Imperforate bowl: centrifugal separators – With means for filtering
Reexamination Certificate
2001-06-12
2002-10-15
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
With means for filtering
C494S037000, C494S041000
Reexamination Certificate
active
06464624
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to blood processing apparatus having centrifugation bowls for separating blood and other similar fluids. More specifically, the present invention relates to such apparatus with a centrifugation bowl having a rotating filter core for use in recovering a plasma fraction from whole blood.
BACKGROUND OF THE INVENTION
Human blood predominantly includes three types of specialized cells (i.e., red blood cells, white blood cells, and platelets) that are suspended in a complex aqueous solution of proteins and other chemicals called plasma. Although in the past blood transfusions have used whole blood, the current trend is to collect and transfuse only those blood components of fractions required by a particular patient. This approach preserves the available blood supply and in many cases is better for the patient, since the patient is not exposed to unnecessary blood components, especially white blood cells, which can transmit pathogens. Two of the more common blood fractions used in transfusions are red blood cells and plasma. Plasma transfusions, in particular, are often used to replenish depleted coagulation factors. Indeed, in the United States alone, approximately 2 million plasma units are transfused each year. Collected plasma is also pooled for fractionation into its constituent components, including proteins, such as Factor VIII, albumin, immune serum globulin, etc.
Individual blood components, including plasma, can be obtained from units of previously collected whole blood through “bag” centrifugation. With this method, a unit of anti-coagulated whole blood contained in a plastic bag is placed into a lab centrifuge and spun at very high speed, subjecting the blood to many times the force of gravity. This causes the various blood components to separate into layers according to their densities. In particular, the more dense components, such as red blood cells, separate from the less dense components, such as white blood cells and plasma. Each of the blood components may then be expressed from the bag and individually collected.
U.S. Pat. No. 4,871,462 discloses another method for separating blood. In particular, a filter includes a stationary cylindrical container that houses a rotatable, cylindrical filter membrane. The container and the membrane are configured so as to define only a narrow gap between the side wall of the container and the filter membrane. Blood is then introduced into this narrow gap. Rotation of the inner filter membrane at sufficient speed generates what are known as Taylor vortices in the fluid. The presence of Taylor vortices basically causes shear forces that drive plasma through the membrane and sweep red blood cells away.
Specific blood components may also be obtained through a process called apheresis in which whole blood is transported directly from the donor to a blood processing machine that includes an enclosed, rotating centrifuge bowl for separation of the blood. With this method, only the desired blood component is collected. The remaining components are returned directly to the donor, often allowing greater volumes of the desired component to be collected. For example, with plasmapheresis, whole blood from the donor is transported to the bowl where it is separated into its constituent components. The plasma is then removed from the bowl and transported to a separate collection bag, while the other components (e.g., red blood cells and white blood cells) are returned directly to the donor.
FIG. 1
is a block diagram of a plasmapheresis system
100
with an added filtration step. The system
100
includes a disposable harness
102
that is loaded onto a blood processing machine
104
. The harness
102
includes a phlebotomy needle
106
for withdrawing blood from a donor's arm
108
, a container of anti-coagulant solution
110
, a temporary red blood cell (RBC) storage bag
112
, a centrifugation bowl
114
, a primary plasma collection bag
116
and a final plasma collection bag
118
. An inlet line
120
couples the phlebotomy needle
106
to an inlet port
122
of the bowl
114
, and an outlet line
124
couples an outlet port
126
of the bowl
114
to the primary plasma collection bag
116
. The blood processing machine
104
includes a controller
130
, a motor
132
, a centrifuge chuck
134
, and two peristaltic pumps
136
and
138
. The controller
130
is operably coupled to the two pumps
136
and
138
, and to the motor
132
, which, in turn, drives the chuck
134
.
In operation, the inlet line
120
is fed through the first peristaltic pump
136
and a feed line
140
from the anti-coagulant
110
, which is coupled to the inlet line
120
, is fed through the second peristaltic pump
138
. The centrifugation bowl
114
is also inserted into the chuck
134
. The phlebotomy needle
106
is then inserted into the donor's arm
108
and the controller
130
activates the peristaltic pumps
136
,
138
, thereby mixing anti-coagulant with whole blood from the donor, and transporting anti-coagulated whole blood through inlet line
120
and into the centrifugation bowl
114
. Controller
130
also activates the motor
132
to rotates the bowl
114
via the chuck
134
at high speed. Rotation of the bowl
114
causes the whole blood to separate into discrete layers by density. In particular, the denser red blood cells accumulate at the periphery of the bowl
114
while the less dense plasma forms an annular ring-shaped layer inside of the red blood cells. The plasma is then forced through an effluent port (not shown) of the bowl
114
and is discharged from the bowl's outlet port
126
. From here, the plasma is transported by the outlet line
124
to the primary plasma collection bag
116
.
When all the plasma has been removed and the bowl
114
is full of RBCs, it is typically stopped and first pump
136
is reversed to transport the RBCs from the bowl
114
to the temporary RBC collection bag
112
. Once the bowl
114
is emptied, the collection and separation of whole blood from the donor is resumed. At the end of the process, the RBCs in the bowl
114
and in the temporary RBC collection bag
112
are returned to the donor through the phlebotomy needle
106
. The primary plasma collection bag
116
, which is now full of plasma, may be removed from the harness
102
and shipped to a blood bank or hospital for subsequent transfusion.
Despite the system's generally high separation efficiency, the collected plasma can nonetheless contain some residual blood cells. For example, in a disposable harness utilizing a blow-molded centrifuge bowl from Haemonetics Corporation, the collected plasma typically contains from 0.1 to 30 white blood cells and from 5,000 to 50,000 platelets per micro-liter. This is due, at least in part, to the 8000 rpm rotational limit of the bowl
114
and the need to keep the bowl's filling rate in excess of 60 milliliters per minute (ml/min.) to minimize the collection time, causing slight re-mixing of blood components within the bowl. Furthermore, many countries continue to reduce the permissible level of white blood cells and other residual cells that may be present in their supply of blood components.
Discussion of System Not Found in the Prior Art
It has been suggested to install one or more filters, such as filter
142
, to remove residual cells from the collected plasma in a manner similar to the filtration of collected platelets. Filter
142
may be disposed in a secondary outlet line
144
that couples the primary and final plasma collection bags
116
,
118
together. After plasma has been collected in the primary plasma bag
116
, a check valve (not shown) may be opened allowing plasma to flow through the secondary outlet line
144
, the filter
142
, and into the final plasma collection bag
118
.
Although it may produce a “purer” plasma product, the disposable plasmapheresis harness including a separate filter element is disadvantageous for several reasons. In particular, the addition of a filter and another plasma collection bag increase t
Bromberg & Sunstein LLP
Cooley Charles E.
Haemonetics Corporation
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