Medical soft equipment and its means and instruments for controlling curvature

Abstract: The medical soft equipment and its means and instruments for controlling curvature relates to a piece of curvature controlling equipment of the kind which includes a pressure source, a pressure control unit as well as a soft tube (1) with one or more pressure control cavity or cavities (2) positioned inside, which is conductive to fluid pressure-transmitting medium. By using the pressure source, the pressure control unit, a kind of fluid pressure-transmitting medium and the soft tube with the pressure control cavity or cavities, differential pressures inside the cavity can be used to control the curvature of the needed part of the medical soft equipment.

Description: This invention relates to a bendable medical apparatus as mentioned in the first part of claim 1 describing a catheter. However, the invention is not restricted to catheters, it also can concern an endoscop or an artificial organ e.g. an artificial cochlea electrode etc. In order to maintain people's health it is known to use medical equipments and to insert or plant them by every possible means into various kinds of organs, tissues or cavities inside the body to make diagnosis, to give treatment, to perform surgical operations or to serve as an artificial replacement to restore physiological functions. However, as the insertion or planting passage or the surgical incision always seems to be too small, the shape of the curved organ, the tissue or the body cavity is too narrow. The curvature of the curved organ, the tisssue or the body cavity at each position change too often, in order to make the insertion or plantation less harmless, to minimize tissue injuries and to increase the efficiency and success rate. Therefore, the curvature of the equipment for inserting or planting must be controlled at certain position or direction to be adapted to the shape of the curved organ, the tissue or the body cavity at each position. In prior art, solutions generally adopted are as follows: According to EP-A-0 256 478 and EP-A-0 306 010 a catheter comprises a stiffener consisting of a balloon being inflatable and deflatable as desired by the operator. The balloon is coupled to the distal aspect of the catheter. According to Cardiac Catheter for Examination and Diagnosis", pages 187-190, February 1979, compiled by Mao Jiwen and Sun Ruilong of Fuwai Hospital of the Chinese Medical Academy a preformed and slightly curved catheter is applied and then pushed at the root of the aorta to achieve certain curvature. By searching repeatly for the mouth of the coronary artery it is inserted into the right place. According to Judkins' method, two catheters with different curvatures are used to be inserted respectively into the right and left coronary arteries and then replaced. Such a method as making the equipment into a fixed curve is somewhat of blindness. It demands high operating technique and more time in the application and therefore creates pains and dangers upon the patients with tissue injury and other complications such as vascular thrombosis, embolism, hemorrhage, infection and severe arrhythemia. According to US patent 4 920 980 the curvature of a guide wire is inserted into the inner longitudinal cavity of an equipment. Once the guide wire gets into the body, its curvature is fixed. To change the curvature, the guide wire has to be extracted or replaced. Therefore, an operation like this is very difficult and time-consuming and likely to cause hemorrhage, thrombosis, infection or even the breakage of the guide wire inside the body, which would demand a surgical operation to pull it out, thus increasing the suffering and danger to the patient. According to Medial Optical Instruments", March 1988, compiled by Yu Qinan et al, pages 364-369, The Curvature Control of the Endoscope" the curvature of an endoscope can be controlled by pulling a number of steel wires attached to the links of the mechanism to curve certain part of the equipment. As the curvature is controlled by the wires, the mechanism is complicated and bulky and difficult to be made into a small diameter pipe, thus limiting its application. In addition, if an excessive force is applied in pulling the wires, it shall damage the mechanism or even break the optical fibre, thus affecting the service like of the equipment. Furthermore, a pipe with larger diameter shall increase the difficulty in inserting and the suffering of the patient. It is the object of the present invention to better and easily control the curvature of the bendable medical apparatus which shall be simple in structure. Its diagnostic and therapeutic efficiency shall be favourably increased. As the curvature of the equipment can be easily controlled, it alleviates the patient's suffering with less serious complications such as tissue injury, hemorrhage, thromboembolism, arrhythemia or even sudden death. The invention is claimed in claim 1 and preferred embodiments are claimed in sub-claims. The cross-section, the elastic modulus and the thickness of the wall of the soft flexible tube is selected to change the cross-section by changing the inner pressure in comparison with the outer pressure. In order to change the curvature of the medical soft equipment, a kind of fluid shall be adopted as a sort of pressure-transmitting medium and conducted into at least one pressure control cavity of the specially designed equipment. By changing the pressure of the fluid, the pressure inside the equipment can be changed and the curvature changes at certain part or several parts of the medical soft equipment can be controled according to the shape of the curved organ or body cavity, thus securing a safe and reliable outside control over the inside diagnosis and therapy when the medical soft equipment gets into the body. Inside the soft tube of the medical soft equipment is at least one pressure control cavity an inner longitudinal cavity with either the distal or tip sealed and its mouth connected to the pressure source. Between the curvature in the needed part of the medical soft equipment and the pressure inside the pressure control cavity there exists a specific functional relationship, through which the medical soft equipment can be properly adjucted to the right curvature as is needed by the curved organ or body cavity and reduce the pain to th patient and the complications as well as such as tissue injury, hemorrhage, thromboembolism, arrhthemia and sudden death, thus increasing the reliability and success rate of th operation. As this kind of medical soft equipment controls the curvature through the fluid medium conducted into the pressure control cavity, it can be used for various kinds of medical soft equipment that demands a control of its curvature, such as artificial cochlea and artificial joints, etc. The invention will be further described with reference to the accompanying drawings showing in figure 1 the schematic drawing of the electrode of the artificial cochlea made of the medical soft equipment of the present invention in its stretched state and in figure 2 in its curved state, in figure 3 the enlarged section schematic drawing of A - A" of figure 1 and in figure 4 of B - B" of figure 2, figure 5 the schematic drawing of the coronary arteriographic catheter made of the medical soft equipment in its curved state and figure 6 the enlarged section schematic drawing of A - A", figure 7 of B - B" and figure 8 of C - C" of figure 5, figure 9 the schematic drawing of the coronary arteriographic catheter made of the medical soft equipment of figure 5 in its partially stretched state, figure 10 the enlarged section schematic drawing A - A", figure 11 of B - B" and figure 12 of C - C" of figure 9, figure 13 the schematic drawing of the coronary arteriographic catheter made of the medical soft equipment of figure 5 in its fully stretched state, figure 14 the enlarged section schematic drawing of A - A", figure 15 of B - B" and figure 16 of C - C" of figure 13 The method of controlling the curvature of the medical apparatus according to the present invention is carried out by using a pressure source, a pressure control device, a kind of fluid pressure-transmitting medium and a piece of medical soft equipment with at least one pressure control cavity 2, the inner pressure of which can be used to change the curvature of the equipment and controlled by the specific functional relationship between the curvature in the needed part of the medical soft equipment and the pressure inside the pressure control cavity 2, thus making the curvature suit each position in the cource that the medical soft equipment is inserted into the body. As this method of controlling is safe and reliable, easy to operate and to control, and therefore good for achieving better diagnostic and therapeutic results. Either a gas, a liquid or a gel-type substance shall be adopted as a pressure-transmitting medium, depending on the safty, the reliability as well as the need in the practical application. The curvature-controlling devices of said medical apparatus according to the present invention include a pressure source and other pressure-controlling devices, among which, a. the pressure source can be either a forcing pump, a spring plunger or any other pressure-generating instruments; b. the pressure-controlling devices can be either a pressure-adjusting volve, a spring adjuster or a fluidic control system. The intensity and adjusting range of the pressure depends on the needs of the medical soft equipment in use. As for the medical soft equipment with an endoscope, its air-supplied and water-supplied pumping system can be used as the pressure source. The soft tube 1 of the medical soft equipment as shown in fig.1, 2, 3 and 4 is a kind of thin-walled, hollow angle pipe or spiral tube with one end sealed and a oblate or oval crass section. Its hollow cavity can be used as pressure control cavity 2, or as both pressure control cavity 2 and function cavity. When the inside of the press control cavity 2 is in a state of being pressed, the soft tube 1 is tending to have a round cross section, and a tractive stress appears along the outer edge of the bending part of the soft tube 1 and along the inner edge an expansion stress results. With the increase of the pressure, the soft tube 1 is tending to stetch straight out. This method in controlling the curvature of the medical soft equipment can be used in the light of the Bourdon Tube Principle to exercise control over the pressure inside the pressure control cavity and the curvature in the needed part of the medical soft equipment in accordance with the following function relationship: Δα = K αp E f( A, B, t, R ) In the formula Δα stands for the point turning angle K, empirical constant determined by a certain number of model tests E, the elastic modulus of the material α, the bending angle of the whole medical soft equipment p, the pressure difference between the inner and the outer side of the pressure control cavity A and B stand respectively for the length of the major and the minor axis of the cross section t, the thickness of the wall R, the bending radius. In practical application, the shape of the cross section is determined by the real need, the requirement of the material and the size of the equipment. The medical soft equipment of the present invention as shown in fig. 1, 2, 3 and 4 is the embodiment of a curvature-controllable artificial cochlea electrode designed according to the above-mentioned principle. The soft tube 1 that constitutes the electrode is a hollow spiral tube with an oblate or oval cross section and one end sealed. The controlling of its curvature is realized by adjusting the pressure of the inner cavity, namely, the pressure control cavity 2. Before the artificial cochlea electrode being inserted into the scala tympani, the shape of its cross section is tending to be round and the tube straightened. At this moment, along either the major or the minor axis there exists sufficient rigidity that helps to guide the direction and insertion. When it gets into certain depth, by releasing the pressure inside the cavity (2) gradually, the tube shall become curved by degrees. If, in the entire process of insertion, an appropriate pressure controlling is exercised in making the electrode adapted to the curvature of the scala tympani as it is inserted into different depth, the tissue injury of the scala tympani made by the electrode can be reduced. By selecting the material and the sizes (A, B, t, R) properly, the mechanical requirement mentioned above can be easily met in controlling the curvature of the electrode by adjusting pressure. The soft tube 1 of the medical soft equipment as shown in fig. 5, 6, 7 and 8 is a one-end-sealed soft tube with an eccentric pressure control cavity 2 and a central function cavity 3. When the pressure control cavity 2 is in a state of being pressed ,the soft tube 1 is tending to be straightened. In the light of the principle as is shown in fig. 9, 10, 11 and 12, when a pressure P is exerted inside the pressure control cavity 2, an equivalent stress N=pF shall occur inside its normal plane (cross section area B). The equivalent stress shall, through the center of the soft tube 1, gain a bending moment M = Ne (e refers to eccentricity), which shall make the soft tube 1 being straightened. This method of controlling the curvature of the medical soft equipment is carried out by controlling the pressure inside the pressure control cavity 2 and the curvature in the needed part of the medical soft equipment in accordance with the following functional relationship: Δα = K αp E ( e R 0 - R - 1) In the formula Δα stands for the terminal turning angle K, empirical constant determined by a certain number of model tests E, the elastic modulus of the material α, the bending angle of the whole medical soft equipment P, the pressure difference between the inner and the outer side of the pressure control cavity, e, the eccentricity of the pressure control cavity R, the curvature radius of the curve formed by connecting the central points of the cross sections; R, the curvature radius of the neutral layer or the separating layer. In practical application, if the cross section of the eccentric pressure control cavity is in a fully round shape, its soft tube 1 needs higher controlling pressure to make itself straightened up than any other soft tube with either an oblate or oval cross section. Moreover, the round cross section takes more inner space of the medical soft equipment. Therefore, a combined application of the two above-mentioned methods shall reduce the controlling pressure and save the inner space of the equipemnt, thus bringing the advantages of the two into full display. The medical soft equipment as shown in figures from 5 - 16 are the embodiments of a kind of coronary arteriographic catheter designed through the combined application. Said medical soft equipment, before its pressure control cavity 2 is exerted with a pressure, is similar to Judkins' left coronary arteriographic catheter (as shown in fig. 5). In each position of either "B - B" or "C - C", there is a curved part, the cross sections of which are shown as fig. 7 and 8. In addition to the original cavity, namely, the function cavity 3, there is also a pressure control cavity molded or formed at its flank. As "A - A" is in the normal position, no curvature or curvature controlling there is needed and, therefore, the cross section of the pressure control cavity 2 at "A - A" is in small circle. When being put pressure on, only its axial regidity is increased, thus facilitating the inserting, the pushing as well as the rotating. As the cross section of the pressure control cavity at "B - B" is oblate or oval in shape and the ratio of its major axis to the minor axis is high, it is very sensitive to the controlled pressure and liable to be straightened at the bending part. As the cross section of the pressure control cavity 2 at "C - C" is also oblate in shape but the ratio of its major axis to the minor axis is lower than that at the position of "B - B", it wants higher controlled pressure to be stretched up. The highest pressure is needed at the beginning of the insertion as it is easy to insert or push when the whole soft tube 1 is straightened and the axial rigidity is increased. When it reaches the arcus aortae, the pressure shall be redused properly, thus restoring, first of all, the curve at the position of "C - C" while, at the position of "B - B", it is still kept straight under the pressure as it has a higher ratio of the major axis to the minor axis at the cross section of the pressure control cavity 2. At this moment, the tube of the medical soft equipment appears as Judkins' right coronary arteriographic catheter and therefore is easy to get through the arcus aortae and to be inserted into the right coronary artery. when it is in , the pressure shall be fully reduced to restore the function cavity 3 to its normal size, thus facilitatint the passing through of the radiographol. This method can also be applied in controlling the coronary balloon dilatation catheter to get into the narrow place by making use of the curvature of its front part. As the right coronary arteriography or the balloon dilatation is accomplished, the front part shall be withdraw to the root of the aorta. As the pressure is fully reduced and the curvature at the positions of "B - B" and "C - C" is fully restored, its shape is now similar to Judkins' left coronary arteriographic catheter, and thus the left coronary arteriography or balloon dilatation can be carried out in accordance with Judkins' method without the necessity of changing the medical soft equipment. Since the whole process is accomplished by changing the curvature of the medical soft equipment through the adjustment of the pressure and no replacement for the medical soft equipment is necessary, the method is therefore in possession of not only the advantages of the Sones' method in having less chance of suffering the complications such as hemorrhage and affection but also those of the Judkins' method as being easy to learn and to operate. The medical soft equipment and its means for controlling curvature of the present invention can be equally used for such catherters as pediatric cardiac catheters, PTCA balloon catheters, various kinds of dextrocardiac catheters and pacemaking catheters, renal arteriographic catheters, hepatic catheters used in intervenient therapy as well as catheters used in other vessels or body cavities in order to have an easier and safer operation, to reduce the pain and danger to the patient as well as to heighten the success rate and the curative effect. The medical soft equipment of the present invention in fig. 1, 2, 3 and 4 relates to the electrode of the artificial cochlea, the soft tube 1 of which contains a pressure control cavity 2 with oblate section, together with its various changes when under pressure control. The pressure control cavity can serve at the same time as the function cavity. Before the control cavity is brought under pressure in fig. 2 and 4, it has an oblate section and looks like a spiral. When the control cavity is brought under pressure as shown as shown in fig. 1 and 3, its section is getting round and the tubular body of the soft tube 1 or the electrode of the artificial cochlea is straightened. When the pressure inside the cavity is altered, the tubular body of the soft tube 1 will have different curvatures. The medical soft equipment of the present invention in fig. 5 - 8, 9 - 12 and 13 - 16 relates to the coronary arteriographic catheter, the soft tube (1) of which contains an eccentric pressure control cavity 2 and a central function cavity (3), together with its various changes when under pressure control. As the section "A - A" is in the normal segment of the soft tube and its pressure control cavity 2 is of smaller circle in shape, the section will remain basically the same when under different pressures. The section "B - B" is in the first bending segment and its pressure control cavity is oblate in shape. The section "C - C" is in the second bending segment and its pressure control cavity is also oblate, however its major axis and minor axis as well as their ratio are smaller than those of the section "B - B", thus demanding higher pressure, as compared with the section "A - A", to have a change of its shape and to straighten the second bending segment. The medical soft equipment shown in fig. 5 is in the shape of Judkins' left coronary arteriographic catheter and can be used for left coronary arteriography before its pressure control cavity 2 is exerted with a pressure ( P 0 = 0). When the pressure control cavity 2 is exerted with a pressure P 1 , the external form and the section of the medical soft equipment of the present invention are as shown in fig. 9, 10, 11 and 12. As the major axis of the pressure control cavity 2 of the section "B - B" in the first bending segment is longer than that of the section "C - C" in the second bending segment, the section "B - B" is easy to become round in shape under pressure P 1 . As a result that the section "B - B" in the first bending segment is easy to be straightened while the section "C - C" in the second segment is still in a curved state, the medical soft equipment is similar to Judkin's right coronary arteriographic catheter and can be used for right coronary arteriography. When the pressure control cavity 2 is exerted with a pressure P 2 (P 2 >P 1 ), the external form and the section of the medical soft equipment are as shown in fig. 13, 14, 15 and 16. The pressure control cavity 2 of the section "C - C" in the second bending segment is also tending to be round in shape under the pressure P 2 , thus making this part into a stretched state. As the first bending segment is in a more stretched state, the whole medical soft equipment is basically stretched and, with sufficient axial rigidity, easy to be inserted in or pass through the aorta. The present invention, as compared with the prior art, possesses the following merits: (1). The medical soft equipment takes little space. As its pressure source and pressure control devices are all extracorporeal, the size of the equipment to be inserted into the body is greatly reduced, thus miniaturizing the medical soft equipment of which the curvature needs to be controlled. To be more important, it is also possible to have curvature controlling for those pieces of medical soft equipment that were curvature-uncontrollable and used only with high operative skills, thus reducing the suffering of the patient with less serious complications such as tissure injury, hemorrhage, thrombiembolism, perforating organ, severe arrhythemia or even sudden death, and possessing distinct safety and reliability. (2). The medical soft equipment is simple and reliable in structure. As only one or more pressure control cavity is added to the medical soft equipment in order to control the curvature of the needed part, as there is no movable components or complicated structure inside the medical soft equipment, there is no worry of damage or maintenance. (3). The medical soft equipemnt is likely to find a wide application. As the pressure source and pressure controlling can be provided fully based on the existing technical condition, as the equipment is easy and flexible to operate, it demands no high skill from the manipulator. (4). As the cost is not high, it facilitates batch production.

Claims: Bendable medical apparatus as a catheter, endoscope or the like, comprising a soft flexible tube (1) and at least one pressure control cavity (2) within said tube (1) which cavity (2) being connectable to a pressure source in order to create a pressure difference between the pressure within said cavity (2) and outside said tube (1) by means of a pressure fluid within said cavity (2) extending longitudinally along the flexible tube (1) between a closed distal end and an open proximal end connected to said pressure source, characterized in that the cross-section, the elastic modulus of the material and the thickness of the wall of said tube (1) is selected so that by controlled increasing and decreasing, respectively, the pressure of the fluid within said pressure control cavity (2) the curvature of said tube (1) along said cavity (2) changes in such a way that said tube (1) or at least a part of it is substantially straightly stretched (fig. 1) and the cross-section of said pressure control cavity (2) tends to be round if it is under higher inner pressure, but is curved (fig. 2) and the cross-section of said pressure control cavity (2) tends to be oblate or oval if it is not under higher inner pressure compared with the pressure outside said cavity (2). Apparatus as claimed in claim 1, characterized in that said soft tube (1) is a thin-walled, hollow, bent or spirally formed tube with one end sealed comprising a cavity with an oblate or oval cross-section, which cavity forms said pressure control cavity (2) and is used also as a function cavity, and that said cross-section tends to get a round cross-section, it the inside of said cavity (2) is under pressure. Apparatus as claimed in claim 1, characterized in that said soft tube (1) is a one-end-sealed tube with a central function cavity (3) and with at least one eccentric pressure control cavity (2) eccentrically located with respect to said function cavity (3). Apparatus as claimed in one of the preceding claims characterized in that said soft tube (1) comprises two or more pressure control cavities (2), which are separated by a neutral or separating layer between them in such a manner that, if the pressure inside the pressure control cavities (2) is in an unbalanced state, the soft tube (1) tends to bend or curve to the side of lower pressure. Catheter comprising an apparatus as claimed in one of the preceding claims. Artificial cochlea electrode comprising an apparatus as claimed in one of the preceding claims.

Inventors: HAOJUN LEE, HAOJUN, LEE
Applicants: HAOJUN LEE, HAOJUN, LEE
Application year: 1991
Main classification: A61M25
IPC codes: A61M25