Abstract:
An intravascular catheter having an elongated sheath surrounding an elongated flexible inner structure movable relative thereto is provided with various representative embodiments of flushing apparatus carried by the inner structure. Such flushing apparatus is operative in response to movement of the inner structure relative to the sheath to induce a flow of flushing fluid from a source thereof through the interior of the sheath and then discharge the flushing fluid from the sheath. In one embodiment thereof the flushing apparatus includes an impeller structure disposed on the inner structure. In another embodiment thereof the flushing structure includes an annular seal disposed on the inner structure in sliding and sealing engagement with the interior surface of the sheath.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of the filing dates of provisional U.S. patent application No. 61/733,774 filed Dec. 5, 2012 and provisional U.S. patent application No. 61/737,440 filed Dec. 14, 2012. The entire disclosures of these provisional applications are incorporated herein by this reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present disclosure relate generally to the field of medical devices and, more particularly, to apparatus and methods for flushing catheters used in internal vasculature diagnostic procedures. 
       BACKGROUND 
       [0003]    Various techniques and systems have recently been developed to visualize the anatomy of vascular occlusions by using intravascular ultrasound (IVUS) imaging. IVUS techniques are catheter-based and provide a real-time sectional image of the arterial lumen and the arterial wall. An IVUS catheter includes one or more ultrasound transducers at the distal tip of the catheter by which images containing cross-sectional information of the artery under investigation can be determined. IVUS imaging permits visualization of the configuration of the obstructing material and, in varying degrees, the boundaries of the intimal and medial layers of the arterial wall. 
         [0004]    One common type of IVUS imaging catheter system typically includes an arrangement in which a single transducer at the distal end of the catheter is rotated at high speed (up to about 2000 rpm) to generate a rapid series of 360-degree ultra sound sweeps. Such speeds result in generation of up to about thirty images per second, effectively presenting a real-time image of the diseased artery. 
         [0005]    The transducer is mounted on the end of a drive shaft or cable that is connected to a motor drive at the proximal end of the catheter. The rotating transducer is housed within a sheath that does not interfere with the ultrasound and protects the artery from the rapidly spinning drive shaft. Thus, an IVUS imaging (or “sensing”) catheter may be advanced to the region of an occlusion using conventional angiographic techniques and then may be operated to provide real-time sectional images of the vascular lumen in the arterial wall, including the occluding material and intimal and medial layers of the artery wall. 
         [0006]    Other types of catheter-based systems for use in visualizing the internal anatomy of body portions implementing sheath-enclosed movable sensing/imaging element disposed on elongated drive shaft or cable structures are also known, including photo-acoustic, optical coherence tomography, phased array/multiple transducer, and spectroscopic systems. The performance of each of the above-mentioned catheter-based systems may be adversely affected by the presence of air within the interior of its sheath portion adjacent the movable sensing element(s) therein. Air bubbles may be present in the sheath prior to the operation of the system, or may be generated during system operation by rotation of the flexible drive shaft or cable disposed proximally of the sensing/imaging element(s). The presence of these air bubbles tends to undesirably corrupt the image or data which the system is designed to generate. 
         [0007]    To rid the particular system of air within the sheath portion of the overall catheter structure, a flushing operation is typically performed. As conventionally implemented, such internal air-removal operation is carried out by forcing a flushing liquid, such as a saline solution, distally through the entire length of the sheath for discharge out its open distal end. This previously utilized flushing technique carries with it various known problems, limitations and disadvantages. 
         [0008]    For example, because of the significant length and very small internal diameter of the sheath (typically in the range of from about 0.3 cm to about 20 cm in useable length and in the range of from about 0.05 cm to about 0.1 cm in internal diameter), forcing flushing liquid from the proximal end of the sheath distally through its entire length requires significant pressure. It also requires additional parts in the form of an attached one-way check valve and a detachable syringe and hose apparatus, thereby undesirably adding to the cost of the overall system. The check valve also creates an obstruction near the hand piece portion of the system when the sensing/imaging structure is manipulated manually. Furthermore, there is currently no preventive measure for distally blocking air bubbles, released from the inside of the drive cable during system operation, from reaching the sensing/imaging structure and adversely affecting its performance. 
         [0009]    As can be readily be seen from the foregoing, a need exists for improved apparatus and associated methods for flushing medical catheters of the types generally described above. It is to this need that the present invention is primarily directed. 
       SUMMARY 
       [0010]    In carrying out principles of the present invention in accordance with a first representatively disclosed embodiment thereof, a medical sensing catheter apparatus is provided which is illustratively an IVUS catheter, but could alternatively be another type of medical sensing catheter such as a photo-acoustic, optical coherence tomography, phased array/multiple transducer, or spectroscopic type of catheter. 
         [0011]    The catheter structure provides for improved flushing thereof, and illustratively includes an elongated flexible sheath having a proximal end, and an open distal end insertable into a body area of a patient, and an elongated flexible inner structure longitudinally extending through the interior of the sheath and being movable relative thereto. The inner structure has a distal end portion with a sensing element disposed thereon and operative to generate signals useable to create diagnostic information with respect to the patient body area, representatively an artery. Illustratively, the sensing element is an ultrasound transducer. 
         [0012]    Disposed between the inner structure and the sheath is a substantially barrier free space or passage that circumscribes the inner structure and extends along substantially the entire length of the inner structure received in the sheath. According to a key feature of the invention, an impeller structure is carried by the inner structure and is operative, in response to rotation of the inner structure relative to the sheath, to flow a flushing liquid from a source thereof proximally through the sheath toward the support structure, along the exterior of the support structure, and then through the substantially barrier free space, in a manner preventing air from being interposed between the support structure and a facing interior side surface portion of the sheath. In representatively disclosed embodiments thereof the impeller structure may be external impeller vanes or a spiraling surface groove externally formed on the distal end portion of the inner structure. 
         [0013]    When the catheter is representatively disposed in an artery, blood from within the artery is used as the flushing liquid, and may subsequently be returned to the artery from the substantially barrier free space via an optional blood outlet port formed in the sheath. Alternatively, prior to use of the catheter within the body, the interior of the sheath may be flushed in the same manner using a non-blood flushing liquid such as a saline solution. 
         [0014]    According to another disclosed aspect of the invention, a method is provided for flushing air from within a medical sensing catheter generally having a construction as described above, the method comprising the steps of (1) configuring the distal end portion of the inner structure to draw a flushing liquid from a source thereof inwardly through the open distal end of the sheath in response to rotation of the distal end portion of the inner structure relative to the sheath; and (2) causing flushing liquid from a source thereof to sequentially flow proximally through the sheath toward the distal end portion of the inner structure, along the exterior of the distal end portion of the inner structure, and then proximally through the substantially barrier free space, in a manner preventing air from being interposed between the distal end portion of said inner structure and a facing interior side surface portion of the sheath, by rotating the inner structure relative to said sheath. In the catheter flushing technique provided by this exemplary method, either blood or a non-blood flushing liquid may be utilized. 
         [0015]    Using the representatively disclosed catheter construction and associated catheter use as provided by the present invention, the proximally driven flow of flushing liquid through the catheter sheath continuously prevents internal sheath air adjacent the support structure from being undesirably interposed between the transducer and a facing interior side surface portion of the sheath, and also forms a moving liquid barrier that prevents air generated by the rotating inner structure from traveling distally to the transducer carrying support structure. 
         [0016]    In a second representatively disclosed embodiment of the present invention, a medical sensing catheter apparatus is provided which is illustratively an IVUS catheter, but could alternatively be another type of medical sensing catheter such as a photo-acoustic, optical coherence tomography, phased array/multiple transducer, or spectroscopic type of catheter. The catheter structure provides for improved flushing thereof and illustratively includes an elongated flexible sheath having a proximal end, and an open distal end insertable into a body area of a patient, and an elongated flexible inner structure longitudinally extending through the interior of the sheath and being movable relative thereto, the inner structure having a distal end portion with a sensing element disposed thereon and operative to generate signals useable to create diagnostic information with respect to the patient body area. According to a key feature of the catheter apparatus, an annular seal structure is coaxially and externally carried by the inner structure proximally of the sensing element, the seal structure slidingly and sealingly engaging the interior surface of the sheath and being movable with the inner structure relative to the sheath. 
         [0017]    According to a structural aspect of the catheter apparatus, the annular seal structure permits a distal end portion of the sheath to be flushed in a manner expelling undesirable air therefrom by proximally moving the inner structure relative to the sheath to draw flushing liquid proximally into the sheath through its distal end, and then moving the inner structure distally relative to the sheath to discharge the received fluid, and air therein, outwardly through the distal sheath end to thereby obviate the previous necessity of performing the necessary flushing operation by forcing flushing fluid distally through the entire length of the sheath. 
         [0018]    In an alternate configuration of the second embodiment of the present invention, an impeller structure is provided on the portion of the inner structure that carries the sensing element and is operative to draw flushing liquid proximally through a distal end portion of the sheath, towards the seal structure, in response to rotation of the inner structure relative to the sheath, to flush a distal tip portion of the sheath without translating the inner structure relative to the sheath. 
         [0019]    In accordance with another disclosed aspect of the present invention, an air flushing method is provided for use with a medical sensing catheter having an elongated flexible sheath with a proximal end and an open distal end insertable into a body area of a patient, and an elongated flexible inner structure longitudinally extending through the interior of the sheath and being movable relative thereto, the inner structure having a distal end portion with a sensing element disposed thereon and operative, during movement of said inner structure relative to said sheath, to generate signals useable to create diagnostic information with respect to the patient body area. 
         [0020]    From a broad perspective, the method comprises the steps of flowing a quantity of flushing fluid inwardly through the open distal end of said sheath toward the sensing element, and then discharging at least a portion of the quantity of flushing fluid, and air previously disposed within the interior of the sheath, outwardly through a distal end portion of the sheath. According to disclosed features of the method, the flowing and discharging steps may respectively include the step of proximally and distally translating the inner structure through the sheath, or may each be performed by rotating the inner structure relative to the sheath. 
         [0021]    Catheter apparatus and associated flushing methods representatively disclosed herein provide substantial improvements in the overall catheter flushing operation. For example, when blood is utilized as a flushing liquid the necessity for the use of a secondary acoustic media is eliminated, thereby desirably lessening the total material cost for the diagnostic procedure, and also reduces the quantity of particulates that may potentially be introduced into the body using a distally directed flushing procedure. Catheter structure and associated methods representatively disclosed herein further improve work flow and ease of catheter use for the operator, reduce the time needed for the flushing procedure, and improve diagnostic image quality via the elimination of air-related image artifacts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a highly schematic partially cross-sectioned view of representative medical sensing catheter apparatus embodying principles of the present invention; 
           [0023]      FIG. 2  is a side elevational view of an alternate embodiment of a transducer support portion of the  FIG. 1  catheter apparatus; 
           [0024]      FIG. 3  is a partially cutaway schematic elevational view of a second embodiment of the  FIG. 1  medical sensing catheter apparatus; 
           [0025]      FIG. 4  is a cross-sectional enlargement of the dashed circle area “4” in  FIG. 3 ; 
           [0026]      FIGS. 5A-5D  sequentially depict, in schematic form, a representative catheter flushing method embodying principles of the present invention; 
           [0027]      FIG. 6  is an enlarged scale schematic cross-sectional view of a distal end portion of an alternate configuration of the catheter apparatus of  FIG. 5D  being flushed by an associated alternate flushing method embodying principles of the present invention; and 
           [0028]      FIG. 7  illustrates an alternate configuration of the distal end portion of the inner catheter structure shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Schematically depicted in  FIG. 1  is medical sensing catheter apparatus which is representatively in the form of an intravascular catheter  10  that may be operatively inserted in an artery  12  of a patient to perform diagnostic artery imaging procedures. By way of non-limiting example, the catheter  10  is an IVUS (Intravascular Ultrasound) catheter of the single rotatable transducer type, but could alternatively be one of a variety of other types of catheter-based systems for use in visualizing the internal anatomy of body portions implementing sheath-enclosed movable sensing/imaging elements disposed on elongated drive shaft or cable structures, including but not limited to photo-acoustic, optical coherence tomography, and spectroscopic systems, without departing from principles of the present invention. 
         [0030]    Catheter  10  includes an elongated flexible tubular outer sheath  14  having an open distal end  16  and a proximal end  17 . The useable length of the sheath  14  (i.e., the length thereof operatively insertable into a patient) is greatly larger than its internal diameter. Illustratively, the useable sheath length is in the range of from about 0.3 cm to about 20 cm, and the internal sheath diameter is in the range of from about 0.05 cm to about 0.1 cm. Movably disposed within the interior of the sheath  14  is an elongated flexible inner structure  18  comprising an elongated flexible drive shaft or cable  20  with a support structure  22  (typically referred to as a “can”) secured to its distal end and carrying a sensing/imaging element illustratively in the form of a single ultrasound transducer  24 . 
         [0031]    The proximal end  17  of the sheath, and the proximal end of the drive shaft or cable  20  therein, are operatively connected to a suitable PIM (patient interface module), of conventional construction, which provides electrical power to the transducer  24  and receives imaging signals therefrom. The PIM may also be operative to selectively drive the inner structure  18  translationally and rotationally relative to the sheath  14  as respectively illustrated by the arrows  26 , 28  in  FIG. 1 . Alternatively, a separate drive structure may similarly drive the inner structure  18  relative to the sheath  14 , or such translational and rotational movement of the inner structure  18  relative to the sheath  14  may be manually achieved if desired. 
         [0032]    As can be seen in  FIG. 1 , disposed between the outer sheath  14  and the inner structure  18  is a substantially barrier-free space or passage  30  that circumscribes the inner structure  18  and extends along substantially the entire length of the inner structure  18  received in the sheath  14 . According to a feature of the present invention, an impeller structure is externally disposed on the support structure  22  and is illustratively in the form of a plurality of impeller vanes  32  disposed on the support structure portion  22  of the flexible inner structure  18  proximally of the transducer  24 . Alternatively, as shown in  FIG. 2 , the impeller structure could comprise a suitably spiraled groove  34  formed in the outer side surface of the support structure  22  proximally of the transducer  24 . 
         [0033]    With the catheter  10  received in the artery  12  as shown in  FIG. 1 , the interior of the sheath  14  may be easily flushed, to expel undesirable air therein, by simply rotating the inner structure  18  relative to the sheath  14  as indicated by the arrow  28 . Such rotation, by virtue of the impeller structure  32  (or the  FIG. 2  impeller structure  34  as the case may be) causes blood  36  from within the artery  12  to be flowed inwardly through the open distal end  16  of the sheath  14 , exteriorly along the support structure  22 , and then proximally through the substantially barrier-free annular passage  30 . The proximally flowing blood  36  is thus utilized as a flushing liquid to rid the interior of the sheath  14  of undesirable air and may be transferred back into the artery  12  via an optional side wall blood exit port  38  formed in the sheath  14 . 
         [0034]    This proximally driven flow of flushing liquid through the sheath  14  continuously prevents internal sheath air adjacent the support structure  22  from being undesirably interposed between the transducer  24  and a facing interior side surface portion of the sheath  14 , and also forms a moving liquid barrier that prevents air generated by the rapidly spinning drive shaft or cable  20  from traveling distally to the support structure  22 . 
         [0035]    Schematically depicted in  FIGS. 3 and 4  is an alternate embodiment  10   a  of the previously described medical sensing catheter apparatus  10 . Catheter  10   a  may be operatively inserted in artery  12  of a patient to perform diagnostic artery imaging procedures. By way of non-limiting example, the catheter  10   a  is an IVUS (Intravascular Ultra Sound) catheter of the single rotatable transducer type, but could alternatively be one of a variety of other types of catheter-based systems for use in visualizing the internal anatomy of body portions implementing sheath-enclosed movable sensing/imaging elements disposed on elongated drive shaft structures, including photo-acoustic, optical coherence tomography, phased array/multiple transducer, and spectroscopic systems, without departing from principles of the present invention. 
         [0036]    Catheter  10   a  includes an elongated flexible tubular outer sheath  14   a  having an open distal end  16   a  and a proximal end  17   a.  The useable length of the sheath  14   a  (i.e., the length thereof operatively insertable into a patient) is greatly larger than its internal diameter. Illustratively, the useable sheath length is in the range of from about 0.3 cm to about 20 cm, and the internal sheath diameter is in the range of from about 0.05 cm to about 0.1 cm. Movably disposed within the interior of the sheath  14   a  is an elongated flexible inner structure  18   a  comprising an elongated flexible drive shaft or cable  20   a  with a housing structure  22   a  secured to its distal end and carrying a sensing element illustratively in the form of a single ultrasound transducer  24   a.    
         [0037]    The proximal end  17   a  of the sheath  14   a,  and the proximal end of the drive cable  20   a  therein, are operatively connected to a suitable PIM (patient interface module), of conventional construction, which provides electrical power to the transducer  24   a  and receives imaging signals therefrom. The PIM may also be operative to selectively drive the inner structure  18   a  translationally and rotationally relative to the sheath  14   a  as respectively illustrated by the arrows  26   a , 28   a  in  FIG. 3 . Alternatively, a separate drive structure may similarly drive the inner structure  18   a  relative to the sheath  14   a,  or such translational and rotational movement of the inner structure  18   a  relative to the sheath  14   a  may be manually achieved if desired. 
         [0038]    Referring now to  FIG. 4 , according to a key aspect of the present invention, the catheter  10   a  also comprises an annular seal structure  40  which coaxially circumscribes and is anchored to the housing portion  22   a  of the inner structure  18   a  proximally adjacent the transducer  24   a.  The seal structure  40  slidably and sealingly engages the interior surface of the sheath  14   a  and is translationally and rotationally movable with the inner structure  18   a  relative to the sheath  14   a . By way of non-limiting example, the seal structure  40  may be of various types including one or more metal rings (illustratively welded stainless steel rings), a tape material such as a PTFE tape material, or at least one annular resilient seal member overmolded onto the inner structure  18 . 
         [0039]    The unique provision of the seal structure  40  permits the sheath portion  14   a  of the catheter  10   a  to be flushed, to remove air from its interior, without the previous problems, limitations and disadvantages associated with forcing a flushing liquid distally through the entire length of the interior of the sheath  14   a.  An example of how such improved flushing may be achieved via the present invention is sequentially depicted in schematic form in  FIGS. 5A-5D . 
         [0040]    First, as shown in  FIG. 5A , with the housing structure  22   a  adjacent the downwardly facing open distal end  16   a  of the sheath  14   a,  the distal sheath end  16   a  is dipped into a quantity of flushing liquid, representatively a saline solution  42 , within a suitable container  44 . The inner structure  18   a  is then raised within the sheath  14   a  (as indicated by the arrow  46  in  FIG. 5A ) to its  FIG. 5B  position. This raising of the seal structure  40  creates a vacuum in the interior portion of the sheath  14   a  below it, thereby drawing a quantity  42   a  of the saline solution  42  upwardly into the interior portion of the sheath  14   a  below the seal structure  40 . 
         [0041]    Next, as shown in  FIG. 5C , the distal sheath end  16   a  is inverted to face upwardly, and the sheath  14  is tapped (as indicated by the arrow  48  in  FIG. 5C ) to cause air  50  within the sheath  14   a  distally of the seal structure  40  to rise to the distal sheath end  16   a.  Finally (as indicated by the arrow  52  in  FIG. 5D ), the inner structure  18   a  is forced upwardly toward the distal sheath end  16   a  to thereby discharge saline solution  42   a  (with the air  50  entrained therein) outwardly through the open distal sheath end  16   a,  thereby completing the catheter sheath flushing operation. 
         [0042]    It should be noted that using this improved flushing technique requires that only a distal tip end portion of the overall sheath  14   a  need be flushed to ready the catheter  10   a  for patient use, and that the overall flushing operation is greatly simplified and quickened. Further, the equipment cost to achieve the necessary flushing is desirably reduced. The efficiency of the flushing operation is also enhanced due to the fact that the seal structure  40  forms a barrier against air bubbles, generated by the rapid operational rotation of the flexible drive cable  20   a , distally reaching and interfering with the imaging performance of the transducer  24   a.    
         [0043]      FIG. 6  schematically depicts an alternate flushing method carried out using, in an alternate catheter embodiment  10   b,  modified sheath and housing structures  14   b , 22   b  embodying principles of the present invention. The sheath  14   b  shown in  FIG. 6  is modified by forming a side wall vent opening  54  therein adjacent its open distal end  16   b.  The housing  22   b  shown in  FIG. 6  is modified by forming externally thereon an impeller structure, representatively a plurality of impeller vanes  56 , disposed between the transducer  24   b  and the seal structure  40   b.    
         [0044]    With the distal end  16   b  of the sheath  14   b  dipped into the saline solution  42 , the housing structure  22   b  adjacent the distal end  16   b,  and the seal structure  40  disposed proximally of the vent opening  54 , the inner structure  18   b  is rotationally driven, as indicated by the arrow  58 , without translating the inner structure  18   b  relative to the sheath  14   b.  The rotating impeller structure  56  upwardly draws a portion  42   b  of the saline solution  42  into the interior of the sheath  24   b  and discharges it (with air from below the seal structure  40 ) outwardly through the vent opening  54  to complete the flushing operation. 
         [0045]      FIG. 7  schematically depicts an alternate embodiment  22   c  of the housing structure  22   b  shown in  FIG. 6 . The  FIG. 7  housing structure  22   c  is identical to the  FIG. 6  housing structure  22   b  with the exception that the impeller structure externally formed on the  FIG. 6  housing structure  22   c  (which performs the same function as the vanes  56  in  FIG. 6 ) is defined by a spiraling exterior side wall groove  60  formed in the outer surface of the housing structure  22   c  and disposed between the transducer  24   c  and the annular seal structure  40   c.    
         [0046]    As can be seen, the present invention in the illustrative embodiments thereof described above provides substantial improvements in the overall catheter flushing operation. For example, when blood is utilized as a flushing liquid the necessity for the use of a secondary acoustic media is eliminated, thereby desirably lessening the total material cost for the diagnostic procedure, and also reduces the quantity of particulates that may potentially be introduced into the body using a distally directed flushing procedure. The above-described flushing structure and method further improve work flow and ease of use for the operator, reduce the time needed for the flushing procedure, and improve diagnostic image quality via the elimination of air-related image artifacts. 
         [0047]    The foregoing detailed description is to be clearly understood as being given by of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.