fig1 shows in diagrammatic form an on line blood processing system 10 that embodies features of the invention . according to the invention , the on line system 10 provides a finished , high quality platelet - rich blood product ( plt fin ), with a significantly reduced residual population of leukocytes and / or other enhanced physiological properties , suited for long term storage and transfusion . as used in this specification , the term “ on line blood separation process ” refers to a blood separation system or method that ( i ) establishes communication between a blood source ( typically , a human blood donor ) and an extracorporeal flow path ; ( ii ) draws a blood volume from the donor into the flow path ; and ( iii ) maintains communication with the circulatory system of the donor for at least a portion of the time that the blood volume undergoes separation within the extracorporeal flow path . as used in this specification , an “ on line blood separation process ” can separate the blood volume either in a continuous manner or in an interrupted manner . however , an “ on line blood separation process ” maintains communication between the flow path and the donor for at least a portion of the time the separation process occurs within the flow path , regardless of specific timing or sequencing of the separation process itself . as used in this specification , an “ on line blood separation process ” can include external or internal valves or clamps to interrupt flow within the path to or from the donor . however , in the context of this specification , such valves or claims do not break the communication between the blood donor and the flow path . instead , the valves or clamps control fluid flow within the path while maintaining communication between it and the blood donor . the on line system 10 draws whole blood ( wb ) from a donor through a phlebotomized tubing flow path 12 . wb contains , as its principal components , red blood cells , platelets , leukocytes , and plasma . the system 10 adds anticoagulant to the drawn wb and conveys anticoagulated wb into a centrifugal field 14 for processing . in the centrifugal field 14 , the system 10 ultimately separates anticoagulated wb into two components . the first component is a red blood cell concentration . it is desirable that the red blood cell concentration also carry with it a majority of the leukocyte population ( lk ) present in the wb . for this reason , the first component is referred to as rbc lk + . rbc lk + is returned to the donor during processing . this avoids depletion of the donor &# 39 ; s red blood cell and leukocyte populations while high volume yields of platelets are obtained . the second component comprises an unfinished platelet - rich plasma suspension plt un . plt un is considered “ unfinished ” because the platelet - rich plasma suspension still lacks the desired physiologic characteristics imposed by the end user ( typically a blood bank or hospital ) for long term storage and transfusion . centrifugal processing within the field 14 often cannot provide these desired characteristics . the specific physical makeup of the platelet - rich suspension comprising plt un can vary . the makeup will largely depend upon the efficiency of the centrifugal separation process in terms of the how many platelets are separated ( i . e ., the platelet yields ) and how much platelet - poor plasma product is withdrawn and not returned to the donor . as used in this specification , plt un is intended to encompass any suspension in which platelets are present in concentrations greater than in whole blood . plt un can comprise what is commonly referred to as platelet - rich plasma ( prp ) or platelet concentrate ( pc ), or suspensions of platelets and plasma lying in between . plt un can include , in addition to platelets , other components or ingredients , depending upon the choice of the end user . for example , plt un can include essentially only plasma as the platelet suspension media . alternatively or in addition to plasma , plt un can include a specially formulated platelet storage media to suspend the platelets . the structural details of the centrifugation field 14 can vary and are not essential to the invention . for example , the field 14 can comprise a centrifuge and multiple stage centrifugal processing chambers of the type shown in brown u . s . pat . no . 5 , 427 , 695 or brown u . s . pat . no . 5 , 370 , 802 , both of which are incorporated herein by reference . as fig2 shows in diagrammatic form , the multiple stage processing chambers that brown &# 39 ; 695 and &# 39 ; 802 embody separate wb into rbc and prp in a first stage separation chamber 16 . the special fluid flow dynamics that occur in the first stage chamber 16 shown in brown &# 39 ; 802 or &# 39 ; 695 keep a large majority of leukocytes out of prp and with the rbc in the first stage chamber 16 for return to the donor as rbc lk + . the special fluid flow dynamics occurring in the first stage chamber 16 in brown &# 39 ; 802 or brown &# 39 ; 695 also provide a high yield of platelets in the prp . in brown &# 39 ; 802 or &# 39 ; 695 , prp is transported from the first stage chamber 16 . a portion is recirculated back to the wb entering the first stage chamber 16 , and the rest is conveyed into a second stage chamber 18 . the prp is separated in the second stage chamber 18 into pc and platelet - poor plasma ( ppp ). pc retained in the second stage chamber 18 is later resuspended in a volume of ppp or ( optionally ) a suitable platelet storage medium for transfer from the second stage chamber as plt un . a portion of the ppp is returned to the donor , while another portion of ppp is retained for use as a recirculation or keep - open or rinse - back or resuspension media , or for storage for fractionation or transfusion . one reason why plt un can be considered “ unfinished ” in the context of the above described system is the presence of residual leukocytes in the platelet suspension . this residual population of leukocytes with the platelets , while small , still can be greater than the leukocyte population standards demanded by the end user . often , centrifugal processing alone often is not effective at isolating enough leukocytes from prp to meet these demands . unintended perturbations and secondary flows along the interface between rbc and plasma , where leukocytes reside , can sweep lighter leukocyte species away from rbc into the plasma . other desirable flow patterns that sweep heavier leukocytes species in the interface back into the rbc mass can also fail to develop to their fullest potential . the dynamic processes under which leukocytes are separated from platelets during centrifugation are complex and subject to variation from donor to donor . additional steps can be provided to augment the primary centrifugal separation process to thereby reduce the number of residual leukocytes present in plt un . for example , as disclosed in brown &# 39 ; 695 , a leukocyte filter 20 can be provided after the first stage chamber 16 to filter leukocytes from prp before entering the second stage chamber 18 for separation into pc and ppp . the filter 20 is preferably located outside the centrifugal field 14 , being connected by a rotating umbilicus arrangement 22 of conventional construction . alternatively , though , the filter 20 can be located within the centrifugal field 14 . alternatively , or in combination with such other ancillary leukocyte - reduction devices , plt un can be subject to particle bed separation effects within the centrifugal field 14 to separate leukocytes from the platelets . still , the degree of leukocyte reduction demanded by the user can exceed the capabilities of even these ancillary steps during the centrifugal separation process . for this reason ( see fig1 ), the system 10 includes an in line finishing device 24 located outside the centrifugal field 14 . a pump 26 conveys plt un under pressure from the centrifugal field 14 through the finishing device 24 . in fig1 , the pump 26 is shown downstream of the centrifugal field 14 . alternatively , the pump 26 could be located upstream of the centrifugal field 14 , thereby supplying the requisite machine pressure to convey plt un from the centrifugal field 14 . the finishing device 24 serves to affect a desired alteration in the makeup or physiological of plt un that could not be effectively achieved in the centrifugal field 14 , such as , for example , a further incremental reduction in the leukocyte population . the in line finishing device 24 performs its function on line , while the donor remains connected in communication with the system 10 . the output of the finishing device 24 is a finished platelet - rich suspension ( plt fin ). plt fin is considered “ finished ” because the platelet - rich plasma suspension possesses the desired physiologic characteristics imposed by the end user for long term storage and transfusion . in the context of the illustrated embodiment , the platelet - rich suspension comprising plt fin , possesses a more - reduced leukocyte population and / or additional physiological attributes not present in plt ini . as used in this specification , the term “ reduced ” or “ more - reduced ” does not denote that all the residual leukocytes have been removed . the term is intended to more broadly indicate only that the number of residual leukocytes have been incrementally reduced by the finishing device 24 , compared with the number before processing by the finishing device . other physiological attributes that the finishing device can provide include ( insert . . . . ) the finishing device 24 can accomplish its function by centrifugation , absorption , columns , chemical , electrical , and electromagnetic means . in the illustrated and preferred embodiment , the finishing device 24 comprises a filter that employs a non - woven , fibrous filter media 28 . the composition of the filter media 28 can vary . the media 28 comprises fibers that contain nonionic hydrophillic groups and nitrogen - containing basic functional groups . fibers of this type are disclosed in nishimura et al u . s . pat . no . 4 , 936 , 998 , which is incorporated herein by reference . filter media containing these fibers are commercially sold by asahi medical company . filter media containing these fibers have demonstrated the capacity to remove leukocytes while holding down the loss of platelets . alternatively , the filter media 28 can comprise fibers that have been surface treated as disclosed in gsell et al . u . s . pat . no . 5 , 258 , 127 to increase their ability to pass platelets while removing leukocytes . gsell et al . u . s . pat . no . 5 , 258 , 127 is also incorporated herein by reference . furthermore , because the pump 26 is used to convey plt ini through the finishing device 24 , the external machine pressure it creates can be used to overcome passive resistance of the finishing media 28 . therefore , the finishing media 28 can be densely packed within the finishing device 24 to achieve maximum efficiencies . the system 10 conveys plt fin to one or more containers 30 suitable for transfusion or long term storage . the container ( s ) 30 intended to store plt fin can be made of polyolefin material ( as disclosed in gajewski et al u . s . pat . no . 4 , 140 , 162 ) or a polyvinyl chloride material plasticized with tri - 2 - ethylhexyl trimellitate ( tehtm ). these materials , when compared to dehp - plasticized polyvinyl chloride materials , have greater gas permeability that is beneficial for platelet storage . the system 10 shown in fig1 can be readily incorporated into a continuous single or double needle on line blood processing systems . as used in this specification , the “ on line blood separation process ” differs from a multiple blood bag process . in a multiple blood bag process , the donor &# 39 ; s circulatory system does not remain in communication with the flow path where separation of the collected blood volume occurs . in a multiple blood bag system , after a given blood volume is collected in the primary bag , the donor &# 39 ; s circulatory system is disconnected from the primary bag before separation occurs within the bag . also , in a multiple blood bag system , the separation processes do not occur continuously . the first stage separation of red blood cells and plasma rich in platelets and the second stage separation of platelets from plasma occur at different points in time as separate , discontiguous steps . various features of the inventions are set forth in the following claims .
blood processing systems and methods establish on line communication between a container and a source of blood containing leukocytes and platelets , such as a human donor . the systems and methods create a centrifugal field between the source of blood and the container that separates from the blood an unfinished suspension of platelets having a first physiologic characteristic different than the desired physiologic characteristic . the systems and methods pump the unfinished platelet suspension outside the centrifugal field through a finishing device . the finishing device changes the first physiologic characteristic to the desired physiological characteristic , thereby creating the finished platelet suspension . the systems and methods convey the finished platelet suspension from the finishing device directly into the container . the systems and methods function without interrupting the on line communication between the container and the source of blood .