Blood processing systems and methods using apparent hematocrit as a process control parameter

Abstract

Blood processing systems and methods separate whole blood into red blood cells and a plasma constituent within a rotating centrifugal separation device. The systems and methods convey whole blood into the separation device through an inlet path including a pump operable at a prescribed rate. The systems and methods remove plasma constituent from the separation device through an outlet path including a pump operable at a prescribed rate. The systems and methods derive a value H b representing an apparent hematocrit of whole blood entering the separation device, where: H b = H rbc  ( Q b - Q p ) Q b and where H rbc is a value relating to hematocrit of red blood cells in the separation device. The systems and methods generate outputs and control commands based, at least in part, upon H b .

I claim:  
     
         1 . A blood processing system comprising 
 a centrifugal separation device rotatable at a prescribed rate of rotation,    an inlet path including a pump operable at a prescribed rate Q b  to convey whole blood into the separation device for separation into red blood cells and a plasma constituent,    an outlet path including a pump operable at a prescribed rate Q p  to remove plasma constituent from the separation device,    an element to derive a value H b  representing an apparent hematocrit of whole blood entering the separation device, where:  
         H   b     =         H   rbc          (       Q   b     -     Q   p       )         Q   b                     
   and where H rbc  is a value relating to hematocrit of red blood cells in the separation device.    
     
     
         2 . A system according to    claim 1     and further including an element that generates a control command based, at least in part, upon H b .    
     
     
         3 . A system according to    claim 2     wherein the control command recirculates at least a portion of plasma constituent for mixing with whole blood conveyed into the separation device.    
     
     
         4 . A system according to    claim 2     wherein the control command controls Q b .    
     
     
         5 . A system according to    claim 1     and further including an element that generates an output based, at least in part, upon H b .    
     
     
         6 . A system according to    claim 5     wherein the output comprises a value η representing efficiency of separation in the separation device, where:  
       η   =       Q   p         (     1   -     H   b       )          Q   b                       
   
     
     
         7 . A system according to    claim 1     wherein the value H rbc  represents apparent hematocrit of red blood cells in the separation device, where:  
         H   rbc     =     1   -       (       β     gA                 κ                   S   γ              (       q   b     -     q   p       )       )       1     k   +   1                         
   where:    q b  is inlet blood flow rate (cm 3 /sec), which when converted to ml/min, corresponds with Q b ,    q p  is measured plasma flow rate (in cm 3 /sec), which, when converted to ml/min corresponds with Q p ,    β is a shear rate dependent term, and S Y  is a red blood cell sedimentation coefficient (sec) and β/S Y =15.8×10 6  sec −1 ,    A is the area of the separation device (cm 2 ),    g is the centrifugal acceleration (cm/sec 2 ), which is the radius of the separation device multiplied by the rate of rotation squared Ω 2  (rad/sec 2 ), and    k is a viscosity constant=0.625, and κ is a viscosity constant based upon k and another viscosity constant α=4.5, where:  
       κ   =             k   +   2     α          [       k   +   2       k   +   1       ]         k   +   1       =   1.272                   
   
     
     
         8 . A system according to    claim 7     wherein the separation device is free of an sensor to measure blood hematocrit.    
     
     
         9 . A system according to    claim 1     wherein the inlet path is free of any sensor to measure blood hematocrit.    
     
     
         10 . A blood processing system comprising 
 a centrifugal separation device rotatable at a prescribed rate of rotation,    an inlet path including a pump operable at a prescribed rate Q b  to convey whole blood into the separation device for separation into red blood cells and a plasma constituent,    an outlet path including a pump operable at a prescribed rate Q p  to remove plasma constituent from the separation device,    a recirculation path including a pump operable at a prescribed rate Q Recirc  to recirculate at least a portion of the plasma constituent for mixing with whole blood conveyed into the separation device,    a controller coupled to the recirculation path pump to set Q Recirc  to achieve a desired hematocrit H i  for whole blood conveyed into the separation device as follows:  
         Q   Recirc     =       [         H   b       H   i       -   1     ]     ×     Q   b                     
   where H b  is a value representing an apparent hematocrit of whole blood entering the separation device, where:  
         H   b     =         H   rbc          (       Q   b     -     Q   p       )         Q   b                     
   and where H rbc  is a value relating to hematocrit of red blood cells in the separation device.  
       η   =       Q   b         (     1   -     H   b       )          Q   b                       
   
     
     
         11 . A system according to    claim 10     wherein the value H rbc  represents apparent hematocrit of red blood cells in the separation device, where:  
         H   rbc     =     1   -       (       β     gA                 κ                   S   γ              (       q   b     -     q   p       )       )       1     k   +   1                         
   where:    q b  is inlet blood flow rate (cm 3 /sec), which when converted to ml/min, corresponds with Q b ,    q p  is measured plasma flow rate (in cm 3 /sec), which, when converted to ml/min corresponds with Q p ,    β is a shear rate dependent term, and S Y  is a red blood cell sedimentation coefficient (sec) and β/S Y =15.8×10 6  sec −1 ,    A is the area of the separation device (cm 2 ),    g is the centrifugal acceleration (cm/sec 2 ), which is the radius of the separation device multiplied by the rate of rotation squared Ω 2  (rad/sec 2 ), and    k is a viscosity constant=0.625, and κ is a viscosity constant based upon k and another viscosity constant α=4.5, where:  
       κ   =             k   +   2     α          [       k   +   2       k   +   1       ]         k   +   1       =   1.272                   
   
     
     
         12 . A system according to    claim 11     wherein the separation device is free of an sensor to measure blood hematocrit.    
     
     
         13 . A system according to    claim 10     wherein the inlet path is free of any sensor to measure blood hematocrit.    
     
     
         14 . A system according to    claim 10     wherein H i  is no greater than about 40%.    
     
     
         15 . A system according to    claim 1     wherein H i  is about 32%.    
     
     
         16 . A blood processing method comprising the steps of 
 rotating a centrifugal separation device at a prescribed rate of rotation,    conveying whole blood into the separation device at a prescribed rate Q b  for separation into red blood cells and a plasma constituent,    removing plasma constituent from the separation device at a prescribed rate Q p ,    deriving a value H b  representing an apparent hematocrit of whole blood entering the separation device, where:  
         H   b     =         H   rbc          (       Q   b     -     Q   p       )         Q   b                     
   and where H rbc  is a value relating to hematocrit of red blood cells in the separation device.    
     
     
         17 . A method according to    claim 16     and further including the step of generating a control command based, at least in part, upon H b .    
     
     
         18 . A method according to    claim 17     wherein the control command recirculates at least a portion of plasma constituent for mixing with whole blood conveyed into the separation device.    
     
     
         19 . A method according to    claim 17     wherein the control command controls Q b .    
     
     
         20 . A method according to    claim 16     and further the step of generating an output based, at least in part, upon H b .    
     
     
         21 . A method according to    claim 20     wherein the output comprises a value η representing efficiency of separation in the separation device, where:  
       η   =       Q   b         (     1   -     H   b       )          Q   b                       
   
     
     
         22 . A method according to    claim 16     wherein the value H rbc  represents apparent hematocrit of red blood cells in the separation device, where:  
         H   rbc     =     1   -       (       β     gA                 κ                   S   γ              (       q   b     -     q   p       )       )       1     k   +   1                         
   where:    q b  is inlet blood flow rate (cm 3 /sec), which when converted to ml/min, corresponds with Q b ,    q p  is measured plasma flow rate (in cm 3 /sec), which, when converted to ml/min corresponds with Q p ,    β is a shear rate dependent term, and S Y  is a red blood-cell sedimentation coefficient (sec) and β/S Y =15.8×10 6  sec −1 ,    A is the area of the separation device (cm 2 ),    g is the centrifugal acceleration (cm/sec 2 ), which is the radius of the separation device multiplied by the rate of rotation squared Ω 2  (rad/sec 2 ), and    k is a viscosity constant=0.625, and κ is a viscosity constant based upon k and another viscosity constant α4.5, where:  
       κ   =             k   +   2     α          [       k   +   2       k   +   1       ]         k   +   1       =   1.272                   
   
     
     
         23 . A method according to    claim 22     wherein the method is free of a step of using a sensor to measure blood hematocrit in the separation device.    
     
     
         24 . A method according to    claim 16     wherein the method is free of a step of using a sensor to measure blood hematocrit in the inlet path.    
     
     
         25 . A blood processing method comprising the steps of 
 rotating a centrifugal separation device at a prescribed rate of rotation,    conveying whole blood into the separation device at a prescribed rate Q b  for separation into red blood cells and a plasma constituent,    removing plasma constituent from the separation device at a prescribed rate Q p ,    recirculating at least a portion of plasma constituent from the separation device at a prescribed rate Q Recirc  for mixing with whole blood conveyed into the separation device,    controlling Q Recirc  to achieve a desired hematocrit H i  for whole blood conveyed into the separation device as follows:  
         Q   Recirc     =       [         H   b       H   i       -   1     ]     ×     Q   b                     
   recirculating at least a portion of plasma constituent from the separation device at a prescribed rate Q Recirc  for mixing with whole blood conveyed into the separation device,    controlling Q Recirc  to achieve a desired hematocrit H i  for whole blood conveyed into the separation device as follows:  
         Q   Recirc     =       [         H   b       H   i       -   1     ]     ×     Q   b                     
   where H b  is a value representing an apparent hematocrit of whole blood entering the separation device, where:  
         H   b     =         H   rbc          (       Q   b     -     Q   p       )         Q   b                     
   and where H rbc  is a value relating to hematocrit of red blood cells in the separation device.    
     
     
         26 . A method according to    claim 25     wherein the value H rbc  represents apparent hematocrit of red blood cells in the separation device, where:  
         H   rbc     =     1   -       (       β     gA                 κ                   S   γ              (       q   b     -     q   b       )       )       1     k   +   1                         
   where:    q b  is inlet blood flow rate (cm 3 /sec), which when converted to ml/min, corresponds with Q b ,    q p  is measured plasma flow rate (in cm 3 /sec), which, when converted to ml/min corresponds with Q p ,    β is a shear rate dependent term, and S Y  is a red blood cell sedimentation coefficient (sec) and β/S Y =15.8×10 6  sec −1 ,    A is the area of the separation device (cm 2 ),    g is the centrifugal acceleration (cm/sec 2 ), which is the radius of the separation device multiplied by the rate of rotation squared Ω 2  (rad/sec 2 ), and    k is a viscosity constant=0.625, and κ is a viscosity constant based upon k and another viscosity constant α=4.5, where:  
       κ   =             k   +   2     α          [       k   +   2       k   +   1       ]         k   +   1       =   1.272                   
   
     
     
         27 . A method according to    claim 26     wherein the method is free of a step of using a sensor to measure blood hematocrit in the separation device.    
     
     
         28 . A method according to    claim 25     wherein the method is free of a step of using a sensor to measure blood hematocrit in the inlet path.