with reference to the figures , systems and methods for providing or enhancing antegrade flow through a catheter during an endovascular procedure are described . various aspects of the invention will now be described with reference to the figures . for the purposes of illustration , components depicted in the figures are not necessarily drawn to scale . instead , emphasis is placed on highlighting the various contributions of the components to the functionality of various aspects of the invention . a number of possible alternative features are introduced during the course of this description . it is to be understood that , according to the knowledge and judgment of persons skilled in the art , such alternative features may be substituted in various combinations to arrive at different embodiments of the present invention . fig3 is a schematic diagram of brain vascular anatomy showing the intracranial internal carotid artery ( iica ), anterior cerebral artery ( aca ), m1 segment of the middle cerebral artery and m2 segment of the middle cerebral artery . a clot y is shown within the m1 mca with arrow 12 showing the direction of blood flow prior to any procedure . for the purposes of discussion , it is understood that blood flow 12 a through the aca is supporting collateral perfusion to affected areas of the brain . fig4 is a schematic cross - sectional diagram of a typical triaxial system including a distal access catheter ( dac ), microcatheter and guide wire that may be used during a recanalization procedure . for the purposes of general description , the problem and solution of the present invention are described by a description of a typical clot aspiration procedure . during this procedure , the physician would typically complete the following general steps to remove the clot after gaining access to the femoral artery : a . advance a microguide wire 14 to the clot ( typically a 0 . 038 ″ wire ). b . advance a microcatheter 15 over the microguide wire 14 to the clot y . c . advance a distal access catheter ( dac ) 16 ( may be termed a reperfusion guide catheter ( rgc )) over the microcatheter 15 and microguide wire 14 to the clot y . d . withdraw the microcatheter and microguide wire 14 . turn aspiration on to the dac , advance the dac to engage the clot . a ) if flow is observed through the dac and the clot y gets sucked out followed by blood , stop and check that the vessel is opened ; alternatively , b ) if there is no flow through the dac , the clot may be stuck in the dac or at the tip of the dac in which case , wait a minute and withdraw the dac while maintaining aspiration . as is known , there are numerous variations in this type of recanalization procedure utilizing different clot retrieval or entrapment devices and / or the use of different catheters including balloon guide catheters that are temporarily inflated to occlude flow during the steps of a procedure when an entrapped clot is being withdrawn . importantly , with each technique at one or more steps during the procedure , vessels are either occluded and / or retrograde flow is induced which has the effect of reducing pressure and the ability of non - occluded vessels to support effective collateral flow . with reference to fig6 ( a ) and ( b ), a catheter 20 having the capability of providing antegrade flow during a recanalization procedure is described . generally , the catheter 20 has an outer wall 20 a , a proximal end p and a distal end d . as known to those skilled in the art , the total length of the catheter 20 may be 1 - 2 m and has an outer diameter of approximately 3 mm . as shown , the catheter has a first lumen 22 and a second lumen 24 radial and generally concentric with the first lumen . the first lumen 22 functions in the manner of a typical dac used during a clot removal technique , that is a conduit to enable the passage of guide wires and / or other microcatheters to convey clot removal or retrieval equipment to the clot . in addition , the first lumen functions as a conduit to enable retrograde flow 22 a from the clot site to outside the body during procedural steps where the clot is being physically removed . the second lumen 24 functions to enable antegrade flow 24 a through the catheter 20 during all steps of the procedure but importantly whilst retrograde flow 22 a is initiated . as shown , the second lumen 24 does not progress the entire length of catheter 20 but includes at least one exit port 26 proximal and near the distal end d of the catheter ( typically within 1 - 3 cm but may be as much as 10 , 15 or 25 cm from the distal end d ). as such , and as shown in fig7 , in one example , during procedural steps where retrograde flow is required to physically remove the clot y , antegrade flow 24 a is maintained through the second lumen 24 such that antegrade flow 24 a can be maintained through the vasculature that may be useful or effective in ensuring vessel pressure to maintain collateral flow . that is , as shown in fig7 , the physician has initiated retrograde flow through the first lumen such that fluid / clot is being drawn into the distal end d of the catheter 20 . as shown , the aca is upstream of the clot y and thus is able to receive antegrade flow emanating from the exit port 26 of the catheter 20 . as such , pressure can be maintained within the aca in this example . it is important to note that in order to maintain sufficient flexibility in the tip of the dac whilst the dac is being advanced to the clot to prevent or minimize the risk of it being impossible to advance the catheter , that the second lumen ends some distance from the distal end d . that is , as noted above , the second lumen may end in the range of 10 - 25 cm from the distal end d . in embodiments where the distance x , is in this range , the tip region defined by x may be substantially more flexible than in the double lumen zone . under appropriate fluid and pressure control , this embodiment will still enable appropriate antegrade flow of fluid into the vessels supporting collateral flow . in an alternate embodiment , and as explained in greater detail below , a single lumen dac is utilized as a source of antegrade flow during the initial stages of the procedure . in this case , as the dac is being advanced , antegrade flow is maintained within the dac . antegrade flow will be terminated shortly before the tip of the dac arrives at the clot whereupon retrograde flow is initiated as the dac is advanced into the clot . as shown in fig8 , a pump 32 external to the body and operatively connected to catheter 16 ( having one or first and second lumens ) and a control system 30 and valves 32 supplying one or more nutrients or nutrient solutions 30 a , b , c provide appropriate pressures and flow rates of fluids to achieve both antegrade flow to maintain pressure to support collateral flow and retrograde flow 36 for clot removal . various parameters may be incorporated and considered by the control system to ensure correct flows and pressures . such parameters may include the diameter of the parent vessel , the diameter of the dac and / or pre - determined mathematical calculations to deliver fluid through the dac such that the flow and pressure head in the collateral channels is minimized or unaffected . the fluids that may be circulated through the catheter may themselves include properties to support collateral flow . such properties may include low viscosity fluids to encourage increased flow through collaterals and / or nutrients such as glucose , oxygen , free radical scavengers and / or flushing agents that encourage the removal of metabolic by - products of neurons . in addition , fluids may include properties that reduce the viscosity of blood . in one embodiment , the procedure can include the further step of introducing a colored fluid through the second lumen to guide the suction through the primary catheter . for example , if the fluid being injected is green and the return through the suction catheter is green , this may be an indicator to the physician that the clot is not engaged and most of the pressure is sucking the green fluid back , thus signaling the need to advance the dac further to engage the clot . in another aspect of the invention as introduced above , a regular dac is provided , that is without a double lumen , and an external pump system controls an antegrade flow of fluid through the dac as the dac is being advanced towards the clot . in this case , the antegrade flow will assist the inherent antegrade pressure and flow of blood through the vessels that may be affected as result of the presence of the catheter in the vessels . this procedure may provide significant benefits to patients and particularly those where the physician may be experiencing difficult is moving the catheter into position . that is , depending on a patient &# 39 ; s anatomy , which may be inherent or a result of age and other factors , the length of time to advance a catheter is typically in the range of 3 - 20 minutes where during this time , pressure and flow of blood to the collaterals may be affected . thus , to the extent that a normal or moderately enhanced pressure arid antegrade flow can be maintained , this may improve the functioning of collaterals during the procedure over currently used procedures where during catheter placement no enhancement of pressure and flow is provided . as noted above , the fluid pumped through the catheter may include friction reducing agents and / or various nutrients . in one embodiment , the pumps and the controller that maintains perfusion flows and pressures is based on pre - determined measurements and / or physician based inputs from knowledge of the patient &# 39 ; s circulation . such inputs can include the answers to a series of high level questions that seek to obtain an answer to the effectiveness of circulation within the patient &# 39 ; s brain . for example , the physician seeking to determine the degree of ica circulation may conduct the following analysis : a . is there a possibility of supply to the ipsilateral anterial cerebral artery from the opposite side ( fig2 a )? i . is the anterior communicating artery ( acoma ) absent ? ii . is the acoma hypoplastic ? b . is there further isolation of circulation such that the opposite aca is also supplied by the ipsilateral ica ( fig2 b )? i . is the opposite a1 segment of the aca absent ? ii . is the opposite a1 segment of the aca hypoplastic ? c . is there isolation of the pca circulation ( fig2 d )? i . fetal pca with absent p1 segment of pca ? ii . fetal pca with hypoplastic p1 segment of pca ? based on these factors an isolation score would be determined , that would typically involve result in a rating representing . for example mild , medium , severe or very severe isolation . a . diameter of the ica at the high cervical or intracranial level ( typically a number between 3 . 5 and 5 mm ). b . external diameter of catheter ( balloon guide catheter or dac ) ( typically a number between 2 and 4 mm ). c . degree of tortuosity of the vessels ( typically , a qualitative rating such as mild , moderate , severe with an associated numeric value ). generally , the greater the tortuosity , the longer it will take to advance the catheter to the m1 segment and the greater the fall in perfusion pressure that would result . d . size of the microcatheter inside the dac . in addition , other factors including the systemic blood pressure and / or the properties of the liquid being injected may be considered and used as inputs to the controller to determine the rate that a fluid is being injected to maintain perfusion pressure . that is , based on the various values of the input values ( actual numeric values or correlated qualitative measurements ), the controller determines and maintains a calculated rate of flow of liquid into the catheter . the boundaries of the model used to determine the upper and lower limits of flow are based on empirical data from research . as noted , fluids having properties favorable to maintaining collateral circulation and / or neuron nutrition may be injected that may or may not include blood . in cases where total fluid volume may be of concern , blood 40 may be withdrawn from the patient ( ie . at the femoral artery access point ) and recirculated through the catheter 16 . fig9 is a flowchart showing representative inputs used to determine input flow rates . in each case , the inputs may be input to an appropriate input and display system such as any form of known computer . inputs may be keyed numerical values , values selected from a list of values and / or words that represent a value that are used by the model . although the present invention has been described and illustrated with respect to preferred embodiments and preferred uses thereof , it is not to be so limited since modifications and changes can be made therein which are within the full , intended scope of the invention as understood by those skilled in the art .
the invention relates to systems and methods to improve perfusion flow and pressure during endovascular intervention . in particular , the invention relates to catheters that enable both antegrade and retrograde flow through the catheter during a recanalization procedure and specifically at the step in a procedure where a clot is being withdrawn . additionally , the invention provides systems for supplying fluids and fluid compositions to improve nutrition to ischemic brain .