Abstract:
An emboli detector device receives a blood flow in a perfusion circuit. The connector-like device has a rigid plastic smooth body hermetically sealed from the blood. There is a calculated thin, but rigid window formed as part of the flow-through tubing wall to allow ultrasonic waves to interrogate the flowing blood. A dampening material is included in the ultrasound path to adjust the acoustic levels to an applicable range to monitor emboli. The device incorporates a mechanism to securely hold the transducer during operation and a sensing system for automatically informing a control system of which one of several standard perfusion circuit tubing diameters is being used. The ultrasound echoes detected by the transducer are provided to a controller which detects the emboli and provides a detection signal to warn the surgeon or other operating room personnel of the embolic event.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to co-pending U.S. provisional application Ser. No. 60/659,260, filed Mar. 7, 2005. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not Applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The present invention relates in general to blood monitoring during cardiovascular surgery, and, more specifically, to a device for detecting emboli in the extracorporeal blood during on pump coronary bypass surgery.  
         [0004]     When bypass is used during cardiac surgery, steps must be taken in order to avoid neurological injury. Neurological risks include reduced cognitive abilities and stroke. Emboli (i.e., air bubbles or particulates) entering the blood circuit from the heart, aortic walls or other areas can cause these problems if allowed to enter the brain during surgery. It is desirable to have a method of detecting the emboli in the cardiac perfusion circuit before it reaches the brain so that surgical technique adjustments can be made to reduce or prevent the emboli.  
         [0005]     Transcranial Doppler systems are known for monitoring emboli entering the brain during surgery, but these systems do not detect emboli until after they have reached the brain. A system that detects the emboli earlier in the perfusion circuit would be desirable because preventive measures can then be put in place prior to the emboli reaching the brain. Besides localizing the site where emboli are entering the system (e.g., in the pump and/or at the surgical field), detection prior to entry into the patient may allow rerouting or deactivation of a blood circuit to prevent the detected emboli from reaching the brain.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is a device used to couple an ultrasonic transducer at a fixed prescribed distance from blood flowing through an extracorporeal fluid circuit in order to detect passing emboli without affecting the blood flow. A connector-like device is disclosed wherein the blood can flow through the device in a manner similar to flowing through the circuit tubing. The connector-like device has a rigid plastic smooth body hermetically sealing blood from the environment. There is a calculated thin, but rigid window formed as part of the flow-through tubing wall to allow ultrasonic waves to interrogate the flowing blood. A dampening material is included in the ultrasound path to adjust the acoustic levels to an applicable range to monitor emboli. The connector like device can be preinstalled as a part of a complete extracorporeal tubing circuit or installed into a preexisting circuit using sterile techniques prior to being coupled to a patient. The device incorporates a mechanism to securely hold the transducer during operation and a sensing system for automatically informing a control system of which one of several standard perfusion circuit tubing diameters is being used. The ultrasound echoes detected by the transducer are provided to a controller which detects the emboli and provides a detection signal to warn the surgeon or other operating room personnel of the embolic event. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a schematic diagram showing a perfusion circuit and various potential locations for the extracorporeal emboli detector of the present invention.  
         [0008]      FIG. 2  is an exploded perspective view of the detector.  
         [0009]      FIG. 3  is a perspective view of the assembled device.  
         [0010]      FIG. 4  is a vertical cross-section of the device of  FIG. 3 .  
         [0011]      FIG. 5  is a transverse cross-section through the window and flow passageway.  
         [0012]      FIG. 6  is an exploded view of the transducer element.  
         [0013]      FIG. 7  is a top view of the body member.  
         [0014]      FIG. 8  is a vertical cross-section of the body member.  
         [0015]      FIG. 9  is a vertical cross-section showing a pre-filled body member. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]     Referring to  FIG. 1 , a perfusion system  10  is shown connected to a patient  11 . Circuit tubing  12  circulates blood obtained at a venous catheter  13  and returned to the patient by an arterial cannula  14 . Blood flow is created by a pump  15  using blood from a venous reservoir  16 . A conventional oxygenator  17  provides oxygenated blood to an arterial filter  18 , and a hemoconcentrator recirculates blood and can be used to introduce cardioplegia in a conventional manner.  
         [0017]     An emboli controller/monitor  20  operates in conjunction with the detection apparatus of the present invention to provide monitoring of emboli in the extracorporeal blood circuit. It may be desirable to monitor blood flow for emboli at various locations in the perfusion circuit to maximize the ability to localize sites where emboli are entering the blood flow and to maximize the ability to isolate blood volumes that contain emboli. A first detector  21  is coupled in the circuit tubing between catheter  13  and reservoir  16 . Electrical wiring  22  is connected between detector  21  and controller  20  to conduct signals associated with ultrasonic sensing and with special detection signals for identifying the size of circuit tubing as explained below. A detector  23  located between filter  18  and cannula  14  is connected to controller/monitor  20  by wiring  24 . Additional potential locations for extracorporeal emboli detectors are shown at  25 ,  26 , and  27 .  
         [0018]     The present invention employs ultrasonic interrogation of blood flowing through a tube in order to detect emboli. Due to the sterile nature of the perfusion process, tubing which contacts the blood is typically disposed of after one use. Although a dedicated ultrasonic testing unit for conveying blood to an ultrasonic sensor could be employed, the present invention reduces cost and complexity by providing an inexpensive disposable unit for connecting to the circuit tubing of the perfusion circuit and for receiving a conventional ultrasonic transducer element in a particular manner adapted to be able to sense emboli flowing in the blood. A first embodiment of the invention is shown in  FIG. 2  wherein a disposable body member receives a reusable transducer member  31 . Body member  30  includes a cylindrical flow passage  32  having an inlet  33  and an outlet  34 . Passage  32  has the same internal diameter throughout as the perfusion circuit tubing and is adapted to be connected serially therewith. Body member  30  also includes a barrel piece  35  having an upper transducer mounting section  36  and a lower sound coupling section  37 . Barrel piece  35  has a key slot  40  aligned with a release lever  41 . Transducer member  31  has a keyed feature  42  that is received in key slot  40  as transducer member  31  is seated within upper transducer mounting section  36 . A catch  43  on lever  41  mates with a groove  44  when transducer member  31  is completely seated within barrel piece  30 . A wire cable  45  interconnects a transducer element with the controller and also carries a signal that identifies the size of flow passage  32  as will be described below.  
         [0019]      FIG. 3  shows transducer member  31  fully seated within body member  30 . By pressing on a remote end  46  of lever  41 , catch  43  can be removed from groove  44  so that the transducer member  31  can be disassembled after use.  
         [0020]     As shown in the cross section of  FIG. 4 , transducer member  31  includes an ultrasonic transducer element  50  and an adapter  51  for interfacing a conventional transducer element to the structures of the present invention. A frame  52  is disposed between transducer element  50  and adapter  51  for retaining a magnetic sensor  53 , which may be comprised of a hall sensor. A magnet  54  is fixedly mounted to upper transducer mounting section  36  so that it is in close proximity to sensor  53  when transducer member  31  is properly seated.  
         [0021]     In order to properly couple acoustic waves between transducer element  50  and blood to be interrogated for emboli, an inner chamber within lower sound coupling section  37  contains an acoustic dampening material  55  and an ultrasonic coupling gel  56 . The bottom edge of lower sound coupling section  37  is bounded by an acoustic window  60 . Acoustic dampening material  55  fills a first space at the lower end of section  37  of sufficient thickness and dampening coefficient to eliminate background noise from the received signal picked up by transducer element  50 . Acoustic dampening material  55  may, for example, comprise a commercially available UV “cure-in-place” urethane acrylate A60 durometer gasket material.  
         [0022]     Ultrasonic coupling gel  56  fills a second space between the first space and the transducer mounting section for insuring good acoustic coupling to and from transducer  50 . Flow passage  32  includes a containment wall  61 , which is preferably cylindrical in shape throughout for providing uninterrupted blood flow through the device. Containment wall  61  forms a bottom surface of acoustic window  60  so that the bottom surface is substantially cylindrically shaped. Window  60  has a substantially flat upper surface  62  that contacts dampening material  55 . As shown in  FIG. 5 , acoustic window  60  has a variable thickness with a minimal thickness D min  and a maximum thickness D max . Preferably, the minimum thickness is greater than about 0.025 inches and is preferably in a range from about 0.025 inches to about 0.030 inches. Acoustic window  60  must be sufficiently thin to transmit sufficient acoustic signal therethrough. A minimum thickness in the range specified provides acceptable performance when the body member is formed of a thermoplastic chosen from any biocompatible material currently used in perfusion applications. Preferably, the body member is integrally molded as one piece for simple, disposable use and for ease of manufacturing.  
         [0023]      FIG. 6  is an exploded view of the transducer member showing conventional ultrasonic transducer element  50 , which is received by frame  52  having a ring portion  63  and clip members  64 . Frame  52  receives transducer element  50  such that ring  63  may be captured in a groove  65  on the exterior of transducer element  50 . Magnetic detectors  53  are respectively retained by clips  64  and are coupled via cable  45  to the controller by additional wiring (not shown). Frame  52  is keyed for insertion into adapter  51  in a single orientation so that each magnetic sensor is disposed at a predetermined position relative to keyed feature  42 . Frame  52  may be retained within adapter  51  in the predetermined orientation by press-fitting, gluing, sonic welding, or any other known means of attachment.  
         [0024]      FIG. 7  shows a top view of body member  30  showing the interior of upper transducer mounting section  36 . Three longitudinal slots  66 ,  67 , and  68  are provided, which are coincident with a respective clip  64  of the transducer member when it is inserted according to the matching key. Perfusion circuits typically are made up using one of three standard tubing sizes depending upon the size and/or sex of the patient. Correspondingly, the body member is manufactured according to one of the three standard sizes so that flow passage  32  provides a matching diameter. Depending upon which diameter is present for any particular unit, a small magnet is glued or otherwise attached into one of the respective slots  66 - 68  in order to identify the flow passage diameter. As shown in  FIG. 7 , a magnet  70  is provided in slot  66  for indicating one of the three possible diameters. When the transducer member is attached to any particular body member, the corresponding one of the magnetic sensors determines which of slots  66 - 68  contains a magnet and thereby infers the tubing diameter. This information is transmitted to the emboli controller/monitor in order to adapt the ultrasonic detection algorithm to the diameter of blood flow.  
         [0025]      FIG. 8  shows a cross-section of body member  30  revealing a collar  71  at the lower end of upper transducer mounting section  36  which closely mates with transducer element  50  in order to accurately locate the transducer. Chamber  72  in lower sound coupling section  37  receives acoustic dampening material and then ultrasonic coupling gel which should completely fill the space within chamber  72  without air bubbles in order to provide the best ultrasonic performance. Therefore, it is preferable to overfill chamber  72  with ultrasonic coupling gel and to allow excess amounts to flow through a plurality of relief passages  73  cut into collar  71 . Thus, as transducer element  50  is seated inside collar  71 , the excess coupling gel is removed without the introduction of air bubbles.  
         [0026]     In another preferred embodiment as shown in  FIG. 9 , body member  30  may be pre-filled with acoustic coupling gel during manufacture, prior to distribution to the site of use. In that regard, a lid  75  may be provided within collar  71  so that coupling gel  56  is retained during transit. A pull tab  76  may be provided integral with lid  75  for easy removal of lid  75  at the time of use. In an alternative embodiment, lid  75  may be located at the top of collar  71  with ultrasonic coupling gel filling the space all the way up to lid  75 .  
         [0027]     By virtue of the construction of the emboli detection apparatus of the present invention, an especially convenient method can be employed to install the emboli detection system in a perfusion circuit in preparation for cardiac bypass surgery. The mounting connector (i.e., body member) is serially connected with the perfusion circuit tubing to receive blood flow at the desired location within the perfusion circuit using conventional tubing and methods. The space above the acoustic dampening material within the lower sound coupling section of the barrel piece is filled with ultrasonic coupling gel. Alternatively, if the unit was pre-filled with ultrasonic coupling gel, then the peel-off lid is removed. The ultrasonic transducer element is seated to the upper transducer mounting section in a keyed manner so that the circuit diameter can be automatically detected. As the transducer element is seated, excess ultrasonic coupling gel flows through the relief passages in the barrel piece to avoid air bubbles forming within the space between the ultrasonic transducer and the acoustic dampening material.