Title:
ARTERIAL DILATION DEVICE
United States Patent 3557794
Abstract:
An improved catheter is disclosed in which the length of the active portion of the instrument is divided longitudinally into four or more beams, preferably of rectangular cross section. The beams are constituted of spring steel and are held between two abutments on the catheter, one of which is adapted to be retracted toward the other by an actuator wire controlled by a micrometer screw. The beams are positioned independently of one another and normally rest snugly about a metal tubing so that when the abutment is caused to move the compressive force causes the beams to flex outwardly except at their ends since the tubing prevents any movement inwardly. The beams therefore execute a smooth flexing effect and define an enlarged outline which, when contained in a blood vessel, artery, etc., causes a dilation of that member. When the pull in the actuator wire is released at the micrometer screw, the beams spring back into their normal rest position to allow ready retraction of the catheter. A standard form of strain gage using the Wheatstone Bridge principle may be applied to the actuator wire to determine the counterforce exerted by the blood vessel against the deployment of the dilator.
US Patent References:
SURGICAL EXPANDING ARM DILATOR
Hines - June 1970 - 3517128
Surgical drain
Innes - June 1932 - 1863057
Catheter
Wallace - August 1953 - 2649092
Teat bistoury with expansible cutter knives
Hoffman - January 1956 - 2730101
Cylindrical strain gauge
Shipley - March 1961 - 2976865
SURGICAL EXPANDING ARM DILATOR
Hines - June 1970 - 3517128
Surgical drain
Innes - June 1932 - 1863057
Catheter
Wallace - August 1953 - 2649092
Teat bistoury with expansible cutter knives
Hoffman - January 1956 - 2730101
Cylindrical strain gauge
Shipley - March 1961 - 2976865
Application Number:
04/748737
Publication Date:
01/26/1971
Filing Date:
07/30/1968
View Patent Images:
Export Citation:
Primary Class:
International Classes:
A61M29/00; A61B17/22; A61M29/00
Field of Search:
128/341,345,348--350,305,304,242--244
Primary Examiner:
Truluck, Dalton L.
Claims:
I claim
1. A catheter comprising an elongated tubular device having an end portion adapted to be inserted into a vessel of the body and a base portion adapted to be grasped by the hand, an actuating wire extending along the axis of said tubular device from said end to the base portion and having a rounded terminal member tightly fitted thereto at the insertable end, a tubing loosely surrounding said wire and extending between the rounded member and the base portion of the device, cylindrical ferrules spaced from and surrounding said actuating wire and tubing at the insertable end of the device and at the base portion, leaving annular spaces therebetween, the ferrule at the insertable end being affixed to said rounded member and movable lengthwise of the tubular device when a pull is exerted on the actuating wire, the ferrule at the base portion of the device being stationary with respect to said portion, and a plurality of flexure beams having their ends detachably and slidably positioned respectively within the spaces between the ferrules and the actuating wire, the intermediate portions of said beams normally resting on said tubing, whereby when a pull is exerted on said wire, the movable ferrule moves toward the stationary ferrule and the flexure beams are caused to bow outwardly from said tubing so as to expand the blood vessel in which the catheter is inserted.
2. A catheter according to claim 1 and in which said beams are constituted of rectangularly shaped beams arranged in a circular outline, said ferrules having slots at their inside surfaces extending radially outward for slidable receiving the ends of the beams, said slots being of a shape and size as snugly but detachably to hold the beams in position.
3. A catheter according to claim 1 and means for measuring the strain in the actuator wire to determine the counter-force that the vessel exerts against the deployment of the dilating device.
4. A catheter according to claim 3, said means comprising a normally balanced Wheatstone Bridge device in which one of the resistance arms is secured to the actuator wire to partake of the strain imparted to the wire for measurement by said device.
1. A catheter comprising an elongated tubular device having an end portion adapted to be inserted into a vessel of the body and a base portion adapted to be grasped by the hand, an actuating wire extending along the axis of said tubular device from said end to the base portion and having a rounded terminal member tightly fitted thereto at the insertable end, a tubing loosely surrounding said wire and extending between the rounded member and the base portion of the device, cylindrical ferrules spaced from and surrounding said actuating wire and tubing at the insertable end of the device and at the base portion, leaving annular spaces therebetween, the ferrule at the insertable end being affixed to said rounded member and movable lengthwise of the tubular device when a pull is exerted on the actuating wire, the ferrule at the base portion of the device being stationary with respect to said portion, and a plurality of flexure beams having their ends detachably and slidably positioned respectively within the spaces between the ferrules and the actuating wire, the intermediate portions of said beams normally resting on said tubing, whereby when a pull is exerted on said wire, the movable ferrule moves toward the stationary ferrule and the flexure beams are caused to bow outwardly from said tubing so as to expand the blood vessel in which the catheter is inserted.
2. A catheter according to claim 1 and in which said beams are constituted of rectangularly shaped beams arranged in a circular outline, said ferrules having slots at their inside surfaces extending radially outward for slidable receiving the ends of the beams, said slots being of a shape and size as snugly but detachably to hold the beams in position.
3. A catheter according to claim 1 and means for measuring the strain in the actuator wire to determine the counter-force that the vessel exerts against the deployment of the dilating device.
4. A catheter according to claim 3, said means comprising a normally balanced Wheatstone Bridge device in which one of the resistance arms is secured to the actuator wire to partake of the strain imparted to the wire for measurement by said device.
Description:
BACKGROUND OF THE INVENTION
In medical research relating to cardiovascular physiology, it is occasionally desirable to positively position or stabilize some device within the lumen of a blood vessel or to dilate the vessel by mechanical means. Catheters of various sizes are generally employed for this purpose. For dilating the blood vessels it has been customary to attach to the catheter, and operated from an exterior position, an "umbrella" type of mechanism or to employ the spring force stored in compressed wire fingers. However, several problems arise in connection with the construction of extremely small linkage mechanisms when it is considered that catheters of this type are hardly ever greater than one-eighth of an inch in diameter and the linkage would necessarily have to fit within the confines of this diminutive member. In those cases where the compressive forces are used for causing a dilation effect in the arterial system, high bending stresses are encountered which demand close control of the temper in the spring materials. Furthermore, the retraction of an expanded unit of the finger spring type, once it had been deployed in a vessel, it was often difficult to compress it to its normal size from the enlarged condition preparatory to being withdrawn from the body. Moreover, catheters of the type mentioned, when in a dilated form, may not always define a symmetrical body, and therefore it becomes difficult to center themselves within the artery being dilated. The lop-sided position of the forward end of the catheter may actually cause damage to the tissue and, in aggravated cases, sever pain to the patient.
SUMMARY OF THE INVENTION
One object of the invention is to provide an improved form of catheter of such diameter as to be useful in human as well as animal work and will align itself with the axis of the vessel to ensure positive position.
Another object is to provide a catheter of the type mentioned and in which the member can be mechanically dilated up to at least 2 centimeters without the use of linkage or spring force stored in compressed wire fingers.
Still another object is to provide an improved catheter in which, having been dilated, the member can be easily compressed and withdrawn from the body without the slightest complication.
The final object is to provide a catheter structure which lends itself to the use of ancillary apparatus which would enable the doctor to measure the amount of dilation remotely or to measure the forces related to the dilation.
Other objects and features will be apparent as the following description and the accompanying drawing are perused in connection with the improved invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 represents a longitudinal section, greatly enlarged of the improved catheter, portions of which are shown in elevation for clearness and together with certain ancillary apparatus shown partly by diagram and partly in elevation;
FIG. 2 is a view similar to FIG. 1 but showing the improved catheter in expanded form for dilating a blood vessel. All of the ancillary apparatus are shown in elevation; and
FIG. 3 represents a view taken at about the two lines 3-3 in FIG. 1 and looking in the direction of the arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, reference character 1 designates a length of standard No. 8 X-ray catheter material of about one-eighth of an inch diameter and constructed usually of surgical stainless steel. There is a proximal fitting 2 of similar material at the base portion of the catheter and secured thereto in any suitable and well known manner, for example, by a proper metal-to-metal cement. This fitting comprises a collar portion having a stem 3 which fits snugly within the interior of the catheter piece 1. The fitting has a central opening 4 for slidably receiving an actuator wire 5. The latter preferably is constituted of music wire of special steel, approximately .013 inch diameter and the purpose of which will be explained hereinafter.
Next to the fitting 2 there is a metal ferrule 6 of about the same size as the fitting and it is secured to the latter in any suitable and well known manner. The ferrule is relatively thick and has an opening 7 (FIG. 3) larger than that of the fitting 2 and this opening is provided with a plurality of square shaped milled out slots 8 spaced equidistantly apart. The slots have a bottom surface which is curved outwardly as indicated at 9 (FIG. 1) for reasons which will be apparent hereinafter. These slots have a width and depth of such dimensions as to provide a close slip fit with the left-hand end of the flexure beams 10. The latter are of rectangular shape, preferably greater in width than in thickness, as seen in FIG. 3, and are constituted of stainless spring steel of highest surgical quality.
At the other or distal end of the catheter, there is a ferrule 11 similar to the member 6 and having an opening 7 (FIG. 3) through which the right-hand end of the actuator wire 5 passes. This ferrule, like its left-hand counterpart, is provided with four slots 8, having bases which are rounded upwardly and outwardly as indicated at 9; quite similar to those shown and described hereinbefore. These slots are of such size as to provide a close slip fit with the right-hand tips of the flexure beams 10. The end of the catheter which is inserted into the body, blood vessel, or other body cavity, terminates in a cylindrical member 12 of the same diametral size as the ferrule 11 but of greater length. This distal fitting has a hemispherical end 13 and is provided with a central opening which tightly receives the right-hand end of the actuator wire 5. The latter is rigidly secured in any suitable manner to the member so that there is not the slightest movement therebetween, regardless of the stresses or stains imposed upon the actuator wire. The member 12 can be made of surgical stainless steel or of a plastic material such as that sold under the names "Teflon" or "Nylon." The ferrule 11 is cemented or otherwise secured to the member 12. A tube composed of a length of hypodermic needle tubing of surgical stainless steel is employed within the body of the catheter; this tubing being cut to a length of approximately 5 mm less than the distance between the inside surface of the fitting 2 and the cylindrical member 12. The opening is the tubing is slightly larger than the diameter of the actuator wire 5 so as to permit a sliding fit. The outside diameter of the tubing is somewhat less than the distance between the inside surfaces of the opposite pairs of the beams 10. The purpose of the tubing will be explained hereinafter.
The dilator assembly is built up as follows: first, the proximal fitting 1 is installed in the distal end of the standard X-ray catheter. Next, the actuator wire (.013 diameter) is fed through the lumen of the catheter. The limiting tube 14 is next slipped over the actuator wire and the beam ferrules 6, 11 are placed in position with their curved inside edges 9 facing one another. Next, the distal fitting 12 is secured to the end of the actuator wire and held in this position in any suitable and well known manner. It will be noted that the end view of the distal fitting 12 and the ferrule 11 is approximately the same as the view of the proximal fitting 2 and the ferrule 6 as shown by the fact that the viewing line 3-3 may be applied to both portions.
When the ferrules are pressed in place or otherwise secured to the proximal and distal fittings, the flexure beams 10 are next fitted into the beam pockets in each fitting formed by the milled out slots referred to hereinbefore. These beams are held within the slots solely by friction since the slots have been cut snugly to receive the ends of the beams, Suitable dimensions for the beams, of which there are four, and made of spring steel, are .010 inch (.025 mm.) in thickness and .020 inch to .030 inch (.508 mm. to .562 mm.) in width. The four beams have a length that they can be gently flexed and inserted into the beam pocket in each ferrule. This completes the basic assembly.
At the operator end of the catheter, the amount of deployment of the beams 10 may be controlled by attaching to the end of the actuator wire 5 an enlarged member or lug 15 of rectangular cross section which is attached freely to slide within a rectangular opening 16. The latter is formed in a circular web element 17, secured at its periphery to the interior surface of the base portion of the catheter designated at 1. The purpose of the member 15, slidably contained within the web member 17, is to prevent rotation of the actuator wire while it is being pulled or released to dilate or compress the beams 10. In order to apply a pulling or releasing effort to the wire, and particularly in view of the diminutiveness of the wire, it may be desirable to attach a second enlarged member 18 to the wire and of circular configuration. This member carries fine threads on its periphery. An apertured drum 19, threaded along its bore and having a micrometer scale 20 engages the threads of the enlargement 18 and is caused to press lightly against the square or cut end of the base portion of the catheter when being operated. By rotating the drum in one direction or the other, according to the scale on the drum, a pulling or releasing effect can be applied to the actuator wire for purposes explained hereinafter. An indexing pointer 21 is secured as by screw 22 to the catheter in order to show the amount of rotation and, therefore, the amount of longitudinal movement of the actuator wire.
To operate the device within a blood vessel, the actuator wire is pulled by turning the micrometer drum 19 so that the distal fitting 11 approaches the proximal fitting 2, thus decreasing the distance between the assembly 11, 12 and assembly 2, 6. The pull on the wire subjects the flexure beams to a coaxial compressive stress. The limiting tube 14 prevents the beams from flexing inwardly and limits the amount of shortening possible between the movable ferrule 11 and the stationary ferrule 6. Since the slender beams are restrained from flexing inwardly they will, under the axial compressive stress, bow outwardly, as seen in FIG. 2 to provide a structure which dilates the vessel to the degree desired. This bulging effect or dilation is indicated in FIG. 2 and can be as much as 2 centimeters or more. The deployed diameter may of course be controlled by varying the dimensions of the assembly. It will be noted that the lack of a rigid (i.e. soldered) connection at each beam end and the curved ferrule contour (indicated at 9) and the close slip fit of the fitting assemblies allow both sliding and bending to occur at the beam surfaces, thereby relieving the high bending stresses which could be incurred with a rigid joint. It is also apparent that the 2:1 or 3:1 width/thickness ratio of the beams also prevents the torsional bending and lateral displacements which might be encountered with beams of circular cross section. The amount of deployment of the beams 10 may be readily determined by the final micrometer setting at the dial 20 which previously had been calibrated.
In order to compress the beams 10 to their original position of resting against the periphery of the tubing 14, it is merely necessary to turn the micrometer head in the direction opposite from that when obtaining dilation. The ferrule 11, together with its terminating head 12, will then move to the right under the urge of the spring effect left in the beams so that the latter will again compress to coincide over their entire length with their original position preparatory to retraction from the vessel.
In applications in which it is desirable to measure the counter-force exerted by the blood vessel against the deployment of the dilator, a sensitive strain gage of any suitable and well known type can be applied to the actuator wire when the beams 10 are under dilation. A Wheatstone Bridge arrangement indicated generally at 23 may be used to advantage in which one of the resistance arms is constituted of a short metal strip indicated broadly at 24, cemented or otherwise firmly attached to the wire 5 (not shown but merely indicated), so as to react to the strain in the latter. The bridge is balanced in the absence of any strain in the resistance strip so that the galvanometer 25 can be calibrated in terms of strain units when the micrometer head 19 is turned to cause the beams to bow outwardly as explained hereinbefore. There is a direct relationship between the strain at which the wire is subjected and the counter-force exerted by the vessel and this strain produces a change in resistance of the arm 24 of the bridge. Consequently the meter 25 will, assuming that it had been balanced in the absence of any strain in the wire 5, now provide a visual determination of the magnitude of the counter-force. This information is also of invaluable assistance to the operator in determining the tonicity or elasticity of the arterial walls.
From the foregoing, it is apparent that I have disclosed an improved catheter which provides a considerable degree of dilation and uses no linkages of any kind. There are no solid connections at the point where the flexure beams are held in position within the slots at the ferrules 6, 11, and there are no high bending stresses are involved demanding close control or temper in the spring materials. Finally, the automatic compression of the dilated beams, when the pulling pressure is relieved at the micrometer head and provided solely by the spring condition of the beams, is of great benefit when it is desired to withdraw the catheter from the body, particularly in the case of arteries and blood vessels of small size.
In medical research relating to cardiovascular physiology, it is occasionally desirable to positively position or stabilize some device within the lumen of a blood vessel or to dilate the vessel by mechanical means. Catheters of various sizes are generally employed for this purpose. For dilating the blood vessels it has been customary to attach to the catheter, and operated from an exterior position, an "umbrella" type of mechanism or to employ the spring force stored in compressed wire fingers. However, several problems arise in connection with the construction of extremely small linkage mechanisms when it is considered that catheters of this type are hardly ever greater than one-eighth of an inch in diameter and the linkage would necessarily have to fit within the confines of this diminutive member. In those cases where the compressive forces are used for causing a dilation effect in the arterial system, high bending stresses are encountered which demand close control of the temper in the spring materials. Furthermore, the retraction of an expanded unit of the finger spring type, once it had been deployed in a vessel, it was often difficult to compress it to its normal size from the enlarged condition preparatory to being withdrawn from the body. Moreover, catheters of the type mentioned, when in a dilated form, may not always define a symmetrical body, and therefore it becomes difficult to center themselves within the artery being dilated. The lop-sided position of the forward end of the catheter may actually cause damage to the tissue and, in aggravated cases, sever pain to the patient.
SUMMARY OF THE INVENTION
One object of the invention is to provide an improved form of catheter of such diameter as to be useful in human as well as animal work and will align itself with the axis of the vessel to ensure positive position.
Another object is to provide a catheter of the type mentioned and in which the member can be mechanically dilated up to at least 2 centimeters without the use of linkage or spring force stored in compressed wire fingers.
Still another object is to provide an improved catheter in which, having been dilated, the member can be easily compressed and withdrawn from the body without the slightest complication.
The final object is to provide a catheter structure which lends itself to the use of ancillary apparatus which would enable the doctor to measure the amount of dilation remotely or to measure the forces related to the dilation.
Other objects and features will be apparent as the following description and the accompanying drawing are perused in connection with the improved invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 represents a longitudinal section, greatly enlarged of the improved catheter, portions of which are shown in elevation for clearness and together with certain ancillary apparatus shown partly by diagram and partly in elevation;
FIG. 2 is a view similar to FIG. 1 but showing the improved catheter in expanded form for dilating a blood vessel. All of the ancillary apparatus are shown in elevation; and
FIG. 3 represents a view taken at about the two lines 3-3 in FIG. 1 and looking in the direction of the arrows.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, reference character 1 designates a length of standard No. 8 X-ray catheter material of about one-eighth of an inch diameter and constructed usually of surgical stainless steel. There is a proximal fitting 2 of similar material at the base portion of the catheter and secured thereto in any suitable and well known manner, for example, by a proper metal-to-metal cement. This fitting comprises a collar portion having a stem 3 which fits snugly within the interior of the catheter piece 1. The fitting has a central opening 4 for slidably receiving an actuator wire 5. The latter preferably is constituted of music wire of special steel, approximately .013 inch diameter and the purpose of which will be explained hereinafter.
Next to the fitting 2 there is a metal ferrule 6 of about the same size as the fitting and it is secured to the latter in any suitable and well known manner. The ferrule is relatively thick and has an opening 7 (FIG. 3) larger than that of the fitting 2 and this opening is provided with a plurality of square shaped milled out slots 8 spaced equidistantly apart. The slots have a bottom surface which is curved outwardly as indicated at 9 (FIG. 1) for reasons which will be apparent hereinafter. These slots have a width and depth of such dimensions as to provide a close slip fit with the left-hand end of the flexure beams 10. The latter are of rectangular shape, preferably greater in width than in thickness, as seen in FIG. 3, and are constituted of stainless spring steel of highest surgical quality.
At the other or distal end of the catheter, there is a ferrule 11 similar to the member 6 and having an opening 7 (FIG. 3) through which the right-hand end of the actuator wire 5 passes. This ferrule, like its left-hand counterpart, is provided with four slots 8, having bases which are rounded upwardly and outwardly as indicated at 9; quite similar to those shown and described hereinbefore. These slots are of such size as to provide a close slip fit with the right-hand tips of the flexure beams 10. The end of the catheter which is inserted into the body, blood vessel, or other body cavity, terminates in a cylindrical member 12 of the same diametral size as the ferrule 11 but of greater length. This distal fitting has a hemispherical end 13 and is provided with a central opening which tightly receives the right-hand end of the actuator wire 5. The latter is rigidly secured in any suitable manner to the member so that there is not the slightest movement therebetween, regardless of the stresses or stains imposed upon the actuator wire. The member 12 can be made of surgical stainless steel or of a plastic material such as that sold under the names "Teflon" or "Nylon." The ferrule 11 is cemented or otherwise secured to the member 12. A tube composed of a length of hypodermic needle tubing of surgical stainless steel is employed within the body of the catheter; this tubing being cut to a length of approximately 5 mm less than the distance between the inside surface of the fitting 2 and the cylindrical member 12. The opening is the tubing is slightly larger than the diameter of the actuator wire 5 so as to permit a sliding fit. The outside diameter of the tubing is somewhat less than the distance between the inside surfaces of the opposite pairs of the beams 10. The purpose of the tubing will be explained hereinafter.
The dilator assembly is built up as follows: first, the proximal fitting 1 is installed in the distal end of the standard X-ray catheter. Next, the actuator wire (.013 diameter) is fed through the lumen of the catheter. The limiting tube 14 is next slipped over the actuator wire and the beam ferrules 6, 11 are placed in position with their curved inside edges 9 facing one another. Next, the distal fitting 12 is secured to the end of the actuator wire and held in this position in any suitable and well known manner. It will be noted that the end view of the distal fitting 12 and the ferrule 11 is approximately the same as the view of the proximal fitting 2 and the ferrule 6 as shown by the fact that the viewing line 3-3 may be applied to both portions.
When the ferrules are pressed in place or otherwise secured to the proximal and distal fittings, the flexure beams 10 are next fitted into the beam pockets in each fitting formed by the milled out slots referred to hereinbefore. These beams are held within the slots solely by friction since the slots have been cut snugly to receive the ends of the beams, Suitable dimensions for the beams, of which there are four, and made of spring steel, are .010 inch (.025 mm.) in thickness and .020 inch to .030 inch (.508 mm. to .562 mm.) in width. The four beams have a length that they can be gently flexed and inserted into the beam pocket in each ferrule. This completes the basic assembly.
At the operator end of the catheter, the amount of deployment of the beams 10 may be controlled by attaching to the end of the actuator wire 5 an enlarged member or lug 15 of rectangular cross section which is attached freely to slide within a rectangular opening 16. The latter is formed in a circular web element 17, secured at its periphery to the interior surface of the base portion of the catheter designated at 1. The purpose of the member 15, slidably contained within the web member 17, is to prevent rotation of the actuator wire while it is being pulled or released to dilate or compress the beams 10. In order to apply a pulling or releasing effort to the wire, and particularly in view of the diminutiveness of the wire, it may be desirable to attach a second enlarged member 18 to the wire and of circular configuration. This member carries fine threads on its periphery. An apertured drum 19, threaded along its bore and having a micrometer scale 20 engages the threads of the enlargement 18 and is caused to press lightly against the square or cut end of the base portion of the catheter when being operated. By rotating the drum in one direction or the other, according to the scale on the drum, a pulling or releasing effect can be applied to the actuator wire for purposes explained hereinafter. An indexing pointer 21 is secured as by screw 22 to the catheter in order to show the amount of rotation and, therefore, the amount of longitudinal movement of the actuator wire.
To operate the device within a blood vessel, the actuator wire is pulled by turning the micrometer drum 19 so that the distal fitting 11 approaches the proximal fitting 2, thus decreasing the distance between the assembly 11, 12 and assembly 2, 6. The pull on the wire subjects the flexure beams to a coaxial compressive stress. The limiting tube 14 prevents the beams from flexing inwardly and limits the amount of shortening possible between the movable ferrule 11 and the stationary ferrule 6. Since the slender beams are restrained from flexing inwardly they will, under the axial compressive stress, bow outwardly, as seen in FIG. 2 to provide a structure which dilates the vessel to the degree desired. This bulging effect or dilation is indicated in FIG. 2 and can be as much as 2 centimeters or more. The deployed diameter may of course be controlled by varying the dimensions of the assembly. It will be noted that the lack of a rigid (i.e. soldered) connection at each beam end and the curved ferrule contour (indicated at 9) and the close slip fit of the fitting assemblies allow both sliding and bending to occur at the beam surfaces, thereby relieving the high bending stresses which could be incurred with a rigid joint. It is also apparent that the 2:1 or 3:1 width/thickness ratio of the beams also prevents the torsional bending and lateral displacements which might be encountered with beams of circular cross section. The amount of deployment of the beams 10 may be readily determined by the final micrometer setting at the dial 20 which previously had been calibrated.
In order to compress the beams 10 to their original position of resting against the periphery of the tubing 14, it is merely necessary to turn the micrometer head in the direction opposite from that when obtaining dilation. The ferrule 11, together with its terminating head 12, will then move to the right under the urge of the spring effect left in the beams so that the latter will again compress to coincide over their entire length with their original position preparatory to retraction from the vessel.
In applications in which it is desirable to measure the counter-force exerted by the blood vessel against the deployment of the dilator, a sensitive strain gage of any suitable and well known type can be applied to the actuator wire when the beams 10 are under dilation. A Wheatstone Bridge arrangement indicated generally at 23 may be used to advantage in which one of the resistance arms is constituted of a short metal strip indicated broadly at 24, cemented or otherwise firmly attached to the wire 5 (not shown but merely indicated), so as to react to the strain in the latter. The bridge is balanced in the absence of any strain in the resistance strip so that the galvanometer 25 can be calibrated in terms of strain units when the micrometer head 19 is turned to cause the beams to bow outwardly as explained hereinbefore. There is a direct relationship between the strain at which the wire is subjected and the counter-force exerted by the vessel and this strain produces a change in resistance of the arm 24 of the bridge. Consequently the meter 25 will, assuming that it had been balanced in the absence of any strain in the wire 5, now provide a visual determination of the magnitude of the counter-force. This information is also of invaluable assistance to the operator in determining the tonicity or elasticity of the arterial walls.
From the foregoing, it is apparent that I have disclosed an improved catheter which provides a considerable degree of dilation and uses no linkages of any kind. There are no solid connections at the point where the flexure beams are held in position within the slots at the ferrules 6, 11, and there are no high bending stresses are involved demanding close control or temper in the spring materials. Finally, the automatic compression of the dilated beams, when the pulling pressure is relieved at the micrometer head and provided solely by the spring condition of the beams, is of great benefit when it is desired to withdraw the catheter from the body, particularly in the case of arteries and blood vessels of small size.