Implantable cerebral apoplexy treatment stimulator

Abstract

The invention discloses an implantable cerebral apoplexy treatment stimulator, which comprises at least two electrode parts and at least two skull nails, the at least two electrode parts are suitable for being respectively implanted into implantation holes of at least two skull, the electrode parts are connected with wires, the wires are connected with a pulse generator, each skull nail comprises a stud part and a screwing part, and the stud part is connected with the pulse generator. The stud part is suitable for being screwed into the implantation hole, the bottom of the stud part abuts against the top of the electrode part, the screwing part is connected to the top of the stud part, an operation groove is formed in the top of the screwing part, and a screw driver can be inserted into the operation groove to rotate the skull nail. The implantable cerebral apoplexy treatment stimulator is simpler in structure and more convenient to fix on the skull, the stimulation intensity can be improved, small-range lesions can be accurately targeted, stimulation is more accurate, in addition, stimulation parameters and stimulation areas can be adjusted and controlled, the implantable cerebral apoplexy treatment stimulator dynamically adapts to cerebral injury conditions of different patients, and the cerebral apoplexy treatment effect is better.

Description

Technical Field

[0001] This invention relates to the field of brain-computer interface technology, and in particular to an implantable stroke treatment stimulator. Background Technology

[0002] Stroke (commonly known as "apoplexy") is a type of acute cerebrovascular disease. The core pathological mechanism is the sudden blockage or rupture of blood vessels in the brain, leading to ischemia and hypoxia of brain tissue or irreversible damage caused by hematoma compression, which in turn causes neurological deficits such as limb paralysis, speech disorders, and cognitive decline. It is characterized by rapid onset, rapid progression, and high rates of disability and death, and is the leading cause of adult disability worldwide.

[0003] Currently, the main rehabilitation treatments for stroke include transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). These methods generate magnetic or electrical stimulation through the electrodes of the stimulator to regulate the excitability of brain regions and improve motor and language functions, showing some effectiveness in clinical practice. However, existing stimulators have electrodes fixed to the outer surface of the scalp, requiring the current to penetrate the scalp and skull, resulting in a very high attenuation rate. The actual current intensity that produces an effect is only 10% to 20% of the output value. Secondly, the current diffuses in a hemispherical shape, covering a large radius of the stimulation target, making it impossible to precisely target small lesions, which is not conducive to precise stimulation and rehabilitation. In addition, existing stimulators have complex structures, are cumbersome to fix to the skull, and have poor practicality. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes an implantable stroke treatment stimulator that not only improves the stimulation intensity but also precisely targets small lesions, resulting in more accurate stimulation and better treatment effects. Furthermore, it has a simpler structure and is easier to fix to the skull.

[0005] An implantable stroke treatment stimulator according to an embodiment of the present invention is adapted to the skull, wherein the skull has at least two implantation holes, and the walls of the implantation holes have wiring grooves. The implantable stroke treatment stimulator includes at least two electrode portions and at least two skull nails. The at least two electrode portions are adapted to be implanted into the at least two implantation holes respectively. The electrode portions are connected to wires, which are adapted to run through the wiring grooves. The wires are used to connect to a pulse generator. The skull nails include stud portions and screwing portions. The outer peripheral wall of the stud portion is formed with external threads. The at least two stud portions are adapted to be screwed into the at least two implantation holes respectively. The bottom of the stud portion abuts against the top of the electrode portion. The screwing portion is connected to the top of the stud portion. The top of the screwing portion is provided with an operating groove, which is adapted to allow a screwdriver to be inserted to rotate the skull nail. The implantable stroke treatment stimulator according to embodiments of the present invention has at least the following beneficial effects: The electrode is placed in the implantation hole, and then the stud of the skull screw is screwed into the implantation hole, with the stud abutting against the electrode to secure it. This effectively prevents the electrode from loosening, simplifies the structure, and makes it easier to fix to the skull, reducing the workload of medical staff. A wiring groove is created in the wall of the implantation hole for easier wiring and to prevent the wires from interfering with the installation of the skull screw. In this application, the electrode and skull screw are implanted into the implantation hole through minimally invasive surgery. The electrode serves as a current target, which can be positioned to a predetermined brain region, allowing for precise targeting of small lesions, resulting in more accurate stimulation and less error in the stimulation range. Simultaneously, the electrode penetrates deep into the skull, avoiding the attenuation of the current by the scalp and skull, resulting in high current transmission efficiency and good current stimulation effect. Furthermore, by adjusting the current intensity, controlling the switching sequence of stimulation pulses from multiple electrode sections, and matching the positive and negative poles of the electrode sections, stimulation parameters can be adjusted. By connecting the pulse generator with the electrical conduction of different electrode sections, the stimulation area can be controlled, dynamically adapting to the brain injury conditions of different patients, resulting in better stroke treatment effects, especially suitable for patients for whom existing TMS / tDCS devices are ineffective.

[0006] According to some embodiments of the present invention, the implantable stroke treatment stimulator further includes at least two springs adapted to be implanted in at least two of the implantation holes respectively, the top of the spring abutting against the bottom of the stud portion, and the bottom of the spring abutting against the top of the electrode portion.

[0007] According to some embodiments of the present invention, the length of the stud portion is 3mm-4mm, the length of the spring in its natural state is 2mm-4mm, and the minimum length of the spring in its compressed state is 1mm-2mm.

[0008] According to some embodiments of the present invention, the spring is made of medical-grade stainless steel.

[0009] According to some embodiments of the present invention, the cranial nail is made of polyetheretherketone.

[0010] According to some embodiments of the present invention, the skull nail is made of medical titanium alloy, and the outer surface of the skull nail is formed with an electrically insulating layer by anodizing.

[0011] According to some embodiments of the present invention, the outer peripheral wall of the bottom of the stud portion is chamfered.

[0012] According to some embodiments of the present invention, the outer peripheral wall of the conductor is covered with an electrically insulating layer.

[0013] According to some embodiments of the present invention, the pulse generator includes a housing, a circuit board, a feedthrough connector, an energy coil, and a data antenna. The circuit board is disposed inside the housing, the feedthrough connector is disposed in the housing and connected to the circuit board, the wire is connected to the feedthrough connector, the energy coil is connected to the feedthrough connector, and the data antenna is connected to the feedthrough connector.

[0014] According to some embodiments of the present invention, the operating frequency of the energy coil is 135.6 kHz, and the operating frequency of the data antenna is 2.4 GHz.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and some of these additional aspects and advantages will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a schematic diagram of the installation of an implantable stroke treatment stimulator according to an embodiment of the present invention; Figure 2 for Figure 1 A partial sectional view; Figure 3 for Figure 2 A schematic diagram of the implantation hole penetrating the skull; Figure 4 This is a schematic diagram of the skull nail structure; Figure 5 This is a schematic diagram of the spring structure; Figure 6 A schematic diagram showing the connection between the electrode and the wire; Figure 7 This is a schematic diagram showing the arrangement of multiple implantation holes; Figure 8 for Figure 7 A magnified view of a portion of the image; Figure 9 This is a schematic diagram of the pulse generator. Figure 10 This is a schematic diagram illustrating the interaction between the pulse generator and external devices.

[0017] Icon labels: Electrode part 100; Wire 101; Skull nail 200; stud part 201; screwing part 202; operating groove 203; Spring 300; Grinding surface 301; Pulse generator 400; housing 401, circuit board 402; feedthrough connector 403; energy coil 404; data antenna 405; electrode connector 406; Skull 500; Implantation hole 501; Cable routing groove 502; Dura mater 503. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] The following is for reference. Figures 1 to 10 An implantable stroke treatment stimulator according to an embodiment of the present invention is described.

[0020] refer to Figures 1 to 3 , Figure 7 and Figure 8 As shown, the implantable stroke treatment stimulator according to an embodiment of the present invention is adapted to a skull 500, the skull 500 having at least two implantation holes 501, the number of implantation holes 501 being determined according to actual needs, for example, referring to... Figure 7 As shown, nine implantation holes 501 can be opened.

[0021] refer to Figure 2 , Figure 3 and Figure 8 As shown, the wall of the implantation hole 501 can be cut with a wire routing groove 502 by reciprocating sawing. The top end of the wire routing groove 502 can extend to the top end of the implantation hole 501 and pass through it, and the bottom end of the wire routing groove 502 can extend to the bottom end of the implantation hole 501.

[0022] refer to Figures 1 to 6 As shown, the implantable stroke treatment stimulator includes at least two electrode parts 100 and at least two skull nails 200. The number of electrode parts 100 and skull nails 200 is determined according to the number of implantation holes 501. Each implantation hole 501 is provided with one electrode part 100 and one skull nail 200.

[0023] At least two electrode portions 100 are adapted to be implanted into at least two implantation holes 501 respectively. The electrode portions 100 are connected to wires 101, which are adapted to run through wire channels 502. One end of the wires 101 extending out of the implantation holes 501 is used to connect to a pulse generator 400. The pulse generator 400 generates pulse electrical signals, and the electrode portions 100 receive the pulse electrical signals and emit corresponding stimulation waveforms and stimulation currents to perform treatment.

[0024] It should be noted that when there are two implantation holes 501, the electrode portion 100 in one implantation hole 501 is the negative electrode, and the electrode portion 100 in the other implantation hole 501 is the positive electrode. When there are three or more implantation holes 501, some of the electrode portions 100 in the implantation holes 501 can be negative electrodes, and the electrode portions 100 in the remaining implantation holes 501 can be positive electrodes. For example, refer to... Figure 1 and Figure 7 As shown, when there are nine implantation holes 501, the nine implantation holes 501 can be arranged in an array. The electrode portion 100 in the middle implantation hole 501 can be a negative electrode, and the electrode portions 100 in the remaining implantation holes 501 are positive electrodes, surrounding the middle negative electrode. A current stimulation region is formed between the positive and negative electrodes. The number of implantation holes 501 and the positive and negative electrode arrangement of the electrode portions 100 can have various possible combinations, and the present invention is not limited thereto.

[0025] It should be noted that the reference Figure 2 As shown, the implantation hole 501 can be a blind hole structure, meaning that the bottom of the implantation hole 501 does not penetrate through the skin. In this case, the electrode portion 100 does not adhere to the patient's dura mater 503. (Reference) Figure 3 As shown, the implantation hole 501 can also be a through hole structure, that is, the bottom end of the implantation hole 501 is through-hole. In this case, the bottom surface of the electrode part 100 can be attached to the patient's dura mater 503.

[0026] The cranial nail 200 includes a stud portion 201 and a screwing portion 202. The outer peripheral wall of the stud portion 201 is formed with external threads. At least two stud portions 201 are adapted to be screwed into at least two implantation holes 501 respectively. The bottom of the stud portion 201 abuts against the top of the electrode portion 100. The screwing portion 202 is connected to the top of the stud portion 201. The top of the screwing portion 202 is provided with an operating groove 203. The operating groove 203 can be cross-shaped or slotted. The operating groove 203 is adapted to allow a screwdriver to be inserted to rotate the cranial nail 200. The screwdriver can be an ordinary screwdriver or an electric screwdriver, which will not be described in detail here.

[0027] In this application, at least two implantation holes 501 are made on the patient's skull 500, and a wiring groove 502 is made in the wall of the implantation hole 501. Then, the electrode part 100 is placed at the bottom end in the implantation hole 501. The wire 101 connected to the electrode part 100 runs through the wiring groove 502 and connects to the pulse generator 400. Then, a screwdriver is inserted into the operating groove 203 of the screwing part 202 of the skull nail 200. By operating the screwdriver, the stud part 201 of the skull nail 200 is screwed into the implantation hole 501, so that the bottom of the stud part 201 abuts against the top of the electrode part 100, thereby pressing the electrode part 100 tightly and effectively preventing the electrode part 100 from loosening. The fixing structure of the electrode part 100 is the skull nail 200, which has a simple structure and is easy to operate when fixed to the skull 500, which can greatly reduce the workload of medical staff. In addition, a wiring groove 502 is opened in the wall of the implantation hole 501, which makes wiring more convenient and at the same time can prevent the wire 101 from affecting the installation of the skull nail 200.

[0028] Furthermore, through minimally invasive surgery, the electrode portion 100 and the skull nail 200 are implanted into the implantation hole 501 of the skull 500. The electrode portion 100, acting as a current target, can be precisely located to a predetermined brain region, accurately targeting small lesions (such as directly acting on the penumbra area after large vessel occlusion in ischemic stroke, damaged neurons around hematoma in hemorrhagic stroke, or specific functional areas such as the inferior frontal gyrus and motor cortex), resulting in more precise stimulation and smaller stimulation range errors. Simultaneously, the electrode portion 100, deeply embedded in the skull 500, avoids current attenuation by the scalp and skull 500, resulting in high current transmission efficiency and good current stimulation effect. As one embodiment, the electrode portion 100 of this invention can also be used to collect electroencephalographic signals.

[0029] Furthermore, multiple electrode sections 100 and cranial nails 200 can be implanted first. Postoperatively, based on the patient's brain injury CT / MRI images, different stimulation waveforms and stimulation currents can be generated by adjusting the current intensity of the pulse generator 400, controlling the switching sequence of stimulation pulses from multiple electrode sections 100, and matching the positive and negative poles of the electrode sections 100, thereby improving the effectiveness of stimulation therapy. Additionally, the pulse generator 400 can be electrically connected to electrode sections 100 at different locations; for example, only some electrode sections 100 can be discharged for stimulation, i.e., at least one electrode section 100 can be set to a de-energized state, to regulate the stimulation area.

[0030] In this way, by adjusting the stimulation parameters and stimulation area, it is possible to dynamically adapt to the different brain injury conditions of different patients (such as adapting to different infarct sizes and different hemorrhage absorption), resulting in better stroke treatment and rehabilitation effects. It can effectively improve the motor, language and cognitive functions of stroke patients, and is especially suitable for patients who have not responded to existing TMS / tDCS equipment treatment.

[0031] refer to Figure 2 , Figure 3 and Figure 5 As shown, in some embodiments of the present invention, the implantable stroke treatment stimulator further includes at least two springs 300, which are adapted to be implanted into at least two implantation holes 501 respectively. The top of the spring 300 abuts against the bottom of the stud portion 201, and the bottom of the spring 300 abuts against the top of the electrode portion 100. For example, the spring 300 can be a helical compression spring, and the effective number of turns of the spring 300 can be 3 to 5 turns.

[0032] In this embodiment, a spring 300 is provided between the electrode part 100 and the stud part 201. The spring 300 can not only apply elastic pressure to the electrode part 100 to avoid damage to the electrode part 100 and to avoid injuring the patient's brain, but also fill the distance difference when the thickness of the skull 500 is different or the depth of the stud part 201 of the skull nail 200 into the implantation hole 501 is different, so that the stud part 201 of the skull nail 200 in each implantation hole 501 can abut against the corresponding electrode part 100, thereby making the placement of the electrode part 100 more stable.

[0033] In some embodiments of the present invention, the length of the stud portion 201 is set at 3mm-4mm, the length of the spring 300 in its natural state is 2mm-4mm, and the minimum length of the spring 300 in its compressed state is 1mm-2mm. This is just right to accommodate the fact that the thickness of an adult skull 500 is typically 7 to 10mm, which allows for the clamping of the electrode portion 100 while avoiding excessive pressure that could damage the electrode portion 100 or injure the patient's head.

[0034] In some embodiments of the invention, the spring 300 is made of medical-grade stainless steel. For example, the spring 300 may be made of biocompatible medical-grade stainless steel 316LVM or other suitable medical-grade stainless steel.

[0035] In this embodiment, the spring 300 is made of medical-grade stainless steel, which not only has excellent corrosion resistance, but also reliable biocompatibility, is non-toxic and non-allergenic to human tissues, and also has good elastic properties.

[0036] refer to Figure 5 As shown, in some embodiments of the present invention, the two ends of the spring 300 are respectively ground to form a polished surface 301. The polished surface 301 at the top of the spring 300 is attached to the bottom surface of the stud portion 201, and the polished surface 301 at the bottom of the spring 300 is attached to the top surface of the electrode portion 100. In this way, stress concentration can be reduced, which not only improves the effect of pressing the electrode portion 100, but also reduces the damage to the electrode portion 100.

[0037] In some embodiments of the present invention, the cranial nail 200 is made of polyetheretherketone (PEEK). In this embodiment, the cranial nail 200 is made of PEEK, which has reliable biocompatibility, is non-toxic and non-allergenic to human tissue, and has excellent electrical insulation properties, thus preventing current on the electrode portion 100 from leaking through the cranial nail 200 to non-treatment areas of the patient's head.

[0038] In some embodiments of the present invention, the cranial nail 200 is made of medical-grade titanium alloy, and the outer surface of the cranial nail 200 is formed with an electrically insulating layer by anodizing. For example, the cranial nail 200 can be made of medical-grade titanium alloy Ti 6Al4V-ELI or other suitable types of medical-grade titanium alloy.

[0039] The cranial nail 200 is made of medical-grade titanium alloy, which has reliable biocompatibility, is non-toxic and non-allergenic to human tissue, and is lightweight and corrosion-resistant. An anodized layer forms an electrically insulating layer on the outer surface of the cranial nail 200, preventing current from the electrode portion 100 from leaking through the cranial nail 200 to non-treatment areas of the patient's head.

[0040] In some embodiments of the present invention, the thickness of the electrically insulating layer formed by anodizing on the outer surface of the skull nail 200 is 4 to 6 μm. This not only improves the leakage prevention effect of the skull nail 200, but also avoids the impact of an excessively thick electrically insulating layer on the use of the skull nail 200.

[0041] In some embodiments of the present invention, the outer peripheral wall of the bottom of the stud portion 201 is chamfered. In this embodiment, the chamfering of the outer peripheral wall of the bottom of the stud portion 201 makes it easier for the stud portion 201 of the skull nail 200 to be screwed into the implantation hole 501 of the skull 500 via self-tapping.

[0042] In some embodiments of the present invention, the outer peripheral wall of the lead wire 101 is covered with an electrically insulating layer. For example, the electrically insulating layer covering the outer peripheral wall of the lead wire 101 can be made of polyimide or other suitable electrically insulating materials. In this way, leakage of current on the electrode portion 100 through the lead wire 101 to non-treatment areas of the patient's head can be prevented.

[0043] In some embodiments of the present invention, both the electrode portion 100 and the wire 101 may be made of platinum-iridium alloy, and the electrode portion 100 and the wire 101 may be welded, for example by laser welding.

[0044] In some embodiments of the present invention, the pulse generator 400 may be an implantable pulse generator (IPG) that can be implanted in the skull 500, the anterior chest, or other locations. When the pulse generator 400 is implantable, it can be powered by wireless charging or a built-in battery. Of course, the pulse generator 400 may also be disposed externally, as long as it can be electrically connected to the electrode part 100.

[0045] refer to Figure 9 As shown, in some embodiments of the present invention, the pulse generator 400 includes a housing 401, a circuit board 402, a feedthrough connector 403, an energy coil 404, and a data antenna 405.

[0046] The circuit board 402 is located inside the housing 401, the feedthrough connector 403 is located in the housing 401 and connected to the circuit board 402, the wire 101 is connected to the feedthrough connector 403, the energy coil 404 is connected to the feedthrough connector 403, and the data antenna 405 is connected to the feedthrough connector 403. For example, the feedthrough connector 403 can be a ceramic feedthrough connector. The feedthrough connector 403 can be located at the opening of the housing 401 and seal the housing 401. The feedthrough connector 403 is connected to the circuit board 402 inside the housing 401. The wire 101 can be directly connected to the feedthrough connector 403, or the wire can be connected to the feedthrough connector 403 through the electrode connector 406. The energy coil 404 and the data antenna 405 can be located on the outside of the housing 401 and covered by a protective structure. The energy coil 404 receives electrical energy provided by a power source, such as a portable power supply, through electromagnetic induction to achieve wireless power supply. Of course, the pulse generator 400 can also have a built-in battery, which will not be described in detail here. The data antenna 405 is used to exchange signals with external devices, providing bidirectional signal transmission.

[0047] In this embodiment, the pulse generator 400 can be implanted in the human body and can transmit data and energy wirelessly, making it more convenient to use.

[0048] The following is for reference. Figure 10 As shown, taking the pulse generator 400 as an implantable pulse generator (IPG) as an example, the interaction between the pulse generator 400 and external devices is briefly described. It should be noted that the following description is only an illustrative example and is not intended to limit the solution of this application.

[0049] External devices may include computers, programmable controllers, etc. The software in the computer, such as DAC software, uses the Bluetooth module to set up the system and configure the parameters of the programmable controller. The portable power supply provides power to the programmable controller and allows for parameter fine-tuning via buttons; The programmable controller provides system power and bidirectional data communication to the implantable pulse generator via wireless transmission. Specifically, the energy coil 404 provides power to the implantable pulse generator via wireless power transmission; the data antenna 405 uses wireless communication to provide stable bidirectional data transmission for the system. The implantable pulse generator is configured according to the stimulation parameters sent by the programmable controller. After being processed by the MCU on the circuit board 402, it sends the corresponding stimulation waveform and stimulation current to the brain tissue through the electrode section 100.

[0050] In some embodiments of the present invention, the energy coil 404 operates at a frequency of 135.6 kHz, and the data antenna 405 operates at a frequency of 2.4 GHz. This prevents mutual interference between the energy coil 404 and the data antenna 405.

[0051] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. An implantable stroke treatment stimulator, comprising: The implantable stroke treatment stimulator is suitable for a skull which is provided with at least two implant holes, and the hole wall of the implant hole is provided with a wire slot. The implantable stroke treatment stimulator comprises: at least two electrode parts which are suitable for being implanted in the at least two implant holes respectively, and the electrode part is connected with a wire which is suitable for being wired from the wire slot and is used for connecting a pulse generator; at least two skull nails which comprise a stud part and a screw part, the outer peripheral wall of the stud part is formed with external threads, the at least two stud parts are suitable for being screwed into the at least two implant holes respectively, the bottom of the stud part abuts against the top of the electrode part, the screw part is connected to the top of the stud part, and the top of the screw part is provided with an operation slot which is suitable for being inserted by a screw driver to rotate the skull nail.

2. The implantable stroke treatment stimulator of claim 1, wherein, The implantable stroke treatment stimulator further comprises: at least two springs which are suitable for being implanted in the at least two implant holes respectively, the top of the spring abuts against the bottom of the stud part, and the bottom of the spring abuts against the top of the electrode part.

3. The implantable stroke treatment stimulator of claim 2, wherein, The length of the stud part is 3mm-4mm, the length of the spring in a natural state is 2mm-4mm, and the minimum length of the spring in a compressed state is 1mm-2mm.

4. The implantable stroke treatment stimulator of claim 2, wherein, The spring is made of medical stainless steel.

5. The implantable stroke treatment stimulator according to any one of claims 1 to 4, characterized in that, The skull nail is made of polyether ether ketone.

6. The implantable stroke treatment stimulator according to any one of claims 1 to 4, characterized in that The skull nail is made of medical titanium alloy, and the outer surface of the skull nail is formed with an electrically insulating layer through anodic oxidation.

7. The implantable stroke treatment stimulator according to any one of claims 1 to 4, characterized in that The outer peripheral wall of the bottom of the stud part is formed with a chamfer.

8. The implantable stroke treatment stimulator according to any one of claims 1 to 4, characterized in that The outer peripheral wall of the wire is covered with an electrically insulating layer.

9. The implantable stroke treatment stimulator according to any one of claims 1 to 4, characterized in that The pulse generator comprises: a shell; a circuit board which is arranged in the shell; a feedthrough connector which is arranged in the shell and is connected to the circuit board, and the wire is connected to the feedthrough connector; an energy coil which is connected to the feedthrough connector and is used for wireless charging; a data antenna which is connected to the feedthrough connector.

10. The implantable stroke treatment stimulator of claim 9, wherein, The working frequency of the energy coil is 135.6KHz, and the working frequency of the data antenna is 2.4Ghz.

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