CA2083544A1 - Expressor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An expressor for varying the amount of fluid in a variable-volume container connected to at least one conduit includes a housing defining an enclosed chamber which can accommodate the container. The housing has at least one opening through which a conduit can extend. A pressure regulating mechanism is coupled to the housing to vary the pressure of fluid in the chamber and thereby vary the volume of the container.

Description

AUTOMATIC EXPRESSOR

FIELD OF THE INVENTION
The present invention relates to a system for expressing fluids from a fluid container, and more particularly to an apparatus for expressing fluids from a container using a pressurized housing. ~;

BACKGROUND OF THE INVENTION
Whole blood is rarely administered to patients.
Rather, patients needing red blood cells are given packed red cells (PRC), patients needing platelets are given platelet concentrate (PC), and patients needing plasma are given plasma. For this reason, the separa-tion of blood into components has substantial thera-peutic and monetary value.
The separation of a single unit of donated ~hole blood into its components is typically accomplished by use of differential sedimentation using centrifuga-tion, as is well known to thvse skilled in the art.
A typical procedure used in the United States utilizes ~O a series of steps to separate donated blood into three co~ponents, each component having substantial thera-peutic and monetary valueO The procedure typically utilizes a blood collectio~ bag whic.h is integrally attached via flexible tubing to at l~ast one, ~nd preferably two or more, satellite bags. Using cen trifugation, whole blood may be separated by differen- :~
tial sedimentation into such valuable blood components as plasma, packed red cells (PRC), platelet-rich plasma (P~P), and platelet concentrate (PC).
A typical blood processing procedure may include the following:
(1) The donated whole blood is collected fro~
the donor's vein directly into the blood collect:ion bag which contains a nutrient and anti-coagulant fluid.

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12) The blood collection bag, together with its sat~llite bags, are placed in a centrifuge bucket.
The centrifuge bucket is then placed in the centri~
fuge. The centrifuge bucket, blood collection bag, and satellite bags are centrifuged together at a slow speed (~Isoft-spin~l centrifugation). Red cells are heavier than other components of the blood. The centr;fugal force of the centrifuge concentrates red cells as packed red cells ~PRC3 in a lower portion, i.e.r the sediment layer~ of the blood collection bag.
The PRC fluid is bright red in color. The volume of the PRC fluid varies considerably depending on the number of red cells contained in the drawn whole blood (typically 37 54 percent by volume~. A suspension of platelets in cl~ar plasma, known as platelet-rich plasma (PRP) remains in the upper portion, i.e., the supernatant layer of the ~lood collection bag. The PRP ~luid is light yellow in color. The interface between the supernatant PRP layer and the sPdi~ent PRC
layer is kno~n as the buffy coat inter~ace. The location o~ the buffy coat interface can be determined by a ~isual insp~ction of the blood collection bag.
This int~r~ace is seen as the point where the light yellow PRP ~luid merges with the bright red PRC fluid.
(3) After centri~ugation, the blood collection bag is trans~erred~ with care not to disturb the buffy coat interface, into a device known as an expressor.
A typical expressor is ~ormed by a front and a back plate which are hinged together ~t their lower ends and spring biased toward each other. The blood collection bag is placed between the plates. The spring is released, and the plates are forced togeth~
er, compressing the blood collection bag. A valve or clamp in the flexible tubing is opened, and the fluid is squee~ed out of the blood collection bag by the 40027/mht/ves -2-, .

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expressor. The supernatant PRP layer is positioned at the top of the blood collection bag, an<l is therefore the f irst f luid to flow out of the collection bag .
The supernatant PRP fluid flows into a f.irst satellite bag.
An alternative means o~ expressing the fluid is a pressure cuf f . The pressure cuff is constructed similar to a blood pres~3ure cuff commonly used to determine a patient ' s blood pressure. The pressure cuf~ is wrapped around the blood collection hag. As the pressure cu~f is inf lated, *he pressure cuf f expands and bears against the collection bag, express-ing the blood from the collection bag. Gravity may also be used to express the f luid :erom the blood 15 collection bag.
As the PRP flows out of the blood collection bag, the }:uffy coat interface with the PRC rises. The operator clo~;ely o~serves the position of the buffy coat interface as it rises and clamps off the connect-2 0 ing tube when in his judgment as much PRP has beentransferred as is possi~le, without allowing red cells to enter the first satellite bag. This is a labor intensive and time consuming operation during which the opera~or must visually monitor the bag and judli-ciou~ly and arbi$rarily ascertain when to shut-off the connecting tube.
The blood collection bay, now containing only PRC, may be detached and stored until required for transfusion into a patient. Alternatively, a valve or seal in the tubing may be opened so that the PRC may be transferred to a second satellite bag by means of the expressor.
~ 43 The PRP-containing satellite bag and another satellite bag are then removed from tha expressor and centrifuged at an elevated G force (high speed or 40027/mht/ves -3- ;

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"hard-spin" centrifug~tion) with the time and speed adjusted so as to concentrate the platelets into the lower portion of the PRP bag. When centrifugation is complete, the PRP bag contains sediment platelet layer 5 (light yellow in color) in its lower portion and supernatant clear plasma layer in its upper portion~
(5~ The PRP bag is then placed in the e~pressor, ~nd ~ost oP the clear plasma is expressed into a satellite bag, leaving the PRP bag containing only the sediment platelet layer and a small amount of residual plasma. In a subsequent step, the sedimented platelet fluid may be processed to make platelet concentrate (PC~O ~he PRP bag, now containing a PC product, is then detached and stored until needed for a transfu-sion of platelets. For use with adult patients, th~platelet~ from 4-8 donors may be pooled into a ~ingle platelet transfusion.
(6) The plasma in the satellite bag may itself be transfused into a patient, or the plasma may be separated by complex processes into a varie*y of valuable products.
In the above described procedures it is important to determine where the supernatant PRP fraction ends and the sediment PRC fraction b~gin~. In separating the PRC and P~P fractions (e.g., step 3 above), blood bank personnel have attempted to ensure that the entire P~P fraction is recovered. This has often proved to ~e counterproductive since ~he PRP fraction may become contaminated by red cells ~rom the buffy .30 coat interface or the PRC fraction - giving a pink or red color to the normally light yellow PC. The presence of red cells in PC is so highly undesirable that pink or red PC is frequently discarded, or subjected to re-centrifugation, both o~ which increase operating costs and are labor intensive. As a result, 40027/mhtlves -4-$ ~

blood bank personnel must err on the side of caution carefully observing the buffy coat interface and by stopping the flow of PRP before it has been fully expressed. Although the PRP is Imcontaminated, valuable unexpressed plasma may be wasted.
Conventional expressors used in the above-de-scribed procedures have ~any drawbacks. For example, they apply an uneven pressure to the blood collection bag and may create wrinkles and folds in the bags.
Blood products become trapped in these wrinkles and folds, preventing ~00~ of the fluid from being ex-pressed. Uneven pressure also tends to disturb the bu~fy coat interfaca and reduce the amount of PRP
which can bP reliably collected. Additionally, because the bag may be distorted and because the structure of convention expressors can hinder observa~
tion of the container, lt is very difficult to watch the buffy coat interface level to determine wh~n to terminate ~he flow of the PRP ~raction.
Further, in some applîcations, it is desirable to draw fluid into a container. For example, after a supernat~nt PRP layer has been expressed from a collection bag, it may bs desirable to draw an addi-tive solution into t~e collection bag and add it to the remaining PRC layer. However, conventional expressors are merely capable o~ squeezing a contain-er. So while they can force fluid out o~ the contain-er, they are unable to draw fluid into the container~
SUMMARY OF THE INVENTION
The object of the present invention is to allevi~
ate the above-mentioned disadvantages by offeriny reliable, economical, and easy-to operate mechanism for expressing fluid from a container such as a collection bag. Other objects of the invention include allowing for easy detection and observation of 40027/mht/ves -5-.: - , , . . : . . .

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. the buffy coat interface, minimizing the disturbance of the buffy ooat interface as fluid is expressed from the container, applying an even pressure to the container, eliminating the formation of wrinkles and folds in the flexible bag while it is being expressed, ~aximizing the expression of fluid from the container and allowing fluid to be drawn into as well ~5 forced out of the container.
Accordingly, the present invention provides an expressor for varying the amount of fluid in a vari-able-volume fluid container connected to at least one conduit. The expressor comprises a housing defining an enclosed chamber which can accommodate the contain-er, the housing having at least one opening through which the conduit can extend, and a pressure regulat-ing mechanism coupled to the housing to vary the pressure of a fluid in the chamber and thereby vary the volume of the fluid container.
In preferred embodiments, the pressure regulating mechanism supplies and/or withdraws ambient air to and/or from ~he housing to vary the pressure on the fluid container within the chamber. If fluid is to be expressed from the fluid container, the pressure regulating ~echanism increase~ the air pressure in the housing to a level above the pressure of the fluid in the container. If fluid is to be drawn into the fluid container, the pressure regulating mechanism decreases the air pressure in the housing to a level below the pressure of the fluid in the container.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a first embodi-ment of an expressor according to the present inven tion.
Figures 2A is a side viewr Figure 2B is a bottom 40027fmht/ves -6-. ~ . , . , -.
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view, and Figure 2C is a side view fro~ another angle of a latch for the housing of the embodiment of Figure 1.
Figure 3 is an enlarged perspective view of the housing of the embodiment of Figur~
Figure 4 i5 a block diagram of the embodiment of Figure 1.
Pigure 5 is a partially cross-sectional side elevation of a second embodiment of an expressor according to the present invention.
Figure 6 is a top view of the embodiment of Figure 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
An expressor embodying the invention may be used to ~acilitate the operation of many types of fluid processing systems. For exa~ple, the expressor may be coupled to one or more interconnected sterile blood collection bags and used to transport fluid from one bag to ~nother. Alternatively, thP exprei~sor may ~e coupled to a bag containing a therapeutic or medical solution and be used to administer the solution to a patient via an aidministration se~. ~n particular, the expressor may ~e used to process a biological fluid where ~iologiaal fluid refers to any treated or untreated ~luid associated with livi~g organisms~
especially blood, including whole blood, warm or cold blood, stored or fresh blood, treated blood t such as blood diluted with a physiological solution including salina, nutrient, and/or anticoagulant ~iolutions, one or more blood ~o~ponents, such as PC, PRP, platelet-free plasma, platelet-poor plasma, plasma, PRC,- or bu~fy coat, analogous blood products derived from blood or a blood component or from bone marrow, and similar b.iological fluids obtained by other means and 40027/mht/ves -7-"
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with similar properties to the fluids described above.
As shown in Figure 1, an exemplary expressor embodying the present invention comprises a housing 10 which define~ an enclosed cha~ber 11 and a pressure regulating mechanism 30 coupled to the housing 10 by a flexible hose 31 or other conduit to vary the pressure within the chamber 11. A variable-volume fluid container 25, such as a flexible bag containing a biological fluid, may be placed in the chamber 11 with a conduit 26 extending from the fluid container 25 through an opening 17 in the housing 10 to the exterior of the housing 10. The fluid container 25 need not be flexible, but it preferably is constructed so that its internal volume can be varied by control-ling the fluid pressure applied to the outside surfaceof the container 25. The pressure regulating mecha-nism 30 supplies and/or withdraws a fluid (i.e., either a gas or a liquid~ to and/or from the chamber 11 in order to vary the pressure exerted on the container within the chamber 11. This, in turn, varies the volume of th~ fluid container 25 and thereby forces fluid (i.e., either a liquid or a gas) out of or into the fluid container 25 through the ~onduit 26.
~e housing 10 may be formed from any suitable material which has sufficient structural integrity to withstand the di~ferences in pressure between the chamber 11 and the exterior~o~ the housing 10. The housing 10 may have a variety o~ configurations. For example, in the expressor shown in Figure 1, the housing 10 is a parallelepiped and compris~s a base 12 and a cover 13 which may be releasably mountPd to the base 12 in any suitable manner to form the chamber 11 and envelop the container 25.
In the exemplary expressor, the cover 13 is 40027/mht/ves -8-: , ~

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releasably mounted to the base 1~ by means of hinges 14 on one side of the base 12 and cover 13 and at least one and preferably two latches 15 on the other side. Although the latches may be con~igured in a variety of ways, they are preferably arranged to egualize the pressure between the chamber 11 and the exterior of the housing 10 before the cvver 13 is completely released from the base 12. This prevents the cover 13 from suddenly and forcefully opening when th~ chamber 11 is at a higher pressure than the exterior of the housing 10.
In the embodiment of Fi~ure 1, each latch 15 is rotatably mounted on the base 12 and is designed to engage with a corresponding pin 1~ mounted on the cover 13. Figures 2A - 2C illustrate the structure of one of the latches 15 in detailO As shown in these figures~ the latch 15 has a generally disk-shaped base 15a from the top surface of which extend lugs 15b by which the latch 15 can be grasped. As ~hown in Figure 2B, the bottom surface of the base lSa has a track 15c ~ormed therein for receiving a correspondin~ pin 16, the track 15c lying betwe~n an inner cam surface 15d and an outer ¢am surface lSe. ~ pin groove lSf is formed in tha wall of thP base 15a between the track 25 15c and the outside of the base 15a. The latch 15 may be biased, e.g., by a spring, so that the pin groo~e 15f is normally in position to receive the pin 16.
Once the pin 16 enters the latch 15 through the pin groove 15f, it settles into the track 15c between the cam surfaces 15e and 15d. As the latch lS is rotated to close the cover 13 on the base 12, the pin 16 rides along the outer cam sur~ace 15e, which is eccentric to the center of rotation of the latch 15. Thi~ pulls the pin 16 toward the center of rotation and tightens the cover 13 against the base 12. A stop (not shown) 400271mht/ves -9-3 ~ : :

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may b~ provided, for example, 180 from the pin groove 15f, to lock the pin 16 in place once the cover 13 is properly s~aled to the base 12.
To remove the cover 13 from the base 12, the latch 15 is ~gain rotated. If the pressure within the chamber 11 is higher than the pressure e:xterior to the housing 10~ the pin 16 will again ride along the outer c~m surface 15e. This allow~ the pin 16 to move away from the center of rotation of the latch 15 while the 10 pin 16 is maintained within ~he track 15c between the cam surfaces 15d and 15e~ Thus, the cover 13 may separate somewhat from the base 12, equalizing the pressure in the chamber 11 and the pressure exterior to the housing 10, while the latch 15 remains engaged with the pin 16, preventing the cover 13 from flying open.
On the other hand, the pres~ure in the chamber 11 may be less than the pressure exterior to ~he housing 10. Thent as the latch 15 is rotated to open the cover 13, the pin 16 will ride in the track 15a along the inner cam surface 15d, which is also eccentric to the center of rotation of the latch 15. This force~
the pin 16 away from the center of rotation, jacking the cover 13 off of the base 12 a distance sufficient to egualize the pre~sure in the chamber 11 and the pressure exterior to the housing 10.
To maintain a press~re differential between the chamber 11 and the exterior of the housing 10, the expressor preferably includes a sealing mechanism between the base 1~ and the cover 13. For example, the sealing mechanism may include an elastomeric gasket l8, which may be disposed along the cover- 13 where it interfaces with the base 12. The conduit opening 17 is preferably disposed so that the gasket 18 will create an air-tight seal around the conduit 26 40027/mht/ves -10 , - ~ .

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as the cover 13 is sealed to the base 12. In the illustrated expressor only one conduit opening 17 is shown and it is disposed between the cover 13 and the base 12~ Alternatively, the housing m'ay have two or more openings to accommodate a plurality of conduitsO
For example, first and second openings on opposite sides of the housing could acco~msdate conduits extending from opposite ends of the fluid container.
Further, the openings on the housing miay be disposed other than between the cover and the base, and an additional seal, such as an O-ring, ~ay be used to seal the conduit to the housing.
The housing also preferably in~ludes a transpar-ent portion positioned to permit o~servation of the fluid container. For example, the transparent portion may be a window 19 in the cover 13. Alternatively, the entire housing by be formed from a transparent material such as a transparent plastic.
The housing 10 may further include a structure æuitable for adjusting the orientation of the cha~ber 11. For example, the housing o~ the illustrated embodiment includes an adjustable leg 20 at each corner, and the legs 20 may be adjusted to orient the housing 11 in a hori~ontal position or in any desired tilted position. For example, it may be preferable to express air from the fluid container before any liquid is expressed. Consequently, as shown in Figure 3, the legs 20 may be adjusted to tilt the chamber 11 so that the end of the fluid container 25 which communicates with the ronduit 26 is higher than the opposite end of the container 25. One or more hooks 21 may be mounted inside the chamber 11 at the same end as the conduit opening 17 and~or at the end opposite from the conduit opening 17 to support the fluid container 25 when the housing 10 is tilted as shown in Figure 3. Further, 40027/mht/ves - ~ ~ . ................... ..

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the housing 11 may be stood on the encl opposite the conduit opening 17 or hung from either end when it is preferred to orient the housing in a vertical posi~
tion. :;
The pres~ure regulating machanism 30 may include any suitable pumping device 32 for supplyin~ a fluid (i.e., either a liquid or a gas~ ~o the chamber 11 o~
the housing 10 to elevate the pressure in the chamber 11 above the pressure within the container 25. In a preferred embodiment, the pumping device 32 is also capable of evacuating fluid from the chamber 11 to ~:
lower the pressure in the chamber 11 below the pres-sure within ~he container 25. By raising the pressure within the chamber 11, the volume of the fluid aon-tainer 25 may be reduced and fluid (i.e., either a gas or a liquid) may be expressed from the fluid contain-er4 By lowering the pressure in the chamber 11, the -~
volume o~ the ~luid container 25 may be increased and fluid (i.e., either a gas or a liquid) may be drawn into the fluid container 25. The chamber ~1 may be sized to limit expansion of the container 25 and thereby prevent the container from leaking or burst-ing. The absolute Yalue o~ the differe~ce between the chamber pressure and the pressure exterior to the housing ~ay be relatively small~ ~uch as less than about 15 PSID. .
Although the fluid ~upplied to and/or withdrawn ~rom the chamber by the pressure regulatin~ mechanism 30 may be a gas or a liquid, in a preferred embodi-ment, the fluid is ambient air. Air is convenient to ~andle and is readily availa~le. Further, the air need not be sterile since it does not communicate wlth the interior of the fluid container 25. Devices for supplying and/or evacuating air from the chamber 11 are readily available. ~he suction and air pressure 40027/mht/ves -12 .~ .

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lines commonly available in many laboratories may also be used to avacuate or pressurize the housing.
In the example illustrated in :Figure 4, the pumping device 32 is elPctrically operated and re ceives electrical power from an unillustrated power supply via a plug 33 connQcted to the pumping device 32 through a fuse 34 and a power switch 35 which can be opened and closed to switch the pumping device 32 on and off~ An indicator light 36 may be connected to the power line so as to be illuminated when the power switch 35 is closed. The pumping device 32 may be connected to the hose 31 ~y a valve 37, which can be switched between a position in which the pumping device communicates with the hose 31 and a position in which the pumping device communicates with a vent 38.
A pressure relief valve 39 may be disposed between the pumping device and the housing 10 to prevent pressuxe within the chamber 11 of the housing 10 from being greater than or less than a predetermined level. A
pressure gauge 40 may be provided to visually indicate the current pressure in the chamber 11. Further, a control mechanism (not shown~ may be coupled to the pumping device to increase or decrease the pressure b~
a predetermined amount or rate or to maintain the pressure at a predetermined level.
Th~ pressure regulating mechanism 30 and the housing 11 need not be coupled in the manner shown in Figure 1~ Figures 5 and 6 illustrate a second embodi-ment of the present invention in which a housing 10 and a pressure regulating mechanism 60 are configured as a single unit. The housing 10 of this embodiment is substantially identical to that of the previous embodiment, although the adjustable leys 20 may be omitted. The pressure regulating mechanism 60 in-cludes a casing 61 having a support surface 62 which 40027/mht/ves -13-; .:,,, :. ., -:
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supports the housing 10 vertically. Although the support surface ~2 is shown vertically fixed~ it may be arranged to swing through a variety of angles and support the housing at any suitable angle from verti-cal through horizontal. The housing 10 can be perma-nently or detachably connected to the support surface 62 in any suitable Manner. In the illust:rated embodi ~ent, the housing 10 is pivotably mounted on the support surface 62 by means of a swivel mount 63 comprising a bearing 63a secured to the support surface 62 and a hollow shaft 63b secured to the bottom surface of the housing 10 and rotatably sup~
ported by the bearing 63a. A stop (not shown) ~ay be arranged to lock the housing in place once it has been swiveled to an appropriate position.
A pumping device 64 similar to the pumping device 32 of the first embodiment may be disposed inside the casing 61 and connected by a conduit, ~uch as a hose 65~ to the inside of the housing 10 and to a pre~sure 20 gauge 66 mounted on the casing 61. The hose 65 can pas~ through the center of the hollow shaft 63b and connect to the housing 10 via a suitable ~itting so that the housing can pivot about the axis of the pipe 63b without disturbing the hose 65. As shown in Figure 6, controls and indicators for the pumping device 64 can he installed in the upper surface of the casing 61 for eas~ of use and observation. If agita-tion of the fluid in the container is desirable, a motor may be coupled to the housing in any suitable manner. For example, a motor 66 may be connected to the shaft 63b in order to oscillate the housing lO
axially along or circumferentially about the shaft 63b, thereby agitating the fluid in the container in the housing.
3S In a preferred mode of operation, the container 40027lmht/ves -14-.
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25, such as a flexible bag containing a biological fluid, is mounted to the base 12 of the housing 10 with the conduit 26 extending through the opening 17.
The cover 13 is then sealed to the base 12 so that the container 25 is completely enclosed within and envel-oped by the housing 10. The housing 10 is then oriented in a desired direction. For example, if the container 25 contains whole blood which ha~ been centrifuged to ~orm sediment and supernatant layers, the housing 10 is preferably oriented vertically~ The conduit 26 may extend through the housing ~.0 from the lower end of the container 25, where the conduit 26 communicates directly with the sediment layer~ or the conduit Z6 may extend through the housing 10 rom the upper end of the container 25, where the conduit 26 communicates directly with any air in the container 25 or with the supernatant layer.
With the housing 10 suitably orientedl fluid may be forced from or into the contai~er 25 by supplying or withdrawing fluid from the chamber 11 of the housing 10 by means of the pressure regulating mecha-nism 30,60. For example, the pressure regulating mechanism 30,60 may ~upply ambient air into the chamber 11, increasing the pressure on the container 25. If the conduit ~6 extends from the upper end of the container 25, the increase in pressure wi~hin the chamber 11 will first force any air and then the supernatant layer from the container 25 via the conduit 26. The interface between the supernatant layer and the sediment layer may be observed through the window 19 and it will rise as the supernatant layer is expressed from the container 25. Because it is frequently desirable to prevent the sediment layer from following the supernatant layer through the conduit 26 r the pressurized fluid in the chamber 11 40027/mht/ves -15-. . ,, ~ ~ . : ,: :

, ;, : : ,: , . - ., may be vented once the interface reaches the conduit 26/ terminating flow through the conduit 17.
The fluid pressure inside the chamber 11 of an e~pressor embodying the present invention will be substantially uniform throughout the chamber 11, ~o the outer surface of thP fluid container 25 will be exposed to substantially uniform pressure. As a rasult, the fluid container 25 will be subjected to much less wrinkling, folding, or other forms of distortion than in conventional mechanioal expressor6 or pressure cuffs. Because the fluid container 25 develops fewer wrinkles or folds and hecause fluid pressure is applied to the entire external surface of the fluid container 25, substantially all of the ~luid in the fluid container 25 can be expressed from the container 25 rather than trapped in the folds and wrinkles. In addition, when the fluid container 25 contains centrifuged bl~od, the uniform external pressure applied to the fluid container 25 tends not to disturb the buffy coat interfaceO ~urther, the smaller amount of distortion of the fluid container 25 due to th~ uniform pressure and the absence of any structure such as a pressure cuff which can obstruct the view of an operator makes it much easier for the operator to visually dete~mine the location of the buffy coat interface and to accurately control the transfer of fluid from the fluid container 25.

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Claims (9)

1. An expressor for varying the amount of fluid in a variable-volume container connected to at least one conduit, the expressor comprising:
a housing defining an enclosed chamber which can accommodate the container, the housing having at least one opening through which the conduit can extend, and a pressure regulating mechanism coupled to the housing to vary the pressure of fluid in the chamber and thereby vary the volume of the container.

2. The expressor of claim 1 further comprising a swivel arrangement mounted to the housing and arranged to allow the housing to swivel about an axis.

3. The expressor of claim 1 wherein the housing includes a base and a cover mounted to the base.

4. The expressor of claim 3 wherein the housing further includes a seal which seals the cover to the base.

5. The expressor of claim 3 wherein the opening is formed between the cover and the base.

6. The expressor of claim 1 wherein the housing includes at least first and second openings oppositely disposed in the housing, each opening being adapted to accommodate a conduit.

7. The expressor of claim 1 wherein the housing includes a transparent portion which is positioned to allow observation of the container.

8. The expressor of claim 1 further comprising a motor coupled to the housing to agitate fluid in the container.

9. A method for processing a biological fluid comprising:
positioning a variable-volume container of biological fluid in an enclosed chamber with at least one conduit extending from the container to the exterior of the chamber; and varying the pressure within the chamber which is exerted on the container to vary the volume of the container and thereby force fluid out of or draw fluid into the container via the conduit.