Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
1999-07-02
2001-04-03
Kim, John (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S085000, C210S646000, C073S861000, C073S861050
Reexamination Certificate
active
06210591
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the field of blood treatment or measurement systems, and in particular, to processes for measuring arteriovenous shunt blood flow during hemodialysis.
BACKGROUND OF THE INVENTION
Hemodialysis is a process by which an artificial kidney replaces the function of a patient's kidney. Blood is removed from the patient's vascular system via suitable equipment such as an arterial needle, tube, or line, is passed through a dialyzer and is returned to the patient via a venous needle, tube, or line for normal circulation through the patient's vascular system. A majority of dialysis patients have an arteriovenous shunt implanted to create a location having a high blood flow that simplifies the withdrawal of blood through a line connected to the part of the shunt that is closer to the arterial side of the shunt and the return of purified blood through a line connected to the shunt downstream of the withdrawal site, closer to venous side of the shunt. In some cases the shunt clots or stenoses with the resulting reduction in blood flow necessitates surgery that is costly and invasive for the patient. If there is low blood flow in the shunt or any other problem with the venous outflow, some part of the freshly dialyzed blood from the venous return line flows directly to the arterial withdrawal line where it is again filtered. This access recirculation is a well-known problem during hemodialysis, and if such undesired direct recirculation is at a high enough level, some amount of blood is repeatedly refiltered so that the rest of the patient's blood is not sufficiently filtered for adequate dialysis.
One method of measuring shunt blood flow currently uses color coded duplex sonography. This is very expensive and involves operation by highly qualified professionals. Measurements are therefore made only rarely, so that the onset of reduced flow is not detected at a time when the problem can be corrected without surgery.
The standard test for undesired direct recirculation requires three blood samples while the patient is on dialysis. This method requires blood samples from the patient, time from the nurses, and high laboratory costs. Since dialysis patients generally have lower hematocrit than the normal population and are at greater risk from losing blood, this test is not very satisfactory.
Another technique for measuring access recirculation involves introducing an indicator, such as a saline solution, into the venous line and recording changes of blood properties due to the presence of the indicator in the arterial line. The problem with this technique is that the indicator can reenter the arterial line by two pathways: directly by the access shunt (“shunt recirculation”) and by way of the patient's cardiopulmonary pathway. Existing technologies cannot separate shunt recirculation from cardiopulmonary recirculation (CPR). This can led to a false diagnosis of shunt recirculation in cases where only CPR is present.
SUMMARY OF THE INVENTION
The present invention avoids the problem encountered with previous methods and techniques by providing an accurate determination of shunt blood flow and recirculation at lower cost. In particular, it provides methods and techniques for identifying access recirculation with high specificity so as to permit accurate measurement of undesirable shunt in the presence of normal (and desirable) cardiopulmonary recirculation.
Briefly stated, a device for determining shunt flow in a hemodialysis shunt connected between two points in a cardiovascular-hemodialysis system includes a flow sensor connected to either the hemodialysis inflow (arterial) line or the outflow (venous) line. An indicator is preferably introduced into the system that is sensed by first and second sensors that are spaced apart and disposed effective for sensing the indicator at two locations in the cardiovascular-hemodialysis system. Natural indicators produced by the body, such as density variations in the blood caused by rhythmic breathing, are optionally used instead of an introduced indicator. A detector connected to the flow sensor and the first and second sensors determines, at a first flow rate, a first time a first indicator takes to move between the two locations, and at a second flow rate, a second time a second indicator takes to move between the two locations. The shunt flow is then calculated from the first and second times and the first and second flow rates.
According to an embodiment of the invention, a method for determining shunt flow in a shunt connected between first and second points in a circulating system includes the steps of:
a) establishing a first flow rate in the circulating system,
b) measuring, during the first flow rate, a first time a first indicator takes to move between a first location and a second location, the first and second locations being within the shunt,
c) establishing a second flow rate in the circulating system,
d) measuring, during the second flow rate, a second time a second indicator takes to move between the first location and the second location, and
e) calculating the shunt flow from the first and second times and the first and second flow rates.
According to an embodiment of the invention, a method for determining shunt flow in a shunt connected between first and second points in a circulating system includes the steps of:
a) establishing a first flow rate in the circulating system;
b) determining, during said first flow rate, a first time it takes for an indicator to move from a first location to a second location;
c) establishing a second flow rate in the circulating system;
d) determining, during the second flow rate, a second time it takes for the indicator to move from the first location to the second location; and
e) calculating the shunt flow from the first and second times and the first and second flow rates.
According to an embodiment of the invention, a method for determining shunt flow in a shunt connected between first and second points in a circulating system includes the steps of:
a) establishing a first flow rate in the circulating system,
b) measuring, during the first flow rate, a first time a first indicator takes to move between a first location and a second location, the first location being within the circulating system at a known position, and the second location being in the shunt,
c) establishing a second flow rate in the circulating system,
d) measuring, during the second flow rate, a second time a second indicator takes to move between the first location and the second location, and
e) calculating the shunt flow from the first and second times and the first and second flow rates.
According to an embodiment of the invention, a device for determining shunt flow in a shunt connected between first and second points in a circulating system includes first means for establishing a first flow rate in the circulating system; first means for measuring, during the first flow rate, a first time a first indicator takes to move between a first location and a second location, the first and second locations being within the shunt; second means for establishing a second flow rate in the circulating system; second means for measuring, during the second flow rate, a second time a second indicator takes to move between the first location and the second location; and means for calculating the shunt flow from the first and second times and the first and second flow rates.
According to an embodiment of the invention, a device for determining shunt flow in a shunt connected between first and second points in a circulating system includes first means for establishing a first flow rate in the circulating system; first means for determining, during the first flow rate, a first time it takes for an indicator to move from a first location to a second location; second means for establishing a second flow rate in the circulating system; second means for determining, during the second flow rate, a second time it takes for the indicator to move from the first location to the sec
Harter Secrest & Emery LLP
Kim John
Salai Esq. Stephen B.
Shaw Esq. Brian B.
Transonic Systems Inc.
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