Abstract:
A blood conditioning device having a housing with a helical blood acceleration section which includes a helical flow path for impressing centrifugal forces on the entrained bubbles in the blood to concentrate them towards the center of the flow path, a bubble pick off tube aligned with the centerline of the acceleration section which collects and recirculates the bubbles to the cardiotomy reservoir upstream of the device during operation, and a blood filtration section to intercept the flow of particles in the blood.

Description:
This application claims priority to the provisional application 60/246,200 filed Nov. 6, 2000 

   FIELD OF THE INVENTION 
   The present invention relates generally to the extracorporeal circulation of blood during open heart surgery, and more particularly to a device for conditioning blood prior to returning the blood to the patient. 
   BACKGROUND OF THE INVENTION 
   Open heart surgery is performed on a “still” heart. The patient&#39;s blood is circulated by an extracorporeal system, which includes a blood pump, a cardiotomy reservoir and an oxygenator. In operation, blood is drawn from the patient and pumped through the oxygenator and then returned to the patient. In many instances blood is scavenged from the surgical site and this recovered blood is added to the system through the cardiotomy reservoir. As a consequence, surgical debris and air bubbles may be introduced into the system at this point and it is important that the particulate debris and bubbles not be administered to the patient. 
   It is the conventional standard of care to place a so-called “arterial filter” in the blood line to intercept and capture particles and gas bubbles before the blood is returned to the patient&#39;s body. Filters of this type capture both gas bubbles and particles on a filter mesh. However conventional arterial filters are problematic. Typically the volume of an atrial filter is large to maximize the ability of the device to collect and hold gas bubbles. Captured bubbles are retained on the mesh during the entire surgical procedure. Each bubble that is retained reduces the filter mesh surface area available for particulate collection. It is possible that a large particle load will increase the pressure drop across the filter. This “clogging” effect can increase the pressure on the captured bubbles and force them though the filter. As a consequence of this problem the size of the physical membrane of the arterial filter is very large to provide a margin of safety. However this increases the surface area in contact with blood which is undesirable and increases priming volume which is undesirable. It should also be noted that the mesh size of a typical filter is inadequate to capture small bubbles. Consequently the conventional arterial filter is not efficient at handling bubbles and it is improperly sized for the typical particulate load. 
   It must also be noted that blood is a very delicate organ and surface contact, turbulence and pressure drops within the system can injure the blood. These properties of blood must be accommodated as well. 
   SUMMARY 
   In the present invention the blood conditioning device has two main connections. There is a blood input port and a blood output port. A third connection is used to purge or prime the device. In some embodiments of the device this line is always open and is used for continuous recirculation of blood containing bubble to the cardiotomy reservoir. 
   The blood conditioning device relies on a first dynamic stage to remove bubbles from the mixed flow of bubbles and particles in blood. 
   The dynamic stage passes the bubble free but particle laden blood flow to a second mechanical filter media stage where the particles are trapped. The gas bubbles maybe collected and retained in the device or returned with a modest blood flow to the cardiotomy reservoir through the third purge or recirculation connection. 
   The blood conditioning device is disposable and used once. The particulate debris is retained in the device and discarded at the conclusion of the procedure. 
   In the first dynamic stage, the blood is delivered to a blood centrifuge section, which imparts a strong radial acceleration to the blood flow. The pressure gradient is created by forcing the blood along a helical flow path. The radial acceleration causes bubbles both large and small to migrate toward the center streamline of the flow. A bubble pick up may be placed in the zone where the bubbles accumulate. The bubble pick up collects the bubbles and it is connected to the cardiotomy reservoir to extract the bubbles from the device. In an alternate embodiment of the device there is no extraction tube or bubble pick off tube and the bubbles are allowed to coalesces and accumulate in the device during operation. This dynamic stage is referred to as the “helix” in the description. 
   To purge or prime the device a momentary operation valve is placed on top of the device. The preferred versions of this valve opens side holes in the bubble pick up tube in order to release gross air from the device to the cardiotomy reservoir. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Throughout the several figures of the drawing identical reference numerals indicate identical structure, wherein: 
       FIG. 1  is a schematic cross section of a first embodiment of the device; 
       FIG. 2  is a schematic cross section of a second embodiment of the device; 
       FIG. 3  is a schematic cross section of a third embodiment of the device; 
       FIG. 4  is a schematic cross section of a fourth embodiment of the device; 
       FIG. 5  is a schematic cross section of a fifth embodiment of the device; 
       FIG. 6A  is a schematic cross section of a sixth embodiment of the device; 
       FIG. 6B  is a schematic cross section of a sixth embodiment of the device; 
       FIG. 7A  is a schematic cross section of a seventh embodiment of the device; and, 
       FIG. 7B  is a schematic cross section of a seventh embodiment of the device. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a first embodiment of the blood conditioning device  10 . This representative device is shown in a schematic cross section and it is generally symmetric about axis  12 . In use this device is mounted vertically with the purge/recirculation port  14  located at the “top”. Although the device can be used for conditioning blood in any perfusion circuit it is preferred to couple the input port  16  to the source of blood and to connect the output port  18  directly to the cannula used to deliver blood to the patient. The blood pump supplies the modest pressure difference required to operate the device. The oxygenator and cardiotomy reservoir are of conventional design and they are used in the conventional fashion. 
   In the various figures the small squares typified by square  20  represent surgical debris with a density slightly greater than blood. The small circles typified by circle  22  represent bubbles or micro bubbles in the blood flow  24 . The bubbles have a size of approximately 40 microns or more and micro-bubbles have a diameter of 40 microns or less. At the inlet port  16 , the blood flow  24  has a uniform distribution of particles and bubbles in the input stream, and is called a “mixed blood flow” herein. The mixed blood flow  25  enters an acceleration chamber or “helix”  33 ” of the dynamic section  41 . One or more blades  32  form a helical flow path in the acceleration chamber  33 . The blood flow, which leaves the helix  33 , has a spiral motion as indicated by blood flow arrow  26 . The radial acceleration is strong enough to cause the bubbles to accumulate along the centerline or axis  12  of the device  10 . The length of the discharge tube  34  is sufficiently long to permit nearly complete separation of the bubbles from the particles. In this first embodiment of the device these bubbles coalesce and migrate toward zone  46 . 
   Eventually the spiral motion of the blood flow is reduced as indicated by blood flow  27  and the bubble free blood flow  28 , leaves the dynamic section  41  and turns to enter the mechanical separation section  40 . 
   The blood now free of bubbles enters a flow path that intercepts a membrane  42 . The annular membrane  42  filters the blood flow and the particles adheres to the surface of the membrane while the blood passes through the membrane as depicted by blood flow  29 . The blood accumulated behind the membrane  42  is delivered to the output port  18  and the now conditioned blood flow  30  is introduced into the patient. 
   In operation the particles and blood turn into the mechanical separation section  40  while the buoyancy of the bubbles causes them to coalesce into larger bubble and form a bubble rich volume or zone  46  trapped near the stopcock  44 . The purge stopcock  44  may be used to prime the device during setup and may be used to periodically return the bubble rich accumulated volume  46  to the blood cardiotomy reservoir during operation. 
     FIG. 2  is a schematic cross section of a second embodiment of the blood conditioning device  10 . In this second embodiment a bubble pick off tube  48  is positioned to intercept the stream of micro-bubbles from the dynamic section  41 . The opening  47  of the bubble pick off tube  48  is sized to capture the blood flow near the centerline  12  of the dynamic section. The opening  47  establishes a small regulated blood flow  49  from the device to the cardiotomy reservoir (not shown) which carries the bubbles back to the cardiotomy reservoir. This recirculation line  13  is always open. 
     FIG. 3  is an alternate embodiment incorporating a bubble pick off  48  which pulls bubbles from the device through opening  47 . In this device operates similar to  FIG. 2  but in contrast the particles can directly engage the filter mesh  42  as the blood flow flows in an outward direction from the center of the device. 
     FIG. 3  also shows the preferred form of momentary operation valve  50 . The momentary operation valve  50  is provided at the top of the housing to allow the user to purge or prime the device. When “open” the valve  50  allows the gross air from the interior volume of the device to be purged into the cardiotomy reservoir. When closed the interior volume of the device is closed off but the bubble pick off tube remains open to the cardiotomy reservoir. 
   The preferred form of the valve includes a ring  51  which can slide between two positions. In the first position the ring covers side holes  47  in the bubble pick up tube  48  and is in the “closed” position. The valve  50  in  FIG. 7A  is shown in this state. In the second “open” position the ring  51  uncovers the side holes  47  in the bubble pick off tube  48  as seen in the  FIG. 3  among others. In the “open” position the interior volume of the housing  13  is open to the reservoir. 
   This valve may be operated to bleed the system both prior to use and during a surgery. In general the valve  50  is closed and remains open only while operated by the perfusionist. 
     FIG. 4  is an alternate embodiment of the invention which includes a diverging channel  53  to decrease the velocity of the blood flow after the bubbles have been picked off at opening  47 . It is expected to be advantageous to decrease the velocity in the mechanical filtration section  40 . 
     FIG. 5  is an alternate embodiment of the device having a “side by side” configuration the dynamic section  41  located substantially next tot he mechanical filtration section  40 . The principle advantage of this configuration is the ability to see the bubble pick off  48  and related area of the dynamic section during operation and provides more options for flow dynamic optimization in the two sections. 
     FIG. 6A  is side elevation of an alternate embodiment of the device. In this configuration the device is very compact. In this version of the device the particles  20  are captured on the outer surface of the annular filter mesh  42 . while the bubbles pass the helix  33  in advance and are picked up in line  48 . On top of the device the preferred momentary operation valve  50  is schematically shown, opening side hole to the recirculation line to release gross air upon operation. 
     FIG. 6B  is top view of an alternate embodiment of the device. In this view one can see that the helix  33  is located in a circular flow path. In general the input mixed blood flow  24  turns through about 90 degrees before it enters the helix  33 . 
   The dynamic section  41  extends around the circle and the bubble pick off  48  is downstream through another 90 degrees of turning. 
     FIG. 7A  is side elevation of an alternate embodiment of the device. In this embodiment in contrast to  FIG. 6  the blood flow carrying particulates is from the interior of the device to the exterior as typified by the location of particle  20 . In this embossment conical surface or funnel is used to accelerate blood flow as it enters the filter zone. 
     FIG. 7B  is top view of an alternate embodiment of the device. In this version of the device the helix  33  is located part way round the circumference of the device with a bubble pick off  48  located downstream of the helix  33 .