Mechanical Resonant Pulse Relief Valve for Assisted Removal of Obstructive Aspirates

Abstract

The aspiration system includes a suction catheter, a suction source fluidly coupled to the suction catheter to establish an aspiration flow path between the suction catheter and the suction source, a pressurized fluid source, and a passive pressure oscillation assembly fluidly coupled between the pressurized fluid source and the aspiration flow path. The passive pressure oscillation assembly is configured to operate between a normal mode that prevents fluid communication between the pressurized fluid source and the aspiration flow path and an oscillation mode that pulses fluid communication between the pressurized fluid source and the aspiration flow path. The passive pressure oscillation assembly is configured to be activated to switch from the normal mode to the oscillation mode in response to an obstruction in the suction catheter.

Description

[Technical Field]

[0001] The present disclosure relates generally to medical devices and intravascular medical procedures, and more particularly to devices used to aspirate objects from anatomical structures, such as, for example, blood clots from a patient's vasculature. [Background technology]

[0002] It is often desirable to remove tissue from the body as minimally invasively as possible to avoid damaging other tissues. For example, removing tissue such as a blood clot from within the vasculature can improve a patient's condition and quality of life.

[0003] Many vascular problems result from insufficient blood flow through the blood vessels. One cause of insufficient or irregular blood flow is an obstruction within a blood vessel called a blood clot or thrombus. A blood clot or thrombus can embolize and form an embolus within a patient's vasculature. A blood clot can develop for many reasons, including damage to the arterial wall due to atherosclerotic disease, trauma resulting from surgery, or other causes.

[0004] When a thrombus forms, it can effectively stop blood flow through the area where it formed. In some cases, such thrombi dissolve harmlessly into the bloodstream. However, in other cases, such thrombi can remain lodged within a blood vessel, where they can partially or completely block blood flow. If a partially or completely blocked blood vessel supplies blood to a susceptible tissue, such as the brain, lungs, or heart, serious tissue damage can occur. For example, thrombosis of one of the carotid arteries can cause a stroke due to insufficient oxygen supply to important nerve centers within the skull. As another example, if one of the coronary arteries is 100% thrombotic, blood flow is stopped within this artery, resulting in a shortage of oxygen-carrying red blood cells to supply, for example, the muscle of the heart wall (myocardium). The lack of oxygen can reduce or prevent muscle activity, causing chest pain (angina pectoris), and even lead to necrosis of the myocardium, resulting in a degree of permanent cardiac damage. When myocardial cell death is widespread, the heart is unable to pump enough blood to supply the body with vital nutrients. In fact, a significant percentage of the more than 1.2 million heart attacks in the United States are caused by blood clots (thrombi) forming in the coronary arteries.

[0005] When signs of a vascular obstruction, such as a vascular occlusion leading to a stroke, appear, prompt action should be taken to reduce or eliminate the resulting tissue damage. Indeed, clinical data indicate that clot removal can be beneficial and even essential to improve outcomes. For example, in the peripheral vasculature, clot removal can reduce the need for amputation by 80%. The ultimate goal of all modalities for treating these conditions in the arterial or venous systems is rapid, complete, and cost-effective clearance of the obstruction, i.e., recanalization. One approach is to treat patients with thrombolytic drugs. However, these drugs do not rapidly dissolve clots in patients and generally become ineffective after a limited window, usually 2–3 hours, after the onset of clot-related symptoms. Another approach involves thrombectomy, i.e., removal of the clot by aspiration, mechanical retrieval, or a combination thereof. Mechanical retrieval is often complex and risky to perform, as it typically involves a deployable mesh lattice such as a stent retriever.

[0006] Aspiration thrombectomy is generally an effective and commonly used treatment for removing blood clots from blood vessels, particularly in cases of ischemic stroke. In a typical endovascular aspiration thrombectomy procedure, a catheter is introduced into a patient's vasculature until the distal end of the catheter is immediately proximal to the clot, and a vacuum is applied to the proximal end of the catheter, thereby drawing at least a portion of the clot into the catheter for subsequent removal. Many aspiration systems are susceptible to tip blockage when the clot being aspirated is excessively large compared to the aspiration conduit at the distal end of the catheter. The current technology for endovascular thrombectomy in ischemic stroke utilizes static loading. When tip blockage occurs, the pressure within the system rapidly drops to a level that often causes vaporization or cavitation of the aspirate within the system. As a result, water vapor enters the system, which reduces the efficiency of the aspiration, which in turn makes it more difficult, if not impossible, to draw the clot into the catheter.

[0007] In some cases, obstructions can be disrupted or forced through the aspiration conduit by dynamically or cyclically filling the aspiration conduit. This involves using pressure pulsations to aspirate the obstructing clot. One method of cyclically filling the aspiration conduit uses a periodically actuated valve or similar device to achieve pressure pulsations by blocking the main stream flow. This is typically done manually or via an electromechanical or pneumatic valve that blocks aspiration flow to the pump for a specified time interval. In some cases, pressure-sensing feedback has been proposed as a means to determine when to actuate the valve. One cyclic filling method, described in Simon S, Gray CP, Massenzo T, et al., "Exploring the efficacy of cyclic vs. static aspiration in a cerebral thrombectomy model: an initial proof-of-concept study," Journal of NeuroInterventional Surgery, 2014;6:677-683, and PCT Publication WO2014151209A8, employs a venting mechanism that is automatically placed into an oscillating pulse mode in response to the application of vacuum to the aspiration conduit. However, these methods require user intervention to periodically fill the aspiration conduit in response to a finding that the aspiration conduit is blocked (which would interfere with the user performing the aspiration procedure manually) or immediately after applying vacuum to the aspiration conduit, thus reducing the efficiency of the aspiration procedure during free flow (i.e., when the aspiration conduit is not blocked). [Brief explanation of the drawings]

[0008] The drawings illustrate the design and utility of preferred embodiments of the disclosed invention, where similar elements are designated with common reference numerals. Note that the figures are not to scale, and that elements of similar structure or function are designated by similar reference numerals throughout the views. Furthermore, note that the figures are intended only to aid in the description of the embodiments. These figures are not intended to be comprehensive descriptions of the invention, nor are they intended to limit the scope of the invention, which is defined solely by the appended claims and their equivalents. In addition, a depicted embodiment of the disclosed invention need not possess all of the depicted aspects or advantages. Furthermore, an aspect or advantage described in connection with a particular embodiment of the disclosed invention is not necessarily limited to this embodiment alone, and may be implemented in any other embodiment, even if not shown.

[0009] In order that the manner in which the above-mentioned advantages and objects of the disclosed invention may be better understood, as well as other advantages and objects, a more particular description of the disclosed invention as briefly described above will be rendered by reference to specific embodiments of the invention which are illustrated in the accompanying drawings, in which the invention will be described and explained with more specificity and detail, with the understanding that these drawings depict only exemplary embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

[0010] [Figure 1] 1 is a block diagram illustrating one embodiment of an aspiration system constructed in accordance with the present invention. [Figure 2] 2 is a plan view of an exemplary aspiration catheter used in the aspiration system of FIG. 1. [Figure 3] 3 is a plan view of the distal end of the aspiration catheter of FIG. 2 used to aspirate vascular obstruction material from the vasculature of a patient. [Figure 4] 2 is a timing diagram illustrating a negative pressure differential over time between a pressurized fluid source and an aspiration flow path established within the aspiration system of FIG. 1. [Figure 5] FIG. 2 is a block diagram illustrating one embodiment of a passive pressure oscillation assembly used in the aspiration system of FIG. 1. [Figure 6] 2 is a block diagram illustrating another embodiment of a passive pressure oscillation assembly used in the aspiration system of FIG. 1. [Figure 7] 1. FIG. 4 is a block diagram illustrating yet another embodiment of a passive pressure oscillation assembly for use in the aspiration system of FIG. [Figure 8A] 2 is a top view of one embodiment of a passive pressure oscillation assembly used in the aspiration system of FIG. 1, particularly showing the passive pressure oscillation assembly in a closed position. [Figure 8B] 8B is a top view of the passive pressure vibration assembly of FIG. 8A, particularly showing the passive pressure vibration assembly in an open position. [Figure 9A] 1. FIG. 4 is a plan view of another embodiment of a passive pressure oscillation assembly for use in the aspiration system of FIG. 1, particularly showing the passive pressure oscillation assembly in a closed position. [Figure 9B] 9B is a top view of the passive pressure vibration assembly of FIG. 9A, particularly showing the passive pressure vibration assembly in an open position. FIG. [Figure 10A] 2 is a plan view of another embodiment of a passive pressure oscillation assembly for use in the aspiration system of FIG. 1, particularly showing the passive pressure oscillation assembly in a first state. [Figure 10B] 10B is a plan view of the passive pressure vibration assembly of FIG. 10A, particularly showing the passive pressure vibration assembly in a second state. [Figure 10C] 10B is a plan view of the passive pressure vibration assembly of FIG. 10A, particularly showing the passive pressure vibration assembly in a third state. [Figure 10D] 10B is a plan view of the passive pressure vibration assembly of FIG. 10A, particularly showing the passive pressure vibration assembly in a fourth state. [Figure 11A] 1. FIG. 4 is a plan view of another embodiment of a passive pressure oscillation assembly for use in the aspiration system of FIG. 1, particularly showing the passive pressure oscillation assembly in a closed position. [Figure 11B] 11B is a top view of the passive pressure vibration assembly of FIG. 11A, particularly showing the passive pressure vibration assembly in an open position. FIG. [Figure 12] 2 is a flow chart illustrating one method of operating the aspiration system of FIG. 1 to aspirate vascular obstructions from a patient's vasculature. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1, one embodiment of a vascular obstruction aspiration system 10 constructed in accordance with the disclosed invention will be described. The vascular obstruction aspiration system 10 generally includes an aspiration catheter 12, a suction source 14, a pressurized fluid source 16, a tissue collection container 18, and a manifold 20.

[0012] 2 and 3, the aspiration catheter 12 comprises an elongate catheter body 22 and an aspiration conduit 24 (shown in phantom in FIG. 3) extending through the catheter body 22 between a proximal end 28 and a distal end 30 of the catheter body 22. The proximal end 28 of the aspiration catheter 12 remains external to the patient 1 and is accessible to the operator during use of the vascular occlusion material aspiration system 10, while the distal end 30 of the catheter body 22 is sized and dimensioned to reach vascular occlusion material 2 (e.g., a blood clot) at a remote location in the patient's vasculature 1, as best shown in FIG. 3. The aspiration catheter 12 comprises a distal inlet port 32 in communication with the aspiration conduit 24 of the aspiration catheter 12, into which the vascular occlusion material 2 is aspirated by the aspiration catheter 12.

[0013] The aspiration catheter 12 can have multiple regions along its length having various configurations and / or properties. For example, the distal portion of the catheter body 22 can have a smaller outer diameter than the proximal portion of the catheter body 22 to reduce the profile of the distal portion of the catheter body 22 and aid in navigation within tortuous vasculature. Furthermore, the distal portion of the catheter body 22 can have greater flexibility than the proximal portion of the catheter body 22. Generally, the proximal portion of the catheter body 22 can be formed from a material having a higher stiffness than the distal portion of the catheter body 22, such that the proximal portion has sufficient pushability for advancement through the patient's vasculature 1, while the distal portion can be formed from a more flexible material, such that the distal portion remains flexible and can more easily be tracked over a guidewire to access remote locations within tortuous regions of the vasculature 1. The catheter body 22 may be constructed from a suitable polymeric material, metal, and / or alloy, such as polyethylene, stainless steel, or other suitable biocompatible material, or a combination thereof. In some examples, the proximal portion of the catheter body 22 may have a reinforcing layer, such as a braided or coiled layer, to improve the pushability of the catheter body 22. The catheter body 22 may have a transition region between the proximal and distal portions of the catheter body 22.

[0014] Referring again to FIG. 1 , the suction source 14 may be, for example, a conventional pump (e.g., a rotary vane pump, a diaphragm pump, a peristaltic pump, or a Venturi pump) or a syringe configured to generate a low pressure within the aspiration conduit 26 of the aspiration catheter 12. This low pressure is lower than ambient air pressure and, therefore, may be considered a vacuum capable of aspirating the vascular occlusion material 2 within the aspiration conduit 26 of the aspiration catheter 12. The vascular occlusion material 2 may be sucked into the aspiration catheter 12 in one piece, or may be broken into multiple pieces and sucked piece by piece into the aspiration catheter 12. During operation, the suction source 14 provides a base level of vacuum to the aspiration catheter 12. This vacuum level can be controlled and adjusted as needed by the user to aspirate tissue. The user can set the vacuum level constant or vary the vacuum level over any given period of time during the tissue removal procedure.

[0015] The pressurized fluid source 16 may be, for example, a reservoir containing a liquid such as saline (e.g., a saline drip bag) or ambient air. It should be appreciated that the fluid source 16 is pressurized to a degree that causes the fluid to have a pressure higher than the lowest vacuum level achieved within the suction conduit 24 of the suction catheter 12 during operation of the suction source 14. Thus, even though the fluid source 16 of the illustrated embodiment may be under a lower pressure (i.e., ambient pressure or one absolute atmosphere), the fluid source 16 is pressurized relative to the pressure experienced by the suction conduit 24 of the suction catheter 12 during operation of the suction source 14. The tissue collection container 18 may be any suitable container fluidly connected to the suction source 14 via an exhaust line to enable aseptic collection and disposal of aspirated tissue. Alternatively, the tissue collection container 18 may be located between the suction source 14 and the suction catheter 12.

[0016] The suction catheter 12, suction source 14, pressurized fluid source 16, and tissue collection container 18 may be conventional in nature.

[0017] In contrast, the manifold 20 is non-conventional and provides an interface between the suction catheter 12, the suction source 14, and the pressurized fluid source 16 in a manner that assists the suction catheter 12 in aspirating the thrombus 2 during zero-flow or low-flow conditions (e.g., when a thrombus 2 blocks the suction conduit 24 of the suction catheter 12 or when there is otherwise a flow anomaly in the aspiration circuit of the system 10), while maximizing the efficiency of the aspiration process during free-flow conditions (e.g., when the suction conduit 24 is not blocked and the aspiration circuit of the system 10 is operating as intended).

[0018] The manifold 20 includes a suction inlet 36 coupled to the suction catheter 12 and a suction outlet 38 coupled to the suction source 14, and a relief inlet 40 coupled to the pressurized fluid source 16, to form an aspiration flow path 46 from the suction catheter 12 to the suction source 14. The manifold 20 may be coupled to the suction catheter 12, suction source 14, and pressurized fluid source 16 through the use of a conventional catheter (not shown), or alternatively, may be integrated thereto without the use of connectors. The manifold 20 further includes a passive pressure oscillation assembly 44 coupled between the relief inlet 40 and the aspiration flow path 46. Importantly, the passive pressure oscillation assembly 44 is configured to dynamically fill (i.e., rapidly change vacuum levels) the aspiration conduit 24 of the aspiration catheter 12, and particularly to periodically fill the aspiration conduit 24 only during zero or low flow conditions. The passive pressure oscillation assembly 44 accomplishes this without user input and without the use of electronic sensors. Additionally, the passive pressure oscillation assembly 44 can be made very compact, so that it can fit within the manifold 20 with little increase in size. The passive pressure oscillation assembly 44 may not be able to simply block the relief inlet 40.

[0019] To this end, the passive pressure oscillation assembly 44 is configured to operate between a normal mode in which fluid communication along the relief path 48 between the pressurized fluid source 16 and the aspiration flow path 46 is prevented (so that the absolute pressure in the aspiration flow path 46 remains relatively constant and is acted upon only by the aspiration source 14), and an oscillation mode in which fluid communication along the relief path 48 between the pressurized fluid source 16 and the aspiration flow path 46 is pulsed (so that the absolute pressure in the aspiration flow path 46 oscillates within a predetermined frequency range). The passive pressure oscillation assembly 44 is configured to be activated to switch from the normal mode to the oscillation mode in response to an obstruction in the aspiration conduit 24 of the aspiration catheter 12 or other flow anomaly in the aspiration conduit of the system 10, and conversely, to be activated to switch from the oscillation mode to the normal mode in response to the removal or clearance of an obstruction from the aspiration conduit 24 of the aspiration catheter 12 or other resolution of the flow anomaly in the aspiration circuit of the system 10. In the embodiment shown, pulsing of the fluid communication between the pressurized fluid source 16 and the aspiration channel 46 causes pressure pulses at a predetermined frequency to propagate along the aspiration conduit 24 of the aspiration catheter 12. Simultaneously, pulsing of the fluid communication between the pressurized fluid source 16 and the aspiration channel 46 causes a backflow of fluid to propagate along the aspiration conduit 24 of the aspiration catheter 12.

[0020] The passive pressure oscillation assembly 44 may be designed to pulse the fluid communication along the relief path 48 between the pressurized fluid source 16 and the aspiration fluid line 46 at a predetermined frequency, causing the absolute pressure in the aspiration fluid line 46 to oscillate at the predetermined frequency. As one example, the predetermined frequency of pressure oscillations induced in the aspiration fluid line 46 by the passive pressure oscillation assembly 44 may match the natural resonance of the fluid column in the aspiration conduit 24 of the aspiration catheter 12, thereby maximizing energy transfer from the aspiration fluid line 46 to the aspiration conduit 24 of the aspiration catheter 12 and, therefore, the propagation of pressure pulses along the aspiration conduit 24 of the aspiration catheter 12. As another example, the predetermined frequency of pressure oscillations induced in the aspiration fluid line 46 by the passive pressure oscillation assembly 44 may be selected based on the viscoelastic properties of the thrombus 2 expected to be drawn by the aspiration catheter 12. That is, an occlusive thrombus 2 having a softer consistency may be more susceptible to maceration and then respiration in response to relatively low frequency and high amplitude vibrations, whereas an occlusive thrombus 2 having a harder consistency may be more susceptible to maceration and then respiration in response to relatively high frequency and low amplitude vibrations.

[0021] The vibrations of the passive pressure oscillation assembly 44 can optionally emit sound and serve as an automatic audio signal to the user that an obstruction has occurred in the aspiration conduit 24 of the aspiration catheter 12. In an optional embodiment, the passive pressure oscillation assembly 44 can be designed to pulse the fluid communication between the pressurized fluid source 16 and the aspiration channel 46 at two or more different frequencies simultaneously. For example, because the type of material property of the thrombus 2 is not known, it may be desirable to pulse the fluid communication between the pressurized fluid source 16 and the aspiration channel 46 at a relatively high frequency and a relatively low frequency simultaneously, resulting in a pressure profile in the aspiration conduit 24 of the aspiration catheter 12 that is a composite of low- and high-frequency oscillations.

[0022] In the illustrated embodiment, the passive pressure oscillation assembly 44 utilizes the correlation between different flow conditions of the suction catheter 12 and the resulting fluid pressure levels within the aspiration flow path 46. Specifically, in the case of a zero-flow or low-flow condition, in which an obstruction is present in the aspiration conduit 24 of the aspiration catheter 12 or other flow anomaly exists within the aspiration circuit of the system 10, it is expected that the vacuum within the aspiration flow path 46 will rapidly increase (i.e., the absolute pressure within the aspiration flow path 46 will rapidly decrease), thereby increasing the negative pressure differential between the external ambient pressure and the aspiration flow path 46 to a very high level (e.g., at least −55 kPa), which, absent intervention by the passive pressure oscillation assembly 44, may further cause evaporation or cavitation of aspirant within the aspiration flow path 46 (e.g., if such negative pressure differential is less than −95 kPa). In contrast, in the case of a free-flow condition, where the aspiration catheter 12 is not blocked or the flow anomaly in the aspiration circuit of the system 10 is otherwise resolved, it is expected that the vacuum in the aspiration flow path 46 will drop sharply (i.e., the absolute pressure in the aspiration flow path 46 will increase sharply) to a lower level (e.g., below −50 kPa), thereby reducing the negative pressure differential between the external ambient pressure and the aspiration flow path 46 to a lower level. The passive pressure oscillation assembly 44 keys off these negative pressure differentials when switching between normal and oscillation modes.

[0023] To this end, the passive pressure oscillation assembly 44 includes an inlet port 50 (shown in FIG. 5) in fluid communication with the pressurized fluid source 16 and an outlet port 52 (shown in FIG. 5) in fluid communication with the suction passage 46, such that the passive pressure oscillation assembly 44 is exposed to a negative pressure differential between the pressurized fluid source 16 and the fluid in the suction passage 46. The passive pressure oscillation assembly 44 is activated based on this negative pressure differential to switch from normal mode to oscillation mode and vice versa.

[0024] Specifically, the passive pressure oscillation assembly 44 is designed to be activated to switch from normal mode to oscillation mode in response to a drop in absolute pressure within the aspiration flow path 46 to create a negative activation pressure differential between the inlet port 50 and the outlet port 52 of the passive pressure oscillation assembly 44 that correlates to a negative pressure difference between the aspiration flow path 46 and the blood pressure experienced by the aspiration catheter 12 when the aspiration conduit 24 of the aspiration catheter 12 is occluded or the aspiration circuit of the system 10 is otherwise experiencing a flow anomaly (a zero flow or low flow condition); and conversely, the passive pressure oscillation assembly 44 is designed to create a negative cessation pressure differential that correlates to a negative pressure difference between the aspiration flow path 46 and the blood pressure experienced by the aspiration catheter 12 when the aspiration conduit 24 of the aspiration catheter 12 is not occluded or the aspiration circuit of the system 10 is operating as intended (a free flow condition). The passive pressure oscillator 44 is designed to be activated to switch from the oscillatory mode to the normal mode in response to an increase in absolute pressure within the suction passage 46 that creates a differential pressure between the inlet port 50 and the outlet port 52 of the passive pressure oscillator assembly 44.

[0025] In the case where the pressurized fluid source 16 is external ambient pressure, the actuation negative pressure differential of the passive pressure oscillation assembly 44 during zero or low flow conditions differs substantially by a known offset from the negative pressure differential between the aspiration flow path 46 and the blood pressure experienced by the aspiration catheter 12, and similarly, the actuation negative pressure differential of the passive pressure oscillation assembly 44 during free flow conditions differs substantially by a known offset from the negative pressure differential between the aspiration flow path 46 and the blood pressure experienced by the aspiration catheter 12. In this manner, the passive pressure oscillation assembly 44 can be configured to self-calibrate to the time-varying external environment.

[0026] In this case, the design range of the negative pressure differential for actuation of the passive pressure oscillation assembly 44 may have an upper limit of −55 kPa such that the passive pressure oscillation assembly 44 will be rapidly activated to switch from normal mode to oscillation mode, but not so low as to activate the passive pressure oscillation assembly 44 to switch from normal mode to oscillation mode during actuation and active and productive suction of the thrombus 2 into the distal end 30 of the aspiration catheter 12, and may have a lower limit of −95 kPa to ensure that the boiling point of the fluid in the aspiration flow path 46 (i.e., blood at 37° C.) is not reached. However, the passive pressure oscillation assembly 44 may be designed to have an actuation negative pressure differential anywhere within the range of −55 kPa to −95 kPa. The deactivation negative pressure differential of the passive pressure oscillation assembly 44 should be designed relative to the activation negative pressure differential of the passive pressure oscillation assembly 44 and is preferably significantly lower than the activation negative pressure differential (e.g., 10 kPa to 25 kPa greater than the activation negative pressure differential), thereby building hysteresis into the passive pressure oscillation assembly 44. This ensures that pressure oscillations induced in the aspiration flow path 46 by the passive pressure oscillation assembly 44 do not inadvertently activate the passive pressure oscillation assembly 44 and return it to normal mode until the aspiration catheter 12 is in a free-flow state. In low resonant frequency scenarios, the activation and deactivation negative pressure differentials may be equal, and in such cases, the passive pressure oscillation assembly 44 will be reactivated after each increase in the negative pressure differential in the aspiration flow path 46 to switch from normal mode to oscillation mode in response to a drop in absolute pressure in the aspiration flow path 46 caused by the suction source 18.

[0027] In an optional embodiment, the passive pressure oscillation assembly 44 may be designed to have multiple actuation negative pressure differentials and thus multiple deactivation negative pressure differentials. For example, the passive pressure oscillation assembly 44 may be designed to have a first actuation negative pressure differential, e.g., −50 kPa, such that the passive pressure oscillation assembly 44 is activated to switch from a normal mode to a relatively high-speed oscillation mode to assist in drawing thrombus 2 into the distal end 30 of the aspiration catheter 12 before the aspiration conduit 24 of the aspiration catheter 12 is blocked. Operation of the passive pressure oscillation assembly 44 in the relatively high-speed oscillation mode may propagate high-frequency, low-volume pulses along the aspiration conduit 24 of the aspiration catheter 12, thereby assisting in drawing thrombus 2 without unduly impeding volumetric flow. The passive pressure oscillation assembly 44 may further be designed to have a second actuating negative pressure differential, e.g., −55 kPa, such that the passive pressure oscillation assembly 44 is activated to operate in a relatively slow oscillation mode to assist in dislodging the occlusive thrombus 2 within the distal end 30 of the aspiration catheter 12. slow speed Operation of the passive pressure oscillation assembly 44 in the high-speed oscillation mode can propagate low-frequency, high-volume pulses along the aspiration conduit 24 of the aspiration catheter 12 in an attempt to dislodge the occlusive thrombus 2 from the distal end 30 of the aspiration catheter 12. Thus, if a thrombus 2 is aspirated without blocking the distal end 30 of the aspiration catheter 12, only the high-speed oscillation mode of the passive pressure oscillation assembly 44 is activated, whereas if a thrombus 2 blocks the distal end 30 of the aspiration catheter 12, only the low-speed oscillation mode of the passive pressure oscillation assembly 44 is activated.

[0028] It should be appreciated that the pressurized fluid source 16 may have a pressure significantly different from the external ambient pressure experienced by the aspiration catheter 12, such that during zero or low flow conditions, the actuation negative pressure differential of the passive pressure oscillation assembly 44 will be significantly different from the negative pressure differential between the aspiration channel 46 and the surrounding external environment experienced by the aspiration catheter 12, and similarly, during free-flow conditions, the deactivation negative pressure differential of the passive pressure oscillation assembly 44 will be significantly different from the negative pressure differential between the aspiration channel 46 and the surrounding external environment experienced by the aspiration catheter 12. In this latter case, this difference can be taken into account when designing the actuation and deactivation negative pressure differentials of the passive pressure oscillation assembly 44. For example, if the pressurized fluid source 16 has a pressure significantly higher than the external ambient pressure, the passive pressure oscillation assembly 44 should be designed to have a larger actuation and deactivation negative pressure differential to account for the higher fluid pressure that will be experienced at the inlet port 50 of the passive pressure oscillation assembly 44.

[0029] 4, the suction source 14 is first activated, causing the suction catheter 12 to enter a free-flow state between any times t0 and t1, such that the negative pressure difference between the absolute pressure within the suction flow path 46 and the external ambient pressure experienced by the suction catheter 12 (in this case, the negative pressure difference between the inlet port 50 and the outlet port 52 of the passive pressure oscillation assembly 44) constitutes a free-flow negative pressure difference, in which the suction catheter 12 draws only blood. During this time, the passive pressure oscillation assembly 44 remains in normal mode. This maximizes the suction efficiency of the system 10 during the free-flow state.

[0030] Between any times t1 and t2, thrombus 2 is actively sucked into distal end 30 of aspiration catheter 12, causing the negative pressure differential between the absolute pressure within aspiration flow path 46 and the external ambient pressure experienced by aspiration catheter 12 to drop below the free-flow negative pressure differential for actuation of passive pressure oscillation assembly 44 (designed for zero or low flow conditions indicative of a blocked aspiration catheter 12 or flow abnormalities within the aspiration conduit of system 10). At any times t0 and t2, passive pressure oscillation assembly 44 remains in normal mode.

[0031] However, at any time t2, the aspiration catheter 12 becomes occluded with a thrombus 2, causing the negative pressure difference between the absolute pressure in the aspiration flow channel 46 and the external ambient pressure experienced by the aspiration catheter 12 to suddenly drop to a level below the actuation negative pressure difference, which is −75 kPa in the illustrated case. Thus, at or shortly after any time t2, the occluded aspiration catheter 12 (in a zero or low flow state) activates the passive pressure oscillation assembly 44 to switch from normal mode to oscillation mode, causing pressure oscillations in the aspiration flow channel 46, which in turn propagate pressure pulses along the aspiration conduit 24 of the aspiration catheter 12, thereby assisting in dislodging the occlusive thrombus 2 at the distal end 24 of the aspiration catheter 12 at any time t3. Dislodging the occlusive thrombus 2 at the distal end 24 of the aspiration catheter 12 causes the negative pressure difference between the absolute pressure in the aspiration flow channel 46 and the external ambient pressure experienced by the aspiration catheter 12 to suddenly increase to a level above the actuation negative pressure difference, which is −50 kPa in the illustrated case. Thus, at any time t3 or shortly after any time t3, an unobstructed suction catheter 12 (free flow condition) activates the passive pressure oscillation assembly 44 to switch from oscillation mode to normal mode, thereby stopping the pressure oscillations in the suction flow path 46 and thereby stopping the pressure pulses propagating along the suction conduit 24 of the suction catheter 12.

[0032] In an optional embodiment in which the passive pressure oscillation assembly 44 operates in multiple oscillation modes (e.g., a high-frequency oscillation mode and a low-frequency oscillation mode), the passive pressure oscillation assembly 44 may be operated in the high-frequency oscillation mode between any time t1 and any time t2, so that active suction of the thrombus 2 into the distal end 30 of the aspiration catheter 12 is assisted by high-frequency, low-volume pressure pulses propagating along the aspiration conduit 24 of the aspiration catheter 12; and, in the event that a thrombus 2 blocks the distal end 30 of the aspiration catheter 12, the passive pressure oscillation assembly 44 may be operated in the low-frequency oscillation mode between any time t2 and any time t3, so that removal of the occlusive thrombus 2 from the distal end 30 of the aspiration catheter 12 is assisted by low-frequency, high-volume pressure pulses propagating along the aspiration conduit 24 of the aspiration catheter 12.

[0033] 5, the passive pressure oscillator assembly 44 includes a pressure-activated valve 54 and a fluid resonator 56 (e.g., a hydraulic or pneumatic resonator). The pressure-activated valve 54 is configured to open to allow fluid flow from the pressurized fluid source 16 through the pressure-activated valve 54 in response to a decrease in absolute pressure in the aspiration flow path 28 creating an actuating negative pressure differential between the inlet port 50 and the outlet port 52 (e.g., indicating an obstruction in the aspiration conduit 24 of the aspiration catheter 12), and conversely, to close to prevent fluid flow from the pressurized fluid source 16 through the pressure-activated valve 54 in response to an increase in absolute pressure in the aspiration flow path 28 creating an actuating negative pressure differential between the inlet port 50 and the outlet port 52 (e.g., indicating an obstruction has been removed or cleared from the aspiration conduit 24 of the aspiration catheter 12). A fluid resonator device 56 is configured to resonate at a predetermined frequency in response to fluid flow from the pressurized fluid source 16 through the pressure-operated valve 54 to pulse fluid communication between the pressurized fluid source 16 and the suction passage 46 at this predetermined frequency, and conversely, to cease resonating in response to blocking of fluid flow from the pressurized fluid source 16 through the pressure-operated valve 54.

[0034] In one embodiment, the pressure-actuated valve 54 and the fluid resonator 56 are mechanically coupled to each other. In this embodiment, the mechanically coupled pressure-actuated valve 54 and fluid resonator 56 must be designed dependently to meet both opening and resonant frequency criteria, but mechanically coupling the pressure-actuated valve 54 and fluid resonator 56 to each other results in a simpler mechanical design that may be more easily implemented in the passive pressure oscillation assembly 44. In another embodiment, the pressure-actuated valve 54 and fluid resonator 56 are mechanically isolated from each other. In this embodiment, the mechanically isolated pressure-actuated valve 54 and fluid resonator 56 allow for independent optimization of the opening / closing criteria and the resonant oscillation criteria, but still results in a mechanical design that may be more complex than the mechanical design of an embodiment having a mechanically coupled pressure-actuated valve 54 and fluid resonator 56.

[0035] As discussed above, the passive pressure oscillation assembly 44 may optionally be designed to have two actuating negative pressure differentials and / or two deactivating negative pressure differentials and / or to pulse fluid communication between the pressurized fluid source 16 and the suction passage 46 simultaneously at two different frequencies.

[0036] In an alternative embodiment, the fluid resonator device 56 automatically responds to an obstruction within the suction catheter 12 by blocking the suction flow path 46 and pulsing fluid communication between the pressurized fluid source 16 and the suction flow path 46, thereby directing pulsed fluid communication between the pressurized fluid source 16 and the suction flow path 46 toward the suction catheter 12.

[0037] 6, an alternative embodiment of a passive pressure oscillation assembly 44' includes two parallel sets of pressure-actuated valve assemblies and fluid resonators. Specifically, the passive pressure oscillation assembly 44' includes a first pressure-actuated valve 54a, a first fluid resonator 56a, a second pressure-actuated valve 54b, and a second fluid resonator 56b.

[0038] The first pressure-actuated valve 54a is configured to open to allow fluid flow from the pressurized fluid source 16 through the first pressure-actuated valve 54a in response to a decrease in absolute pressure in the suction passage 28 creating a first actuating negative pressure differential between the inlet port 50 and the outlet port 52, and conversely, to close to prevent fluid flow from the pressurized fluid source 16 through the pressure-actuated valve 54 in response to an increase in absolute pressure in the suction passage 28 creating a first blocking negative pressure differential between the inlet port 50 and the outlet port 52. The first fluid resonator 56a is configured to resonate at a first predetermined frequency in response to fluid flow from the pressurized fluid source 16 through the first pressure-actuated valve 54a to pulse fluid communication between the pressurized fluid source 16 and the suction passage 46 at this first predetermined frequency, and conversely, to stop resonating in response to a blockage of fluid flow from the pressurized fluid source 16 through the first pressure-actuated valve 54a.

[0039] The second pressure-actuated valve 54b is configured to open to allow fluid flow from the pressurized fluid source 16 through the second pressure-actuated valve 54b in response to a decrease in absolute pressure in the suction passage 28 creating a second actuating negative pressure differential between the inlet port 50 and the outlet port 52, and conversely, to close to prevent fluid flow from the pressurized fluid source 16 through the pressure-actuated valve 54 in response to an increase in absolute pressure in the suction passage 28 creating a second blocking negative pressure differential between the inlet port 50 and the outlet port 52. The second fluid resonator 56b is configured to resonate at a second predetermined frequency in response to fluid flow from the pressurized fluid source 16 through the second pressure-actuated valve 54b to pulse fluid communication between the pressurized fluid source 16 and the suction passage 46 at this second predetermined frequency, and conversely, to stop resonating in response to a blockage of fluid flow from the pressurized fluid source 16 through the second pressure-actuated valve 54b.

[0040] The first and second actuating negative pressure differentials may be equal (e.g., both indicate an obstruction in the aspiration conduit 24 of the aspiration catheter 12) or may be different (e.g., one indicates active suction of a clot into the aspiration catheter 12, while the other indicates that the aspiration conduit 24 of the aspiration catheter 12 is blocked). The first and second stopping negative pressure differentials may be equal (e.g., both indicate suction or removal of an obstruction in the aspiration conduit 24 of the aspiration catheter 12). However, in alternative embodiments, the first and second stopping negative pressure differentials may be different. The first and second predetermined frequencies may be equal or different (e.g., one relatively high frequency for disrupting an occlusive thrombus 2 having a lower viscosity, and the other relatively low frequency for disrupting an occlusive thrombus 2 having a higher viscosity). The first pressure actuated valve 54a and the first fluidic resonator 56 may be mechanically coupled to each other or mechanically isolated from each other, and similarly, the second pressure actuated valve 54b and the second fluidic resonator 56b may be mechanically coupled to each other or mechanically isolated from each other. Furthermore, the first pressure actuated valve 54a and the second pressure actuated valve 54b may be coupled to each other to essentially form a valve assembly having multiple outlets that distribute flow to one or the other or both of the fluidic resonators 56a, 56b in response to various levels of a single sensed pressure differential.

[0041] Although the passive pressure oscillation assembly 44' is shown in FIG. 6 as having only two sets of pressure actuated valve assemblies and fluid resonators in parallel, the passive pressure oscillation assembly 44' may alternatively have more than two sets of pressure actuated valve assemblies and fluid resonators in parallel.

[0042] Referring to FIG. 7, another alternative embodiment of a passive pressure oscillation assembly 44'' includes a single pressure actuated valve 54, a first fluid resonator 56a, and a second fluid resonator 56b.

[0043] The pressure-actuated valve 54 is configured to open to allow fluid flow from the pressurized fluid source 16 through the first pressure-actuated valve 54 in response to a decrease in absolute pressure in the aspiration flow path 28 creating an actuating negative pressure differential between the inlet port 50 and the outlet port 52, and conversely, to close to prevent fluid flow from the pressurized fluid source 16 through the pressure-actuated valve 54 in response to an increase in absolute pressure in the aspiration flow path 28 creating an actuating negative pressure differential between the inlet port 50 and the outlet port 52 (e.g., indicating that an obstruction has been removed or cleared from the aspiration conduit 24 of the aspiration catheter 12).

[0044] The first fluid resonator device 56a is configured to resonate at a first predetermined frequency in response to fluid flow from the pressurized fluid source 16 through the pressure-operated valve 54 to pulse fluid communication between the pressurized fluid source 16 and the suction flow path 46 at the first predetermined frequency, and conversely configured to cease resonating in response to fluid flow being blocked from the pressurized fluid source 16 through the pressure-operated valve 54. The second fluid resonator device 56b is configured to resonate at a second predetermined frequency in response to fluid flow from the pressurized fluid source 16 through the pressure-operated valve 54 to pulse fluid communication between the pressurized fluid source 16 and the suction flow path 46 at the second predetermined frequency, and conversely configured to cease resonating in response to fluid flow being blocked from the pressurized fluid source 16 through the pressure-operated valve 54.

[0045] The first and second predetermined frequencies may be equal or different (e.g., one may be a relatively high frequency for disrupting an occlusive thrombus 2 having a lower viscosity, and the other may be a relatively low frequency for disrupting an occlusive thrombus 2 having a higher viscosity). The first fluid resonator 56a and the second fluid resonator 56b may be mechanically separated from the pressure-activated valve 54.

[0046] 8A and 8B, one embodiment of a passive pressure oscillation assembly 44a will be described. The passive pressure oscillation assembly 44a comprises an inlet channel 60 fluidly coupled to the pressurized fluid source 16 via an inlet port 50 and an outlet channel 62 fluidly coupled to the suction flow path 46 via an outlet port 52. The passive pressure oscillation assembly 44a further comprises a valve seal in the form of a seat 64 fluidly coupled to the inlet port 50 via the inlet channel 60, a movable valve element in the form of a valve disc 66 operably connected to the valve seat 64, and an enlarged flow cavity 68 fluidly coupled between the valve seat 64 and the suction flow path 46 via the outlet channel 62 and the outlet port 52. The valve disc 66 is configured to be alternately displaced between a closed position (see FIG. 8A), in this case within the valve seat 64, to form a seal against the valve seat 64, and an open position (see FIG. 8B), in this case outside the valve seat 64, away from the valve seat 64. The passive pressure oscillation assembly 44a further includes a restoring spring 70 affixed within the enlarged flow cavity 68 and mechanically coupled to the valve disc 66 for applying a biasing force to the valve disc 66 to maintain the valve disc 66 in a closed position within the valve seat 64 until the passive pressure oscillation assembly 44a is activated to switch from normal mode to oscillation mode, as will be described in more detail below.

[0047] The valve disc 66 and valve seat 64 have the same geometric profile (in this case, a low trapezoidal cross section), so that when the valve disc 66 is in a closed position within the valve seat 64 (see FIG. 8A ), it forms a seal against the valve seat 64 to prevent the flow of fluid from the pressurized fluid source 16 (in this case, fluid introduced into the inlet channel 60 via the inlet port 50) into the enlarged flow cavity 68. The enlarged flow cavity 68 has a geometric profile larger than that of the valve disc 66, so that when the valve disc 66 is in an open position outside the valve seat 64 and within the enlarged flow cavity 68 (see FIG. 8B ), it allows the fluid from the pressurized fluid source 16 (in this case, fluid introduced into the inlet channel 60 via the inlet port 50) to pass into the enlarged flow cavity 68 and further through the outlet channel 62 and into the suction passage 46 via the outlet port 52.

[0048] In response to the occurrence of an occlusion in the aspiration conduit 24 of the aspiration catheter 12 or other abnormality in the aspiration circuit of the system 10, a zero or low flow condition occurs in the aspiration flow path 46, causing the absolute pressure in the aspiration flow path 46 to decrease to a level that creates an actuating negative pressure differential between the inlet port 50 (and thus the inlet channel 60) and the outlet port 52 (and thus the enlarged flow cavity 68), causing the fluid in the inlet channel 60 to exert a counteracting force on the valve disc 66 that overcomes the biasing force exerted against the valve disc 66 by the restoring spring 70. As a result, the valve disc 66 is displaced from the closed position (see FIG. 8A) to the open position (see FIG. 8B). The actuation negative pressure differential of the passive pressure oscillation assembly 44a will be determined by the area of the valve disc 66 exposed to the fluid in the inlet channel 60 (the actuation negative pressure differential decreases in proportion to the exposed area of the valve disc 66) and the spring constant of the restoring spring 70 (the action negative pressure differential increases in proportion to the spring constant of the restoring spring 70). Thus, by appropriately selecting the exposed area of the valve disc 66 and the spring constant of the restoring spring 70, the actuation negative pressure differential of the passive pressure oscillation assembly 44a can be selected.

[0049] The passive pressure vibration assembly 44a is designed to resonate the passive pressure vibration assembly 44a (i.e., the valve disc 66 is caused to alternate (oscillate) between the closed and open positions) when the valve disc 66 is displaced from a closed position to an open position (i.e., the valve is "gapped"). At this point, the passive pressure vibration assembly 44a has been activated to switch from normal mode to oscillation mode.

[0050] Specifically, the biasing force exerted against the valve disc 66 by the restoring spring 70, the opposing force exerted against the valve disc 66 by the fluid in the inlet channel 60, and the mass of the valve disc 66 are selected to cause the valve disc 66 to oscillate between the closed and open positions at a predetermined frequency (e.g., in the range of 100 Hz to 400 Hz).

[0051] That is, when the valve disc 66 first reaches its fully open position, the opposing force exerted against the valve disc 66 by fluid flowing from the inlet channel 60, through the valve seat 64, and into the enlarged flow cavity 68 decreases to a level where the biasing force exerted by the restoring spring 70 overcomes the opposing fluid force on the valve disc 66 and the momentum of the valve disc 66, thereby displacing the valve disc 66 from the open position back to the closed position (see FIG. 8A ) within the valve seat 64. At this point, the temporary flow of fluid from the pressurized fluid source 16 into the suction passage 46 (via the inlet port 50, the inlet channel 60, the valve seat 64, the enlarged flow cavity 68, the outlet channel 62, and the outlet port 52) increases the negative pressure differential between the inlet port 50 and the outlet port 52. However, because the valve disc 66 is now in the closed position, thereby preventing fluid flow from the pressurized fluid source 16 to the aspiration passageway 46, the negative pressure differential between the inlet port 50 and the outlet port 52 decreases until an actuation negative pressure differential is reached, thereby increasing the opposing force exerted on the valve disc 66 by the fluid in the inlet channel 60 to a level that overcomes the biasing force exerted against the valve disc 66 by the restoring spring 70. As a result, the valve disc 66 is displaced from the closed position back to the open position (see FIG. 8B). In this manner, the valve disc 66 is continually displaced alternately between the closed position (see FIG. 8A) and the open position (see FIG. 8B) until the aspiration conduit 24 of the aspiration catheter 12 is cleared of an obstruction or the abnormality in the aspiration circuit of the system 10 is otherwise resolved.

[0052] The frequency at which the valve disc 66 vibrates depends on the mass of the valve disc 66 (the frequency of vibration decreases as the mass of the valve disc 66 increases), the spring constant of the restoring spring 70 (the frequency of vibration increases as the spring constant of the restoring spring 70 increases), and the length of the valve seat 64 (the frequency of vibration increases as the length of the valve seat 64 decreases), as well as the damping effect of friction between the valve seat 64 and the valve disc 66 and the dynamic force exerted on the valve disc 66 by the fluid flowing from the inlet channel 60 through the valve seat 64 and into the expanding flow cavity 68 (the frequency of vibration decreases as the damping effect increases). Thus, by appropriately selecting the mass of the valve disc 66, the spring constant of the restoring spring 70, the length of the valve seat 64, and the pre-compression length of the spring 70, the frequency at which the valve disc 66 vibrates (i.e., the resonance of the passive pressure vibration assembly 44a) can be selected, taking into account the friction between the valve seat 64 and the valve disc 66 and the damping effect that the pressure drop associated with fluid flow from the inlet channel 60 through the valve seat 64 and into the enlarged flow cavity 68 has on the valve disc 66. This damping effect can itself be adjusted by varying the design size and geometry of the inlet port 50, the outlet port 52, the inlet channel 60, and the outlet channel 62.

[0053] In response to removal of an obstruction in the aspiration conduit 24 of the aspiration catheter 12 or otherwise resolving an abnormality in the aspiration circuit of the system 10, the absolute pressure in the aspiration flow path 46 increases to a level that creates a blocking negative pressure differential between the inlet port 50 (and thus the inlet channel 60) and the outlet port 52 (and thus the enlarged flow cavity 68), thereby preventing the fluid in the inlet channel 60 from exerting a counterforce on the valve disc 66 that overcomes the biasing force exerted by the restoring spring 70 against the valve disc 66. That is, when the valve disc 66 is in the closed position, the negative pressure differential between the inlet port 50 and the outlet port 52 does not drop below the actuating negative pressure differential because the aspiration flow path 46 is free-flowing. As a result, the biasing force exerted by the restoring spring 70 maintains the valve disc 66 in the closed position. At this point, the passive pressure oscillation assembly 44a has been activated to switch from the oscillation mode back to the normal mode.

[0054] It should be noted that the passive pressure oscillation assembly 44a shown in Figures 8A and 8B includes a pressure-actuated valve 54 and a fluidic resonator 56 (shown in Figure 5) that are mechanically coupled to one another in terms of topology. That is, the valve seat 64 and movable valve disc 66 form the pressure-actuated valve 54, while the valve disc 66, enlarged flow cavity 68, and restoring spring 70 form the fluidic resonator 56, where the pressure-actuated valve 54 and the fluidic resonator 56 are mechanically coupled to one another via the valve disc 66. In this embodiment, because the valve disc 66 forms part of both the pressure-actuated valve 54 and the fluidic resonator 56, the actuation and deactivation negative pressure differentials and the resonant frequency must be designed taking into account one another and therefore cannot be optimized independently. However, the resulting design of the passive pressure oscillation assembly 44a can be mechanically simple.

[0055] 9A and 9B, another embodiment of a passive pressure oscillation assembly 44b will be described. Passive pressure oscillation assembly 44b is similar to passive pressure oscillation assembly 44a shown in Figures 8A and 8B, except that passive pressure oscillation assembly 44b includes a valve seal that is longer relative to the movable valve element with which it interacts, resulting in a significantly reduced resonant frequency than passive pressure oscillation assembly 44a.

[0056] Specifically, passive pressure oscillation assembly 44b includes an inlet channel 80 fluidly coupled to pressurized fluid source 16 via inlet port 50 and an outlet channel 82 fluidly coupled to suction flow path 46 via outlet port 52. Passive pressure oscillation assembly 44b further includes a valve seal in the form of a valve cylinder 84 fluidly coupled to inlet port 50 via inlet channel 80, a movable valve element in the form of a valve disc 86 operably connected to valve cylinder 84, and an enlarged flow cavity 88 fluidly coupled between valve cylinder 84 and suction flow path 46 via outlet channel 62 and outlet port 52. Valve disc 86 is configured to be alternately displaced between a closed position (see FIG. 9A) to seal within valve cylinder 84 and an open position (see FIG. 9B) in which valve disc 86 is within enlarged flow cavity 88. The passive pressure oscillation assembly 44b further includes a restoring spring 90 disposed in a spring cavity 92 between the enlarged flow cavity 88 and the outlet channel 82 and mechanically coupled to the valve disc 86 via a boss 94 affixed to the valve disc 86 for applying a biasing force against the valve disc 86 to maintain the valve disc 86 in a closed position within the valve cylinder 84 until the passive pressure oscillation assembly 44b is activated to switch from the normal mode to the oscillation mode.

[0057] Valve disc 86 and valve cylinder 84 have the same geometric profile (in this case, essentially cylindrical), such that when valve disc 86 is in a closed position within valve cylinder 84 (see FIG. 9A ), it forms a seal with valve cylinder 84 that prevents the flow of fluid from pressurized fluid source 16 (in this case, fluid introduced into inlet channel 80 via inlet port 50) into enlarged flow cavity 88. Enlarged flow cavity 88 has a geometric profile that is larger than that of valve disc 86, such that when valve disc 86 is in an open position outside valve cylinder 84 but within enlarged flow cavity 88 (see FIG. 9B ), it allows fluid from pressurized fluid source 16 (in this case, fluid introduced into inlet channel 80 via inlet port 50) to pass into enlarged flow cavity 88 and further through outlet channel 82 and into suction passage 46 via outlet port 52.

[0058] In response to the occurrence of an occlusion in the aspiration conduit 24 of the aspiration catheter 12 or other abnormality in the aspiration circuit of the system 10, a zero or low flow condition occurs in the aspiration flow path 46, causing the absolute pressure in the aspiration flow path 46 to drop to a level that creates an actuating negative pressure differential between the inlet port 50 (and thus the valve cylinder 84) and the outlet port 52 (and thus the enlarged flow cavity 88), causing the fluid in the inlet channel 80 to exert a counteracting force on the valve disc 86 that overcomes the biasing force exerted against the valve disc 86 by the restoring spring 90. As a result, the valve disc 86 is displaced from the closed position (see FIG. 9A) to the open position (see FIG. 9B). The negative pressure differential for actuation of the passive pressure oscillation assembly 44b will be based on the area of the valve disc 86 exposed to the fluid in the valve cylinder 84 (the negative pressure differential for actuation decreases in proportion to the exposed area of the valve disc 86) and the spring constant of the restoring spring 90 (the negative pressure differential for action increases in proportion to the spring constant of the restoring spring 90). Thus, by appropriately selecting the exposed area of the valve disc 86 and the spring constant of the restoring spring 90, the negative pressure differential for actuation of the passive pressure oscillation assembly 44b can be selected.

[0059] The passive pressure vibration assembly 44b is designed to resonate (i.e., cause the valve disc 86 to alternate (oscillate) between the closed and open positions) when the valve disc 86 is displaced from a closed position to an open position (i.e., the valve is "gapped"). At this point, the passive pressure vibration assembly 44b has been activated to switch from normal mode to vibration mode.

[0060] Specifically, the biasing force exerted against the valve disc 86 by the restoring spring 90, the opposing force exerted by the fluid in the valve cylinder 84, and the mass of the valve disc 86 are selected to cause the valve disc 86 to oscillate between the closed and open positions at a predetermined frequency (e.g., in the range of 100 Hz to 200 Hz).

[0061] That is, as the valve disc 86 reaches its full open position, the opposing force exerted against the valve disc 86 by fluid flowing from the inlet channel 80, through the valve cylinder 84, and into the enlarged flow cavity 88 decreases to a level where the biasing force exerted by the restoring spring 90 overcomes the opposing fluid force on the valve disc 86 and the momentum of the valve disc 86, thereby displacing the valve disc 86 from the open position back to the closed position (see FIG. 9A ) within the valve cylinder 84. At this point, the temporary flow of fluid from the pressurized fluid source 16 into the suction passage 46 (via the inlet port 50, the inlet channel 80, the valve cylinder 84, the enlarged flow cavity 88, the spring cavity 92, the outlet channel 82, and the outlet port 52) increases the negative pressure differential between the inlet port 50 and the outlet port 52. However, because valve disc 86 is now in the closed position, thereby preventing fluid flow from pressurized fluid source 16 to aspiration passageway 46, the negative pressure differential between inlet port 50 and outlet port 52 decreases until an actuation negative pressure differential is reached, thereby increasing the opposing force exerted on valve disc 86 by fluid in valve cylinder 84 to a level that overcomes the biasing force exerted against valve disc 86 by restoring spring 90. As a result, valve disc 86 is again displaced from the closed position to the open position (see FIG. 9B). In this manner, valve disc 86 continues to be displaced alternately between the closed position (see FIG. 9A) and the open position (see FIG. 9B) until the aspiration catheter 12 is cleared of an obstruction or the abnormality in the aspiration circuit of system 10 is otherwise resolved.

[0062] The frequency at which the valve disc 86 vibrates depends on the mass of the valve disc 86 (the frequency of vibration decreases as the mass of the valve disc 86 increases), the spring constant of the restoring spring 90 (the frequency of vibration increases as the spring constant of the restoring spring 90 increases), and the length of the valve cylinder 84 (the frequency of vibration increases as the length of the valve seat 64 decreases), as well as the damping effect of friction between the valve cylinder 84 and the valve disc 86 and the dynamic force exerted on the valve disc 86 by the fluid flowing from the inlet channel 60 through the valve cylinder 84 and into the expanding flow cavity 88 (the frequency of vibration decreases as the damping effect increases). Therefore, by appropriately selecting the mass of the valve disc 86, the spring constant of the restoring spring 90, the length of the valve cylinder 84, and the pre-compression length of the spring 90, the frequency at which the valve disc 86 vibrates (i.e., the resonance of the passive pressure vibration assembly 44b) can be selected, taking into account the friction between the valve cylinder 84 and the valve disc 86 and the damping effect that the fluid flow from the inlet channel 80 through the valve cylinder 84 and into the enlarged flow cavity 88 has on the valve disc 86. This damping effect can itself be adjusted by varying the design sizes and geometries of the inlet port 50, the outlet port 52, the inlet channel 80, and the outlet channel 82.

[0063] In response to removal of an obstruction in the aspiration conduit 24 of the aspiration catheter 12 or otherwise rectifying an abnormality in the aspiration circuit of the system 10, the absolute pressure in the aspiration flow path 46 increases to a level that creates an actuating negative pressure differential between the inlet port 50 (and thus the valve cylinder 84) and the outlet port 52 (and thus the enlarged flow cavity 88), thereby preventing the fluid in the inlet channel 80 from exerting a counterforce on the valve disc 86 that overcomes the biasing force exerted by the restoring spring 90 against the valve disc 86. That is, when the movable valve cylinder 86 is in the closed position, the negative pressure differential between the inlet port 50 and the outlet port 52 does not fall below the actuating negative pressure differential because the aspiration flow path 46 is free-flowing. As a result, the biasing force exerted by the restoring spring 90 maintains the valve disc 86 in the closed position. At this point, the passive pressure oscillation assembly 44b has been activated to switch from the oscillation mode back to the normal mode.

[0064] It should be noted that the passive pressure oscillation assembly 44b shown in Figures 9A and 9B includes a pressure-actuated valve 54 and a fluidic resonator 56 (shown in Figure 5) that are mechanically coupled to one another in terms of topology. That is, the valve cylinder 84 and valve disc 86 form the pressure-actuated valve 54, while the valve disc 86, enlarged flow cavity 88, and restoring spring 90 form the fluidic resonator 56, where the pressure-actuated valve 54 and the fluidic resonator 56 are mechanically coupled to one another via the valve disc 86. In this embodiment, because the valve disc 86 forms part of both the pressure-actuated valve 54 and the fluidic resonator 56, the actuation and deactivation negative pressure differentials and the resonant frequency must be designed taking into account one another and therefore cannot be optimized independently. However, the resulting design of the passive pressure oscillation assembly 44b can be mechanically simple.

[0065] 10A-10D, another embodiment of a passive pressure oscillation assembly 44c will be described. Passive pressure oscillation assembly 44c is similar to passive pressure oscillation assembly 44a shown in FIGS. 6A and 6B, except that passive pressure oscillation assembly 44c includes an additional oscillation enhancement mechanism that ensures that passive pressure oscillation assembly 44c remains in oscillation mode as long as an occlusion in aspiration conduit 24 of suction catheter 12 remains or an abnormality in the aspiration circuit of system 10 is otherwise resolved.

[0066] The passive pressure oscillation assembly 44c includes an inlet channel 100 fluidly coupled to the pressurized fluid source 16 via an inlet port 50 and an outlet channel 102 fluidly coupled to the suction flow path 46 via an outlet port 52. The passive pressure oscillation assembly 44c further includes a valve seal in the form of a seat 104, a movable valve element in the form of a valve disc 106 operably coupled to the valve seat 104, and an enlarged flow cavity 108 fluidly coupling the valve seat 104 to the suction flow path 46 via the outlet channel 102 and the outlet port 52. The valve disc 106 is configured to be alternately displaced between a closed position (see FIGS. 10A and 10D), in this case within the valve seat 104, forming a seal against the valve seat 104, and an open position (see FIGS. 10B and 10C), in this case external to the valve seat 104, away from the valve seat 104. The passive pressure oscillation assembly 44c further includes a restoring spring 110 disposed within the enlarged flow cavity 108 and mechanically coupled to the valve disc 106 for applying a biasing force against the valve disc 106 to maintain the valve disc 106 in a closed position within the valve seat 104 until the passive pressure oscillation assembly 44c is activated to switch from the normal mode to the oscillation mode.

[0067] The passive pressure oscillation assembly 44c further comprises a plunger cavity 114, a plunger head 116 slidably disposed within the plunger cavity 114, a reduced-profile central cavity 118, a plunger stop 120 disposed between the plunger cavity 114 and the reduced-profile central cavity 118, and a separate restoring spring 122 mechanically coupled to the plunger head 116 via a boss 124 affixed to the plunger head 116 for applying a biasing force to the plunger head 116 to maintain the plunger head 116 away from the plunger stop 120. In the embodiment shown, the profile of the reduced-profile central cavity 118 is smaller than the profile of the plunger cavity 114, such that the plunger stop 120 is formed by the wall of the plunger cavity 114 adjacent the reduced-profile central cavity 118. The plunger head 116 has a fluid pressure equalization channel 126 extending therethrough. The plunger cavity 114 is fluidly coupled between the valve seat 104 and the plunger cavity 114 such that the valve seat 104 is always in fluid communication with the inlet port 50 via the fluid pressure equalization channel 126 extending through the plunger head 116, allowing fluid from the pressurized fluid source 16 to flow into the reduced-profile central cavity 118. The fluid pressure equalization channel 126 extending through the plunger head 116 thus functions to equalize pressure between the pressurized fluid source 16 and the reduced-profile central cavity 118.

[0068] The valve disc 106 and valve seat 104 have the same geometric profile (in this case, a low trapezoidal cross-section) so that when the valve disc 106 is in a closed position within the valve seat 104 (see FIGS. 10A and 10D ), it prevents fluid from the pressurized fluid source 16 (in this case, fluid introduced from the inlet channel 100 via the inlet port 50, through the fluid pressure equalization channel 126 in the plunger head 116, and into the reduced-profile central cavity 118) from flowing into the enlarged flow cavity 108. The enlarged flow cavity 108 has a geometric profile larger than that of the valve disc 106, such that when the valve disc 106 is in the open position (see FIGS. 10B and 10C ), outside the valve seat 104 and inside the enlarged flow cavity 108, it allows fluid from the pressurized fluid source 16 (in this case, fluid introduced into the plunger cavity 140 from the inlet port 50 and the inlet channel 100 via the fluid pressure equalization channel 126) to flow into the enlarged flow cavity 108, through the outlet channel 102, and into the suction flow passage 46 via the outlet port 52. The plunger head 116 and plunger cavity 114 have the same geometric profile (in this case, essentially cylindrical), allowing fluid from the pressurized fluid source 16 to enter the reduced-profile central cavity 118 only via the fluid pressure equalization channel 126 of the plunger head 116.

[0069] In response to the occurrence of an occlusion in the aspiration conduit 24 of the aspiration catheter 12 or other abnormality in the aspiration circuit of the system 10, a zero or low flow condition occurs in the aspiration flow path 46, causing the absolute pressure in the aspiration flow path 46 to decrease to a level that creates an actuating negative pressure differential between the inlet port 50 (and thus the reduced-profile central cavity 118) and the outlet port 52 (and thus the expanded flow cavity 108), causing the fluid in the plunger cavity 114 and thus the fluid in the reduced-profile central cavity 118 to exert a counteracting force on the valve disc 106 that overcomes the biasing force exerted against the valve disc 106 by the restoring spring 110. As a result, the valve disc 106 is displaced from the closed position (see FIG. 10A ) to the open position (see FIG. 10B ). The actuation negative pressure differential of the passive pressure oscillation assembly 44c will be based on the area of the valve disc 106 exposed to the fluid in the inlet channel 100 (the actuation negative pressure differential decreases in proportion to the exposed area of the valve disc 106) and the spring constant of the restoring spring 110 (the action negative pressure differential increases in proportion to the spring constant of the restoring spring 110). Thus, by appropriately selecting the exposed area of the valve disc 106 and the spring constant of the restoring spring 110, the actuation negative pressure differential of the passive pressure oscillation assembly 44c can be selected.

[0070] The passive pressure vibration assembly 44c is designed to resonate the passive pressure vibration assembly 44c (i.e., the valve disc 106 is caused to alternate (oscillate) between the closed and open positions) when the valve disc 106 is displaced from a closed position to an open position (i.e., the valve is "gapped"). At this point, the passive pressure vibration assembly 44c has been activated to switch from normal mode to vibration mode.

[0071] Specifically, the biasing force exerted against the valve disc 106 by the restoring spring 110, the opposing force exerted against the valve disc 106 by the fluid in the reduced-profile central cavity 118, and the mass of the valve disc 106 are selected to oscillate the valve disc 106 between the closed and open positions at a predetermined frequency. Additionally, the dynamic displacement of the plunger head 116 within the plunger cavity 114 ensures that the valve disc 106 does not stick in the open position when fluid flowing from the reduced-profile central cavity 118 into the expanding flow cavity 108 exerts a force on the valve disc 106.

[0072] Specifically, when the valve disc 106 is displaced from the closed position to the open position (see FIG. 10C ), fluid flows from the plunger cavity 114 in front of the plunger head 116, through the reduced-profile central cavity 118, and through the valve seat 104 into the enlarged flow cavity 108, thereby displacing the plunger head 116 within the plunger cavity 114 toward the reduced-profile central cavity 118 until the plunger head 116 abuts the plunger stop 120, allowing additional fluid to flow from the pressurized fluid source 16 through the inlet port 50 and the inlet channel 100 and into the plunger cavity 114 behind the plunger head 116. When the plunger head 116 abuts the plunger stop 120, fluid flow from the reduced-profile central cavity 118, through the valve seat 104, and into the enlarged flow cavity 108 is significantly reduced and limited to fluid flow only through the fluid pressure equalization channel 126 through the plunger head 116. Thus, the opposing force exerted against the valve disc 106 by fluid flowing from the reduced-profile central cavity 118, through the valve seat 104, and into the enlarged flow cavity 108 is reduced to a level where the biasing force exerted by the restoring spring 110 overcomes the opposing fluid force on the valve disc 106 and the momentum of the valve disc 106. As a result, the valve disc 106 is displaced from the open position back to the closed position (see FIG. 10D ) within the valve seat 104. Fluid pressure between reduced-profile central cavity 118 and plunger cavity 114 is equalized via fluid pressure equalization channel 126 through plunger head 116, thereby reducing the opposing force exerted on plunger head 116 by the fluid in plunger cavity 114 to a level where the biasing force exerted by restoring spring 122 overcomes the opposing fluid force exerted on plunger head 116 and the momentum of plunger head 116. As a result, plunger head 116 is displaced away from plunger stop 120 within plunger cavity 114 and returns to its neutral position (see FIG. 10A ).In this way, unlike the passive pressure oscillation assembly 44a shown in Figures 8A-8B and also in Figures 9A-9B, which allow fluid to flow unimpeded past the valve seat, which can, under certain circumstances, hold the valve disc open and thereby prevent oscillation of the valve seat between the closed and open positions, the action of the plunger head 116 in the plunger cavity 114 prevents the valve disc 106 from "stuck" in the open position by significantly reducing the flow of fluid through the valve seat 104 that would otherwise prevent the valve disc 106 from returning to its closed position within the valve seat 104.

[0073] The frequency at which the valve disc 106 vibrates depends on the frequency at which the plunger head 116 vibrates within the plunger cavity 114, which in turn depends on the mass of the plunger head 116 (the frequency of vibration decreases as the mass of the plunger head 116 increases), the spring constant of the restoring spring 122 (the frequency of vibration increases as the spring constant of the restoring spring 122 increases), the diameter of the equalization channel 126, the damping effect of friction between the plunger cavity 114 and the plunger head 116, and the dynamic forces of the fluid within the plunger cavity 114, including the fluid flowing through the fluid pressure equalization channel 126 of the plunger head 116 during fluid pressure equalization within the plunger cavity 114 (the frequency of vibration decreases as the damping effect increases). Thus, by appropriately selecting the mass of plunger head 116, the spring constant of restoring spring 122, and the diameter of equalization channel 126, the frequency at which valve disc 106 vibrates (i.e., the resonance of passive pressure oscillation assembly 44c) can be selected, taking into account the damping effect that friction between plunger cavity 114 and plunger head 116 and the dynamics of the fluid within reduced-profile central cavity 118 have on plunger head 116. This damping effect can itself be adjusted by varying the design sizes of inlet port 50, outlet port 52, inlet channel 100, and outlet channel 102.

[0074] In response to removal of an obstruction in the aspiration conduit 24 of the aspiration catheter 12 or otherwise resolving an abnormality in the aspiration circuit of the system 10, the absolute pressure in the aspiration flow path 46 increases to a level that creates a blocking negative pressure differential between the inlet port 50 (and thus the inlet channel 100) and the outlet port 52 (and thus the enlarged flow cavity 108), thereby preventing the fluid in the reduced-profile central cavity 118 from exerting a counterforce against the valve disc 106 that overcomes the biasing force exerted by the spring 100 against the valve disc 106. That is, when the valve disc 106 is in the closed position, the negative pressure differential between the inlet port 50 and the outlet port 52 does not drop below the actuating negative pressure differential because the aspiration flow path 46 is free-flowing. As a result, the biasing force exerted by the restoring spring 110 maintains the valve disc 106 in the closed position. At this point, the passive pressure oscillation assembly 44c is activated to switch from the oscillation mode to the normal mode.

[0075] While the movable valve elements in passive pressure oscillation assemblies 44a-44c shown in Figures 8-10 have been described as valve discs, it should be appreciated that the movable valve elements may have any suitable form that can be operatively coupled to corresponding valve seals to alternately allow and prevent fluid from the pressurized fluid source 16 from flowing therethrough. For example, with reference to Figures 11A and 11B, an alternative embodiment of passive pressure oscillation assembly 44d is similar to passive pressure oscillation assembly 44a of Figures 8A-8B, except that the movable valve element takes the form of a ball.

[0076] Specifically, passive pressure oscillation assembly 44d includes an inlet channel 130 fluidly coupled to pressurized fluid source 16 via inlet port 50 and an outlet channel 132 fluidly coupled to suction flow path 46 via outlet port 52. Passive pressure oscillation assembly 44d further includes a valve seal in the form of a seat 134 fluidly coupled to inlet port 50 via inlet channel 130, a movable valve element in the form of a valve ball 136 operably coupled to valve seat 134, and an enlarged flow cavity 138 fluidly coupled between valve seat 134 and suction flow path 46 via outlet channel 132 and outlet port 52. Valve ball 136 is configured to be alternately displaced between a closed position (see FIG. 11A) to form a seal against valve seat 134 and an open position (see FIG. 11B) in which it is spaced apart from, and in this case external to, valve seat 64. The passive pressure oscillation assembly 44d further includes a spring 140 affixed within the enlarged flow cavity 138 and mechanically coupled to the valve ball 136 for applying a biasing force to the valve ball 136 in a manner that maintains the valve ball 136 in a closed position against the valve seat 134 until the passive pressure oscillation assembly 44d is activated to switch from normal mode to oscillation mode, as will be described in more detail below.

[0077] The surface of the valve seat 134 that contacts the valve ball 136 preferably has a spherical profile such that, when the valve ball 136 is in a closed position relative to the valve seat 134 (see FIG. 11A ), it forms a seal against the valve seat 134 to prevent the flow of fluid from the pressurized fluid source 16 (in this case, fluid introduced into the inlet channel 130 via the inlet port 50) into the enlarged flow cavity 138. The enlarged flow cavity 138 has a geometric profile that is larger than that of the valve ball 136 such that, when the valve ball 136 is in an open position (see FIG. 11B ) away from the valve seat 134 and within the enlarged flow cavity 138, it allows the flow of fluid from the pressurized fluid source 16 (in this case, fluid introduced into the inlet channel 130 via the inlet port 50) into the enlarged flow cavity 138, through the outlet channel 132, and into the suction passage 46 via the outlet port 52.

[0078] In response to the occurrence of an occlusion in the aspiration conduit 24 of the aspiration catheter 12 or other abnormality in the aspiration circuit of the system 10, a zero or low flow condition occurs in the aspiration flow path 46, causing the absolute pressure in the aspiration flow path 46 to decrease to a level that creates an actuating negative pressure differential between the inlet port 50 (and thus the inlet channel 130) and the outlet port 52 (and thus the enlarged flow cavity 138), causing the fluid in the inlet channel 130 to exert an opposing force against the valve ball 136 that overcomes the biasing force exerted against the valve ball 136 by the spring 140. As a result, the valve ball 136 is displaced from the closed position (see FIG. 11A) to the open position (see FIG. 11B). The actuation negative pressure differential of the passive pressure oscillation assembly 44d will be based on the area of the valve ball 136 exposed to the fluid in the inlet channel 130 (the actuation negative pressure differential decreases in proportion to the exposed area of the valve ball 136) and the spring constant of the spring 140 (the action negative pressure differential increases in proportion to the spring constant of the spring 140). Thus, by appropriately selecting the exposed area of the valve ball 136 and the spring constant of the spring 140, the actuation negative pressure differential of the passive pressure oscillation assembly 44d can be selected.

[0079] The passive pressure vibration assembly 44d is designed to resonate (i.e., cause the valve ball 136 to alternate (oscillate) between the closed and open positions) when the valve ball 136 is displaced from a closed position to an open position (i.e., the valve is "gapped"). At this point, the passive pressure vibration assembly 44d has been activated to switch from normal mode to oscillation mode.

[0080] Specifically, the biasing force exerted by spring 140 against valve ball 136, the opposing force exerted by fluid in inlet channel 130 against valve ball 136, and the mass of valve ball 136 are selected to cause valve ball 136 to oscillate between closed and open positions at a predetermined frequency (e.g., 320 Hz to 400 Hz).

[0081] That is, when the valve ball 136 first reaches its fully open position, the opposing force exerted against the valve ball 136 by fluid flowing from the inlet channel 60, through the valve seat 134, and into the enlarged flow cavity 138 decreases to a level where the biasing force exerted by the spring 140 overcomes the opposing fluid force on the valve ball 136 and the momentum of the valve ball 136. As a result, the valve ball 136 is displaced from the open position back to the closed position (see FIG. 11A ) within the valve seat 134. At this point, the temporary flow of fluid from the pressurized fluid source 16 into the suction flow path 46 (via the inlet port 50, the inlet channel 130, the valve seat 134, the enlarged flow cavity 138, the outlet channel 132, and the outlet port 52) increases the negative pressure differential between the inlet port 50 and the outlet port 52. However, because valve ball 136 is now in the closed position, thereby preventing fluid flow from pressurized fluid source 16 to aspiration flow path 46, the negative pressure differential between inlet port 50 and outlet port 52 decreases until an actuation negative pressure differential is reached, thereby increasing the opposing force exerted on valve ball 136 by fluid in inlet channel 60 to a level that overcomes the biasing force exerted against valve ball 136 by spring 140. As a result, valve ball 136 is displaced from the closed position back to the open position (see FIG. 11B). In this manner, valve ball 136 is continually displaced alternately between the closed position (see FIG. 11A) and the open position (see FIG. 11B) until the aspiration conduit 24 of aspiration catheter 12 is cleared of an obstruction or otherwise corrected within the aspiration circuit of system 10.

[0082] The frequency at which the valve ball 136 vibrates depends on the mass of the valve ball 136 (the frequency of vibration decreases as the mass of the valve ball 136 increases), the spring constant of the spring 140 (the frequency of vibration increases as the spring constant of the spring 140 increases), and the damping effect of the dynamic forces exerted on the valve ball 136 by the fluid flowing from the inlet channel 130, through the valve seat 134, and into the enlarged flow cavity 138 (the frequency of vibration decreases as the damping effect increases). Therefore, by appropriately selecting the mass of the valve ball 136, the spring constant of the spring 140, the length of the valve seat 134, and the pre-compression length of the spring 140, taking into account the damping effect that the fluid flow from the inlet channel 130, through the valve seat 134, and into the enlarged flow cavity 138 has on the valve ball 136, the frequency at which the valve ball 136 vibrates (i.e., the resonance of the passive pressure vibration assembly 44a) can be selected. The attenuation effect itself can be adjusted by varying the design size and geometry of the inlet port 50, outlet port 52, inlet channel 130, and outlet channel 132.

[0083] In response to removal of an obstruction in the aspiration conduit 24 of the aspiration catheter 12 or otherwise resolving an abnormality in the aspiration circuit of the system 10, the absolute pressure in the aspiration flow path 46 increases to a level that creates a blocking negative pressure differential between the inlet port 50 (and thus the inlet channel 130) and the outlet port 52 (and thus the enlarged flow cavity 138), thereby preventing the fluid in the inlet channel 130 from exerting a counterforce on the valve ball 136 that overcomes the biasing force exerted by the spring 140 against the valve ball 136. That is, when the valve ball 136 is in the closed position, the negative pressure differential between the inlet port 50 and the outlet port 52 does not drop below the actuating negative pressure differential because the aspiration flow path 46 is free-flowing. As a result, the biasing force exerted by the spring 140 maintains the valve ball 136 in the closed position. At this point, the passive pressure oscillation assembly 44d has been activated to switch from the oscillation mode back to the normal mode.

[0084] 11A and 11B includes a pressure-actuated valve 54 and a fluidic resonator 56 (shown in FIG. 5) mechanically coupled to one another. That is, the valve seat 134 and the movable valve ball 136 form the pressure-actuated valve 54, while the valve ball 136, the enlarged flow cavity 138, and the spring 140 form the fluidic resonator 56, where the pressure-actuated valve 54 and the fluidic resonator 56 are mechanically coupled to one another via the valve ball 136. In this embodiment, because the valve ball 136 forms part of both the pressure-actuated valve 54 and the fluidic resonator 56, the actuation and deactivation negative pressure differentials and the resonant frequency must be designed taking into account one another and therefore cannot be optimized independently. However, the resulting design of the passive pressure oscillation assembly 44d can be mechanically simple.

[0085] 12, one method 150 of operating the aspiration system 10 to aspirate vascular obstruction material 2 from a patient's vasculature 1 is described. The method 150 includes introducing the aspiration catheter 12 into the patient's vasculature 1 until the distal end 30 of the catheter body 22 is adjacent to the vascular obstruction material 2 (step 152). The aspiration source 14 is then operated to create an aspiration flow path 46 between the aspiration catheter 12 and the aspiration source 14 for the purpose of actively aspirating the vascular obstruction material 2, while the passive pressure oscillation assembly 44 is operated in a normal mode to prevent fluid communication between the pressurized fluid source 16 and the aspiration flow path 46 (step 154). Thus, at this point, aspiration of the vascular obstruction material 2 is performed as efficiently as possible.

[0086] Optionally, in response to the active suction of the vascular obstruction material 2 (e.g., when the absolute pressure in the aspiration channel 46 drops to a level that creates a first actuating negative pressure differential of less than −50 kPa between the pressurized fluid source 44 and the aspiration channel 46), the passive pressure oscillation assembly 44 is activated to switch from the normal mode to the first oscillation mode, such that fluid communication between the pressurized fluid source 16 and the aspiration channel 46 is pulsed at an appropriate amplitude and frequency (e.g., high frequency, low amplitude) to enhance the active suction of the vascular obstruction material 2 (step 156). Pulsing the fluid communication between the pressurized fluid source 16 and the aspiration channel 46 at a high frequency and low amplitude can minimize obstruction to the aspiration channel 46, thereby making the active suction of the vascular obstruction material 2 as efficient as possible.

[0087] Next, if an obstruction occurs in the aspiration flow path 24 of the aspiration catheter 12 (e.g., if the absolute pressure in the aspiration flow path 46 drops to a level that creates a second actuation negative pressure differential of less than −55 kPa between the pressurized fluid source 44 and the aspiration flow path 46) (step 158), the passive pressure oscillation assembly 44 is activated to switch from the normal mode (or, optionally, the first oscillation mode) to a (second) oscillation mode, such that fluid communication between the pressurized fluid source 16 and the aspiration flow path 46 is pulsed at an appropriate amplitude and frequency (e.g., low frequency, high amplitude) to enhance the removal of the obstruction (step 160). Optionally, fluid communication between the pressurized fluid source 16 and the aspiration flow path 46 can be pulsed simultaneously at different frequencies. If no obstruction occurs in the suction conduit 24 of the suction catheter 12 (e.g., the absolute pressure in the suction flow path 46 does not drop to a level that creates a second operating negative pressure difference of less than -55 kPa between the pressurized fluid source 44 and the suction flow path 46) (step 158), the passive pressure oscillation assembly 44 remains in the normal mode (or, optionally, the first oscillation mode) until the vascular obstruction 2 is completely sucked in.

[0088] If an obstruction occurs in the aspiration conduit 24 of the aspiration catheter 12 and is removed, or if the abnormality in the aspiration circuit of the aspiration system 10 is otherwise resolved (e.g., if the absolute pressure in the aspiration flow path 46 increases to a level that creates a deactivating negative pressure differential between the pressurized fluid source 44 and the aspiration flow path 46, preferably between 10 kPa and 25 kPa, greater than the activation negative pressure differential) (step 162), the passive pressure oscillation assembly 44 is activated to switch from oscillation mode to normal mode, thereby again preventing fluid communication between the pressurized fluid source 16 and the aspiration flow path 46, and the aspiration procedure continues (step 164). If an obstruction occurs in the suction conduit 24 of the suction catheter 12 and is not removed, or if the abnormality in the suction circuit of the suction system 10 is not otherwise resolved (e.g., if the absolute pressure in the suction flow path 46 does not increase to a level that creates a negative pressure difference between the pressurized fluid source 44 and the suction flow path 46 for stopping, preferably between 10 kPa and 25 kPa, which is greater than the negative pressure difference for activation), the passive pressure oscillation assembly 44 will remain in the (second) oscillation mode until the vascular obstruction 2 is removed or the abnormality in the suction circuit of the suction system 10 is otherwise resolved.

Claims

1. In the suction system: an aspiration catheter having a distal end sized and dimensioned to reach a vascular obstruction distal to the patient's vasculature; a suction source fluidly coupled to the suction catheter to create a suction flow path between the suction catheter and the suction source; a source of pressurized fluid; a passive pressure oscillation assembly fluidly coupled between the pressurized fluid source and the aspiration flow path, the passive pressure oscillation assembly configured to operate between a normal mode that prevents fluid communication between the pressurized fluid source and the aspiration flow path and an oscillation mode that pulses fluid communication between the pressurized fluid source and the aspiration flow path, the passive pressure oscillation assembly configured to be activated to operate in the oscillation mode in response to an obstruction in the aspiration catheter; A suction system comprising:

2. The aspiration system of claim 1 , wherein pulsing fluid communication between the pressurized fluid source and the aspiration flow path propagates a pressure pulse within the aspiration flow path.

3. The aspiration system of claim 1 , wherein pulsing fluid communication between the pressurized fluid source and the aspiration flow path propagates a backflow of fluid into the aspiration flow path.

4. The suction system of any one of claims 1 to 3, wherein the source of pressurized fluid comprises ambient air or a reservoir containing a liquid.

5. 5. The aspiration system of claim 1, wherein the passive pressure oscillation assembly is configured to be activated to operate in the normal mode in response to the obstruction being removed from the aspiration catheter.

6. The passive pressure oscillation assembly comprises: a pressure-activated valve configured to open in response to an obstruction in the aspiration catheter to allow fluid from the pressurized fluid source to flow through the pressure-activated valve; a fluid resonator configured to resonate in response to the flow of fluid from the pressurized fluid source through the pressure-activated valve to pulse the fluid communication between the pressurized fluid source and the suction flow path; The suction system according to any one of claims 1 to 5, comprising:

7. The aspiration system of claim 6 , wherein the pressure-activated valve and the fluid resonator are mechanically coupled to one another.

8. The aspiration system of claim 6 , wherein the pressure-activated valve and the fluid resonator are mechanically isolated from each other.

9. 7. The suction system of claim 6, further comprising another fluid resonator configured to resonate at a first frequency in response to the flow of fluid from the pressurized fluid source through the pressure-operated valve to pulse the fluid communication between the pressurized fluid source and the suction flow path at the first frequency, and the pressure-operated valve configured to resonate at a second frequency different from the first frequency in response to the flow of fluid from the pressurized fluid source through the pressure-operated valve to pulse the fluid communication between the pressurized fluid source and the suction flow path at the second frequency.

10. The passive pressure oscillation assembly comprises: a valve seal fluidly coupled to the source of pressurized fluid; a movable valve element; an enlarged flow cavity fluidly coupled to the suction passage, the enlarged flow cavity having a profile greater than a profile of the movable valve element; a spring configured to apply a biasing force to the movable valve element to maintain the movable valve element in a closed position against the valve seal to prevent the flow of the fluid from the pressurized fluid source into the enlarged flow cavity; the movable valve element is configured to be displaced from the closed position to an open position within the enlarged flow cavity, away from the valve seal, to allow fluid from the pressurized fluid source to flow through the valve seal, through the enlarged flow cavity, and into the aspiration flow path, in response to an obstruction within the aspiration catheter exerting an opposing force on the movable valve element by fluid from the pressurized fluid source that exceeds the biasing force exerted on the movable valve element by the spring; the biasing force exerted by the spring against the movable valve element, the opposing force exerted by the fluid from the pressurized fluid source, and the mass of the movable valve element are selected to oscillate the movable valve element between the closed position and the open position. The suction system of claim 3 .

11. The aspiration system of claim 10 , wherein the movable valve element comprises one of a disc and a ball, and the valve seal comprises a valve cylinder.

12. The aspiration system of claim 10 , wherein the movable valve element comprises a disk and the valve seal comprises a valve cylinder.

13. The passive pressure oscillation assembly further comprises: a plunger cavity disposed between the valve seal and the source of pressurized fluid; a reduced profile central cavity fluidly connected between the valve seal and the plunger cavity; a plunger head slidably disposed within the plunger cavity, the plunger head having a channel extending therethrough such that the valve seal is fluidly connected to the pressurized fluid source to equalize pressure between the pressurized fluid source and the plunger cavity; a plunger stop disposed between the plunger cavity and the reduced profile central cavity; a further spring applying a biasing force to the plunger head to maintain the movable valve element away from the plunger stop; fluid present in the plunger cavity from the pressurized fluid source that exerts a counterforce on the movable valve element in response to an obstruction in the aspiration catheter; 11. The aspiration system of claim 10, wherein flow from the plunger cavity, through the valve seal, through the enlarged flow cavity, and into the aspiration flow path causes fluid from the pressurized fluid source to exert an opposing force against the plunger head until the opposing force overcomes the biasing force exerted on the plunger head by the further spring, and the plunger head moves within the plunger cavity until it contacts the plunger stop, thereby preventing flow from the plunger cavity, through the valve seal, through the reduced profile central cavity, and into the aspiration flow path, and the biasing force exerted on the movable valve element by the spring displaces the movable valve element from the open position to the closed position.

14. 14. The aspiration system of claim 13, wherein the plunger stop is formed by a wall of the plunger cavity adjacent the reduced profile central cavity.

15. 15. The suction system of claim 1, wherein the vibration mode pulses fluid communication between the pressurized fluid source and the suction flow path while maintaining fluid communication between the suction source and the suction flow path.

16. 16. The aspiration system of claim 1, wherein the vibration mode pulses fluid communication between the pressurized fluid source and the aspiration flow path at an amplitude and frequency that enhances removal of obstructions from the aspiration catheter.

17. the vibration mode is a second vibration mode, 16. The aspiration system of claim 1, wherein the passive pressure oscillation assembly is further configured to operate between the normal mode, a first oscillation mode in which fluid communication between the pressurized fluid source and the aspiration flow path is pulsed at a first amplitude and a first frequency to enhance active suction of vascular obstruction material, and a second oscillation mode in which fluid communication between the pressurized fluid source and the aspiration flow path is pulsed at a second amplitude and a second frequency to enhance removal of obstruction material from the aspiration catheter.

18. 18. The aspiration system of claim 17, wherein the first frequency is greater than the second frequency and the second amplitude is greater than the first amplitude.

19. 18. The aspiration system of claim 17, wherein the passive pressure oscillation assembly is configured to be activated to switch from the normal mode to the first oscillation mode in response to active suction of a vascular obstruction by the aspiration catheter, and to be activated to switch from the second oscillation mode to the normal mode in response to the obstruction being removed from the aspiration catheter.

20. 20. The aspiration system of claim 19, wherein the passive pressure oscillation assembly is configured to be activated to switch from the first oscillation mode to the normal mode in response to complete suction of the vascular obstruction by the aspiration catheter, and to be activated to switch from the second oscillation mode to the normal mode in response to removal of the obstruction from the aspiration catheter.

21. 18. The aspiration system of claim 17, wherein the passive pressure oscillation assembly is activated to switch from the normal mode to the first oscillation mode in response to an absolute pressure in the aspiration flow path decreasing to create a first operating negative pressure differential between the pressurized fluid source and the aspiration flow path, and is activated to switch from the normal mode or the first oscillation mode to the second oscillation mode in response to an absolute pressure in the aspiration flow path decreasing to create a second operating negative pressure differential that is less than the first operating negative pressure differential.

22. 16. The aspiration system of claim 1, wherein the vibration mode simultaneously pulses fluid communication between the pressurized fluid source and the aspiration flow path at a first amplitude and a first frequency and at a first amplitude and a second frequency different from the first amplitude and the first frequency, respectively, to enhance removal of obstructions from the aspiration catheter.

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