluid heating apparatus. 
     In various embodiments, the fluid channel interface  104  may be a “stainless” material, such as stainless steel or glass. Alternatively, as discussed above, the fluid channel interface  104  can be a copper plate. Optionally, the inner portion of the copper plate that would otherwise contact the fluid can have a surface treatment thereon. For example, the surface treatment may be an anti-corrosion treatment. Optionally, the surface treatment may be a multi-layer film, plate, or laminate comprised of nickel and gold, with the gold layer forming the fluid contacting surface of the fluid channel interface. Alternatively or optionally, the surface treatment can be a metal vapor deposition. 
     The seal  110  can be made of any suitable material, in various embodiments of a material different from the fluid channel interface  104 , and can create a liquid and/or air-tight seal with the fluid channel interface  104 , thereby creating a liquid and/or air-tight fluid channel  102 . The seal  110  also can be made of copper, for instance, with a multi-layer film or laminate comprised of nickel and gold, for instance. 
     On top and bottom of the fluid channel interface  104  are heat spreaders  106 , and coupled to the heat spreaders  106  are a plurality of heating elements (the embodiment shown in  FIGS. 1A and 1B  includes two heating elements  108   a ,  108   b ). In various embodiments, heat spreaders  106  may be metallic, for example, aluminum. Heat spreaders  106  can have a relatively large surface area for heat transfer from heating elements  108   a ,  108   b  to a fluid flowing through the fluid channel  102 . 
     First and second heating elements  108   a ,  108   b  can be of any suitable material and can be comprised of a shell, a heat producing element (not explicitly shown), and electrical connections or terminals (not shown) to couple the heat producing element to a controller, for example. For instance the shell of heating elements  108   a ,  108   b  can be made of a material that is highly thermally conductive as well as highly electrically insulative (i.e., having a high dielectric strength). The shell material also may exhibit or provide uniform temperature distribution, a relatively high durability at a low mass, a relatively rapid temperature ramp-up rate, and a low coefficient of thermal expansion. The heating elements may be comprised of one or more transistors, such as power transistors. Optionally, the one or more transistors may provide the only heating source. 
     Each shell may be made of a ceramic, an alumina ceramic, for example, of high thermal conductivity aluminum nitride (AlN). Another example can be beryllium oxide (BeO), for example, 1 mm thick. The heat producing element (or elements) can be internal, external, or have a portion that is internal and a portion that is external of the highly thermally conductive and highly electrically insulative shell and can be thermally matched to the shell, for example. Thus, optionally, the highly thermally conductive and highly electrically insulative shell may partially or fully enclose the heat producing element. 
     Heating elements  108   a ,  108   b  may be removably attached or fixedly attached to their respective heat spreaders  106 . For example, the heating elements  108   a ,  108   b  may be fixedly attached to heat spreaders  106  via a thermally resistant epoxy or glue that maintains its bond with the heating element  108   a ,  108   b  and heat spreader  106  even at elevated temperatures. Alternatively, a heating element  108   a ,  108   b  can be removably attached to a corresponding heat spreader  106  by way of retaining slide grooves, snap-fit, or the like. Embodiments having removably attachable and detachable heating elements  108   a ,  108   b  can offer an advantage of being able to switch out heating elements in the case of a defective heating element, or in order to change a size, an output power, a maximum output temperature, and/or an output temperature range of a heating element of the fluid heating apparatus  100 . 
     Each heating element  108   a ,  108   b  can have a configuration so as to produce substantially no leakage current or low leakage current, in various embodiments, 10 μA or less, less than 10 μA, 5 μA or less, or 1 μA or less. 
     The heating elements can be of any suitable shape, size, and/or configuration. Heating elements  108   a ,  108   b  can be relatively thin as shown in  FIG. 1A  and rectangular in the plan view per  FIG. 1B , for instance. Each heating element  108   a ,  108   b  can have a heating element surface of 10 cm2 and a thickness of 1.6 mm, for example. Moreover, heating elements can be arranged at any suitable position on the heat spreaders  106 .  FIGS. 1A and 1B , for example, show heating elements  108   a ,  108   b  being located on the top and bottom, respectively, of the fluid heating apparatus  100 , on their respective heat spreaders  106  and not on or adjacent the fluid channel interface  104 . Of course the heating elements can be of any suitable shape, size, and/or configuration and do not have to be elongated, and can be square shape. In various embodiments, heating elements can be formed to take the shape and contour of the heat spreaders to which they are attached. 
     Temperature sensor  112  can be any suitable sensor to sense a temperature of a heat spreader  106 , such as an RTD (Resistance Temperature Detectors) sensor or a thermocouple, for example. 
       FIG. 1B  shows temperature sensor  112  being a plate temperature sensor that is located on top of heat spreader  106 . Optionally, another temperature sensor  112  can be arranged on the bottom heat spreader  106 . As discussed above, temperature sensor(s)  112  can be electrically coupled to a controller, for example, to provide temperature-related feedback signals to a controller. A controller may use these feedback signals to adjust the output of one or more heating elements, such as heating elements  108   a ,  108   b.    
     Temperature sensor  112  can be located as shown in  FIG. 1B  or somewhere else. For example, as another option, a temperature sensor  112  may be located at an input of the fluid heating apparatus  100  and/or a temperature sensor  112  can be located at an output of the fluid heating apparatus  100 . In various embodiments, temperature sensor  112  can be located on or adjacent heating elements  108 . 
     Optionally or alternatively, a temperature sensor may be arranged closer to the fluid channel  102  or with a face forming part of the fluid channel  102 . In the latter case, the face of the temperature sensor can be non-fouling. Further, temperature sensors may have faces forming part of the fluid channel at the input of the fluid heating apparatus  100  and at the output of the fluid heating apparatus  100 . Such a configuration can provide for monitoring of a temperature of the fluid as it enters the heating apparatus  100  and as it is about to exit the fluid heating apparatus  100 . Thus, a change in temperature of the fluid as it passes through the fluid heating apparatus  100  can be determined and monitored using feedback signals from the temperature sensors provided to a controller. 
       FIGS. 1A and 1B  show an embodiment of a fluid heating apparatus  100 . However, fluid heating apparatuses can be differently configured.  FIGS. 2-7  show alternative, non-limiting embodiments. 
       FIG. 2A  illustrates a cross section view of another embodiment of a fluid heating apparatus  200  according to the disclosed subject matter.  FIG. 2B  illustrates a cross section view of a variation of the fluid heating apparatus  200 . Fluid heating apparatuses  200  shown in  FIGS. 2A and 2B  are similar to fluid heating apparatus  100  discussed above, but include differently sized and shaped fluid channels and fluid interfaces.  FIG. 2A , for example, shows fluid channel  202   a  and fluid interface  204   a  being circular in cross section.  FIG. 2B  on the other hand shows fluid channel  202   b  and fluid interface  202   b  being square shaped in cross sectional view. Not explicitly shown, optionally, the circular and square channels can run the entire length of the fluid heating apparatuses  200 , or either can run only a portion of the length of the fluid heating channel (e.g., only the middle, only the ends, only one end, etc.). Also note that fluid seal  110  can extend inwardly to “meet” the fluid interfaces  202   a ,  202   b . Alternatively, fluid seal  110  can be omitted and the fluid interfaces  202   a ,  202   b  can be enclosed structures that can fully encase the fluid flowing through fluid channels  202   a ,  202   b.    
       FIG. 3A  is an illustration of a cross section view of another embodiment of a fluid heating apparatus  300 .  FIG. 3B  shows cross section of a variation of the fluid heating apparatus  300  shown in  FIG. 3A . 
     Fluid heating apparatuses  300  shown in  FIGS. 3A and 3B , generally, can incorporate a heat coupling feature, whereby heat from the heating elements  108   a ,  108   b  can be coupled via the area of the heating elements to fluid interface  304  and thus to fluid in fluid channel  302  via heat conduction elements  314 . Substrate portions  316  in  FIGS. 3A and 3B  can be heat spreaders as discussed above, or, alternatively, they can be non-heat spreading or conducting components. Substrate portions  316  may be of a different material than heat conduction elements  314 . Also, fluid channel  302  and fluid interface  304  are not necessarily square shaped in cross section and can be a non-square rectangle or circular, for example, in cross sectional view. Note also that the heat conduction elements  314  may form to a point or a wedge having a pointed planar surface, for example, at the fluid interface  304 . 
       FIG. 4A  illustrates a cross section of a fluid heating apparatus according to another embodiment of the disclosed subject matter. The fluid heating apparatus shown in  FIG. 4A  is similar to fluid heating apparatus  100  shown in  FIGS. 1A and 1B , but fluid seal  110  is omitted. Thus, heat spreaders  106  can be coupled directly together to seal the fluid channel  102 . Alternatively, fluid interface  104  can completely surround the fluid channel  102 . 
       FIG. 4B  illustrates an overhead view of a fluid heating apparatus according to another embodiment of the disclosed subject matter. The fluid heating apparatus of  FIG. 4B  is similar to fluid heating apparatus  100  shown in  FIGS. 1A and 1B , but with side heating elements  108   c ,  108   d  (bottom heating element  108   b  not explicitly shown). 
       FIG. 4C  illustrates a cross section view of a fluid heating apparatus according to another embodiment of the disclosed subject matter.  FIG. 4D  illustrates a cross section view of a variation of the fluid heating apparatus of  FIG. 4C . The fluid heating apparatuses of  FIGS. 4C and 4D  have circular cross sections, with four heating elements  108   a ,  108   b ,  108   c ,  108   d  spaced equidistance from adjacent heating elements on the outside of the fluid heating apparatus body. The heating elements can be flat plates or they can be shaped based on the shape of the fluid heating apparatus body. For example, the heating elements  108   a ,  108   b ,  108   c ,  108   d  may have a curvature based on the radius of curvature of the fluid heating apparatus body. Optionally, the entire heating element may have a curvature based on the curvature of the fluid heating apparatus. Alternatively, only one side—the side coupled to the fluid heating apparatus body—may be curved. 
     In alternative embodiments  FIGS. 4A, 4B, 4C, and 4D , there may only be one heat spreader  106  that completely surrounds the fluid channel  102 / 202  (i.e., the heat spreader is formed in one piece with the fluid channel formed therein). 
       FIG. 5A  illustrates a cross section view of yet another embodiment of a fluid heating apparatus  500  according to the disclosed subject matter.  FIG. 5B  illustrates a side view of the fluid heater  500 . As can be seen, fluid heating apparatus  500  includes one heating element  508  surrounding in a radially inward direction a portion of the fluid heating apparatus  500 . The fluid channel  502  (shown as dashed lines in  FIG. 5B ) is surrounded by fluid interface  504 , which is surrounded by heat spreader  506 , which in turn has a portion surrounded by heating element  508 . The portion of the heating element  508  which surrounds heat spreader  506  can be the portion shown in  FIG. 5A , another portion of same size, or the entire portion of the heat spreader  506 , for example. Fluid heating apparatus  500  also can have a temperature sensor  512 . Heating element  508  can be positioned closer to the input of the fluid heating apparatus  500 , or it can be positioned closer to the output of the fluid heating apparatus  500 .  FIG. 5B , for example, shows the heating element  508  being positioned an equal distance from the input and output of the fluid heating apparatus  500 . Moreover, optionally, in various embodiments, heating element  508  may be slidable or movable along the length of the fluid heating apparatus  500  such that it can be repositioned. Locking devices, such as detents, hooks, etc. may be provided to hold the heating element  508  in desired position. 
       FIGS. 6A-6D  show channel configurations for heating apparatuses according to embodiments of the disclosed subject matter. Note that for  FIGS. 6A-6D , additional heating apparatus components, such as heating element(s), temperature sensor(s), fluid interface(s), etc., are not shown. 
       FIG. 6A  is an overhead view of a side-by-side multi-channel fluid heating apparatus  600 A according to embodiments of the disclosed subject matter. Fluid channels  602   a   1 ,  602   a   2 , shown by dashed lines, are positioned side-by-side in overhead view. Optionally, they may be at a same level in side view.  FIG. 6B  is a side view of an over/under multi-channel fluid heating apparatus  600 B according to embodiments of the disclosed subject matter. Fluid channel  602   b   1  is shown as being positioned above fluid channel  602   b   2 . Optionally, fluid channels  602   b   1 ,  602   b   2  can be directly above/below one another in overhead view. 
       FIG. 6C  is an illustration of an overhead view of a fluid heating apparatus  600 C with a fluid channel  602   c  having a bifurcated portion according to embodiments of the disclosed subject matter. The bifurcated portion can be at the input and/or output side of the fluid heating apparatus  600 C.  FIG. 6D  is a side view of a fluid heating apparatus  600 D having a fluid channel  602   d  with a non-uniform flow path. The fluid path can increase or decrease from the input side of the fluid heating apparatus  600 D. 
     In the embodiments discussed herein, a number of different fluid channels have been described and shown. However, fluid channels are not limited to those described above, and can take other configurations. In various embodiments, the interior of the fluid channel can be smooth. Alternatively, some or all of the interior can be irregular, for example grooved, threaded, corkscrew, ridged, etc. Optionally, the configuration of the fluid channel can optimize fluid flow, for instance, to create a vortex. Other channel configurations can also be implemented, such as a looping system comprised of one or more channel loops arranged generally horizontally. Additionally, the fluid channel can have formed or arranged therein or at inputs or outputs thereof, one or more filter elements to filter the fluid flowing through the fluid channel. 
     Fluid heating apparatuses according to embodiments of the disclosed subject matter can have ends thereof coupled to any suitable attachment. For example,  FIG. 7A  shows a fluid heating apparatus  700  with an attachment  750  in the form of tubing (e.g., miniature polymeric tubing) coupled to fluid heating apparatus  700  in alignment with fluid channel  702 . Attachment  750  can be attached to the input of the fluid heating apparatus  700 , the output of the fluid heating apparatus  700 , or both.  FIG. 7B  shows fluid heating apparatus  700  with another attachment  760  in the form of a syringe. Thus, the fluid heating apparatus  700  shown in  FIG. 7B  can be implemented as a syringe heater. Leak detectors can also be implemented at the input(s) and/or output(s) of fluid heating apparatuses according to embodiments of the disclosed subject matter. Such leak detectors can be used to detect leaks at interfaces between the fluid heating apparatus and attachments. Note that for  FIGS. 7A and 7B , additional heating apparatus components, such as heating element(s), temperature sensor(s), fluid interface(s), etc. are not shown. 
     In the embodiments discussed herein, a number of fluid heating apparatuses have been described and shown. However, fluid heating apparatuses are not limited to those described above, and can take any suitable configuration. In various embodiments, fluid heating apparatuses may include a window or windows to view fluid levels and/or to monitor for air bubbles. Various embodiments also may employ a bubble trap. 
       FIG. 8  shows a system  800  having the fluid heating apparatus of  FIGS. 1A and 1B . Not shown in  FIG. 8  are the fluid connections into and out of fluid heating apparatus  100 . System  800  can be used with any suitable medical equipment, such as a dialysis system. 
     System  800  can include fluid heating apparatus  100 , a controller  825 , and a driver  835 . As shown in  FIG. 8 , fluid heating apparatus  100  is electrically coupled to controller  825  and driver  835 . More specifically, controller  825  is electrically coupled to temperature sensor  112  and can receive feedback signals from temperature sensor  112 , such as temperature-related feedback signals. In the case of an embodiment where multiple temperature sensors are implemented, controller  825  can be coupled to each temperature sensor to receive individual temperature sensor signals. 
     Controller  825  is coupled to driver  835  and can provide control signals to driver  835 , for example, in response to feedback signals from temperature sensor  112 . Control signals provided by the controller  825  to driver  835  may be to control operation of the heating element(s)  108 , such as on/off operation, the amount of heat output by the heating element(s), ramp up heating time, applied current, to promote unity power factor, to balance transistor power, to control current to make constant the power as the line voltage varies, etc. 
     Controller  825  also may provide control signals to driver  835  by measuring measure RMS voltage during a half cycle of the line and setting the command ratio for the next cycle. A PWM output by controller  825  may be used for generating a multiplication factor. Any of the foregoing control can be used to accurately set a temperature of a heating element to a predetermined temperature (or within a predetermined temperature range) and maintain the heating element at such temperature (or within the temperature range). 
     Not shown in  FIG. 8 , controller  825  may be coupled to another “master” controller as part of an overall fluid processing system. Additionally, in various embodiments, controller  825  may be located on-board the fluid heating apparatus  100 , or, alternatively, it can be located remotely from fluid heating apparatus  100  and coupled thereto via electrical connections. Optionally, only driver  835  may be located on-board fluid heating apparatus  100 . 
     Additionally, controller  825  or a fluid processing system according to embodiments of the disclosed subject matter, can monitor in real-time temperature of a fluid flowing through a fluid channel of a fluid heating apparatus and set a temperature of the a fluid heating apparatus in order to heat the fluid flowing through the fluid channel to a predetermined temperature. Controller  825  or a fluid processing system according to embodiments of the disclosed subject matter can also determine whether electricity is supplied to any of its components, such as controller  825 , heating element  108 , etc. Controller  825  or a fluid processing system according to embodiments of the disclosed subject matter can also determine whether fluid is present or flowing through the fluid heating apparatus  100  (e.g., infrared detection) and/or can generate an alarm in response to monitoring of temperature (e.g., a low temperature alarm and/or a high temperature alarm). Controller  825  may turn off heating elements  108  or cause output thereof to be reduced if it is determined that a temperature of the element and/or the fluid is above a predetermined upper threshold. 
       FIGS. 9A-9E  illustrate examples of circuitry that can be used as part or all of driver  835  to control fluid heating apparatuses according to embodiments of the disclosed subject matter.  FIG. 9F  shows a current command signal output of the circuitry of  FIG. 9E . Generally speaking, the control circuitry shown in  FIGS. 9A-9E  can operate under linear controlled resistance control. Further, circuitry according to embodiments of the invention can implement solid state devices such as solid state power regulators (e.g., transistors, such as MOSFETs, IGBTs, BJTs, or combinations thereof). 
       FIGS. 9A and 9B  show driver circuitry using IGBTs and MOSFETs, respectively, as dissipative elements. Each transistor may be controlled, for example, to conduct for an AC half cycle.  FIG. 9C  is circuitry for a current control signal. The circuitry in  FIG. 9C  for current control signal can be designed and operative such that the current is proportional to a line AC voltage for unity power factor, for instance. 
     In various embodiments, the AC input voltage may be rectified with a bridge and the transistors can dissipate for each half cycle. See, for example,  FIG. 9D . The emitter resistors can be used to balance the current between the IGBTs when the design is implemented with the gates connected in parallel, for example. Alternately, operation amplifiers (e.g., six op-amps) can be used to drive each gate, independently closing the loop on current sensing for the associated emitter resistor. Each collector can be fused in case there is a failure. 
     In various embodiments, a current command for a load may be proportional to the AC voltage in order to get unity power factor. Yet as the line voltage fluctuates the load current can be controlled as 1/AC VRMS to keep power constant. In various embodiments, processor uP can provide this control function. Processor uP can measure the RMS voltage during a half cycle of the line voltage and set a command ratio for the next cycle. A PWM signal could be used for generating the multiplication factor. Thus, in various embodiments, processor uP may control PWM signals to provide a dissipated power per the command it receives from a master controller. This power can be held constant as the line voltage varies or is caused to vary. Alternatively, processor uP may provide the command to another controller, such as another microprocessor or controller  825 . See  FIGS. 9D-9F , for example.  FIG. 9E , for example, shows processor uP outputting an output PWM signal to a switch to produce a rectified line voltage signal, which can be passed through a low pass filter, for instance, to produce a current command as indicated above.  FIG. 9F  shows an example of a rectified current command having an amplitude proportional to the PWM duty cycle. 
       FIGS. 10A and 10B  systems in which fluid heating apparatuses according to embodiments of the disclosed subject matter may be incorporated. 
       FIG. 10A  shows FIG. 12 from U.S. Pat. No. 7,780,619 issued Aug. 24, 2010 modified to incorporate fluid heating apparatus FH according to embodiments of the disclosed subject matter. The entire content of U.S. Pat. No. 7,780,619 is hereby incorporated by reference in its entirety into the present application. Fluid heating apparatus FH can be located as shown in  FIG. 10A , or it can be positioned at any suitable location, either inside or outside of an enclosure of the blood processing apparatus in U.S. Pat. No. 7,780,619. Multiple fluid heating apparatuses FH also may be employed, for instance, in series in a patient line. 
       FIG. 10B  shows FIG. 1 from U.S. Pat. No. 7,419,597 issued Sep. 2, 2008 modified to incorporate fluid heating apparatus FH according to embodiments of the disclosed subject matter. The entire content of U.S. Pat. No. 7,419,597 is hereby incorporated by reference in its entirety into the present application. Fluid heating apparatus FH can be located as shown in  FIG. 10B , or it can be positioned at any suitable location, such as inside hemofiltration device 1 in U.S. Pat. No. 7,419,597. Further, multiple fluid heating apparatuses FH also may be employed, for instance, in series in the patient line  90 . Optionally, a heating plate may be employed under bag  81  in  FIG. 10B , for example. Optionally, the heating plate can be significantly smaller in area than the overall surface on which the bag  81  rests. 
     Accordingly, fluid heating apparatuses according to embodiments of the disclosed subject matter can be used with or as a component of any suitable fluid processing systems or devices, such as those indicated above regarding  FIGS. 10A and 10B . 
       FIG. 11  illustrates a method  1100  according to embodiments of the disclosed subject matter. 
     Fluid may be introduced to a fluid heating apparatus as described herein S 1102 . The fluid can be heated using the fluid heating apparatus as described herein S 1104 . In various embodiments a controller can provide control signals to a heating element so that the heating element is heated to a desired temperature in order to heat the fluid to a desired temperature. The temperature of the fluid and/or the fluid heating apparatus can be monitored, for example, via a temperature sensor or sensors located on the fluid heating apparatus, to maintain the temperature at the desired temperature or within the desired temperature range  51106 . If the temperature of the fluid or the fluid heating apparatus is not at a desired temperature (or within a desired temperature range), the method can provide control signals to adjust the temperature so that it is at the desired temperature or within the desired temperature range. Fluid may be output from the fluid heating apparatus at the desired temperature or within the desired temperature range  51108 . 
       FIG. 12  shows an embodiment of a heater device  1202  with ports  1204  and a channel  1212  formed by machining suitable recesses in metal plates  1210 . Each port has a blind end recess  1214  that is deeper than the channel which can facilitate uniform distribution of flow in the channel inlet  1224 . Incidentally, either end may be used as in inlet in the present embodiment although only one blind end recess  1214  may be provided in alternative embodiments. A ceramic insulator  1208 , as in other embodiments, can provide for high thermal contact, high electrical (including capacitive coupling) isolation of the heating elements (e.g., transistors; not shown but as describe elsewhere). The metal plates may be of copper or other highly thermally conductive material. 
     The heating elements may be urged by resilient urging members to accommodate differential thermal expansion according to known methods and devices, such as springs. As in any of the present embodiments, thermal paste may be used to ensure high thermal contact between layered components. The internal channel  1212  may be defined by recesses milled into the plates  1210 . The internal surfaces may be plated for biocompatibility. For example, copper plates may be plated with nickel then gold. O-rings  1206  may be used to provide high pressure seal to tubular channels. The sandwich structure of the heating device  1202  may be held together using a single compression device, bonded by suitable means or other fasteners may be used. This assembly structure may be applied to any of the embodiments described herein. The entire assembly, and any other embodiments described herein, may be potted in a resilient material such as RTV. 
     Although particular configurations have been discussed herein, other configurations can also be employed. It is, thus, apparent that there is provided, in accordance with the present disclosure, fluid heating devices, systems, and methods. Many alternatives, modifications, and variations are enabled by the present disclosure. Features of the disclosed embodiments can be combined, rearranged, omitted, etc., within the scope of the invention to produce additional embodiments. Furthermore, certain features may sometimes be used to advantage without a corresponding use of other features. Accordingly, Applicant intends to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present invention.