Rotational Pressure Drive for a Medical Syringe

This invention relates general to medical devices for obtaining, maintaining, and releasing fluid pressures in a syringe and, in particular, to device for threadably engaging the external flanges of a syringe for obtaining high fluid pressures in the syringe chamber.

High fluid pressures are required for the inflation of balloons used in medical procedure such as angioplasty and radial dilation of the urethra. The balloons are typically inflated for an extended period of time using a syringe filled with fluid. However, maintaining high fluid pressures for an extended period of time is difficult by simply applying manual force to commercially available syringe.

One approach to this problem is to use a custom-made or modified syringe. All of these syringes commonly include an outer, internally threaded member and an inner, externally threaded member for rotational advancement of the plunger in a syringe barrel.

A disadvantage of each of these custom-made or modified syringes is that they are relatively expensive to manufacture in comparison to standard, commercially available syringes. Another disadvantage is that these syringes are more complicated to use than a standard syringe. Therefore, the physician has to become skilled at operating the device. The physician's familiarity with the device is also critical for maintaining or releasing pressure when a threshold is reached. A timely release prevents bursting the balloon or overdilating tissue. Yet another disadvantage is that these custom-made syringes are fitted with pressure gauges or indicator rods that require visual monitoring by the physician during use. The physician must actuate the modified syringe while watching a pressure indicator for a threshold pressure to be obtained. When the threshold is obtained, these custom-made syringes are manually operated for permitting fluid to exit the syringe chamber, thereby decreasing the fluid pressure therein.

Another prior art device utilizes an internally threaded outer sleeve that fixedly engages the radial projections at the proximal end of a standard syringe barrel. The device includes an externally threaded plunger that attaches to the proximal end of a standard syringe plunger for longitudinal movement of the syringe plunger with respect to the pair of radial projections at the proximal barrel end. A problem with this device is that it is expensive to manufacture. From a user's perspective, the device is large, heavy, and cumbersome, and therefore difficult and inconvenient to use.

The foregoing problems are solved and a technical advance is achieved in an illustrative rotational pressure drive for engaging a standard, commercially available medical syringe and obtaining, maintaining, and releasing a desired fluid pressure therein. The drive comprises an elongated member such as a hollow cylindrical chamber having a passageway extending longitudinally between a closed end for engaging the proximal end of the syringe plunger and an open end for receiving the plunger and extending it through the passageway to the closed end. The drive further includes first and second pluralities of internal threads extending radially into and longitudinally along the passageway for engaging the flanges extending radially and laterally from the proximal end of the syringe barrel. Use of the pressure drive involves fully extending the plunger proximally from the syringe barrel and inserting the extended plunger into the open end of the drive, through the passageway, and to the closed end. The syringe barrel flanges engage the individual starts of the first and second pluralities of internal threads. The drive is then advantageously rotated with respect to the syringe barrel to thread the flanges into the passageway of the drive and to push the plunger into the syringe barrel As the plunger is pushed into the syringe barrel, the fluid pressure within the barrel is increased. Any desired pressure may be maintained in the barrel depending on how far the flanges of the syringe are threaded into the passageway of the drive. A pressure limiting assembly is attached to the distal end of the syringe barrel, which releases fluid from the syringe when a threshold pressure is obtained.

A departure in the art is that the internal threads of the pluralities are a modified form of an Acme thread with multiple starts. The crest and root of an Acme thread are typically of the same width or thickness, with each thread having a flank surface angle of approximately 14.5 degrees. The threads of the present invention have a crest thickness that is different from the width of the thread root. Furthermore, the pluralities of the internal threads are positioned alternatingly between each other with each plurality having a separate start. The first and second starts of the pluralities are opposite each other about the open end of the passageway for engaging the diametrically opposed flanges of a standard, commercially available syringe. The multiple starts of the threads advantageously engage the flanges of the syringe without distorting or deforming the flanges as they are threaded into the passageway. The thread root width preferably matches the width of the syringe barrel flanges with the flank surface angle being significantly reduced from that of an Acme thread for advantageously advancing the flanges without distortion within the passageway of the drive. Preferably this flange surface angle is 2 degrees for minimizing distortion of the syringe barrel flanges, reducing rotational force, and reducing thread thickness.

Each plurality of internal threads comprises a continuous helix of which the threads of the pluralities are positioned alternatingly between each other.

The passageway includes a minor diameter slightly larger than that of the plunger cross-section for permitting insertion through the passageway of the drive and a major diameter approximating the largest radial dimension of the flanges. Thus, the major and minor diameters bound the height of the internal threads. Advantageously, the height of the various thread pluralities may be varied depending on the radial dimension of each syringe flange. Furthermore, the root between adjacent threads of the pluralities may also be varied to accommodate various thickness flanges.

Positioned about the closed end of the elongated member and extending radially into the passageway along the longitudinal axis thereof is a projection for pivotally engaging the proximal end of the plunger during rotation of the drive with respect to the syringe barrel. This advantageously prevents distortion or deformation of the plunger during rotation of the drive, thus preventing loss or leakage of fluid from the syringe barrel and variations in fluid pressure levels.

The device further includes a plurality of reinforcements extending longitudinally about the outer surface of the drive for minimizing the bulk of the drive, while maintaining the structural integrity and rigidity of the drive. Also included is a pressure relief assembly including a cylinder and a spring actuated piston positioned within the cylinder attached about the distal end of the syringe for advantageously limiting the fluid pressure within the syringe. This prevents bursting a treatment balloon as well as overdilating or traumatizing tissue.

In another aspect, the rotational pressure drive is considered a plurality of internal threads having multiple first and second starts for engagement respectively of the flanges of the syringe barrel. Each thread of the plurality has a predetermined height, a crest with a predetermined thickness, along with a root having a predetermined width to match the thickness of the syringe barrel flanges.

FIG. 1 depicts the rotational pressure drive and pressure relief assembly of the present invention for a medical syringe;

FIG. 2 depicts an end view of the pressure drive of FIG. 1;

FIG. 3 depicts a cross-sectional thread profile of the pressure drive of FIGS. 1 and 2;

FIG. 4 depicts a longitudinal, cross-sectional view of the pressure drive of FIG. 2 along the line 4--4;

FIG. 5 depicts the pressure drive of FIG. 4 with a medical syringe positioned therein;

FIG. 6 depicts a partial, cross-sectional view of the pressure relief assembly of FIG. 1 attached to the distal end of a medical syringe; and

FIG. 7 depicts an enlarged partial cross-sectional view of the piston and cylinder of the pressure relief assembly of FIG. 6.

FIG. 1 depicts rotational pressure drive 100 that is positionable about and rotationally engageable with a standard, commercially available, 10 cc syringe 101 for engaging and pushing syringe plunger 102 into syringe barrel 103 to control the pressure of a fluid contained therein. The rotational pressure drive comprises elongated member 104 such as a hollow cylindrical chamber. The elongated member of the drive has closed proximal end 105 for engaging proximal end 119 of plunger 102, open distal end 106 for receiving the plunger, and hollow passageway 107 extending longitudinally between the open and closed ends for passage of the plunger therethrough to the closed end. The drive also includes a first plurality of internal threads 108 with start 109 and a second plurality of internal threads 110 with start 111 for engaging diametrically opposed syringe barrel flanges 112 and 113. These flanges extend radially and laterally from proximal end 114 of syringe barrel 103. Internal thread pluralities 108 and 110 extend radially into and longitudinally along the outer circumference of hollow longitudinal passageway 107 for threading the syringe barrel flanges longitudinally into the passageway toward closed proximal end 105. Syringe plunger 102 includes crisscrossed elongated members 116 and 117 with disk-like flange 118 transversely positioned and molded with the crisscrossed plunger members at the proximal end thereof.

Plunger 102 of the syringe is extended proximally from open proximal end 114 of the syringe barrel and inserted into open distal end 106 of the pressure drive. The plunger is then extended through hollow passageway 107 to engage closed proximal end 105 of the drive. Diametrically opposed syringe barrel flanges 112 and 113 are inserted into the open end of the drive to engage thread starts 109 and 111, respectively. The syringe barrel and drive are rotated with respect to each other to engage and thread syringe barrel flanges 112 and 113 into internal thread pluralities 108 and 110. Rotation of the drive with respect to the syringe barrel causes closed proximal end 105 of the drive to engage and push proximal end 119 of the plunger into the syringe barrel, thus increasing the pressure of the fluid within the syringe barrel. Continued rotation of the drive with respect to the syringe barrel further increases the pressure of the fluid contained within the barrel.

The drive also includes pressure relief assembly 120 for limiting the pressure of the fluid within the syringe barrel. Pressure relief assembly 120 is connected to distal end 121 of the syringe barrel which has a female Luer lock connector 122 positioned thereat. Pressure relief assembly 120 is well-known and includes cylinder 123 that communicates with a passageway extending longitudinally through the assembly between proximally positioned, male Luer lock connector 124 and inflation tube 125 extending distally from the assembly through end cap 126. Pressure relief assembly 120 further includes a well-known cylindrical piston 127 that is positioned within cylinder 123 and forced therein with actuation spring 128 and end cap 129. An O-ring seal 130 is also positioned around the piston and within the cylinder to maintain a seal between the cylinder and piston. Actuation spring 128 exerts a force against the proximal end of the piston to maintain the piston within the cylinder. As the fluid pressure within the syringe barrel and pressure relief assembly builds up to exceed the counteracting force of the actuation spring, the piston is pushed out of the cylinder. Thus, the spring actuated piston limits the pressure within the cylinder as well as inflation tube 125 and syringe barrel 103.

Syringe 101 is a standard, well-known, and commercially available 10 cc syringe from Becton Dickinson & Company, Rutherford, N.J. This syringe has an outer barrel diameter of approximately 0.630" with an overall length of 3.75". Flanges 112 and 113 extend an equal distance laterally and radially from the proximal end of the barrel and have a maximum cross-sectional dimension of 1.107" and a minimum cross-sectional dimension of 0.74". The overall length of plunger 102 is approximately 4" with the crisscrossed elongated members being approximately 0.500" in width. The disk-like flange 118 has a diameter of approximately 0.730".

FIG. 2 depicts an end view of drive 100 looking into open distal end 106 of elongated member 104 through longitudinal passageway 107 toward closed proximal end 105. Also depicted are first plurality of internal threads 108 with first start 109 and second plurality of internal threads 110 with second start 111. As previously indicated, starts 109 and 111 are diametrically opposite each other in the passageway about distal open end 106 of the drive. Extending from closed proximal end 105 into hollow longitudinal passageway 107 is pivot projection 115 for engaging and pushing against the proximal end of the plunger and, in particular, the disk-like plunger flange. As the drive is rotated with respect to the barrel, the plunger flange pivots about projection 115 without deforming or twisting the plunger. Also shown is elongated member wall 131 with a plurality of longitudinally positioned reinforcement ribs 132 positioned about external surface 133 of the member. The thickness of wall 131 is approximately 0.050". Longitudinal passageway 107 has a major diameter 142 of approximately 1.134" and a minor diameter 143 of approximately 0.774". Rotational pressure drive 100 is molded from a commercially available medical grade nylon material. The overall length of the drive is approximately 3.375" with an outside surface diameter of 1.238". The six reinforcement ribs 132 are each comprised of a 0.187" diameter semicircular longitudinal rib which are spaced equally around and longitudinally along the outer surface 133 of the elongated member, which extends longitudinally for approximately 3.0". The outside diameter of closed proximal end 105 is approximately 1.017", which is annularly recessed from the outer surface of the drive and extends longitudinally for approximately 0.285".

FIG. 3 depicts a partial, longitudinal, cross-sectional profile view of internal threads 134 and 135 of first plurality 108 and internal threads 136 and 137 of second plurality 110. Internal threads 134 and 135 of plurality 108 include respective crests 138 and 139 with a thickness of approximately 0.034" to 0.035". Crests 140 and 141 of respective internal threads 136 and 137 of second plurality 110 are also approximately 0.034" to 0.035" in thickness. Height 160 of internal threads 134-137 is equal to half the difference between major and minor diameters 142 and 143, which is approximately 0.180". Pitch 161 between internal threads 134 and 136 is approximately 0.125", whereas pitch 162 between internal threads 134 and 135 of first plurality 108 is approximately 0.250". Roots 144-146 are approximately 0.081" in width. However, the width of roots 144 and 145 may independently vary depending on the thickness of syringe barrel flanges 112 and 113. The width of internal threads 134-137 at diameter 142 of the passageway is approximately 0.044". Leading flank surfaces 147-150 of respective threads 134-137 each have a well-known flank angle 163 of approximately 2 degrees as opposed to an Acme flank angle of approximately 14.5 degrees. This angle can preferably range from 1.8 to 2.2 degrees for a 10 cc Becton and Dickinson syringe. Pressure flank surfaces 151-154 of respective internal threads 134-137 each have a predetermined flank angle 164 of approximately 2 degrees, again in contrast to a 14.5 degree Acme flank surface angle. Again, depending on the type of flanges utilized, the leading and pressure flank surfaces may have different flank angles as well as having different leading and pressure flank angles on each of the two internal thread pluralities. Alternatively, internal thread pluralities 108 and 110 may also be considered as a single plurality of threads with multiple starts 109 and 111. The aforedescribed thread profile clearly constitutes a departure and modification from that of an Acme thread profile with dual starts and equal width crests and roots. The reader is referred to Machinery's Handbook. Twenty-first and Twenty-third Editions, Industrial Press Incorporated, New York, N.Y., for a more detailed description of the terms utilized herein to describe the internal threads and their constituent parts. Many of the definitions contained therein to describe thread parts are hereby incorporated by reference.

FIG. 4 depicts a longitudinal cross-sectional view of drive 100 of FIG. 2 along the line 4--4. As shown, elongated member 104 of the drive, such as a hollow cylindrical chamber, has closed proximal end 105 and open distal end 106 with passageway 107 extending therebetween. Closed proximal end 105 has a wall thickness of approximately 0.115". Pivot projection 115, with a height of 0.025", extends into the passageway along the longitudinal axis thereof. As shown, first plurality of internal threads 108 extends almost the entire length of the passageway, and similarly, second plurality of internal threads 110 is alternatingly positioned between the threads of first plurality 108. Start 111 of second plurality of internal threads 110 begins about open distal end 106 of the passageway.

FIG. 5 depicts the longitudinal cross-sectional view of drive 100 of FIG. 4 with syringe 101 positioned within passageway 107 of elongated member 104. Plunger 102 extends proximally from syringe barrel 103 with disk-like flange 118 engaging and making contact with pivot projection 115. Syringe barrel flanges 112 and 113 are positioned in diametrically opposed roots of internal thread pluralities 108 and 110. As a result, distal end 155 of plunger 102 is pushed into chamber 156 of the syringe barrel as drive 100 is rotated with respect to syringe barrel 103. Furthermore, the pressure of fluid 157 contained within the chamber of the barrel is increased.

FIG. 6 depicts pressure relief assembly 120 attached to distal end 121 of syringe 101 via syringe connector 122 and assembly connector 124. Extending through end cap 126 is inflation tube 125, which communicates with the interior of an angioplasty balloon or other medical dilation device (not shown). As the pressure of fluid 157 in chamber 156 of the syringe increases, a force is exerted against distal end 158 of pressure relief piston 127. When the fluid pressure exceeds the counteracting force exerted by actuation spring 128, the piston is pushed toward end cap 129 releasing fluid 157 around piston 127 and through cylinder 123 and aperture 159 of end cap 129 until the fluid pressure and spring force are once again equal.

FIG. 7 is an enlarged view of cylinder 123 and piston 127 of pressure relief assembly 120. As illustrated, the pressure of fluid 157 has exceeded the force exerted by actuation spring 128, thereby pushing piston 127 out of cylinder 123, thereby releasing fluid 157 around piston 127 and through cylinder 123 and out aperture 159 of end cap 129.

It is to be understood that the above-described rotational pressure drive is merely an illustrative embodiment of the principles of this invention and that other rotational pressure drives may be devised by those skilled in the art without departing from the spirit and scope of this invention. In particular, the height of the threads as well as the root and crest may be varied according to the length, width, and thickness of the radially extending syringe flanges. These may be varied to accommodate two or more flanges with a corresponding number of starts and pluralities of internal threads within the passageway of the hollow elongated member. It is also contemplated that the threads about the open end of the chamber may be spaced closer together to provide less force to initiate the initial progress of the syringe plunger in the syringe barrel. As the pressure in the syringe barrel is increased, the threads positioned further in the passageway of the drive may be spread apart to provide greater longitudinal movement through the hollow passageway. In the preferred embodiment, one rotation of the drive corresponds to a decrease in the volume of the fluid within the syringe barrel of 1 cc. The pitch of the threads may be lengthened or shortened to vary the amount of fluid compression within the syringe barrel. It is also contemplated that the actuation spring of the pressure relief assembly may also be varied to provide different threshold release pressures along with other pressure relief mechanisms being attached to the distal end of the syringe barrel. In the preferred embodiment, the rotational pressure drive has been designed for a commercially available and commonly used 10 cc syringe. The dimensions of the drive may be varied to accommodate any commercially available syringe without any modification to the syringe, therefore making the use of this drive very economical and efficient without having to modify the structure of the syringe in any aspect. It is also contemplated that other forms of multiple start threads, such as the buttress, square, and other threads or combinations thereof may also be modified for the rotational pressure drive.