Abstract:
The invention relates to an applicator for sensors to be used in medicine, which serves to screw in a sensor in the skin of a living organism, specially in a non-observable area, e.g. the head skin of a child in the womb. In this respect the torque while screwing the sensors into the tissue of the patient is limited to least to a maximum, while ensuring at the same time that the torque is kept to an indispensable minimum. The applicant ( 1 ) interacts with a torque limiter ( 5 ) and comprises a device that makes it possible to detect the threshold value of the torque limiter.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an applicator for sensors used in the field of medicine. 
     2. Description of the Related Art 
     In the field of medicine it is known to insert sensors, especially spiral sensors, into the skin of the patient by rotation, i.e., to screw a spiral sensor with its usually very sharp front end into the skin of the patient in a spiral type motion consisting of application-pressure and torque. 
     This is the case for example with the wide-spread fetal scalp electrodes which are used to anchor a sensor in the scalp of an unborn child in order to measure the ECG of the unborn child after membranes are ruptured. 
     Optical sensors can be housed in the tip of such spiral sensors, too, for example for fetal pulse oximetry, with the help of which a direct monitoring of the oxygen saturation in the blood of the unborn child can be established. 
     Such a sensor is disclosed in the DE-C 3810 008. C1 
     Since the spiral sensors are applied at a location which is out of view, that is to say behind the vagina of the mother within the uterus, it is a problem for the user to apply these spiral sensors with the correct amount of torque. If too much of a torque is applied, injuries of the fetal scalp are possible as well as a damage of the sensor and the applicator respectively or the perfusion at the site of the application can be restricted by too high an axial pressure of the sensor relative to the patient. 
     If too small of a torque is applied, the sensor is only poorly anchored in the skin of the patient and it comes loose due to the dynamic stresses occurring during the delivery and the vaginal examinations during the delivery respectively. Moreover too weak an application results in distortions of the signals derived from the sensor. 
     The application of the correct torque gets even more difficult because the sensor is located at the front end of a thin, long plastic rod or plastic tube respectively and because the user is able to turn only the rear end of this rod-like applicator. With a 20 cm long but just 2 or 3 mm thick rod the bending and the torsion of this rod-like applicator limits the user&#39;s feeling for the correct torque. 
     It is therefor the object of the present invention to provide an applicator which limits the torque during the insertion of the sensor into the tissue of the patient at least in respect to a maximal torque on the one hand, but on the other hand guarantees a necessary minimal torque during the application as well. 
     Thus the minimal torque guaranteed by the torque limiter may coincide with maximal torque to form a threshold value, that is to say, the very threshold value at which the torque limiter slips. 
     SUMMARY OF THE INVENTION 
     By providing the torque limiter in or on the applicator it is guaranteed that during the insertion no torque higher than the one the torque limiter is adjusted to can be applied. 
     In addition it is important that there is a perceptibility of the slipping through phenomenon of the torque limiter, that is to say, a device that allows to see the slip through phenomenon or at least to sense it with the operating hand. 
     A torque limiter of this type can be set to both a maximum and a minimum torque so that the torque limitation towards the minimal value avoids too soft an application and thus likewise too poor a fixation of the sensor in the tissue of the patient. 
     An especially simple embodiment of a torque limiter is represented by a sliding clutch which can be either mechanical, i.e. a force fitting or form-fitting operating by friction, as well as a magnetic, especially an electromagnetic, sliding clutch. The upper and lower limits of the torque can be easily adjusted, easily controlled and can be quickly deactivated in an easy manner too, by electrically influencing the magnetic forces of the sliding clutch. 
     At a first glance it would seem to be useful to position the torque limiter, for example the sliding clutch, as close as possible to the sensor, that is to say, at the front or the sensor end of the applicator, between the applicator and the sensor, in order to exclude the influence of the twistable applicator on the torque applied to the patient. 
     The drawback of this solution lies in the fact that the torque limiter is, during the fetal application, within the maternal body and thus under the influence of body fluids and mechanical pressure of the surrounding vagina, which could undesirably influence the function of the torque limiter. 
     If the torque limiter is positioned at the rear handling end of the applicator rod which is positioned outside of the body of the mother during the application, those interfering influences by body fluids and so on are avoided. In order to avoid a disturbance on the torque at the sensor caused by the twistable applicator rod which is positioned between torque limiter and sensor, the maximal torque applicable by the torque limiter must be lower than the torque by which the applicator rod collapses. A slight torsion of the applicator rod is harmless, since this torsion just causes an angle deviation between the handling end and the sensor end of the applicator rod but does not change the level of the torque having an influence on the patient, as long as this torque is the maximal applicable torque to which the torque limiter is preadjusted. 
     Such a fixed, preadjusted torque based on the torque limitation has a variety of advantages: 
     The evaluating devices linked to the sensor provide meaningful values since both the electric and the optic coupling to the tissue is more reliable, the influence on tissue perfusion of the patient remains minimal, its tissue physiology remains undisturbed and the traumatization of the tissue remains minimal. In addition the probability of tissue injuries of the patient becomes minimal so that all this can be used as a legal argument during a dispute with the patient since this torque limiter excludes the application of too high a torque and at the same time too low a torque. Further, the destruction of the sensor due to overstraining is avoided as well as a need for a reapplication after a too superficial fixation due to too small an application-torque. Also, less experienced users can feel safe beginning with the first experience with application. 
     When positioning the torque limiter in the handle of the applicator, especially a mating with a handle end is recommended since it can be disconnected from the single-use-applicator and is reusable. 
     Also the torque limiter can be positioned at the transition between the applicator rod and the grip part or between two parts of the handling part which are moveable relative to each other that is to say the applicator flange to which the handling end of the applicator rod can be attached and the handle which the user holds in his hand. 
     Further it is important, that the handle has a diameter which resembles the common applicators without a torque limiter attached thereto, in order not to change the accustomed subjective feeling for the torque to which the torque limiter is preset by a different handle diameter. This may cause the users to lose confidence in the torque limiter. 
     If the torque limiter is positioned at the front end of the applicator i.e. for example between the applicator rod and the sensor, then due to the single use concept of the applicator just a mechanically simple, easily and inexpensively producible form can be considered. This could be for example a concept where the front end of the applicator and the part which directly carries the sensor interact as a mechanical sliding clutch so that one of the parts has a non-round exterior shape, e.g. an ellipse or a polygonal shape, and is surrounded by another part which has an analog interior shape. 
     If one of the components, especially the surrounding component, shows a relatively high material-elasticity, and if there is enough play between the inner and outer outlines, the inner part will slip through relative to the exterior part at a maximum applicable torque, which creates the maximum torque limitation. After the application of this maximal torque the applicator rod is removed as usual, so that just the sensor and the cable leading to and from the sensor remain on the patient. 
     To position a magnetic sliding clutch within the one way item, that is to say between applicator and sensor would be too costly. 
     Such a solution however is feasible in the form of a reusable item, which is made of a stable metal in contrast to the applicator which usually consist of plastic. At the applicator flange of the handling part, the rear handling end of the applicator rod can be quickly and easily attached by engagement, attachment with a setscrew, etc. The handling part consists of two components, movable relative to each other, which house a sliding clutch between themselves. 
     This sliding clutch can be of the formerly described type or of a more sophisticated mechanical sliding clutch comprising springloaded engaging parts, or a magnetic or electromagnetic sliding clutch respectively. 
     In a magnetic sliding clutch the engaging magnets can be positioned at the opposing areas of the applicator flange that is to say, of the handle. If all magnets of one part are positioned so that they oppose with their e.g. positive ends versus the other part and the magnets of the other part are mounted in reverse, then the applicator flange and the handling part will have a minimum distance relative to each other due to the attracting power of the magnets, that is to say the user, who additionally needs to push in an axial direction (during the application), applies this axial pressure directly onto the patient&#39;s tissue, without thereby initially reducing a functional distance between the parts of the sliding clutch. 
     When positioning the magnets with opposing directed faces, a well defined distance between these facing areas must be set, making use of a spacer-disc, which is e.g. made of plastic, in order to adjust the attraction power for mass production of the handling part, since the attraction power greatly varies with distance changes of the magnets, which determine the maximal achievable torque. 
     This problem does not exist if the magnets are housed in areas radially opposite to each other, one area belonging to the applicator flange, the other area belonging to the handle, and these components are positioned next to each other in order to maintain the same radial distance relative to each other. 
     Such a magnetic sliding clutch provides a torque limitation avoiding maximal torque forces. If electromagnets are used as the magnets, the maximum transmittable torque can be adjusted. If with such a magnetic solution an additional minimal torque is to be provided, this can be achieved for example with a friction between the two components of the sliding clutch which needs to be overcome, as long as there is no magnetic flow during the rotation of the components of the sliding clutch relative to each other. This for example is possible if just one or only very few pairs of magnets are positioned along the circumference of the sliding clutch, so that there is no magnetic interaction in the area in between, but just the mechanic friction between the two components of the sliding clutch. Due to the axial pretension between the two components this sliding clutch can provide a torque limitation towards the minimal values. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment according to the invention is described hereinafter in greater detail with reference to the drawings. In the following 
     FIG.  1 A: shows a side view of an applicator with a magnetic sliding clutch and 
     FIG.  1 B: shows a tip view of an applicator with a magnetic sliding clutch 
     FIG.  2 A: shows a side view of an applicator with a mechanic sliding clutch 
     FIG.  2 B: shows a top view of an applicator with a mechanic sliding clutch 
     FIG.  3 : shows a side view of longitudinal section through a mechanical sliding clutch, and 
     FIG. 4 shows a longitudinal cross section through a sliding clutch along the lines IV—IV according to FIG. 3 
     FIG.  5 : shows a longitudinal cross section through a sliding clutch along the lines IV-VI according to FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1A shows an applicator  1 , which includes a very long and slender applicator rod  17  slidable within protective tube  21  which at the back or hand manipulation end  4  exhibits a widening or thickening, with which the applicator rod  17  is fixable by means of clamping screw  18  as well as rotatably fixed in a corresponding face recess of a manipulation part  6 , which contains the torque limiter  5 . 
     At the front free end, the sensor end  3 , there is seated in the applicator rod  17  the sensor  2 , which has the shape of a rotating spiral with a very pointed, sharpened end. With this tip the spiral shaped sensor  2  can be screwed into for example the scalp of an unborn child. 
     The hand manipulation part  6  is comprised besides the applicator flange  7 , in which the hand manipulation end  4  of the applicator rod  17  is received, of a hand grip part  8 , which the user holds in his hand. The applicator flange  7  exhibits towards the back, on the side facing away from the applicator rod  17  an outward projecting extension  19  with round cross-section, upon which the hand grip part  8  by means of a corresponding central blind hole is seated and rotatably mounted. 
     With the help of a pretensioning adjuster  14  in the form of a central screw the axial pretensioning between the applicator flange  7  and the hand grip part  8  can supplementally be influenced from the back side of the hand grip part  8  through this into the projection  19  of the applicator flange  7 . 
     In the right half of FIG. 1, there are positioned—radial outside the projection  19 —the applicator flange  7  and the hand grip part  8  with surfaces facing against each other, wherein magnets  15   a ,  15   b  are oriented against each other upon these opposing lying faces. As FIG. 1 b  shows, there are herein on each of the faces in 90° separation four such magnets  15   a  or as the case may be  15   b  provided, this so that the two oppositely directed magnets respectively attract each other. 
     Between the applicator flange  7  and the hand grip part  8 , which in this mode and manner are axially drawn towards each other to contact, a spacer ring  16  is interposed. The thickness of this spacer ring  16  determines in the attracting magnet pairs  15   a ,  15   b  their respective magnetic attraction force, which at a different separation between the magnets  15   a  and  15   b  likewise strongly would vary. 
     If one would securely hold the applicator flange  7 , and rotate the hand grip part  8 , so a predetermined force is necessary in order to rotate a particular magnet  15   a  past a initially oppositely lying magnet  15   b  and to overcome the therebetween existing magnetic attraction force, whereupon the rotated magnet  15   b  will position itself opposite to the next magnet  15   a  in the rotation direction. 
     When for screwing in of the sensor  2  in the tissue of the patient the user no longer takes the applicator rod  17 , but rather exclusively the hand grip part  8  of the hand manipulator part  6  and turns, it is insured, that the sensor  2  never is screwed in with greater torque than is necessary for slipping past the rotation moment limiter  5 , that is, for relative turning of the magnet  15   b  with respect to the magnets  15   a.    
     If one supplementally employs the applicator  1  so that the user is instructed to rotate the hand grip part  8  at least so far, until at least one relative rotation between the magnets  15   a  and  15   b  has occurred, so it is further insured, that the sensor  2  is screwed in with a torque, which corresponds at least to that torque necessary for the overcoming of the magnetic forces. 
     In this case the minimal exercised torque corresponds at the same time to the maximal exercised torque. 
     In the left half of FIG. 1, in contrast to the right figure half, the magnets  15   a  and  15   b  are positioned radially opposing. For this purpose one magnet  15   a  is provided along the outer circumference of the hand grip part  8  and the outer circumference of which lies opposite to an inner circumference of an at the back end face side cartridge like bored out applicator flange  7 , in which the opposing magnets  15   a  are provided with the same positioning over the circumference. 
     Since the grip part  8  is mounted rotatably with small as possible slack or play on the projection  19  of the applicator flange  7 , the magnets  15   a  and  15   b  always assume the same radial separation from each other, so that the employment of a spacer disk  16 , which with respect to its thickness is essential in the right half of FIG. 1 a , is not required, and therewith also the wearing out thereof results in no changes in the effective torque. However in the case of the embodiment shown in the left half of the figure, the production expenditure for the hand manipulation part  6  is greater. 
     FIG. 2A shows in comparison a mechanical variant of the slip clutch, which serves as torque limiter  5 . 
     In contrast, the hand manipulation part  6  is comprised of a flange applicator  7  and a hand grip part  8  mounted rotatably with respect thereto upon the end projection  19 . 
     Herein the design of the applicator flange  7  as well as the securing of the applicator rod  17  as well also the mounting of the hand grip part  18  with respect to the applicator flange corresponds overall with the solution according to FIG.  1 . 
     The hand grip part  8  serves herein as base part  9  of a slip clutch, while the applicator flange  7  functions as counterpart  12  of the slip clutch. In the base part  9  detent or engagement bodies  10 , for example balls, are pre-tensioned in corresponding recesses by means of respectively a spring  11  in the direction away from the base part, so that the detent or engagement bodies  10  project out from the base part  9 , in the axial direction shown in FIG.  2 . In the oppositely lying face of the counterpart  12  there are formed recesses  13 , in which the engagement bodies  10  partially penetrate into and there form fittingly lock. The direct axial separation between the base part  9  and the counter part  12  is again maintained by an axial working pre-tensioning disk  14 , as in FIG. 1 an axially screwed in screw, since without this the spring  11  of the locking body  10  would push the base part  9  and the counterpart  12  apart from each other. 
     Radially outside of the locking part  10  a spacer ring  16  is introduced between the base part  9  and the counterpart  12  and with the help of a pre-tensioning disk  14  is somewhat clamped. 
     In order to rotate the base part and the counterpart  12 , that is, the hand grip part  8  and the flange applicator  7 , relative to each other, the forces of the springs  11  must be overcome, which produces the maximal rotational torque limitation. 
     When, as shown in FIG. 2 b , over the circumference only two such engagements are provided, then the torque to be brought to bear in the rotation area between the two engagement parts corresponds only to the friction between the hand grip part  8  and the flange applicator  7 , that is, the sliding rubbing between the spacer ring  16  and the friction with respect to the engagement part  10 . This engagement resistance represents the minimal rotational torque limitation by screwing of the pre-tensioning adjuster  14  the distance ring  16  is wedged more strongly between the two adjacent parts and therewith the friction is increased, whereby also the minimal necessary torque for screwing in of the sensor  2  is increased. 
     The force for overcoming the locking and therewith the maximal possible torque to be brought to bear is not necessarily increased thereby, when the spring characteristic of the spring  11  is so selected, that small axial changes of base part  9  and counterpart  12  do not bring about an increase in the axial pressure force upon the engagement part  10  as consequence. Of course, the form fittingness of the engagement part  10  and the engagement recesses  13  must be so selected, that for overcoming this engagement or locking necessary forces basically lie higher than the pure rubbing frictional forces on the basis of the friction between the spacer ring  16  and the engagement part  10 . 
     FIGS. 3-5 show a further variant of a mechanical slip clutch, which without moving parts essentially is based upon material elasticity. 
     FIG. 3 shows a longitudinal section through such a slip clutch, which is comprised of a base part  9  and a counterpart  12 . Therein there can again—as already discussed on the basis of FIG. 2 a —base part  9  and counterpart  12  of the applicator flange  7  or as the case may be the hand grip part  8 , or also reversed, form the hand manipulation part  6  which carries the applicator  1 . 
     FIG. 3 shows, that one of the parts, for example the counterpart  12 , exhibits an in axial direction running projection  19 , which exhibits a changing cross-section, namely from its base at the counterpart  12  is relatively small and continuously increases in cross-section towards the free end. 
     The cross-section of the projection  19  is elliptic, and this with a larger diameter “a” and small diameter “e” at the position of the larger cross-section, that is at the free end of the projection  19 , which is shown in the sectional representation V—V in FIG.  3  and in FIG.  5 . At the juncture of the projection  19  on the counterpart  12  the larger diameter with “c” is significantly smaller than at the free end indicated with “a” which is shown in the sectional representation IV—IV in FIG.  3  and in FIG.  4 . 
     The counterpart  12  is seated with this projection  19  in a recess  22  in the base part  9 , which exhibits an analogous, however in cross-section larger inner contour and a depth, which is somewhat larger than the axial length of the projection  19 . 
     Since additionally the largest cross-section of the projection  19  on its free end is slightly smaller than the smallest cross-section of the recess  22 , which is situated at the opening  23  side facing the counterpart  12 , the projection  19  can, in the correct rotation position or orientation, be completely introduced into the recess  22 , so that the base part  9  and the counterpart  12  at their faces lie planar against each other. The cross-section of the recess  22  is therein so selected, that in this into each other assembled condition the smallest diameter “g” of the elliptic recess  22  is smaller than the largest diameter “a” of the elliptic post  19  at the same axial position. 
     When the cross-section of the projection  19  changes in the axial course just as fast as the cross-section of the recess  22 , that is their flanks have the same pitch with respect to the axial longitudinal direction, then this condition is valid for the entire length of the projection  19 , and not only at the free end as shown in FIG.  5 . 
     A relative turning about the longitudinal direction between base part  9  and counterpart  12  about 90° or more is thereby only possible, when by material elasticity of either the larger diameter of the projection  19  and/or the smaller diameter of the surrounding inner contour of the recess  22  can be so deformed, that a slipping through of the two parts with respect to each other is possible. 
     Therewith besides the material elasticity of the projection  19  of the counterpart  12  or, as the case may be, the base part  9 , also the size differential between the larger diameter of the projection  19  and the at the same position existing smaller diameter of the elliptic cross-section of the recess  22  determine or dictate the force, which is necessary for turning through of this form locking or form engaging mechanical slip clutch.