Differential conductivity recirculation monitor

An apparatus for determining a degree of recirculation flow of blood in a surgically formed fistula in a patient, the fistula being connected to a blood processing device by an inlet conduit for withdrawing blood from the fistula and delivering the blood to the blood processing device and an outlet conduit for returning blood to the fistula from the blood processing device, comprising:

• an outlet conductivity cell formed in the outlet conduit, the outlet conductivity cell having an upstream connection in fluid communication with the blood processing device, a downstream connection in fluid communication with the fistula and two branches connecting the upstream connection to the downstream connection with a continuous path configuration from the upstream connection to the downstream connection through one of the two branches and returning to the upstream connection through the other one of the two branches;
• an inlet conductivity cell formed in the inlet conduit, the arterial conductivity cell having an upstream connection in fluid communication with the fistula, a downstream connection in fluid communication with the blood processing device and two branches connecting the upstream connection to the downstream connection with a continuous path configuration from the upstream connection to the downstream connection through one of the two branches and returning to the upstream connection through the other one of the two branches;
• a hypodermic needle access site in the inlet conduit located between the upstream connection of the inlet conductivity cell and the blood processing means;
• an exciting electromagnetic coil encircling one of the branches of the outlet conductivity cell at an exciting location and one of the branches of the inlet conductivity cell at the exciting location to induce a first electrical current in blood in the outlet conductivity cell in an electrical direction with respect to the exciting coil and to induce a second electrical current in blood in the inlet conductivity cell in the same electrical direction with respect to the exciting coil as the first electrical current;
• a sensing electromagnetic coil encircling the other one of the branches of the outlet conductivity cell at a sensing location and the other one of the branches of the inlet conductivity cell at the sensing location, the other branches being oriented with the first electrical current and the second electrical current in opposite electrical directions with respect to the sensing coil;
• and
• means electrically connected to the sensing electromagnetic coil for producing a signal representative of the difference between the magnitude of the first electrical current and the magnitude of the second electrical current.

A method for quantitatively determining a degree of recirculation flow of fluids having a physical property within a zone of a vessel into which a first fluid having a first initial value of the physical property is being inserted and from which a second fluid having a second initial value of the physical property is simultaneously being withdrawn, comprising:

• altering the value of the physical property of the first fluid;
• measuring the value of the physical property of the first fluid after the value of the physical property is altered and before the first fluid is inserted into the zone of the vessel;
• measuring the value of the physical property of the second fluid after it is withdrawn from the zone of the vessel;
• and
• comparing the measured altered value of the physical property of the first fluid with the measured value of the physical property of the second fluid to quantitatively determine the degree of recirculation flow in the zone of the vessel.

An apparatus for determining a degree of recirculation flow of fluids having a physical property within a zone of a vessel into which a first fluid having a first initial value of the physical property is being inserted and from which a second fluid having a value of the physical property is simultaneously being withdrawn, comprising:

• means for altering the value of the physical property of the first fluid;
• means for measuring the value of the physical property of the first fluid after the value of the property is altered and before the first fluid is inserted into the zone of the vessel;
• means for measuring the value of the physical property of the second fluid after it is withdrawn from the zone of the vessel;
• and
• means for comparing the measured altered value of the physical property of the first fluid with the measured value of the physical property of the second fluid to quantitatively determine the degree of recirculation flow in the zone of the vessel.