the devices and methods disclosed herein are most useful in treating patients suffering from global cerebral ischemia due to systemic circulatory failure , and focal cerebral ischemia due to thromboembolic occlusion of the cerebral vasculature . however , it will be understood that the devices and methods can be used in other medical conditions , such as hypertension and spinal cord conditioning . systemic arterial circulation relevant to the methods of the present invention is described in fig1 . during systole , oxygenated blood leaving heart 8 enters aorta 10 , which includes ascending aorta 12 , aortic arch 14 , and descending aorta 22 . the aortic arch gives rise to brachiocephalic trunk 16 , left common carotid artery 18 , and left subclavian artery 20 . the brachiocephalic trunk branches into right common carotid artery 24 and right subclavian artery 26 . the right and left subclavian arteries , respectively , give rise to right vertebral artery 28 and left vertebral artery 34 . the descending aorta gives rise to a multitude of arteries , including lumbar ( i . e ., spinal ) arteries 38 , which perfuse the spinal cord , renal arteries 40 , which perfuse the kidneys , and femoral arteries 42 , which perfuse the lower extremities . fig2 depicts occlusion catheter 100 for use in the methods described herein . the device includes elongate catheter 102 , distally mounted expandable constrictor , i . e ., occluder , 104 having distal opening 124 and variable flow mechanism 108 . the constrictor , when expanded , has maximum periphery 110 , which conforms to the inner wall of a vessel to form a secure seal with the vascular wall , such that blood flow through the vessel can be effectively controlled . opening 124 receives blood from distal the constrictor and controls the passage of blood proximal the constrictor . variable flow mechanism 108 , connected to rotary unit 150 , operates the constrictor , thereby controlling ( 1 ) the flow rate through the occlusion , and ( 2 ) upstream blood pressure . preferably , the device includes manometer 112 , which is connected to pressure monitor 156 and pressure limiter 114 . rotary unit 150 receives blood pressure measurements from the manometer . pressure limiter 114 , connected to the rotary unit and the pressure monitor , prevents the upstream and downstream blood pressure from exceeding , respectively , a set maximum and minimum pressure differential . a proximal end of the catheter is equipped with adapter 103 , from which pull wires 132 can be manipulated for collapsing the occluder and to which the rotary unit , pressure monitor , and / or pressure limiter can be connected . referring to fig3 , the occlusion device comprises catheter 102 and constrictor 104 . the catheter is constructed from a biocompatible and flexible material , e . g ., polyurethane , polyvinyl chloride , polyethylene , nylon , etc . the catheter includes lumen 116 through which various operative elements pass . alternatively , the catheter may include more than one lumen to support various operative elements . the catheter also includes proximal adapter 103 ( see fig2 ), which provides an interface between the catheter and the various instruments received by the catheter . the occluding mechanism consists of outer conical shell 118 and inner conical shell 136 , each having a distal open base and a proximal apex . pre - shaped ring 130 is affixed to base 120 of the outer shell to facilitate expansion of the constrictor . the ring is formed of a resilient material , capable of expanding the occluder to achieve a maximum periphery , which is defined by the outer circumference of the ring . ring 130 , may , in certain embodiments , further include an anchoring mechanism , such as hooks , bonded to the outer circumference of the ring . expansion of the ring causes the grasping structure to engage the surface of the vessel wall , thereby securing the occluder and preventing displacement in the vessel due to force exerted by blood flow . in other embodiments , the anchoring is provided by an adhesive strip , vacuum , or merely by frictional engagement of the vessel lumen by the ring . the constrictor can be collapsed to facilitate insertion into and removal from a vessel . a plurality of pull wires 132 ( fig2 ) are disposed within torque cable 148 , and are distally connected to base 120 of outer shell 118 and proximally passes through adapter 103 . the constrictor is collapsed by applying a tensile force on wires 132 , using torque cable 148 to provide leverage to the pull wires , thereby drawing the circumference of the open base 120 towards its center and collapsing the occluder . a guide sheath ( not shown ) can be alternatively used to collapse the constrictor . using this technique , the guide sheath would cover the constrictor and be withdrawn to release the constrictor and advanced to collapse the constrictor . opening 124 is formed in base 138 and 120 of the respective inner and outer conical shells to provide an inlet for blood flow . conical interior 106 communicates with ports 128 of the outer shell . when the constrictor is deployed , blood flows into opening 124 , through interior 106 , and exits through ports 128 . the occluding mechanism comprises inner conical shell 136 ( partially shown in phantom in fig3 ), which is rotatably disposed within outer shell 118 as shown in fig8 , 9 , and 10 . the inner shell can be rotated relative to the outer shell through torque cable 148 , which is disposed in lumen 116 of catheter 102 . manometer 112 comprises upstream pressure tube 152 and downstream pressure tube 154 , both connected proximally to a pressure monitor to provide respective blood pressure measurements upstream and downstream the constrictor . the upstream pressure tube extends distal to opening 124 , or may be attached to the inner shell . the downstream pressure tube extends through an orifice in the catheter proximal to the constrictor . the upstream and downstream blood pressure measurements are recorded and displayed by the pressure monitor at a proximal end of the catheter . a pressure limiter , programmed with a maximum pressure threshold to limit the upstream blood pressure and a minimum pressure threshold to limit the downstream blood pressure , is connected to the pressure monitor to receive pressure measurements therefrom , and transmits information to a rotary unit . the limiter thereby prevents the rotary unit from rotating the inner shell relative to the outer shell in a manner that would cause the upstream blood pressure to exceed the maximum threshold , or the downstream blood pressure to fall below the minimum threshold . without the rotary unit , torque cable 148 can also be manually rotated to obtain desired upstream and downstream blood pressures . an audible alarm may be incorporated into the pressure limiter to sound when blood pressures exceeds the thresholds . the pressure limiter may further comprise an interlocking device . the interlocking device , in operative association with upstream and downstream tubes 152 and 154 , can lock inner shell 136 with respect to outer shell 118 as blood pressures approach the set thresholds . it should be noted that although the rotary unit , pressure monitor , and pressure limiter are shown as separate units , they may be incorporated into an integral unit . referring to fig4 a and 4b , the expanded constrictor comprises outer conical shell 118 having base 120 and apex 122 , and inner conical shell 136 having base 138 and apex 140 . the constrictor is preferably composed of a biocompatible material coated with heparin to prevent blood clotting . the conical shape of the expanded constrictor minimizes turbulence caused by placement of the occluder in the vessel . the outer and inner shells include 2 , 3 , 4 , 5 , 6 , or any other number of ports 128 and 144 , respectively , in communication with the conical interior to permit blood flow through the occluder . the inner shell can be rotated relative to the outer shell , so that ports 144 communicate with ports 128 . apices 122 and 140 of the respective outer and inner shells further comprise collar 126 and 142 . the collars may include engaging threads , so that collar 142 can be inserted and secured into collar 126 , and bonded to a distal end of the torque cable , such that the inner shell is coupled to and rotates with the torque cable . a rotary unit , preferably including a stepper motor ( not shown ), may be mechanically coupled to a proximal end of the torque cable to provide precise rotational position of the inner shell relative to the outer shell , thereby providing variable flow through the occluder . instead of having the circular ports in the inner and outer shells as depicted in fig4 a and 4b , the constrictor may include 2 , 3 , 4 , 5 , 6 , or any other number of ports having other suitable geometric shapes . fig5 depicts constrictor 104 having a plurality of ports constructed as elongate rectangular slots 175 . fig6 depicts another embodiment of the constrictor , which comprises beveled lip 140 having distal end 142 and proximal end 141 . the proximal end is affixed to base 120 of the outer conical shell . the proximal end has a larger diameter than the distal end and is everted to prevent the constrictor from being displaced in the direction of blood flow , thereby securing the constrictor in the vessel . still another embodiment of the occluder may includes 1 , 2 , 3 , 4 , 5 , or any other number of graduated inflatable rings . in fig7 , ring 151 is affixed to the base of the conical shell . ring 153 , having the smallest inflated diameter , is attached to ring 152 , which is then attached to ring 151 , having the largest inflatable diameter . the fully inflated rings will have a thickness of approximately 2 to 3 millimeters . similar to the beveled lip of fig8 , the rings prevent the outer conical shell from being displaced in the direction of blood flow , thereby securing the constrictor in the vessel . the flow rate of blood through the constrictor can be easily controlled by rotating inner conical shell 136 ( shown with dotted lines ) relative to outer conical shell 118 as depicted in fig8 , 9 , and 10 . in fig8 , the inner shell is rotated so that ports 144 and 128 are completely misaligned , thereby achieving no flow through the ports and complete vascular occlusion distally . as the inner shell is rotated clockwise relative to the second shell in fig9 , ports 144 on the inner shell become partially aligned with ports 128 on the outer shell , thereby achieving partial flow through the ports and partial vascular occlusion . in fig1 , with continuing clockwise rotation of the inner shell , ports 144 become completely aligned with ports 128 , thereby achieving maximum flow through the ports . to provide a broader and more predictable range of blood flow through the conduit , the ports of the inner and outer shells are preferably of equal size and number such that they may align with each other . fig1 depicts another embodiment of the occlusion device for partial occlusion of blood flow in a vessel . device 200 comprises elongate catheter 202 , distally mounted expandable constrictor 204 with maximum periphery 210 , opening 224 , and variable flow mechanism 208 operatively associated with the constrictor . the catheter includes adapter 203 at its proximal end . preferably , the device includes manometer 212 and pressure limiter 214 , and pressure monitor 240 . the pressure monitor records and displays blood pressure data received from the manometer . longitudinal positioning unit 208 , receiving signals from pressure limiter 214 , and controls variable flow mechanism 208 to provide variable blood flow through the constrictor . referring to fig1 , catheter 202 includes lumen 216 . constrictor 204 comprises hollow conical shell 218 having base 220 and apex 222 . the inner circumference of the base forms opening 224 , which provides a distal inlet for blood flow through the constrictor . the inner circumference of apex 222 forms collar 228 with proximal opening 226 , which provide an outlet for blood flow through the constrictor . the conical interior , disposed within shell 218 , communicates with opening 224 distally and opening 226 proximally . when the base of the constrictor is positioned upstream in a vessel , blood flows into opening 224 , through the conical interior , and exits downstream through opening 226 . the catheter is bonded to collar 228 about a portion of its inner circumference . the constrictor is expanded by operation of ring 230 , a beveled lip , or a series of graduated toroidal balloons as described above . the constrictor is collapsed and may be delivered to a vessel location by using a guide sheath . the manometer comprises upstream pressure tube 236 and downstream pressure tube 238 , which are disposed in lumen 216 of the catheter and connected proximally to a pressure monitor . the upstream pressure tube extends distal from the constrictor or may be bonded to the inner surface of the conical shell , thereby providing upstream blood pressure measurement . the downstream pressure tube extends through an orifice in the catheter proximal to the constrictor , thereby providing downstream blood pressure measurement . the variable flow mechanism comprises a plurality of flaps 230 pivotally affixed to base 220 . the flaps are preferably made of a resilient material , such as nitinol , to resist movement caused by blood flow through the conduit . a plurality of pull wires 232 , disposed through lumen 216 , are distally connected to flaps 230 , such that applying a tensile force to the wires pivotally displaces flaps 230 from their preformed position . three of the flaps ( shown in dotted lines ) are displaced inward . releasing the wires allows the resilient flaps to relax and return to their preformed position . the pull wires are coupled proximally to the longitudinal positioning unit , which provides precise displacement of the flaps relative to opening 224 . alternatively , wires 232 can be manually tensed to operate the flaps . the pressure limiter receives pressure measurements from the pressure monitor and transmits signals to the longitudinal positioning unit to prevent the upstream and downstream blood pressures from exceeding the set thresholds . fig1 a , 13 b , 13 c , and 13 d depict frontal views of the constrictor having flaps in various positions for controlling blood flow . in fig1 a , preformed flaps 230 extend radially inward toward the longitudinal axis of the catheter , as in the absence of a displacing force , i . e ., an external force other than that created by blood flow . when the constrictor is positioned in the descending aorta , for example , the size of opening 224 and blood flow through the opening is minimized , thereby providing maximal aortic occlusion . in the presence of a displacing force , such as pulling the wires to displace flaps 230 from their preformed position as depicted in fig1 b , the size of aperture 224 and blood flow through the conduit increases , thereby providing partial aortic occlusion . alternatively , preformed flaps 230 extend parallel to the longitudinal axis of opening 224 in the absence of a displacing force as depicted in fig1 c . the size of opening 224 and blood flow through the conduit are maximized , thereby providing minimal blood flow occlusion . in the presence of a displacing force , flaps 230 are pivotally displaced from their preformed position as depicted in fig1 d . the size of opening 224 and blood flow through the opening are minimized , thereby providing maximal blood flow occlusion . thus , by pivotally displacing flaps 230 relative to opening 224 , the size of the opening and flow rate through the constrictor is controlled to provide variable vessel occlusion . the constrictor shown in fig1 can be alternatively mounted on catheter 202 , such that base 220 is proximal to apex 222 as shown in fig1 a . in this embodiment , flaps 230 are formed on open apex 222 . when constrictor 204 is inserted downstream in the aorta , for example , pressure tube 238 extends distally from opening 226 to provide downstream blood pressure measurements , whereas pressure tube 236 extends proximally through an orifice in the catheter to provide upstream blood pressure measurements . in fig1 , another embodiment of the device comprises catheter 302 , a distally mounted occluder 304 with maximum periphery 310 , blood passage 306 disposed within the constrictor , and variable flow mechanism 308 in operative association with the blood conduit . inflation device 334 communicates with the constrictor , and inflation device 338 communicates with the variable flow mechanism . the device preferably includes proximal adapter 303 , manometer 312 , and pressure limiter 314 . pressure monitor 312 records and displays blood pressure data from the manometer . the pressure limiter is connected to the pressure monitor and to an interlocking valve on inflation device 338 , such that the blood pressure upstream and downstream the constrictor can be controlled to prevent from exceeding set thresholds . referring to fig1 , constrictor 304 is mounted to a distal end of catheter 302 having lumen 316 . the constrictor comprises a sleeve or cylindrical balloon 318 having outer wall 320 and inner wall 322 , which enclose chamber 323 . the cylindrical balloon has first end 324 with opening 328 and second end 326 with opening 330 . catheter 302 is bonded to inner wall 322 of the cylindrical balloon . inflation tube 332 , housed within lumen 316 of the catheter , communicates distally with the cylindrical balloon and proximally with a syringe or other inflation device . the cylindrical balloon can be expanded or collapsed by injecting or removing air , saline , or other medium . occlusion is provided by toroidal balloon 334 disposed about the outer or inner surface of sleeve 318 and communicating with inflation tube 336 and a syringe . the inflation device may include an interlocking valve to prevent unintended deflation . lumen 306 communicates with opening 328 distally and opening 328 proximally . when deployed in a vessel , blood flows through lumen 306 and exits downstream opening 330 . the constrictor may further include an anchoring structure , shown in fig1 as rings 333 , which are disposed about outer wall 320 of the cylindrical sleeve and define maximum periphery 310 of the occluder . manometer 312 comprises upstream pressure tube 340 and downstream pressure tube 342 , which are operatively connected proximally to a pressure monitor . pressure tube 340 is bonded to the lumen of the cylindrical balloon and extends distal to provide upstream blood pressure measurements , while tube 342 emerges from the catheter proximal the occluder to provide downstream blood pressure measurements . in fig1 , fluid is injected to expand balloon 334 , thereby constricting sleeve 318 . as a result , blood flow is constricted . in fig1 , balloon deflation allows sleeve 318 to revert back to its pre - shaped geometry , increasing blood flow therethrough . thus , balloon 334 can be inflated and deflated to vary the cross - sectional diameter of lumen 306 to vary flow rate . the occlusion devices described herein can be employed with a variety of therapeutic catheters to treat vascular abnormalities . for example , as depicted in fig1 , suction / atherectomy catheter 402 can be inserted through lumen 306 , such that the suction / atherectomy catheter is independently movable relative to occlusive device 300 . catheter 402 includes elongate tube 404 and distally located aspiration port 406 , cutting device 408 , and balloon 410 for removing thromboembolic material in a vessel . in fig2 , infusion catheter 502 and eps catheter 504 are inserted through opening 206 of occlusion device 200 , such that catheter 502 and 504 are independently movable relative to occlusion device 200 . the infusion catheter , which includes elongate tube 506 , distally located perfusion port 508 , and expandable balloon 510 , can be used to remove thromboembolic material in a vessel . eps catheter 504 , which includes elongate tube 512 and distally located ablation device 514 , may be used to map out or ablate an extra conduction pathway in the myocardial tissue , e . g ., in patients suffering from wolff - parkinson - white syndrome . the occlusion device , capable of augmenting cerebral perfusion , is therefore useful not only in facilitating definitive treatment but also in cerebral ischemia prevention during eps and other cardiac interventions or cardiac surgery , such as coronary catheterization , where sudden fall in cerebral blood flow may occur due to arrhythmia , myocardial infarction , or congestive heart failure . referring to fig2 a , occlusion device 100 described above can be used to partially occlude blood flow in aorta 10 of a patient suffering from global cerebral ischemia due to , e . g ., septic shock , congestive heart failure , or cardiac arrest . constrictor 104 can be introduced in its collapsed geometry through an incision on a peripheral artery , such as the femoral , subclavian , axillary , or radial artery , into the patient &# 39 ; s aorta . a guide wire may first be introduced over a needle , and the collapsed constrictor is then passed over the guide wire and the needle to position distal to the takeoff of left subclavian artery 20 in the descending aorta . the constrictor is expanded , such that maximum periphery 110 of the occluder , formed by expandable ring 130 , sealingly contacts the inner aortic wall . the position and orientation of the collapsed or expanded device can be checked by tee , tte , aortic arch cutaneous ultrasound in the emergency room , or ivus and angiography in the angiogram suite . the expanded constrictor is maintained during systole , during diastole , or during systole and diastole , during which blood distal to the brachiocephalic artery is forced to pass through opening 106 , thereby providing a continuous partial occlusion of aortic blood flow . alternatively , partial occlusion of aortic blood flow can be intermittent . as a result , blood flow to the descending aorta is partially diverted to brachiocephalic artery 16 , left subclavian artery 20 , and left carotid artery 18 , thereby augmenting blood flow to the cerebral vasculature . in treating global ischemia , such as in shock , cerebral perfusion is increased by increasing blood flow through both carotid and vertebral arteries . additionally , blood flow to the aorta is partially diverted to the coronary arteries by using the occlusion device , thereby augmenting flow to the coronary arteries . using the partial occlusion methods during systemic circulatory failure may , therefore , improve cardiac performance and organ perfusion . by selectively increasing cerebral and coronary blood flow in this manner , the dosage of commonly used systemic vasoconstrictors , such as dopamine and norepinephrine , may be reduced or eliminated . alternatively , the device of fig1 , much like the device used to extinguish the flame of a candle , can be introduced through an incision on left subclavian artery 36 as depicted in fig2 b . constrictor 204 is inserted in aorta 22 distal to the takeoff of the left subclavian artery to provide partial , variable , and / or continuous aortic occlusion and is advanced antegrade into the descending aorta . this device is particularly useful in situations where peripheral incision can not be made on the femoral arteries due to arteriosclerosis , thrombosis , aneurysm , or stenosis . the devices and methods described in fig2 a and 21b are useful in treating stroke patients within few minutes of stroke symptom , and the treatment can be continued up to 96 hours or more . for example , in treating focal ischemia due to a thromboembolic occlusion in the right internal carotid artery the constrictor may be position distal to the takeoff of the left subclavian . as a result , blood flow is diverted to brachiocephalic artery 16 and left cca to augment both ipsilateral and contralateral collateral circulation by reversing direction of flow across the circle of willis , i . e ., increasing flow in the right external carotid artery and left common carotid artery . the collateral cerebral circulation is further described in details in u . s . application ser . no . 09 / 228 , 718 , incorporated herein by reference . in treating focal ischemia due to a thromboembolic occlusion in the left internal carotid artery , for example , the constrictor can be positioned proximal to the takeoff of left carotid artery 18 and distal to the takeoff of brachiocephalic artery 16 as shown in fig2 . contralateral collateral enhancement is provided by increasing flow through the brachiocephalic artery , thereby reversing blood flow in the right posterior communicating artery , right pca , left posterior communicating artery 68 and anterior communicating artery , resulting in increased perfusion to the ischemic area distal to the occlusion and minimizing neurological deficits . alternatively , the constrictor may be positioned distal to the takeoff of the left subclavian artery to provide both ipsilateral and contralateral collateral augmentation . ipsilateral circulation is enhanced by increasing flow through the left external carotid artery and reversing flow along the left ophthalmic artery , both of which contribute to increased flow in the left ica distal to the occlusion . as a result of partially occluding aortic blood flow , blood pressure distal to the aortic occlusion may decrease , and this may result in a reduction in renal output . blood pressure proximal the aortic occlusion will increase and may result in excessive rostral hypertension . the blood pressures , measured by the manometer , are monitored continuously , and based on this information the occlusion is adjusted to avoid peripheral organ damage . after resolution of the cerebral ischemia , the constrictor is collapsed and removed , thereby removing the aortic occlusion and restoring normal blood flow in the aorta . in fig2 , constrictor 304 is inserted in aorta 10 and can be used to remove thromboembolic material 72 from left common carotid artery 18 , while augmenting and maintaining cerebral perfusion distal to the occluding lesion . the occluder may be introduced through a guide sheath until it is positioned distal to left subclavian artery 20 . in emergency situations , the constrictor can be inserted through a femoral incision in the emergency room , and atherectomy / suction catheter 402 can be inserted through the constrictor under angioscopic vision in the angiogram suite after the patient is stabilized hemodynamically . the atherectomy / suction catheter , which includes expandable balloon 410 , distal aspiration port 406 , and atherectomy device 408 , is introduced through opening 306 until its distal end is positioned in left common carotid artery 18 proximal to the thromboembolic occlusion . constrictor 304 is then expanded to partially occlude aortic blood flow , thereby increasing perfusion to the ischemic region distal to the occluding lesion by enhancing ipsilateral collateral flow through left external carotid artery 46 and left vertebral artery 34 and contralateral collateral flow to right carotid artery 24 and right vertebral artery 28 . the variable flow mechanism of constrictor 304 can be adjusted to control blood flow to the cerebral vasculature and the blood pressure . balloon 410 of catheter 402 is expanded in the left common carotid artery , thereby creating a closed chamber between constrictor 410 and the thromboembolic occlusion . suction can be applied to aspiration port 406 to create a negative pressure in the closed chamber , thereby increasing the pressure differential across the thromboembolic occlusion , which may dislodge the occluding lesion onto the aspiration port and remove the occluding lesion . thromboembolic material 72 may be further removed by atherectomy device 408 . the methods herein can also be used to remove thromboembolic occlusion in the vertebral artery . the occlusion device 304 , therefore , not only augments cerebral perfusion in patients suffering from focal stroke or global ischemia , but also maintains cerebral perfusion while waiting for invasive or noninvasive intervention . the devices and methods of using atherectomy / suction catheter 102 are further described in u . s . application ser . no . 09 / 228 , 718 , incorporated herein by reference . during abdominal aortic aneurysm ( aaa ) surgery , lumbar or spinal arteries , which provide blood supply to the spinal cord , are often dissected away from the diseased abdominal aorta , resulting in reduction of blood flow to the spinal cord . the devices herein disclosed may be used to condition the spinal cord prior to aaa repair , thereby reducing the damage resulting from spinal ischemia during surgery . in fig2 , constrictor 104 is inserted in aorta 10 and expanded preferably distal to left subclavian artery 20 and proximal to lumbar arteries 38 . as a result , blood flow to the lumbar or spinal arteries is reduced . when this device is used in patients anticipating a major thoracoabdominal surgery , such as aaa repair , approximately 24 hours prior to surgery , blood flow to the lumbar arteries can be intentionally reduced to induce mild spinal ischemia , thereby conditioning the spinal cord to produce neuroprotective agents which may protect the spinal cord from more significant ischemic insult during surgery . in hypertension , end organ damage often results , e . g ., cardiac , renal , and cerebral ischemia and infarction . the devices and methods herein may be employed in hypertension to protect the kidneys from ischemic insult . in fig2 , constrictors 104 , which can be introduced through a femoral artery , are inserted in right renal artery 80 and left renal artery 82 . the constrictors are expanded to partially occlude blood flow from descending aorta 10 to the renal arteries , thereby reducing blood pressure distal to the occlusion . the constrictors can be deployed for the duration of any systemic hypertensive condition , thereby protecting the kidneys from damage that might otherwise be caused by the hypertension . the length of the catheter will generally be between 20 to 150 centimeters , preferably approximately between 30 and 100 centimeters . the inner diameter of the catheter will generally be between 0 . 2 and 0 . 6 centimeters , preferably approximately 0 . 4 centimeters . the diameter of the base of the outer conical shell will generally be between 0 . 3 and 3 . 0 centimeters , preferably approximately 0 . 5 and 2 . 0 centimeters . the diameter of the inflated balloon occluder will generally be between 0 . 3 and 3 . 0 centimeters , preferably approximately 0 . 5 and 2 . 0 centimeters . the ports of the inner and outer conical shells will generally have a diameter of between 1 to 6 millimeters , preferably approximately 3 to 4 millimeters . the foregoing ranges are set forth solely for the purpose of illustrating typical device dimensions . the actual dimensions of a device constructed according to the principles of the present invention may obviously vary outside of the listed ranges without departing from those basic principles . although the foregoing invention has , for the purposes of clarity and understanding , been described in some detail by way of illustration and example , it will be obvious that certain changes and modifications may be practiced which will still fall within the scope of the appended claims .
methods are provided for partial aortic occlusion for cerebral perfusion augmentation in patients suffering from global or focal cerebral ischemia . the descending aorta is accessed . a device is then located downstream from the takeoff of the brachiocephalic artery . the device is operated to at least partially obstruct blood flow in the aorta during systole and diastole . a physiologic parameter can be measured . the device can then be adjusted to modify the degree of obstruction based on the measured physiologic parameter .