Patent Application
20080261261
In general, the invention relates to systems and techniques for analyzing and characterizing mammalian blood clots, especially techniques that quantify and track parameters and properties thereof. Herein, focus is on a new system/analyzer-unit and method/platform—using information obtained from a plurality of magnetoelastic sensor elements in contact with one or more samples comprising blood from a patient—for automatically quantifying one or more parameters of the patient's blood. The new analyzer-unit and associated technique provides trained clinicians, surgeons, emergency room personnel, medical technicians—indeed, a wide variety of both human medical and veterinary care-providers—in the field, in the lab, in an operating room, and so on, with a handy, portable, non-invasive diagnostic tool for on-the-spot testing, periodic or long-term monitoring, to gather information about the condition of a patient's blood, whether of a critical nature or not.
Information obtained from emissions measured from each of the magnetoelastic sensor elements is uniquely processed to determine a quantification about the blood taken from a patient, such as, quantifying platelet aggregation to determine platelet contribution toward clot formation; quantifying fibrin network contribution toward clot formation; quantifying platelet-fibrin clot interactions; quantifying kinetics of thrombin clot generation; quantifying platelet-fibrin clot strength; and so on. The unique structure of the analyzer-unit permits simultaneous measurement to be made of emissions from several different sensor elements, of special interest in the event more than one quantitative assessment is sought of the patient's blood during a test.
so as to provide the information needed for processing to quantify/assess more than one blood parameter/property, automatically. The new analyzer-unit and method contemplated herein, allow assessments to be made about ‘whole blood’ or platelet-rich plasma (PRP) of a patient (any mammal, including humans and non-human mammals such as livestock, wildlife, and domesticated pets).
More-particularly, a first aspect of the invention is directed to a system/analyzer-unit and associated method for measuring emissions from a first, second, and third magnetoelastic sensor element while being exposed to a time-varying magnetic field. The method includes the steps of: measuring first emissions collected from a first magnetoelastic sensor element in contact with a first blood sample from a mammal; measuring second emissions collected from a second magnetoelastic sensor element in contact with a second blood sample from the mammal; measuring third emissions collected from a third magnetoelastic sensor element in contact with a third blood sample from the mammal; and processing information from the first, second, and third emissions so collected to make at least one quantitative assessment/quantification about the blood.
A second aspect of the invention is directed to a system/analyzer-unit and associated method for measuring emissions from a first and second magnetoelastic sensor element in contact with a first blood sample from a mammal while each of the elements is being exposed to a time-varying magnetic field. The emissions measured from the first magnetoelastic sensor element to provide first information relating to a property of the blood; the emissions measured from the second magnetoelastic sensor element to provide second information relating to a property of the blood, said first information being different from said second information, such that at least one quantitative assessment/quantification is made of/about the blood.
Excitation of resonator-type sensing elements. In earlier patented work, one of which is entitled “Magnetoelastic Sensor for Characterizing Properties of Thin-film/Coatings” U.S. Pat. No. 6,688,162, one or more of the applicants hereof detail the excitation of magnetoelastic elements, in operation as sensing units:
Applications/uses of resonator-type sensing elements. Tracking the resonant behavior of magnetoelastic resonator sensors has enabled physical property measurements including pressure, temperature, liquid density and viscosity, and fluid flow velocity and direction. Magnetoelastic sensors have been developed for the detection and quantification of a number of physical properties including pressure, temperature, liquid density and viscosity, flow velocity, and determining the elastic modulus of thin films. In combination with chemically active mass-elasticity changing films magnetoelastic chemical sensors have been used for gas-phase sensing of humidity, carbon dioxide, and ammonia. In combination with chemically active mass-elasticity changing films magnetoelastic chemical sensors have been used for liquid-phase sensing of pH, salt concentrations, glucose, trypsin, and acid phosphatase. Sensors for the detection of different biological agents including ricin, staphylococcal endotoxin B, and E. coli 0157:H7 have been fabricated by antigen-antibody coatings on the magnetoelastic sensor surface. Many of these prior systems were developed by the applicant hereof, as principal or a co-principal investigator.
U.S. Pat. No. 6,688,162, granted to L. Bachas, G. Barrett, *C. A. Grimes, D. Kouzoudis, S. Schmidt on 10 Feb. 2004, entitled Magnetoelastic Sensor for Characterizing Properties of Thin-Film/Coatings, “Bachas, et al. (2004),” provides basic technological background discussion concerning the operation of resonator-type sensor elements in connection with direct quantitative measurement of parameters and characteristics of an analyte of interest (in that case, especially one in the form of a thin film/layer atop a surface of the element). U.S. Pat. No. 6,688,162 to Bachas, et al. (2004) is incorporated herein by reference for its detailed background technical discussion of a sensing innovation co-designed by the applicant hereof, while obligated under an assignment to another assignee.
Another patent, U.S. Pat. No. 7,113,876, was granted for the threshold-crossing counting technique to three co-applicants hereof (Drs. K. Zeng, K. G. Ong, and C. A. Grimes). Other patents and published manuscripts that share at least one applicant hereof describe applications of resonator-type sensing elements in sensing an environment, itself, and/or the presence, concentration, chemical make up, and so on, of an analyte of interest (e.g., toxins or other undesirable chemical or substance, etc.), include: U.S. Pat. No. 6,639,402 issued 28 Oct. 2003 to Grimes et al. entitled “Temperature, Stress, and Corrosive Sensing Apparatus Utilizing Harmonic Response of Magnetically Soft Sensor Element(s);” U.S. Pat. No. 6,393,921 B1 issued 28 May 2002 to Grimes et al. entitled “Magnetoelastic Sensing Apparatus and Method for Remote Pressure Query of an Environment;” U.S. Pat. No. 6,397,661 B1 issued 4 Jun. 2002 to Grimes et al. entitled “Remote Magneto-elastic Analyte, Viscosity and Temperature Sensing Apparatus and Associated Method of Sensing;” Grimes, C. A., K. G. Ong, et al. “Magnetoelastic sensors for remote query environmental monitoring,” Journal of Smart Materials and Structures, vol. 8 (1999) 639-646; K. Zeng, K. G. Ong, C. Mungle, and C. A. Grimes, Rev. Sci. Instruments Vol. 73, 4375-4380 (December 2002) (wherein a unique frequency counting technique was reported to determine resonance frequency of a sensor by counting, after termination of the excitation signal, the zero-crossings of the transitory ring-down oscillation, damping was not addressed); and Jain, M. K., C. A. Grimes, “A Wireless Magnetoelastic Micro-Sensor Array for Simultaneous Measurement of Temperature and Pressure,” IEEE Transactions on Magnetics, vol. 37, No. 4, pp. 2022-2024, 2001.
Reference may be made, herein by way of example, to sensing and analysis samples of bovine blood (i.e., relating or belonging to the genus: Bos of ruminant animals that includes mammals often simply referred to as ‘livestock’, namely, cattle, oxen, and buffalo). The unique sensing element, associated sensing platform/device, and method contemplated hereby are intended and adapted for use in the analysis, diagnosis, and study of whole blood and platelet-rich plasma (PRP) of all mammals (occasionally, “mammalian blood” and “mammalian PRP”, or more-simply as, blood and PRP). Here, focus is on the use of magnetoelastic sensor elements to study platelet aggregation in whole blood or PRP, and for use in distinguishing fibrin and thrombin generated clotting cascades in whole blood or PRP.
Blood clotting commonly represents a process of blood solidification that occurs upon external injury to tissue or blood vessels. Blood clotting is an essential part of the complex physiological process referred to as the coagulation cascade, or hemostasis, that requires a delicate balance between blood cells, platelets, coagulation and tissue factors. An injury to a blood vessel results in a series of enzymatic reactions between these various components with a final objective of stopping blood flow (clotting) at the wound site. While, in the case of an external injury it is desirable to form a clot in a short period of time to minimize blood loss, inside the body formation of even the smallest of clots can lead to a fatal hemorrhage. Conventional techniques for characterizing and analyzing blood clots are identified in The Clotting Times, October 2004, labeled ATTACHMENT A, hereof—the whole of which is incorporated herein by reference as a general technical background reference—page 6 discusses current techniques employed in the study of platelet function.
Platelets play a crucial role in the hemostasis process. Created in the bone marrow platelets have a half-life of 8-12 days in blood, during which they remain functional. The clotting cascade critically depends on the activation and aggregation of functional platelets, in particular for smaller blood vessels, where a vascular hole at the site of injury is blocked by a ‘platelet plug’ rather than by a blood clot. Standard platelet counts are 150,000/μL to 400,000/μL, while platelet counts lower than 50,000/μL often lead to spontaneous bleeding from capillary vessels, i.e. thrombocytopenia. Abnormal platelet count and activity influence other hemostatic disorders such as cerebrovascular disease, peripheral vascular disease and venous thromboembolism. An assessment of the platelet function, measured in terms of either platelet number or extent of aggregation, can be of critical importance for patients with hemostatic disorders.
Platelet aggregometry was first developed by Born in 1962 for platelet rich plasma (PRP); light transmission through the plasma was measured as a function of time after it was activated with adenosine di-phosphate (ADP) agonist. Previous to Born it had been shown that ADP caused platelets to form aggregates. Born showed that as the platelets formed aggregates under the influence of ADP the optical density of the plasma decreased, resulting in increased transmittance. The transparency of the plasma was directly proportional to the extent of aggregation which, in turn, was proportional to the number of functional platelets in the plasma. This technique has long been considered a standard in platelet aggregation studies. However, there are a number of issues that limit the utility of light transmission aggregometry.
Another technique, whole blood impedance aggregometry, requires an anti-coagulated whole blood sample to be diluted 1:1 with 0.9% saline, with two electrodes inserted into the blood to measure electrical impedance with time. As the platelets aggregate under the influence of an agonist such as ADP they adhere to the immersed electrodes resulting in a change of electrical impedance. The impedance change is proportional to the extent of platelet aggregation in the blood sample. Impedance aggregometry, although in use to study the platelet function of whole blood, likewise has limitations: It is insensitive to microaggregate formation.
Two other conventional methods for platelet aggregation studies of whole blood are: single platelet counting techniques and flow cytometry. The single platelet counting technique measures the fall in the number of platelets in a whole blood sample subjected to an agonist, with the reduction in the platelet number being proportional to the platelet aggregation. A modification of this technique has resulted in ‘flow cytometry’, which detects platelet aggregation in an ADP mixed blood sample labeled with platelet specific fluorescent antibodies. While flow cytometry may be able to detect both macro and micro-aggregate formation of platelets (since the fluorescent signal differs according to the size of the platelet clusters), the mixing of florescent markers leaves the blood sample open to contamination.
“A Modified Thromboelastographic Method for Monitoring c7E3 Fab in Heparinized Patients,” by Philip E. Greilich, MD, et al. Anesth Analg (1997) 84:31-8 (hereafter, Greilich, et al. 1997), describes an assay it refers to as “MTEG” for monitoring effects of potent antiplatelet drugs, stating:
“Use of abciximab-Modified Thrombelastography in Patients Undergoing Cardiac Surgery,” by S. C. Kettner, MD, et al. Anesth Analg (1999) 89:580-4 (hereafter, Kettner, et al. 1999), describes an assay it refers to as abciximab-modified Thrombelastography (TEG) for monitoring coagulation when abciximab-fab, a platelet function inhibitor, is used, as follows:
I. Mammalian Blood, Coagulation Cascade, etc.
Mammalian Blood is a biological fluid that circulates throughout mammals and consists of plasma and blood cells, namely, red blood cells (also called RBCs or erythrocytes), white blood cells (includes both leukocytes and lymphocytes), and platelets (also called thrombocytes). Blood plasma, the liquid component of blood in which blood cells are suspended, is predominantly water. However, it also contains many vital proteins including fibrinogen (a clotting factor), globulins and human serum albumin. Red blood cells are the most abundant cells in blood: They contain hemoglobin, an iron-containing protein, which facilitates transportation of oxygen and carbon dioxide. White blood cells help to resist infections. Platelets are important in the clotting of blood (as further explained).
Platelets, or thrombocytes, are the cells circulating in the blood that are involved in the cellular mechanisms of primary hemostasis leading to the formation of blood clots. Dysfunction or low levels of platelets predisposes a mammal to bleeding, while high levels may increase the risk of thrombosis. Platelet functions are generalized into several categories: adhesion and aggregation; clot retraction; pro-coagulation; cytokine signalling; and phagocytosis. Adhesion and aggregation refers to the activity of platelets to adhere to each other via adhesion receptors, or integrins, and to the endothelial cells in the wall of the blood vessel forming a haemostatic plug (or, clot) in conjunction with fibrin.
Coagulation is the complex process by which blood forms solid clots. It is an important part of hemostasis (the cessation of blood loss from a damaged vessel) whereby a damaged blood vessel wall is covered by a platelet- and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Coagulation is initiated once an injury to a blood vessel lining occurs. Platelets immediately form a hemostatic plug at the site of injury; this is called primary hemostasis. Secondary hemostasis—which occurs simultaneously—is where proteins (coagulation factors) in the blood plasma respond in a coagulation cascade to form fibrin strands which strengthen the platelet plug. Disorders of coagulation can lead to an increased risk of bleeding, or clotting and embolism. Thrombosis is the pathological development of blood clots: an embolism is said to occur when a blood clot (thrombus) migrates to another part of the body.
Quantification is the act of quantifying, that is, of giving a numerical value to a measurement of something.
II. Blood Clotting Kinetics: Shown in
III. Digital computers. A processor is the set of logic devices/circuitry that responds to and processes instructions to drive a computerized device. The central processing unit (CPU) is considered the computing unit of a digital electrically-driven or other type of computerized system. A conventional CPU, often referred to simply as a processor, is made up of a control unit, program sequencer, and an arithmetic logic unit (or, ALU)—circuitry that handles calculating and comparing tasks of a CPU. Numbers are transferred from memory into the ALU for calculation, and the results are sent back into memory. Alphanumeric data is sent from memory into the ALU for comparing. The CPUs of a computer may be contained on a single ‘chip’, often referred to as microprocessors because of their tiny physical size. As is well known, the basic elements of a simple computer include a CPU, clock and main memory; whereas a complete computer system requires the addition of control units, an operating system, and input, output and storage devices. The very tiny devices referred to as ‘microprocessors’ typically contain the processing components of a CPU as integrated circuitry, along with associated bus interface. A microcontroller typically incorporates one or more microprocessor, memory, and I/O circuits as an integrated circuit (IC). Computer instruction(s) are used to trigger computations carried out by the CPU.
IV. Computer Memory and Computer Readable Storage/Media. While the word ‘memory’ has historically referred to that which is stored temporarily, with storage traditionally used to refer to a semi-permanent or permanent holding place for digital data—such as that entered by a user for holding long term—more-recently, the definitions of these terms have blurred. A non-exhaustive listing of well known computer readable storage device technologies are categorized here for reference: (1) magnetic tape technologies; (2) magnetic disk technologies include floppy disk/diskettes, fixed hard disks (often in desktops, laptops, workstations, etc.), (3) solid-state disk (SSD) technology including DRAM and ‘flash memory’; and (4) optical disk technology, including magneto-optical disks, PD, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD-RAM, WORM, OROM, holographic, solid state optical disk technology, and so on.
Briefly described, in one characterization, the invention is directed to a system/analyzer-unit and associated method for measuring emissions from a first, second, and third magnetoelastic sensor element while being exposed to a time-varying magnetic field. The method includes the steps of: measuring first emissions collected from a first magnetoelastic sensor element in contact with a first blood sample from a mammal; measuring second emissions collected from a second magnetoelastic sensor element in contact with a second blood sample from the mammal; measuring third emissions collected from a third magnetoelastic sensor element in contact with a third blood sample from the mammal; and processing information from the first, second, and third emissions so collected to make at least one quantitative assessment/quantification about the blood.
In a second characterization, the invention is a system/analyzer-unit and associated method for measuring emissions from at least a first and second magneto-elastic sensor element in contact with a first blood sample from a mammal while each of the elements is being exposed to a time-varying magnetic field. The emissions measured from the first magnetoelastic sensor element to provide first information relating to a property of the blood; the emissions measured from the second magnetoelastic sensor element to provide second information relating to a property of the blood, said first information being different from said second information, such that at least one quantitative assessment/quantification is made of/about the blood.
As mentioned, information obtained from the emissions measured from each sensor element is uniquely processed to determine a quantification about the blood taken from a patient, such as, quantifying platelet aggregation to determine platelet contribution toward clot formation; quantifying fibrin network contribution toward clot formation; quantifying platelet-fibrin clot interactions; quantifying kinetics of thrombin clot generation; quantifying platelet-fibrin clot strength; and so on. In the event more than one quantitative assessment is sought of a patient's blood during a test, the unique structure of the analyzer-unit can make substantially-simultaneous measurements of emissions, to provide requisite information for automatic determination of a quantification of more than one blood parameter/property.
The new system/analyzer-unit and method using magnetoelastic sensor elements as contemplated herein, may also be employed for quantitative assessment of the blood of a patient to which some drug is being administered, for example, an antiplatelet drug (as typically administered, inhibit platelet aggregation and clot retraction).
Unique structural aspects of a new analyzer-unit include: a cartridge having at least one bay within which a magnetoelastic sensor element is positioned; each bay is in fluid communication with both (a) an entry port for injecting a first blood sample composed of blood taken from a patient (human or other mammal), and (b) a gas vent through which air displaced by injecting the first blood sample into the bay, can be expelled to accommodate the first blood sample. The gas vent comprises a porous plug through which air can be expelled upon injecting the first blood sample. Once air has been expelled through the porous plug, it generally seals against loss of the blood sample. The analyzer-unit is adaptable for testing a sample of blood from a patient to whom a drug is being administered, and therefore likely present in the patient's blood (e.g., an antiplatelet drug discussed, further, below). The analyzer-unit may be comprised of a plurality of bays, all in fluid communication with the same entry port for injecting a first blood sample composed of blood taken from a patient, and (b) a gas vent through which air displaced by injecting the first blood sample into the bay, can be expelled to accommodate the first blood sample. Alternatively, the analyzer-unit may be comprised of a plurality of bays, each bay being in fluid communication with a respective entry port and an associated gas vent through which air displaced by injecting a respective blood sample into the respective bay, can be expelled.
For purposes of illustrating the innovative nature plus the flexibility of design and versatility of the new system and associated technique set forth herein, the following background references and several figures are included. One can readily appreciate the advantages as well as novel features that distinguish the instant invention from conventional sensing systems and techniques. Where similar components are represented in different figures or views, for purposes of consistency, effort has been made to use similar reference numerals. The figures, as well as background technical materials, are included to communicate the features of applicants' innovative device and technique by way of example, only, and are in no way intended to limit the disclosure hereof. Any enclosure identified and labeled an ATTACHMENT, is hereby incorporated herein by reference for purposes of providing background technical information.
a,b show the TEG curves for three different blood concentrations (whole blood, 1:4 dilution and 1:8 dilution) measured by:
ATTACHMENT A (8 pages) The Clotting Times, October 2004, incorporated by reference for the background technical discussion contained therein.
ATTACHMENT B (1 page) The Coagulation Cascade, © 2003 American Association for Clinical Chemistry, updated Feb. 19, 2004, incorporated by reference for further background technical information contained therein, see also
By viewing the figures which depict representative structural embodiments, and associated process steps, one can further appreciate the unique nature of core as well as additional and alternative features of the new blood test system/unit, and associated technique/platform. Back-and-forth reference has been made to the various figures—schematics, graphical representations of functional relationships, and flow diagrams which, collectively, detail core as well as further-unique features—in order to associate respective features, for a better appreciation of the unique nature of the invention.
Parameters of interest for TEG pattern 18 include: R the latency before clotting (the time to initial fibrin formation), K the clotting time, MA the maximum amplitude (clot strength), and α the rate of clot strengthening. To health care providers and testing laboratories that regularly test patient blood, TEG plots (as labeled with variables R, K, MA, α, and so on) are familiar, as are the shapes in
As shown in
Each blood sample 89a, b, c composed of blood taken from a patient (any mammal, including humans and non-human animals) is inserted (along arrow 88) into a respective receiving port 87a, b, c of cartridge assembly 84 which is in communication with a respective bay 85a, b, c within which a sensor element 83a, b, is located. As depicted here, each syringe 86a, b, c is initially ‘loaded’ with a particular blood sample 89a, b, c. As explained more-fully elsewhere herein, each blood sample 89a, b, c is composed of blood from a patient mixed with one or more additive, such as a thrombin activator, a fibrinogen activator, platelet activator, an antiplatelet drug (which might already have been administered to the patient before drawing the blood therefrom). While three bays are depicted in
Once each bay 85a, b, c is positioned into a cavity area 82a, b, c within a respective coil (not shown for simplicity) undergoing excitation so as to create a time-varying magnetic field, emissions are measured from each magnetoelastic sensor element 83a, b, c in contact with a respective blood sample. In operation, emissions are measured from the first magnetoelastic sensor element 83a to provide first information relating to a property of the blood in sample 89a; emissions are also measured from the second sensor element 83b to provide second information relating to a property of the blood in second sample 89b, as are emissions measured from the third sensor element 83c to provide third information relating to a property of the blood in third sample 89c. Jumping to alternative embodiment shown in
The measuring of emissions to obtain information about the blood in a respective sample, is preferably accomplished by employing one or more of the techniques co-developed by applicants hereof, such as any suitable technique described and referenced in applicants' co-pending parent application Ser. No. 11/710,294. While co-pending application Ser. No. 11/710,294 is directed to an impedance analysis technique applied to measure steady-state vibration of a magnetoelastic sensor element forced by a constant sine wave excitation, the co-pending parent application Ser. No. 11/710,294 also references an earlier technique, namely, the threshold-crossing counting technique invented by three co-applicants hereof (Drs. K. Zeng, K. G. Ong, and C. A. Grimes) and detailed in U.S. Pat. No. 7,113,876 for “Technique and Electronic Circuitry for Quantifying a Transient Signal using Threshold-crossing Counting to Track Signal Amplitude.” As further detailed in applicants' co-pending parent application Ser. No. 11/710,294 and the earlier-filed (now granted) U.S. Pat. No. 7,113,876 directed to threshold-crossing counting technique, one can measure resonance frequency of sensor element emissions, Q of the resonance, or amplitude of the resonance. Alternatively, as explained by applicants earlier, one can set and select an initial (‘listening’) frequency and measure the amplitude at this initial, listening frequency. Listening frequency, in this case, is not synonymous with sensor element resonance frequency, as resonance shifts with whatever is happening within blood sample, e.g., clotting, to change its viscosity over time.
As explained in parent application Ser. No. 11/710,294: An electronic implementation of the impedance analysis technique can, for example, include a single circuit board that, when interfaced with a processor unit (e.g., within a palmtop, laptop, handheld, remote hard-wired, remote wireless, and so on), uses a solenoid coil unit to characterize sensor resonance behavior in the frequency domain, after having obtained the complex (magnitude, phase) impedance spectrum of the sensor element from a measured impedance (a ‘combined’ impedance for the system of sensor element plus coil); see, also,
The magnetoelastic sensors are preferably made from elongated magnetostrictive ferromagnetic amorphous alloys (see for example, Vacuumschemaltze Corporation, distributor of a suitable sensor material) that generate both longitudinal elastic waves and magnetic flux when exposed to a time varying magnetic field. The elastic waves can be detected by a microphone (audio sensor pick-up device) while the magnetic flux can be sensed by a remotely placed inductive pick-up coil. The resonance frequency of the magnetoelastic wave depends on the Young's modulus of elasticity of the sensor (E), density (ρs), the Poisson ratio (σ), and length (L) of the sensing element. Mathematically, the fundamental resonance frequency f0 of the elastic vibrations is expressed as:
For a specific magnetoelastic material, E, ρs, and σ remain constant, hence the resonance frequency can be varied by changing the length of the sensor element. For the Vacuumschemaltze material the resonance frequencies of illustrative 6 mm wide 28 μm thick sensors in air, 12 mm and 15 mm length, are approximately 180 kHz and 145 kHz respectively.
When an elongated magnetoelastic sensor element is immersed in a liquid the viscosity of the surrounding medium acts as a damping force to the sensor oscillations that result in a downward shift of the resonance frequency, which is expressed as:
Where f0 is the resonance frequency of the sensor in air, ρs and d the density and thickness of the sensor, and ρl and η the density and viscosity of the liquid, respectively. This implies a change in liquid density and/or viscosity results in a corresponding shift in the resonance characteristics of a liquid immersed magnetoelastic sensor. The (ηρi)1/2 term arises from the wave equation describing the propagation of shear waves in a liquid. The effect of liquid density ρl arises from the force=mass×acceleration term, while liquid viscosity η appears as a drag term. The shift in resonant frequency is proportional to the square-root of ηρl as the wave equation contains the square of the wave velocity.
Although Eqn. (2) explains the behavior of a magnetoelastic sensor in a liquid of changing viscosity, such as a blood sample undergoing a clotting cascade, it does not fully explain the change in sensor characteristics when the sensor is mass-loaded. It has been shown that when a small mass Δm is loaded on the surface of a magnetoelastic sensor of mass m0, the shift in resonance frequency Δf is given by:
where f0 is the resonance frequency without mass any mass loading. Eqn. (3) quantifies the change in resonance frequency due to mass loading and is particularly useful is describing the sensor behavior in blood samples due to settling of red blood cells or aggregated platelets.
However, Eqn. (3) does not take into account the elastic stress in the applied mass load. Considering a uniform mass adhered to the sensor surface the rate and sign of the frequency change due to the mass coating depends on the elasticity and density of the coating in comparison with that of the sensor. If m0 and mt are the mass of the sensor and the total mass after coating, the ratio of the measured frequencies before (fo) and after (f) applying a coating is:
Ec and Es are the modulus of elasticity of the coating and the sensor, respectively, and ρc and ρs are the density of the coating and the sensor, respectively. Eqns. (3) and (4) describe the overall behavior of a magnetoelastic sensor immersed in a complex liquid, blood (considered an ‘infectious material’ and on occasion referred to as a non-Newtonian liquid), taking into account effects settling, e.g. blood cells and platelets falling onto the sensor surface, and clot formation where the sensor is encased in a solid-like substance.
Similar to the resonance frequency, the resonance amplitude of a magnetoelastic sensor is also dependent on the mass loading and elasticity of the coatings. Since mass loading dampens the amplitude of vibration, it decreases the measured voltage amplitude of the sensor. In most cases the percentage change in voltage amplitude is an order of magnitude greater than the corresponding frequency shift; thus for applications such as measuring blood clotting characteristics—as uniquely done here—the resonance amplitude, instead of resonance frequency, can be measured as a function of time.
Magnetoelastic sensors have been employed by applicants in earlier work in a number of sensing applications through the tracking of the systematic variation of the resonance frequency and resonance amplitude of the sensor. As mentioned, various physical parameters such as temperature, pressure, liquid density and viscosity, fluid flow velocity, and thin film elastic modulus have been quantified using magnetoelastic sensors. In combination with analyte-responsive coatings, magnetoelastic sensors have been used as chemical sensors for pH and glucose, as gas sensors. As mentioned by applicants in their co-pending parent app., magnetoelastic bio-sensors have been used for the quantification of E.-Coli 0157:H7 bacteria, Staphyloccocal enterotoxin B, avidin, trypsin, and ricin.
According to one aspect of the present invention, the extent of clot formation in whole blood due to thrombin and fibrin generation and platelet aggregation has been measured by tracking the time dependent change in the sensor vibration amplitude under respective clotting conditions. Although Bachas, et al. (2004) mentioned use of magnetoelastic sensors to monitor blood clot formation, it was through subsequent work by applicants, mentioned elsewhere herein, whereby a compact microprocessor based magnetoelastic sensor system was produced based on a time domain analysis technique. The microprocessor based electronics enable characterization of sensor resonance characteristics in ≈10 ms, with a measurement resolution of a few Hz. The instant sensing platform is useful for measuring activated clotting time (ACT), as well as determination of Erythrocyte Sedimentation Rate (ESR), and Thromboelastograph (TEG) analyses of whole blood.
For this aspect of the invention—see, for example,
As identified herein, in order to distinguish the contributions of thrombin and of fibrin in the clotting cascade of hemostasis, isolation and quantification of platelet activity is necessary. With thrombin mediated clotting, which resembles a normal clotting cascade (see, for example,
Turning to
Blood sample analysis is carried out according to the unique technique set forth diagrammatically in more-detail in
By way of example, a cartridge device built according to that depicted in
A gas vent device, examples of which are shown in greater detail in
The alternative cartridge structure 54′ shown in
The cartridge can be fabricated to accommodate one, two, three, four, five, six, seven, and so on, sensor elements—whether each element is sized and calibrated to collect information about one or more sample of patient's blood—according to the following structural embodiments, among others:
For case (c) contemplated above, steps may include: measuring first emissions collected from sensor element 53a/53a′ while in contact with a sample of blood; measuring second emissions collected from another of the sensor elements while in contact with the sample of blood, both sensor elements having been calibrated (sized and shaped) to provide a first type of information (for example, as suggested in
In one embodiment, the analyzer-unit (e.g., 51, 81) utilizes a compact user interface display (not shown in detail, but would be on the exterior of housing 51, 81), with separate multi-sensor-element cartridges (e.g., at 54,54′, 154) adapted to determine a quantification, or provide a quantitative assessment such as: {1} determining activated clotting time (ACT) as a function of heparin concentration; {2} simultaneously monitor the blood coagulation profile (TEG) and settling rate (ESR); and {3} determine platelet aggregation by comparison of a thrombin, fibrin, and fibrin+platelet induced clots. The baseline resonance characteristics of the sensor elements 53a-d, 53a′, 83a-d within the cartridge would enable automatic identification by the reader. To perform a measurement, the user first collects a blood sample (with or without additive mixed) with a syringe device 56, 56′, 86a-c, then injects the blood into the cartridge. The user then inserts the cartridge into the sensor detector unit 51, 81, for an automatic quantitative assessment of the blood. Once made, the cartridge sub-unit can be disposed (so as not to cause contamination since it contained a patient's blood).
Turning, first, to
By measuring changes in the resonance frequency and resonance amplitude of each sensor when in contact with a respective blood sample taken from a mammal/patient (each blood sample having been combined with one or more selected agent), three separate parameters are determined: measurements are taken from the first magnetoelastic sensor element in contact with the first blood sample, regarding behavior of a ‘total activated’ clot; measurements are taken from the second magnetoelastic sensor element in contact with the second blood sample, regarding behavior of the fibrin effect (fibrin clotting cascade) of that mammal's blood; and measurements are taken from the third magnetoelastic sensor element in contact with the third blood sample, regarding the effect due to fibrin and platelets (fibrin and platelet clotting behavior) of that mammal's blood. Information gleaned from measurements taken from the second sensor element about the fibrin effect alone, is subtracted from that gleaned from measurements taken from the third sensor element regarding the combined effect of fibrin and platelets to isolate a collection of diagnostic information about the platelet clotting behavior, alone (box 97).
An associated system system/analyzer-unit includes a detection unit housing a device for generating the time-varying magnetic field(s), the first, second, and third magnetoelastic sensor elements, and a bay/cavity for receiving, respectively, each of the first, second, and third blood samples. As explained elsewhere herein, each sample can be received by ‘injection’ into a respective cavity within which a respective one of the sensor elements is positioned. In operation, an analyzer-unit associated with
The characterization of the invention as depicted in
As mentioned, quantitative assessment(s)—different types of quantifications—which can be made as contemplated herein, include among others: quantifying platelet aggregation to determine platelet contribution toward clot formation; quantifying fibrin network contribution toward clot formation; quantifying platelet-fibrin clot interactions; quantifying kinetics of thrombin clot generation; and quantifying platelet-fibrin clot strength. The first blood sample comprising a blood product obtained from the mammal selected from the group consisting of: whole blood; and platelet-rich plasma.
Unique structural aspects of an analyzer-unit, FIGS. 12,13,14,15,16A-16B, and 17A-17B include, among others: a cartridge having at least one bay within which a magnetoelastic sensor element is positioned; each bay is in fluid communication with both (a) an entry port for injecting a first blood sample composed of blood taken from a patient (human or other mammal), and (b) a gas vent through which air displaced by injecting the first blood sample into the bay, can be expelled to accommodate the first blood sample. The gas vent comprises a porous plug through which air can be expelled upon injecting the first blood sample. Once air has been expelled through the porous plug, it generally seals against loss of the blood sample. The analyzer-unit is adaptable for testing a sample of blood from a patient to whom a drug is being administered, and therefore likely present in the patient's blood (e.g., an antiplatelet drug discussed, further, below). The analyzer-unit may be comprised of a plurality of bays, all in fluid communication with the same entry port for injecting a first blood sample composed of blood taken from a patient, and (b) a gas vent through which air displaced by injecting the first blood sample into the bay, can be expelled to accommodate the first blood sample. Alternatively, the analyzer-unit may be comprised of a plurality of bays, each bay being in fluid communication with a respective entry port and an associated gas vent through which air displaced by injecting a respective blood sample into the respective bay, can be expelled.
The new system/analyzer-unit and method using magnetoelastic sensor elements as contemplated herein, may also be employed for quantitative assessment of the blood of a patient to which some drug is being administered, for example, an antiplatelet drug (as typically administered, inhibit platelet aggregation and clot retraction). As is known, inhibition of platelet function by administering an antiplatelet drug to a patient permits a care giver to make a general quantitative assessment of the contribution of fibrinogen to clot strength. For instance, one such technique (MTEG)—i.e., a modification of the classic thromboelastograph (TEG) test—uses monoclonal antibody, c7E3 Fab, an antiplatelet drug, was developed by another group, Greilich, et al. (1996). Furthermore, prior use has been made by others in the monitoring of blood coagulation using another modification of traditional thrombelastography (TEG), of an antibody fragment that binds to platelet glycoprotein IIb/IIIa (known as “abciximab-fab”); this antibody fragment abciximab-fab blocks the interaction of platelets with fibrin. The new system/platform/unit and method may also be employed for quantitative assessment of a patient's blood in the event abciximab-fab is being administered to the patient.
A larger sensor tends to provide a stronger signal and better accuracy, but longer sensors are prone to bending that lowers the desired signal amplitude. On the other hand, a sensor element on the smaller size tends to have a weaker signal and lower signal-to-noise ratio. More likely than not, sensor dimension affects the sensitivity because sensors of different dimension have different magnetoelastic properties due to the ΔE-effect, which leads to different stress and mass sensitivities. The dimension of each rectangular-shaped sensor element may be on the order of, say, 10 mm×4 mm. This size is small enough for compact sensor cartridges, but large enough for a strong signal and ease of handling in fabrication. The sensor dimensions can be varied (within the limits of the coil size) according to the sensitivity requirements in a particular measurement with the analyzer-unit generally only requiring a re-calibration in connection with an anticipated new resonance frequency for the sensor element.
Magnetoelastic sensor elements for this example were used on a disposable basis. Total sensor cost is largely determined by the cost of processing, i.e., material handling, the available magnetoelastic ribbon material is quite inexpensive. While sensor elements may be fabricated by a variety of cutting means from a continuous piece of ribbon, mechanical shearing was preferred for this example for its low cost and ease of manufacture. When mechanically sheared, the raw sensor material (ribbon form) can be fed through a metal cutting machine and chopped to a preselected dimension. When a sensor element is mechanically sheared, it contains stresses around the edges that may alter the sensor response in unpredictable ways. Hence, preferably, the magnetoelastic strips are annealed to release these stresses, resetting all sensors to the same magnetic and magnetoelastic states, and also increasing the permeability and magnetoelastic coupling of the sensors. The annealing temperature can be optimized depending on the sensor size, and can also be performed in the presence of a magnetic biasing field to induce an overall magnetic moment in the sensor.
Fresh bovine blood from healthy cows was drawn into citrate and heparin tubes (Vacutainer system, BD Biosciences, New Jersey). Activated Clotting Time (ACT) tubes containing 12 mg of kaolin, and ADP tubes containing 20 μM ADP for 1 mL blood were obtained from Helena Laboratories (Texas, USA). Reptilase (Batroxobin™ Maranhao) in the form of 100BU/vial was used Centerchem, Inc. (Connecticut, USA).
To generate a thrombin activated clot, 2 mL citrate anti coagulated blood was injected into an ACT mixed by inversion. 50 μL of 1M CaCl2 was then pipetted into the blood-kaolin mixture, and the resultant blood sample placed in a glass vial containing a magnetoelastic sensor. The resonance amplitude of the sensor was continuously recorded for ˜10 mins. For activating a fibrin induced clot 50 μL of Batroxobin™ solution (100 BU/vial powder reconstituted in 1 mL of de-ionized water) was added to 1 mL of heparinized blood, and the resulting blood mixture placed in a glass vial containing a magnetoelastic sensor and the resonance amplitude of a sensor immersed in this blood sample recorded. Another sample (targeting the effect of platelet aggregation) was prepared with 1 mL of the Batroxobin™ treated blood added to a tube containing 20 μM ADP and mixed gently. The resonance amplitude of a magnetoelastic sensor immersed in this blood sample was then recorded.
It was observed that blood cells tend to settle onto the magnetoelastic sensor surface affecting resonance amplitude at the beginning of the clotting process. To isolate the effect of settling, i.e., precipitation from the blood onto the gravimetric sensors, the resonance amplitude of a magnetoelastic sensor was measured in a 1 mL citrated blood sample without any additives.
As a result of blood ‘settling’ on the magnetoelastic sensor surface, the amplitude decreases to about 0.85 from the initial value of 1. In case of reptilase (denoted as Activator-F, or Act-F) activated blood, a relatively weak clot formed due to the fibrin network formation and the amplitude decreases to about 0.80. A relatively stronger clot is formed as a result of ADP activation in combination with Activator F (denoted FADP) due to platelet aggregation with the amplitude reducing to 0.73. Finally, when a blood sample is activated with kaolin, the strongest possible clot formed due to thrombin formation and the amplitude saturates at 0.51.
With the saturation amplitude values proportional to the clot strength as measured by a conventional TEG system, platelet aggregation can be estimated using this data. Percentage platelet aggregation is expressed as:
% platelet aggregation=[(MAFADP−MAFibrin)/(MAThrombin−MAFibrin)]×100 (5)
Where MA represents the normalized saturation measured amplitude value with subscripts indicating the respective activating agents.
Case 1: Settling Not Accounted for in Data Analysis
Using the normalized data without taking into account changes seen in the sensor performance due to settling, platelet aggregation using magnetoelastic sensor amplitude data can be expressed as:
[{MAFADP−MAFibrin}/{MAThrombin−MAFibrin}]×100 (6)
MAFADP=0.73; MAFibrin=0.8; MAThrombin=0.51. For which the calculated platelet aggregation is 24.1%.
Case 2: Settling Accounted for in Data Analysis
Compensating the data by the amplitude reduction due to blood settling, platelet aggregation using magnetoelastic sensor amplitude data can be expressed as:
[{(MASettle−MAFADP)−(MASettle−MAFibrin)}/{(MASettle−MAThrombin)−(MASettle−MAFibrin)}]×100 Eqn. (7)
Using the data from
Initial experiments to obtain TEG and ESR profiles using an analyzer-unit structured as contemplated herein, were performed on bovine blood injected into the sensor chambers of the cartridge using a 1 mL syringe. The blood for the ESR tests preferably can be citrated to prevent clotting; a suitable amount of calcium chloride (1 M solution in saline) was added to blood samples bound for TEG analysis to nullify the effect of the anticoagulant. Once the cartridge bays were at least partially filled with blood it was placed (with or without syringe attached) inside the coils for detection.
A magnetoelastic sensor element was immersed in a blood sample and both were exposed to a time-varying magnetic field, emissions from which were captured the clot profile of a blood sample by determining the changes in the resonance amplitude of the sensor.
One effective way to correlate settling profiles to ESR values is to perform side-by-side comparisons. This process begins by determining the settling rate S from the measured settling profile (see
where V2 and V1 are respectively the sensor signal amplitude at the beginning of the experiment and after a time duration (for example, 10 minutes), and t2 and t1 are the times corresponding to V2 and V1. A reference data sheet can be constructed with the ESR values of a large number of similar blood samples run on an ESR device. These two data sets can be plotted and a function F defined, such that B=F(A), where A and B represents ESR data points obtained from the magnetoelastic sensor and a commercial device respectively. By obtaining the function F, the actual ESR value B can be determined by substituting the measured S value for any blood sample as A in Eqn. (8).
While certain representative embodiments and details have been shown for the purpose of illustrating features of the invention, those skilled in the art will readily appreciate that various modifications, whether specifically or expressly identified herein, may be made to these representative embodiments without departing from the novel core teachings or scope of this technical disclosure. Accordingly, all such modifications are intended to be included within the scope of the claims. Although the commonly employed preamble phrase “comprising the steps of” may be used herein, or hereafter, in a method claim, the applicants do not intend to invoke 35 U.S.C. §112¶6 in a manner that unduly limits rights to its innovation. Furthermore, in any claim that is filed herewith or hereafter, any means-plus-function clauses used, or later found to be present, are intended to cover at least all structure(s) described herein as performing the recited function and not only structural equivalents but also equivalent structures.
This application claims the benefit of: (1) pending U.S. provisional Pat. App. No. 61/007,495 filed 12 Dec. 2007 describing developments of one of the applicants hereof, on behalf of the assignee; and (2) is a continuation-in-part (CIP) of pending U.S. patent application Ser. No. 11/710,294 filed 23 Feb. 2007 for the applicants on behalf of the assignee. The specification and drawings of both provisional app. No. 61/007,495 and the parent application Ser. No. 11/710,294 are hereby incorporated herein by reference, in their entirety, providing further edification of the advancements set forth herein.
| Number | Date | Country | |
|---|---|---|---|
| 60787945 | Mar 2006 | US | |
| 61007495 | Dec 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11710294 | Feb 2007 | US |
| Child | 12080472 | US |
