Abstract:
A medical breath component analyzer which maintains a data-base profile of a patient over time. The apparatus may be used chronically by a patient so that a baseline status for that patient may be determined. Acute variations from the baseline are identified as clinically significant. The acquired data can be reported to the patient using the device at home and transmitted electronically to a physician or health care provider. Multiple tests may be provided, ranging from quantitative tests to qualitative tests to quantitative approximations using qualitative devices. A set of tests is selected for a particular patient, and may be customized to the patient&#39;s condition. One of the tests may include passing multiple laser beams of differing wavelengths through a breath sample and using pattern recognition to correlate from spectral analysis of all the laser beams.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This Application dais the benefit of U.S. Provisional Application No. 60/184,039 filed Feb. 22, 2000 
     
    
     
         [0002]    This invention relates generally to medical apparatus and in particular to apparatus for analyzing medically significant components in exhaled breath.  
         BACKGROUND OF THE INVENTION  
         [0003]    The potential for the use of exhaled breath as a diagnostic tool has long been recognized. Hypocrites taught the physician to be aware of the smell of the patient&#39;s breath, as a clue to the patient&#39;s condition. In 1784 Antoine Lavoisier and Pierre Laplace analyzed breath of a guinea pig, finding that an animal inhales oxygen and expires carbon dioxide. This was the first direct evidence that the body uses a combustion process to obtain energy from food. Since that time, as many as 200 compounds have been detected in human breath, some of which have been correlated with various diseases.  
           [0004]    Detection apparatus for breath components employ varying technologies. Infrared light has been used to measure breath alcohol content by Bowlds U.S. Pat. No. 5,422,485 and Paz U.S. Pat. No. 5,515,859. Sauke et al. U.S. Pat. No. 5,543,621 used a laser diode spectrometer. Other types of lasers and absorption spectroscopes have been used including cavity-ringdown spectroscopy. See, for example. “Absorption Spectroscopes: From Early Beginnings to Cavity-Ringdown Spectroscopy” B. A. Paldus and R. N. Zare, American Chemical Society Symp. Ser. (1999), Number 720, pp. 49-70. Other techniques include direct head space analysis, gas-liquid chromatography, atmospheric pressure ionization mass spectrometry, tandem mass spectrometry and chemical methods. See, for example., “The Diagnostic Potential of Breath Analysis”, Antony Manolis, Clinical Chemistry, 29/1 (1983) pp. 5-15. Among the chemical sensors are so-called electronic noses, which rely on patterns of physical or chemical characteristics to identify components. Such sensors are commercially available from Cyrano Sciences, Pasadena, Calif., for example, and their use in detecting medical conditions such as pneumonia, halitosis and malignant melanoma has been suggested.  
           [0005]    Many of these technologies are complex, expensive and difficult to calibrate. They have not been economically adapted for individual health care use. It has been suggested, however, that self-administered breath alcohol tests could be used (See, Brown et al. U.S. Pat. No. 5,303,575) by multiple individuals at bars or other locations where alcoholic beverages are served to detect a predetermined level of breath alcohol.  
         SUMMARY OF THE INVENTION  
         [0006]    To overcome the difficulties of calibration, patient-to-patient variation, and other problems, we have invented a medical breath-component analyzer, which maintains a database profile of a patient over time. It is intended that our invention be used chronically by a patient so that a baseline status for that patient may be determined. Acute variations from baseline are identified as clinically significant. The acquired data can be reported to the patient using the device at home and transmitted electronically to a physician or health care provider. Multiple tests may be provided, including quantitative tests, qualitative tests, and quantitative approximations using qualitative devices. In particular, laser spectroscopy with multiple lasers having different output characteristics may be used on a single breath sample. The merged output of the plurality of lasers can form a template or pattern, characteristic of a particular patient, whereby complex conditions may be more easily recognized. A set of tests is selected for a particular patient, and may be customized to the patient&#39;s condition. If a change in condition is detected, additional environmental and user-supplied information may be acquired to determine if a change is clinically significant. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a perspective drawing of a diagnostic breath analysis system according to the present invention.  
         [0008]    [0008]FIG. 2 is a block diagram of the system of FIG. 1.  
         [0009]    [0009]FIG. 3 is a drawing showing the relationship of FIG. 3A, FIG. 3B and FIG. 3C.  
         [0010]    [0010]FIG. 3A is a portion of a flowchart for the system of FIG. 1.  
         [0011]    [0011]FIG. 3B is an additional portion of the flowchart for the system of FIG. 1.  
         [0012]    [0012]FIG. 3C is a final portion of the flowchart for the system of FIG. 1.  
         [0013]    [0013]FIG. 4 is an additional flowchart including use of the system of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    We will now describe our invention in connection with the accompanying figures, wherein like numerals are used to designate like parts in each drawing. FIG. 1 illustrates a diagnostic breath analysis system  10  according to our invention. The system comprises an analysis unit  12 , which receives a breath sample from a patient  14  and provides quantitative and qualitative analysis of that sample as will be more fully explained below. Analysis of breath samples for diagnostic purposes has the advantage that the sample is collected non-invasively with a minimum of discomfort or inconvenience. The data resulting from the analysis is transferred to and stored in a computer  16 , preferably a microcomputer having an input device or devices  18 , such as a keyboard or mouse, an output device  20  such as a video monitor, printer, or other means of displaying data, memory  22  and an appropriate CPU  24 . The computer  16  is preferably connected to an information grid  26  such as a telephone system or the Internet.  
         [0015]    The basic components of the breath analysis system  10  can be further understood with reference to FIG. 2. The breath analyzer  12  comprises a mouthpiece  28  connected to a sampling device  30 . The sampling device  30  captures a portion of the patient&#39;s exhaled breath, preferably alveolar breath from deep within the lungs. The first part of exhaled breath usually contains “dead space” air, that is, air from the upper airways such as the trachea, mouth and nasal cavities. Dead space air does not contain many of the components that are of interest in making a diagnosis. In general, the first 150 ml of expiration is dead space air. About 500 ml is exhaled in each breath. About ninety percent of the breath is nitrogen and oxygen. The breath sample may be captured in a chamber or in a trap or both, depending on the apparatus employed for qualitative and quantitative analysis of the sample. Generally, traps fall into three categories: chemical, cryogenic, and adsorptive.  
         [0016]    It is important that the sample be representative of the breath of the user, and not contaminated by other influences. The system  10  should be calibrated from time to time. This may be done by injecting a gas of known composition into the sampling device. A gas-filled canister may be provided for this purpose. It is also important to purge the sampling device after use to discharge excess moisture or other components. This can also be accomplished by the injection of a gas and the two functions of calibration and purging may be performed in a single step. Certain types of analyzers are more stable and require less calibration than others. Cavity ring-down spectroscopy, for example, may require reference or “zero” calibration, but will remain stable unless the associated laser or cavity is changed.  
         [0017]    Although calibration is important, our invention reduces reliance on absolute standards by maintaining the patient profile or history. Thus a particular patient will usually be able to provide a consistent volume of breath for a sample. The volume will vary from patient to patient, but because records are maintained for the patient, the criticality of sample volume and other repetitive or consistent background factors (for example, air quality) is reduced or removed. Such features contribute to the usefulness of the apparatus in, for example, individual homes where each family member would develop their own profile by entering identifying information into the computer in connection with providing a sample.  
         [0018]    Certain portions of the sample are processed in a quantitative analyzer  32 . Quantitative analyzers may include laser spectroscopic devices, cavity ring down spectrometers and even certain electronic nose sensor arrays capable of performing quantitative measurements. Electronic nose sensor systems may be based on several different types of solid state sensor elements, the most sensitive of which are polymer-coated surface acoustic wave (“SAW”) oscillators that operate in the 100 megahertz range. Each element can easily sense as little as a femtogram (10 −15  gram) of absorbed mass. Upon exposure to vapor-phase samples, patterns of change in the masses of these elements are than seen as frequency shifts and interpreted by signal processing networks. These “neural networks” are computational layers of signal processing that compare these patterns to known responses characteristic of the target vapors “learned” in prior exposures to known compounds. The system then reports the result, usually along with statistical significance, or probability of correctness. The advantages of the electronic nose sensor include compactness and low cost due to an absence of moving parts. Improvements in on-chip memory capacities and signal processing speeds contribute to the usefulness of electronic nose sensor arrays for tracking vapors.  
         [0019]    A qualitative analyzer  34  may also be provided. Electronic nose sensor arrays may be also used in a qualitative configuration. Other possibilities include ion mobility spectrometer detectors, acoustic wave detectors, and fiber optic detectors. Processed data from both the quantitative analyzer  32  and the qualitative analyzer  34  are stored in memory  22  of the computer  16 . Preferably both quantitative and qualitative analyzers may be based on solid-state technology with consideration for reliability, accuracy and cost.  
         [0020]    In our invention, data from a particular patient is stored so that multiple samples over an extended period of time may be taken. This permits a baseline to be established for a particular patient, and trend analysis can be performed on the resulting data. If there is an acute and significant change in the chronic condition of the patient&#39;s breath, indications of this change may be sent by communications  26  to a physician or healthcare provider. It is important, therefore, that the patient  14  be identified through the user interface such as the keyboard  18 . Moreover, a clock  36  should be provided and connected to the computer  16 . Quartz crystal-based real-time clocks are common features of personal computers. The computer  16  should distinguish between multiple samples taken during a single session of data acquisition and multiple sessions of data acquisition that occur over an extended period of time, for instance, days, weeks, or months. The rate of change of the components of the breath over time is important in determining if a change in the patient&#39;s health, diet, or other condition has occurred. Additional sensors  37  may also be provided. These sensors may include an environmental thermometer, a barometer, a hygrometer, or other sensors for determining the condition in which the sample is given. The sensors may also include additional patient sensors, such as a patient thermometer, heart rate or blood pressure sensors. The output from the sensors  37  would be stored with the data obtained from the breath analysis and might also be used to determine if a particular change in breath components were significant or not.  
         [0021]    Processing of the sample by the analysis unit  12  and the computer  16  can be further understood in connection with the flowchart as illustrated in FIGS. 3A, 3B, and  3 C. FIG. 3 shows the relationship of FIGS. 3A, 3B, and  3 C to each other. The combined FIGS. illustrate a process system  50  for analyzing a patient&#39;s breath. Initially, the system  50  should be customized for the particular patient by selecting the tests  52  to be employed, as shown in FIG. 3A. Tests may also be added to or removed from the profile for a particular patient at any time during the use of the apparatus, particularly in response to changes in the patient&#39;s condition or for other reasons. The types of tests that may be employed include carbon dioxide content, breath temperature, alcohol, lipid degradation products, aromatic compounds, thio compounds, ammonia and amines or halogenated compounds. As an example of the usefulness of detecting these components, lipid degradation products such as breath acetone are useful in monitoring diabetes. Thio compounds such as methanethiol, ethanethiol, or dimethyl sulfides have diagnostic significance in the detecting widely differing conditions, such as psoriasis and ovulation. Increased ammonia has been associated with hepatic disease. Halogenated compounds may be indicative of environmental or industrial pollutants.  
         [0022]    Another set of tests may be based on analysis of certain breath components after the patient has taken a diagnostic reagent, in accordance with instructions from a physician. For example, urea, especially C 13  labeled urea, or C 13  labeled carbohydrates may be taken orally and the C 13 -based CO 2  analyzed in the exhaled breath to determine if the patient has heliobactor pylori infection of the stomach lining (urea=&gt;NH 3  and CO 2 ) or carbohydrate malabsorbtion, glucose intolerance, lactase deficiency or small bowel bacterial overgrowth. Carbon 13 isotopes can be differentiated by laser spectroscopy. See, for example., G. B. U.S. Pat. No. 2,218,514. As explained hereafter (step  140 ), the resulting data would be transmitted to the attending physician for appropriate action.  
         [0023]    With particular tests selected for the patient, the system would be initialized  54  to begin to build a baseline or chronic breath condition history for a particular patient. Both during initialization and thereafter, as tests are taken over an extended period of time, a sample would be received from the patient at step  56 . The microprocessor  16  determines if quantitative tests  58  have been selected for this particular patient. If quantitative tests have been selected, a quantitative test segment  60  would be performed. Quantitative tests are performed for selected components α, either simultaneously or serially, depending on the capacity of the quantitative test device  32 . The tests would be performed  62  using a suitable quantitative device  32 , as mentioned above, including, for instance, laser spectroscopic devices, cavity ring down lasers, certain electronic nose sensor arrays, or other quantitative apparatus. The last stored or baseline test data  64  would then be recalled from memory and the change or delta information between the new test data and stored test data is determined  66 . New test data and delta information  68  is stored in memory  22 . It is determined at step  70  if the tested component α is the last component for which quantitative tests have been selected. If it is not the last component or α, a new α is set at step  72  and tests for the next component α are then performed. This may be done simultaneously or serially on a single sample if the quantitative device  32  is capable of multiple analysis or an additional sample may be requested of the patient at step  73 . Cavity-ring-down spectroscopy, for example, is capable of measuring multiple components simultaneously. If the last quantitative test has been performed, control of the device inquires at step  74  whether any qualitative tests should be performed.  
         [0024]    If no qualitative tests are to be performed, data would be reported through a report process  76 , as will be more fully described below. If qualitative tests are to be performed, the tests may fall into three different types. First, the presence  78  of the breath component alone may be significant to the health of the patient. See FIG. 3B. This may particularly be important where the chronic monitoring of the breath components of the patient have indicated the absence of a component and that component appears in a new test. The converse change may also be significant, that is, if a component formerly present is absent in the new test. Both conditions can be detected by a device because of the maintenance of a patient&#39;s specific data history in memory  22 .  
         [0025]    Second, it may be significant that a newly detected component falls within a given range  80 . See FIG. 3C. Although the components may be detected by a qualitative device  34 , estimates of the range may be obtained by certain manipulations of the qualitative device. This may be important where it is economically infeasible to employ a quantitative device with respect to a particular component but an approximation can be obtained which is sufficient to alert an attending physician of the need for a more detailed analysis or which is sufficient to allow the patient to follow a course of treatment, as in diet control, either for weight loss or for diabetes.  
         [0026]    Third, a more specific approximation  82  may be obtained using the qualitative device as will be more particularly described below. See FIG. 3C. The results of both testing for presence, range and approximation, together with quantitative results would then be reported  76 .  
         [0027]    Referring now to FIG. 3B, the presence of  78  of a component β may be tested with a qualitative device, for example, an electronic nose sensor array, by recalling  84  the patient&#39;s last settings for detection of the desired components at a level of detection (“LOD β”) for that particular component. Qualitative tests would then be performed at  86 . At step  88 , it is determined if the component β is present. If the test for component β is negative, it should be determined  90  if the minimum or most sensitive setting for the LOD β has been used. If greater sensitivity can be employed, the sensitivity would be adjusted  92  to maximum or LOD min and, if necessary, an additional sample  94  requested of the patient before the test  86  is performed again. In a particular qualitative device it may not be necessary to take an additional sample  94 . However, successive approximations using qualitative tests to acquire an approximate quantitative result may require that additional samples be taken from time to time. The computer  16  would alert the user  14  of the need to supply an additional sample. All such initial and additional samples would then be considered a single data acquisition event.  
         [0028]    If the component is determined to be present at  88 , or if the minimal setting LOD β has already been used, indicating that a component is not present within the limits of the detection device, it should be determined if this is the last component β for which a test is required. If it is not the last component, the test for the next component  98  would be initiated which may involve taking an additional sample  100 . As with the quantitative test, however, it is also possible to simultaneously identify multiple components from a single sample or sample cycle. This is particularly the case for pattern recognition type technology, such as an electronic nose sensor array. Tunable diode lasers are also effective in identifying multiple components simultaneously. Thus, in addition to the diagnostic significance of a compound present in the breath, and the amount of compound present, the presence of the compound in a familiar pattern with other compounds may also be diagnostically significant.  
         [0029]    After the qualitative components have been identified, it may be desirable to quantify certain of those components at step  102 . Of course, only components determined to be present need be quantified. If no quantitative approximation is desired, the report  76  would again be generated. If a quantitative approximation is desired, it is determined whether a range  104  is requested or if a more narrow approximation is to be sought.  
         [0030]    If a range is desired, a range test  80  is initiated, as shown in FIG. 3C. A first limit  106  for the particular patient is recalled from memory  22 . This may involve setting the level of detection LOD to a particular level such that the component β will no longer be detected because the qualitative detector is no longer sensitive enough to recognize that component. This would indicate that the component is below a selected maximum. If necessary, a new sample is taken  108  and it is determined if the component β is present  110  at that level of detection LOD. If the component β is no longer detected, it would be reported  112  that the component falls below the selected limit. On the other hand, if the component continues to be detected, it would be reported that the component&#39;s concentration exceeds the selected limit  114 . The data would be stored  1   16  indicating that for the particular component met or did not meet the selected criteria. This may be sufficient to determine if the component is low enough for health or if it exceeds a healthy range. If it is desired to place the component within a maximum and minimum range, a test for a second limit  118  should be performed. If the second limit test is performed, a new setting for the LOD is provided  120  and the cycle is repeated at the second selected setting. Results of the test are then delivered to the report section  76 .  
         [0031]    It may also be desired to obtain an approximation of the quantitative level for a particular component, employing a qualitative test device at subroutine  82 , as shown in FIG. 3C. This may also be accomplished by adjusting the level of detection of the qualitative device and performing iterative tests. Because the patient&#39;s data is maintained over a longer period of time, the last level of detection for the component β can be recalled from memory at step  120 . This provides a starting point for the search for the present level of the component. A new level of detection LOD NEW  is obtained from the last level of detection plus or minus a selected a constant or “delta”  122 . The LOD NEW  must be lowered by taking new approximation  130  comprising LOD LAST  plus the minimum LOD MIN  divided by two. If it is determined  132  that the difference between LOD NEW  and LOD LAST  is less than a preselected limit, then the process should be halted as the desired degree of accuracy has been obtained. The information would then be stored  134  before. Otherwise, the microprocessor would repeat the process by applying LOD NEW  to either an existing sample or a new sample  124 .  
         [0032]    We have described here one method for obtaining a quantitative approximation utilizing a qualitative device. Methods of numerical analysis known to persons skilled in the art will suggest other techniques that could be applied to obtain a similar result without departing from the teachings of our invention.  
         [0033]    The results obtained from the quantitative tests  60 , the presence test  78 , range test  80  and qualitative approximation  82  are examined in the report algorithm  76  by the computer  16 . Computer  16  should check for significant changes  136  in the selected components either α (quantitative) or β (qualitative) as set in a profile for the particular patient selected by the physician or as part of the step of identifying the selected tests  52 . Significant deviations from the patient&#39;s chronic condition are reported both to the patient  138  and by the communications connection  26  through transmission  140  to the physician or healthcare provider. In addition significant components that exceed predetermined levels or are less than acceptable levels will be reported. Two-way communication across the information grid  26  would also permit the remote care-giver to select additional tests, initiate apparatus self-diagnostics, or perform other functions associated with setting or testing the apparatus from a remote location.  
         [0034]    Maintaining the patient&#39;s chronic history of breath analysis enables our device to identify acute changes of significance to the patient&#39;s treatment and health. Background influences and variation from patient to patient can be reduced or eliminated by establishing this baseline condition for the patient. The tests described herein will be terminated  142  and may be performed again at a subsequent time thus allowing the patient to monitor his condition over time.  
         [0035]    Significant changes in a patient&#39;s condition may be identified by suitable statistical or analytical methods. One such method for determining significant changes in multivariate data is described by Beebe et al., U.S. Pat. No. 5,592,402, incorporated herein by reference. Components of breath identified by the selected tests represent a multivariate data set which can be analyzed to determine whether abnormal features are present. Variations can be identified by establishing a calibration set from which a set of average values and expected statistical deviation from those values may be determined. Variations of a predetemined magnitude, for example more than three standard deviations from the expected average value, may be declared statistically significant and reported as such. Average values and statistical deviations may be set by providing an initial test period or series of initial samples taken under controlled conditions, or they may be continually updated by the apparatus either by calculating a cumulative average and deviation or by maintaining a rolling average and deviation. Moreover, the complex set of data may be separated into various sub-parts to further identify significant variation. Such sub-parts may include peak or minimum values, noise, baseline offset or baseline shape. Each of the sub-parts can be monitored to see if it is within the normal range expected for analysis. This may help in identifying which type of feature is abnormal. For example, different patients may have the same absolute value for a particular breath component. In one patient, this value may be associated with a with a particularly high baseline level. In another patient, the baseline may be rising sharply. In another, it may be falling slowly. In another, the value may have been reached by an acute change, exceeding a peak value and statistically significant. Yet another patient may routinely have much wider variation in the selected component and the change in value may not be statistically significant. For each patient, a different report may be provided, based on the learned pattern for the particular patient. Of course, absolute maximum or minimum values for given components may also be set, and measurements exceeding those maximum or minimum values may be reported without regard to patient history.  
         [0036]    The use of the breath analyzer  10  is further explained in connection with the flow chart  150  of FIG. 4. As shown in the flow chart  150 , use of the breath analyzer  10  begins with calibration  152 . This may be accomplished by injecting a gas of known composition into the device. A canister of such gas may be provided for this purpose. After calibration, a sample  154  is taken. This step includes the procedures described in greater detail above in connection with FIG. 3. The analyzer  10  may acquire environmental data at step  156 , using the additional sensors  37  described above. The analyzer  10  would then compare  158  the stored history of the patent to present readings to determine  160  if a change has taken place. If there is a change, it is determined  162  if the change is significant in view of the patient&#39;s history and the environmental factors measured at step  156 . If the change is determined to be significant, the analyzer may request additional tests  164 . Such tests may include further breath tests for additional components not ordinarily in the set of tested components, repeat tests, or additional tests for which sensors  37  are provided, for example, blood pressure, blood oxygen (through, for example, an infrared sensor placed on the patient&#39;s finger), heart rate, or body temperature. A cardiac pacemaker programming and data transfer wand may be one such sensor  37 . Cardiac pacemakers often store historic data including numbers of pacing beats, number of ectopic beats, incidents of atrial fibrillation or tachyarrhythmia, or (for cardiovertor/defibrillators) ventricular fibrillation or tachyarrhythmia. Information on applied therapies, threshold levels, and even recorded electrocardiograms may be stored by a pacemaker or implantable cardiovertor/defibrillator. This information may be associated with the data records maintained by our device after transmission from the implanted cardiac stimulator. Techniques for such data transfer are well known.  
         [0037]    The analyzer may also request the user or patient to enter certain data through the microcomputer user interface (for example., keyboard or mouse). The requested data might include diet information, perceived general state of health, amount and duration of recent exercise and similar factors which might either explain an acute change in breath components (that is, indicate that the change is not in fact significant) or provide important information for a health care provider.  
         [0038]    After gathering additional information (steps  164  and  166 ) or if there was no change (step  160 ) or no significant change (step  162 ), a report will be generated  168  for the user and the information stored as part of the patient&#39;s history. The report or data may be transmitted  170  to a remote health care provider, either immediately or in response to a request for data. Finally, the system would be purged  172  to prevent contaminants from building up in the sampling device. As mentioned above, this may be accomplished by providing a gas of known composition and may be combined with the calibration step  172 .  
         [0039]    Multiple tests performed on a single sample may be independent or the results of several tests may be combined to produce a template or pattern representative of a patient&#39;s condition or representative of the presence of a particular compound or set of compounds. E-nose techniques have used pattern recognition to detect the presence of particular compounds. Multiple lasers could also be used on a single sample to extend the band width for detection and pattern recognition could than be applied to the combined output of the several lasers. A single laser is generally capable of emitting light at certain limited frequencies. Although some tuning or variation of frequencies is possible, the elements or compounds that can be effectively recognized by a single laser device are limited by the frequency characteristics of the selected laser. The detector  34  of our invention may include multiple lasers having different emission frequencies. The lasers may be directed into a single sample by being physically offset around the sample, by being fired at slightly different times, or other techniques. Optical apparatus such as mirrors, lenses or prisms may be used to direct a beam from a selected laser along a path through the sample and into a detector. By adjusting the optical apparatus, beams from other lasers may be directed along the same or a similar path through the sample. By using lasers with different emission characteristics with the same sample, A wider set of data points may be obtained. Instead of three or four data points for a single laser, three lasers may obtain twelve or more data points from the same sample. This information may be expected to be both more selective and more quantitatively precise than similar information obtained by electronic nose technology. The resulting more accurate information from all the laser beams can nevertheless be processed together, using pattern recognition methods in similar to those used in connection with e-nose techniques. As a result, a wider range of conditions or compounds may be identified by correlating the data pattern or changes in the data pattern over time.  
         [0040]    The foregoing examples of embodiments of our invention should be deemed exemplary only. Persons skilled in the art will recognize that changes and modifications could be made in the design or construction without departing from the scope or teachings of our invention. It is intended, therefore, that the scope of our invention should be defined by the accompanying claims.