Device for repeated registration of thermal cycles

Abstract: A device for repeated registration of the number of thermal cycles to which a part for medical usage has been subjected comprises a temperature- and/or pressure-sensitive element (20) arranged in conjunction with the said part. This element reversibly changes its physical shape with the temperature and/or pressure, variations in pressure being invariably associated with changes in temperature. A registration means (12, 14, 16, 18) is further devised to register this change in shape when it exceeds a specific threshold value.

Description: Device for repeated registration of the number of thermal cycles to which a part for medical usage has been subjected The present invention relates to a device for repeated registration of the number of thermal cycles to which a part for medical usage has been subjected. A large number of parts or components in medical devices require sterilisation between each use. This is often accomplished by heating the part or component in an autoclave. For safety reasons, these parts or components may not be re-used more than a limited number of times. Therefore, careful monitoring and reliable, tamper-proof checking of the number of times parts and components are re-used are very important. The number of times a part has been autoclaved has hitherto often been determined with the aid of a logbook of varying reliability. US-A-5,383,874 describes a system for identifying and monitoring the use of ablation catheters. This system employs a usage register, whose contents are incremented by one every time the catheter is put to authorised use, to ensure that the catheter is not used too frequently. The Swedish patent application no. 9702679-3 describes a device for counting the number of usage cycles by a sensor for intracorporeal electrophysiological measurement and/or therapy. Here, a counter connected to the sensor contains an identification code specific to the sensor, and connection/ disconnection of the sensor to/from external measurement equipment and/or therapeutic equipment is detected. The identification code is used here for determining, from information stored in a main computer on previous usage, whether conditions for a new usage cycle have been met and, if so, incrementing counter contents by one usage cycle. Another system for counting usage cycles is disclosed in US 5,400,267. Disinfecting indicators are known per se. US 4,449,518 discloses one indicator, using a memory alloy. The indicator is deformed when the devise is used and re-assumes its shape when exposed to heat. This system does not register the number of disinfecting or heat cycles. US 5,313,935; US 5,359,993; US 5,452,335; and EP 581 400 all essentially show devices for indicating the number of thermal cycles by moving a cog wheel one step for each cycle. On the cogs, indicator numbers are placed. Through a window one at a time of the indicator numbers can be viewed, indicating a present number of thermal cycles. However, none of these devices can indicate whether the device has gone through a thermal cycle before a new use of the device. Since the indicator numbers are placed on the cogwheels, the total number of thermal cycles is limited to fairly low numbers. This because the indicator numbers must be significantly large for a user to read. The ability to distinguished sterilised replaceable items from unsterilised items is also of the greatest importance in this field. At present, unsterilised and sterilised components are usually stored at different locations, but mix-ups could then occur because the appearance of an item does not indicate whether or not the item has been sterilised. One of the objectives of the present invention is to resolve the mentioned problems with the prior art devices and supply the part or component for medical usage with an indicator showing the user not only the number of uses/thermal cycles but also whether or not the part or component has completed the prescribed thermal cycle after its most recent use. Another objective of the present invention is to provide a device for repeated registration, where the number of cycles is almost unlimited. These objectives are achieved in accordance with the invention with a device of the initially described kind with the features set forth in claim 1. Advantageous improvements and embodiments of the device are set forth in the dependent claims to claim 1. When a temperature- and/or pressure-sensitive element, whose physical shapes changes in a reversible fashion with changes in temperature and/or pressure, variations in pressure then being invariably associated with changes in temperature, is attached to the part or component, any change in shape can be utilised for linearly moving an indicator element from a first indication position to a second indication position, thereby providing e.g. a visual indication of whether or not the part or component has completed the thermal cycle. Hereby, the risk of non-autoclaved parts being put to use is eliminated. The linear movements of the indicator element can be registered by a registration means. Thus, the invention is based on linear movements of an indicator element from a first indication position to a second indication position a large number of times. The relevant thermal cycle is not limited to autoclaving but could also comprise e.g. washing in hot water. According to advantageous embodiments of the device according to the invention, reset means are arranged to automatically reset the indicator element to a first indication position when the part for medical usage is put to use or attached to a mother unit. When the mother unit is a ventilator and the part for medical use is an expiration line cassette, the reset means can be arranged to reset the indicator element to the first indication position when an expiratory valve opens the first time. Alternately, the indicator element can be reset with e.g. a small pulse magnet, motor or the like. According to another advantageous embodiment of the device according to the invention, the indicator element comprises a plate with two, different coloured fields, said plate being moveable in a window to display one of the fields in the first indication position and the other field in the second indication position. In addition to direct visual observation of the plate's position, the position of the plate can also be detected e.g. with an optical detector. Alternately, the plate can control a mechanical switch for opening and closing an electric circuit, or the plate's movement can be detected with an inductive or capacitive sensor. According to other advantageous embodiments of the device according to the invention, a memory is provided for accumulating storage of the total number of registered shape changes made by the temperature- and/or pressure-sensitive element. The memory can be arranged in the part for medical usage, in a separate reader unit or in a mother unit in which the said part for medical usage is intended for use. In this manner, the total number of thermal cycles completed by the part for medical usage can be reliably counted. According to another advantageous embodiment of the device according to the invention, the part for medical usage is assigned a specific identification code, and the reader unit or the mother unit contains a sensor unit for sensing that code and incrementing the number of shape changes registered for the identified part by one when the part for medical usage is connected to the reader unit or mother unit after completing a thermal cycle. This makes it possible to count the total number of thermal cycles completed by the part for medical usage, even in instances in which the part is used in different mother units. This is particularly advantageous in environments using computer networks and databases for controlling, monitoring and/or supervising medical equipment. According to another advantageous embodiment of the device according to the invention, the indicator element is adapted to perform accumulating, one-way movement, whereby the second indication position in one thermal cycle corresponds to the first indicator position in a following thermal cycle. In this manner, registration is linked to the part for medical usage and the number of registered changes in shape, i.e. the number of completed thermal cycles, can be easily read, e.g. visually on a graded scale. No special sources of energy, batteries, active electronic components, chemicals etc. are required, and a simple, sturdy, reliable, encapsulated, relatively small and inexpensive device is achieved. According to yet another advantageous embodiment of the device according to the invention, the registration means comprises a tube whose interior surface is provided with notches along the length of the tube. Inside the tube, the temperature- and/or pressure-sensitive element and indicator element are coupled together to form a moving body which reversibly changes its length with the temperature, said body provided with a set of wings or flanges which mesh with the said notches in the wall of the tube, forming a ratchet pawl so the said moving body performs an accumulating movement along the tube only when its change in length during a thermal cycle exceeds the distance between two consecutive notches. In this manner, the moving body only 'climbs' when its change in length is greater than or equal to the distance between two consecutive notches. This prevents any 'climbing' caused by normal thermal expansion of the body without the body completing the prescribed thermal cycle in which a specific threshold temperature T 1 is exceeded. This also eliminates the risk of the body being intentionally shifted or moved in the wrong direction in some other way. The device's reliability is accordingly enhanced in this embodiment. According to other advantageous embodiments of the device according to the invention, the registration means comprises a tube and the moving body comprises a threaded rod arranged inside the tube and two nut wheels, equipped with ratchet pawl wings pressing on the interior wall of the tube and installed with a gap between them, and the nut wheels are connected to the temperature- and/or pressure-sensitive element, whose shape changes in a jump when the temperature exceeds a threshold value, causing the nuts to rotate one-way and advance along the threaded rod in steps every time the temperature cycle exceeds a temperature threshold. The interior of the tube is advantageously devised with notches at specific distances around the circumference. In this embodiment, a helical movement is employed, making the device more reliable, more accurate and less sensitive to jolts, acceleration and vibration than is the case with linear movement. Moreover, a far greater number of thermal cycles can be registered for any given device size. Providing the interior of the tube with notches also increases reliability in a way analogous to the method employed in the aforementioned embodiment with linear movement by the registering body. When the interior of the tube is smooth, 'resolution' is infinitely great in theory but finite in practice due to friction, the resiliency of the wings etc. If expansion is very slight, the moving body will not 'climb' but remain in place and quiver. According to another advantageous embodiment of the device according to the invention, the number of notches around the circumference of the tube's interior wall and the number of ratchet wings differ. High resolution can accordingly be achieved with a few wings and notches, thereby facilitating fabrication. According to yet another advantageous embodiment of the device according to the invention, the said temperature-and/or pressure-sensitive element is made of memory metal. Such an element reversibly changes its physical shape at a specific 'switching temperature' that can be selected within wide limits. The change in shape as well as the mechanical force developed can be made large. In this way, a distinct change in shape can be achieved when the switching temperature is exceeded. This change in shape can be used for registering the thermal cycle. The switching temperature and elongation of the body when this temperature is reached can be set with a tempering and deformation procedure at the time the body is manufactured. The memory metal's change in shape when the switching temperature is reached is of a different order of magnitude than conventional, linear, thermal expansion. Since a body made of memory metal can develop considerable force, friction between the body and the wall of the tube can be made relatively great to keep jolts, vibration, forces of acceleration etc. from moving the body inside the tube. According to an additional advantageous embodiment of the device according to the invention, the said temperature-and/or pressure-sensitive element is made of a bimetal. A bimetal can deliver a large change in shape, which, however, is linear with the temperature. The bimetallic element is advantageously devised so its linear elongation with the temperature is equal to the distance between two consecutive notches at a pre-selected temperature threshold exceeded at some point in the thermal cycle in question. The moving body will then advance one step for every cycle in which the temperature exceeds this threshold. According to another advantageous embodiment of the device according to the invention, the thermal cycle entails autoclaving under positive pressure, i.e. steam autoclaving. The moving body then consists of a hermetically sealed bellows arranged to be compressed by the positive pressure. Elongation of the bellows after autoclaving produces the body's movement in the tube. As a result of the positive pressure, considerable compressive force develops, and a desired elongation of the bellows in an autoclaving cycle can be achieved through an appropriate choice of bellows stiffness. According to yet another advantageous embodiment of the device according to the invention, the tube is transparent. The position of the moving body, designating the number of thermal cycles completed, can then be conveniently read from e.g. a scale, as with an conventional thermometer. According to additional advantageous embodiments of the device according to the invention, the moving body, or a device or an appliance attached to the moving body, is arranged to act successively on a component with variable resistance and/or inductance and/or capacitance related to the body's movement. In this manner, electronic reading and display of the number of thermal cycles completed can be realised, preferably in the mother apparatus, since the part for medical usage should be relatively simple and inexpensive and is also exposed to moisture, high temperatures etc. In the device according to the invention, a coil is wound around the tube in turns which increase linearly from one end of the coil to the other, and a small part of ferromagnetic, non-magnetised material can be attached to the moving body so it moves successively inside the coil when the body moves. This coil can advantageously be arranged in the mother apparatus. The coil can accordingly be made to encircle the tube when the part for medical usage is mounted on the mother apparatus. In the aforementioned embodiments, a commercially available standard component, such as a component whose resistance and/or inductance and/or capacitance changes with the body's movement, can naturally be used. Yet another advantageous embodiment of the device according to the invention is an optical reading fork arranged to register light transmitted across the tube, and the moving body tapers at one end, or is connected to an appliance with a tapered end, so the body's movement gradually shadows the flow of light. In this version, the reading fork can be mounted on the tube or be located in the mother apparatus. According to yet another advantageous embodiment of the device according to the invention, two separate wheels, which only rotate in one direction, are arranged on a rod, the wheels being interconnected to the temperature- and/or pressure-sensitive element which is devised so the wheels rotate in steps a specific accumulating angle each time a thermal cycle exceeds a temperature threshold. In this embodiment, the angular rotation of the wheels designates the number of completed thermal cycle. This rotary movement can obviously be used to e.g. move a piece of iron inside a coil so rotation changes inductance, rotate a potentiometer shaft to change resistance, move a cone in an optical reading fork in order to shadow transmitted light and rotate a variable capacitor or a variable inductor etc. in order to achieve a measurable parameter that varies with rotation. Commercially available electrical components can obviously also be used advantageously. In order to explain the invention more closely, exemplifying embodiments of the device according to the invention will now be described in greater detail, referring to the attached drawings in which FIGS. 1-3 illustrate the function of a first embodiment of an arrangement for indicating whether or not the part for medical usage has completed a prescribed thermal cycle, a spring made of memory metal being used as a temperature-sensitive element; FIGS. 4-5 schematically depict an alternative temperature-and/or pressure-sensitive element in the form of a bellows; FIG. 6 schematically depicts a first embodiment of a non-volatile memory for accumulating registration of the number of thermal cycles completed by the part for medical usage; FIG. 7 and 8 depict in greater detail a moving body shown in FIG. 6 for registering the number of thermal cycles; FIG. 9 shows an alternative embodiment of the moving body in the form of a hermetically sealed, gas-filled metal bellows; FIG. 10 illustrates a version of the embodiment in FIG. 6, the moving body's movement causing a change in the resistance of an electrical conductive pathway and accordingly making possible electrical measurement of the moving body's position; FIGS. 11 and 12 show two other alternative embodiments in which the position of the moving body can be determined by measuring electrical inductance; FIG. 13 is a more general illustration of the principle for determining the position of the moving body, the moving body's movement affecting an electrical component with variable resistance, inductance or capacitance or some combination thereof, making it possible for the moving body's position to be determined by measurement of the said electrical parameters; FIG. 14 shows another alternative embodiment of the moving body which advances a specific distance for every thermal cycle completed by the part for medical usage; FIG. 15 shows yet another alternative embodiment for registering the position of the moving body and, accordingly, for determining the number of thermal cycles with the aid of an optical reading fork; FIG. 16 shows another embodiment of the moving body, which advances a specific distance for each thermal cycle; FIGS. 17 and 18 show two versions of the embodiment in FIG. 16 in cross-section across the tube in which the moving body is arranged; and FIG. 19 shows yet another embodiment of the device according to the invention for registering the number of thermal cycles with a moving body whose movement is translated into a measurable electrical parameter. FIG. 20 shows the use of the devise according to the invention in a ventilator. FIGS. 1-3 are schematic depictions of the function of a device for registering a thermal cycle. The device comprises an indicator element in form of a plate 12 with two indication fields 14, 16, e.g. a green field and a red field. The plate 12 can be moved with a memory metal spring 20 which changes shape with the temperature. The first field 14 or the second field 16 is then visible to an operator through a window 18 depending on whether the plate 12 is in a first indication position (showing first field 14) or in a second indication position (showing second field 16). FIG. 1 shows the 'cold' state with the spring 20 retracted and the plate 12 in the first indication position in which the first (red) field 16 is visible through the window 18. The device pictured in FIGS. 1-3 is designed to be arranged on a part for medical usage. When the part is heated for sterilisation purposes, the spring 20 changes shape by elongation as the temperature passes a predetermined threshold value. When the spring 20 presses against a firm support 22, it shifts the plate 12 to the right in the FIG. (see FIG. 2) until the second (green) field 16 becomes visible through the window 18. This shows the operator that the part in question has been subjected to sufficient sterilisation heating and is ready for use. The spring 20 contracts when the part cools (see FIG. 3). The plate 12 can then be reset to the position shown in FIG. 1, i.e. with the first (red) field 14 displayed in the window 18. Alternately, as also indicated in FIGS. 1-3, an optical system 17 can be used for automatic registration of the position of the plate 12. Instead of using different colours of the fields 14, 16, different reflection characteristics can be used. Registration of the plate's 12 movements by the optical system 17 is transferred to a monitoring unit 19. Within the monitoring unit 19 is a memory 23 for accumulative counting of the number of sterilisation cycles. This number, as well as indication of the plate's 12 present position, can be displayed to an operator via a screen or other display means (not shown). The plate can be automatically reset by a resetting means 21 when the part for medical usage is attached to a mother unit or put to use, causing the plate 12 to be reset. The resetting means 21 can be controlled from the monitoring unit 19 or in any other conceivable manner, such as a separate pulse magnet, motor or the like. A bimetallic spring could also be used for shifting the plate 12, instead of the spring 20 made of memory metal. Alternately, a gas-filled hermetically sealed bellows 24 can be used as the temperature- and/or pressure-sensitive element for shifting the plate in autoclaving under positive pressure. See FIGS. 4 and 5. One end of the bellows 24 is affixed to a firm support 26, and its other end 28 is able to move as the volume of the bellows changes. An operating pin 30, which passes through the bellows 24 and through the support 26, is attached to the end 28 to move the indicator plate (not shown in FIGS. 4 and 5) when the bellows 24 is compressed. When the part for medical usage, equipped with the device according to the invention, is at atmospheric pressure, the bellows assumes the position shown in FIG. 4, and the end of the operating pin 30 is at a distance a from the support 26. When the medical part with the device according to the invention is autoclaved under positive pressure, the bellows 24 is compressed. The pin 30 will move to project a distance b beyond the support 26, b then being > a (see FIG. 5). The movement will shift the plate in such a way that the second field becomes visible in the inspection window, as shown in FIGS. 1-3 above. In the alternative, the operating pin 30 can by itself be used as the indicator element. The operating pin 30 can then be arranged to translate its movement into measurable changes in inductance or capacitance. Or, the indicator element can be arranged so its movement opens and closes an electronic circuit via a mechanical switch 29, as shown in FIGS. 4 and 5. The embodiments shown in FIG. 1-5 are intended for attachment to the medical part or component. Information on sterilisation or autoclaving is therefore incorporated into the part itself. The part is also able to add up the total number of autoclaving cycles as disclosed above. Use of the device in a ventilator 100 is shown in FIG. 20. The ventilator 100 is connected to a patient 102 via an inspiration tube 104 and an expiration tube 106. Breathing gas is connected to the ventilator 100 via a first gas line 108A and a second gas line 108B. The expiration tube 106 leads exhaled gas to an expiration line cassette 110 in the ventilator 100. An expiration valve 112, either placed in the cassette 110 or coupled to it during use, is used to regulate the outflow of gas via evacuation line 114. The expiratory cassette 110 must be autoclaved for each new patient 102. The cassette 110 can only withstand a limited number of autoclaving or sterilisation cycles e.g. 100. The cassette 110 is therefore equipped with a device according to the invention. When a device according to any of FIGS 1-3 is used, resetting of the indicator element can be made the first time the expiration valve 112 opens for a new patient 102. FIG. 6 shows a first embodiment of such a device for accumulating storage of the number of thermal cycles to which a part has been subjected. Here, a temperature- and/or pressure-sensitive element is utilised. The element is appropriately made of e.g. memory metal, usually a NiTi alloy which reversibly changes its physical shape at a specific switching temperature T 1 that is selectable within wide limits. The change in shape, as well as the mechanical force developed in the shape change, can be made large. The force of this shape change can also be used in the embodiments according to FIGS. 1-3 for shifting the plate, as described above. In the embodiment according to FIGS. 6-8, the change in shape can be used for accumulating, one-way, linear movement of an indicator element. The device comprises a tube 1, preferably made of glass or transparent plastic, which is hermetically sealed at both ends. A moving body 2 is arranged inside the tube 1 and held relatively firmly in place by two sets of wings or flanges 3, made of thin plastic, rubber or metal, which press against the wall of the tube 1. When the angle α of the wings 3 in relation to the tube's longitudinal axis is appropriately selected, the wings 3 serve as ratchet pawls, preventing the moving body 2 from moving in any direction except to the right in the tube 1. The moving body 2 is formed by the temperature- and/or pressure-sensitive element coupled together with the indicator element and suitably consists of an element made of memory metal which, when the temperature rises to a switching temperature T 1 , increases its length a distance of Δx (see FIG. 8). The moving body 2 resumes its original length when the temperature drops below T 1 . This elongation and subsequent contraction cause the moving body 2 to move the distance Δx inside the tube 1. In other words, for each thermal cycle the moving body 2 moves from a first indication position to a second indication position. The switching temperature T 1 and the elongation Δx are set with a tempering and deformation procedure at the time the moving body 2 is manufactured. Depending on the accuracy and desired system dynamics, Δx can be selected to vary from short distances, i.e. on the order of about 0.01 mm, up to several millimetres. The tube 1 can typically be 5 cm long and about 10 mm in diameter. Simple reading of the number of completed thermal cycles, in which T > T 1 , could consist of direct reading of the moving body's 2 position, as with a thermometer, when the tube 1 is transparent. Graduations are shown at 4. In order to indicate whether the device has gone through a thermal cycle since the last use, an indicator as shown in FIGS. 1-3 can suitably be combined with the device of FIG. 6. The interior of the tube 1 can be completely smooth or somewhat roughened, as shown at 5, to increase friction between the wall and wing 3. The tube 1 can also be equipped with serrated notches 6 with a specific pitch, approximately equal to Δx. This enables the moving body 2 to 'climb' only if the moving body's 2 expansion is greater than or equal to Δx. This accordingly prevents 'climbing' caused by ordinary thermal expansion in cycles in which T < T 1 . If correct magnitudes are selected for the angle α (see FIG. 8), the correct material is chosen for wings and the tube, a correct angle is selected for the 'serrations' etc. the risk of the moving body 2 'climbing' because of temperatures consistently less than the switching temperature T 1 is completely eliminated. At the same time, the risk of intentional movement by the moving body 2 in the 'wrong' direction when the device is shaken or for some other reason is completely eliminated. Since a moving body 2 including a memory metal can develop great force during thermal elongation, friction between the moving body 2 and the wall of the tube 1 can be made relatively large to prevent acceleration forces, jolts, vibration etc. from causing the moving body 2 to move inside the tube 1. Thus, the advantage of using memory metal in the moving body 2 is that memory metal, at a specific temperature, undergoes a sudden and relatively large change in shape of a completely different magnitude than the change in shape occurring in conventional linear thermal expansion, as noted above. In instances in which the inside wall of the tube 1 is provided with notches 6, a moving body 2 consisting of e.g. a bimetallic element can also be used. A bimetal produces a large change in shape which, however, is linear as a function of temperature. In this version, the moving body 2 inside a smooth-walled tube 1 would move in every temperature cycle, even if the actual temperature remained consistently below the threshold T 1 . However, if the interior wall of the tube 1 were provided with notches 6, the bimetallic moving body 2 could be devised so its temperature-related linear elongation Δx is equal to the pitch of the serration at the temperature threshold T 1 . The moving body 2 would then advance one notch 6 when, and only when, the temperature in the cycle exceeds the threshold T 1 . The same function is achieved as in a version with a moving body 2 made of a memory metal in a tube 1 with smooth walls. In instances in which the interior walls of the tube 1 are devised with notches 6 at specific distances from one another, the moving body 2 can also be made of other materials, such as polymers, gases, other metals etc., whose thermal expansion is employed to produce the moving body's 2 motion. A pressure-sensitive element in the form of a hermetically sealed gas- or air-filled metal bellows 32 can also be used as a moving body, see FIG. 9. Pressure inside the bellows 32 can amount to e.g. 1 bar absolute. During heating, the gas expands, and the bellows 32 elongates a distance of Δx, depending on the stiffness of the bellows 32 and the temperature rise. In autoclaving under positive pressure, the moving body is shifted according to another principle. The process is then performed in a kind of 'pressure cooker' in which the pressure is 3.6 bar at a temperature of 140° C. According to the gas law, P×V / T = constant, in which P designates pressure, V Volume and T temperature, the bellows 32 will be compressed to about 0.38 times its original length if the stiffness of the bellows 32 is disregarded. The compressive force is considerable here. When the bellows has a diameter of 5 mm, the force will initially be about 5 N. When an appropriate stiffness is selected for the bellows 32, a desired change in length in an autoclaving cycle can be obtained. Also see FIGS. 4 and 5. The bellows 32 is equipped with two sets of ratchet pawl wings or flanges 34, as also noted in the description of FIGS. 6-8. Embodiments for direct reading of the number of completed thermal cycles on a graduated scale were described above. However, the device according to the invention can also be devised for electronic reading and display of the number of cycles in the mother unit, e.g. a ventilator. Since the device according to the invention must be simple and inexpensive and is also exposed to moisture, high temperatures etc., complex parts, electronics, batteries etc. should preferably be housed in the mother apparatus to the greatest possible extent. Several versions in which this function is realised are described below. FIG. 10 shows a tube of the kind depicted in FIG. 6 with two conductive pathways 38 made of a resistive material, resistor wire etc. deposited on the interior walls of the tube. These conductive pathways 38 are short-circuited by the moving body 40. This means that electrical resistance R between the wires 42 decreases the farther the body 40 advances to the right in the tube 36. The body's 40 position and, accordingly, the number of completed thermal cycles can therefore be determined by measuring the resistance R. FIG. 11 shows an alternative in which a rod 44 made of ferromagnetic, unmagnetised material is connected to the moving body 46. When the body 46 moves to the right in the tube 48, the rod 44 is thrust into a coil 50 that is wound around the exterior of the tube 48 along about half the length of the tube. Inductance L increases as the rod is inserted into the coil 50. The position of the body 46 in the tube 48 can therefore be determined by measuring inductance L. Alternately, a rod made of non-magnetic conductive material can be used, inductance then declining as the rod is inserted into the coil, i.e. field constriction. FIG. 12 shows an additional embodiment in which a small ferromagnetic, unmagnetised body 52 is arranged on the moving body 54. The tube 56 is enclosed in a coil 58 whose turns increase linearly per unit of distance to the right in the FIG. The coil's 58 inductance will also increase in this instance when the moving body 54 and, accordingly, the ferromagnetic body 52 advances to the right in the tube 56. This makes it possible to determine the position of the moving body 54 by measuring inductance L. The coils in the embodiments shown in FIGS. 11 and 12 do not need to be affixed to the tube but can be in the mother apparatus so the tube is automatically inserted into the coils when the part for medical usage is placed in the mother apparatus. In an analogous fashion, varying capacitance can be achieved in determining the position of the moving body in the tube. Thus, the tube can be provided with a conductive coating on its interior or exterior. The coating would not cover the entire surface but decline from one end of the tube to the other. It could decline e.g. conically so the coated area per unit of length declines linearly along the length of the tube. Capacitance between the outer capacitor plate accordingly formed and the moving body, or an appliance connected to the moving body, declines linearly when the body moves, i.e. the position of the body can be determined by measuring the varying capacitance. FIG. 13 is a general illustration of the way the moving body 60 acts, by means of a moving shaft 62, on an electrical component 64 with variable resistance, inductance or capacitance or a combination of these parameters. Here, commercially available standard components can be used advantageously. For all embodiments of FIGS. 11-13 a monitoring unit similar to the one shown in FIGS. 1-3 can be utilised for storing and displaying accumulated number of thermal cycles, as well as whether the device has passed a thermal cycle after the most recent usage (and before the next usage). FIG. 14 shows an alternative version of the moving body. Two identical discs 11 are mounted on a rod 13 through a hole 15 in the discs. The diameter of the rod 13 is slightly less than the diameter of the holes 15. The discs are interconnected by a temperature-sensitive element 21, suitably made of memory metal, and the element is pretensioned so the discs 11 press against the rod 12 in the normal position, as shown in the FIG. When the length of the temperature-sensitive element 21 increases when the temperature T > the switching temperature T 1 during the thermal cycle, the right disc 11 will shift to the right. When the temperature subsequently drops, the left disc 11 will follow, causing the entire body to shift to the right on the rod 13. Movement to the left in the FIG. is prevented by the 'drawer' effect. Movement of the moving body 11, 21 can also be used to add up the total number of thermal cycles to which the medical part with the device according to the invention has been subjected. A number of mechanical switches, similar to the one shown in FIGS. 4-5 can be arranged so one switch at a time is effected at each thermal cycle. Thus indicating that a thermal cycle has passed before the next usage of the device. FIG. 15 shows an additional embodiment of the device according to the invention. Here, a conical body 66 is attached to one end of the moving body 68. A reading fork 70 is arranged to register light transmitted across the tube 72 when the conical body 66 is gradually introduced into the light path as the moving body 68 advances to the right in the tube 72. The reading fork 70 can be mounted on the tube 72 or located in the mother apparatus, enabling it to measure light transmitted across the tube 72 when the medical part with the device according to the invention is mounted on the mother apparatus. FIGS. 16-19 shows two additional advantageous embodiments of the device according to the invention. They utilise helical movement, instead of linear movement, in totalling the number of thermal cycles. The embodiment shown in FIG. 16 has two small, identical nut wheels on a finely threaded rod 73 inside a tube 75 which can be transparent or opaque. The wheels 82 are equipped with a number of small, flexible wings 76 which press against the wall of the tube 75. The wheels 82 can be made of e.g. a polymer material, possibly combined with pressed-on standard metal nuts 83. The interior walls of the tube 75 can be completely smooth. The wings 76 then form an angle with the tube wall, creating a ratchet effect, or can be provided with serrations 74. The wheels 82 are connected to a temperature-sensitive element 84, suitably made of memory metal or a bimetal, as described above for other embodiments. When the switching temperature T1 is exceeded, the shape of the element 84 changes, causing the moving body 82, 84 to be screwed in steps and advance along the threaded rod 73. Great accuracy can be obtained and a large number of cycles accommodated with a limited length of tubing by suitable selection of the pitch of the thread, the shape of the temperature-sensitive element 84, the number of wings 76 and their placement in relation to one another and, where applicable, the number of serrated notches 74. Other types of ratchet wheel functions can obviously be used. Some friction between the nuts 82, 83 and the thread is permissible, even desirable, to prevent wheel rotation caused by vibration etc. This is possible, since memory metal can develop considerable force when changing shape. The type of device according to the invention is more reliable, more accurate, and less sensitive to jolts, acceleration and vibration and is able, for a given size, to register a much larger number of thermal cycles than the linear version. In theory, 'resolution' in the version with a smooth tubular wall is infinitely high but is finite in practice due to friction, the resilience of the wings 76 etc. If the change in shape is very small, the body will not move but remain in place and quiver, as noted above. FIG. 17 shows about 30 serrated notches around the circumference of the tube. This would yield a resolution of 360/30 = 12°. FIG. 18 shows how a resolution of 18°, i.e. 20 temperature cycles for each wheel revolution, can be achieved with four ratchet wings 76 and only five serrated notches. Generally speaking, if the number of wings is k and the number of notches n x k + 1, where n is an integer 1,2,3..., the increment 360 / n × k + 1 × 1 / k degrees is obtained for each meshing by the wings. For example, 4 wings result in, i.e. k = 4 and n = 5, i.e. a total of 4 x 5 + 1 = 21 notches, an increment of 4.3°. This corresponds to 84 temperature cycles per revolution on the threaded rod 73. So high resolution can be obtained with just a few wings and notches, thereby facilitating fabrication. Combinations between the shown embodiments, other than those explicitly mentioned, are also possible. In particular combinations involving registration and display of information.

Claims: A device for repeated registration of the number of thermal cycles to which a part (110) for medical usage is subjected, comprising a temperature- and/or pressure-sensitive element (2, 3; 20; 24; 32; 40; 46; 54; 60; 21; 68; 84) is arranged in conjunction with the said part (110), the element (2, 3; 20; 24; 32; 40; 46; 54; 60; 21; 68; 84) reversibly changing its physical shape with the temperature and/or pressure, variations in pressure being invariably associated with temperature changes, characterised in that an indicator element (2, 3; 12; 30; 44; 52; 62; 66) is arranged to linearly move from a first indication position to a second indication position when the change in shape exceeds a predetermined threshold value and a registration means (4; 17, 19, 23; 29, 31; 38, 42; 50; 58; 64; 11, 13, 15; 70) is arranged to register the linear movement of the indicator element (2, 3; 12; 30; 44; 52; 62; 66) from the first indication position to the second indication position. The device according to claim 1, characterised in that the registration means (4; 17, 19, 23; 29, 31; 38, 42; 50; 58; 64; 11, 13, 15; 70) comprises a memory (23) for accumulative storage of the total number of registered linear changes of the indicator element (2, 3; 12; 30; 44; 52; 62; 66) from the first to the second indication position. The device according to claim 1 or 2, characterised in that a resetting means (21) is arranged to automatically reset the indicator element (12) to the first indication position when the part for medical usage is put to use or mounted on a mother unit. The device according to claim 3, wherein the mother unit is a ventilator (100) and the part for medical usage is an expiration line cassette (110), characterised in that the resetting means (21) is devised to reset the indicator element (12) to the first indication position the first time an expiratory valve (112) opens. The device according to claim 1 or 2, characterised in that the indicator element (2, 3; 44; 52; 62; 66) is adapted to perform an accumulating one-way linear movement, whereby the second indication position in one thermal cycle corresponds to the first indication position in a following thermal cycle. The device according to claim 5, characterised in that the registration means comprises a tube (1, 36, 48, 56, 60, 75), and the temperature- and/or pressure-sensitive element and the indicator element (2, 3; 44; 52; 62; 66) are coupled together to form a moving body (2, 40, 46, 54, 82, 84) inside the tube, the moving body (2, 40, 46, 54, 82, 84) being adapted to linearly move in one direction inside the tube during each temperature cycle. The device according to claim 6, characterised in that the tube's (1) interior surface is devised with notches (6) at specific distances along the length of the tube, and the moving body (2), is equipped with a set of wings or flanges (3) which mesh with the notches in the wall of the tube in order to form a ratchet pawl enabling the moving body (2) to perform an accumulating linear movement inside the tube only if the change in length during a thermal cycle exceeds the said distance between two consecutive notches. The device according to claim 6 or 7, characterised in that the moving body comprises a threaded rod (73), arranged inside the tube and two nut wheels (82), with ratchet pawl wings (76) which press against the interior surface of the tube, being arranged at intervals on the rod, the nut wheels are adapted to turn in one direction and, accordingly, advance linearly along the threaded rod in steps every time the temperature cycle passes the said temperature threshold. The device according to claim 1 or 2, characterised in that the registration means comprises a rod (13) and the indicator element comprises two disks (11) with holes arrayed at intervals on the rod (13), the holes (15) being somewhat larger than the diameter of the rod, and the disks are interconnected to the temperature- and/or pressure-sensitive element (21) which is devised to normally press the disks against the rod in a locked position and cause the disks to advance one-way along the rod as a result of the element's elongation when the temperature exceeds a threshold value. The device according to any of the preceding claims, characterised in that the said temperature- and/or pressure-sensitive element (2, 20, 40, 46, 54, 60, 21, 68, 84) is made of memory metal. The device according to any of claims 1-7 and 9, characterised in that the said temperature- and/or pressure-sensitive element (2, 20, 40, 46, 54, 60, 68, 84) is made of a bimetal. The device according to any of claims 1-7, characterised in that the moving body consists of a hermetically sealed gas-filled bellows (32) which is elongated by expansion of the gas when the temperature rises. The device according to any of claims 1-7, the thermal cycle then comprising autoclaving under positive pressure, characterised in that the moving body consists of a hermetically sealed bellows (24, 32) arranged to be compressed by the positive pressure, elongation of the bellows after autoclaving producing the body's linear movement in the tube. The device according to any of claims 8-9, claim 10 in combination with any of claims 8-9 or claim 11 in combination with claim 9, characterised in that the registration means comprises a component (38, 42, 50, 58, 64, 86) arranged to successively interact with the moving body (40, 46, 54, 60, 86), or an appliance (44, 52, 62) connected to the moving body, the interaction resulting in a variable resistance and/or inductance and/or capacitance related to the body's linear movement. The device according to claim 14, characterised in that the component comprises two longitudinal conductive pathways (38) made of a resistive material, resistor wire or the like arranged in the interior of the tube (36), the pathways being short-circuited by the moving body (40), or by the appliance connected to the moving body, causing electrical resistance between the conductive pathways to change as the body advances inside the tube. The device according to claim 14, characterised in that the component comprises a coil (50) wound around at least part of the tube (48), and the appliance comprises an axially oriented rod (44) made of a magnetic or non-magnetic material for successive insertion into the coil as the moving body advances. The device according to claim 14, characterised in that the component comprises a coil (58) wound around at least part of the tube with coil turns that increase linearly per unit of length from one end of the coil to the other, and the appliance comprises a small component (52) made of ferromagnetic unmagnetised material for successive insertion into the coil as the moving body (54) advances. The device according to claim 14, characterised in that the component comprises a conductive coating provided on at least part of the tube's interior and exterior, the coating surface varies from one end of the tube to the other, thereby causing capacitance between the coating and the moving body, or the appliance connected to the body, to vary with the moving body's linear movements. The device according to any of claims 6-13, characterised in that the registration means comprises an optical reading fork (70) arranged to register light transmitted across the tube (72), and the moving body (68) tapers towards one end, or is connected to a tapering appliance (66), thereby gradually shadowing the light beam as the body advances. The device according to claim 5, characterised in that the indicator element comprises two wheels (82) arranged at intervals on a rod (73), the wheels (82) are only able to rotate in one direction and are interconnected to the temperature- and/or pressure-sensitive element (84) which is devised so the wheels rotate in steps, i.e. a specific angle, for each temperature cycle in which a temperature threshold is exceeded.

Inventors: KRAHBICHLER ERIK, SKOG GOERAN, SLETTENMARK BRUNO, KRAHBICHLER, ERIK, SKOG, GOERAN, SLETTENMARK, BRUNO, Skog, Göran
Applicants: MAQUET CRITICAL CARE AB
Application year: 1999
Main classification: A61L2
IPC codes: A61B17, A61L2, A61B18