in the drawings , like numerals indicate like elements throughout . certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention . the term “ distal ” in meant to describe the portion of a catheter according to the present invention that is inserted into a patient , and the term “ proximal ” is meant to describe the portion of a catheter according to the present invention that remains exterior of the patient . the terminology includes words specifically mentioned , derivatives thereof , and words of similar import . the following describes preferred embodiments of the invention . however , it should be understood based on this disclosure , that the invention is not limited by the preferred embodiments described herein . referring now to fig1 , a catheter 100 according to a first embodiment of the present invention is shown . the catheter 100 is a dual lumen catheter used for hemodialysis , wherein a first lumen 110 is used to draw blood from a vessel , such as the internal jugular vein , and a second lumen 130 is used to return blood to the vessel . further , while the second lumen 130 is used to return blood to the vessel , the second lumen 130 may also be used to administer other fluids , such as medication , to the vessel . the inventive aspect of the present invention is the distal end 102 of the catheter 100 . consequently , the proximal end of the catheter 100 , which typically includes : a hub at the proximal ends of the first and second lumens 110 , 130 ; a pair of extension tubes extending proximally from the hub , such that each extension tube is in fluid communication with one of the first and second lumens 110 , 130 through the hub ; and a luer connector on a proximal end of each of the extension tubes , is not shown , as the proximal end of the catheter 100 is known to those skilled in the art . as seen in fig1 a , the first lumen 110 preferably has a d - shaped cross section and the second lumen 130 preferably has a circular cross section . however , those skilled in the art will recognize that the cross sections may be other shapes , such as “ double d ”, “ circle c ”, or other lumen cross section configurations known to those skilled in the art . a cross - sectional view of the distal end 102 of the catheter 100 is shown in fig1 . the first and second lumens 110 , 130 are adjacent to and parallel to each other , and are separated from each other by a septum 104 . the second lumen 130 extends more distally than the first lumen 110 . the first and second lumens 110 , 130 provide a smooth outer surface for insertion into a patient &# 39 ; s blood vessel . the distal end 112 of the first lumen 110 is enlarged in fig2 . the distal end 112 includes a flap 114 that extends obliquely from a connected distal portion 116 to a free proximal portion 118 . the flap 114 closes the distal end 112 of the first lumen 110 to restrict fluid flow into or out of the first lumen 110 . the connected distal portion 116 is sufficiently pliable to allow the flap 114 to pivot about the distal portion 116 to open the first lumen 110 during use , such as when blood is either being drawn into the first lumen 110 or when blood is being expelled from the first lumen 110 . referring back to fig1 and 1 a , the second lumen 130 includes an internally concave distal end 132 that is generally closed , but with a plurality of slits 134 that allow the distal end 132 to open under pressure from the second lumen 130 . a generally curved lip portion 135 is formed between each slit 134 . as seen in fig1 a , four lip portions 135 are formed , although those skilled in the art will recognize that more or less than four lip portions 135 may be formed . the shape of the distal end 132 and the cut of the slits 134 allow fluid flow from the second lumen 130 , through the distal end 132 and out of the second lumen 130 , but restrict fluid flow into the second lumen 130 from the distal end 132 . a plurality of side ports 136 are formed in the walls of the second lumen 130 proximal of the distal end 132 , with a flap 137 covering each side port 136 . each flap 136 is preferably generally bulbous - shaped , with a distal connected end 138 and a free proximal end 140 . in an unpressurized condition , each flap 137 closes off its respective side port 136 to restrict fluid flow through the side port 136 . to manufacture the catheter 100 , it is preferred that the lumens 110 , 130 are co - extruded according to procedures well known to those skilled in the art . the distal end 102 is inserted into a tipping machine that forms the flap 114 over the distal end 112 of the first lumen 110 and forms the internally concave distal end 132 of the second lumen 130 . the flap 114 is then die cut to separate the free end 118 of the flap 114 from the distal end and to allow the flap 114 to rotate about the connected end 116 . the slits 134 are also cut to form the lip portions 135 in the distal end 132 of the second lumen 130 . the flaps 137 are also die cut to separate the free end 140 of each flap 137 from the wall of the second lumen 130 . in operation , the catheter 100 is inserted into the patient &# 39 ; s blood vessel according to techniques well known to those skilled in the art . when the proximal end of the catheter 100 is connected to an exterior device , such as a hemodialysis machine ( not shown ), blood flows from the vessel , through the catheter 100 , to the exterior device , back through the catheter 100 , and into the vessel again . when the catheter 100 is correctly connected to the exterior device , standard operation of the catheter 100 is shown schematically in fig3 . blood is drawn from the vessel v into the distal end 112 of the first lumen 110 along the direction of arrow “ a ”. blood pressure acting on the flap 114 pivots the flap 114 about the connected end 116 so that the free end 118 travels generally proximally , opening the distal end 112 and allowing the blood to flow into the first lumen 110 . the blood then travels to the exterior device , where the blood is processed . the processed blood is then transported to the second lumen 130 , where the blood enters the proximal end of the second lumen 130 and travels through the second lumen 130 to the distal end 132 of the second lumen 130 . the pressure of the flowing blood against the distal end 132 of the second lumen 130 separates the lip portions 135 from each other , opening the distal end 132 , and allowing the blood to exit the second lumen 130 along the direction of arrow “ b ”. occasionally , however , the catheter 100 may be incorrectly connected to the exterior device such that blood is drawn into the second lumen 130 and discharged through the first lumen 110 . operation of the catheter 100 in this manner is shown schematically in fig4 . blood is drawn into the vessel v into the second lumen 130 through the flaps 137 in the distal end 132 of the second lumen 130 , as shown by the arrows “ c ” in fig4 . the flaps 137 open into the second lumen 130 to allow blood to be drawn from the vessel v into the second lumen 130 . the blood then travels to the exterior device , where the blood is processed . the processed blood is then transported to the first lumen 110 , where the blood enters the proximal end of the first lumen 110 and travels through the first lumen 110 to the distal end 112 of the first lumen 110 to the flap 114 . blood pressure acting on the flap 114 pivots the flap 114 about the connected end 116 so that the free end 118 travels generally distally , opening the distal end 112 and allowing the blood to flow back into the vessel v , as indicated by arrow “ d ”. in between treatments , when blood is not flowing through the catheter 100 , a catheter lock solution is injected into each of the first and second lumens 110 , 130 from the proximal end of each of the first and second lumens 110 , 130 . regarding the first lumen 110 , the flap 114 biases toward the closed position to close the distal end 112 of the first lumen 110 and prevent the lock solution from dispersing from the first lumen 110 into the vessel v . regarding the second lumen 130 , the lip portions 135 bias toward a closed position to close the distal end 132 , and the flaps 137 bias toward the wall of the second lumen 130 to close the flaps 137 to prevent the lock solution from dispersing from the second lumen 130 into the vessel v . to prepare the catheter 100 for a subsequent treatment , a syringe ( not shown ) is connected to the proximal end of the first lumen 110 and the lock solution is vacuum drawn from the first lumen 110 into the syringes . the flap 114 biases toward the open position to allow blood into the distal end 112 of the first lumen 110 to make up for the now - depleted lock solution . the syringe ( or a subsequent syringe ) is connected to the proximal end of the second lumen 130 and the lock solution is vacuum drawn from the second lumen 130 into the syringe . the flaps 137 open to allow blood into the distal end 132 of the second lumen 130 to make up for the now - depleted lock solution . the syringe is removed and the proximal end of the catheter 100 is able to be connected to a hemodialysis machine . in an alternate embodiment , shown in fig5 , a catheter 200 includes a first lumen 210 and a second lumen 230 that have distal ends 212 , 232 , respectively , that are split apart from each other . a septum 204 that divides the first lumen 210 from the second lumen 230 splits off at a predetermined location to allow the distal end 212 of the first lumen 210 to separate from the distal end 232 of the second lumen 230 . optionally , as will be recognized by those skilled in the art , the septum 204 may be splittable , to allow the distal end 212 of the first lumen 210 to be split away from the distal end 232 of the second lumen 230 at a variable location , as determined by the inserting physician during insertion of the catheter into the patient . it will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof . it is understood , therefore , that this invention is not limited to the particular embodiments disclosed , but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims .
a catheter having a first lumen having a first distal tip and a second lumen having a second distal tip . the first and second distal tips include openable portions that are normally closed when undeflected by lumen fluid pressure imbalance relative to the blood pressure of the patient . the first lumen has an openable portion , flap that opens proximally into the first lumen when the first lumen is under negative pressure to withdraw blood from the vessel through the first lumen to be dialysed . the second lumen extends distally beyond the first distal tip to its second distal tip , and its openable portion is several lip sections that are normally closed against each other when undeflected but that open outwardly when the second lumen is positively pressurized during hemodialysis , permitting blood to return to the patient &# 39 ; s vessel .