Fluid viscoelastic test apparatus and method
First Claim
1. An instrument for measuring one or more viscoelastic properties of a fluid sample, the instrument comprising:
- probe means disposed in contact with the fluid sample;
electromechanical transducer means coupled to the probe means for providing mechanical displacement of the probe means relative to the fluid sample;
first circuit means, connected to the electromechanical transducer means, said first circuit means comprising drive circuitry providing a drive signal for generating oscillatory mechanical displacement of the probe means relative to the fluid sample, said first circuit means further comprising response circuitry for monitoring a response signal generated by the electromechanical transducer means, the response signal being representative of the one or more viscoelastic properties of the fluid sample, said drive circuitry and response circuitry forming a feedback loop wherein the drive signal is developed from the response signal and vice versa;
second circuit means for regulating an amplitude of a first signal within said feedback loop, while allowing said feedback loop to operate at resonant oscillatory frequency determined by said probe means, said electromechanical transducer means, and said first circuit means; and
microcontroller means for receiving and analyzing said response signal to determine the one or more viscoelastic properties of the fluid sample represented by said response signal; and
digital output means, coupled to said microcontroller means, for visually displaying to a user one or more numbers representative of the one or more viscoelastic properties, respectively, of the fluid sample, as determined by said microcontroller means.
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Abstract
An instrument for testing the viscoelastic characteristics of fluids, such as blood, exhibits improved temperature regulation of the blood sample under test, includes probe drive circuitry to simplify calibration and signal conditioning, incorporates resonant frequency monitoring to detect mechanical noise disturbances, and provides automated analysis of a graphical signature, over time, of the viscoelastic characteristics of the blood sample, including a visual indication to the user of the activated clotting time period (ACT) and the rate of clot formation (RATE) of the blood sample under test, thereby improving the accuracy of the test results and simplifying operation of the instrument to permit its use by surgical personnel.
29 Citations
25 Claims
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1. An instrument for measuring one or more viscoelastic properties of a fluid sample, the instrument comprising:
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probe means disposed in contact with the fluid sample; electromechanical transducer means coupled to the probe means for providing mechanical displacement of the probe means relative to the fluid sample; first circuit means, connected to the electromechanical transducer means, said first circuit means comprising drive circuitry providing a drive signal for generating oscillatory mechanical displacement of the probe means relative to the fluid sample, said first circuit means further comprising response circuitry for monitoring a response signal generated by the electromechanical transducer means, the response signal being representative of the one or more viscoelastic properties of the fluid sample, said drive circuitry and response circuitry forming a feedback loop wherein the drive signal is developed from the response signal and vice versa; second circuit means for regulating an amplitude of a first signal within said feedback loop, while allowing said feedback loop to operate at resonant oscillatory frequency determined by said probe means, said electromechanical transducer means, and said first circuit means; and microcontroller means for receiving and analyzing said response signal to determine the one or more viscoelastic properties of the fluid sample represented by said response signal; and digital output means, coupled to said microcontroller means, for visually displaying to a user one or more numbers representative of the one or more viscoelastic properties, respectively, of the fluid sample, as determined by said microcontroller means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An instrument for measuring a plurality of viscoelastic properties of a fluid sample, the instrument comprising:
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probe means disposed in contact with the fluid sample; electromechanical transducer means coupled to the probe means for providing mechanical displacement of the probe means relative to the fluid sample; first circuit means, connected to the electromechanical transducer means, said first circuit means comprising drive circuitry providing a drive signal for generating oscillatory mechanical displacement of the probe means relative to the fluid sample, said first circuit means further comprising response circuitry for monitoring a response signal generated by the electromechanical transducer means, the response signal being representative of the plurality of viscoelastic properties of the fluid sample, said drive circuitry and response circuitry forming a feedback loop wherein the drive signal is developed from the response signal and vice versa; second circuit means for regulating an amplitude of a first signal within said feedback loop; and microcontroller means for receiving and analyzing said response signal to determine said plurality of viscoelastic properties of the fluid sample represented by said response signal; and digital output means, coupled to said microcontroller means, for visually displaying to a user one or more numbers, representative of one or more of said plurality of viscoelastic properties, respectively, of the fluid sample, as determined by said microcontroller means. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A process for computing the activated clotting time of a fluid sample, the process comprising:
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inserting a sensor into the fluid sample, the sensor producing a time varying signal responsive to a viscoelastic characteristic of said fluid sample; determining a minimum value of said viscoelastic characteristic over a predetermined period of time; comparing a current value of said viscoelastic characteristic with said minimum value; determining a point in time at which the current value of said viscoelastic characteristic exceeds said minimum value by a predetermined amount, said point in time being the activated clotting time of said fluid sample; and visually displaying said activated clotting time to a user.
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24. A process for computing the rate of clot formation of a fluid sample, the process comprising:
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inserting a sensor into the fluid sample, the sensor producing a time varying signal responsive to a viscoelastic characteristic of said fluid sample; determining an instantaneous rate of change in the viscoelastic characteristic of said fluid sample; comparing a current instantaneous rate of change in the viscoelastic characteristic of said fluid sample with a stored maximum value of the determined instantaneous rate of change in the viscoelastic characteristic of said fluid sample; determining if the current instantaneous rate of change in the viscoelastic characteristic of said fluid sample is less than said stored maximum value by a predetermined amount; and visually displaying said stored maximum value as said rate of clot formation if said current instanteous rate of change in the viscoelastic characteristic of said fluid sample is determined to be less than said stored maximum value by said predetermined amount.
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25. A process for detecting the presence of mechanical noise during a measurement of one or more viscoelastic properties of a fluid sample, the process comprising:
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inserting a mechanically oscillating sensor into the fluid sample, the frequency of oscillation of the mechanically oscillating sensor being responsive to a viscoelastic property of the fluid sample, and the mechanically oscillating sensor producing a time varying signal for analysis that is responsive to a viscoelastic property of the fluid sample; measuring a time characteristic of each oscillation of the mechanically oscillating sensor; comparing consecutive measurements of said time characteristic; determining if any two consecutive measurements of said time characteristic differ from each other by more than a predetermined amount; and suppressing analysis of said time varying signal for a predetermined period of time if any two consecutive measurements of said time characteristics are determined to differ from each other by more than said determined amount.
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Specification