DISPOSABLE TEMPERATURE PROBE FOR PHOTOACTIVATION PATIENT TREATMENT SYSTEM

Abstract: There is provided an inexpensive disposable temperature monitoring probe for use in a patient treatment system wherein photoactivatable agents, in contact with patient cells, are irradiated extracorporeally to photoactivate said agents and then returned to the patient.

Description: This invention relates to the field of treating cells with photoactivatable compounds and radiation which activates the compound, thereby affecting the cells and specifically, relates to clinically useful systems for the extracorporeal treatment of blood cells, including disposable irradiation chambers having a disposable temperature probe associated therewith for monitoring the temperature of the cells during photoactivation. It is well-known that a number of human disease states may be characterized by the overproduction of certain types of leukocytes, including lymphocytes, in comparison to other populations of cells which normally comprise whole blood. Excessive or abnormal lymphocyte populations result in numerous adverse effects to patients, including the functional impairment of bodily organs, leukocyte mediated autoimmune diseases and leukemia related disorders, many of which often ultimately result in fatality. U.S. Patent Nos. 4,321,919; 4,398,906; 4,428,744; and 4,464,166 to Edelson describe methods for treating blood whereby the operation or viability of certain cellular populations may be moderated, thereby providing relief for these patients. In general, the methods comprise treating the blood with a dissolved photoactivatable drug, such as psoralen, which is capable of forming photoadducts with DNA in the presence of U.V. radiation. It is believed that covalent bonding results between the psoralen and the lymphocyte nucleic acid, thereby effecting metabolic inhibition of the thusly treated cells. Following extracorporeal radiation, the cells are returned to the patient where they are thought to be cleared by natural processes but at an accelerated pace believed attributable to disruption of membrane integrity, alteration of DNA within the cell, or the like conditions often associated with substantial loss of cellular effectiveness or viability. Although a number of photoactivatable compounds in the psoralen class are known, 8-methoxy psoralen is presently the compound of choice. An effective radiation for this compound, and many psoralens in general, is the ultraviolet spectrum in the range of approximately 320 to 400 nanometers, alternatively referred to as the U.V.A. spectrum. As the development of photoactivatable compounds proceeds, it may be expected that changes in the preferred activation radiation spectrum will be necessary. Suitable selection of radiation sources will, of course, increase treatment efficiency and is contemplated as an obvious optimization procedure for use with the inventions disclosed herein. Although Edelson's methods have been experimentally shown to provide great relief to patients suffering from leukocyte mediated diseases, numerous practical problems require solutions. In particular, Edelson fails to provide a suitable apparatus for applying radiation to the cells, e.g. via a treatment station, in an economical and efficacious manner, or a system for incorporating a treatment station providing for the treatment of a patient in a clinically acceptable format. Conventional techniques for photoactivating compounds associated with cells have relied on a plurality of devices including flasks, filtration columns, spectrophotometer cuvettes, and petri dishes. The sample to be irradiated is added to the container and the container placed adjacent to the radiation source. Such systems tend to be laboratory curiosities as they fail to provide the necessary safeguards intrinsically necessary where patient bodily fluids are concerned, particularly since these fluids must be returned to the patient, thereby necessitating strict avoidance of contamination. Further, such methods tend to be volume limited, are characterized by many mechanical manipulations and are generally unacceptable from a clinical and regulatory viewpoint. It is an object of the present invention to provide methods and apparatus suitable for use with the Edelson methods to overcome the limitations associated with the conventional expedients. EP-A-O 138 489 describes a practical device for coupling the radiation provided by commercially available light sources, such as the so-called "black-light" fluorescent tubes, to cells for treatment by Edelson's photoactivated drug methods. In summary, the disposable casssette described therein comprises a plurality of fluorescent tube-like light sources such as the U.V.A. emitting Sylvania F8TS/BLB bulb, which are individually, coaxially mounted in tubes of larger diameter which are, in turn, coaxially mounted in sealing arrangement within second outer tubes of even larger diameter, thereby forming a structure having two generally elongated, cylindrical cavities about each radiation source. The inner cavity preferably communicates with the atmosphere, thereby facilitating cooling of the radiation source. The second tube forming the outer cavity further comprises inlet and outlet means for receiving and discharging, respectively, the cells to be irradiated. A plurality of these structures are "ganged" and suitable connections made between inlets and outlets of adjacent members to provide for serpentine flow of cells through each outer cavity. Thus, continuous flow of the cells through the plurality of cavities surrounding the centrally disposed radiation sources facilitates thorough treatment of the cells. Additional, detailed description of the above device may be obtained by direct reference to EP-A-O 138 489. To be fully practical, the device described in EP-A-O 138 489 requires a clinically acceptable instrument to house the device and to provide the cells to be treated in an appropriate form. Such an instrument is the object of the inventions described in U.S. Patent Nos. 4,573,960, 4,568,328 4,578,056, 4,573,961, 4,596,574, 4, 623,328 and 4,573,962. While the instruments described therein work well, it is an object of the instant application to describe improved systems capable of implementing, in advance fashion, the medical treatment principles first taught by Edelson. It is another object of the present invention to provide still further improvement in greater patient safety and comfort while reducing treatment time and cost, by utilizing a newly designed disposable irradiation chamber in an appropriate instrument which incorporates a photoactivating light array, more fully described in EP-A-O 240 152 and EP-A-O 240 149 respectively. It is yet another object to provide an improved instrument which meets the above criteria while maintaining along with all the positive attributes of the prior system; compactness, mobility, completeness, full automation and monitoring, coupled with ease of operation. It is a further related object of this invention to provide, in contrast to the time consuming batch like processing of the prior system, continuous on-line patient treatment wherein collection, separation, and cell treatment occur simultaneously, thereby reducing treatment time and increasing patient safety and comfort. These and still other objects of the invention will become apparent upon study of the accompanying drawing wherein: Figure 1 illustrates a preferred configuration of the system during collection, separation, and treatment; Figure 2 shows a preferred embodiment of the flat plate irradiation chamber, recirculation pump, and photoactivating light source array; Figure 3 shows a bottom view of the structures of Figure 2; Figure 4 shows a perspective view of the disposable temperature probe mounted on the irradiation chamber; Figure 5 shows the assembly of the thermocouple element; and Figure 6 shows another view of the construction of the thermocouple element and its manner of electronic connection to the patient treatment system. FR-A-2 330 410 describes a temperature probe assembly comprising a thermally conductive tube segment; a thermocouple junction thermally connected to the surface of the tube segment and having two output leads for providing a signal responsive to temperature; contact means for providing electrical connection to the output leads; and electronic processing means for processing the thermocouple signal. The present invention provides a temperature probe assembly, for use in a patient treatment system wherein patient cells, in contact with a photoactivatable agent, are irradiated for photoactivating the agent extracorporeally while the agent and the cells are contained in an irradiation chamber, the assembly being characterised in that: the thermally conductive tube segment is adapted to be arranged in fluid communication with the irradiation chamber; and the assembly includes temperature stabilizing means upon which the contact means are mounted, the temperature stabilizing means being thermally and electrically in contact with the electronic processing means. Preferred features of the assembly of the present invention are set out in the subclaims. In accordance with the present invention there is provided a disposable temperature probe for use with apparatus for "on-line" extracorporeally photoactivating a photoactivatable reagent in contact with blood cells by collecting and separating,on a continuous basis, blood from a patient while the patient is connected to the apparatus, returning undesired blood portions obtained during separation while the desired portion is photoactivatably treated and thereafter returning the thusly treated cells to the patient. As a result of this novel approach, the treatment system optimizes and minimizes treatment time by concurrently conducting various aspects of such photoactivation treatment which were previously performed sequentially. More specifically, the apparatus collects and separates blood on a continuous basis as it is withdrawn from the patient and returns unwanted portions to the patient while concurrently energizing the irradiation sources for photoactivating the photoactivatable reagent in contact with the desired blood portion. Following photoactivation, the treated cells may then be facilely returned to the patient utilizing a drip chamber gravity feed infusion line incorporated in the tubing set. Photoactivation occurs when the cells are present within an irradiation chamber which is illuminated by a light array assembly. Prudent safety measures dictate that one monitor the heating effects upon the cells during photoactivation. The instant invention provides a disposable temperature probe for this purpose which, in a most preferred embodiment, comprises a thermocouple associated with a metal tubing segment inserted in the pumping tubing line, connected to the irradiation chamber, and associated with a pump block. Figure 1 shows various aspects of the system developed for extracorporeally treating a patient based in part upon the scientific discoveries of Edelson. The specific design, construction and operation of the apparatus 10 is the result of a number of separate inventions some of which form the subject matter of previously described issued US patents and published European applications. Some form the subject matter of the following concurrently filed European patent applications: 0 239 256; 0 236079; 0 241 123; 0 240 149; 0 240 154; 0 239 255; 0 242 031; and 0 240 152 A brief description of the contents of these applications is included herein in order to assist in the understanding of the present invention. The operation of the device and its performance can be divided into two basic phases or modes, depicted in part by Figure 1. The first phase is shown substantially in Figure 1 wherein the patient is connected at the point shown, preferably by venipuncture or the like methods well-known and developed to a high degree in the dialysis arts. Patient blood, as it flows to the apparatus 10 (alternately referred to herein as the puvapheresis apparatus or system) is preferably infused, under control of pump 11, with an anti-coagulant agent contained in container 20 hung from stand 15. Control of the flow of patient blood to the remainder of apparatus 10 is controlled largely by clamping means 16a which has the dual function of also controlling flow in the reverse direction as well as flow to return container 21. Clamp 16a acts as an "or" valve. Normally the blood flows through tubing 24 through blood pump 12 (preferably a roller pump such as that described in U.S. Patent No. 4,487,558) into continuous centrifuge 13. This continuous centrifuge, available commercially from suppliers such as Dideco and others, is preferably capable of continuously separating blood based on the differing densities of the individual blood components. "Continuously", as used herein means that, as blood flows into the centrifuge through line 24, it accumulates within the rotating centrifuge bowl and is separated so that low density components are emitted after a certain minimum volume has been reached within the centrifuge bowl and as additional blood is added. Thus, the continuous centrifuge in effect acts as a hybrid between a pure online system and a pure batch system. This occurs because the centrifuge bowl has a capacity to hold most, if not all, of the most dense portion. typically erythrocytes or red blood cells while emitting lower density portions such as plasma and leukocytes (white blood cells) as whole blood is continuously added. At some point, however, the reservoir volume of the centrifuge is filled with the higher density components and further separation cannot be effectively obtained. Prior to that point, the operator, by viewing the uppermost portion of the centrifuge bowl through the centrifuge cover, can detect qualitatively when the centrifuge emits plasma (as opposed to priming solution), leukocyte enriched portions and the remainder. i.e., nonleukocyte enriched portions, including erythrocyte enriched portions. Based on the operator's observations, he or she enters through control panel 19 (specifically via panel portion 42) the identification of the individual blood portions as they are emitted from the centrifuge. This information is entered by keys 44 (e.g. PLASMA, BUFFY COAT or leukocyte enriched portion) on control panel 19, (shown in Figure 1) and in response thereto, the apparatus 10 controls valve mechanism 16c to direct the leukocyte enriched portion and a predetermined volume of plasma into plasma-leukocyte enriched container 22 while excess plasma, air, priming fluids, erythrocytes etc, are directed to container 21. Once the centrifuge is no longer capable of further separation due to the attainment of its capacity, the operator directs that the bowl be emptied by suitable data key entry on panel 19 and the fluid contents of centrifuge 13 are advantageously pumped into return container 21 by means of pump 12 under the control of valves 16a and c. The foregoing steps may be repeated a number of times or cycles before the desired volume of leukocyte enriched blood and plasma is obtained for further treatment, in each instance the undesired portions being collected in return container 21. Between cycles, the fluids, including erythrocytes which have been pumped into return bag 21 are gravity fed back to the patient through a drip infusion operation and controlled by valve 16b. It is preferred that gravity feed be employed rather than pumping the blood back to the patient via pump 12 in order to avoid potential pressurization problems at the infusion insertion site at the patient, and also to avoid foaming or other air related dangers. As may be already appreciated, when initially set up, the centrifuge bowl and line 24 may be expected to contain sterilized air which is preferably removed by suitable priming operations advantageously accomplished by utilizing the anticoagulation agent in container 20: both the air and a portion of priming solution being collected in container 21. Also to be noted is the predetermination of the desired leukocyte enriched volumes and plasma volume to be collected within container 22 as well as the number of cycles to be employed to collect same. These volumes are selected largely in accordance with the individual volume capacities of the containers as well as the treatment irradiation chamber to be described later. Accordingly. these volumes are set in order to preferably optimize handling efficiency and to ensure patient safety. For instance, one preferred selection would include the following settings: 250 ml total buffy coat or leukocyte enriched portion and 300 ml of plasma to be collected within container 22. This might require any number of cycles, preferably on the order of three or four, bearing in mind that the more cycles that are selected, the lower the total volume of blood withdrawn from the patient at any one time. If blood collection meets the minimum capacity limits of the centrifuge bowl, the patient's capacity to withstand temporary blood volume depletions, and the treatment procedure in general is increased. Further, more cycles will permit more discriminating selection of leukocyte enriched blood as it is emitted from the centrifuge. The buffy coat and plasma volumes as well as the number of cycles are typically physician selected. Accordingly, the controls governing these selections are preferably paced within the apparatus 10, such as behind door 18a where their inadvertent alteration may be advantageously avoided, especially since no operator interaction is normally required with respect to these data inputs. The leukocyte enriched container 22 is connected via tubing line 34 to the flat plate treatment chamber behind assembly door 17 with a return line 35 to reservoir container 22. Referring now to Figures 2 and 3, the leukocyte enriched blood, plasma, and priming solution contained in reservoir 22 (Figure 1) is delivered through line 34 to the inlet 209 of the flat plate irradiator 200. The fluid flows upward through the serpentine pathway in cavity 208 in the irradiation chamber to the outlet 210. While a serpentine pathway is preferred in order to avoid or minimize stagnant areas of flow, other arrangements are contemplated. Tubing from the outlet 211 passes through the pump block 201 [described in greater detail in EP-A-0 240 154], affixed to the end of the flat plate irradiator 200, and then connects to return line 35 which returns fluids from the irradiation chamber to container 22. Recirculation pump rotor 203, which is located internally in the machine (mounting not shown), engages the tubing in the pump block in the semi-circular tract 212 and thereby provides and controls the recirculating flow of fluid, from container 22 up through irradiation chamber 200 and back to container 22. In a preferred embodiment, a metal segment 220 in the tubing line from outlet 211 incorporates a thermocouple 213 which permits monitoring of the fluid temperature. Sterile air initially contained in the irradiation chamber cavity 208 is displaced by entering fluid and stored in the top of container 22. By reversing the rotation of recirculation pump rotor 203, the air stored in container 22 can be pumped back into the outlet 210 of the chamber 200 thereby displacing all fluids back into container 22. Once fluid is initially delivered to container 22, the recirculation pump rotor 203 is energized filling the irradiation cavity 208 and displacing sterile air to container 22. When the irradiation chamber is filled and BUFFY COAT button 44 on panel 19 is pressed, the light array assembly which surrounds the irradiation chamber is energized. Continued operation of the recirculation pump rotor 203 continuously recirculates the leukocyte enriched fluid from container 22 through the chamber for receiving photoactivating radiation from the energized light array assembly 401 (Figure 3) and back to container 22. Figure 3, illustrating the light array assembly 401 from a bottom view, shows two rows, in the most preferred embodiment although one row can be used, of radiation source 400 powered through contacts 216. Such sources are conveniently chosen so that illumination is reasonably constant over the entire irradiation cavity 208 (Figure 2). Suitable sources include the Sylvania FR15"T8/350BL/HO/180° with 2011 phosphorus bulb which is in the so-called fluorescent tube form. As is apparant from Figure 3, the irradiation chamber 200 slides between the rows of radiation source 400 so that pump block 201 engages pump rotor 203 driven by motor 250. Other aspects of the radiation array 400 are discussed in EP-A-0 240 149. Thus, photoactivation of the leukocyte enriched fluid by irradiation is initiated at the outset and continues through and after the collection and separation process. In the most preferred mode, the light array assembly [described more fully in EP-A-0 240 149] will comprise sources of ultraviolet radiation, most preferably of the UVA type for activating the photoactivatable agent presently of choice, 8-methoxy psoralen. The flat plate irradiation chamber treatment module is described more fully in EP-A-0 240 152. In operation, and with respect to Figure 1, the exposure time on the right hand portion of the panel 43 is set in accordance with physician determined criteria via knob 41. The central control means of the apparatus 10 calculates and displays (50), via central processing unit and memory stored software, the exposure time remaining at the onset of irradiation treatment and as the treatment progresses. Section 43 of the control panel also includes three operator controlled entry data keys 44a whereby the operator can de-energize the photoactivating light array and stop the recirculation process if desired. Actual photoirradiation treatment preferably commences automatically under control of the central processing unit when fluid is first directed to container 22, continues while leukocyte enriched blood portion from container 22 is pumped through the irradiation chamber back into container 22, and terminates when the preset exposure time has expired. At that time, the light array assembly is de-energized and the recirculation pump reverses, emptying the contents of the irradiation chamber 200 into container 22. Thereafter container 22 is ideally removed to stand 15 (Figure 1) where it is connected to tube 36, provided on the common drip chamber 21a also associated with return container 21, for reinfusion of the treated blood portion into the patient. To enhance patient safety and decrease the risk of contamination to the patient blood and blood portions, each time a connection is made or broken, it is preferably only done once. Thus, container 22 would ideally have four connection points or ports; one for the collection of the leukocyte enriched blood portion, two for connection to the flat plate irradiation chamber (feed and return), and the fourth for connection to the drip chamber (21a) for reinfusion of treated blood to the patient. With reference to Figure 1, the control panel 19 of the apparatus 10 is shown with the keyboard entry buttons 44, each ideally having a light which, when lit, preferably indicates the stage of the operation. The keyboard entry buttons 44 are preferably placed in sequential order thereby assisting the operator in learning the system and performing the steps in the correct order. Indeed, the central control microprocessor will preferably be programmed to prevent out of step sequences from being implemented. A visual display indicates the volume of leukocyte enriched blood collected in container 22. Panel 19 will preferably also contain a power switch, as well as a blood pump speed control whereby the operator may select the speed with which the blood is withdrawn from the patient and pumped through the system during collection. Also preferably included is an alpha-numeric display for indicating the machine's status and identifying alarm conditions throughout system operation. Optional accessory status lights, preferably provided in green, yellow, and red colors, provide at a glance the overall operating status of apparatus 10. Further included is a mute/reset button for quieting an audible alarm activated in the event an alarm condition occurs and operator input is required. Other features may be readily apparent from the drawings such as the preferable inclusion of casters and caster brakes for enhancing the mobility of the apparatus. Further, side panel 23 will preferably include mechanical means (e.g. hanging pegs and the like) for assisting in the securement of container 22. It may also optionally be outfitted with a transparent or translucent opening 18b in the area beneath container 22 for providing at a glance information regarding the illumination status of the irradiation treatment chamber during the treatment phase. For instance, if the window is of sufficient size, the operator may readily determine that each irradiation source within the treatment chamber is illuminated as desired. Naturally, the material comprising such window is preferably selected in order to contain harmful radiation, if any, within apparatus 10. The aforedescribed photopheresis blood treatment apparatus is made largely possible by an automated control method for directing the blood portions, derived from the continuous centrifuge, into particular containers. The automated method performs in accordance with preset volume determinations which are manually entered behind panel 18a pursuant to a physician's direction. These predetermined volumes specify the volume to be contained within container 22 by setting forth the volume of plasma and the volume of leukocyte enriched blood portion to be directed thereto. Additionally included within these condition setting parameters is preferably the ability to set forth the number of cycles of blood collection and separation required or desired in order to obtain the desired blood volumes. The volumes collected are determined in accordance with the blood volume pumped by the blood pump. This may be suitably monitored and communicated to the central control means by specifically monitoring the number of step pulses input to the pump to cause rotations of the blood pump. Typically, 200 pulses results in one revolution. Rotation may also be conveniently monitored such as by attachment of a slotted disk to the shaft and the passage of slots determined by an optical sensor means such as that described in US-A-4 623, 328 and by monitoring shaft rotation. The resultant periodic signal may be conveniently correlated with speed and number of rotations by circuit designs well-known in the art. The number of rotations by any of the foregoing methods coupled with the known volume pumping characteristics of the pump , will provide the necessary information regarding the volume of blood pumped. It will readily be appreciated that the sensors need not be optical but may be electronic or mechanical instead. In actual operation, a most preferred procedure would be as follows. The operator presses the PRIME CENT. key on control panel section 19 which primes the tubing set, the blood pump, and the centrifuge with the anti-coagulation solution contained in container 20. Displaced sterile air is collected in container 21. When priming solution emerges from the exit of the centrifuge, the operator presses PRIME UV key on control panel section 42 which closes the tubing line to container 21 and opens the tubing line to container 22 by means of valve 16c. Recirculation roller pump rotor 203 is energized to prime the flat plate irradiation chamber and displace sterile air to container 22. The priming process stops automatically after a preset volume of fluid is delivered to container 22. Blood collection is started by the operator pressing START key on control panel 19. Thereafter, blood is withdrawn from the patient and pumped by the blood pump into the rotating centrifuge. As the blood enters the centrifuge, it displaces the priming solution which emerges first in accordance with its preferably lighter density. This priming solution is automatically directed into container 22 until a preset volume is delivered, after which the emerging solution is redirected to container 21 by means of valve 16c. At some point, the priming solution will be completely displaced from the rotating centrifuge and plasma will begin to emerge. This emergence may be directly observed through port 14 whereupon the operator presses the PLASMA key on control panel 19. Thereafter, the central control means automatically directs the plasma into container 22 by altering valve 16c, keeping track of the volume as it does so since the volume entering the centrifuge equals the volume emerging therefrom. This continues until the operator indicates the leukocyte enriched portion, i.e. buffy coat, has begun by pressing the respective data entry key in control panel section 42, whereupon the leukocyte enriched portion continues to container 22. However, the volume so directed is monitored as buffy coat volume. Alternately, if all of the predetermined plasma volume is collected prior to the emergence of the buffy coat, then the central control means automatically diverts, by valve 16c, the emerging plasma fluid stream to container 21. In that instance, upon the emergence of the buffy coat and the keying of the BUFFY COAT data entry switch 44, the central control means diverts the emerging buffy coat into container 22, by means of valve 16c, again keeping track of its volume. The collection of the buffy coat will preferably continue in accordance with both the predetermined buffy coat volume as well as the number of cycles, another condition predetermined by the physician. If this most preferred embodiment is employed, then a representative example might be as follows. Assume, that the predetermined volume and cycle conditions are set as follows: 350 mls of plasma, 250 mls of buffy coat, and 5 cycles. In each cycle, the apparatus will collect 250/5 or 50 mls of buffy coat before ending the cycle and thereupon emptying the centrifuge bowl and returning all nonleukocyte fluids, predominantly erythrocytes and perhaps excess plasma, to the patient. Prior to the collection of the 50 mls, plasma will emerge from the centrifuge and will be collected in container 22 either until the full 350 mls are collected or until the buffy coat emerges. During the next cycle, the central control means will direct the further collection of plasma, if needed, in order to reach the 350 ml predetermined volume and then collect an additional 50 mls of buffy coat. The total volume to be contained within container 22 will then equal 600 mls and would be indicated on display 46 as it is accumulated. Thus, the system serves automatically to keep track of the volumes as they are collected thereby facilitating the institution of a convenient number of cycles whereby the removal of large blood volumes from the patient is avoided. Not only is patient safety enhanced thereby, but the automated nature of the procedure further increases safety since, in accordance with the programmed conditions supplied to the central control microprocessor or computer, the operator need not attempt to keep track of plasma and leukocyte enriched volumes collected, while still being assured that the final solution for treatment will contain the predetermined and desirable leukocyte concentration. As may be readily apparent, the foregoing described automated methods used in the photopheresis apparatus, described with respect to Figures 1 through 3, rely in large measure upon the advantages provided by a disposable irradiation chamber. The instant invention further enhances the advantages of the disposable irradiation chamber by providing for use therewith a disposable temperature probe assembly and the means for generating a signal for monitoring the temperature of fluids contained within the irradiation chamber as they are circulated therethrough and subject to photoactivation. It is advantageous in blood handling medical instrumentation to be able precisely to monitor blood temperature over a relatively narrow critical range. For example, during dialysis procedures, heat is often applied to prevent patient chilling, but excessive heating can cause cell damage and consequently serious injury to the patient. During photoactivation in the patient treatment systems described above, the irradiation process also causes heating of the circulating patient fluid. Accordingly, the temperature of the patient fluid must be carefully monitored to warn of excessive temperatures which could cause cell damage and thus serious patient injury. This problem is further exacerbated by the fact that a safe operating temperature and hazardous high temperature differ by only a few degrees. With respect to the instant patient treatment photoactivation methods, a generally safe operating temperature is considered to be 35 to 38°C while a hazardous temperature would be 41 to 43°C. Thus, the preferred temperature probe will be able to monitor temperature accurately over this narrow range to prevent patient hazard. As will be readily appreciated, in most preferred embodiment, the patient fluid or blood is contained within sterile yet disposable treatment elements including tubing sets and irradiation chambers. The temperature probe must be capable of interacting with such sterile, sealed treatment elements in a practical and economical fashion which avoids introducing contaminating substances. It has been found that invasive temperature monitoring probes are generally too expensive to be practical, particularly since insertion of an invasive, nondisposable probe into sterile treatment elements is a dangerous and training intensive procedure. Such procedures also require additional accessory procedures between treatments to resterilize the invasive temperature probe after use. Noninvasive coupling of such a nondisposable probe generally cannot be accomplished with the reliability and precision required for such critical monitoring. The present invention overcomes these limitations by providing an inexpensive, disposable temperature probe assembly which can be included with each sterile disposable treatment set for supplying a highly reliable, precise and safe means of temperature monitoring without deleteriously affecting sterility. With reference to Figure 4 and 5, pump block 201, associated with irradiation chamber 200 (Figure 2), comprises discharge tubing line 211 having temperature probe 213/220. A short length of biocompatable tubing 220 having high thermal conductivity, the most preferred material being stainless steel, is inserted in sealing communication into discharge tubing line 211. Biocompatible as used herein means that the metal has no measureable deleterious effects upon the patient fluid during the period of time and under treatment conditions when the fluid is in residence in the irradiation chamber and comes in contact with the metal tubing. A thermocouple bead 213, capable of monitoring over the desired temperature range, is ideally permanently affixed centrally to the outer surface of the metal tubing. For the photactivated, patient treatment methods described, it has been found most advantageous to employ a bead of capacitance discharge welded iron-constantan wire construction. However, other constantan thermocouple combinations are also contemplated and include copper-constantan, chromel-constantan as well as other combinations including for example chromel-alumel and platinum-platinum rhodium. One lead 504 (either iron or constantan) from the bead 213 is stretched across the recessed flat 500, through notches 225, and is bent over and terminates in cavity 501. Similarly, the other lead 505 (the other metal), passes through opening 503 in the pump block, across the flat area 500, and through notches 225 on the backside of the pump block, and is bent into cavity 501. An electrically insulating plug 502 is inserted into cavity 501 to retain the leads within cavity 501 and prevent the leads from touching each other. Since in a preferred embodiment, the patient is connected intravenously while photoactivation is occurring and the temperature is being monitored, direct metallic contact between bead 213 and leads 505 with metal tubing 220 is preferably avoided since such contact provides direct electrical connection between the patient's circulatory system and the patient treatment systems. Such a high degree of electrical isolation, advantageous for patient safety, can be achieved by the most preferred embodiment shown in detail in Figure 5. To obtain the electrical isolation in this embodiment, a very thin layer 510, of electrically insulating but thermally conductive coating, preferably a material such as Omegabond 101 brand from Omega Engineering Inc., is applied to the tubing to electrically separate the bead and its leads from the tubing while retaining a good thermal connection between the bead 213 and tube 220 in contact with the fluid undergoing photoactivation. Alternately, electrical isolation need not be maintained if the circuitry connected to the temperature probe is isolated from ground. In another preferred embodiment, layer 510 is obviated by utilizing a circuit with a standard of electrical leakage so that no patient harm is threatened thereby. It has also been found helpful to apply a similar coating onto the bead, shown by 511, to secure the bead in place. If used, the width and thickness of the band 510 is ideally sufficient to ensure electrical insulation at the maximum voltages incurred within the patient treatment apparatus or as required by safety standards. In the instant invention, a width of approximately 3.2mm (1/8") was found sufficient to hold-off in excess of a thousand volts. Unlike other thermocouple sensors, such as thermistors, the instant invention is preferred because it is less expensive, inherently more precise and reproduceable, and is rugged enough to withstand handling and sterilizing. Several commercially available integrated circuits are available to condition and process the signal voltage generated by the thermcouple into temperatures. A preferred microelectronic chip device is the AD594, made by Analog Devices. As is known with such temperature processing chips, it is generally preferable to extend the materials of the thermocouple junction directly to the processing device to avoid producing emf generating metallic junctions. Otherwise, compensation for the additional junctions will be required; a difficult task advantageously avoided. Since long temperature probe leads or special connectors on the disposable pump block would defeat the cost and convenience objectives of a disposable, a new connection method had to be developed. It was found possible to avoid the need for additional compensation and to connect directly the short exposed thermocouple leads on the disposable by ensuring that the temperature at the input pins on the microelectronic chip is the same temperature as connection to the thermocouple leads. This was surprisingly found to be possible with the embodiment shown in Figure 6. Two relatively large spring clips 512, preferably of phosphor bronze or similar material, slidably engage the thermocouple leads 504 and 505 when the disposable is mounted into position. The spring contacts 512 are soldered to relatively large areas of copper foil 513 on a printed circuit board located physically close to the connection between clips 512 and leads 504 and 505. The signal input pins 514 for process circuit chip 515 are in turn soldered to the large foil areas 513. In this manner, the large areas of intimately connected, thermally conductive metal, comprising the spring clips and foil areas, form a stable heat sink which ensures the temperature at input pins 514 is the same as the temperature of the junction between spring clips 512 and thermocouple leads 504, 505. A further feature of the present invention concerns the manner in which the signal conditioning chip 515 is calibrated. Because each new disposable irradiation chamber pump block used presents a new thermocouple, it is greatly preferred that the temperature processor chip be initially calibrated to produce consistently reliable results regardless of the identity of the input thermocouple. It was surprisingly discovered that thermocouples made according to the instant invention utilizing wire of consistent quality and source, provided voltage signals (emf) which were characteristically very similar. The major source of error was instead found to be associated with the commercially available signal conditioning chip. Normally, such a chip is calibrated using external components, such as resistors, to produce the greatest accuracy over the widest temperature range. This normally involves adjustment of the signal offset to give a predetermined output at 0°C, and then adjusting the gain, or slope of the response curve, to give desired output at 25°C. In contrast, temperature monitoring in the instant patient treatment ranges involves a narrow temperature range, for example 35°C to 45°C, where maximum precision is required. To obtain precision in that range with the temperature probe of the instant invention, the precision of the output signal is ideally optimized by adjusting the signal offset to be exactly correct at mid-range, approximately 40°C. Thereafter, and despite normal variations in response curve slope, the output signal will be highly accurate and reproducible from chip to chip and thermocouple to thermocouple. Indeed, it has been found that typical overall system precision over the preferred narrow range, using this calibration technique, is less than 1°C error. Upon study of the accompanying figures, and the foregoing description, it will become readily apparent to the skilled artisan that numerous physical alterations or substitutions may be made to the foregoing without departing from the scope of the instant invention as defined in the accompanying claims.

Claims: A temperature probe assembly, for use in a patient treatment system wherein patient cells, in contact with a photoactivatable agent, are irradiated for photoactivating the agent extracorporeally while the agent and the cells are contained in an irradiation chamber, the assembly comprising: a thermally conductive tube segment (220); a thermocouple junction (213) thermally connected to the surface of the tube segment (220) and having two output leads (504, 505) for providing a signal responsive to temperature; contact means (512) for providing electrical connection to the output leads (504, 505); and electronic processing means (515) for processing the thermocouple signal, characterised in that: the thermally conductive tube segment (220) is adapted to be arranged in fluid communication with the irradiation chamber; and the assembly includes temperature stabilizing means (513) upon which the contact means (512) are mounted, the temperature stabilizing means (513) being thermally and electrically in contact with the electronic processing means (515). The assembly of claim 1, wherein the tube segment (220) is made of stainless steel. The assembly of claim 1 or claim 2, wherein the thermocouple junction (213) is formed by a junction between and iron and a constantan wire. The assembly of any one of claims 1 to 3, wherein the thermocouple junction (213) is electrically isolated from the tube segment (220) by means of a coating (510) of thermally conductive, electrically non-conductive plastic material interposed between the tube segment (220) and the thermocouple junction (213). The assembly of any one of claims 1 to 4, which is calibrated to provide an output signal which is correct at or about 40°C. The assembly of any one of claims 1 to 5, wherein the temperature stabilizing means comprises metallic foil (513). The assembly of any one of claims 1 to 6, wherein the electronic processing means is a microelectronic chip (515).

Inventors: GOSS, JACK
Applicants: MCNEILAB, INC.
Application year: 1987
Main classification: A61M1
IPC codes: A61M1