Abstract:
A system for controlling the deglycerolization of red blood cells includes a cell sorter having multiple fluid channels each having a unique cross-sectional area for directing a fluid mixture consisting essentially of a saline solution and a plasma solution having glycerized red blood cell products through one or more of the fluid channels based on the sizes of the red blood cell products. An optical energy source illuminates the fluid mixture in the cell sorter, whereupon an optical detector generates a data signal in response to receiving light signals that propagate through the fluid mixture. A processor generates a control signal in response to receiving the data signal that is used by a servo-controlled device to control the ratio of the saline and plasma solutions in the fluid mixture so that the red blood cell products substantially flow only through one or more of the fluid channels having particular cross-sectional areas.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to the deglycerolization of blood, and more particularly, to a system which controls the deglycerolization of blood by monitoring the segregation of erythrocytes by size. 
     The Armed Services Blood Program Office (ASBPO) has established a policy of maintaining pre-positioned stockpiles of frozen red blood cells, and utilizing these stockpiles in times of conflict for U.S. combat casualties. In order to implement this policy, glycerol is allowed to be absorbed by red blood cells, which then are frozen and stored. The glycerol prevents damage to the erythrocytes. Presently, the only method approved by the Food and Drug Administration (FDA) for processing thawed-frozen red blood cells uses an open, nonsterile wash system that is manually monitored and operated. This system generally requires about 1½ to 2 hours to thaw and deglycerolize red blood cells from a cryogenic state. Because this system is not sterile, the FDA mandates that thawed-frozen red blood cells processed this way must be transfused within 24 hours or discarded. However, the time restrictions and requirement to discard the blood are not compatible with the logistics of the ASBPO policy. Therefore, a need exist for a sterile, automated method for monitoring and controlling the deglycerolization of thawed red blood cells in a more timely manner compared to the processing time of the standard method. 
     SUMMARY OF THE INVENTION 
     The present invention provides a system and method for controlling the deglycerolization of red blood cells. A system for controlling the deglycerolization of red blood cells includes a cell sorter having multiple fluid channels each having a unique cross-sectional area for directing a fluid mixture consisting essentially of a saline solution and a plasma solution having glycerized red blood cell products through one or more of the fluid channels based on the sizes of the red blood cell products. An optical energy source illuminates the fluid mixture in the cell sorter, whereupon an optical detector generates a data signal in response to receiving light signals that propagate through the fluid mixture. A processor generates a control signal in response to receiving the data signal that is used by a servo-controlled device to control the ratio of the saline and plasma solutions in the fluid mixture so that the red blood cell products substantially flow only through one or more of the fluid channels having particular cross-sectional areas. 
     These and other advantages of the invention will become more apparent upon review of the accompanying drawings and specification, including the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a block diagram of a system for controlling deglycerolization of red blood cells embodying various features of the present invention. 
     FIG. 2 illustrates a plan view of the cell sorter. 
     FIG. 3 is a view of the cell sorter taken along section  3 — 3  of FIG.  2 . 
     FIG. 4 is a view of the cell sorter taken along section  4 — 4  of FIG.  2 . 
    
    
     Throughout the several view, like elements are referenced using like references. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the present invention is directed to a system  10  for controlling deglycerolization of red blood cells. System  10  includes an optical energy source  12 , cell sorter  14 , optical element  15 , lens  20 , photo detector  22 , processor  24 , and servo-controlled device  26 . In the operation of system  10 , input fluid  11  enters fluid inlet  16  of cell sorter  14  and is deglycerolized as described further herein. Input fluid  11  generally consists of two components: 1) a solution  8  consisting essentially of glycerolized blood cells suspended in plasma; and 2) a saline solution  6 . Generally deglycerolized output fluid  13 , containing blood and glycerol products, exits cell sorter  14  through fluid outlet  18 . Optical energy source  12  generates an optical beam  21  that is directed to cell sorter  14  by optical element  15 . In the preferred embodiment, optical beam  21  is both polarized and quasi-monochromatic light. Polarized light enhances the contrast between the plasma and surrounding structures. Quasi-monochromatic light greatly reduces or eliminates chromatic aberration that could cause false indications of cell sizes. Quasi-monochromatic light has frequency components strongly peaked about a certain frequency. Examples of optical energy sources which generate quasi-monochromatic light suit suitable for use as optical energy source  12  include solid-state lasers, gas type lasers (such as an He—Ne laser), laser diodes, and light emitting diodes. 
     Optical beam  21  interrogates the contents of cell sorter  14  and is transformed into reflective optical signal  25  through interaction with fluid that transitions from solution  11  to solution  13  in the cell sorter. The characteristics of signal  25  represent the sizes of red blood cells in cell sorter  14 . Next, optical signal  25  propagates through transparent window  19  and optical element  15 , and then is focused by lens  20  onto photo detector  22 . By way of example, optical element  15  may be a partially reflective mirror or a prism. Photodetector  22  transforms optical signal  25  into an electrical output signal  27  representing the sizes of the red blood cells in cell sorter  14 . Photo detector  22  may be implemented as a charge coupled device, photo transistor array, vidicon, or any other type of device that provides sufficient pixel resolution of the field of view of the cell sorter. 
     The exposure of solution  8 , containing glycerolized red blood cells, to saline solution  6 , causes glycerol to be expelled through the walls of red blood cells (erythrocytes) at a rate determined by the osmotic pressure difference between the interior of the red blood cells and that of saline solution  6 . Control of the osmotic pressure difference is very important because if the pressure gradient is too great, red blood cells will rupture. If the osmotic pressure difference is too small, the rate at which glycerol is expelled through the wall of the red blood cells will be very slow. The osmotic pressure difference increases as the ratio of the volume of solution  6  to solution  8  increases in fluid  11 . 
     Processor  24  employs signal  27  to generate a control signal  33  that is used to supervise servo-controlled device  26 . Control signal  33  has characteristics functionally related to the sizes of red blood cells found in cell sorter  14  within the field of view of photo detector  22 . Servo-controlled device  26  is used to establish the ratio of saline solution  6  to the glycerolized red blood cells in solution  8  in input solution  11  in response to the sizes of red blood cells found in cell sorter  14  which are encoded in signal  25 . Servo-controlled device  26  may, for example, be a pump or valve. Regulation of the ratio of solution  6  to solution  8  is used to optimize the rate at which glycerol is expelled from the red blood cells, an important goal of system  10 . 
     As described with reference to FIGS. 2 and 3, cell sorter  14  includes an external body  17  on which an optically transparent window  19  is attached so as to create a water tight, or more generally, fluid tight seal. External window  19  may be made from materials such as glass, quartz, polycarbonate, sapphire or of any other type of optically transparent material that is essentially chemically inert to blood components and chemicals to which the window is be exposed, and which may be sterilized. External body  17  also supports a flow divider insert  29  having multiple flow dividing channels for input fluid  11  into several flow streams having different cross-sectional areas. By way of example, insert  29  is shown to include seven fluid flow dividing channels  31 ,  32 ,  34 ,  36 ,  38 ,  40 , and  42 , each of which are in fluid communication with inlet  16  and outlet  18  of cell sorter  14 . After entering inlet  16 , input fluid  11  is divided into separate fluid streams by channels  31 ,  32 ,  34 ,  36 ,  38 ,  40 , and  42 . The separate fluid streams then merge before exiting cell sorter  14  through outlet  18 . Although the invention has been described as having seven flow channels, the scope of the invention includes the use of any number of flow channels required to suit the requirements of a particular application. Each flow channel preferably has a unique cross-sectional area in a plane orthogonal to the direction of fluid flow. FIG. 4 shows a cross-sectional view of channels  31 ,  32 ,  34 ,  36 ,  38 ,  40 , and  42 . Exemplary dimensions for the channels are provided in TABLE 1 below. Insert  29  may be fabricated from bulk silicon using standard photolithographic techniques. A layer  43  supported by and attached to insert  29  generally consists of a material that should be essentially chemically resistant to blood components and which may be sterilized. Layer  43  should be optically reflective in the regions of cell sorter  14  through which fluid containing blood products flows. Examples of reflective materials suitable for layer  43  include gold, nickel, passivated aluminum, and silicon dioxide (SiO 2 ). Reflective layer  43  caused incoming light beam  21  to be reflected out of cell sorter  14  as light signal  25 . A further requirement of cell sorter  14  is that it be made of materials that can be sterilized. Techniques for sterilizing cell sorter  14  may include exposure to gamma radiation or heat. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Channel 
                 Width (μ) 
                 Height (μ) 
               
               
                   
               
             
             
               
                 31 
                 H ≈ 3 mm 
                 G ≈ 1.4-1.6 
               
               
                 32 
                 F ≈ 18-22 
                 G ≈ 1.4-1.6 
               
               
                 34 
                 E ≈ 12-15 
                 G ≈ 1.4-1.6 
               
               
                 36 
                 D ≈ 8-9 
                 G ≈ 1.4-1.6 
               
               
                 38 
                 C ≈ 5-7 
                 G ≈ 1.4-1.6 
               
               
                 40 
                 B ≈ 2-3 
                 G ≈ 1.4-1.6 
               
               
                 42 
                 A &lt; 2 
                 G ≈ 1.4-1.6 
               
               
                   
               
             
          
         
       
     
     Saline causes glycerolized red blood cells to expel the glycerol due to the osmotic pressure difference between glycerol and saline. If the osmotic pressure is too much, i.e., when the ratio of saline to glycerolized red blood cells in input solution  11  exceeds some level, the red blood cells rupture, a process referred to as hemolysis. If the red blood cells rupture, then fragments of red blood cells having some linear dimensions of about 2-3μ would find their way into channel  40 . Red blood cells, however, are too small to enter channel  40 . This may be referenced as a case  1  situation. A case  1  situation means that the ratio of saline solution  6  to solution  8  is too high. In such case, processor  24  generates signal  24  whereby servo-controlled device  26  reduces the ratio of solution  6  to solution  8  in solution  11 . Plasma may enter channel  42 . However, red blood cell fragments are too large to enter channel  42 . Therefore, the optical detection of plasma in channel  42  may be used as a reference to normalize reflected light signal  25  due to variations in the optical transparency characteristics of the plasma. 
     At the opposite extreme of case  1  is the case  2  situation where unconfined red blood cells swollen with glycerol have minimum linear dimensions of about 15-16μ. Cells of this size will not be able to enter any of channels  32 ,  34 ,  36 ,  38 , and  40 , but will be able to pass through channel  31 . A case  2  situation means that the glycerol is not being emitted from the cells. Therefore, processor  24  generates signal  33  that directs servo-controlled device  26  to respond so that the ratio of saline solution  6  to solution  8  of glycerolized red blood cells is increased by some predetermined increment. As the ratio is increased the red blood cells will emit more glycerol and become smaller. 
     In the preferred operation of system  10 , deglycerolized red blood cells progressively find their way into increasingly smaller channels  34 ,  36 , and  38  as characteristics of signal  33  are changed so that servo-controlled device  26  effectuates an optimum ratio of saline solution  6  to glycerolized blood solution  8 . Under ideal operating conditions, red blood cells are found in channel  38 , but essentially no red blood cell fragments are found in channel  40 . Such a condition indicates that practically all of the glycerol has been expelled from the red blood cells, but the cells have not fragmented due to hemolysis. Therefore, the cross-sectional area of channel  38  is sized so that unconfined red blood cells which are engorged with glycerol are able to pass through. However, channel  40  is sized so that nothing larger than blood cell fragments may transit. Thus, channel  40  has insufficient area to admit red blood cells that are not engorged with glycerol. Channel  42  is sized to admit plasma, but has too small a cross-sectional area to admit red blood cell fragments or anything larger. Channels  34  and  36  are sized to have progressively smaller cross-sectional areas that admit red blood cells which are decreasingly engorged with glycerol to facilitate monitoring the process of expelling glycerol from the cells. 
     Characteristics of signal  33  that may be used to control a servo-controlled mechanism such as device  26  include pulse width, amplitude, frequency, logic level, and any other type of signal characteristic that may be used to control a servo-controlled device. Thus, it may be appreciated that the present invention provides an automated system for monitoring and controlling the deglycerolization of red blood cells in real time so that the cells expel glycerol at a timely rate without causing, or at least minimizing hemolysis. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.