A catheter and shock wave generating system

Abstract

The present invention relates to a catheter and a shock wave generating system. The catheter comprises a catheter body, an electrode group, a first wire and a second wire. The electrode group comprises a plurality of electrodes. The plurality of electrodes are sequentially distributed along the axial direction of the catheter body, and a gap is provided between two adjacent electrodes. The first wire is connected to the first electrode, and the second wire is connected to the last electrode. An insulating layer is provided on the surface of the electrode. A conductive opening is provided on the insulating layer so that the exposed electrode portion forms a conductive area. The conductive areas on the two adjacent electrodes are located at the same position on the respective electrodes or the conductive areas on the two adjacent electrodes are arranged relative to each other to form an area for generating shock waves. The present invention generates directional shock waves by arranging a conductive area on the electrode to better control the area on the electrode where the shock wave is generated; the number of connecting wires is reduced, the overall outer diameter of the catheter is reduced, the applicability of the catheter in any lesion site is improved, the service life of the catheter is increased, and the cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of medical equipment, and in particular relates to a catheter and a shock wave generating system. Background Art

[0002] Cardiovascular stenosis refers to the abnormal lipid metabolism in the human arteries and veins, including the coronary, peripheral, and intracranial blood vessels. The lipids in the blood are deposited on the originally smooth vascular endothelium, gradually accumulating into atherosclerotic lipid plaques. Over time, these plaques increase and even calcify, causing stenosis in the vascular lumen, obstructing blood flow, leading to ischemia of downstream blood vessels and the body, and producing corresponding clinical manifestations. If the stenosis occurs in the coronary arteries, it will cause palpitations, chest pain, dyspnea, and angina pectoris. In severe cases, it will lead to myocardial insufficiency or myocardial necrosis; if it occurs in the periphery, it will cause a decrease in skin epidermal temperature, muscle atrophy, intermittent claudication, and even necrosis or amputation of distal limbs; if it occurs in the brain, it will cause dizziness, syncope, and even brain tissue damage and brain dysfunction.

[0003] Referring to Chinese patent CN111568500A, a vascular recanalization system for cardiovascular stenosis lesions is disclosed, including a balloon, an energy generation controller, and a catheter. The catheter includes a main tube, one end of the catheter is connected to the energy generation controller, and the main tube at the other end of the catheter is connected to one end of the balloon. The balloon mainly includes a balloon body, an inner tube, and an electrode pair. The inner tube is arranged inside the balloon body. The energy generation controller can emit and regulate a vibration signal of a specific frequency so that the electrode pair generates an oscillation wave.

[0004] However, the electrodes of the electrode pair in the balloon are ring-shaped and conductive as a whole, which is equivalent to countless points in parallel. It is impossible to know which area on the electrode generates the shock wave, and therefore it is impossible to control the area where the shock wave is generated. In addition, the electrode pair in the balloon needs to be connected to the energy generation controller through a wire. On the one hand, the wiring is complicated, and on the other hand, the wire is arranged inside the catheter. Usually, multiple wires need to be connected to the electrodes of each electrode pair. Due to the excessive number of wires, the outer diameter of the catheter will be too large. When used in certain lesions with smaller blood vessels, the catheter with an outer diameter that is too large cannot reach the lesion smoothly, which weakens the effect of the system in lesion treatment. Summary of the invention

[0005] One object of the present invention is to provide a catheter and shock wave generating system for cardiovascular stenosis, so as to solve the problem that the shock wave generating area cannot be controlled.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A catheter comprises a catheter body, an electrode group arranged on the catheter body, a first wire and a second wire, wherein the electrode group comprises a plurality of electrodes, the plurality of electrodes are sequentially distributed along the axial direction of the catheter body, and a gap is provided between two adjacent electrodes, the first wire is connected to the first electrode, and the second wire is connected to the last electrode, an insulating layer is provided on the surface of the electrode, a conductive opening is provided on the insulating layer so that the exposed electrode portion forms a conductive area, the conductive areas on two adjacent electrodes are located at the same position on each electrode or the conductive areas on two adjacent electrodes are arranged oppositely, and an area for generating shock waves is formed between the conductive areas on the two adjacent electrodes located at the same position or the conductive areas arranged oppositely.

[0008] Preferably, the electrode at least partially surrounds the outer circumference of the catheter body, that is, the electrode can be non-annular and closed, such as C-shaped, or the electrode can also be annular.

[0009] Further preferably, the electrode is ring-shaped.

[0010] Preferably, when the number of the electrodes is two, only one conductive area is provided on each of the electrodes.

[0011] Preferably, when the number of the electrodes exceeds two, only one conductive area is provided on the first electrode and the last electrode, and two conductive areas are provided on each intermediate electrode between the first electrode and the last electrode.

[0012] Preferably, the two conductive areas 5 of the intermediate electrode are distributed at an angle greater than 0° and less than or equal to 180° along its circumference.

[0013] Preferably, the conductive areas on all the electrodes are distributed in an angle greater than 0° and less than or equal to 180° along the circumferential direction. Further preferably, the conductive areas on all the electrodes are distributed in an angle of 90°-180° along the circumferential direction.

[0014] Preferably, the gap between two adjacent electrodes is 0.05-2 mm.

[0015] Preferably, the electrode is a tube, a spring tube or a coil, and the material of the electrode is metal, conductive glue or graphene, wherein the metal includes stainless steel, tungsten alloy, platinum-iridium alloy, copper, gold or silver.

[0016] Preferably, the number of the electrode groups is 1-10.

[0017] Preferably, the insulating layer is made of polyimide, UV curing glue or AB glue.

[0018] Preferably, the catheter further comprises a balloon connected to the catheter body, and the plurality of electrodes are arranged on the catheter body located inside the balloon.

[0019] Preferably, the first wire, the second wire and the electrode are connected by welding and / or crimping and / or bonding.

[0020] Another object of the present invention is to provide a shock wave generating system.

[0021] In order to achieve the above object, the technical solution adopted by the present invention is:

[0022] A shock wave generating system comprises a catheter and an energy generating unit. The catheter comprises a first wire and a second wire. The first wire and the second wire are respectively connected to a positive electrode and a negative electrode of the energy generating unit.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] The present invention generates shock waves with specific directionality by setting a conductive area at a specific position of the electrode, so as to better control the area on the electrode where the shock waves are generated; the number of connecting wires is reduced, the overall outer diameter of the catheter is reduced, the applicability of the catheter to any lesion site is improved, the service life of the catheter is increased, the cost is reduced, and the structure is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attached Figure 1 It is a schematic diagram of the catheter body and the electrode when no conductive area is provided on the electrode;

[0026] Attached Figure 2 is a schematic diagram of the distribution position of the conductive area on the electrode of the first embodiment;

[0027] Attached Figure 3 is a schematic diagram of the distribution position of the conductive area on the electrode of the second embodiment;

[0028] Attached Figure 4 is a schematic diagram of the distribution position of the conductive area on the electrode of the third embodiment;

[0029] Attached Figure 5 is a top cross-sectional view of the distribution position of the conductive area on the electrode of the third embodiment;

[0030] Attached Figure 6 is a schematic diagram of the distribution position of the conductive area on the electrode of the fourth embodiment;

[0031] Attached Figure 7 Schematic diagram of the distribution position of the conductive area on the electrode of the fifth embodiment.

[0032] In the above attached figure:

[0033] 1. Catheter body, 2. Electrode, 21. First electrode, 22. Second electrode, 23. Third electrode, 24. Fourth electrode, 25. Fifth electrode, 3. First wire, 4. Second wire, 5. Conductive area. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] like Figures 1 to 7 The catheter shown includes a catheter body 1, an electrode group arranged on the catheter body 1, a first wire 3 and a second wire 4. The electrode group includes a plurality of electrodes 2. The plurality of electrodes 2 are sequentially distributed along the axial direction of the catheter body 1, and there is a gap between two adjacent electrodes 2. The first wire 3 is connected to the first electrode, and the second wire 4 is connected to the last electrode.

[0038] Position of electrode 2 on catheter body 1: electrode 2 is at least partially arranged around the outer circumference of catheter body 1. Preferably, electrode 2 is annular, such as a circular ring, a square ring, a triangular ring or an elliptical ring. If it is a circular ring, the diameter of electrode 2 is slightly larger than the diameter of catheter body; or electrode 2 is non-annular and closed, such as C-shaped, and is annular with a gap.

[0039] When the electrode 2 is at least partially disposed around the outer circumference of the catheter body 1 , the surface of the electrode, that is, the entire outer circumference of the electrode 2 , is covered with an insulating layer.

[0040] The electrode 2 is a tube, a spring tube or a coil. The tube is made of metal and is sleeved on the catheter body 1. The spring tube is elastic. The spring tube and the coil can be completely bent as the product is bent, and have better compliance and longer service life.

[0041] In order to facilitate control and obtain the area on the electrode 2 where the shock wave is generated, an insulating layer is provided on the surface of the electrode 2, and a conductive opening is opened on the insulating layer so that the exposed part of the electrode 2 forms a conductive area 5. The conductive areas 5 on two adjacent electrodes 2 are located at the same position on each electrode or the conductive areas on two adjacent electrodes are arranged oppositely. An area for generating shock waves is formed between the conductive areas 5 located at the same position on two adjacent electrodes 2 or the conductive areas arranged oppositely, that is, the insulating layer at the same position on two adjacent electrodes 2 or the conductive areas arranged oppositely are removed to form the conductive area 5.

[0042] Figures 2 to 7 The conductive areas 5 on two adjacent electrodes 2 are shown to be located at the same position on the respective electrodes, while the situation where the conductive areas on two adjacent electrodes are arranged relative to each other is not shown in the figure. The same position means that when multiple electrodes 2 are fixed on the catheter body, if the insulating layer is removed at one position of one electrode to form a conductive area, the insulating layer is also removed at the corresponding position of the electrode adjacent to the electrode to form a conductive area, and the same positions of the two electrodes are close to each other, and the insulating layer can be removed at the same position along a circle along the radial direction (not the circumference of the electrode) to form a conductive area.

[0043] The conductive areas on two adjacent electrodes are arranged oppositely, which means that the insulating layers at opposite positions on the two adjacent electrodes are removed, so that the conductive areas arranged oppositely are formed on the two adjacent electrodes.

[0044] The material of the electrode 2 is metal, conductive glue or graphene, wherein the metal includes stainless steel, tungsten alloy, platinum-iridium alloy, copper, gold or silver. The material of the insulating layer is polyimide, UV curing glue or AB glue. The electrode 2 can be embedded and fixed on the catheter body 1 by UV curing glue or AB glue, so that an insulation effect is formed between each electrode 2, and then at the position where conduction is required, the UV curing glue or AB glue at the position is removed to form a conductive area 5.

[0045] The principle of generating shock waves is as follows: when multiple electrodes 2 are immersed in a conductive fluid medium, when a certain voltage is applied to the first wire 3 and the second wire 4, the conductive area 5 between two adjacent electrodes 2 is connected to form a loop, generating a shock wave effect. The conductive fluid medium is blood or saline.

[0046] The conductive area 5 of each electrode 2 can be made into various shapes and sizes, such as one or more of round, square, and elliptical shapes.

[0047] The number of electrodes 2 is set to two or more. When the number of electrodes 2 is two, only one conductive area 5 is set on each electrode 2.

[0048] When the number of electrodes 2 exceeds two, only one conductive area 5 is provided on the first electrode and the last electrode, and two conductive areas 5 are provided on each intermediate electrode between the first electrode and the last electrode, with a gap between the two conductive areas 5. The two conductive areas 5 of each intermediate electrode are distributed at an angle greater than 0° and less than or equal to 180° along its circumference, and each intermediate electrode does not need to be connected to the first wire 3 and the second wire 4, so that the circuit can be connected, the structure is simplified, the number of connecting wires is reduced, the overall outer diameter of the catheter is reduced, the applicability of the catheter in any lesion site is improved, the service life of the catheter is increased, the cost is reduced, and the structure is simple and easy to implement.

[0049] The conductive areas 5 on all electrodes 2 are distributed at an angle greater than 0° and less than or equal to 180° along the circumferential direction, preferably at an angle of 90-180°. The conductive areas 5 on all electrodes 2 are distributed at a certain angle along the circumference of the catheter body 1, so that the generated shock wave has directionality, so that the outer periphery (whole circle) of the catheter body 1 can generate shock waves, which can increase the area where shock waves are generated to act on narrow diseased blood vessels with larger areas, thereby breaking up calcified plaques and improving the treatment effect. The conductive area 5 can be set according to the required direction to generate shock waves with specific directionality at the required direction position, so as to better control the area where shock waves are generated on the electrode 2.

[0050] In order to generate shock waves, arc discharge that generates cavitation bubbles must be allowed, and there must be a gap between two adjacent electrodes 2. The gap between two adjacent electrodes 2 is preferably 0.05-2 mm.

[0051] Preferably, a plurality of electrode groups are arranged along the axial direction of the catheter body 1, and the number of the electrode groups is 1-10, so as to act on a larger area of ​​narrow diseased blood vessels, thereby breaking up the calcified plaques and improving the treatment effect.

[0052] The catheter further comprises a balloon connected to the catheter body 1. The plurality of electrodes 2 are arranged on the catheter body 1 located inside the balloon. The balloon contains a conductive fluid medium, and the plurality of electrodes 2 can be immersed in the conductive fluid medium.

[0053] The first wire 3 and the second wire 4 are made of metal wires, and the metal wires are wrapped with insulating paint or insulating tubes. The first wire 3, the second wire 4 and the electrode 2 are connected by welding and / or crimping and / or bonding.

[0054] A shock wave generating system comprises a catheter and an energy generating unit. The catheter comprises a first wire 3 and a second wire 4. The first wire 3 and the second wire 4 are respectively connected to the positive electrode and the negative electrode of the energy generating unit (the first wire 3 is connected to one of the positive electrode and the negative electrode of the energy generating unit, and the second wire 4 is connected to the other of the positive electrode and the negative electrode of the energy generating unit). When all electrodes 2 are immersed in a conductive fluid and the energy generating unit discharges thereto, the conductive areas 5 on two adjacent electrodes 2 generate shock waves.

[0055] The following embodiments 1 to 5 specifically illustrate the case where the number of electrodes is set to 2-6.

[0056] Embodiment 1:

[0057] In this embodiment, see Figure 2 There are two electrodes 2, one electrode 2 is the first electrode, and the other electrode 2 is the last electrode 2. Only one conductive area 5 is set on each electrode 2. The conductive areas 5 on the two electrodes 2 are located at the same position on each electrode, on the same circumferential side of the catheter body 1, one electrode 2 is connected to the first wire 3, and the other electrode 2 is connected to the second wire 4.

[0058] Embodiment 2:

[0059] This embodiment is basically the same as the first embodiment, except that:

[0060] In this embodiment, see Figure 3 , the number of electrodes 2 is three, the three electrodes are respectively a first electrode, a last electrode and an intermediate electrode located between the first electrode and the last electrode, wherein only one conductive area 5 is provided on the first electrode and the last electrode, two conductive areas 5 are provided on the intermediate electrode, and the conductive areas 5 on the three electrodes are distributed at an angle of 180° along the circumferential direction, wherein the conductive area on the first electrode and one conductive area on the intermediate electrode are located at the same position on their respective electrodes, and the other conductive area on the intermediate electrode and the conductive area on the last electrode are located at the same position on their respective electrodes, and the same position here is the same circumferential side of the catheter body 1; the first electrode 2 is connected to the first wire 3, the last electrode 2 is connected to the second wire 4, and one intermediate electrode does not need to be connected to a wire.

[0061] Embodiment three:

[0062] This embodiment is basically the same as the first embodiment, except that:

[0063] In this embodiment, see Figure 4 and Figure 5, the number of electrodes 2 is four, the four electrodes are respectively a first electrode, a last electrode and two intermediate electrodes located between the first electrode and the last electrode, wherein only one conductive area 5 is provided on the first electrode and the last electrode, two conductive areas 5 are provided on the two intermediate electrodes, and the conductive areas 5 on the four electrodes 2 are distributed at an angle of 120° along the circumferential direction, wherein a conductive area on the first electrode and a conductive area on the first intermediate electrode are located at the same position on the respective electrodes, another conductive area on the first intermediate electrode and a conductive area on the second intermediate electrode are located at the same position on the respective electrodes, another conductive area on the second intermediate electrode (not shown in the figure) and a conductive area on the last electrode (as shown in the figure) are located at the same position on the respective electrodes. Figure 4 The same position (indicated by a) is located at the same position on each electrode, and the same position here is the same circumferential side of the catheter body 1. Figure 4 In the figure, the conductive area indicated by a is located on the back side of this view; the first electrode 2 is connected to the first wire 3, the last electrode 2 is connected to the second wire 4, and the two middle electrodes do not need to be connected with wires.

[0064] Embodiment 4:

[0065] This embodiment is basically the same as the first embodiment, except that:

[0066] In this embodiment, see Figure 6 , the number of electrodes 2 is five, the five electrodes 2 are respectively a first electrode, a last electrode and three intermediate electrodes located between the first electrode and the last electrode, wherein only one conductive area 5 is provided on the first electrode and the last electrode, two conductive areas 5 are provided on the three intermediate electrodes, and the conductive areas 5 on the five electrodes are distributed at an angle of 90° along the circumferential direction, wherein a conductive area on the first electrode and a conductive area on the first intermediate electrode are located at the same position on their respective electrodes, another conductive area on the first intermediate electrode and a conductive area on the second intermediate electrode are located at the same position on their respective electrodes, another conductive area on the second intermediate electrode and a conductive area on the third intermediate electrode are located at the same position on their respective electrodes, and another conductive area on the third intermediate electrode (such as Figure 6 a in the figure) and a conductive area on the last electrode (such as Figure 6 The same position (indicated by a) is located at the same position on each electrode, and the same position here is the same circumferential side of the catheter body 1. Figure 6 The conductive area indicated by a is located on the back side of this view; the first electrode 2 is connected to the first wire 3, the last electrode 2 is connected to the second wire 4, and the three middle electrodes do not need to be connected to wires.

[0067] Embodiment five:

[0068] This embodiment is basically the same as the first embodiment, except that:

[0069] In this embodiment, see Figure 7 , the number of electrodes 2 is six, which are the first electrode 21, the second electrode 22, the third electrode 23, the fourth electrode 24, the fifth electrode 25 and the sixth electrode 26 from left to right, the first electrode 21 is the first electrode, the sixth electrode 26 is the last electrode, the second electrode 22, the third electrode 23, the fourth electrode 24 and the fifth electrode 25 are intermediate electrodes, only one conductive area 5 is arranged on the first electrode 21 and the sixth electrode 26, two conductive areas 5 are arranged on the second electrode 22, the third electrode 23, the fourth electrode 24 and the fifth electrode 25, and the conductive areas 5 on the six electrodes are distributed at an angle of 90° along the circumferential direction, wherein one conductive area on the first electrode 21 and one conductive area on the second electrode 22 are located at the same position on their respective electrodes, another conductive area on the second electrode 22 and one conductive area on the third electrode 23 are located at the same position on their respective electrodes, another conductive area on the third electrode 23 and one conductive area on the fourth electrode 24 are located at the same position on their respective electrodes, and another conductive area on the fourth electrode 24 (such as Figure 6 a in the figure) and a conductive area of ​​the fifth electrode 25 (such as Figure 6 The conductive area of ​​the fifth electrode 25 and the conductive area of ​​the sixth electrode 26 are located at the same position on the respective electrodes, and the same position here is the same circumferential side of the catheter body 1. Figure 7 The conductive area indicated by a is located at the back of this view. The first electrode 21 is connected to the first wire 3, the sixth electrode 26 is connected to the second wire 4, and the four middle electrodes do not need to be connected to wires.

[0070] Embodiment 5 Figure 7 The first five electrodes (the first electrode 21, the second electrode 22, the third electrode 23, the fourth electrode 24, and the fifth electrode 25) form a repeating unit. When the number of electrodes exceeds six, the first five electrodes are the fifth electrode. Figure 7 The first five electrodes are the same as those in Example 5. Figure 7 The first five electrodes can be set repeatedly in sequence. For example, when the number of electrodes is seven, the first six electrodes and Figure 7 For example, when the number of electrodes is eight, the conductive area 5 on the eighth electrode is the same as the conductive area 5 on the third electrode 23 in the fifth embodiment; when the number of electrodes is nine, the conductive area 5 on the ninth electrode is the same as the conductive area 5 on the fourth electrode 24 in the fifth embodiment; when the number of electrodes is ten, the conductive area 5 on the tenth electrode is the same as the conductive area 5 on the fifth electrode 25 in the fifth embodiment. When the number of electrodes exceeds ten, the above rules are repeated.

[0071] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A catheter, comprising a catheter body, an electrode group arranged on the catheter body, a first wire and a second wire, wherein the electrode group comprises a plurality of electrodes, the plurality of electrodes are sequentially distributed along the axial direction of the catheter body, and there is a gap between two adjacent electrodes, the first wire is connected to the first electrode, and the second wire is connected to the last electrode, characterized in that: The surface of the electrode is provided with an insulating layer, and a conductive opening is opened on the insulating layer so that the exposed electrode portion forms a conductive area, and the conductive areas on two adjacent electrodes are located at the same position on each electrode, and a region for generating shock waves is formed between the conductive areas on the two adjacent electrodes located at the same position, wherein the same position is the same circumferential side of the catheter body, and the insulating layer is removed along a radial circle at the same position to form a conductive area; The plurality of electrodes are in the same circular shape; When the number of the electrodes is two, only one conductive area is provided on each electrode; or, when the number of the electrodes exceeds two, only one conductive area is provided on the first electrode and the last electrode, and two conductive areas are provided on each intermediate electrode between the first electrode and the last electrode; The angle between the two conductive areas of the intermediate electrode in the circumferential direction is greater than 0° and less than or equal to 180°; the gap between two adjacent electrodes is 0.05-2 mm.

2. The catheter according to claim 1, characterized in that: The angle of the conductive areas on all the electrodes in the circumferential direction is greater than 0° and less than or equal to 180°.

3. The catheter according to claim 1, characterized in that: The electrode is a tube, a spring tube or a coil, and the material of the electrode is metal, conductive glue or graphene, wherein the metal includes stainless steel, tungsten alloy, platinum-iridium alloy, copper, gold or silver.

4. The catheter according to claim 1, characterized in that: The electrode group comprises 2-6 electrodes.

5. The catheter according to claim 1, characterized in that: The catheter further comprises a balloon connected to the catheter body, and the plurality of electrodes are arranged on the catheter body located in the balloon.

6. The catheter according to claim 1, characterized in that: The first wire, the second wire and the electrode are connected by welding and / or crimping and / or bonding.

7. A shock wave generating system, comprising a catheter and an energy generating unit, characterized in that: The catheter is the catheter according to any one of claims 1 to 6, and the first wire and the second wire of the catheter are respectively connected to the positive electrode and the negative electrode of the energy generating unit.

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