Patent Description:
It is often desirable to remove tissue from the body in a minimally invasive manner as possible, so as not to damage other tissues. For example, removal of tissue from within a vasculature, such as blood clots, may improve patient conditions and quality of life.

Many vascular system problems stem from insufficient blood flow through blood vessels. One cause of insufficient or irregular blood flow is a blockage within a blood vessel referred to as a blood clot or thrombus. Blood clots or thrombi may embolize and form an embolus in a patient vasculature. Thrombi can occur for many reasons, including damage to the arterial wall from atherosclerotic disease, trauma caused by surgery, or due to other causes.

When a thrombus forms, it may effectively stop the flow of blood through the zone of formation. Sometimes such thrombi are harmlessly dissolved in the blood stream. At other times, however, such thrombi may lodge in a blood vessel where they can partially or completely occlude the flow of blood. If the partially or completely occluded vessel feeds blood to sensitive tissue such as, the brain, lungs or heart, for example, serious tissue damage may result. For example, thrombosis of one of the carotid arteries can lead to stroke, because of insufficient oxygen supply to vital nerve centers in the cranium. As another example, if one of the coronary arteries is <NUM>% thrombosed, the flow of blood is stopped in that artery, resulting in a shortage of oxygen carrying red blood cells, e.g., to supply the muscle (myocardium) of the heart wall. Oxygen deficiency reduces or prohibits muscular activity, can cause chest pain (angina pectoris), and can lead to death of myocardium, which permanently disables the heart to some extent. If the myocardial cell death is extensive, the heart will be unable to pump sufficient blood to supply the body's life sustaining needs. Indeed, a large percentage of the more than <NUM> million heart attacks in the United States are caused by blood clots (thrombi) which form within a coronary artery.

When symptoms of an occlusion are apparent, such as an occlusion resulting in a stroke, immediate action should be taken to reduce or eliminate resultant tissue damage. Indeed, clinical data indicates that clot removal may be beneficial or even necessary to improve outcomes. For example, in the peripheral vasculature, clot removal can reduce the need for an amputation by <NUM> percent. The ultimate goal of any modality to treat these conditions of the arterial or venous system is to remove the blockage or restore patency, quickly, safely, and cost effectively. One approach is to treat a patient with clot dissolving drugs. These drugs, however, do not immediately dissolve the clot from the patient, and are typically ineffective after a predefined window, usually at <NUM>-<NUM> hours after the symptoms arise from the clot. Other approaches involve thrombectomy, i.e., the removal of the clot by aspiration, mechanical retrieval, or a combination thereof. Mechanical retrieval usually involves a deployable mesh-like grid, such as a stent retriever, and is often complicated and dangerous to perform.

Aspiration thrombectomy is generally an effective and common treatment for removing a clot from a blood vessel, especially in the case of ischemic stroke. In a typical endovascular aspiration thrombectomy procedure, a catheter is introduced into the vasculature of the patient until the distal end of a catheter is just proximal to the clot, and a vacuum is applied at the proximal end of the catheter, resulting in the ingestion and subsequent removal of at least a portion of the clot into the catheter. Most aspiration systems are susceptible to tip clogging when the clot that is being aspirated is too large for the aspiration conduit at the distal end of the catheter. Current technology for endovascular thrombectomy in ischemic stroke utilizes static loading. Once tip clogging occurs, the pressure in the system precipitously drops to a level that often results in boiling or cavitation of the aspirate within the system. As a result, water vapor is introduced into the system, thereby decreasing the efficiency of the aspiration, and in turn, making it more difficult, if not impossible, to ingest the clot into the catheter.

In some cases, the clog can be disrupted or forced to squeeze through the aspiration conduit by dynamically or cyclically loading the aspiration conduit, which involves using pressure pulsing to ingest the clogged clot. One method of cyclically loading the aspiration conduit uses a cyclically activated valve or similar configuration to achieve the pressure pulsing by blocking main stream flow. Typically, this is done by hand, or via an electro-mechanical or pneumatic valve which blocks aspirate flow to the pump for a specified time interval. In some instances, pressure sensing feedback has been suggested as a means for determining when to activate the valve. One cyclical loading method, described in <NPL> and <CIT>, employs a venting mechanism that is automatically placed in an oscillatory pulse mode in response to the application of vacuum to the aspiration conduit. However, these methods either require user intervention to cyclically load the aspiration conduit in response to the realization that the aspiration conduit it has been clogged, which would distract the user from performing the aspiration procedure at hand, or cyclically load the aspiration conduit immediately upon the application of vacuum to the aspiration conduit, and thus, decreases the efficiency of the aspiration procedure during free flow (i.e., when the aspiration conduit is not clogged).

<CIT> discloses an intermittent regulator for the suction of fluids in the stomach area of a patient, in which the regulator is switched from a continuous-on operation to an intermittent operation upon sensing occlusion in the aspiration line.

<CIT> discloses a medical aspirator for removing blood or fluids from an incision or wound, including an automatic valve means to reverse the flow of air upon stoppage of the suction system whereby the stoppage may be dislodged and the normal suction function of the aspirator is reinstituted. The aspirator includes a spring-loaded suction responsive trigger means to rotate the valve means.

<CIT> discloses an aspiration system similar to the pre-amble of claim <NUM>.

The invention is directed to an aspiration system according to claim <NUM>.

The drawings illustrate the design and utility of preferred embodiments of the disclosed inventions, in which similar elements are referred to by common reference numerals. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention, which is defined only by the appended claims and their equivalents. In addition, an illustrated embodiment of the disclosed inventions needs not have all the aspects or advantages shown. Further, an aspect or an advantage described in conjunction with a particular embodiment of the disclosed inventions is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated.

In order to better appreciate how the above-recited and other advantages and objects of the disclosed inventions are obtained, a more particular description of the disclosed inventions briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:.

Referring to <FIG>, one embodiment of an occlusion aspiration system <NUM> constructed accordance with the disclosed inventions will now be described. The occlusion aspiration system <NUM> generally comprises an aspiration catheter <NUM>, an aspiration source <NUM>, a pressurized fluid source <NUM>, a tissue collection container <NUM>, and a manifold <NUM>.

Referring further to <FIG>, the aspiration catheter <NUM> comprises an elongated catheter body <NUM>, an aspiration conduit <NUM> (shown in phantom in <FIG>) extending through the catheter body <NUM> between a proximal end <NUM> and the distal end <NUM> of the catheter body <NUM>. The proximal end <NUM> of the aspiration catheter <NUM> remains outside of a patient <NUM> and accessible to the operator when the occlusion aspiration system <NUM> is in use, while the distal end <NUM> of the catheter body <NUM> is sized and dimensioned to reach an occlusion <NUM> (e.g., a clot) with a remote location of the vasculature <NUM> of the patient, as best shown in <FIG>. The aspiration catheter <NUM> comprises a distal inlet port <NUM> in communication with the aspiration conduit <NUM> of the aspiration catheter <NUM>, and into which the occlusion <NUM> is ingested by the aspiration catheter <NUM>.

The aspiration catheter <NUM> may include a plurality of regions along its length having different configurations and/or characteristics. For example, a distal portion of the catheter body <NUM> may have an outer diameter less than the outer diameter of a proximal portion of the catheter body <NUM> to reduce the profile of the distal portion of the catheter body <NUM> and facilitate navigation in tortuous vasculature. Furthermore, the distal portion of the catheter body <NUM> may be more flexible than the proximal portion of the catheter body <NUM>. Generally, the proximal portion of the catheter body <NUM> may be formed from material that is stiffer than the distal portion of the catheter body <NUM>, so that the proximal portion has sufficient pushability to advance through the vasculature <NUM> of the patient, while the distal portion may be formed of a more flexible material so that it may remain flexible and track more easily over a guidewire to access remote locations in tortuous regions of the vasculature <NUM>. The catheter body <NUM> may be composed of suitable polymeric materials, metals and/or alloys, such as polyethylene, stainless steel or other suitable biocompatible materials or combinations thereof. In some instances, the proximal portion of the catheter body <NUM> may include a reinforcement layer, such a braided layer or coiled layer to enhance the pushability of the catheter body <NUM>. The catheter body <NUM> may include a transition region between the proximal portion and the distal portion of the catheter body <NUM>.

Referring back to <FIG>, the aspiration source <NUM> can be, e.g., conventional a pump (e.g., a rotary vane, diaphragm, peristaltic or Venturi pump) or a syringe, configured for generating a low pressure within the aspiration conduit <NUM> of the aspiration catheter <NUM>. The low pressure is below the ambient air pressure, and thus, can be considered a vacuum capable of aspirating the occlusion <NUM> within the aspiration conduit <NUM> of the aspiration catheter <NUM>. The occlusion <NUM> may be wholly ingested into the aspiration catheter <NUM> or may be broken up into pieces and ingested piece-by-piece into the aspiration catheter <NUM>. In operation, the aspiration source <NUM> provides a base level of vacuum for the aspiration catheter <NUM>. This vacuum level may be controlled and adjusted as needed by the user for aspirating tissue. Over any given time period during a tissue removal procedure, the user may set the level of vacuum to be constant or may vary the vacuum level.

The pressurized fluid source <NUM> may be, e.g., 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 <NUM> is pressurized to the extent that the fluid has a pressure that is higher than the lowest vacuum level achieved in the aspiration conduit <NUM> of the aspiration catheter <NUM> when the aspiration source <NUM> is operating. Thus, even though the fluid source <NUM> in the illustrated embodiment may be under low pressure (i.e., at ambient or one atmosphere absolute pressure), the fluid source <NUM> is pressurized relative to the pressures experienced by the aspiration conduit <NUM> of the aspiration catheter <NUM> during operation of the aspiration source <NUM>. The tissue collection container <NUM> may be any suitable receptacle in fluid communication with the aspiration source <NUM> via an exhaust line for enabling collection and disposal of aspirated tissue in a sterile manner. Alternatively, the tissue collection container <NUM> may be located between the aspiration source <NUM> and the aspiration catheter <NUM>.

The aspiration catheter <NUM>, aspiration source <NUM>, pressurized fluid source <NUM>, and tissue collection container <NUM> may be conventional in nature.

In contrast, the manifold <NUM> is unconventional, and provides an interface between the aspiration catheter <NUM>, aspiration source <NUM>, and pressurized fluid source <NUM> in a manner that facilitates ingestion of the thrombus <NUM> by the aspiration catheter <NUM> during no-flow or low-flow conditions (e.g., if the thrombus <NUM> clogs the aspiration conduit <NUM> of the aspiration catheter <NUM> or otherwise there is a flow anomaly in the aspiration circuit of the system <NUM>), while maximizing efficiency of the aspiration process during free-flow conditions (e.g., when the aspiration conduit <NUM> is not clogged and the aspiration circuit of the system <NUM> is operating as intended).

The manifold <NUM> comprise an aspiration inlet <NUM> coupled to the aspiration catheter <NUM>, and an aspiration outlet <NUM> coupled to the aspiration source <NUM>, such that an aspiration flow path <NUM> is formed from the aspiration catheter <NUM> to the aspiration source <NUM>, and a relief inlet <NUM> coupled to the pressurized fluid source <NUM>. The manifold <NUM> may be coupled to the aspiration catheter <NUM>, aspiration source <NUM>, and pressurized fluid source <NUM> via the use of conventional catheters (not shown) or may alternatively be integrated with the aspiration catheter <NUM>, aspiration source <NUM>, and pressurized fluid source <NUM> without the use of connectors. The manifold <NUM> further comprises a passive pressure oscillation assembly <NUM> coupled between the relief inlet <NUM> and the aspiration flow path <NUM>. Significantly, the passive pressure oscillation assembly <NUM> is configured for dynamically loading (i.e., rapidly changing the vacuum level) the aspiration conduit <NUM> of the aspiration catheter <NUM>, and in particular, cyclically loading the aspiration conduit <NUM> only during the no-flow or low-flow conditions. The passive pressure oscillation assembly <NUM> accomplishes this without user input and without the use of electronic sensors. Furthermore, the passive pressure oscillation assembly <NUM> may be made to be very compact, such that it can be fitted within manifold <NUM> will little additional bulk. The passive pressure oscillation assembly <NUM> may be disabled simply be blocking the relief inlet <NUM>.

To this end, the passive pressure oscillation assembly <NUM> is configured for being operated between a normal mode that prevents fluid communication along a relief path <NUM> between the pressurized fluid source <NUM> and the aspiration flow path <NUM>, such that the absolute pressure in the aspiration flow path <NUM> remains relatively constant and is only acted upon by the aspiration source <NUM>, and an oscillatory mode that pulses fluid communication along the relief path <NUM> between the pressurized fluid source <NUM> and the aspiration flow path <NUM>, such that the absolute pressure in the aspiration flow path <NUM> oscillates within a range of predetermined frequencies. The passive pressure oscillation assembly <NUM> is configured for being triggered to switch from the normal mode to the oscillatory mode in response to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM> or otherwise a flow anomaly in the aspiration conduit of the system <NUM>, and conversely, for being triggered to switch from the oscillatory mode to the normal mode in response to removal or clearance of the clog from the aspiration conduit <NUM> of the aspiration catheter <NUM> or otherwise resolution of the flow anomaly in the aspiration circuit of the system <NUM>. In the illustrated embodiment, fluid communication pulsing between the pressurized fluid source <NUM> and the aspiration flow path <NUM> causes pressure pulses to propagate down the aspiration conduit <NUM> of the aspiration catheter <NUM> at the predetermined frequency. Simultaneously, fluid communication pulsing between the pressurized fluid source <NUM> and the aspiration flow path <NUM> causes fluid backflows to propagate down the aspiration conduit <NUM> of the aspiration catheter <NUM>.

The passive pressure oscillation assembly <NUM> may be designed to pulse fluid communication along the relief path <NUM> between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at a predetermined frequency, such that the absolute pressure in the aspiration flow path <NUM> oscillates at that predetermined frequency. As one example, the predetermined frequency of the pressure oscillations induced in the aspiration flow path <NUM> by the passive pressure oscillation assembly <NUM> may match the natural resonance of the fluid column within the aspiration conduit <NUM> of the aspiration catheter <NUM>, such that energy transfer from the aspiration flow path <NUM> to the aspiration conduit <NUM> of the aspiration catheter <NUM>, and thus propagation of the pressure pulses down the aspiration conduit <NUM> of the aspiration catheter <NUM>, is maximized. As another example, the predetermined frequency of the pressure oscillations induced in the aspiration flow path <NUM> by the passive pressure oscillation assembly <NUM> may be selected based on the visco-elastic properties of thrombus <NUM> expected to be ingested by the aspiration catheter <NUM>. That is, a clogged thrombus <NUM> with a softer consistency may be more susceptible to maceration, and thus subsequent ingestion, in response to relatively low-frequency, high-amplitude oscillations, whereas a clogged thrombus <NUM> with a harder consistency may be more susceptible to maceration, and thus subsequent ingestion, in response to relatively high-frequency, low-amplitude oscillations.

The oscillation of the passive pressure oscillation assembly <NUM> may optionally cause sound to emanate, and can serve as an automatic audible signal to the user that a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM> has occurred. In an optional embodiment, the passive pressure oscillation assembly <NUM> may be designed to pulse fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> simultaneously at two or more different frequencies. For example, because determining the type of material properties of the thrombus <NUM> will not be known ahead of time, it may be desirable to pulse fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> simultaneously at a relatively high frequency and at a relatively low frequency, such that the pressure profile in the aspiration conduit <NUM> of the aspiration catheter <NUM> is a composite of the low-frequency and high-frequency oscillations.

In the illustrated embodiment, the passive pressure oscillation assembly <NUM> takes advantage of the correlation between the different flow conditions of the aspiration catheter <NUM> and the resulting fluid pressure levels in the aspiration flow path <NUM>. In particular, it is expected that, in the case of a no-flow or low-flow condition where there is a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise a flow anomaly in the aspiration circuit of the system <NUM>, the vacuum in the aspiration flow path <NUM> will precipitously increase (i.e., the absolute pressure in the aspiration flow path <NUM> will precipitously decrease), thereby causing the negative pressure differential between the external ambient pressure and the aspiration flow path <NUM> to increase to a very high level (e.g., at least -55kPa), which, assuming no intervention by the passive pressure oscillation assembly <NUM>, may even cause boiling or cavitation of the aspirate within the aspiration flow path <NUM> (e.g., if the such negative pressure differential below -95kPa). In contrast, it is also expected that, in the case of a free-flow condition where the aspiration catheter <NUM> has been unclogged, or otherwise, the flow anomaly in the aspiration circuit of the system <NUM> has been resolved, the vacuum in the aspiration flow path <NUM> will precipitously decrease (i.e., the absolute pressure in the aspiration flow path <NUM> will precipitously increase) to a lower level (e.g., less than -50kPa), thereby causing the negative pressure differential between the external ambient pressure and the aspiration flow path <NUM> to decrease to a lower level. The passive pressure oscillation assembly <NUM> keys off these negative pressure differentials when switching between the normal mode and the oscillatory mode.

To this end, the passive pressure oscillation assembly <NUM> comprises an inlet port <NUM> (shown in <FIG>) in fluid communication with the pressurized fluid source <NUM> and an outlet port <NUM> (shown in <FIG>) in fluid communication with the aspiration flow path <NUM>, such that the passive pressure oscillation assembly <NUM> is exposed to a negative pressure differential between pressurized fluid source <NUM> and the fluid in the aspiration flow path <NUM>. The passive pressure oscillation assembly <NUM> is triggered to switch from the normal mode and the oscillatory mode, and conversely, from the oscillatory mode to the normal mode, based on this negative pressure differential.

In particular, the passive pressure oscillation assembly <NUM> is designed to be triggered to switch from the normal mode to the oscillatory mode in response to a drop in absolute pressure in the aspiration flow path <NUM> that creates a negative activation pressure differential between the inlet port <NUM> and the outlet port <NUM> of the passive pressure oscillation assembly <NUM> correlated to the negative pressure differential between the aspiration flow path <NUM> and the blood pressure experienced by the aspiration catheter <NUM> when the aspiration conduit <NUM> of the aspiration catheter <NUM> is clogged or the aspiration circuit of the system <NUM> otherwise experiences a flow anomaly (no-flow or low-flow condition); and conversely, the passive pressure oscillation assembly <NUM> is designed to be triggered to switch from the oscillatory mode to the normal mode in response to an increase in absolute pressure in the aspiration flow path <NUM> that creates a negative cessation pressure differential between the inlet port <NUM> and the outlet port <NUM> of the passive pressure oscillation assembly <NUM> correlated to the negative pressure differential between the aspiration flow path <NUM> and the blood pressure experienced by the aspiration catheter <NUM> when the aspiration conduit <NUM> of the aspiration catheter <NUM> is unclogged or the aspiration circuit of the system <NUM> is operating as intended (free-flow condition).

In the case where the pressurized fluid source <NUM> is at the external ambient pressure, the negative activation pressure differential of the passive pressure oscillation assembly <NUM> will essentially differ from the negative pressure differential between the aspiration flow path <NUM> and the blood pressure experienced by the aspiration catheter <NUM> by a known offset during a no-flow or low-flow condition, and likewise, the negative cessation pressure differential of the passive pressure oscillation assembly <NUM> will essentially differ from the negative pressure differential between the aspiration flow path <NUM> and the blood pressure experienced by the aspiration catheter <NUM> by a known offset during a free-flow condition. In this manner, the passive pressure oscillation assembly <NUM> may be configured to self-calibrate to a time-varying ambient external environment.

In this case, the range in which the negative activation pressure differential of the passive pressure oscillation assembly <NUM> is designed may have an upper limit of -55kPa, such that the passive pressure oscillation assembly <NUM> is quickly triggered to switch from the normal mode to the oscillatory mode, but not so low that the passive pressure oscillation assembly <NUM> is triggered to switch from the normal mode to the oscillatory mode during active and productive ingestion of the thrombus <NUM> into the distal end <NUM> of the aspiration catheter <NUM>, and may have a lower limit of - 95kPa to ensure that the boiling point of fluid (i.e. blood at <NUM>) in the aspiration flow path <NUM> is never reached, although it should be appreciated that the passive pressure oscillation assembly <NUM> may be designed to have a negative activation pressure differential that falls anywhere within the range of -55kPa to -95kPa. The negative cessation pressure differential of the passive pressure oscillation assembly <NUM> should be designed relative to the negative activation pressure differential of the passive pressure oscillation assembly <NUM>, preferably, substantially less than the negative activation pressure differential (e.g., within the range of 10kPa-25kPa greater than the negative activation pressure differential), such that hysteresis is built into the passive pressure oscillation assembly <NUM>. In this manner, the pressure oscillations induced in the aspiration flow path <NUM> by the passive pressure oscillation assembly <NUM> will not inadvertently trigger the passive pressure oscillation assembly <NUM> back into the normal mode until the aspiration catheter <NUM> is in a free-flow condition. It should be noted that, in low-resonant frequency scenarios, the negative activation pressure differential and the negative cessation pressure differential may be the same, in which case, the passive pressure oscillation assembly <NUM> will be re-triggered after each increase in the negative pressure differential in the aspiration flow path <NUM> to switch from the normal mode to the oscillation mode in response to the decrease in the absolute pressure in the aspiration flow path <NUM> caused by the aspiration source <NUM>.

In an optional embodiment, the passive pressure oscillation assembly <NUM> may be designed with multiple negative activation pressure differentials, and correspondingly, multiple negative cessation pressure differentials. For example, the passive pressure oscillation assembly <NUM> may be designed to have a first negative activation pressure differential, e.g., at -50kPa, such that the passive pressure oscillation assembly <NUM> is triggered to switch from the normal mode to a relatively fast oscillatory mode to facilitate ingestion of the thrombus <NUM> into the distal end <NUM> of the aspiration catheter <NUM> prior to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>. Operation of the passive pressure oscillation assembly <NUM> in the relatively high oscillatory mode may cause high frequency, but low volume, pulses to propagate down the aspiration conduit <NUM> of the aspiration catheter <NUM>, thereby facilitating ingestion of the thrombus <NUM> without overly impeding volume flow. The passive pressure oscillation assembly <NUM> may be further designed to have a second negative activation pressure differential, e.g., at -55kPa, such that the passive pressure oscillation assembly <NUM> is triggered to operate in a relatively slow oscillatory mode to facilitate clearing of a thrombus <NUM> that is clogged in the distal end <NUM> of the aspiration catheter <NUM>. Operation of the passive pressure oscillation assembly <NUM> in the relatively high oscillatory mode may cause low frequency, but high volume, pulses to propagate down the aspiration conduit <NUM> of the aspiration catheter <NUM> in an attempt to dislodge the clogged thrombus <NUM> from the distal end <NUM> of the aspiration catheter <NUM>. Thus, if the thrombus <NUM> is ingested without ever clogging the distal end <NUM> of the aspiration catheter <NUM>, only the relatively fast oscillatory mode of the passive pressure oscillation assembly <NUM> will be triggered, whereas the relatively slow oscillatory mode of the passive pressure oscillation assembly <NUM> will only be triggered when the thrombus <NUM> clogs the distal end <NUM> of the aspiration catheter <NUM>.

It should be appreciated that the pressurized fluid source <NUM> may have a pressure substantially different from the external ambient pressure experienced by the aspiration catheter <NUM>, in which case, the negative activation pressure differential of the passive pressure oscillation assembly <NUM> will be substantially different from the negative pressure differential between the aspiration flow path <NUM> and the ambient external environment experienced by the aspiration catheter <NUM> during a no-flow or low-flow condition, and likewise, the negative cessation pressure differential of the passive pressure oscillation assembly <NUM> will be substantially different from the negative pressure differential between the aspiration flow path <NUM> and the ambient external environment experienced by the aspiration catheter <NUM> during a free-flow condition. In this latter case, this difference can be taken into account when designing the negative activation pressure differential and negative cessation pressure differential of the passive pressure oscillation assembly <NUM>. For example, if the pressurized fluid source <NUM> has a pressure substantially higher than the external ambient pressure, then the passive pressure oscillation assembly <NUM> should be designed to a negative activation pressure differential and negative cessation pressure differential that is higher to account for the higher fluid pressure that will be experienced by the inlet port <NUM> of the passive pressure oscillation assembly <NUM>.

As one example, and with reference to <FIG>, the aspiration source <NUM> is first activated, such that the aspiration catheter <NUM> is in a free-flow condition between arbitrary time t<NUM> and t<NUM>, and the negative pressure differential between the absolute pressure in the aspiration flow path <NUM> and the external ambient pressure experienced by the aspiration catheter <NUM> (in this case, the negative pressure differential between the inlet port <NUM> and the outlet port <NUM> of the passive pressure oscillation assembly <NUM>) is at a free-flow negative pressure differential where the aspiration catheter <NUM> is only ingesting blood. During this time, the passive pressure oscillation assembly <NUM> remains in the normal mode. In this manner, the aspiration efficiency of the system <NUM> is maximized during free-flow conditions.

Between arbitrary time t<NUM> and arbitrary time t<NUM>, the thrombus <NUM> is actively being ingested into the distal end <NUM> of the aspiration catheter <NUM>, such that the negative pressure differential between the absolute pressure in the aspiration flow path <NUM> and the external ambient pressure experienced by the aspiration catheter <NUM> drops below the free-flow negative pressure differential, but not below the negative activation pressure differential of the passive pressure oscillation assembly <NUM>, which is designed for a no-flow or low-flow condition indicative of a clogged aspiration catheter <NUM> or flow anomaly in the aspiration conduit of the system <NUM>. During arbitrary time t<NUM> and time t<NUM>, the passive pressure oscillation assembly <NUM> remains in the normal mode.

At arbitrary time t<NUM>, however, the aspiration catheter <NUM> becomes clogged with the thrombus <NUM>, resulting in a precipitous decrease in the negative pressure differential between the absolute pressure in the aspiration flow path <NUM> and the external ambient pressure experienced by the aspiration catheter <NUM> to a level below the negative activation pressure differential, which in the illustrated case, is at - 75kPa. Thus, at or just after the arbitrary time t<NUM>, the clogged aspiration catheter <NUM> (no-flow or low-flow condition) triggers the passive pressure oscillation assembly <NUM> to switch from the normal mode to the oscillatory mode, resulting in pressure oscillations in the aspiration flow path <NUM> that cause pressure pulses to propagate down the aspiration conduit <NUM> of the aspiration catheter <NUM>, thereby facilitating clearance of the clogged thrombus <NUM> at the distal end <NUM> of the aspiration catheter <NUM> at the arbitrary time t<NUM>. Clearance of the clogged thrombus <NUM> at the distal end <NUM> of the aspiration catheter <NUM> results in a precipitous increase in the negative pressure differential between the absolute pressure in the aspiration flow path <NUM> and the external ambient pressure experienced by the aspiration catheter <NUM> to a level above the negative cessation pressure differential, which in the illustrated case, is at - 50kPa. Thus, at or just after the arbitrary time t<NUM>, the cleared aspiration catheter <NUM> (free-flow condition) triggers the passive pressure oscillation assembly <NUM> to switch from the oscillatory mode to the normal mode, ceasing pressure oscillations in the aspiration flow path <NUM>, and thus ceasing pressure pulses from propagating down the aspiration conduit <NUM> of the aspiration catheter <NUM>.

In the optional embodiment where the passive pressure oscillation assembly <NUM> operates in multiple oscillatory modes (e.g., a high frequency oscillatory mode and a low frequency oscillatory mode), the passive pressure oscillation assembly <NUM> may be operated in the high frequency oscillatory mode between the arbitrary time t<NUM> and arbitrary time t<NUM>, such that active ingestion of the thrombus <NUM> into the distal end <NUM> of the aspiration catheter <NUM> is facilitated by the high-frequency, but low volume, pressure pulses propagating down the aspiration conduit <NUM> of the aspiration catheter <NUM>, and then if the thrombus <NUM> clogs the distal end <NUM> of the aspiration catheter <NUM>, may be then operated in the low frequency oscillatory mode between the arbitrary time t<NUM> and the arbitrary time t<NUM>, such that clearance of the clogged thrombus <NUM> from the distal end <NUM> of the aspiration catheter <NUM> is facilitated by the low-frequency, high volume, pressure pulses propagating down the aspiration conduit <NUM> of the aspiration catheter <NUM>.

Referring to <FIG>, the passive pressure oscillation assembly <NUM> comprises a pressure actuated valve <NUM> and a fluid (e.g., hydraulic or pneumatic) resonator <NUM>. The pressure actuated valve <NUM> is configured for opening in response to a drop in absolute pressure in the aspiration flow path <NUM> that creates a negative activation pressure differential between the inlet port <NUM> and the outlet port <NUM> (e.g., indicative of a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>), thereby allowing the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>; and conversely, for closing in response to an increase in absolute pressure in the aspiration flow path <NUM> that creates a negative cessation pressure differential between the inlet port <NUM> and the outlet port <NUM> (e.g., indicative of the removal or clearance of a clog from the aspiration conduit <NUM> of the aspiration catheter <NUM>), thereby preventing the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>. The fluid resonator <NUM> is configured for resonating at a predetermined frequency in response to the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>, thereby pulsing the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at the predetermined frequency; and conversely, configured for ceasing resonation in response to the prevention of the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>.

In one embodiment, the pressure actuated valve <NUM> and fluid resonator <NUM> are mechanically coupled to each other. In this embodiment, although the mechanically coupled pressure actuated valve <NUM> and fluid resonator <NUM> must be dependently designed to satisfy both the opening and resonant frequency criteria, it results in a simpler mechanical design that can be more easily implemented into the passive pressure oscillation assembly <NUM>. In another embodiment, the pressure actuated valve <NUM> and fluid resonator <NUM> are mechanically decoupled from each other. In this embodiment, the mechanically decoupled pressure actuated valve <NUM> and fluid resonator <NUM> allows the opening/closing criteria and resonant frequency criteria to be independently optimized, although resulting in a mechanical design that may be more complicated than the mechanical design of the embodiment with the mechanically coupled pressure actuated valve <NUM> and fluid resonator <NUM>.

As discussed above, the passive pressure oscillation assembly <NUM> may optionally be designed to have two negative activation pressure differentials, and/or two negative cessation pressure differentials, and/or pulse fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> simultaneously at two different frequencies.

In an alternative embodiment, the fluid resonator <NUM> pulses fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> automatically in response to a clog in the aspiration catheter <NUM> by interrupting the aspiration flow path <NUM>, such that the pulsing fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> is directed towards the aspiration catheter <NUM>.

Referring to <FIG>, an alternative embodiment of a passive pressure oscillation assembly <NUM>' comprises two parallel sets of pressure actuated valve assemblies and fluid resonators. In particular, the passive pressure oscillation assembly <NUM>' comprises a first pressure actuated valve 54a, a first fluid resonator 56a, a second pressure actuated valve 54b, and a second fluid resonator 56b.

The first pressure actuated valve 54a is configured for opening in response to a drop in absolute pressure in the aspiration flow path <NUM> that creates a first negative activation pressure differential between the inlet port <NUM> and the outlet port <NUM>, thereby allowing a flow of fluid from the pressurized fluid source <NUM> through the first pressure actuated valve 54a; and conversely, for closing in response to an increase in absolute pressure in the aspiration flow path <NUM> that creates a first negative cessation pressure differential between the inlet port <NUM> and the outlet port <NUM>, thereby preventing the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>. The first fluid resonator 56a is configured for resonating at a first predetermined frequency in response to the flow of fluid from the pressurized fluid source <NUM> through the first pressure actuated valve 54a, thereby pulsing the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at the first predetermined frequency; and conversely, configured for ceasing resonation in response to the prevention of the flow of fluid from the pressurized fluid source <NUM> through the first pressure actuated valve 54a.

The second pressure actuated valve 54b is configured for opening in response to a drop in absolute pressure in the aspiration flow path <NUM> that creates a second negative activation pressure differential between the inlet port <NUM> and the outlet port <NUM>, thereby allowing a flow of fluid from the pressurized fluid source <NUM> through the second pressure actuated valve 54b; and conversely, for closing in response to an increase in absolute pressure in the aspiration flow path <NUM> that creates a second negative cessation pressure differential between the inlet port <NUM> and the outlet port <NUM>, thereby preventing the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>. The second fluid resonator 56b is configured for resonating at a second predetermined frequency in response to the flow of fluid from the pressurized fluid source <NUM> through the second pressure actuated valve 54b, thereby pulsing the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at the second predetermined frequency; and conversely, configured for ceasing resonation in response to the prevention of the flow of fluid from the pressurized fluid source <NUM> through the second pressure actuated valve 54b.

The first and second negative activation pressure differentials may be the same (e.g., both indicating a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>) or may be different (e.g., one indicating active thrombus ingestion into the aspiration catheter <NUM>, and the other indicating clogging of the aspiration conduit <NUM> of the aspiration catheter <NUM>). The first and second negative cessation pressure differentials may be the same (e.g., both indicating ingestion or removal of a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>), although in alternative embodiments, the first and second negative cessation pressure differentials may be different. The first and second predetermined frequencies may be the same or may be different (e.g., one being a relatively high-frequency for disrupting a clogged thrombus <NUM> with a harder consistency, and the other being a relatively low-frequency for disrupting a clogged thrombus <NUM> with a softer consistency). The first pressure actuated valve 54a and the first fluid resonator 56a may be mechanically coupled to each other or mechanically decoupled from each other, and the second pressure actuated valve 54b and the second fluid resonator 56b may likewise be mechanically coupled to each other or mechanically decoupled 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 multi-outlet valve assembly that distributes flows to either one or the other or both of the fluid resonators 56a, 56b in response to various levels of a single sensed pressure differential.

Although the passive pressure oscillation assembly <NUM>' is illustrated in <FIG> as comprising only two parallel sets of pressure actuated valve assemblies and fluid resonators, the passive pressure oscillation assembly <NUM>' may alternatively comprise more than two parallel sets of pressure actuated valve assemblies and fluid resonators.

Referring to <FIG>, another alternative embodiment of a passive pressure oscillation assembly <NUM>" comprises a single pressure actuated valve <NUM>, a first fluid resonator 56a, and a second fluid resonator 56b.

The pressure actuated valve <NUM> is configured for opening in response to a drop in absolute pressure in the aspiration flow path <NUM> that creates a negative activation pressure differential between the inlet port <NUM> and the outlet port <NUM>, thereby allowing the flow of fluid from the pressurized fluid source <NUM> through the first pressure actuated valve <NUM>; and conversely, for closing in response to an increase in absolute pressure in the aspiration flow path <NUM> that creates a negative cessation pressure differential between the inlet port <NUM> and the outlet port <NUM> (e.g., indicative of the removal or clearance of a clog from the aspiration conduit <NUM> of the aspiration catheter <NUM>), thereby preventing the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>.

The first fluid resonator 56a is configured for resonating at a first predetermined frequency in response to the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>, thereby pulsing the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at the first predetermined frequency; and conversely, configured for ceasing resonation in response to the prevention of the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>. The second fluid resonator 56b is configured for resonating at a second predetermined frequency in response to the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>, thereby pulsing the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> at the second predetermined frequency; and conversely, configured for ceasing resonation in response to the prevention of the flow of fluid from the pressurized fluid source <NUM> through the pressure actuated valve <NUM>.

The first and second predetermined frequencies may be the same or may be different (e.g., one being a relatively high-frequency for disrupting a clogged thrombus <NUM> with a harder consistency, and the other being a relatively low-frequency for disrupting a clogged thrombus <NUM> with a softer consistency). The first and second fluid resonators 56a, 56b may be mechanically decoupled from the pressure actuated valve <NUM>.

Referring now to <FIG>, one embodiment of a passive pressure oscillation assembly 44a will be described. The passive pressure oscillation assembly 44a comprises an inlet channel <NUM> fluidly coupled to the pressurized fluid source <NUM> via the inlet port <NUM>, and an outlet channel <NUM> fluidly coupled to the aspiration flow path <NUM> via the outlet port <NUM>. The passive pressure oscillation assembly 44a further comprises a valve seal in the form of a seat <NUM> fluidly coupled to the inlet port <NUM> via the inlet channel <NUM>, a movable valve element in the form of a valve disk <NUM> operably associated with the valve seat <NUM>, and an enlarged flow cavity <NUM> fluidly coupled between the valve seat <NUM> and the aspiration flow path <NUM> via the outlet channel <NUM> and outlet port <NUM>. The valve disk <NUM> is configured for being alternately displaced between a closed position to seal against the valve seat <NUM>, and in this case, within the valve seat <NUM> (see <FIG>), and an open position away from the valve seat <NUM>, and in this case outside of the valve seat <NUM> (see <FIG>). The passive pressure oscillation assembly 44a further comprises a restoring spring <NUM> affixed within the enlarged flow cavity <NUM> and mechanically coupled to the valve disk <NUM> for applying a biasing force to the valve disk <NUM> in a manner that maintains the valve disk <NUM> in the closed position within the valve seat <NUM> until the passive pressure oscillation assembly 44a is triggered to switch from the normal mode to the oscillatory mode, as will be described in further detail below.

The valve disk <NUM> and valve seat <NUM> have the same geometric profile (in this case, a flattened trapezoidal shape cross-section), such that the valve disk <NUM>, when in the closed position within the valve seat <NUM> (see <FIG>), seals against the valve seat <NUM> to prevent the flow of fluid originating from the pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>) into the enlarged flow cavity <NUM>. The enlarged flow cavity <NUM> has a geometric profile that is larger than the geometric profile of the valve disk <NUM>, such that the valve disk <NUM>, when in the open position outside of the valve seat <NUM> and within the enlarged flow cavity <NUM> (see <FIG>), allows the flow of fluid originating from pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>), into the enlarged flow cavity <NUM>, through the outlet channel <NUM>, and into the aspiration flow path <NUM> via the outlet port <NUM>.

In response to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the occurrence of an anomaly in the aspiration circuit of the system <NUM>, a no-flow or low-flow condition occurs in the aspiration flow path <NUM>, and as a result, the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a negative activation pressure differential between the inlet port <NUM> (and thus the inlet channel <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which causes the fluid in the inlet channel <NUM> to apply an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the closed position (see <FIG>) to the open position (see <FIG>). The negative activation pressure differential of the passive pressure oscillation assembly 44a will be based on the area of the valve disk <NUM> exposed to the fluid in the inlet channel <NUM> (the negative activation pressure differential will decrease in proportion to the exposed area of the valve disk <NUM>) and the spring constant of the restoring spring <NUM> (the negative action pressure differential will increase in proportion to the spring constant of the restoring spring <NUM>). Thus, the negative activation pressure differential of the passive pressure oscillation assembly 44a may be selected by judicially selecting the exposed area of the valve disk <NUM> and the spring constant of the restoring spring <NUM>.

The passive pressure oscillation assembly 44a is designed in such a manner that, once the valve disk <NUM> is displaced from the closed position to the open position (i.e., the valve "cracks"), the passive pressure oscillation assembly 44a resonates (i.e., the valve disk <NUM> alternately switches (oscillates) between the closed position and the open position. At this point, the passive pressure oscillation assembly 44a has been triggered to switch from the normal mode to the oscillatory mode.

In particular, the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>, the opposing force applied by the fluid in the inlet channel <NUM> to the valve disk <NUM>, and the mass of the valve disk <NUM> are selected, such that the valve disk <NUM> oscillates between the closed position and the open position at a predetermined frequency (e.g., in the range of <NUM>-<NUM>).

That is, when the valve disk <NUM> initially reaches the fully open position, the opposing force applied to the valve disk <NUM> by the fluid flowing from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, drops to a level, such that the biasing force applied by the restoring spring <NUM> overcomes the opposing fluid force applied to the valve disk <NUM> and the momentum of the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the open position back into the closed position within the valve seat <NUM> (see <FIG>). At this point, the momentary flow of fluid from the pressurized fluid source <NUM> into the aspiration flow path <NUM> (via the inlet port <NUM>, inlet channel <NUM>, valve seat <NUM>, enlarged flow cavity <NUM>, outlet channel <NUM>, and outlet port <NUM>), has caused the negative pressure differential between inlet port <NUM> and the outlet port <NUM> to increase. However, because the valve disk <NUM> is now in a closed position, thereby preventing the flow of fluid from the pressurized fluid source <NUM> to the aspiration flow path <NUM>, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> decreases until it reaches the negative activation pressure differential, causing the opposing force applied to the valve disk <NUM> by the fluid in the inlet channel <NUM> to rise to a level that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the closed position back to the open position (see <FIG>). The valve disk <NUM> continues to alternately be displaced between the closed position (see <FIG>) and the open position (see <FIG>) in this manner until the clog is removed from the aspiration conduit <NUM> of the aspiration catheter <NUM> or otherwise the anomaly in the aspiration circuit of the system <NUM> is resolved.

The frequency at which the valve disk <NUM> oscillates depends on the mass of the valve disk <NUM> (the frequency of the oscillation decreases as the mass of the valve disk <NUM> increases), the spring constant of the restoring spring <NUM> (the frequency of the oscillation increases as the spring constant of the restoring spring <NUM> increases), and the length of the valve seat <NUM> (the frequency of the oscillation increases as the length of the valve seat <NUM> decreases), as well as the dampening effect of the friction between the valve seat <NUM> and the valve disk <NUM> and the dynamic forces of the fluid flowing from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, on the valve disk <NUM> (the frequency of the oscillation decreases as the dampening effect increases). Thus, the frequency at which the valve disk <NUM> oscillates (i.e., the resonance of the passive pressure oscillation assembly 44a) may be selected by judicially selecting the mass of the valve disk <NUM>, spring constant of the restoring spring <NUM>, length of the valve seat <NUM>, and pre-compression length of the spring <NUM>, with due regard to the dampening effect that the friction between the valve seat <NUM> and the valve disk <NUM> and the fluid flow associated pressure drop from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, has on the valve disk <NUM>. Such dampening effect, itself, may be adjusted by varying the designed sizes and geometries of the inlet port <NUM>, outlet port <NUM>, inlet channel <NUM>, and outlet channel <NUM>.

In response to removal of the clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the resolution of the anomaly in the aspiration circuit of the system <NUM>, the absolute pressure in the aspiration flow path <NUM> increases to a level that creates a negative cessation pressure differential between the inlet port <NUM> (and thus the inlet channel <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which prevents the fluid in the inlet channel <NUM> from applying an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. That is, when the valve disk <NUM> is in the closed position, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> will never drop below the negative activation pressure differential due to the free flow condition of the aspiration flow path <NUM>. As a result, the biasing force applied by the restoring spring <NUM> maintains the valve disk <NUM> in the closed position. At this point, the passive pressure oscillation assembly 44a has been triggered to switch from the oscillatory mode back to the normal mode.

It should be noted that the passive pressure oscillation assembly 44a illustrated in <FIG> topologically comprises a pressure actuated valve <NUM> and a fluid resonator <NUM> (shown in <FIG>) that are mechanically coupled to each other. That is, the valve seat <NUM> and movable valve disk <NUM> form the pressure actuated valve <NUM>, whereas the valve disk <NUM>, enlarged flow cavity <NUM>, and restoring spring <NUM> form the fluid resonator <NUM>, with the pressure actuated valve <NUM> and fluid resonator <NUM> being mechanically coupled to each other via the valve disk <NUM>. In this embodiment, because the valve disk <NUM> forms a portion of both the pressure actuated valve <NUM> and the fluid resonator <NUM>, the negative activation and cessation pressure differentials and the resonance frequency must be designed with due regard to each other, and thus, may not be able to be independently optimized, although the resulting design of the passive pressure oscillation assembly 44a may be mechanically simple.

Referring now to <FIG>, another embodiment of a passive pressure oscillation assembly 44b will be described. The passive pressure oscillation assembly 44b is similar to the passive pressure oscillation assembly 44a illustrated in <FIG>, with the exception that the passive pressure oscillation assembly 44b comprises a long valve seal relative to the movable valve element in which it interacts, such that its resonant frequency is much slower than that of the passive pressure oscillation assembly 44a.

In particular, passive pressure oscillation assembly 44b comprises an inlet channel <NUM> fluidly coupled to the pressurized fluid source <NUM> via the inlet port <NUM>, and an outlet channel <NUM> fluidly coupled to the aspiration flow path <NUM> via the outlet port <NUM>. The passive pressure oscillation assembly 44b further comprises a valve seal in the form of a valve cylinder <NUM> fluidly coupled to the inlet port <NUM> via the inlet channel <NUM>, a movable valve element in the form of a valve disk <NUM> operatively associated with the valve cylinder <NUM>, and an enlarged flow cavity <NUM> fluidly coupled between the valve cylinder <NUM> and the aspiration flow path <NUM> via the outlet channel <NUM> and outlet port <NUM>. The valve disk <NUM> is configured for being alternately displaced between a closed position to seal within the valve cylinder <NUM> (see <FIG>), and an open position residing within the enlarged flow cavity <NUM> (see <FIG>). The passive pressure oscillation assembly 44b further comprises a restoring spring <NUM> disposed in a spring cavity <NUM> between the enlarged flow cavity <NUM> and the outlet channel <NUM>, and mechanically coupled to the valve disk <NUM> via a boss <NUM> affixed to the valve disk <NUM> for applying a biasing force to the valve disk <NUM> in a manner that maintains the valve disk <NUM> into the closed position within the valve cylinder <NUM> until the passive pressure oscillation assembly 44b is triggered to switch from the normal mode to the oscillatory mode.

The valve disk <NUM> and valve cylinder <NUM> have the same geometric profile (in this case, a cylindrical in nature), such that the valve disk <NUM>, when in the closed position within the valve cylinder <NUM> (see <FIG>), seals against the valve cylinder <NUM> to prevent the flow of fluid originating from the pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>) into the enlarged flow cavity <NUM>. The enlarged flow cavity <NUM> has a geometric profile that is larger than the geometric profile of the valve disk <NUM>, such that the valve disk <NUM>, when in the open position outside of the valve cylinder <NUM> and within the enlarged flow cavity <NUM> (see <FIG>), allows the flow of fluid originating from pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>), into the enlarged flow cavity <NUM>, through the outlet channel <NUM>, and into the aspiration flow path <NUM> via the outlet port <NUM>.

In response to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the occurrence of an anomaly in the aspiration circuit of the system <NUM>, a no-flow or low-flow condition occurs in the aspiration flow path <NUM>, and as a result, the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a negative activation pressure differential between the inlet port <NUM> (and thus the valve cylinder <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which causes the fluid in the inlet channel <NUM> to apply an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the closed position (see <FIG>) to the open position (see <FIG>). The negative activation pressure differential of the passive pressure oscillation assembly 44b will be based on the area of the valve disk <NUM> exposed to the fluid in the valve cylinder <NUM> (the negative activation pressure differential will decrease in proportion to the exposed area of the valve disk <NUM>) and the spring constant of the restoring spring <NUM> (the negative action pressure differential will increase in proportion to the spring constant of the restoring spring <NUM>). Thus, the negative activation pressure differential of the passive pressure oscillation assembly 44b may be selected by judicially selecting the exposed area of the valve disk <NUM> and the spring constant of the restoring spring <NUM>.

The passive pressure oscillation assembly 44b is designed in such a manner that, once the valve disk <NUM> is displaced from the closed position to the open position (i.e., the valve "cracks"), the passive pressure oscillation assembly 44b resonates (i.e., the valve disk <NUM> alternately switches (oscillates) between the closed position and the open position. At this point, the passive pressure oscillation assembly 44b has been triggered to switch from the normal mode to the oscillatory mode.

In particular, the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>, the opposing force applied by the fluid in the valve cylinder <NUM>, and the mass of the valve disk <NUM> are selected, such that the valve disk <NUM> oscillates between the closed position and the open position at a predetermined frequency (e.g., in the range of <NUM>-<NUM>).

That is, when the valve disk <NUM> fully reaches the open position, the opposing force applied to the valve disk <NUM> by the fluid flowing from the inlet channel <NUM>, through the valve cylinder <NUM>, and into the enlarged flow cavity <NUM>, drops to a level, such that the biasing force applied by the restoring spring <NUM> overcomes the opposing fluid force applied to the valve disk <NUM> and the momentum of the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the open position back into the closed position within the valve cylinder <NUM> (see <FIG>). At this point, the momentary flow of fluid from the pressurized fluid source <NUM> into the aspiration flow path <NUM> (via the inlet port <NUM>, inlet channel <NUM>, valve cylinder <NUM>, enlarged flow cavity <NUM>, spring cavity <NUM>, outlet channel <NUM>, and outlet port <NUM>), has caused the negative pressure differential between inlet port <NUM> and the outlet port <NUM> to increase. However, because the valve disk <NUM> is now in a closed position, thereby preventing the flow of fluid from the pressurized fluid source <NUM> to the aspiration flow path <NUM>, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> decreases until it reaches the negative activation pressure differential, causing the opposing force applied to the valve disk <NUM> by the fluid in the valve cylinder <NUM> to rise to a level that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. As a result, the valve disk <NUM> is again displaced from the closed position to the open position (see <FIG>). The valve disk <NUM> continues to alternately be displaced between the closed position (see <FIG>) and the open position (see <FIG>) in this manner until the clog is removed from the aspiration catheter <NUM> or otherwise the anomaly in the aspiration circuit of the system <NUM> is resolved.

The frequency at which the valve disk <NUM> oscillates depends on the mass of the valve disk <NUM> (the frequency of the oscillation decreases as the mass of the valve disk <NUM> increases), the spring constant of the restoring spring <NUM> (the frequency of the oscillation increases as the spring constant of the restoring spring <NUM> increases), and the length of the valve cylinder <NUM> (the frequency of the oscillation increases as the length of the valve seat <NUM> decreases), as well as the dampening effect of the friction between the valve cylinder <NUM> and the valve disk <NUM> and the dynamic forces of the fluid flowing from the inlet channel <NUM>, through the valve cylinder <NUM>, and into the enlarged flow cavity <NUM>, on the valve disk <NUM> (the frequency of the oscillation decreases as the dampening effect increases). Thus, frequency at which the valve disk <NUM> oscillates (i.e., the resonance of the passive pressure oscillation assembly 44b) may be selected by judicially selecting the mass of the valve disk <NUM> and the spring constant of the restoring spring <NUM>, length of the valve cylinder <NUM>, and pre-compression length of the spring <NUM>, with due regard to the dampening effect that the friction between the valve cylinder <NUM> and the valve disk <NUM> and the fluid flowing from the inlet channel <NUM>, through the valve cylinder <NUM>, and into the enlarged flow cavity <NUM>, has on the valve disk <NUM>. Such dampening effect, itself, may be adjusted by varying the designed sizes and geometries of the inlet port <NUM>, outlet port <NUM>, inlet channel <NUM>, and outlet channel <NUM>.

In response to removal of the clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the resolution of the anomaly in the aspiration circuit of the system <NUM>, the absolute pressure in the aspiration flow path <NUM> increases to a level that creates a negative activation pressure differential between the inlet port <NUM> (and thus the valve cylinder <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which prevents the fluid in the inlet channel <NUM> from applying an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. That is, when the movable valve cylinder <NUM> is in the closed position, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> will never drop below the negative activation pressure differential due to the free flow condition of the aspiration flow path <NUM>. As a result, the biasing force applied by the restoring spring <NUM> maintains the valve disk <NUM> in the closed position. At this point, the passive pressure oscillation assembly 44b has been triggered to switch from the oscillatory mode to the normal mode.

It should be noted that the passive pressure oscillation assembly 44b illustrated in <FIG> topologically comprises a pressure actuated valve <NUM> and a fluid resonator <NUM> (shown in <FIG>) that are mechanically coupled to each other. That is, the valve cylinder <NUM> and valve disk <NUM> form the pressure actuated valve <NUM>, whereas the valve disk <NUM>, enlarged flow cavity <NUM>, and restoring spring <NUM> form the fluid resonator <NUM>, with the pressure actuated valve <NUM> and fluid resonator <NUM> being mechanically coupled to each other via the valve disk <NUM>. In this embodiment, because the valve disk <NUM> forms a portion of both the pressure actuated valve <NUM> and the fluid resonator <NUM>, the negative activation and cessation pressure differentials and the resonance frequency must be designed with due regard to each other, and thus, may not be able to be independently optimized, although the resulting design of the passive pressure oscillation assembly 44b may be mechanically simple.

Referring now to <FIG>, still another embodiment of a passive pressure oscillation assembly 44c will be described. The passive pressure oscillation assembly 44c is similar to the passive pressure oscillation assembly 44a illustrated in Figs. 6A and 6B, with the exception that the passive pressure oscillation assembly 44c comprises an additional oscillation enhancement mechanism that ensures that the passive pressure oscillation assembly 44c remains in the oscillatory mode as long as the clog in the aspiration conduit <NUM> of the aspiration catheter <NUM> remains, or otherwise the anomaly in the aspiration circuit of the system <NUM> is not resolved.

The passive pressure oscillation assembly 44c comprises an inlet channel <NUM> fluidly coupled to the pressurized fluid source <NUM> via the inlet port <NUM>, and an outlet channel <NUM> fluidly coupled to the aspiration flow path <NUM> via the outlet port <NUM>. The passive pressure oscillation assembly 44c further comprises a valve seal in the form of a seat <NUM>, a movable valve element in the form of a valve disk <NUM> operably associated with the valve seat <NUM>, and an enlarged flow cavity <NUM> that fluidly couples the valve seat <NUM> to the aspiration flow path <NUM> via the outlet channel <NUM> and outlet port <NUM>. The valve disk <NUM> is configured for being alternately displaced between a closed position to seal against the valve seat <NUM>, and in this case, within the valve seat <NUM> (see <FIG>), and an open position away from the valve seat <NUM>, and in this case outside of the valve seat <NUM> (see <FIG>). The passive pressure oscillation assembly 44c further comprises a restoring spring <NUM> disposed in the enlarged flow cavity <NUM> and mechanically coupled to the valve disk <NUM> for applying a biasing force to the valve disk <NUM> in a manner that maintains the valve disk <NUM> into the closed position within the valve seat <NUM> until the passive pressure oscillation assembly 44c is triggered to switch from the normal mode to the oscillatory mode.

The passive pressure oscillation assembly 44c further comprises a plunger cavity <NUM>, a plunger head <NUM> slidably disposed within the plunger cavity <NUM>, a reduced profile center cavity <NUM>, a plunger stop <NUM> disposed between the plunger cavity <NUM> and the reduced profile center cavity <NUM>, and another restoring spring <NUM> mechanically coupled to the plunger head <NUM> via a boss <NUM> affixed to the plunger head <NUM> for applying a biasing force to the plunger head <NUM> to maintain the plunger head <NUM> away from the plunger stop <NUM>. In the illustrated embodiment, the profile of the reduced profile center cavity <NUM> is smaller than the profile of the plunger cavity <NUM>, such that the plunger stop <NUM> is formed by the wall of the plunger cavity <NUM> adjacent the reduced profile center cavity <NUM>. The plunger head <NUM> has a fluid pressure equalization channel <NUM> extending through the plunger head <NUM>. The plunger cavity <NUM> is fluidly coupled between the valve seat <NUM> and the plunger cavity <NUM>, such that the valve seat <NUM> is always in fluid communication with the inlet port <NUM> via the fluid pressure equalization channel <NUM> extending through the plunger head <NUM>, and fluid originating from the pressurized fluid source <NUM> can flow into the reduced profile center cavity <NUM>. Thus, the fluid pressure equalization channel <NUM> extending through the plunger head <NUM> serves to equalize the pressure between the pressurized fluid source <NUM> and the reduced profile center cavity <NUM>.

The valve disk <NUM> and valve seat <NUM> have the same geometric profile (in this case, a flattened trapezoidal shape cross-section), such that the valve disk <NUM>, when in the closed position within the valve seat <NUM> (see <FIG>), prevents the flow of fluid originating from the pressurized fluid source <NUM> (in this case, fluid that has been introduced into the reduced profile center cavity <NUM> from the inlet channel <NUM> via the inlet port <NUM>, and through the fluid pressure equalization channel <NUM> of the plunger head <NUM>) into the enlarged flow cavity <NUM>. The enlarged flow cavity <NUM> has a geometric profile that is larger than the geometric profile of the valve disk <NUM>, such that the valve disk <NUM>, when in the open position outside of the valve seat <NUM> and inside the enlarged flow cavity <NUM> (see <FIG>), allows the flow of fluid originating from pressurized fluid source <NUM> (in this case, fluid that has been introduced into plunger cavity <NUM> from the inlet port <NUM> and the inlet channel <NUM> via the fluid pressure equalization channel <NUM>), into the enlarged flow cavity <NUM>, through the outlet channel <NUM>, and into the aspiration flow path <NUM> via the outlet port <NUM>. The plunger head <NUM> and plunger cavity <NUM> have the same geometric profile (in this case, a cylindrical in nature), such fluid from the pressurized fluid source <NUM> can only enter the reduced profile center cavity <NUM> via the fluid pressure equalization channel <NUM> of the plunger head <NUM>.

In response to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the occurrence of an anomaly in the aspiration circuit of the system <NUM>, a no-flow or low-flow condition occurs in the aspiration flow path <NUM>, and as a result, the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a negative activation pressure differential between the inlet port <NUM> (and thus the reduced profile center cavity <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which causes the fluid in the plunger cavity <NUM>, and thus reduced profile center cavity <NUM>, to apply an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the closed position (see <FIG>) to the open position (see <FIG>). The negative activation pressure differential of the passive pressure oscillation assembly 44c will be based on the area of the valve disk <NUM> exposed to the fluid in the inlet channel <NUM> (the negative activation pressure differential will decrease in proportion to the exposed area of the valve disk <NUM>) and the spring constant of the restoring spring <NUM> (the negative action pressure differential will increase in proportion to the spring constant of the restoring spring <NUM>). Thus, the negative activation pressure differential of the passive pressure oscillation assembly 44c may be selected by judicially selecting the exposed area of the valve disk <NUM> and the spring constant of the restoring spring <NUM>.

The passive pressure oscillation assembly 44c is designed in such a manner that, once the valve disk <NUM> is displaced from the closed position to the open position (i.e., the valve "cracks"), the passive pressure oscillation assembly 44c resonates (i.e., the valve disk <NUM> alternately switches (oscillates) between the closed position and the open position. At this point, the passive pressure oscillation assembly 44c has been triggered to switch from the normal mode to the oscillatory mode.

In particular, the biasing force applied by the restoring spring <NUM> to the valve disk <NUM>, the opposing force applied by the fluid in the reduced profile center cavity <NUM> to the valve disk <NUM>, and mass of the valve disk <NUM> are selected, such that the valve disk <NUM> oscillates between the closed position and the open position at a predetermined frequency. Furthermore, dynamic displacement of the plunger head <NUM> within the plunger cavity <NUM> ensures that the valve disk <NUM> does not get stuck in the open position as the fluid flowing from the reduced profile center cavity <NUM> into the enlarged flow cavity <NUM> applies a force to the valve disk <NUM>.

In particular, as the valve disk <NUM> is displaced from the closed position to the open position (see <FIG>), fluid flows from the plunger cavity <NUM> in front of the plunger head <NUM>, through the reduced profile center cavity <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, causing the plunger head <NUM> to be displaced within the plunger cavity <NUM> towards the reduced profile center cavity <NUM> until the plunger head <NUM> abuts the plunger stop <NUM>, and additional fluid to flow from the pressurized fluid source <NUM> into the plunger cavity <NUM> behind the plunger head <NUM> via the inlet port <NUM> and inlet channel <NUM>. Once the plunger head <NUM> abuts the plunger stop <NUM>, the flow of fluid from the reduced profile center cavity <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM> is greatly diminished, limited to the flow of fluid through the fluid pressure equalization channel <NUM> through the plunger head <NUM>. Thus, the opposing force applied to the valve disk <NUM> by the fluid flowing from the reduced profile center cavity <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, drops to a level, such that the biasing force applied by the restoring spring <NUM> overcomes the opposing fluid force applied to the valve disk <NUM> and the momentum of the valve disk <NUM>. As a result, the valve disk <NUM> is displaced from the open position back into the closed position within the valve seat <NUM> (see <FIG>). The fluid pressure between the reduced profile center cavity <NUM> and the plunger cavity <NUM> equalizes via the fluid pressure equalization channel <NUM> through the plunger head <NUM>, thereby dropping the opposing force applied to the plunger head <NUM> by the fluid in the plunger cavity <NUM> to a level, such that the biasing force applied by the restoring spring <NUM> overcomes the opposing fluid force applied to the plunger head <NUM> and the momentum of the plunger head <NUM>. As a result, the plunger head <NUM> is displaced within the plunger cavity <NUM> away from the plunger stop <NUM>, and returns to its neutral position (see <FIG>). In this manner, in contrast to the passive pressure oscillation assembly 44a illustrated in <FIG>, as well as the passive pressure oscillation assembly 44a illustrated in <FIG>, where fluid flows through the valve seat unimpeded, which under certain circumstances, may cause the valve disk to remain open, thereby preventing oscillation of the valve seat between the closed and open positions, the action of the plunger head <NUM> within the plunger cavity <NUM> prevents the valve disk <NUM> from "sticking" in the open position by greatly diminishing the flow of fluid through the valve seat <NUM> that might otherwise prevent the valve disk <NUM> to revert back to its closed position within the valve seat <NUM>.

The frequency at which the valve disk <NUM> oscillates depends on the frequency at which the plunger head <NUM> oscillates within the plunger cavity <NUM>, which in turn, depends on the mass of the plunger head <NUM> (the frequency of the oscillation decreases as the mass of the plunger head <NUM> increases), the spring constant of the restoring spring <NUM> (the frequency of the oscillation increases as the spring constant of the restoring spring <NUM> increases), the diameter of the equalization channel <NUM>, and the dampening effect of the friction between the plunger cavity <NUM> and the plunger head <NUM>, as well as dynamic forces of the fluid within the plunger cavity <NUM>, including the fluid flowing through the channel fluid pressure equalization channel <NUM> of the plunger head <NUM> during equalization of the fluid pressure in the plunger cavity <NUM> (the frequency of the oscillation decreases as the dampening effect increases). Thus, frequency at which the valve disk <NUM> oscillates (i.e., the resonance of the passive pressure oscillation assembly 44c) may be selected by judicially selecting the mass of the plunger head <NUM> and the spring constant of the restoring spring <NUM>, and the diameter of the equalization channel <NUM>, with due regard to the dampening effect that the friction between the plunger cavity <NUM> and the plunger head <NUM>, and the dynamics of the fluid within the reduced profile center cavity <NUM>, have on the plunger head <NUM>. Such dampening effect, itself, may be adjusted by varying the designed size of the inlet port <NUM>, outlet port <NUM>, inlet channel <NUM>, and outlet channel <NUM>.

In response to removal of the clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the resolution of the anomaly in the aspiration circuit of the system <NUM>, the absolute pressure in the aspiration flow path <NUM> increases to a level that creates a negative cessation pressure differential between the inlet port <NUM> (and thus the inlet channel <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which prevents the fluid in the reduced profile center cavity <NUM> from applying an opposing force to the valve disk <NUM> that overcomes the biasing force applied by the spring <NUM> to the valve disk <NUM>. That is, when the valve disk <NUM> is in the closed position, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> will never drop below the negative activation pressure differential due to the free flow condition of the aspiration flow path <NUM>. As a result, the biasing force applied by the restoring spring <NUM> maintains the valve disk <NUM> in the closed position. At this point, the passive pressure oscillation assembly 44c has been triggered to switch from the oscillatory mode to the normal mode.

Although the movable valve elements in the passive pressure oscillation assemblies 44a-44c illustrated in <FIG> have been described as being valve disks, it should be appreciated that the movable valve elements may have any suitable form that can be operatively associated with a corresponding valve seal for alternately allowing and preventing the flow of fluid originating from the pressurized fluid source <NUM> therethrough. For example, with reference to <FIG>, an alternative embodiment of a passive pressure oscillation assembly 44d is similar to the passive pressure oscillation assembly 44a of <FIG>, with the exception that the movable valve element takes the form of a ball.

In particular, the passive pressure oscillation assembly 44d comprises a comprises an inlet channel <NUM> fluidly coupled to the pressurized fluid source <NUM> via the inlet port <NUM>, and an outlet channel <NUM> fluidly coupled to the aspiration flow path <NUM> via the outlet port <NUM>. The passive pressure oscillation assembly 44d further comprises a valve seal in the form of a seat <NUM> fluidly coupled to the inlet port <NUM> via the inlet channel <NUM>, a movable valve element in the form of a valve ball <NUM> operably associated with the valve seat <NUM>, and an enlarged flow cavity <NUM> fluidly coupled between the valve seat <NUM> and the aspiration flow path <NUM> via the outlet channel <NUM> and outlet port <NUM>. The valve ball <NUM> is configured for being alternately displaced between a closed position to seal against the valve seat <NUM> (see <FIG>), and an open position away from the valve seat <NUM>, and in this case outside of the valve seat <NUM> (see <FIG>). The passive pressure oscillation assembly 44d further comprises a spring <NUM> affixed within the enlarged flow cavity <NUM> and mechanically coupled to the valve ball <NUM> for applying a biasing force to the valve ball <NUM> in a manner that maintains the valve ball <NUM> in the closed position against valve seat <NUM> until the passive pressure oscillation assembly 44d is triggered to switch from the normal mode to the oscillatory mode, as will be described in further detail below.

The surface of the valve seat <NUM> that contacts the valve ball <NUM> preferably has a spherical profile, such that the valve ball <NUM>, when in the closed position against the valve seat <NUM> (see <FIG>), seals against the valve seat <NUM> to prevent the flow of fluid originating from the pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>) into the enlarged flow cavity <NUM>. The enlarged flow cavity <NUM> has a geometric profile that is larger than the geometric profile of the valve ball <NUM>, such that the valve ball <NUM>, when in the open position away from the valve seat <NUM> and within the enlarged flow cavity <NUM> (see <FIG>), allows the flow of fluid originating from pressurized fluid source <NUM> (in this case, fluid that has been introduced into the inlet channel <NUM> via the inlet port <NUM>), into the enlarged flow cavity <NUM>, through the outlet channel <NUM>, and into the aspiration flow path <NUM> via the outlet port <NUM>.

In response to a clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the occurrence of an anomaly in the aspiration circuit of the system <NUM>, a no-flow or low-flow condition occurs in the aspiration flow path <NUM>, and as a result, the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a negative activation pressure differential between the inlet port <NUM> (and thus the inlet channel <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which causes the fluid in the inlet channel <NUM> to apply an opposing force to the valve ball <NUM> that overcomes the biasing force applied by the spring <NUM> to the valve ball <NUM>. As a result, the valve ball <NUM> is displaced from the closed position (see <FIG>) to the open position (see <FIG>). The negative activation pressure differential of the passive pressure oscillation assembly 44d will be based on the area of the valve ball <NUM> exposed to the fluid in the inlet channel <NUM> (the negative activation pressure differential will decrease in proportion to the exposed area of the valve ball <NUM>) and the spring constant of the spring <NUM> (the negative action pressure differential will increase in proportion to the spring constant of the spring <NUM>). Thus, the negative activation pressure differential of the passive pressure oscillation assembly 44d may be selected by judicially selecting the exposed area of the valve ball <NUM> and the spring constant of the spring <NUM>.

The passive pressure oscillation assembly 44d is designed in such a manner that, once the valve ball <NUM> is displaced from the closed position to the open position (i.e., the valve "cracks"), the passive pressure oscillation assembly 44d resonates (i.e., the valve ball <NUM> alternately switches (oscillates) between the closed position and the open position. At this point, the passive pressure oscillation assembly 44d has been triggered to switch from the normal mode to the oscillatory mode.

In particular, the biasing force applied by the spring <NUM> to the valve ball <NUM>, the opposing force applied by the fluid in the inlet channel <NUM> to the valve ball <NUM>, and the mass of the valve ball <NUM> are selected, such that the valve ball <NUM> oscillates between the closed position and the open position at a predetermined frequency (e.g., <NUM>-<NUM>).

That is, when the valve ball <NUM> initially reaches the fully open position, the opposing force applied to the valve ball <NUM> by the fluid flowing from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, drops to a level, such that the biasing force applied by the spring <NUM> overcomes the opposing fluid force applied to the valve ball <NUM> and the momentum of the valve ball <NUM>. As a result, the valve ball <NUM> is displaced from the open position back into the closed position within the valve seat <NUM> (see <FIG>). At this point, the momentary flow of fluid from the pressurized fluid source <NUM> into the aspiration flow path <NUM> (via the inlet port <NUM>, inlet channel <NUM>, valve seat <NUM>, enlarged flow cavity <NUM>, outlet channel <NUM>, and outlet port <NUM>), has caused the negative pressure differential between inlet port <NUM> and the outlet port <NUM> to increase. However, because the valve ball <NUM> is now in a closed position, thereby preventing the flow of fluid from the pressurized fluid source <NUM> to the aspiration flow path <NUM>, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> decreases until it reaches the negative activation pressure differential, causing the opposing force applied to the valve ball <NUM> by the fluid in the inlet channel <NUM> to rise to a level that overcomes the biasing force applied by the spring <NUM> to the valve ball <NUM>. As a result, the valve ball <NUM> is displaced from the closed position back to the open position (see <FIG>). The valve ball <NUM> continues to alternately be displaced between the closed position (see <FIG>) and the open position (see <FIG>) in this manner until the clog is removed from the aspiration conduit <NUM> of the aspiration catheter <NUM> or otherwise the anomaly in the aspiration circuit of the system <NUM> is resolved.

The frequency at which the valve ball <NUM> oscillates depends on the mass of the valve ball <NUM> (the frequency of the oscillation decreases as the mass of the valve ball <NUM> increases), and the spring constant of the spring <NUM> (the frequency of the oscillation increases as the spring constant of the spring <NUM> increases), as well as the dampening effect of the dynamic forces of the fluid flowing from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, on the valve ball <NUM> (the frequency of the oscillation decreases as the dampening effect increases). Thus, the frequency at which the valve ball <NUM> oscillates (i.e., the resonance of the passive pressure oscillation assembly 44a) may be selected by judicially selecting the mass of the valve ball <NUM>, spring constant of the spring <NUM>, length of the valve seat <NUM>, and pre-compression length of the spring <NUM>, with due regard to the dampening effect that the fluid flowing from the inlet channel <NUM>, through the valve seat <NUM>, and into the enlarged flow cavity <NUM>, has on the valve ball <NUM>. Such dampening effect, itself, may be adjusted by varying the designed sizes and geometries of the inlet port <NUM>, outlet port <NUM>, inlet channel <NUM>, and outlet channel <NUM>.

In response to removal of the clog in the aspiration conduit <NUM> of the aspiration catheter <NUM>, or otherwise the resolution of the anomaly in the aspiration circuit of the system <NUM>, the absolute pressure in the aspiration flow path <NUM> increases to a level that creates a negative cessation pressure differential between the inlet port <NUM> (and thus the inlet channel <NUM>) and the outlet port <NUM> (and thus the enlarged flow cavity <NUM>), which prevents the fluid in the inlet channel <NUM> from applying an opposing force to the valve ball <NUM> that overcomes the biasing force applied by the spring <NUM> to the valve ball <NUM>. That is, when the valve ball <NUM> is in the closed position, the negative pressure differential between inlet port <NUM> and the outlet port <NUM> will never drop below the negative activation pressure differential due to the free flow condition of the aspiration flow path <NUM>. As a result, the biasing force applied by the spring <NUM> maintains the valve ball <NUM> in the closed position. At this point, the passive pressure oscillation assembly 44d has been triggered to switch from the oscillatory mode back to the normal mode.

It should be noted that the passive pressure oscillation assembly 44d illustrated in <FIG> topologically comprises a pressure actuated valve <NUM> and a fluid resonator <NUM> (shown in <FIG>) that are mechanically coupled to each other. That is, the valve seat <NUM> and movable valve ball <NUM> form the pressure actuated valve <NUM>, whereas the valve ball <NUM>, enlarged flow cavity <NUM>, and spring <NUM> form the fluid resonator <NUM>, with the pressure actuated valve <NUM> and fluid resonator <NUM> being mechanically coupled to each other via the valve ball <NUM>. In this embodiment, because the valve ball <NUM> forms a portion of both the pressure actuated valve <NUM> and the fluid resonator <NUM>, the negative activation and cessation pressure differentials and the resonance frequency must be designed with due regard to each other, and thus, may not be able to be independently optimized, although the resulting design of the passive pressure oscillation assembly 44d may be mechanically simple.

Referring now to <FIG>, one method <NUM> of operating the aspiration system <NUM> to aspirate the occlusion <NUM> from the vasculature <NUM> of a patient will be described. The method <NUM> comprises introducing the aspiration catheter <NUM> into the vasculature <NUM> of the patient until the distal end <NUM> of the catheter body <NUM> is adjacent the occlusion <NUM> (step <NUM>). Next, the aspiration source <NUM> is operated to create an aspiration flow path <NUM> between the aspiration catheter <NUM> and the aspiration source <NUM> to actively ingest the occlusion <NUM>, while operating the passive pressure oscillation assembly <NUM> in the normal mode to prevent fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> (step <NUM>). Thus, aspiration of the occlusion <NUM> is performed as efficiently as possible at this point.

Optionally, the passive pressure oscillation assembly <NUM> is triggered to switch from the normal mode to a first oscillatory mode in response to active ingestion of the occlusion <NUM> (e.g., if the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a first negative activation pressure differential between the pressurized fluid source <NUM> and the aspiration flow path <NUM> less than - 50kPa), such that fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> is pulsed at a suitable amplitude and frequency that enhances active ingestion of the occlusion <NUM> (e.g., high frequency, low amplitude) (step <NUM>). The high frequency, low amplitude pulsing of the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> may minimize disruption to the aspiration flow path <NUM>, such that active ingestion of the occlusion <NUM> may be as efficient as possible.

Next, if a clog occurs in the aspiration conduit <NUM> of the aspiration catheter <NUM> (e.g., if the absolute pressure in the aspiration flow path <NUM> drops to a level that creates a second negative activation pressure differential between the pressurized fluid source <NUM> and the aspiration flow path <NUM> less than -55kPa) (step <NUM>), the passive pressure oscillation assembly <NUM> is triggered to switch from the normal mode (or optionally the first oscillatory mode) to the (second) oscillatory mode, such that fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> is pulsed at a suitable amplitude and frequency that enhances clearing of the clog (e.g., low frequency, high amplitude) (step <NUM>). Optionally, the fluid communication between the pressurized fluid source <NUM> and the aspiration flow path <NUM> may be pulsed simultaneously at different frequencies. If a clog does not occur in the aspiration conduit <NUM> of the aspiration catheter <NUM> (e.g., if the absolute pressure in the aspiration flow path <NUM> does not drop to a level that creates a second negative activation pressure differential between the pressurized fluid source <NUM> and the aspiration flow path <NUM> less than -55kPa) (step <NUM>), the passive pressure oscillation assembly <NUM> remains in the normal mode (or optionally in the first oscillatory mode) until the occlusion <NUM> is fully ingested.

Claim 1:
An aspiration system (<NUM>), comprising:
an aspiration catheter (<NUM>) having a distal end (<NUM>) sized and dimensioned to reach an occlusion (<NUM>) within a remote location of a vasculature (<NUM>) of a patient;
an aspiration source (<NUM>) fluidly coupled to the aspiration catheter (<NUM>) to create an aspiration flow path (<NUM>) between the aspiration catheter (<NUM>) and the aspiration source (<NUM>);
a pressurized fluid source (<NUM>); and
characterised in that the aspiration system further comprises:
a passive pressure oscillation assembly (<NUM>, <NUM>', <NUM>", 44a, 44b, 44c) fluidly coupled between the pressurized fluid source (<NUM>) and the aspiration flow path (<NUM>), the passive pressure oscillation assembly (<NUM>, <NUM>', <NUM>", 44a, 44b, 44c) configured for being operated between a normal mode that prevents fluid communication between the pressurized fluid source (<NUM>) and the aspiration flow path (<NUM>), and an oscillatory mode that pulses fluid communication between the pressurized fluid source (<NUM>) and the aspiration flow path (<NUM>), wherein the passive pressure oscillation assembly (<NUM>, <NUM>', <NUM>", 44a, 44b, 44c) is configured for being triggered to switch from the normal mode or another oscillatory mode to the oscillatory mode in response to a clog in the aspiration catheter (<NUM>).