Patent Publication Number: US-9849222-B2

Title: Multi-unit blood processor with volume prediction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. Utility patent application Ser. No. 13/102,728, filed May 6, 2011, entitled “MULTI-UNIT BLOOD PROCESSOR WITH VOLUME PREDICTION which claims priority benefit of U.S. Provisional Patent Application Serial No. 61/352,106 filed Jun. 7, 2010, entitled “MULTI-UNIT BLOOD PROCESSOR WITH VOLUME PREDICTION,” both applications are hereby incorporated by reference in their entirety as if set forth herein in full. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and method for separating at least two discrete volumes of blood into at least two components each. 
     BACKGROUND 
     U.S. application Ser. No. 11/954,388 filed Dec. 12, 2007 describes an apparatus for separating discrete volumes of a composite liquid such as blood into at least two components. 
     The apparatus and method of this application relate to the separation of biological fluids comprising an aqueous component and one or more cellular components. Examples given include: extracting a plasma component and a cellular component (including platelets, white blood cells, and red blood cells) from a volume of whole blood. A component, such as washed red blood cells, may also be filtered so as to remove residual prions, white blood cells or platelets from the red blood cells. 
     An apparatus for processing blood components that can process at once at least two discrete volumes of a composite liquid, in particular, two unequal volumes wherein the proportions of the various components of the composite liquid that may vary from one discrete volume to another one, is known from U.S. application Ser. No. 11/954,388. A method is described therein for separating at least two discrete volumes of a composite liquid into at least a first component and a second component. The method comprises at least two separation bags containing two discrete volumes of a composite liquid in separation cells mounted on a rotor; storing in at least one container on the rotor at least two first component bags connected to the at least two separation bags respectively; separating at least a first and a second components in each of the separation bags; transferring at least one fraction of a first separated component into a component bag; detecting a characteristic of a component at a location in each separation bag; and stopping transferring the fraction of the first component upon detection of the characteristic of a component at the first determined location. 
     SUMMARY OF THE INVENTION 
     The present invention comprises improvements on a centrifugal blood separation device capable of processing a plurality of blood units at the same time. 
     The invention includes a method of predicting the volume of a component separated from a composite fluid comprising loading a composite fluid into a separation cavity on a centrifuge, sensing the fluid pressure in the separation cavity after the loading step, predicting the volume of the composite fluid from the sensing the fluid pressure step, separating the composite fluid into at least a first and second component, expressing the first separated component from the separation cavity to a collection cavity, sensing the movement of the first separated component, determining the volume of the expressed separated component from the sensing the movement step and predicting the volume of the second component remaining in the separation cavity from the determined volume of the composite fluid and the predicted volume of the expressed first component. 
     The method further may comprise sensing, optically with a photocell, the leading edge of the expressed first component by detecting the presence of fluid in the tubing between the separation cavity and the collection cavity and sensing, optically with a photocell located near the exit of the separation cavity, the trailing edge of the expressed first component by detecting the presence of components not in the first expressed component. 
     The invention further may include separating the composite fluid into at least a first, second and third component; expressing the third separated component from the separation cavity to a collection cavity after the step of expressing the first separated component, sensing the movement of the third separated component, determining the volume of the expressed third separated component from the sensing the movement step, predicting the volume of the second component remaining in the separation cavity from the predicted volume of the composite fluid, the determined volume of the expressed first component and the predicted volume of the expressed third component. The composite fluid can also be whole blood, the first component plasma, the third component platelets and the second component red blood cells. The method may further include centrifugally separating the composite fluid. The expressing step can comprise squeezing the separation bag to transfer the first and the third components to respective collection bags. 
     The method may further comprise sensing the movement of the plasma which may comprise sensing the leading edge of the plasma by detecting the presence of the plasma, and sensing the trailing edge of the plasma by detecting the presence of platelets. Sensing the movement of the platelets may comprise sensing the leading edge of the platelets by detecting the presence of the platelets and sensing the trailing edge of the platelets by detecting the presence of red blood cells. Sensing the movement of the plasma may comprise sensing the leading edge of the plasma by detecting the presence of the plasma and sensing the trailing edge of the plasma by detecting the presence of a cellular component. 
     The invention also may include apparatus for predicting the volume of a separated component, the apparatus comprising a rotor having at least one separation cavity and at least one collection cavity for centrifugally separating the composite fluid, which may be whole blood, into a first separated component, which may be plasma, a second separated component, which may be red blood cells, and an optional third separated component, which may be a platelet component; a separation bag containing a composite fluid in the separation cavity; at least one collection bag in the collection cavity; tubing connecting the separation bag to the at least one collection bag; a pressure sensor for detecting a pressure amount due to the composite fluid in the separation bag; a first sensor for detecting components in the tubing; a second sensor for detecting changes in separated components in the separation bag; and a controller for predicting the volume of the composite fluid from the amount of pressure sensed by the pressure sensor, determining the volume of any separated component passing from the separation bag through the tubing to the collection bag from detection by the first and second sensors, and predicting the volume of any separated component remaining in the separation bag from the volume prediction of the composite fluid and the volume determination of the separated component passing from the separation bag to the collection bag. 
     The apparatus of the invention additionally may use a squeezing system for squeezing the separation bag to transfer separated components to the collection bag. This squeezing system squeezes the separation bag to transfer separated components to the collection bag, wherein the plasma component is transferred from the separation bag to a plasma collection bag and the platelet component is transferred from the separation bag to a platelet collection bag. 
     The apparatus also may comprise a pressure sensor, located on the wall of the separation cavity, that detects a pressure amount due to the fluid level of the composite fluid in the separation bag. In addition a first optical sensor may detect the leading edge of the first separated component and is located to detect fluid in a tube. A second optical sensor, located on a wall of the separation cavity, may detect the trailing edge of a separated component by detecting another component. 
     Other features and advantages of the invention will appear from the following description and accompanying drawings, which are to be considered exemplary only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a first set of bags designed for cooperating with a separation apparatus. 
         FIG. 2  is a schematic view, partly in cross-section along a diametric plane, of the separation apparatus. 
         FIG. 3  is a top plan view of the separation apparatus of  FIG. 2 , showing at least part of a set of bags mounted thereon, along with the separation apparatus valves and sensors. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     For the sake of clarity, the invention will be described with respect to a specific use, namely the separation of whole blood into at least two components, in particular into a plasma component and a red blood cell component, or into a plasma component, a platelet component and a red blood cell component. The discrete volume mentioned hereunder will typically be the volume of a blood donation. The volume of a blood donation may vary from one donor to another one (for example, 500 ml plus or minus 10% in the United States). Also, the proportion of the components of blood usually varies from one donor to another one. It should be understood however that this specific use is exemplary only. 
     It is understood that white blood cells could further be separated and collected with suitable volume predictions in accordance with this invention. Thus the invention may further be used to collect plasma, platelets, white blood cells and red blood cells for a four component collection. 
       FIG. 1  shows an example of a set  10  of bags adapted to be used for the separation of a composite liquid (e.g. whole blood) into at least one component (e.g. plasma, platelets, or both) and a second component (e.g. red blood cells). This bag set comprises a flexible primary separation bag  12  and flexible component or satellite bags  14 ,  16 ,  38  and  44  connected thereto. 
     The bag  10  is shown with an asymmetrical manifold  34  forming an E shape as more fully described below. The manifold  34  is representative in shape in that it is understood that other configurations with varying number of arms or connectors could be used depending on specific use of the apparatus, (namely the separation of whole blood into at least two components, in particular into a plasma component and a red blood cell component, or into a plasma component, a platelet component and a red blood cell component or with a washing feature or white blood cell collection. 
     When the composite liquid is whole blood, the separation bag  12  has two purposes, and is successively used as a collection bag and as a separation bag. It is intended to initially receive a discrete volume of whole blood from a donor (usually about 500 ml but can vary as described above) and to be used later as a separation chamber in a separation apparatus. The separation bag  12  is flat and generally rectangular. It is made of two sheets of plastic material that are welded together so as to define there between an interior space having a main rectangular portion connected to a triangular proximal portion. A first tube  18  is connected to a proximal end of the triangular portion, and a second tube  20  and a third tube  22  are connected on opposite sides adjacent the first tube  18 . The proximal ends of the three tubes  18 ,  20 ,  22  are embedded between the two sheets of plastic material so as to be parallel. The separation bag  12  further, optionally, comprises a hole  24  in each of its two proximal corners that are adjacent to the three tubes  18 ,  20 ,  22 . The holes  24  may be used to optionally secure the separation bag to a separation cell on a centrifugal blood separation apparatus. 
     The separation bag  12  initially contains a volume of anti-coagulant solution (typically about 63 ml of a solution of citrate phosphate dextrose for a blood donation of about 450 ml). The first and third tubes  18 ,  22  are fitted at their proximal ends with a breakable stopper  26 ,  28  respectively, blocking liquid flow therethrough. The breakable stopper is sometimes called a “frangible”. The second tube  20  is a collection tube having a needle  30  connected to its distal end. At the beginning of a blood donation, the needle  30  is inserted in the vein of a donor and blood flows into the separation bag  12 . After a desired volume of blood has been collected in the separation bag  12 , the collection tube  20  is sealed and cut, disconnecting the needle from the bag set  10 . Alternatively, previously collected blood may be transferred to the separation bag  12  through the collection tube  20 , with or without the use of the needle  30 . 
     The first component bag  14  is intended for receiving a plasma component. The bag  14  is flat and substantially rectangular. It is connected through a plasma collection tube  32  and an asymmetric manifold  34  to the first tube  18 . The second component bag  16  is intended for receiving a platelet component. The second component bag  16  is also flat and substantially rectangular. It is connected through a platelet collection tube  36  and the asymmetric manifold  34  to the first tube  18 . A third component bag  38  is intended to receive a red blood cell component (which may be washed), from the primary bag  12 . Red blood cells may be drained through tube  22 , which may include a filter  40 , into third component bag  38 . A breakable stopper  42  or frangible in tube  22  as well as frangible  28  prevents premature flow of red blood cells into the third component bag  38 . 
     An optional wash solution bag  44 , if used, may initially contain wash solution such as saline or the bag  44  may contain storage solution such as SAGM if no washing is desired. Wash solution may be transferred through a wash solution tube  46  and the asymmetrical manifold  34  by way of the first tube  18  into the primary bag  12  when the primary bag  12  contains high hematocrit blood cells. “High hematocrit” means a percentage of red blood cell volume to total fluid volume of at least 80 percent, more preferably 90 percent, and yet more preferably 95 percent. After wash solution is mixed with high hematocrit red blood cells and subsequently separated, used wash solution may be extracted through the first tube  18 , asymmetrical manifold  34 , and discard tube  46  into a wash solution discard bag  44 . The discard bag  44  could also be used to collect a blood component, such as for example, mesenchymal stem cells or white blood cells. 
       FIG. 2  shows a first embodiment of an apparatus  60  for simultaneously separating by centrifugation four discrete volumes of a composite liquid. The apparatus comprises a centrifuge  62  adapted to receive four of the sets  10  of bags shown in  FIG. 1 , with the four discrete volumes of a composite liquid contained in the four primary separation bags  12 ; a component transferring means for transferring at least one separated component from each separation bag into a component bag connected thereto. The apparatus  60  may further comprise means for washing a residual high hematocrit red blood cell component. 
     The centrifuge  62  comprises a rotor  64  that is supported by a bearing assembly  67  allowing the rotor  64  to rotate around a rotation axis  68 . The rotor comprises a cylindrical rotor shaft  70  to which a pulley  72  is connected; a storage means comprising a central cylindrical container  74  for containing component bags, which is connected to the rotor shaft  70  at the upper end thereof so that the longitudinal axis of the rotor shaft  70  and the longitudinal axis of the container  74  coincide with the rotation axis  68 . Four identical separation cells  78  are coupled to the central container  74  so as to form a symmetrical arrangement with respect to the rotation axis  68 . The centrifuge further comprises a motor  80  coupled to the rotor by a belt  82  engaged in a groove of the pulley  72  so as to rotate the rotor about the rotation axis  68 . 
     Each separation cell  78  comprises a container  84  having the general shape of a rectangular parallelepiped. The separation cells  78  are mounted on the central container  74  so that their respective median longitudinal axes  86  intersect the rotation axis  68 , so that they are located substantially at the same distance from the rotation axis  68 , and so that the angles between their median longitudinal axes  86  are substantially the same (i.e. 90 degrees). The median axes  86  of the separation cells  78  are inclined downwardly with respect to a plane perpendicular to the rotation axis  68 . 
     Each container  84  comprises a separation cavity  88  that is so shaped and dimensioned as to loosely accommodate a separation bag  12  full of liquid, of the type shown in  FIG. 1 . The cavity  88  (which will be referred to later also as the “separation compartment”) is defined by a bottom wall, which is the farthest to the rotation axis  68 , a lower wall that is the closest to the container  74 , an upper wall opposite to the lower wall, and two lateral walls. The cavity  88  comprises a main part, extending from the bottom wall, which has substantially the shape of a rectangular parallelepiped with rounded corners and edges, and an upper, or proximal, part, which has substantially the shape of a prism having convergent triangular bases. In other words, the upper part of the cavity  88  is defined by two sets of two opposing walls converging towards the central median axis  86  of the container  84 . One interesting feature of this design is that it causes a radial dilatation of a thin layer of a minor component of a composite fluid (e.g. the platelets in whole blood) after separation by centrifugation, and makes the layer more easily detectable in the upper part of a separation bag. This also reduces mixing between component layers by providing a gradual, funnel-like transition into the tube. The two couples of opposite walls of the upper part of the separation cell  78  converge towards three cylindrical parallel channels (not shown), opening at the top of the container  84 , and through which, when a separation bag  12  is set in the container  84 , the three tubes  18 ,  20 ,  22  extend. (Tube  20  along with needle  30  may be removed before the separation bag  12  is placed in the container  84 ). 
     The container  84  also comprises a hinged lateral lid  96 , which is comprised of an upper portion of the external wall of the container  84 . The lid  96  is so dimensioned as to allow, when open, an easy loading of a separation bag  12  full of liquid into the separation cell  78 . The container  84  comprises a locking means (not shown) by which the lid  96  can be locked to the remaining part of the container  84 . The container  84  also comprises a securing or locating means for securing or locating a separation bag  12  within the separation cell  78 . The bag securing or locating means comprises two pins (not shown) protruding on the internal surface of the lid  96 , close to the top of separation cell  78 , and two corresponding recesses in the upper part of the container  84 . The two pins are so spaced apart and dimensioned as to fit into the two holes  24  in the upper corners of a separation bag  12 . 
     The separation apparatus further comprises a component transferring means for transferring at least one separated component from each separation bag into a component bag connected thereto. The component transferring means comprises a squeezing system for squeezing the separation bags  12  within the separation compartments  88  and causing the transfer of separated components into component bags  14 ,  16 . The squeezing system comprises a flexible diaphragm  98  that is secured to each container  84  so as to define an expandable chamber  100  in the cavity thereof. More specifically, the diaphragm  98  is dimensioned so as to line the bottom wall of the cavity  88  and a large portion of the lower wall of the cavity  88 . The squeezing system further comprises a peripheral circular manifold  102  that forms a ring. Each expansion chamber  100  is connected to the manifold  102  by a supply channel  104  that extends through the wall of the respective container  84 , close to the bottom thereof. The squeezing system further comprises a hydraulic pumping station  106  for pumping a hydraulic liquid in and out of the expandable chambers  100  within the separation cells  78 . The hydraulic liquid is selected so as to have a density slightly higher than the density of the densest of the components in the composite liquid to be separated (e.g. the red blood cells, when the composite liquid is blood). As a result, during centrifugation, the hydraulic liquid within the expandable chambers  100 , whatever the volume thereof, will generally remain in the most external part of the separation cells  78 . The pumping station  106  is connected to the expandable chambers  100 , through a rotary seal  108 , by a duct  110  that extends through the rotor shaft  70 , through the bottom and lateral wall of the central container  74 , and, radially outwardly where it connects to the manifold  102 . The pumping station  106  comprises a piston pump having a piston  112  movable in a hydraulic cylinder  114  fluidly connected via the rotary seal or fluid coupling  108  to the rotor duct  110 . The piston  112  is actuated by a brushless DC motor  116  that moves a lead screw  118  linked to a piston rod. The hydraulic cylinder  114  is also connected to a hydraulic liquid reservoir  120  having an access controlled by two valves  122   a ,  122   b  for selectively allowing the introduction or the withdrawal of hydraulic liquid into and from a reciprocating hydraulic circuit including the hydraulic cylinder  114 , the rotor duct  110  and the expandable hydraulic chambers  100 . A pressure gauge  124  is connected to the hydraulic circuit for measuring the hydraulic pressure therein. 
     The container  84  further comprises a pressure sensor  85  in the wall of the cavity  88 . The pressure sensor  85  has a flexible membrane that moves in response to pressure changes in cavity  88  and such membrane is connected to a pressure transducer to convert such information to pressure information. The pressure sensor  85  senses pressure amount due to the fluid level or head height of fluid in the bag  12 . The outboard area of the cavity  88  is from the sensor  85  to the bottom wall or the wall furthest from the rotational axis. The inboard area of the cavity  88  is that area from the sensor  85  to the upper wall of the cavity  88 . The container  84  further includes a second optical sensor  87  in the wall of the cavity  88  to detect passage of blood component or interface changes as more fully described below. 
     The separation apparatus further comprises four sets of three pinch valves  128 ,  130 ,  132  that are mounted on the rotor around the opening of the central container  74 . Each set of pinch valves  128 ,  130 ,  132  faces one separation cell  78 , with which it is associated. The pinch valves  128 ,  130 ,  132  are designed for selectively blocking or allowing a flow of liquid through a flexible plastic tube, and selectively sealing and cutting a plastic tube. Each pinch valve  128 ,  130 ,  132  comprises an elongated cylindrical body  134  and a head  136  having a jaw  138  forming a gap that is defined by a stationary lower plate or anvil  140  and the jaw  138  movable between a “load” position, an “open” position, and a “closed” position. The gap is so dimensioned that one of the tubes  32 ,  36 ,  46  of the bag sets shown in  FIG. 1  can be snuggly engaged therein when the jaw is in the open position. The elongated body contains a mechanism for moving the jaw and it is connected to a radio frequency generator that supplies the energy necessary for sealing and cutting a plastic tube. It is also noted that a tearable seal could alternatively be used. The pinch valves  128 ,  130 ,  132  are mounted inside the central container  74 , adjacent the interior surface thereof, so that their longitudinal axes are parallel to the rotation axis  68  and their heads protrude above the rim of the container  74 . The position of a set of pinch valves  128 ,  130 ,  132  with respect to a separation bag  12  and the tubes  32 ,  36 ,  46  connected thereto when the separation bag  12  rests in the separation cell  78  associated with this set of pinch valves  128 ,  130 ,  132  is shown in dotted lines in  FIG. 1 . Electric power is supplied to the pinch valves  128 ,  130 ,  132  through a slip ring array  66  that is mounted around a lower portion of the rotor shaft  70 . 
     Rapid placement of tubes, such as tubes  32 ,  36  and  46 , is enhanced by the ability of the valve jaws in the “load” position to optionally swing completely clear of a track or groove adapted to receive a tube. Accurate placement of the tubes is enhanced by the use of the asymmetrical manifold  34 . The manifold is comprised of relatively rigid plastic and forms a junction for at least three, preferably four, flexible tubes. Connections for the tubes are asymmetrically spaced around the manifold. As shown in  FIGS. 1 and 3  an embodiment of the asymmetrical manifold  34  comprises an “E” configuration. The “E” configuration comprises a central rigid tube  166  with three stubs  168 ,  171 , and  173  connected to tubes  32 ,  18  and  36 , respectively. Diametrically across from the three stubs, a fourth stub  175  connects to tube  46  and thence to the auxiliary bag  44 . The fourth stub  175  is asymmetrically placed along the tube  166 . Because of the asymmetrical shape of the manifold, the manifold can be mounted in a shaped recess on the central core  150  in only one direction. Each of the tubes  32 ,  36  and  46  of the bag set  10  will consequently be reliably mounted at the proper valve  128 ,  130 ,  132 . Although the valve jaws swing in the load position, such movement is optional and it is understood that a manifold, depending on shape, can be loaded without such jaw movement. 
     The separation apparatus also comprises a controller  157  including a control unit (e.g. a microprocessor) and a memory unit for providing the microprocessor with information and programmed instructions relative to various separation protocols (e.g. a protocol for the separation of a plasma component and a blood cell component, or a protocol for the separation of a plasma component, a platelet component, and a red blood cell component) and to the operation of the apparatus in accordance with such separation protocols. In particular, the microprocessor is programmed for receiving information relative to the centrifugation speed(s) at which the rotor is to be rotated during the various stages of a separation process (e.g. stage of component separation, stage of a plasma component expression, stage of suspension of platelets in a plasma fraction, stage of a platelet component expression, etc), and information relative to the various transfer flow rates at which separated components are to be transferred from the separation bag  12  into the component bags  14 ,  16 . The information relative to the various transfer flow rates can be expressed, for example, as hydraulic liquid flow rates in the hydraulic circuit, or as rotation speeds of the brushless DC motor  116  of the hydraulic pumping station  106 . The microprocessor is further programmed for receiving, directly or through the memory, information from the pressure sensor  124  and from the sets of sensors  87  and  158  (described below) and for controlling the centrifuge motor  80 , the brushless DC motor  116  of the pumping station  106 , and the four sets of pinch valves  128 ,  130 ,  132  so as to cause the separation apparatus to operate along a selected separation protocol. The microprocessor also receives information from each pressure sensor  85  and sensors  87  and  158  for volume determination or prediction. 
     A first balancing means initially balances the rotor when the weights of the four separation bags  12  contained in the separation cells  78  are different. The first balancing means substantially comprises the same structural elements as the elements of the component transferring means described above, namely: four expandable hydraulic chambers  100  interconnected by a peripheral circular manifold  102 , and a hydraulic liquid pumping station  106  for pumping hydraulic liquid into the hydraulic chambers  100  through a rotor duct  110 , which is connected to the circular manifold  102 . Under centrifugation forces, the hydraulic liquid will distribute unevenly in the four separation cells  78  depending on the difference in weight of the separation bags  12  to balance the rotor. 
       FIG. 3  shows a top plan view of the rotor  64 . Four symmetrically spaced separation cells  78  (each with a lid  96 ) are shown surrounding a central core  150 , which contains four sets of valves  128 ,  130 ,  132  and which supports the asymmetrical manifolds  34  and tubes of the bag sets  10 . The core  150  is supported in the center of the rotor by a spider structure comprised of four radial support arms  152 . The arms  152  define collection cavities  154  between a separation cell  78  and an adjacent set of valves  128 ,  130 ,  132  on the central core  150 . The component bags  14  and  16  (for plasma and platelets respectively) and the red blood cell component bag  38 , with its associated filter  40 , are placed in the cavity  154  when the bag set  10  is loaded into the rotor  64 . The collection and separation bag  12 , which initially contains the collected unit of whole blood, is placed in the adjacent separation cell  78 . The auxiliary bag  44 , which may be used for temporary fluid storage, waste fluid collection or collection of a rare or small-volume blood component, is placed in a well  156  close to the axis of rotation  68  (see  FIG. 3 ) of the rotor. The well  156  is closer to the axis of rotation than at least some of the valves associated with a single set  10  of bags. The well  156  may be cylindrical or rectangular to accommodate a rectangular bag  44 , as shown in  FIG. 1 . The well is positioned such that the processing or primary separation bag  12  is located in a relatively high force region of the centrifugal field produced by the rotation of the rotor, while the component bags  14 ,  16  are located in a lower force region, and the smaller wash solution or discard bag  44  placed in the well would be in the lowest force region. By reason of bag placement in high, intermediate and low force regions of the centrifugal field, air will tend to collect in the wash bag  44  in the well  156 . Moreover, a shorter line or tube can be used to connect the small bag  44  to the entire bag assembly. The three placement zones aid in simplifying the bag assembly and make the process of loading the bag assembly into the rotor easier. 
       FIG. 3  shows an asymmetric manifold  34  having an “E” configuration (also shown in  FIG. 1 ), although other configurations could be used. For each set of valves, outer valves  128 ,  132  are shown in “load” configuration, that is, the jaw of the valve does not extend over an adjacent tube, thereby allowing the manifold  34  and tubes to be installed in their proper configuration on the central core  150 . For each set of valves, an inner or center valve  130  is shown in the closed position with respect to tube  46 . 
     A tube sensor  158  is able to detect the presence or absence of liquid in the tube  18 , such as the detection of plasma, as well as to detect blood cells in a liquid. Each sensor  158  and  87  may comprise a photocell including an infrared LED and a photo-detector. Electric power is supplied to the sensors  87 ,  158  through the slip ring array that is mounted around the lower portion of the rotor shaft  70 . In the process of separating blood into component parts, fluid components, such as plasma or platelets, are expressed out of the separation bag  12  in the separation cell  78  into component bags  14 ,  16  in the cavities  154 . The sensor  158  may detect the beginning of the plasma flow or the presence of platelets or red blood cells. In response, the controller  157  may interrupt or change the processing for the particular set of bags where the new condition was sensed. The second sensor or photocell  87 , similar to  158 , may also be included in container  84  (see  FIG. 2 ). This sensor  87  is also able to detect the presence or absence of liquid such as plasma as well as the presence of platelets or red blood cells. This sensor may be used to detect the trailing edge of a separated layer or fraction. 
     Since the process of blood separation proceeds at different rates for different blood units, the volumes and weights of fluids in different bags and locations on the rotor will differ. A second balancing means  160  balances the rotor when the weights of the components transferred into the component bags  14 ,  16  in the cavities  154  are different. For example, when two blood donations have the same hematocrit and different volumes, the volumes of plasma extracted from each donation are different, and the same is true when two blood donations have the same volume and different hematocrit. The second balancing means comprises a balance assembly or ring  160 , more particularly described in U.S. patent application Ser. No. 11/751,748, filed May 22, 2007, and incorporated herein by reference. The balancing apparatus of the separation apparatus comprises one or two balancing assemblies, each including a series of ponderous satellites or balls that can move freely on a specific circular orbit centered on and perpendicular to the axis of rotation of the rotor. The housing comprises a container for spherical ponderous satellites (balls)  162 , which are housed in a cylindrical outer race, in which the balls slightly engage, and on which they roll, when the rotor rotates. The balancing means  160  comprises a plurality of balls. When the balls are in contact with each other, they occupy a sector of the ring of about 180 degrees. The balancing means  160  also comprises a damper or dampening fluid or element for providing resistance to the movement of the balls. 
     The method of using the apparatus described above will now be described. 
     Each procedure to separate composite fluid or whole blood begins with collection of the whole blood or fluid into bag  12  of bag set  10 . The bag set  10  is then loaded onto apparatus  60 . Before loading the bag set  10 , needle  30  and tube  20  may be removed by sterile welding or other procedure. The bag  12  containing the composite fluid or whole blood is placed in the cavity  88 . This may be done for each cavity  88  of the apparatus  60 . The collection bags and other fluid bag, if any, is placed in the respective cavity  154  or  156 . The rotation of the rotor  64  begins and the rotor  64  is rotated until it reaches an rpm suitable for separation, (for example 1800 to 3200 rpm). A pressure sensing value at a designated rpm is provided by pressure sensor  85  to the control unit  157 . Pressure sensor  85  senses the fluid pressure in the cavity  88  due to the head height or fluid level of the composite fluid. The valves may be opened or closed during the pressure sensing step. Pressure may be determined also after loading of bag  12  but before the rotor  64  begins its rotation. The fluid pressure measurement is used by the controller to predict the volume of the composite fluid or whole blood. The pressure amount corresponds to the fluid level or head height and thus corresponds to the composite fluid volume. 
     During centrifugation, fluid in the separation bag  12  is subject to a radial acceleration gradient. This causes a pressure gradient along a radial line passing through the fluid volume. The resulting pressure depends on the angular velocity, radius and fluid density. 
     Pressure sensor  85  measures the fluid pressure at a known radial location in the separation bag  12 . The rotor speed or rpm of the rotor  64  is known as is the radial location of the pressure sensor  85  on the centrifuge  62 . The sensor  85  is further located at a specific location along the wall of the separation compartment  88 . A portion of the composite liquid will be outboard or between the sensor  85  and the bottom of the separation compartment  88 . The volume of composite fluid can be determined from the volume of the outboard area containing such fluid. Fluid variations may occur in the inboard area of the separation compartment due to the overall volume of the composite fluid. Larger volumes of fluid cause more fluid to be located in the inboard area or the area between the sensor  85  and the top of the separation compartment. As fluid volume increases inboard of the pressure sensor  85  the magnitude of the pressure at the sensor  85  location also increases. The radial distance from the fluid surface to the pressure sensor location can be determined. The volume of the outboard area is known from the separation compartment  88  geometry and the volume of the inboard area can be estimated by variations in pressure due to the pressure sensor  85 . Adding the outboard volume to the inboard volume provides an estimate or prediction of the total volume of the composite fluid. 
     As rotation continues, valve  128  opens or remains opens and plasma, the least dense component in whole blood, flows into bag  14 . The hydraulic fluid from reservoir  120  flows through duct  110  and channel  104  and under bladder or diaphragm  98  to squeeze bag  12  to facilitate plasma transfer to bag  14 . Photocell  158  optically sees the leading edge of the plasma flow and provides such information to controller  157 . When photocell or sensor  57  senses a cellular component approaching tubing  18  from the top of bag  12 , it also provides the information including the trailing edge of the plasma interface to the controller  157 . The controller sends a signal to close valve  128  and open valve  132  for cellular component. The hydraulic flow rate corresponds to the fluid flow rate into the collection bag  14  and  16 . From this flow rate and the sensor signals  57 ,  158  determining the start (leading edge) and end (trailing edge) of the plasma collection, the volume of plasma or an expressed component can be determined. 
     Sensors  57  and  158  further can sense the change of cellular component from, for example, platelets to red blood cells. Photocell  158  indicates the leading edge of the platelet layer with photocell  57  indicating the trailing edge. This sensing of an interface change between different layers or sedimented blood components will cause the controller to signal valve  132  to close and end the platelet collection. The leading edge sensor  158  signal indicating platelets along with the trailing edge sensor  57  signal indicating the end of the platelet layer is provided to the controller, along with the fluid flow rate, to determine or estimate the volume of platelets transferred. The estimated plasma volume as well as the determined platelet volume along with the initial whole blood volume estimate can be used by the controller to provide an estimate of the remaining component or components such as red blood cells in bag  12 . 
     If it is desired to add wash solution or storage solution into the remaining red blood cells, the hydraulics  112  may be pulled back to drain out from under diaphragm or membrane  98  to release the squeezing pressure on the previously squeezed bag  12 . Valve  130  may be opened and wash or storage solution may be introduced from bag  44  through tubing  46  to bag  12 . 
     If washing is the desired protocol, the wash solution may be mixed with the red blood cells and resulting supernatant can be expressed back to bag  44  using the hydraulic fluid to squeeze bag  12  for the transfer. 
     If the storage solution is added from bag  44 , the centrifuge will be stopped. The bag set  10  may be removed from the centrifuge and all tubing but  22  can be discarded. 
     Storage solution can be also gravity drained from bag  38  through filter  40  to mix with remaining red blood cells in bag  12 . 
     Valves  128 ,  130  and  132  can provide heat sealing of the tubing  32 ,  46  and  36 . Any remaining tubing can also be heat sealed by the operator for removal leaving bag  12 , tubing  22 , filter  40  and bag  38  remaining. The residual product, such as red blood cells and storage solution, is drained from bag  12  to  42 . Frangibles  28  and  42  are opened and bag  12 , is elevated to gravity drain the red blood cells through leukoreduction filter  40  to bag  38 . 
     The above procedure is only exemplary to describe the invention as it is understood that variations can occur. Although sensors  57  and  58  are described, it is understood that sensor  158  or sensor  57  only may be used to detect both a leading or trailing edge or interface change. Also, additional optical sensors may be provided around container  84  similar to sensor  57  to detect fluid or cells. Also, white blood cells may also be collected. 
     It will be apparent to those skilled in the art that various modifications can be made to the apparatus and method described herein. Thus, it should be understood that the invention is not limited to the subject matter discussed in the specification. Rather, the present invention is intended to cover modifications and variations.