Patent Description:
During hemodialysis, impurities and toxins are removed from the blood of a patient by drawing the blood out of the patient through a blood access site, typically via a catheter, and then passing the blood through an artificial kidney (often referred to as a "dialyzer"). The artificial kidney includes a semi-permeable membrane that separates a first conduit from a second conduit. Generally, a dialysis solution (often referred to as a "dialysate") flows through the first conduit of the dialyzer while the patient's blood flows through the second conduit of the dialyzer, causing impurities and toxins to be transferred from the blood to the dialysate through the semi-permeable membrane. The impurities and toxins can, for example, be removed from the blood by a diffusion process. After passing through the dialyzer, the purified blood is then returned to the patient.

Maintaining a substantially constant concentration of sodium in the patient's blood throughout the hemodialysis treatment can help to reduce or prevent discomfort experienced by the patient. Therefore, sodium concentrations in the patient's blood and in the dialysate can be monitored during hemodialysis treatment.

<CIT> describes an electrical sensor for sensing electromagnetic properties of process fluids in a dialysis machine or a similar medical device can include a probe for interfacing with the fluids that is made from electronic fabric materials. The electronic fabric probe can include one or more conductors embedded in a non-conductive fabric layer. The electronic fabric probe is accommodated an enclosure which establishes a flow path with respect to the probe to establish fluid contact between the process fluids and the conductors. The conductors can apply or sense current and/or voltage with respect to the fluid. A portion of the electronic fabric probe can be disposed externally of the enclosure to provide electronic communication externally of the enclosure.

<CIT> describes device for measuring the pressure of a medium. The device includes a measuring chamber through which the medium can flow and which has at least one elastically deformable wall, at least one wall that is more rigid by comparison to said first wall, and an inlet and outlet for the medium. At least one excitation electrode is provided in or on the at least one more rigid wall of the measuring chamber, and at least one signal electrode is provided on the elastically deformable wall for impedance measurement.

<CIT> describes a flow-through conductivity cell.

<CIT> describes a method of flushing a dialyzer with a flushing liquid, wherein the dialyzer is arranged in a dialysate-side circuit of a blood treatment device and wherein the dialyzer has at least one dialysate-side chamber which has at least one inlet and at least one outlet for the flushing liquid and which is flowed through by the flushing liquid, wherein at least one property of the flushing liquid is measured at the outlet of the dialyzer or downstream of the dialyzer in the dialysate-side circuit to obtain one or more outlet-side measured values, wherein the property depends on the quantity of the air in the flushing liquid.

According to the invention, a device and method for measuring conductivity of a fluid is provided as defined in the appended claims.

Implementations of the present disclosure are directed to a disposable device for measuring electrical characteristics of medical fluids, such as blood in dialysis systems. The device has a configuration that directs bubbles in the fluid away from electrodes that measure the electrical characteristics of the fluid.

Implementations of the present disclosure provide one or more of the following technical advantages and/or technical improvements over previously available solutions. The implementations allow monitoring fluid parameters (e.g., concentration, fluid elements, etc.) of a medical fluid by measuring electrical characteristics of the fluid. For example, a dialysate should have a conductivity that indicates that a certain amount and ratio of sodium bicarbonate is present, because an imbalance could impact the health of the patient and cause discomfort. The present implementations provide a contactless sensor that can measure conductivity of the dialysate without making direct contact (e.g., via electrodes) with the patient's body.

The implementations include a pre-calibrated and disposable data collecting cell that collects data of the fluid's electrical characteristics (e.g., electrical voltage). The pre-calibrated cell eliminates a need to calibrate the cell for each use, which makes it easier for an unsophisticated patient to use the cell at home and without assistance of a medical staff. For example, a patient may insert or attach the cell to a dialysis system to monitor their blood parameters and adjust the dialysis system accordingly without being worried about calibrating the cell before use. In addition, the cell can be very light weighted and substantially small, which makes it easy to carry, store, and use. Further, the cell is designed to improve accuracy in measuring the fluid's electrical characteristics by directing gas (e.g., air) bubbles away from the cell's electrodes.

Implementations of the present disclosure provide a device that can be used to measure one or more electrical characteristics (e.g., electrical conductivity) of fluids such as blood in dialysis systems. The device has a disposable data collecting cell that can be replaced after a certain number of uses, for example, after every use. The cell includes a chamber with an inlet and an outlet. Fluid enters the chamber through the inlet and flows out of the chamber through the outlet. Multiple electrodes are located within the chamber to measure electrical characteristics of the fluid.

The chamber is designed to direct bubbles within the fluid away from the electrodes. In some implementations, moving along the length of the chamber from the inlet to the outlet, a distance between an upper surface and a lower surface of the chamber varies so that the bubbles would be directed from the lower distance region to the higher distance region. The electrodes can be located at the lower distance region of the chamber. For example, the upper surface of the chamber can be in concave shape and the electrodes can be located away from edges of the concaved upper surface to which the bubbles are directed.

<FIG> depicts an example application of the implementations of the present disclosure. As depicted, a system <NUM> is connected to a patient <NUM>. The system <NUM> can include a dialysis system (e.g., a peritoneal dialysis machine) to dialyze the patient's blood. The system <NUM> includes a data collecting unit <NUM>, and a measurement unit <NUM>.

Patient's blood flows from the patient <NUM>'s body to the data collecting unit <NUM> through a first conduit <NUM>, and flows back from the data collecting unit <NUM> to the patient's body through a second conduit <NUM>. During this process, the data collecting unit <NUM> collects data of the patient's blood. Data collected by the data collecting unit <NUM> is transferred to the measurement unit <NUM> through the communication channel <NUM>. The communication channel can be a wired and/or a wireless channel.

The measurement unit <NUM> includes one or more devices to measure electrical characteristic(s) of the blood based on the data received from the data collecting unit <NUM>. For example, the measurement unit <NUM> can include an impedance analyzer to measure impedance or conductivity of the blood. The measurement unit <NUM> can also include one or more power supplies that generate an electrical current, which is transmitted through the communication channel <NUM> to the data collecting unit <NUM> to excite the blood.

<FIG> shows an example of the system <NUM> of <FIG>. In particular, <FIG> shows an example peritoneal dialysis system <NUM> that can may include the data collecting unit <NUM> and the measurement unit <NUM> described above. The peritoneal dialysis system <NUM> includes a PD machine (also generally referred to as a PD cycler) <NUM> seated on a cart <NUM>. The PD machine <NUM> includes a housing <NUM>, a door <NUM>, and a cassette interface <NUM> that contacts a disposable PD cassette <NUM> when the cassette <NUM> is disposed within a cassette compartment <NUM> formed between the cassette interface <NUM> and the closed door <NUM>. A heater tray <NUM> is positioned on top of the housing <NUM>. The heater tray <NUM> is sized and shaped to accommodate a bag of PD solution such as dialysate (e.g., a <NUM> liter bag of dialysate). The PD machine <NUM> also includes a user interface such as a touch screen display <NUM> and additional control buttons <NUM> that can be operated by a user (e.g., a caregiver or a patient) to allow, for example, set up, initiation, and/or termination of a PD treatment.

Dialysate bags <NUM> are suspended from fingers on the sides of the cart <NUM>, and a heater bag <NUM> is positioned in the heater tray <NUM>. The dialysate bags <NUM> and the heater bag <NUM> are connected to the cassette <NUM> via dialysate bag lines <NUM> and a heater bag line <NUM>, respectively. The dialysate bag lines <NUM> can be used to pass dialysate from dialysate bags <NUM> to the cassette <NUM> during use, and the heater bag line <NUM> can be used to pass dialysate back and forth between the cassette <NUM> and the heater bag <NUM> during use. In addition, a patient line <NUM> and a drain line <NUM> are connected to the cassette <NUM>. The patient line <NUM> can be connected to a patient's abdomen via a catheter and can be used to pass dialysate back and forth between the cassette <NUM> and the patient's peritoneal cavity during use. The catheter may be connected to the patient line <NUM> via a port such as a fitting. The drain line <NUM> can be connected to a drain or drain receptacle and can be used to pass dialysate from the cassette <NUM> to the drain or drain receptacle during use.

The PD machine <NUM> also includes a control unit <NUM> (e.g., a processor). The control unit <NUM> can receive signals from and transmit signals to the touch screen display <NUM>, the control panel <NUM>, and the various other components of the PD system <NUM>. The control unit <NUM> can control the operating parameters of the PD machine <NUM>. In some implementations, the control unit <NUM> is an MPC823 PowerPC device manufactured by Motorola, Inc.

Referring back to <FIG>, the data collecting unit <NUM> includes a data collecting cell that has multiple electrodes to electrically excite the blood and to measure electrical voltage within the blood. <FIG> illustrates a perspective view of an example data collecting cell <NUM>. The cell <NUM> includes a chamber <NUM> with an inlet <NUM> and an outlet <NUM>. Fluid (e.g., blood, medical fluids) enters the chamber <NUM> through the inlet <NUM> and flows out of the chamber through the outlet <NUM>. Multiple electrodes 304a, 304b, 304c, and 304d are located within the chamber to measure electrical parameters (such as electrical voltage) of the fluid in response to applying an electrical current to the fluid.

The chamber <NUM> contains multiple electrodes 304a, 304b, 304c, and 304d. Two or more electrodes are used to apply electrical current to the fluid, and two or more electrodes are used to measure electrical voltage. For example, electrodes 304a and 304d can be connected to a power supply of the measurement unit <NUM>, and electrodes 304b and 304c can be connected to a measuring device, such as an impedance analyzer, in the measurement unit <NUM>. Alternatively, the same electrodes that apply current can also measure voltage.

The chamber <NUM> has an upper surface <NUM> and a lower surface <NUM>. Moving along the length of the chamber from the inlet <NUM> to the outlet <NUM> (in direction x), the distance between the upper surface <NUM> and the lower surface <NUM> varies. In the illustrated example, the distance between the upper and the lower surfaces is greater at about the inlet and the outlet regions of the chamber than at the region where the electrodes are located. Such configuration directs the gas bubbles (e.g., air bubbles) in the fluid away from the electrodes and towards the outlet (or towards the inlet depending on the fluid flow's speed).

In the example cell <NUM>, the upper surface of the chamber has a concave shape, and the distance between the upper and the lower surfaces is minimum at a region halfway between the inlet and the outlet. However, the minimum distance can be at any part of the cell. For example, the minimum distance may be in the first half of the chamber along direction x (i.e., closer to the inlet than to the outlet) or in the second half of the chamber along direction x (i.e., closer to the outlet than to the inlet).

In the example cell <NUM>, the distance between the upper and the lower surfaces is greatest close to the inlet and the outlet regions of the chamber. In other embodiments, the greatest distance may be at any part of the chamber, e.g., other than where the electrodes are located. In other words, the upper surface <NUM> is not at its greatest distance from the lower surface <NUM> directly above the electrodes (but does not have to be at its minimum distance directly above the electrodes, either).

The illustrated upper surface <NUM> of the example cell <NUM> is curved. Alternatively, the upper surface can be designed as a set of multiple inclined plates. For example, the upper surface can include two diverging plates that intersect at a common line at a region between the inlet and outlet (along direction x), forming a V-shape upper surface. An upper surface of a cell can have a combination of curved and plate surfaces.

The illustrated upper surface <NUM> in <FIG> is connected to the inlet and the outlet by respective connector walls <NUM>. Alternatively, one or both of the connector walls can be eliminated so that the inlet and/or the outlet is formed on a portion of the upper surface <NUM>.

The upper surface <NUM> is connected to the bottom surface <NUM> through side walls of the chamber (now shown in FIG. <FIG> illustrates a bottom view of the cell <NUM> that depicts a bottom profile of the side walls <NUM> and <NUM>. As illustrated, the side walls <NUM> and <NUM> of the chamber are curved. For example, the chamber <NUM> can have an elliptical cross section. Curved side walls help in reducing turbulent fluid flow and provide a laminar fluid flow through the chamber.

<FIG> illustrates fluid flow in an elliptical chamber <NUM>. As illustrated, since the chamber <NUM> does not have any corners, the fluid does not get trapped in any particular part of the chamber, and rather flows smoothly throughout the chamber.

Referring back to <FIG>, the example cell <NUM> includes four electrodes, however, cells with more or less number of electrodes (e.g., two or three electrodes) can also be designed. For example, a cell can be designed to have only two electrodes, where the same electrodes apply the electrical current and measure the voltage of the two electrodes. Additional electrodes (e.g., four) can improve measurement accuracy as separate set of electrodes can be used for applying current and measuring voltage. Relatively fewer electrodes (e.g., two) can help in reducing the size of the cell.

Once connected to the power supply, the cell <NUM> can provide an excitation electrical current to the fluid. The electrical current can have a frequency ranging from DC to <NUM>. The excitation current can be in any bipolar or unipolar AC form such as sinusoidal, sawtooth, square wave shape, etc..

The excitation current that is being applied to the electrodes can be limited to a predetermined threshold. The threshold can be below <NUM> milliAmpere (mA), e.g., <NUM> mA. Limiting the current to a low threshold value guaranty safety in handling the device. Further, a chance of electrical shortening or damages by the exposed electrode contacts can be reduced by limiting the current that can pass through the circuitry that transmits current from the power supply to the cell. For example, the circuitry can have bidirectional diodes that limit the maximum voltage across different sections of the circuit to a threshold voltage, e.g., <NUM> volt.

As noted above, the data collecting cell is disposable and can be detached from system <NUM> (e.g., a dialysis system, such as the PD system <NUM> of <FIG>) after a certain number of uses (e.g., one-time use). The each cell can be pre-calibrated during the manufacturing process before being provided to consumers. This feature provides a consumer-friendly feature that allows patients to replace the cell after a certain number of use without being worried about recalibrating the cell before each use.

To eliminate a need to calibrate the data collection cell for each use, each cell can be designed for a specific cell constant. The calibration can stay accurate for a predetermined number of use, and the cell can be disposed afterwards. For example, a cell may be calibrated for <NUM> millisiemens (mS) and may be set for one time use. The calibration may be set for a specific temperature, e.g., <NUM> Celsius, and/or a specific type of fluid (e.g., blood, urine, saline, etc.).

A cell constant (that is used to calibrate a cell) is a measurement of the fluid volume contained between the two measuring electrodes, for example, electrodes 304b and 304c that measure the electrical voltage. A data collecting cell may be designed for a particular cell constant. Parameters of the measurement unit <NUM> to which the data collecting cell is to be attached, may determine the particular cell constant. For example, the data collecting cell can be designed to have a cell constant between <NUM>-<NUM> millisiemens (mS), for example, <NUM>.

A cell constant of a data collecting cell depends on the geometry of and the distance between two measuring electrodes of the cell. The electrodes can have any shape. However, electrodes with curved cross section (e.g., cylindrical electrodes similar to the electrodes depicted in <FIG>) are preferred to electrodes that have one or more corners (e.g., cubic or pyramid shaped electrodes) because curvature reduces fluid turbulence in the chamber as compared to edges.

Electrical conductivity of a fluid in a cell can be calculated based on the cell constant of the cell using the following formula: <MAT> where K is the cell constant, Z is an impedance (e.g., in ohm) of the fluid, and Φ is phase angle (e.g., in degrees). Conductivity can be measured in milliSiemens per centimeter (mS/cm).

In order to get an accurate measurement of the fluid's electrical characteristics, at least the measuring electrodes that measure electrical voltage (or at least the conductive portion of the measuring electrodes) should be completely immersed/sunk in the fluid. An exposure of a conductive portion of a measuring electrode to air can lead to inaccuracy in measuring electrical characteristics of the fluid.

A data collecting cell can include a gas detector sensor that alerts an exposure of one or more electrodes to air (or to other gasses within the chamber, or to vacuum). <FIG> illustrates an example data collecting cell <NUM> including a gas detector sensor <NUM> within the cell's chamber. The gas detector sensor <NUM> includes multiple sensor electrodes 502a and 502b. Each sensor electrode is an insulated conductors and has a respective conductive portion. The conductive portions are configured to transmit an electrical current when sunk in a fluid. However, no current is transmitted between the conductive portions of the two sensor electrodes when the conductive portions are exposed to a gaseous environment such as air. Accordingly, when no current is transmitted between the sensor electrodes, the sensor <NUM> detects that the fluid level is too low and at least one of the measuring electrodes is exposed to air.

In the example data collecting cell <NUM>, the conductive portions of the sensor electrodes 502a and 502b are at their respective tips <NUM>. At least one of the two sensor electrodes 502a and 502b can be designed to be taller than at least one of the measuring electrodes (e.g., the measuring electrode <NUM>) of the cell <NUM> in order to detect situations when the measuring electrode (or a portion of it) is exposed to air. For example, in the tilted position illustrated in <FIG>, the fluid level is dropped below the measuring electrode <NUM>'s height, causing a portion of the measuring sensor <NUM> to stick out of the fluid and be exposed to air.

In some embodiments, the sensor electrodes are taller than any of the excitation electrodes (i.e., electrodes that apply the excitation electrical current) or measuring electrodes (i.e., electrodes that measure electrical voltage,) of the cell. In some embodiments, two or more sensor electrodes are assigned to particular excitation or measuring electrode(s). For example, the electrodes 502a and 502b may be set to detect exposure of electrode <NUM> to air, irrespective of whether or not any other electrode is sunk in the fluid or exposed to air.

Referring back to <FIG> and <FIG>, the system <NUM> can also include a pump configured to pressurize the fluid inside the data collecting cell <NUM> of the data collecting unit <NUM>. The pump (not shown) can be attached to the data collecting unit <NUM>, or either of the first or the second conduits <NUM>, <NUM>. The pump can be a peristaltic pump that applies pressure pulses to the fluid. Such pulses force gas bubbles that are attached to any part of the data collecting cell (e.g., the electrodes, the side walls, or the lower or upper surfaces of the chamber,) to be detached and be moved towards the outlet. Using peristaltic pumps is particularly helpful in removing smaller bubbles that may be harder to remove, especially in a constant or low-speed fluid current.

The cell's size and weight are substantially small, which provide convenient handling and carrying by a single person. For example, the device can have dimensions smaller than <NUM> x <NUM> x <NUM> (e.g., <NUM> x <NUM> x <NUM>), and can be made of plastic.

<FIG> depicts an example process <NUM> that can be executed in accordance with the implementations of the present disclosure. The process <NUM> can be implemented by system <NUM> (e.g., the PD system <NUM>) including the data collecting cell <NUM>, or by any other system capable of performing the process <NUM>.

In this process, fluid is received through an inlet of a chamber and flows about multiple electrodes located within the chamber (<NUM>). For example, fluid can be received at the chamber <NUM> through the inlet <NUM>. The fluid passes through the chamber and about the electrodes 304a through 304d. The electrodes can be connected to a measurement unit, a power supply, and/or a dialysis machine.

An electrical current is applied to a first set of electrodes within the chamber (<NUM>). For example, the electrodes 304a and 304d may transmit electrical current through the fluid within the chamber. The electrodes 304a and 304d are connected to a power supply, for example, located in the measurement unit <NUM>.

Electrical voltage is measured between a second set of electrodes within the chamber (<NUM>). For example, the electrodes 304b and 304c can measure the electrical voltage upon the application of an electrical current to the fluid. The second set of electrodes can be the same or different from the first set of electrodes. Having the two sets separate would improve measurement accuracy but would also increase the chamber size needed for setting the electrodes.

Fluid can be pumped out of the chamber through an outlet of the chamber (<NUM>). For example, pressure pulses can be applied to the fluid to pump the fluid out of the chamber. Such pressure pulses help in removing small bubbles from the fluid.

Conductivity (or any other desired electrical characteristics) of the fluid is measured (or calculated) based on the applied electrical current and the measured electrical voltage (<NUM>). For example, the electrodes that measured the electrical voltage can transmit their measured data to a measurement unit (e.g., an impedance analyzer) to calculate the conductivity of the current.

The chamber is designed so that bubbles within the fluid are directed away from the electrodes. For example, the chamber can have a lower surface, and an upper surface separated from the lower surface. In some implementations, the lower surface is parallel to a portion of the upper surfaces in which the inlet and outlet are formed. Moving along a length of the chamber from the inlet to the outlet, a distance between the upper surface and the lower surface changes in at least one dimension of the chamber (e.g., in a direction perpendicular to the lower surface). The upper surface can be similar to the upper surface <NUM> in <FIG>.

<FIG> is a block diagram of an example computer system <NUM> that can be used as part of the system <NUM> of <FIG>, for example to perform the measurements or analysis of the measurement unit <NUM>. For example, a control unit, a computing device, and/or a microcontroller could be examples of the system <NUM> described here. The system <NUM> includes a processor <NUM>, a memory <NUM>, a storage device <NUM>, and an input/output device <NUM>. Each of the components <NUM>, <NUM>, <NUM>, and <NUM> can be interconnected, for example, using a system bus <NUM>. The processor <NUM> is capable of processing instructions for execution within the system <NUM>. The processor <NUM> can be a single-threaded processor, a multi-threaded processor, or a quantum computer. The processor <NUM> is capable of processing instructions stored in the memory <NUM> or on the storage device <NUM>. The processor <NUM> may execute operations such as causing the dialysis system to carry out dialysis functions.

In some implementations, the memory <NUM> is a computer-readable medium. The memory <NUM> can, for example, be a volatile memory unit or a non-volatile memory unit. In some implementations, the memory <NUM> stores information for causing the pumps of the dialysis system to operate as described herein.

In some implementations, the storage device <NUM> is a non-transitory computer-readable medium. The storage device <NUM> can include, for example, a hard disk device, an optical disk device, a solid-date drive, a flash drive, magnetic tape, or some other large capacity storage device. The storage device <NUM> may alternatively be a cloud storage device, e.g., a logical storage device including multiple physical storage devices distributed on a network and accessed using a network.

In some implementations, the input/output device <NUM> includes one or more of network interface devices (e.g., an Ethernet card), a serial communication device (e.g., an RS-<NUM><NUM> port), and/or a wireless interface device (e.g., an <NUM> card, a <NUM> wireless modem, or a <NUM> wireless modem). In some implementations, the input/output device <NUM> may include short-range wireless transmission and receiving components, such as Wi-Fi, Bluetooth, and/or near field communication (NFC) components, among others. In some implementations, the input/output device includes driver devices configured to receive input data and send output data to other input/output devices, e.g., keyboard, printer and display devices (such as the touch screen display <NUM>). In some implementations, mobile computing devices, mobile communication devices, and other devices are used.

In some implementations, the system <NUM> is a microcontroller. A microcontroller is a device that contains multiple elements of a computer system in a single electronics package. For example, the single electronics package could contain the processor <NUM>, the memory <NUM>, the storage device <NUM>, and input/output devices <NUM>.

The measurement unit and/or the data collection unit described herein can be part of any medical system, such as dialysis systems (e.g., a hemodialysis system), a heart lung machine, a chemotherapy system, or any other system that introduces fluid into body.

While blood was used herein as an example fluid for describing the functionality of the embodiments, the data collecting unit, in general, and the data collecting cell, in particular, can be used for determining electrical characteristics of any other type of fluids, or any medical fluids such as plasma, saline, or urine, to name a few.

Claim 1:
A device for measuring conductivity of a fluid, the device comprising:
a chamber (<NUM>) that includes:
an inlet (<NUM>),
an outlet (<NUM>), wherein the fluid enters the chamber through the inlet and flows out of the chamber through the outlet,
an upper surface (<NUM>), and
a lower surface (<NUM>) that runs separate from the upper surface; and
two electrodes (<NUM>) located within the chamber and configured to measure electrical voltage in the fluid that enters the chamber through the inlet and flows out of the chamber through the outlet,
characterized in that,
moving along a length of the chamber from the inlet to the outlet or from the outlet to the inlet, a distance between the upper surface and the lower surface changes in at least one dimension of the chamber such that bubbles in the fluid are directed from a lower distance region to a higher distance region away from the electrodes and towards the outlet or inlet, wherein a greatest distance between the upper surface and the lower surface is in a part of the chamber other than where the electrodes are located.