1. Field of the Invention
The present invention relates, in general, to medical devices and, in particular, to test meters and related methods.
2. Description of Related Art
The determination (e.g., detection and/or concentration measurement) of an analyte in a fluid sample is of particular interest in the medical field. For example, it can be desirable to determine glucose, ketone bodies, cholesterol, lipoproteins, triglycerides, acetaminophen and/or HbA1c concentrations in a sample of a bodily fluid such as urine, blood, plasma or interstitial fluid. Such determinations can be achieved using a hand-held test meter in combination with analytical test strips (e.g., electrochemical-based analytical test strips).
The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings, in which like numerals indicate like elements, of which:
The following detailed description should be read with reference to the drawings, in which like elements in different drawings are identically numbered. The drawings, which are not necessarily to scale, depict exemplary embodiments for the purpose of explanation only and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.
As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein.
In general, hand-held test meters for use with an analytical test strip (such as an electrochemical-based analytical test strip) in the determination of an analyte (e.g., glucose) in a bodily fluid sample include a housing, an electrical signal receiving block disposed in the housing, a signal recovery block disposed in the housing, and a microcontroller block disposed in the housing. In addition, the electrical signal receiving block is configured to receive an electrical signal from an analytical test strip inserted in the hand-held test meter that has been distorted into a distorted electrical signal. Furthermore, the signal recovery block and microcontroller block are configured to recover the electrical signal from the distorted electrical signal by generating a recovered electrical signal based on (i) a predetermined recovered electrical signal frequency, (ii) a recovered electrical signal amplitude estimated from the distorted signal, (iii) a recovered electrical signal offset estimated from the distorted electrical signal and (iv) a recovered electrical signal phase determined using a least sum squares calculation.
Hand-held test meters according to embodiments of the present invention are beneficial in that, for example, the recovered electrical signal can be employed during use of the hand-held test meter, thus increasing accuracy and reliability of such use. In addition, the hand-held test meters according to embodiments of the present invention generate the recovered electrical signal in a relatively short time period and can employ low power components (e.g., low power microcontroller blocks).
Referring to
Display 102 can be, for example, a liquid crystal display or a bi-stable display configured to show a screen image. An example of a screen image may include a glucose concentration, a date and time, an error message, and a user interface for instructing an end user how to perform a test.
Strip port connector 106 is configured to operatively interface with an analytical test strip TS, such as an electrochemical-based analytical test strip configured for the determination of glucose in a whole blood sample. Therefore, the analytical test strip is configured for operative insertion into strip port connector 106 and to operatively interface with electrical signal receiver block 112 and microcontroller block 116 via, for example, suitable electrical contacts.
USB Interface 108 can be any suitable interface known to one skilled in the art. USB Interface 108 is essentially a passive component that is configured to power and provide a data line to hand-held test meter 100.
Once an analytical test strip is interfaced with hand-held test meter 100, or prior thereto, a bodily fluid sample (e.g., a whole blood sample) is introduced into a sample chamber of the analytical test strip. The analytical test strip can include enzymatic reagents that selectively and quantitatively transform an analyte into another predetermined chemical form. For example, the analytical test strip can include an enzymatic reagent with ferricyanide and glucose oxidase so that glucose can be physically transformed into an oxidized form.
Memory block 118 of hand-held test meter 100 includes a suitable analyte determination algorithm and is configured to store a received distorted signal. Moreover, memory block 118 can also be configured, along with microcontroller block 116 to determine an analyte based on the electrochemical response of analytical test strip.
Microcontroller block 116 is disposed within housing 110 and can include any suitable microcontroller and/or micro-processer known to those of skill in the art. One such suitable microcontroller is a microcontroller commercially available from Texas Instruments, Dallas, Tex. USA and part number MSP430F5636. This microcontroller can function as a signal generation block as described further below. MSP430F5636 also has Analog-to-Digital (ND) processing capabilities suitable for processing voltages (e.g., voltages received from a transimpedance amplifier of electrical signal receiving block 112).
Electrical signal receiving block 112 is configured to receive an electrical signal (such as a sine wave signal) from an analytical test strip inserted in the hand-held test meter that has been distorted into a distorted electrical signal. In other words, the electrical signal that is generated at the analytical test strip can be distorted by an interfering electromagnetic field into a distorted electrical signal and it is that distorted electrical signal that is received by electrical signal receiving block 112. Such a distorted electrical signal is depicted in
A non-limiting example of a sine wave electrical signal is an alternating current (ac) signal generated during measurement of a capacitance of the analytical test strip in response to an applied ac excitation voltage. Such an applied ac excitation voltage can be created by, for example, microcontroller block 116 of hand-held test meter 110.
Signal recovery block 114 and microcontroller block 116 are configured to recover the electrical signal from the distorted electrical signal by generating a recovered electrical signal based on a predetermined recovered electrical signal frequency, a recovered electrical signal amplitude estimated from the distorted signal, a mean offset of the distorted electrical signal and a recovered electrical signal phase determined using a least squares calculation. An exemplary technique for generating the recovered electrical signal is described below.
To generate a recovered electrical signal, a predetermined electrical signal frequency is assigned as the fixed frequency of the recovered electrical signal. The predetermined electrical signal can be, for example, the frequency of an alternating current (AC) excitation voltage that was applied to the analytical test strip to create the electrical signal which was subsequently distorted. A typical but non-limiting example would be a frequency of 109 Hz.
The recovered electrical signal amplitude is estimated as a root-mean-square from the distorted electrical signal. A representative equation for calculating the root-mean-square of a voltage signal (i.e., V(rms)) from a distorted electrical signal consisting of 64 discrete measurements is as follows:
where:
The offset is estimated as an average of all discrete measurements along the distorted electrical signal. For example, if the distorted electrical signal was received as a sequence of 64 discrete measurements, then those 64 measurements points are averaged to estimate the offset.
To estimate the recovered electrical signal phase, an ideal sine wave is generated based on the predetermined electrical signal frequency, the estimated recovered signal amplitude, the estimated recovered signal offset and an arbitrary phase (such as 30 degrees). Such an ideal sine wave (also referred to as an initial generated signal) is depicted in
The difference between the ideal sine wave and the distorted electrical signal is then calculated.
where:
Vdistorted[x]=the voltage of distorted electrical signal measurement x;
and
Videal[x]=the voltage for the ideal sine wave at measurement point x.
For any given arbitrary phase and associated ideal sine wave, a “sum of squares” figure (value) can be obtained. The closer the phase of the ideal sine wave is to the original electrical signal prior to distortion, the smaller the “sum of squares” value will be. Therefore, the best estimation of the phase of the recovered electrical signal occurs when the “sum of squares” value reaches a minimum, hence the Least Sum Square (LSS) nomenclature.
Finally, the recovered electrical signal is generated based on the best estimated phase determined using the LSS method, the predetermined frequency, the estimated amplitude and the estimated offset. Such a recovered electrical signal is depicted in
A benefit of embodiments of the present invention is that the LSS method for determining phase requires only a relatively small amount of computation time, and can, therefore, be performed using a low-power microcontroller. Traditional methods that do not rely on the initial estimation of frequency, phase and offset typically require many hours to run and require powerful power-consuming stand-alone computers that cannot be integrated into a hand-held test meter. Moreover, the techniques employed in embodiments of the present invention have been shown to be robust in that they rarely encounter distorted signals that result in errors.
If desired to reduce computing time, an initial estimate of the phase of the recovered electrical signal can be made using arbitrary phases in 10 degree increments. Next, a final estimation of the phase can be performed using 0.5° increments from a phase starting 5° before the initial phase estimate. This requires, therefore, a maximum of 18 LSS calculations (i.e., 7 for initial estimation and 11 for final estimation).
Once apprised of the present disclosure, one skilled in the art will recognize that any or all of the electrical signal receiver block, signal recovery block, and microcontroller block and memory block can be integrated into a combined block. For example, the electrical signal receiver block, signal recovery block, and microcontroller block can be combined into a single block configured to perform all of the functions performed by the individual blocks.
Subsequently, at step 820 of method 800, the electrical signal is recovered from the distorted electrical signal by employing a signal recovery block and a microcontroller block of the hand-held test meter to generate a recovered electrical signal based on (i) a predetermined recovered electrical signal frequency; (ii) a recovered electrical signal amplitude estimated from the distorted signal; (iii) a recovered electrical signal offset calculated as the mean offset of the distorted electrical signal; and (iv) a recovered electrical signal phase determined using a least squares calculation methodology.
Once apprised of the present disclosure, one skilled in the art will recognize that method 800 can be readily modified to incorporate any of the techniques, benefits and characteristics of hand-held test meters according to embodiments of the present invention and described herein.
While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that devices and methods within the scope of these claims and their equivalents be covered thereby.