in accordance with embodiments of the invention , treatment of ischemia in the brain is achieved by the control of the collapsibility factor in the cerebral vasculature . it may therefore be deemed pertinent to review basic physiological effects , related to collapsibility of intracranial vessels , before discussing specific embodiments of the invention . cerebral vessels like other collapsible tubes tend to collapse when external pressure exceeds intravascular ( negative transmural pressure ). when intravascular pressure is increased ( i . e ., positive transmural pressure ), vessels reopen and their diameter increases . it has been demonstrated that resistance in the collapsible vascular beds decreases when transmural pressure increases . active wall tension also contributes to vessel collapse and results in critical closing pressure . critical closure pressure is the inflow pressure at which flow through the vascular bed stops . due to pressure drop through the feeding arteries and active autoregulation , intravascular pressure at the microcirculation is not directly related to systemic arterial pressure . however , it is directly proportional to the venous pressure . the dependence of intravascular pressure , resistance , and collapsibility on the venous pressure allows venous pressure to be used to modify perifocal blood vessel collapse and flow distribution . increasing venous pressure may seem counterintuitive ; however , this approach or mechanistic modification of the circulatory bed may actually augment cerebral blood flow and open collaterals circuits in penumbral regions that are at - risk for evolving infarction . experimental physiological data indicate that intracerebral vein pressure is slightly above intracranial pressure ( icp ). however , dural sinus pressure is lower than that in the smaller veins and not related to icp . spontaneous increase in icp does not affect jugular vein bulb pressure ( jvbp ). similarly , a small jvbp increase does not affect icp , although a more extensive increase of jvbp raises both cerebral venous pressure and icp to an equal extent . if jvbp is low , its drop does not affect icp or cerebral venous pressure . if jvbp is high , its drop affects icp and cerebral venous pressure to an equal extent . this is caused by an interesting physiological phenomenon referred to as a “ vascular waterfall .” when this happens , flow rate through a collapsible tube will depend only on an upstream pressure at the feeding segment and will be independent of downstream pressure at the exit end . this behavior is similar to that of a mountain waterfall , where the flow rate depends on the quantity of flow at the source and not on the height of the vertical drop or fall . this is in a sharp contrast to ordinary laminar or turbulent flow in rigid pipes , where flow is simply proportional to the pressure gradient between the ends . analysis of vessel collapse shows that under some circumstances provision of resistance to the outflow end might actually enhance flow through a collapsed tube segment . this is because distal resistance increases distending pressure on the collapsed segment , which may eliminate the most effective hindrance to flow , progressive and recurrent narrowing of the collapsed segment . this is because collapsible tubes have an unequivocal and nonlinear flow ( q ) pressure ( p ) interrelationship . when transmural pressure ( ptm ) is positive , the cerebral veins assume a circular cross shape . if external pressures exceed venous pressure , the vein wall is subjected to circumferential compression with subsequential diminution of their cross - sectional area and full collapse . between a fully - distended and fully - collapsed state , the cerebral veins exhibit a highly nonlinear and unequivocal p - q interrelationship , part of which is inverted when veins are partially collapsed . in this part , flow through the vein increases as pressure gradient along it falls . in other words , it is possible to augment cerebral blood flow ( cbf ) by decreasing an extra - intracranial pressure gradient . this is a physiological basis for reestablishing cbf via the collateral circulation in the brain , in accordance with embodiments of the invention . accordingly , embodiments of the invention are used to treat a patient who is suffering from venous steal due to cerebral vessel collapse , which may otherwise lead to cerebral ischemia , by increasing the cerebral venous pressure in the patient . fig1 is diagram of a patient illustrating a portion of the patient &# 39 ; s vascular system , including interior the jugular veins ( ij ), the superior venous cava ( svc ), the right atrium ( ra ), and the azygos vein . fig1 illustrates a oxygen demand directed technique for treating the patient . as illustrated , distal end of an occluding catheter 12 is inserted through a percutaneously accessible vein , such as the jugular or subclavian vein , into the svc . the distal region of the occluding catheter 12 contains an expandable balloon 32 , or other expanding mechanism , which is positioned in the svc at a location above the ra and below where the azygos vein connects to the svc . the position of the occluding catheter 12 and balloon 32 may be confirmed , for example , via x - ray . once the occluding catheter 12 is in place , the balloon 32 is expanded to occlude blood flow in the svc at least partially . the degree of occlusion in the svc may be varied according to the venous pressure , which may be recorded by a pressure sensor that records pressure proximal to the balloon 32 or other portion of the occluding catheter 12 . in addition , the occluding catheter 12 may include mechanisms to measure other physiological parameters . for example , flow may be measured by doppler ultrasonography , electromagnetic flow meters , or heat dilution ; and blood oxygenation may be measured by fiberoptic oximetry or concentration of metabolites or markers . in addition , the patient may be connected to a hemodynamic effect monitor 40 , which measures the cerebral blood flow in the patient &# 39 ; s head . in this way , the hemodynamic effect monitor 40 provides feedback for whether and to what extent the treatment results in the desired increased cerebral blood flow . in one embodiment , the hemodynamic effect monitor 40 uses tcd waveforms to obtain a mapping of the patient &# 39 ; s cerebral blood flow . in other embodiments , the hemodynamic effect may be monitored using spectrometry or ct angiography . fig2 is a diagram of the venous occlusion catheter 12 , which may be used in connection with the embodiment illustrated in fig1 . the catheter 12 is of a length sufficient to extend from an insertion point to the svc . the outer diameter of the catheter is less than the inner diameter of the svc at a location whether the svc is to be occluded . the catheter 12 is preferably opaque to x - rays and may be marked at the tip for easy visualization using conventional x - ray equipment . in one embodiment , the catheter 12 comprises a main lumen 26 opening at the tip 28 of the catheter . the catheter further comprises a balloon lumen 30 that forms a low resistance connection between an inflatable balloon 32 and a pump , e . g ., via a reservoir . the inflatable balloon 32 is preferably made from a highly compliant or easily folding material so that the balloon 32 , the low resistance balloon channel 30 , and the reservoir together form a high compliance system . this system may be filled with a low viscosity gas , such as helium . the catheter 12 may incorporate a conventional optic fiber 34 to allow for oxygen saturation measurement in the svc . the catheter 12 may further incorporate a thermistor 36 , positioned close to the catheter tip 28 and proximally to the balloon 32 for cerebral blood flow ( cbf ) measurement . the main lumen 26 of the catheter 12 is coupled to the controller 22 for pressure sensing of the svc . alternatively the svc pressure can be sensed through a conventional fiberoptic pressure sensor in the catheter 12 . the main catheter lumen 26 is also connected to a pump for fluid injection / withdrawal to actuate the balloon 32 . in another embodiment for treating venous steal due to cerebral vessel collapse , illustrated in fig3 , the occluding catheter 12 may comprise a plurality of expandable balloons 32 , each coupled to controller 22 and individually expandable . in operation , a lower balloon 32 may be positioned between the ra and the inferior venal cava ( ivc ), and the upper balloon 32 positioned between the ra and the svc . this embodiment allows control of flow from the ivc while the outflow in the svc is being occluded . using this dual balloon embodiment , an operator may alternatively or simultaneously occlude only the jugular vein or the jugular with the azygos veins ( which collects blood from the vertebral plexus ). this allows for improved control ; otherwise , the azygos vein outflow can be controlled only with hydrostatic pressure ( e . g ., by placing the patient &# 39 ; s head down ). in another embodiment for treating venous steal due to cerebral vessel collapse , cerebral venous pressure increase is achieved by occluding one or both of the internal jugular veins . this may be achieved , for example , by inserting the distal end of an occluding catheter 12 in the right or the left internal jugular vein . in such an embodiment , the occluding catheter 12 is modified to fit within the structure of the interior jugular vein . a balloon 32 of the occluding catheter 12 is expanded within the jugular vein to occlude the return flow from the brain to the heart . as with occluding flow in the svc , this may also increase the cerebral venous pressure and thereby restore collapsed cerebral veins to increase the cerebral blood flow therethrough . advancing jugular catheter into the intracranial portion of venous circulation ( e . g ., the sigmoid sinus or straight sinus ) allows venous pressure control in the selective part of cerebral venous circulation . in another embodiment , cerebral venous pressure increase can be achieved by inserting the distal ends of an occluding catheter 12 in each of the right and the left internal jugular veins . fig4 illustrates another embodiment in which cervical vein occlusion is achieved with external cervical compression device . in this embodiment , a cervical cuff 54 is placed around a patient &# 39 ; s neck , where the cervical cuff 54 is coupled to the controller 22 via a hose 56 . the controller 22 may include a pump to actuate the cervical cuff 54 via the hose 56 , causing the cervical cuff 54 to tighter around the patient &# 39 ; s neck and partially occlude the cervical veins . in this way , increased cerebral venous pressure can be achieved quickly and without any invasive procedure . there are several advantages in using the various embodiments of the devices and methods disclosed herein for protecting the brain and cerebral vasculature of patients suffering from global or local ischemia due to venous steal . for example , compared with known techniques for retrograde cerebral venous perfusion , the retrograde venous perfusion of the invention ( 1 ) does not produce backflow of blood to the brain , thereby eliminating retroperfusion injury ; ( 2 ) eliminates the need for ivc clamping , thereby avoiding damage to the ivc ; ( 3 ) provides an accurate measurement of the jugular venous pressure ; ( 4 ) is very easy to administer ( akin to placement of central venous catheters that most physicians learn during early training stages ) so does not require specialized medical personnel ; ( 5 ) is expected to have very low complication rates due to its simplicity ; and ( 6 ) can be combined with ivc catheterization procedures for administration of fluids , drugs , and the like . in one embodiment , the degree of vessel occlusion may be controlled by a balloon inflator ( e . g ., a pump ) in the controller 22 , which can be manually or automatically controlled . balloon inflation is preferably limited to a value of pressure and / or volume selected as maximal safe level ( p_balloon_max and / or v_balloon_max ). once the balloon is maximally inflated , a before and after balloon pressure gradient ( dpmax ) is measured . the balloon is then gradually deflated until dp diminishes . the level of balloon inflation that maintains dp near dpmax is p_balloon_submax . in one embodiment , this pressure is selected as the optimal inflation pressure at which to maintain the occluding catheter 12 during treatment of the patient . in one embodiment , the expandable balloon may have a large - volume , high - compliance design with or without a fixed pressure external inflation reservoir . this embodiment allows a fixed - pressure , variable - volume balloon inflation . fixed balloon pressure limits dp increase to p_balloon . in one embodiment of the treatment procedure , a patient is initially selected who is experiencing an acute onset of neurological deterioration due to stroke or cerebral ischemia , cause by venous steal . the patient is screened for an ability to modify cerebral blood flow or collateral flow augmentation by trendelenburg / valsalva . once the patient is determined to be a candidate for the procedure , the occluding catheter 12 is inserted into the patient &# 39 ; s venous system and positioned in the body as desired . in position , the balloon 32 of the occluding catheter 12 is inflated , using for example the controller 22 . ( alternatively , occlusion may be achieved externally using the cervical cuff 54 , shown in fig4 .) the venous pressure is measured using the catheter 12 , and the cerebral blood flow response is assessed using the hemodynamic effect monitor 40 , which data may be provided to the controller 22 . responsive to the venous pressure and cerebral blood flow measurements , the occlusion of the catheter 12 is modulated to achieve an optimal response ( e . g ., maximal cerebral blood flow ). this therapy is continued until the patient &# 39 ; s condition improves , or for a predetermined time period . beneficially , the improvement in the patient &# 39 ; s condition is expected to have a persistent effect even after treatment is ceased , since the increased cerebral blood flow will tend to keep the cerebral venous structure from collapsing without need for continued increased venous pressure . in one embodiment , the following control algorithm is used to determine the optimal occlusion by the occluding catheter 12 . this algorithm optimizes regional cerebral blood flow ( cbf ) by increasing venous pressure via occlusion , responsive to the measured venous pressure and cbf . the steps of the algorithm are : 1 . obtain baseline cbf ( t0 ), map rcbf ( t0 ), collateral flow ( t0 ) 2 . obtain baseline map ( t0 ), cvp ( t0 ) 3 . calculate cpp ( t0 )= map ( t0 )− cvp ( t0 ) 4 . change cvp by dpv ( t0 + dt ) 5 . map rcbf response to dpv : a . ohms response ( rcbf reduction proportional to cpp reduction ): d ( rcbf )=( cbf ( t0 )− 0 )/ cpp ( t0 )− dpv ) b . starling response ( rcbf = const or changes little )— characteristic for the large regions with increased tissue pressure or when cbf autoregulation is preserved ( cbf independent of cpp ): d ( rcbf )& lt ;( cbf ( t0 )− 0 )/ cpp ( t0 )− dpv ); or d ( rcbf )= 0 c . steal response — rcbf increases while cpp decreases — characteristic for heterogenous perifocal regions with rcbf diversion 6 . determine from rcbf mapping ( step 1 ) regions with critically reduced rcbf ( at risk for permanent injury ) 7 . determine from the step 5 whether critical regions have steal response ( 5c ) 8 . elevate cvp to the level where rcbf5c ( steal ) is maximized and exceeds critical flow threshold , while rcbf5a ( ohm &# 39 ; s response ) decreases , but stays above the ischaemic threshold 9 . reassess rcbf response to cvp periodically 10 . result : optimized rcbf distribution with the decreased chance of permanent ischaemic injury in perifocal regions the foregoing description of the embodiments of the invention has been presented for the purpose of illustration ; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed . persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure . some portions of this description describe the embodiments of the invention in terms of algorithms and symbolic representations of operations on information . these algorithmic descriptions and representations are commonly used by those skilled in the data processing arts to convey the substance of their work effectively to others skilled in the art . these operations , while described functionally , computationally , or logically , are understood to be implemented by computer programs or equivalent electrical circuits , microcode , or the like . as used herein , the term “ proximal ” refers to a position closer to the catheter end outside the body and venous circulation part away from the heart . if the catheter is inserted so that is distal part is closer to the brain ( e . g ., inserted via inferior vena cava ), the terms “ proximal ” and “ distal ” still apply to the catheter , but when referred to the venous system they refer to the part closer to the brain ( i . e ., proximal ) or closer to the heart ( i . e ., distal ). usage of the lumens is reversed in the latter case . finally , the language used in the specification has been principally selected for readability and instructional purposes , and it may not have been selected to delineate or circumscribe the inventive subject matter . it is therefore intended that the scope of the invention be limited not by this detailed description , but rather by any claims that issue on an application based hereon . accordingly , the disclosure of the embodiments of the invention is intended to be illustrative , but not limiting , of the scope of the invention , which is set forth in the following claims .
a patient in whom blood diversion due to cerebral venous steal is present , and abolishment of the cerebral venous steal is indicated , is treated by increasing the cerebral venous pressure in the patient . this increase in cerebral venous pressure restores the collapsed cerebral vasculature , thereby increasing cerebral blood flow . the increase in cerebral venous pressure may be achieved using an occluding catheter in the superior vena cava or the internal jugular veins , using external compression of the cervical veins , or any other suitable mechanism . the occlusion may be controlled precisely during treatment , possibly as a function of cerebral blood flow , and after treatment the patient may experience a persistent effect because the cerebral vasculature is no longer collapsed .