External drive unit for implantable heart assist pump

Abstract

To provide an improved external drive unit for an implantable heart assist pump.SOLUTION: A proposed drive unit 7 comprises: a motor housing 51; a transcutaneous drive shaft 3; and a motor 35 for driving the heart assist pump 4. The motor 35 is connectable to the heart assist pump 4 via the drive shaft 3, and the motor 35 is arranged inside the motor housing 51. The drive unit 7 further comprises a catheter 2 surrounding the drive shaft 3 and a purge line 53 for injecting a purge medium into a lumen of the catheter 2 or into a space 41 between the catheter 2 and the drive shaft 3. The purge line 53 is in thermal contact 54, 55 with an outer surface of the motor housing 51 and / or with an outer surface of a proximal section 52 of the catheter 2. Due to the thermal contact 54, 55 heat may be transferred from the outer surface of the catheter 2 in the proximal section 52 and / or from the outer surface of the motor housing 51 to the purge medium.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This application relates to the field of medical technology. This application relates to an external drive unit for an implantable heart assist pump, and a heart assist device including a drive unit and an implantable heart assist pump. This application is related to the assignee's U.S. Patent Application Publication No. 15 / 482,513, entitled "Methods and Systems for an External Drive Unit for an Implantable Heart Assist Pump," filed April 7, 2017, the contents of which are incorporated herein by reference. [Background technology]

[0002] Cardiac assist devices for supporting a patient's cardiac function are known from the state of the art. Such devices may include an implantable blood pump, which may be inserted into a ventricle of the heart by minimally invasive means. Furthermore, an external (or extracorporeal) motor may be provided to drive the blood pump. The motor may be connected to the blood pump via a percutaneous and flexible drive shaft rotatably mounted inside a percutaneous catheter. The implantable components of the device may be inserted through a puncture site in the patient's groin. Related devices are described, for example, in US Pat. No. 5,649,999.

[0003] In the case of such cardiac assist devices, problems can arise related to the heat dissipated by the external motor. In some applications, the motor may be placed close to the patient's body, particularly near the patient's legs, while the blood pump is running. If the heat generated by the motor is not effectively removed, the motor may overheat and cause the motor to malfunction. In addition, motor overheating poses a health risk to the patient when the motor's hot housing comes into contact with the patient's skin, especially if the patient is unable to detect the heat and react appropriately, for example, due to anesthesia. The safe amount of heat absorption by human skin has been studied in the context of heat generated by ultrasound and magnetic resonance imaging probes. For example, Non-Patent Document 1 describes a method for determining safe heat absorption levels.

[0004] To prevent cardiac assist device motors from overheating, the housings of such motors can be provided with numerous cooling fins to effectively draw heat away from the motor and dissipate it into the surrounding air. However, the amount of heat that can be transferred to the air may not be sufficient when the motor is operated in an enclosed environment, such as under a duvet while a patient is resting, or under a surgical drape during surgery. Furthermore, the surface of the housing with the cooling fins may be difficult to clean. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 8,489,190 [Non-patent literature]

[0006] [Non-Patent Document 1] "Human Skin Temperature Response to Absorbed Thermal Power" (SPIE Proceedings-The International Society for Optical Engineering 3037:129-134, March 1997) Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above-mentioned state of the art, it is an object of the present application to provide an improved external drive unit for an implantable cardiac assist pump and an improved cardiac assist device. In particular, it is an object of the present application to provide a drive unit and a cardiac assist device with improved thermal management. Furthermore, it is an object of the present application to propose a drive unit that allows safe and efficient operation of the cardiac assist device. [Means for solving the problem]

[0008] These objects are achieved by an external drive unit with the features of independent claim 1. Further features and further developments, if necessary, will become apparent from the dependent claims and the detailed description in conjunction with the accompanying drawings.

[0009] A proposed external, i.e., extracorporeal, drive unit for an implantable cardiac assist pump includes a motor housing, a percutaneous drive shaft, and a motor that drives the cardiac assist pump. The motor is connectable to the cardiac assist pump via the drive shaft and is disposed inside the motor housing. The drive unit further includes a catheter surrounding the drive shaft and a purge line for injecting a purge medium into the lumen of the catheter or into the space between the catheter and the drive shaft. The purge medium may be a solution, such as a glucose solution or saline. The purge line is in thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter. Through the thermal contact, heat can be transferred from the outer surface of the proximal catheter and / or from the outer surface of the motor housing to the purge medium.

[0010] A catheter typically includes a portion intended for placement inside a patient's body and another portion intended for placement outside the patient's body. The proximal portion of the catheter is typically intended for placement outside the patient's body. A purging medium is injected into the lumen of the catheter or into the space between the catheter and the drive shaft to prevent blood from entering the lumen or space and impairing the rotation of the drive shaft.

[0011] In most embodiments, the purge line is configured to direct the purge medium so that it first makes thermal contact with the exterior surface of the motor housing and / or the exterior surface of the proximal portion of the catheter, and the purge medium is then injected into the lumen of the catheter or into the space between the catheter and the drive shaft. As described below, the purge medium is additionally injected into the fluid gap between the stator and rotor of the motor, and then into the lumen of the catheter or into the space between the catheter and the drive shaft, and then into thermal contact with the exterior surface of the motor housing and / or the exterior surface of the proximal portion of the catheter. The cardiac assist device and / or drive unit may include a fluid conveyor, e.g., a pump, configured to enable flow of the purge medium in any of the manners described above and / or below.

[0012] During operation of a cardiac assist device including a drive unit, the motor may heat up due to heat dissipation. Furthermore, in some embodiments, a proximal portion of the catheter, which may be located near the motor, may also heat up during operation. In particular, during operation, heat may be transferred from the motor to the proximal portion of the catheter and to portions of the catheter adjacent to the proximal portion, which may not be covered by a housing and may contact the patient's skin. Thermal contact of the purge line with the outer surface of the motor and / or the outer surface of the proximal portion of the catheter may transfer heat from the motor and / or the proximal portion of the catheter to the purge medium in the purge line. This may cool the proximal portion of the motor and / or the catheter, reducing the risk of overheating of the drive unit. The proposed drive unit improves the safety of cardiac assist device operation, particularly when the drive unit is placed under a blanket and is not adequately cooled by the atmosphere, and when the drive unit comes into contact with the patient's body, increasing the risk of burns to the patient's tissue.

[0013] Compared to the state of the art, the proposed drive unit does not require additional components, as the purge line serves two purposes simultaneously. First, the purge line guides the purge medium into the patient's body and prevents blood from entering the lumen of the catheter or the space between the catheter and the drive shaft. Second, the purge line according to the invention improves the thermal management of the drive unit. Additionally, the purge medium may be preheated by thermal contact with the motor and / or the proximal part of the catheter, thereby reducing the viscosity of the purge medium and improving the rotatability of the drive shaft. The improved rotatability of the drive shaft can be achieved because the purge medium first comes into thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal part of the catheter, and then the purge medium is injected into the lumen of the catheter or the space between the catheter and the drive shaft, and finally into the patient. Furthermore, because the purge medium enters the patient only after making thermal contact with the motor housing or the proximal portion of the catheter, the initial temperature of the purge medium upon thermal contact is relatively low, allowing for efficient heat transfer from the motor housing and / or the proximal portion of the catheter.

[0014] During operation of the cardiac assist device, the outer surface of the motor housing is typically warmer than the outer surface of the proximal portion of the catheter. In some embodiments, the purge line is in thermal contact with both the outer surface of the motor housing and the outer surface of the proximal portion of the catheter. In these embodiments, cooling the drive unit and preheating the purge medium can be particularly efficient. The purge line can be configured to direct the purge medium so that it first comes into thermal contact with the outer surface of the proximal portion of the catheter and then with the outer surface of the motor housing, allowing for gradual preheating of the purge medium and efficient cooling of the proximal portion of the catheter. The purge medium can then, in some embodiments, be injected into the fluid gap of the motor, as described below. The purge medium can then be injected into the lumen of the catheter or into the space between the catheter and the drive shaft.

[0015] The catheter may include one or more lumens. In some embodiments, the cardiac assist device may be configured so that the purge medium first flows distally into the patient's body through one of the catheter's lumens and then returns to the patient's body through another of the catheter's lumens. In most embodiments, the catheter lumen or the space between the catheter and the drive shaft extends into the proximal portion of the catheter. In particular, the lumen or space may extend the entire length of the proximal portion of the catheter, and in some embodiments, may extend beyond the entire length of the catheter. In this embodiment, heat may be transferred to the proximal portion of the catheter or portions adjacent to the proximal portion via the purge medium within the lumen or space. Therefore, cooling the proximal portion of the catheter via a purge line may be particularly beneficial in this embodiment.

[0016] In most embodiments, the purge line does not form part of the catheter, and in particular, the purge line is not formed by the lumen of the catheter in most embodiments, and may be a separate line located outside the outer wall of the catheter.

[0017] The purge line is typically completely external to the body and therefore does not include any implanted parts. The purge line is typically positioned to be in fluid communication with a space or lumen of the catheter. The drive unit typically includes a purge opening that is in fluid communication with the space or lumen. A purge line may be attached to the purge opening, such that the purge line is in fluid communication with the space or lumen. Typically, during operation of the cardiac assist device, a purge medium flows distally within the space or lumen.

[0018] The motor may be an electric motor. In some embodiments, the motor includes a stator and a rotor. The rotor may be connected to a drive shaft. The rotor typically includes a magnet, particularly a permanent magnet. The stator may include multiple windings. The stator typically surrounds the rotor, and a magnetic gap is formed between the rotor magnets and the stator windings. The rotor may be rotatably mounted. A fluid gap may be formed between the rotor and the stator. The fluid gap may be fluidly connected to a purge opening for injecting a purge medium into the fluid gap. A purge line may be connected or connectable to the purge opening. The purge medium may be injected into the fluid gap and into the lumen of the catheter or into the space between the catheter and the drive shaft. The fluid gap of the motor is typically fluidly connected to the lumen of the catheter or the space between the catheter and the drive shaft. In a typical embodiment, the purge lines and fluid gaps are configured to direct the purge medium so that it first comes into thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter, then is injected into the fluid gap between the rotor and stator, and then into the lumen of the catheter or into the space between the catheter and the drive shaft.

[0019] When a non-purged motor is used, a seal may be required to separate the motor from the space between the catheter and drive shaft to prevent air from entering the space and ultimately the patient. The use of a purged motor has the advantage of eliminating the need for complex seals that create friction and separate the motor from the space between the catheter and drive shaft. Therefore, the motor may be simpler to manufacture and may have reduced frictional losses, resulting in more efficient operation. Furthermore, seals are typically prone to failure, and the risk of cardiac assist device failure may be reduced if a seal is not provided.

[0020] When the motor is purged with the purge medium, the motor can be cooled efficiently. Furthermore, because the purge medium is preheated by thermal contact with the proximal portion of the catheter and / or the motor housing, the purge medium already has a reduced viscosity when it enters the fluid gap of the motor. Therefore, the drive unit reduces friction losses in the fluid gap and / or bearings of the motor, increasing the efficiency of the motor.

[0021] In some embodiments, the purge line is configured to first direct the flow of purge medium to the area of ​​thermal contact with the outer surface of the proximal catheter, then to the area of ​​thermal contact with the outer surface of the motor housing, then into the fluid gap between the rotor and stator, and then into the lumen of the catheter, or into the space between the catheter and the drive shaft, and / or into the fluid gap of the motor (described below). Surprisingly, when a drive unit according to this embodiment is used, it has been found that the motor current required to transport a specific amount of blood using an implantable cardiac assist pump, i.e., the current applied to the stator windings, is independent of the flow rate of the purge medium. In contrast, when there is no thermal contact between the purge line and the outer surface of the motor housing and / or the outer surface of the proximal catheter, the motor current increases with increasing purge flow rate, presumably because the purge medium in the fluid gap cools due to the increased flow rate, thereby increasing viscosity and friction losses in the motor. Preheating the purge medium according to the present invention then results in a constant motor current for different purge flow rates. Thereby, the motor current can be advantageously used as a control parameter for the cardiac assist device, since the undesirable effects of the purge flow rate on the motor current do not need to be taken into account, and therefore the electronic control of the cardiac assist device can be greatly simplified.

[0022] In some embodiments, the purge line is configured to direct the flow of purge medium proximally in the area where the purge line makes thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter, and then inject the purge medium into the lumen of the catheter or into the space between the catheter and the drive shaft. Heat transfer in such a counterflow arrangement is particularly efficient. In this arrangement, the purge medium flows in the opposite direction (proximal flow) in the area of ​​thermal contact with the outer surface of the proximal portion of the catheter compared to the lumen of the catheter or the space between the catheter and the drive line (distal flow), and / or the purge medium flows in the opposite direction (proximal flow) in the area of ​​thermal contact with the outer surface of the motor housing compared to the fluid gap between the stator and rotor (distal flow). In particular, the fluid conveyor may be configured to cause the purge medium to flow distally within the fluid gap.

[0023] In some embodiments, the purge line at least partially surrounds the motor housing and / or the proximal portion of the catheter in the area where the purge line is in thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter. By surrounding the motor housing and the proximal portion of the catheter, the area of ​​heat transfer can be increased, and therefore the efficiency of heat transfer can be improved. Typically, the purge line is in thermal contact with the motor housing and / or the proximal portion of the catheter from multiple sides, for example, over an angular range of at least 180°. In particular, the purge line can completely surround the motor housing and / or the proximal portion of the catheter over the entire angular range.

[0024] In some embodiments, the purge line is flexible. The purge line may have a tubular shape or may even have a round cross section. The outer diameter of the purge line may be at least 1 mm, preferably at least 2 mm, and / or at most 5 mm, preferably at most 3 mm. The inner diameter of the purge line may be at least 0.3 mm, preferably at least 0.7 mm, and / or at most 2 mm, preferably at most 1.5 mm. The purge line may include or be made of a biocompatible material. In some embodiments, the purge line includes or is made of a plastic material such as PU or PEEK, or a metal such as stainless steel. The high thermal conductivity of the purge line material may improve thermal contact between the purge medium and the motor housing and / or the proximal portion of the catheter.

[0025] The purge line may spiral around the motor housing and / or the proximal portion of the catheter in the area where the purge line is in thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter. If the purge line extends in a clear spiral, undercut areas inside the purge line may be prevented, reducing the risk of air pockets remaining in the purge line when the purge line is filled with purge medium. For example, for this purpose, the purge line may include only one serial flow path for the purge medium and no parallel flow paths. This allows for reliable degassing of the purge line. For example, the purge line may be wrapped around the motor housing and / or the proximal portion of the catheter. In this embodiment, the drive unit is easy to manufacture. Furthermore, the drive unit can be easily manufactured with the desired heat transfer efficiency by simply selecting the appropriate number of turns of the purge line, thereby creating the desired heat transfer area. In some embodiments, the purge line makes at least 4 wraps, preferably at least 8 wraps around the proximal portion of the catheter and / or at least 3 wraps, preferably at least 5 wraps around the motor housing.

[0026] The purge line may be attached to the proximal portion of the motor housing and / or catheter. In most embodiments, the purge line contacts the outer surface of the motor housing and / or the proximal portion of the catheter in an area of ​​thermal contact, such that the proximal portion of the motor housing and / or catheter is in direct contact with the purge line. However, in other embodiments, a thermally conductive element may be disposed between the proximal portion of the motor housing and / or catheter and the purge line. The purge line and the proximal portion of the motor housing and / or catheter may then be in direct contact with the thermally conductive element. Such an arrangement allows for reliable thermal contact. In some embodiments, the purge line is at least partially integrated into the motor housing. For example, the purge line may be partially formed by a lumen embedded inside the motor housing. The overall thermal conductance (W / K) between the inner surface of the purge line and the inner surface of the motor housing may be at least five times, preferably at least ten times, the overall thermal conductance between the inner surface of the purge line and the inner surface of the drive unit housing. Furthermore, the overall thermal conductance between the inner surface of the purge line and the interior of the motor, particularly the motor windings, may be the overall thermal conductance between at least the inner surface of the purge line and the inner surface of the motor housing. Such overall thermal conductance considers the series thermal conductance of the material disposed between the inner surface of the purge line and the inner surface of the motor housing, as well as the cross-sectional area, thickness, and thermal contact conductance. Because the thermal conductance between the purge line and the drive unit housing is relatively high, heat generated by the motor may be dispersed within the drive unit housing, for example, by air convection, and localized hot spots on the drive unit housing may be avoided. Furthermore, the interior of the motor is in thermal contact with the motor housing, and heat generated by the motor is transferred to the outer surface of the motor housing. To achieve sufficient heat transfer from the motor's fluid gap to the outer surface of the motor housing, the windings may be cast in a molding material, for example, epoxy resin, to prevent the creation of air spaces between the fluid gap and the outer surface of the motor housing. In some embodiments, the molding material directly bonds the windings and the motor housing together.

[0027] In some embodiments, the drive unit further comprises a heat spreader. The heat spreader may comprise a contact surface configured to contact and / or be in direct contact with and / or lie flat against the patient's skin. The contact surface is connected or connectable to the motor in a thermally conductive manner to transfer heat generated by the motor to the patient's tissue.

[0028] The drive unit including the heat spreader, as discussed in U.S. Patent Application Publication No. 2016 / 0213827, offers a solution that contradicts the commonly held belief in the state of the art that efficient heat removal from a cardiac assist pump motor must occur away from the patient. Instead, efficient heat removal in the proposed drive unit can be achieved, at least in part, by heat transfer to the patient's tissue. Thus, during operation of the cardiac assist pump, heat can be transferred from the motor to the contact surface of the heat spreader. The thermal conductance of the thermal contact between the motor and the contact surface can be sufficiently large to transfer heat generated by the motor through the heat spreader to the patient's tissue.

[0029] The contact surface may be flat or curved. In typical embodiments, the contact surface is stepless. In preferred embodiments, the contact surface is flexible to maximize contact with the tissue. The contact surface may be arranged for heat transfer from the motor to the tissue. The entire contact surface may contact the skin during use of the drive unit. The drive unit may further include a bottom surface formed by the sum of all areas of the drive unit designed to contact the patient's skin. The contact surface typically forms a portion of the bottom surface. However, in some embodiments, the contact surface forms the entire bottom surface.

[0030] The present application further relates to a cardiac assist device comprising the above-mentioned or below-mentioned drive unit, further comprising an implantable cardiac assist pump. The cardiac assist pump may be connected, for example permanently connected, to a drive shaft of the drive unit. In another embodiment, the motor may be connected to the drive shaft via a coupling, for example via a magnetic clutch.

[0031] According to a method for operating a cardiac assist device, a drive unit drives a cardiac assist pump. A purge medium is injected into the lumen of the catheter or into the space between the catheter and the drive shaft. Heat is generated by the motor and transferred to the motor housing. Further, heat is transferred from the outer surface of the motor housing and / or from the outer surface of the proximal portion of the catheter to the purge line.

[0032] In some embodiments, a heat spreader is provided, and heat generated by the motor is transferred to the heat spreader. In further embodiments, the contact surface of the heat spreader is in contact with and / or in direct contact with and / or lies flat against the patient's skin, so that heat generated by the motor is transferred to the patient's tissue. In further embodiments, the contact surface of the heat spreader is in direct contact with the patient's skin. However, in some cases, another material, such as a portion of the patient's clothing, may be placed between the skin and the contact surface.

[0033] The drive unit may include a drive unit housing. The motor housing and / or a proximal portion of the catheter may be disposed within the drive unit housing. A portion of the purge line may extend between the motor housing and the drive unit housing and achieve heat transfer to the purge line as described above. Further, a portion of the purge line may extend between the proximal portion of the catheter and the drive unit housing and achieve heat transfer to the purge line as described above. A portion adjacent to the proximal portion of the catheter may be disposed outside the drive unit housing. Furthermore, the purge line may include a portion disposed outside the drive unit housing. This portion is typically attachable to a source of purge medium. For simple and cost-effective manufacture of the drive unit, the diameter of the purge line may be the same for the portion disposed outside the drive unit housing and the portion in thermal contact with the motor housing and / or the proximal portion of the catheter.

[0034] The heat spreader may be attached to the drive unit housing. In typical embodiments, the drive unit housing is an external housing that is at least partially visible when the drive unit is assembled. The heat spreader may be disposed outside the drive unit housing. The heat spreader is configured to allow heat conduction from the motor to the patient's tissue. In most embodiments, the heat spreader is a passive component that does not require a supply of electrical energy. Furthermore, in most embodiments, the heat spreader does not rely on moving parts and / or moving fluids. The heat spreader may be rigidly or movably connected to the drive unit housing. In some embodiments, the heat spreader is removably connected to the drive unit housing. For example, it may be convenient to implant the cardiac assist pump in a catheterization lab with the heat spreader removed. The drive unit housing may function as a handle for the cardiac assist device in this situation. After the implantation procedure, the drive unit housing may be connected to the heat spreader, such that heat generated by the motor can be efficiently transferred to the patient's tissue. Heat can be transferred from the motor to the motor housing. The motor housing may be in thermal contact with the drive unit housing, so that heat generated by the motor can be transferred from the motor housing to the drive unit housing, and from the drive unit housing to the heat spreader.

[0035] The drive unit may include a holding means configured to attach the drive unit to the patient's thigh. When the cardiac assist device is used, in a typical application scenario, at least the bottom surface of the drive unit comes into contact with the patient's skin. The contact surface may then also come into contact with the skin. The drive unit then allows for particularly efficient removal of heat from the motor during operation of the motor, thereby preventing overheating of the motor.

[0036] The heat spreader, along with the proposed thermal contact between the purge line and the motor housing and / or the proximal portion of the catheter, work together to optimize thermal management of the cardiac assist device. In many embodiments, heat transfer from the drive unit to the atmosphere is not required when the cardiac assist device is operating. Thus, the cardiac assist device can be operated reliably without overheating even when the drive unit is covered with a duvet or surgical drape. In typical embodiments, cooling fins are not required. Thus, the proposed drive unit can be designed to be relatively compact, which improves ease of installation and comfort of wearing the drive unit. Furthermore, the amount of heat removed from the motor is predictable and does not strongly depend on the temperature or flow rate of the atmosphere. Thus, thermal management of the drive unit can be controlled in a reliable manner. Furthermore, because cooling fins are not required, the drive unit housing may have a partially or completely continuous and / or stepless surface. Thus, cleaning the drive unit may be simple.

[0037] Therefore, the drive unit can be beneficially used in different application scenarios.

[0038] First, during cardiac assist device implantation in a catheterization lab, the motor may be placed on a sterile drape because the area below the drape may be considered non-sterile. This situation allows air convection around the motor, reducing the risk of overheating. Furthermore, the likelihood of unintentional patient contact with the motor is low, and contact between the user (physician) and the motor typically occurs with gloves. Therefore, the motor's allowable temperature is higher than in the second application scenario described below. Furthermore, the risk of contamination of the drive unit is relatively high because the user may touch the motor with contaminated, especially blood-stained, gloves.

[0039] Second, it is particularly important that the pump maintain its position within the patient's body during patient transport or in an intensive care unit. In this situation, the motor must be securely fixed relative to the puncture site due to its weight. For this purpose, the motor is typically placed under a blanket or duvet. Therefore, heat transfer from the motor by convection is inefficient, and the risk of overheating of the motor during operation must be considered. Furthermore, in this scenario, the patient may come into direct contact with the pump. Therefore, efficient heat transfer from the motor to the purge medium and / or the patient's tissue, as ensured by the drive unit described above or below, is highly beneficial. Furthermore, since the motor may require cleaning after extended use, the surface geometry achieved with the proposed drive unit is advantageous compared to heat sink designs known in the art, for example, those that include cooling fins.

[0040] The surface area of ​​the contact surface of the heat spreader may be greater than the surface area of ​​the surface of the drive unit housing, the surface of the drive unit housing being the surface of the housing that faces the patient during operation. The heat spreader may be sized to extend beyond the drive unit housing. In some embodiments, the surface area of ​​the contact surface is at least 25 cm 2 , preferably at least 50 cm 2 or at least 100 cm 2 Typically, the surface area is 400 cm 2 The amount of heat transferred to the patient's tissue is typically less than 80 mW / cm of contact surface area. A sufficiently large surface area is necessary to allow efficient transfer of heat from the motor to the patient's tissue. Furthermore, a sufficiently large surface area is important to prevent localized overheating of the tissue and the resulting tissue damage. The amount of heat transferred to the patient's tissue is typically less than 80 mW / cm of contact surface area. 2 , preferably up to 60 mW / cm 2 or up to 40mW / cm 2 Furthermore, the surface area constitutes a key factor in designing the thermal management of the drive unit, allowing the motor to operate at a desired temperature. In most embodiments, the ratio of the surface area of ​​the contact surface to the heat dissipated by the motor during operation of the drive unit is at least 13 cm 2 / W, preferably 25cm2 / W, particularly preferably 50 cm 2 / W, which avoids local overheating of the tissue.

[0041] The heat spreader may be flexible in at least one region, allowing the contact surface to conform to the contoured surface of the skin. For example, the contact surface may conform to the shape of a patient's thigh if the drive unit is attached to the thigh. This may improve the comfort of wearing the drive unit and ensure thermal contact between the heat spreader and the patient's skin. The heat spreader may be flexible in all regions of the heat spreader.

[0042] Heat transferred to the tissue typically serves no therapeutic purpose. To enable efficient transfer of heat from the motor to the patient's tissue, the heat exchanger may include at least a portion of a material with a relatively high thermal conductivity. This region may extend completely over the contact surface. The thermal conductivity of this region may be at least 1 W / (m·K), preferably at least 10 W / (m·K), at least 50 W / (m·K), or at least 100 W / (m·K). In preferred embodiments, the thermal conductivity of the heat spreader is higher parallel to the contact surface of the heat spreader than perpendicular to the contact surface, ensuring that thermal energy is distributed widely across the entire surface and avoiding hot spots.

[0043] Because heat distribution over a surface area is paramount for safe and efficient heat transfer from the motor to the patient's tissue, the weight of the drive unit and the amount of material required can be reduced by designing the heat spreader to be flat. Thus, the heat spreader may have a thickness of less than 2 cm, particularly less than 1 cm or less than 0.5 cm. For example, the heat spreader may be a thin foil.

[0044] The heat spreader may include a thermally conductive layer. The thermally conductive layer may enable rapid and efficient transfer of heat across the contact surface area, thereby avoiding hot spots on the skin. The heat spreader may further include a carrier layer. The carrier layer may have a lower thermal conductivity than the thermally conductive layer. The carrier layer may include an elastomer and / or a plastic. In this manner, the thermally conductive layer, particularly a relatively thin and / or flexible layer, may enable sufficient transfer of heat, while the carrier layer may provide sufficient mechanical stability for the heat spreader. The thermally conductive layer may include a metal, particularly copper, aluminum, and / or pyrolytic carbon. In some embodiments, the heat spreader may include multiple thermally conductive layers.

[0045] Additionally, the heat spreader may include a biocompatible coating. For example, the contact surface of the heat spreader may include the biocompatible coating. The coating may form a portion of the bottom surface of the heat spreader, or may completely form the bottom surface of the heat spreader. The coating may cover and / or surround the thermally conductive layer. In particular, a coating may be applied if the heat spreader or its thermally conductive layer contains harmful substances that may be soluble in sweat. The coating may then prevent the harmful substances from reaching the patient's skin. For example, the biocompatible coating may include parylene, polyurethane, silicone, PEEK, or a biocompatible, e.g., implantable, metal. The biocompatible coating may have a thickness of less than 2 mm, preferably less than 0.5 mm or less than 0.1 mm. The biocompatible coating may be the same as the carrier material from which the biocompatible carrier is constructed.

[0046] Furthermore, the motor and / or the motor housing and / or the housing of the drive unit may be elongated. The extension direction of the motor and / or the motor housing and / or the housing of the drive unit may coincide with the axial direction of the patient's thigh when the drive unit is attached to the thigh. The retaining means is typically connected to the housing of the drive unit. The retaining means of the drive unit may include a strap and / or a hook-and-loop fastener. The retaining means may further include an adhesive. Adhesive attachment of the drive unit to the thigh allows for particularly secure fixation of the drive unit relative to the puncture site. In particular, when the drive unit is attached to the patient's thigh, adhesive fixation can form an effective retaining means, preventing the drive unit from sliding down the tapered portion of the thigh toward the knee. For example, mechanical loads on the puncture site can be reduced by the suggested retaining means. In some embodiments, the heat spreader includes an adhesive surface for attaching the heat spreader to the skin. For example, the heat spreader may be formed by an adhesive patch. According to this embodiment, heat generated by the motor can be transferred to the patient's tissue via the patch. The thermal conductance of the patch may be sufficiently high to transfer heat to the tissue efficiently. The adhesive surface may form part of and / or the entire contact surface. The adhesive may be a biocompatible adhesive, for example as known from adhesive wound closure patches.

[0047] Additionally, the drive unit may include a securing means to prevent the drive unit from moving to a different position on the patient's skin. For example, the securing means may include a rubberized region. The bottom surface of the drive unit may further include a mass.

[0048] The heat spreader may include openings or recesses, particularly through-holes or grooves, to allow evaporation of sweat from the skin. The openings or recesses may be located at least partially adjacent to the contact surface. In a typical embodiment, the heat spreader includes at least three, at least five, or at least eight openings or recesses. During motor operation, heat transferred to the patient's tissues may promote sweating. Thus, the openings or recesses can significantly improve the comfort of wearing the drive unit. To achieve efficient transfer of vapor to the atmosphere, the minimum or uniform diameter of the openings or recesses is typically at least 1 mm or at least 5 mm. The maximum or uniform diameter of the openings or recesses is typically at most 20 mm or 80 mm.

[0049] In some embodiments, the openings are elongated. The ratio of the maximum diameter to the minimum diameter is at least 1.2, or at least 2. In this way, sweat (in the form of vapor) can be efficiently transferred from the body to the atmosphere, while ensuring sufficient mechanical stability and efficient two-dimensional heat conduction in the heat spreader. For example, the openings may be elongated so that, when the drive unit is attached to a patient's thigh, the openings present a larger diameter in the circumferential direction of the thigh and a smaller diameter in the axial direction of the thigh. When the motor is axially elongated, the elongation of the holes allows efficient transfer of heat in the circumferential direction, while vapor is efficiently removed from the skin.

[0050] In some embodiments, the heat spreader includes pores that allow evaporated sweat to travel from the skin to the atmosphere. The heat spreader may include a membrane with pores. The pores may have a diameter of at least 0.02 μm and / or at most 0.3 μm.

[0051] The heat spreader may include a sweat-absorbing material, particularly a fabric or cotton. The sweat-absorbing material may form part of the bottom surface of the heat spreader. The sweat-absorbing material may absorb sweat from the patient's skin and thus improve the comfort of wearing the drive unit.

[0052] In some embodiments, the heat spreader includes a heat pipe. The heat pipe may be flat. For example, the heat pipe may be a heat spreader. Typically, the bottom surface of the heat pipe contacts the patient's skin. In another embodiment, the heat pipe may be disposed between and connected to the motor and the heat spreader. The top surface of the heat pipe may be in thermal contact with the motor. The heat pipe may enable efficient heat transfer from the motor to the tissue or contact surface.

[0053] Friction losses of the purge medium may be expected to result in a decrease in the efficiency of a purged motor compared to a non-purged motor. Surprisingly, any one of the above or following features, or a combination of these features, can avoid the disadvantageous low efficiency of the motor. The width of the fluid gap may be at least 0.1 mm, preferably at least 0.2 mm, and / or at most 1 mm, preferably at most 0.5 or at most 0.3 mm. It should be noted that the minimum size of the magnetic gap is limited by the size of the fluid gap. Typically, the rotor and / or stator include a sleeve or coating that may delimit the fluid gap. The boundary surface of the fluid gap may be smooth and / or stepless, avoiding undercut surfaces and ensuring a reliable ventilation process. This may protect the rotor magnets and / or stator windings from the corrosive effects of the purge medium. As a result, the magnetic gap is typically larger than the fluid gap. While magnetic losses are expected to increase with increasing fluid (and magnetic) gap width, it has surprisingly been found that a relatively large fluid gap width improves the overall efficiency of the motor. This improvement is related to the reduction in friction losses of the purge media.

[0054] As explained above, the proposed drive unit allows for precise control of the thermal management of cardiac assist devices in various application scenarios. In particular, the temperature of the purge medium in the fluid gap can be precisely controlled. This effect can be achieved by preheating the purge medium through thermal contact with the outer surface of the proximal catheter section and / or the outer surface of the motor housing, or by heat removal from the motor to the purge lines and / or heat spreader. In a typical embodiment, the temperature of the purge medium in the fluid gap is at least 50°C, preferably at least 60°C, under steady-state operating conditions. Furthermore, the temperature of the purge medium in the fluid gap is at most 100°C, preferably at most 90°C, under steady-state operating conditions. By controlling the temperature of the purge medium accordingly, the viscosity of the purge medium may be reduced, while the temperature of the purge medium can be maintained safe for the patient and boiling of the purge medium is prevented. Thus, by controlling the temperature of the purge medium, the motor can be operated in a particularly efficient manner, and fluid friction losses are reduced.

[0055] To accurately control the temperature of the purge fluid, it is necessary to analyze and adjust the temperature of the preheated purge medium and the heat transfer between the fluid gap and the patient's skin and / or between the fluid gap and the purge line. For example, heat transfer from the fluid gap to the purge line may be affected by the material of the motor housing. The motor housing may contain or be made of a metal, such as stainless steel or aluminum. In some embodiments, the motor windings may be disposed inside the motor housing. In some embodiments, the motor housing is partially or completely formed by a plastic molding material that encapsulates the windings. The windings may include one or more copper wires. Furthermore, heat transfer from the fluid gap to the heat spreader may be affected by the material of the drive unit housing. The drive unit housing may contain or be made of a plastic material, such as PEEK or ABS. Plastic materials are particularly suitable for enabling the motor to operate in a desired temperature range. In some embodiments, the drive unit housing is molded so that it can be used as a drive unit handle.

[0056] In some embodiments, the drive unit includes insulation disposed between the purge line and the drive unit housing. The insulation may be disposed between the thermal contact area with the proximal portion of the catheter and the drive unit housing. Additionally or alternatively, the insulation may be disposed between the thermal contact area with the motor housing and the drive unit housing. The insulation may surround the purge line. Additionally, the insulation may be tubular in shape. The insulation may include a plastic material, particularly a foamed plastic material. In some embodiments, an air gap or vacuum gap is formed between the purge line and the drive unit housing to achieve thermal insulation between either or both of the thermal contact areas and the drive unit housing. The air gap allows heat generated by the motor within the drive unit housing to be evenly distributed by convection, thereby avoiding localized hot spots on the drive unit housing. Furthermore, the purge line may be partially enclosed in heat shrink tubing in the area of ​​thermal contact with the motor housing and / or the proximal portion of the catheter, improving thermal contact.

[0057] According to some embodiments of the cardiac assist device, the drive unit may or may not comprise a purge line in thermal contact with the proximal portion of the catheter and / or the motor housing. Furthermore, the drive unit may not include a heat spreader as described above or below, and / or the drive unit may include a heat spreader that is not intended to be in contact with the patient's skin. Means for removing heat from the motor may be formed, for example, by a purge line or a heat spreader as described above or below, by cooling fins attached to the motor housing or the housing of the drive unit, or by a heat pipe connected to the motor in a thermally conductive manner. Further embodiments will become apparent when aspects are combined with each other and / or in combination with the above or below description.

[0058] In particular, the present application further relates to, inter alia, the following aspects:

[0059] 1. A method of operating a cardiac assist device including an external drive unit and an implantable or implanted cardiac assist pump, wherein the drive unit includes a motor for driving the cardiac assist pump, the motor connected to the cardiac assist pump via a percutaneous drive shaft, the motor having a stator and a rotatably mounted rotor connectable to the drive shaft, a fluid gap formed between the rotor and the stator, the fluid gap being in fluid communication with a purge opening for injecting a purge medium into the fluid gap, the cardiac assist device including a catheter surrounding the drive shaft, and the purge medium being injected into the fluid gap and into the space between the catheter and the drive shaft or into the lumen of the catheter.

[0060] 2. The method of embodiment 1, wherein the temperature of the purge medium in the fluid gap is at least 50°C, preferably at least 60°C, under steady state operating conditions.

[0061] 3. The method of any one of aspects 1 and 2, wherein the temperature of the purge medium in the fluid gap is at most 100°C, preferably at most 90°C, under steady state operating conditions.

[0062] 4. The method of any one of aspects 1-3, wherein the purging medium is a glucose solution or saline.

[0063] 5. The method of any one of aspects 1-4, wherein the drive unit includes a purge line attached to the purge opening, the purge line being in thermal contact with an outer surface of the motor housing and / or an outer surface of the proximal portion of the catheter, and the purge medium is preheated by thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter, and then the purge medium is injected into the fluid gap.

[0064] 6. An external drive unit for an implantable cardiac assist pump, comprising a motor for driving the cardiac assist pump, the motor being connectable or connected to the cardiac assist pump via a percutaneous drive shaft, the drive unit comprising a heat pipe connected to the motor in a heat conductive manner.

[0065] 7. The drive unit of embodiment 6, wherein the drive unit includes a housing, in particular a motor housing or a drive unit housing, and the heat pipe is connected to the housing in a heat conductive manner.

[0066] 8. A cardiac assist system including a drive unit according to any one of aspects 6 or 7, and further including a console or controller unit having a heat sink, wherein a portion of the heat pipe is connected to the heat sink in a thermally conductive manner to remove heat from the motor.

[0067] 9. An external drive unit for an implantable cardiac assist pump comprising a motor for driving the cardiac assist pump, the motor being connectable to the cardiac assist pump via a percutaneous drive shaft and characterized by a heat spreader having a contact surface configured to contact the patient's skin, the contact surface being connected or connectable to the motor in a thermally conductive manner and transferring heat generated by the motor to the patient's tissue.

[0068] 10. A method of operating a cardiac assist device including an external drive unit and an implantable or implanted cardiac assist pump, wherein the drive unit includes a motor for driving the cardiac assist pump, the motor being connected to the cardiac assist pump via a percutaneous drive shaft, the drive unit further including a motor housing, the motor being disposed inside the motor housing, the drive unit further including a catheter surrounding the drive shaft and a purge line for injecting a purge medium into the lumen of the catheter or into the space between the catheter and the drive shaft, the purge line being in thermal contact with an outer surface of the motor housing and / or an outer surface of a proximal portion of the catheter, such that heat is transferred from the outer surface of the catheter in the proximal portion and / or from the outer surface of the motor housing to the purge medium.

[0069] 11. The method of embodiment 10, wherein the purge line directs the purge medium so that the purge medium first comes into thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter, and is then injected into the lumen of the catheter or into the space between the catheter and the drive shaft.

[0070] 12. The method of embodiment 11, wherein the purge line directs the purge medium so that the purge medium first comes into thermal contact with the outer surface of the motor housing and is then injected into the lumen of the catheter or into the space between the catheter and the drive shaft.

[0071] 13. The method of embodiment 10, wherein the motor includes a stator and a rotatably mounted rotor connected to the drive shaft, a fluid gap is formed between the rotor and the stator, the fluid gap is in fluid communication with the purge opening, a purge medium is injected into the fluid gap, and a purge line is connected to the purge opening.

[0072] 14. The method of embodiment 13, wherein the purge line and fluid gap direct the purge medium so that the purge medium is first in thermal contact with the outer surface of the motor housing and / or the outer surface of the proximal portion of the catheter, then injected into the fluid gap between the rotor and stator, and then into the lumen of the catheter or into the space between the catheter and the drive shaft.

[0073] 15. The method of embodiment 13, wherein the purge medium flows distally within the fluid gap.

[0074] The exemplary embodiments are described in conjunction with the following drawings. [Brief explanation of the drawings]

[0075] [Figure 1] 1 is a schematic diagram showing a cardiac assist device with an implanted cardiac assist pump and an extracorporeal drive unit. [Figure 2] FIG. 2 is a schematic diagram showing a drive unit. [Figure 3] FIG. 10 is another schematic diagram showing the drive unit. [Figure 4] FIG. 10 is another schematic diagram showing the drive unit. [Figure 5] FIG. 2 is a schematic cross-sectional view showing a heat spreader and a housing of a drive unit. [Figure 6] FIG. 2 is a schematic cross-sectional view showing a heat spreader. [Figure 7] FIG. 2 is a schematic cross-sectional view showing a housing and a motor of the drive unit. [Figure 8] FIG. 10 is a schematic cross-sectional view showing a drive unit according to another embodiment. [Figure 9] FIG. 4 is a schematic cross-sectional view showing a purge line and a motor housing. [Figure 10] 10 is a graph comparing measured operating parameters of a drive unit with and without thermal contact between the purge line and the motor housing and proximal portion of the catheter. [Figure 11] FIG. 4 is a schematic diagram illustrating a drive unit according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0076] A schematic diagram of a cardiac assist device 1 is shown in Figure 1. The cardiac assist device 1 includes a catheter 2. A flexible drive shaft 3 is guided inside the catheter 2. The distal end of the catheter 2 and the distal end of the drive shaft 3 are connected to a pump head of a cardiac assist pump 4. The cardiac assist pump 4 includes a housing 5 and a propeller 6. The propeller 6 is connected to the distal end of the drive shaft 3. The proximal end of the drive shaft 3 is connected to an extracorporeal drive unit 7 that includes a motor. The drive unit 7 is configured to drive the rotational motion of the propeller to move the patient's blood.

[0077] The cardiac assist pump 4, catheter 2, and drive shaft 3 are inserted into the patient's femoral artery via a puncture site 8 located in the patient's groin. The illustrated arrangement illustrates the use of the cardiac assist device 1 to assist left ventricular function of the heart, with the cardiac assist pump 4 positioned partially inside the patient's left ventricle 10 in the region of the aortic valve 11. When the cardiac assist device 1 is in operation, the drive shaft 3 is driven by the motor of the drive unit 7, causing the cardiac assist device 1 to pump blood from the left ventricle 10 into the aorta 12, i.e., in a direction from the distal end 13 to the proximal end 14 of the cardiac assist device 1. In another embodiment, the cardiac assist device 1 may be configured to pump blood in a direction from the proximal end 14 to the distal end 13 of the cardiac assist device 1. Such an arrangement is particularly suitable for assisting right ventricular function of the heart.

[0078] The drive unit 7 may be attached to the patient's thigh 15, as shown schematically in FIG. 2. Repeated features in FIG. 2 and subsequent figures are indicated using the same reference numerals. In the illustrated embodiment, the drive unit 7 is held in place relative to the puncture site 8 by a strap 16, e.g., an elastic strap. In most embodiments, the strap is 45-60 cm long. However, other means of fixation are possible, as explained below. The motor is located inside a motor housing. The motor housing is located inside a housing 17 of the drive unit 7, formed, for example, by an injection-molded ABS part. In most embodiments, the surface of the housing 17 of the drive unit 7 is smooth and stepless, making it easy to clean and allowing it to function as a handle for the cardiac assist device 1. The catheter 2 is rigidly connected to the proximal end of the housing 17 of the drive unit 7 in a fluid-tight manner. Additionally, a supply line 18 is shown schematically in the figure. In the illustrated embodiment, supply lines 18 are connected to the proximal end of housing 17 of drive unit 7 and include a power supply line for the motor and a fluid supply or purge line for the purge medium. In another embodiment, the fluid supply or purge line and the power supply line are each routed inside one of multiple separate supply lines. Furthermore, in some embodiments, supply lines 18 and / or fluid supply or purge lines exit housing 17 of drive unit 7 at a distal end or side of housing 17 of drive unit 7.

[0079] The drive unit 7 further includes a heat spreader 19. The heat spreader 19 is rigidly connected to the housing 17 of the drive unit 7, and heat generated by the motor during operation is transferred to the heat spreader 19. The heat spreader 19 is thin, having a thickness of 4 mm or less. For example, the heat spreader 19 may be formed by a patch (described below) or a flat, two-dimensional heat pipe. The bottom surface of the heat spreader 19 is placed flat against the patient's skin at the contact surface, making direct contact, so that heat can be transferred from the heat spreader 19 to the patient's tissue. During motor operation, the temperature of the outer surface of the housing 17 of the drive unit 7 may exceed 43°C before the heat spreader 19 is fixed to the thigh 15. However, the thermal conductivity of the heat spreader 19 ensures that the heat is evenly distributed over a sufficient area and transferred to the thigh 15, so that the temperature of the surface of the housing 17 of the drive unit 7 quickly drops below 42°C, which defines the critical temperature for tissue damage.

[0080] The heat spreader 19 includes an area with a thermal conductivity greater than 100 W / (m·K) to spread heat laterally so that heat is efficiently transferred across the contact surface. The surface area of ​​the contact surface is, in some embodiments, 200 cm 2 The heat spreader 19 further includes openings (through holes), two of which are indicated with reference numerals 20 and 20'. The openings 20, 20' allow evaporated sweat to be transferred to the atmosphere, thus improving wearing comfort.

[0081] A perspective view of the drive unit 7 is shown in FIG. 3. In the illustrated embodiment, the heat spreader 19 has a recess 22 that receives the housing 17 of the drive unit 7. The strap 16 includes a hook-and-loop mechanism with a loop surface 23 that engages with a corresponding hook surface (not shown) located on an end portion of the strap. When the cardiac assist device 1 is in use, the housing 17 of the drive unit 7 is received in the recess 22 and the strap 16 is wrapped circumferentially around the thigh, such that the housing 17 of the drive unit 7 is covered by a portion of the strap 16 and the drive unit 7 is held in place.

[0082] The openings 20, 20' in the heat spreader 19 may be elongated as shown diagrammatically in Figure 4. In this case, the openings 20, 20' present a larger diameter in the circumferential direction 24 relative to the thigh 15, allowing efficient heat transfer in this direction 24 of the heat spreader 19. The housing 17 of the drive unit 7 is elongated in a vertical direction 25 corresponding to the axial direction 25 of the thigh 15.

[0083] The heat spreader 19 may be curved and / or flexible to conform to the shape of the thigh 15. For example, the heat spreader 19 may comprise a foil or patch. FIG. 5 shows an exemplary cross-section of the heat spreader 19 and the housing 17 of the drive unit 7 formed by a first patch 26 and a second patch 27. The patches 26, 27 are each bendable and include adhesive bottom surfaces 28, 29 that face the thigh 15. In the illustrated embodiment, the patches 26, 27 surround the housing 17 of the drive unit 7 and efficiently draw heat away from the motor. In the illustrated embodiment, the adhesive surface of the heat spreader 19 forms a retention means, holding the drive unit 7 in place relative to the puncture site 8. Therefore, a separate retention means, such as the strap 16 described above, may not be necessary, but may still be provided in some embodiments.

[0084] An exemplary cross section of the heat spreader 19 is shown in Figure 6. The heat spreader 19 may be a multi-layer structure. The heat spreader 19 includes a carrier layer 30 that forms the top layer of the heat spreader 19.

[0085] The carrier layer 30 may be formed of an elastomer and / or plastic material. For efficient heat transfer across the contact area, i.e., in the horizontal direction of the figure, the heat spreader 19 further includes a thin thermally conductive layer 31, which may be formed of a highly thermally conductive material, such as a thin layer of copper, aluminum, or pyrolytic carbon. The thermally conductive layer 31 is surrounded on both sides by an inert and biocompatible coating 32, which may be made of parylene, polyurethane, silicone, PEEK, or a biocompatible material, such as an implantable metal. The biocompatible coating 32 further covers the thermally conductive layer 31 on the inner walls of the openings 20 of the heat spreader 19. The stepless bottom surface of the heat spreader is formed by an adhesive layer 33, for example, containing an adhesive, which attaches the heat spreader 19 to the patient's skin.

[0086] Further, the sweat-absorbing portion 34 of the heat spreader 19 or of the drive unit 7 is shown schematically in Figure 6. The sweat-absorbing portion may be made of, for example, fabric and / or cotton. Additionally, the heat spreader 19 or the drive unit 7 includes a rubberized region 48 with rubber lumps 49, 49' to prevent the heat spreader 19 from sliding relative to the puncture site 8. The sweat-absorbing portion 34 and the rubberized region 48 may be evenly distributed across the entire bottom surface of the heat spreader 19.

[0087] A schematic diagram of the motor 35 is shown in Figure 7. The motor 35 is disposed inside a motor housing, which is disposed within the housing 17 of the drive unit 7. The motor 35 includes a rotor 36 with permanent magnets and a stator 37 with windings 38. The rotor 36 is rotatably mounted using a first bearing 39 and a second bearing 40, and can be rotated by current flowing through the windings of the stator 37. The rotor 36 is rigidly connected to the drive shaft 3 and drives the propeller 6.

[0088] The catheter 2 is rigidly connected to the housing 17 of the drive unit 7, and a space 41 is formed between the catheter 2 and the drive shaft 3. This space 41 is in fluid communication with a fluid gap 43 formed between the rotor 36 and the stator 37, a purge opening 42, and the supply line 18. The width of the fluid gap 43 in the radial direction can be between 0.2 and 0.3 mm. When the cardiac assist device 1 is operating, a purge medium, e.g., a glucose solution, is supplied via the supply line 18 and flows through the fluid gap 43, through the space 41 between the catheter 2 and the drive shaft 3 (and ultimately into the patient at the proximal end of the cardiac assist device 1).

[0089] During operation of the motor 35, the motor 35 may heat up due to power dissipation, for example, of 2 W. Heat is removed from the motor 35, as indicated diagrammatically by the arrows with reference numeral 44, to maintain a constant temperature of the glucose solution inside the fluid gap 43 at 75° C. under steady-state operating conditions. To remove the heat, the heat may be transferred to the patient's tissue 45, for example, using the heat spreader 19 as described above, to the atmosphere 46, for example, using a cooling fan in the housing 17 of the drive unit 7, and / or to a heat sink 47 in the console or controller unit, for example, via an elongated heat pipe connected to the housing 17 of the drive unit 7. Additionally or alternatively, the heat may be transferred to a fluid supply line or a purge line, as described below. Any combination of these heat removal mechanisms is possible.

[0090] Additionally, inductors 50 may be provided to reduce eddy current losses if the motor 35 is not driven with full block commutation. These inductors 50 may also be located inside the housing 17 of the drive unit 7, but in a preferred embodiment the inductors 50 are located at the end of the motor cable 18 that connects to the controller unit for the motor 35 (or in the controller unit itself), avoiding additional weight and heat source for the motor 35 and the patient's legs.

[0091] Heat removal to the purge line will be discussed in conjunction with subsequent figures. FIG. 8 schematically illustrates another embodiment of a drive unit 7. This drive unit 7 may include any of the features of the drive unit 7 described above. Furthermore, in the drive unit 7 of FIG. 8, the purge line 53 serves a dual role: as a supply line for purge medium and as a means for heat removal. As shown in FIG. 8, the windings 38 of the stator 37 are enclosed in a motor housing 51. The motor housing 51 is centrally located within the housing 17 of the drive unit 7. However, in another embodiment, the motor housing 51 is located proximally within the housing 17 of the drive unit 7. Furthermore, the catheter 2 includes a proximal portion 52, which is located inside the housing 17 of the drive unit 7. As shown schematically, a supply line 18 is attached to the proximal end of the housing 17 of the drive unit 7. The supply line 18 includes electrical leads for powering the motor 35. The purge line 53 is not included within the supply line 18 in this embodiment. The purge line 53 extends through an opening in the side of the housing 17 of the drive unit 7 at the distal region of the housing 17 of the drive unit 7 .

[0092] An end portion of the purge line 53 is attached to a purge medium source (not shown). The purge line 53 extends inside the housing 17 of the drive unit 7. Inside the housing 17 of the drive unit 7, the purge line 53 is positioned against the outer surface of the proximal portion 52 of the catheter 2. Thermal contact between the proximal portion 52 of the catheter 2 and the purge line 53 is therefore formed, as indicated by the arrows with reference numeral 54. Furthermore, the purge line 53 is positioned against the outer surface of the motor housing 51. Thermal contact between the motor housing 51 and the purge line 53 is therefore formed, as indicated by the arrows with reference numeral 55. The purge line 53 is further attached to the purge openings 42. When the purge medium is supplied, it flows through the drive unit 7 as indicated by the arrows (some of which are marked with reference numeral 56). The purge medium first passes through the thermal contact areas 54, 55, then enters the fluid gap 43, and then enters the space 41 between the catheter 2 and the drive shaft 3. In a further embodiment, the purge medium enters the lumen of the catheter 2. The purge medium flows primarily in a proximal direction as it passes through the thermal contacts 54, 55. The purge medium then flows in a distal direction as it flows through the fluid gap 43 and the space 41 between the catheter 2 and the drive shaft 3.

[0093] During operation of the cardiac assist pump, the injected purge medium cools the proximal portion 52 of the catheter 2 and the motor 35 through the thermal contacts 54, 55 and due to its relatively low temperature. This significantly cools the portion 63 of the catheter 2 that is located distally adjacent to the proximal portion 52 of the catheter 2 and outside the housing 17 of the drive unit 7, so that the portion 63 of the catheter 2 that is not located inside the housing 17 of the drive unit 7 can be touched without risk of injury. Furthermore, the risk of deformation of the catheter 2 due to heating of the portion 63 of the catheter 2 (and thus the risk of deformation and breakage of the flexible drive shaft 3 located inside the catheter 2) is reduced. Furthermore, the purge medium enters the fluid gap 43 after being preheated by the thermal contacts 54, 55. As a result, the purge medium enters the fluid gap 43 at a higher temperature and with a lower viscosity, reducing friction losses in the motor 35 and allowing the motor 35 to operate more efficiently.

[0094] In most embodiments, the motor housing 51 has a cylindrical shape. As shown in FIG. 9 , the purge line 53 is tubular and wrapped around the motor housing 51, so that the purge line 53 directly contacts the outer surface of the motor housing 51, allowing for good thermal contact 55. Furthermore, the purge line 53 may be wrapped around the proximal portion 52 of the catheter 2 in a similar manner. To manufacture the drive unit 7, the purge line 53 can be preformed by thermoforming to form the helical shape of the purge line 53. After the purge line 53 is wrapped around the proximal portion 52 of the catheter 2 and around the motor housing 51, the purge line 53 is embedded in a flexible silicone molding material, or is securely fixed to the motor housing 51 by shrink tubing surrounding the purge line 53, or by adhesive disposed between the motor housing 51 and the purge line 53. Furthermore, the proximal portion 52 of the catheter 2 has a cylindrical shape in most embodiments. The diameter of the purge line 53 may be uniform. The catheter 2, particularly its proximal portion 52, may comprise a plastic material, such as PU, or a polyether block amide (PEBA), such as Pebax®. The catheter 2 may also be braided with metal.

[0095] The drive unit 7 may further include a thermal insulator (not shown) arranged between the purge line 53 and the housing 17 of the drive unit 7, thereby preventing the housing 17 of the drive unit 7 from overheating. Furthermore, the efficiency of the heat exchanger formed by the thermal contacts 54, 55 may be improved in this way. The thermal insulator may completely surround the purge line 53 in the area of ​​the thermal contacts 54, 55 and may be an insulating foam tube made of a plastic material. The thermal insulation may also be formed by an air gap between the purge line 53 and the housing 17 of the drive unit 7.

[0096] FIG. 10 shows graphs of measured operating parameters for different cardiac assist devices 1, first for a drive unit 7 according to FIG. 8 , i.e., including thermal contacts 54, 55 (crosses), and second for a corresponding drive unit 7, but without thermal contact between the purge line 53 and the proximal portion 52 of the catheter 2 or the motor housing 51 (circles). The left vertical axis 57 represents temperature, and the right vertical axis 58 represents the motor current that must be applied to achieve a given blood movement rate. The horizontal axis 59 represents the flow rate of the purge medium. The highest measured values ​​60, 60′ correspond to the right vertical axis, which represents the motor current. The intermediate measured values ​​61, 61′ and the lowest measured values ​​62, 62′ correspond to the left vertical axis and represent the temperature 61, 61′ of the motor 35 and the temperature 62, 62′ of a portion 63 of the catheter 2, which is located adjacent to the proximal portion 52 of the catheter 2. The motor temperatures 61, 61' decrease with increasing purge rate, while the temperatures 62, 62' of the catheter 2 portion 63 increase with increasing purge rate. Measurements indicate that both the motor and the catheter 2 portion 63 can be effectively cooled by using the proposed thermal contacts 54, 55 of the purge line between the motor housing 51 and the proximal portion 52 of the catheter 2. The motor current 60 increases with purge rate when the thermal contacts 54, 55 are not provided. In contrast, when the proposed thermal contacts 54, 55 are used, the motor current 60' can be significantly reduced at reasonable purge rates. Thus, the proposed thermal contacts 54, 55 make the cardiac assist device 1 more effective. Surprisingly, because of the thermal contacts 54, 55, the motor current 60' is completely independent of the flow rate. Therefore, the effect of the purge rate on the motor current 60' can be ignored when the motor current 60' is used as a critical control parameter of the cardiac assist device 1 (e.g., to indicate malfunction of the cardiac assist device 1). The proposed thermal contacts 54, 55' therefore allow for a simplified monitoring circuit of the cardiac assist device 1.

[0097] FIG. 11 illustrates a drive unit 7 according to another embodiment. This drive unit 7 may include any or all of the features described above. The top portion of the housing 17 of the drive unit 7 is not shown, allowing the interior of the drive unit 7 to be seen. The housing 17 of the drive unit 7 functions as a handle for the drive unit 7 and thus presents a curved shape that allows it to be easily held in one hand. A supply line 18 (not shown), including electrical leads for powering the motor, may be attached to a supply plug 64 located at the proximal end of the housing 17 of the drive unit 7. Additional electrical leads (not shown for clarity) connect the supply line to the motor 35, which is located inside the motor housing 51. The catheter 2 includes a portion 63 located adjacent to and outside the housing 17, and a proximal portion 52 located inside the housing 17 and connecting portion 63 to the motor 35.

[0098] The purge line 53 enters the housing 17 of the drive unit 7 at a distal portion of the housing 17. Furthermore, as described above, the purge line 53 is wrapped around the proximal portion 52 of the catheter 2 and the motor housing 51, forming thermal contacts 54, 55. The purge line 53 is further connected to the proximal end of the motor housing 51, forming a fluid connection with the fluid gap 43 of the motor 35. To further improve the thermal contact between the purge line 53 and the motor housing 51, the purge line 53 is enclosed within heat shrink tubing 65 (the position of the purge line 53 below the heat shrink tubing 65 is indicated using a dashed line). The heat shrink tubing 65 presses the purge line 53 against the motor housing 51, thereby improving the thermal contact. Furthermore, the portion of the purge line 53 wrapped around the proximal portion 52 of the catheter 2 may be enclosed within heat shrink tubing (not shown). Additionally, air gaps 66, 66' are formed between the housing 17 of the drive unit 7 and the portion of the purge line 53 that forms thermal contacts 54, 55 with the motor housing 51 and the proximal portion 52 of the catheter 2. The air gaps 66, 66' provide thermal insulation for the motor housing 51 (alternatively or additionally, insulating foam tubing as described above may be provided). Additionally, the air gaps 66, 66' allow heat generated by the motor to dissipate to some extent within the housing 17 by convection, avoiding localized hot spots.

Claims

1. An external drive unit (7) for an implantable cardiac assist pump (4), comprising: a motor housing (51); a percutaneous drive shaft (3); a motor (35) for driving the cardiac assist pump (4), the motor (35) being connectable to the cardiac assist pump (4) via the drive shaft (3) and being disposed inside the motor housing (51); a catheter (2) surrounding the drive shaft (3); a purge line (53) for injecting a purge medium into the lumen of the catheter (2) or into the space (41) between the catheter (2) and the drive shaft (3); Including, An external drive unit (7), characterized in that the purge line (53) is in thermal contact (54, 55) with the outer surface of the motor housing (51) and / or the outer surface of the proximal portion (52) of the catheter (2).

2. 2. The drive unit (7) of claim 1, wherein the purge line (53) is configured to guide the purge medium so that the purge medium first comes into thermal contact (55) with the outer surface of the motor housing (51) and / or the outer surface of the proximal portion (52) of the catheter (2) and is then injected into the lumen of the catheter (2) or into the space (41) between the catheter (2) and the drive shaft (3).

3. 3. A drive unit (7) according to claim 1 or 2, characterized in that the purge line (53) is in thermal contact (54, 55) with both the outer surface of the motor housing (51) and the outer surface of the proximal portion (52) of the catheter.

4. 4. A drive unit (7) according to claim 3, characterized in that the purge line is entirely extracorporeal.

5. 5. The drive unit (7) of claim 3 or 4, characterized in that the purge line (53) is configured to guide the purge medium so that the purge medium first comes into thermal contact (54) with the outer surface of the proximal portion (52) of the catheter (2) and then comes into thermal contact (55) with the outer surface of the motor housing (51).

6. 6. The drive unit (7) according to claim 1, wherein the motor (35) comprises a stator (37) and a rotatably mounted rotor (36) connected to the drive shaft (3), a fluid gap (43) is formed between the rotor (36) and the stator (37), the fluid gap (43) is in fluid communication with a purge opening (42) for injecting the purge medium into the fluid gap (43), and the purge line (53) is connected or connectable to the purge opening (42).

7. 7. The drive unit (7) of claim 6, wherein the purge line (53) and the fluid gap (43) are configured to guide the purge medium so that the purge medium first comes into thermal contact (55) with the outer surface of the motor housing (51) and / or the outer surface of the proximal portion (52) of the catheter (2), and is then injected into the fluid gap (43) between the rotor (36) and the stator (37), and then into the lumen of the catheter (2) or into the space (41) between the catheter (2) and the drive shaft (3).

8. The drive unit (7) according to any one of claims 1 to 7, characterized in that the purge line (53) is configured to guide the flow of the purge medium in a proximal direction in a region where the purge line (53) is in thermal contact (55) with the outer surface of the motor housing (51) and / or with the outer surface of the proximal portion (52) of the catheter (2), and then to inject the purge medium into the lumen of the catheter (2) or into the space (41) between the catheter (2) and the drive shaft (3).

9. A drive unit (7) according to any one of claims 1 to 8, characterized in that the purge line (53) surrounds the motor housing (51) and / or the proximal portion (52) of the catheter (2) in the area where the purge line (53) is in thermal contact (55) with the outer surface of the motor housing (51) and / or the outer surface of the proximal portion (52) of the catheter (2).

10. 10. The drive unit (7) of claim 9, characterized in that the purge line (53) spirally circumvents the motor housing (51) and / or the proximal portion (52) of the catheter (2) in the region where the purge line (53) is in thermal contact (55) with the outer surface of the motor housing (51) and / or the outer surface of the proximal portion (52) of the catheter (2).

11. 11. The drive unit (7) of claim 10, wherein the purge line (53) spirally circumnavigates the proximal portion (52) of the catheter (2) in the region where the purge line (53) is in thermal contact (55) with the outer surface of the proximal portion (52) of the catheter (2).

12. A drive unit (7) according to any one of claims 1 to 11, characterized by a housing (17) of the drive unit (7), wherein the motor housing (51) and / or the proximal portion (52) of the catheter are arranged within the housing (17) of the drive unit (7).

13. The drive unit (7) according to any one of claims 1 to 12, characterized in that the overall thermal conductance between the inner surface of the purge line (53) and the inner surface of the motor housing (51) can be at least 5 times, preferably at least 10 times, the overall thermal conductance between the inner surface of the purge line (53) and the inner surface of the housing (17) of the drive unit (7).

14. 14. Drive unit (7) according to claim 12 or 13, characterized in that a part of the purge line (53) extends between the motor housing (51) and the housing (17) of the drive unit (7).

15. A drive unit (7) according to any one of claims 12 to 14, characterized in that a portion of the purge line (53) extends between the proximal portion (52) of the catheter (2) and the housing (17) of the drive unit (7).

16. The drive unit (7) according to any one of claims 12 to 15, characterized by a thermal insulation material arranged between the purge line (53) and the housing (17) of the drive unit (7).

17. 17. The drive unit (7) according to any one of claims 1 to 16, characterized by a heat spreader (19) having a contact surface configured to contact the skin of a patient, said contact surface being connected or connectable to said motor (35) in a thermally conductive manner and transferring heat generated by said motor (35) to the tissue of said patient.

18. 18. Drive unit (7) according to claim 17, characterized in that the heat spreader (19) is flexible at least in areas.

19. A cardiac assist device (1) comprising the drive unit (7) according to any one of claims 1 to 18 and the implantable cardiac assist pump (4).

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