Smart physiologic parameter sensor and method
A sensor assembly used for the measurement of one or more physiologic parameters of a living subject which is capable of storing both data obtained dynamically during use as well as that programmed into the device. In one embodiment, the sensor assembly comprises a disposable combined pressure and ultrasonic transducer incorporating an electrically erasable programmable read-only memory (EEPROM), the assembly being used for the non-invasive measurement of arterial blood pressure. The sensor EEPROM has a variety of information relating to the manufacture, run time, calibration, and operation of the sensor, as well as application specific data such as patient or health care facility identification. Portions of the data are encrypted to prevent tampering. In a second embodiment, one or more additional storage devices (EEPROMs) are included within the host system to permit the storage of data relating to the system and a variety of different sensors used therewith. In a third embodiment, one or more of the individual transducer elements within the assembly are made separable and disposable, thereby allowing for the replacement of certain selected components which may degrade or become contaminated. Methods for calibrating and operating the disposable sensor assembly in conjunction with its host system are also disclosed.
Pursuant to 35 U.S.C. 119(e), this application claims priority benefit of U.S. provisional patent application Ser. No. 60/152,534 entitled “Smart Blood Pressure Sensor and Method” filed Sep. 3, 1999.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to the field of medical instrumentation, specifically the use of electronic storage devices for storing and retrieving data relating to, inter alia, particular instruments or patients.
2. Description of Related Technology
The ability to readily measure various physiologic parameters associated with a living subject, such as arterial blood pressure or ECG, is often critical to providing effective care to such subjects. Typically, under the prior art, measurement of such parameters is accomplished using a system comprising a host device such as a portable or semi-portable monitoring station that is used in conjunction with a replaceable/disposable probe or sensor assembly, the latter being in direct contact with the subject and measuring the physical parameter (or related parameters) of interest. Such replaceable and disposable sensor assemblies are highly desirable from the standpoint that the risk of transfer of bacterial or other contamination from one patient to the next is significantly mitigated; the portion of the sensor assembly (or for that matter entire assembly) in contact with a given subject is replaced before use on another subject.
However, despite the mitigated risk of contamination, the use of such prior art disposable sensors also includes certain risks. One such risk relates to the potential re-use of what are meant to be single-use only components. Inherently, individuals or health care providers may attempt to re-use such single use components if there is no seeming degradation of the component or perceived threat of contamination. However, in the case of certain devices, the degradation of the component may be insidious and not immediately perceptible to the user. For example, the offset (i.e., difference of voltage generated by the device at certain prescribed conditions) associated with an elastomer-coated pressure transducer used in a non-invasive blood pressure monitoring device may change progressively in small increments over time due to swelling of the elastomer coating resulting from exposure to certain chemical substances. This variation in offset manifests itself as a change in the ultimate blood pressure reading obtained using the device, thereby reducing its accuracy. Hence, the readings obtained using the instrument may appear to be reasonable or correct, but in fact will incorporate increasing amounts of error from the true value of the parameter, which may significantly impact the treatment ultimately provided to the subject. Hence, what is needed is an approach wherein any such degradable or single use components are reliably replaced at the necessary interval such that performance does not appreciably degrade.
A related issue concerns the re-use of such devices on different patients. Specifically, if the “single use” components are perceived by the user not to degrade rapidly, the user may be tempted to use the device (including the single use transducer(s)) on several different patients. Aside from the aforementioned performance issues, such repeated use may be hazardous from a contamination standpoint, as previously discussed. Ideally, portions of the device capable of transmitting bacterial, viral, or other deleterious agents are disposed of and replaced prior to use on another patient.
Another risk concerns the use of third party or non-compliant sensors with the host device of the original equipment manufacturer (OEM). While such third party sensors may ostensibly be manufactured to the design specifications and requirements of the OEM, in many cases they are not, which can result in readings obtained using the system which are less than accurate or even wholly non-representative of the parameter being measured. Even OEM supplied disposable sensors may have defects. Another troubling aspect is the fact that the caregiver or health care professional who is provided with such disposable sensors may have no means by which to verify the quality or acceptability of a given replaceable sensor, and therefore the accuracy of any reading they may obtain using that sensor may be called into question. Hence, even if the majority of sensors within a given lot obtained from the third party manufacturer are acceptable in terms of performance, the caregiver often has no way of knowing whether the next replacement sensor they use will perform as designed or intended by the OEM and yield representative results. In the ideal case, the quality of each individual replacement sensor would be determined by the host system prior to use (such as when the new replacement sensor is first installed on the host), and the caregiver apprised of the results of this determination.
The calibration of the replaceable/disposable sensor, whether OEM or otherwise, and the host system must also be considered. Under the prior art approach, calibration is most often performed on the system as a whole at a discrete point in time, and is generally not performed before each use of the device after a new sensor or probe has been installed. Hence, the calibration of the host system and replaceable sensor as a whole is not specific to each given sensor, but rather to a “nominal” sensor (i.e., the one in place in the system when the calibration was performed). For example, the system may be calibrated before first use, and then periodically thereafter at predetermined intervals, or at the occurrence of a given condition. Under this approach, changes in the physical operating characteristics of the host system may result in changes in the calibration over time. Due to any number of intrinsic or external factors, the device may “drift” between calibrations, such that a reading taken with the device immediately following calibration may be substantially different from that obtained using the same device and identical conditions immediately before the next calibration.
Additionally, due to manufacturing tolerances and variations, the performance of each individual replaceable sensor may vary significantly from other similar devices, as previously described. Such variations are generally accounted for by the OEM by specifying a maximum allowable tolerances or variances for certain critical parameters associated with the sensors; if these tolerances/variances are met for a given replaceable sensor, then the accuracy of the system as a whole will fall within a certain (acceptable) tolerance as well. Ideally, however, the system would be calibrated specifically to each individual replaceable sensor immediately prior to use, a capability which is not present in prior art disposable medical devices.
Another concern relates to the potential for surreptitious alteration of data stored by an instrument prior to or during operation. As with many other types of devices, the ability to make a device “tamperproof” is of significant importance, in that this provides the caregiver and subject with additional assurance that the disposable sensor in use is the correct type of sensor for the host system, that the sensor assembly and host system are properly calibrated, and that the disposable sensor has not been used on other subjects.
Lastly, it is recognized that prior art measurement systems do not include the facility for evaluating the accuracy of a given measurement or host/sensor combination after readings have been taken. Many systems are capable of storing data relating to a measurement obtained from a subject in terms of the estimated value(s) derived by the system, yet none of which the Assignee hereof is aware allow for the retrieval of data specific to a given sensor or permit the system operator to evaluate the performance (and accuracy) of the system historically. Such information is of great potential utility in the medical field, especially with relation to medical malpractice litigation, by enabling the caregiver or OEM to reconstruct the operation of their equipment to demonstrate that a given measurement obtained using a given sensor and host unit was in fact accurate, that the disposable sensor had been replaced prior to use on the patient, and the like. The availability of this information may also produce the added benefit of reduced medical malpractice insurance premiums for facilities using such systems, since the potential for fraudulent claims relating to the system is reduced.
Based on the foregoing, what is needed is an apparatus and associated method useful for measuring one or more physiologic parameters associated with a living subject wherein any degradable or single use components associated with the apparatus may be easily and reliably replaced so as to ensure that (i) the accuracy of the system and any measurements resulting there from do not degrade; (ii) cross-contamination between subjects does not occur; and (iii) the operating history of the replaced components and system as a whole may be subsequently retrieved for analysis.
SUMMARY OF THE INVENTIONThe present invention satisfies the aforementioned needs by an improved apparatus and method for monitoring the physiologic parameters, such as for example arterial blood pressure, of a living subject.
In a first aspect of the invention, an improved sensor assembly incorporating an electronic storage element is disclosed. In a first embodiment, the device comprises one or more ultrasonic transducers and a removable (and disposable) pressure transducer, the latter further including a storage device in the form of an electrically erasable programmable read-only memory (EEPROM) capable of storing data and information relating to the operation of the sensor assembly, host system, and patient. The sensor EEPROM includes a variety of information relating to the manufacture, run time, calibration, and operation of the pressure transducer, as well as application specific data such as patient or health care facility identification. Portions of the data are encrypted to prevent tampering. Furthermore, the host system is programmed such that the sensor assembly will be rejected and rendered unusable by the host if certain portions of the aforementioned data do not meet specific criteria. In this fashion, system operational integrity, maintainability, and patient safety are significantly enhanced. In a second embodiment, one or more additional storage devices (e.g., EEPROMs) are included within the host system to permit the storage of data relating to the system and a variety of different sensors used therewith. In a third embodiment, a single storage device (e.g., EEPROM) is associated with the entire sensor assembly, including ultrasonic transducer(s) and pressure transducer, and adapted to store and provide data relating thereto.
In a second aspect of the invention, an improved sensor housing assembly is disclosed. In one exemplary embodiment, the housing assembly comprises first and second housing elements which are fabricated from a low cost polymer and which include recesses containing the ultrasonic and pressure transducer elements, respectively. The first housing element is adapted to removably receive the second such that the active faces of the ultrasonic and pressure transducer elements are substantially aligned when the housing elements are assembled, and the second housing element (and associated pressure transducer with EEPROM) can be readily disposed of and replaced by the user when required without having to replace or dislocate the first housing element. In a second embodiment, the first housing element is also made optionally removable from the sensor assembly such that the user may optionally replace just the pressure transducer/EEPROM, the ultrasonic transducer(s), or both as desired.
In a third aspect of the invention, an improved system for measuring one or more physiologic parameters of a living subject is disclosed. In one embodiment, the physiologic parameter measured comprises arterial blood pressure in the radial artery of a human being, and the system comprises the aforementioned sensor assembly having at least one ultrasonic transducer capable of generating and receiving ultrasonic signals, a pressure transducer capable of measuring the pressure applied to its active surface, and a storage device associated therewith; a local controller assembly in data communication with the sensor assembly further including an applanation/lateral device and controller, and a remote analysis and display unit having a display, signal processor, and storage device in data communication with the local controller assembly. Calibration and other data pertinent to the sensor assembly which is stored in the storage device (e.g., EEPROM) of the sensor assembly is read out of the EEPROM and communicated to the analysis and display unit, wherein the processor within the unit analyzes the data according to one or more algorithms operating thereon. Signal processing circuits present within the local controller assembly are also used to analyze electrical signals and data relating to the operation of the sensor assembly.
In a fourth aspect of the invention, an improved circuit used in effectuating the calibration of the transducer element(s) of the aforementioned sensor array are disclosed. In one exemplary embodiment, the circuit comprises an analog circuit having a transducer element, a span TC compensation resistor Ra, analog-to-digital converter (ADC), digital-to-analog converter (DAC), and operational amplifiers. The voltage output of the pressure transducer (bridge) is input to a first stage instrumentation amplifier which amplifies the transducer output signal. The amplified output is input to a second stage amplifier, along with the output of the, DAC, which is subtracted from the signal. The output of the second stage amplifier represents the temperature compensated, zero offset output signal of the circuit. The DAC converts a digital signal derived from the system processor to compensate the output for the offset of the bridge, as well as the temperature coefficient of the offset. The ADC is used to measure the bridge voltage, which varies with temperature by virtue of span compensation resistor Ra. Resistor Ra has a near zero TC, while the bridge itself has a positive TC. Thus, the bridge voltage varies with temperature, and can be correlated to the offset variation with temperature. In a second embodiment, the DAC and second amplifier are omitted, and replaced by a high resolution ADC. The converter must have the dynamic range and signal to noise ratio to measure the large output swing from the instrumentation amplifier. This is true, because the output now contains both the signal, and the offset error, and offset TC error. In this embodiment, the bridge voltage still varies with temperature and is digitized by the ADC after amplification, but all the compensation is handled by digital signal processing in the system processor.
In a fifth aspect of the invention, an improved method of operating a disposable sensor in conjunction with its host system is disclosed. In one embodiment, the method comprises storing at least one data field within the aforementioned storage device of the sensor, connecting the sensor to a host system, and determining the compatibility of the sensor with the host device based at least in part on the at least one data field. In a second embodiment of the method, the sensor is operated in order to obtain data from at least one living subject; this data is then stored within the sensor and/or host system in order to provide a retrievable record of the operation of the sensor and of the specific patient tested.
In a sixth aspect of the invention, an improved method of calibrating a transducer element used within a blood pressure monitoring device is disclosed. The method comprises providing a transducer element having a predetermined operating response and associated storage device; determining the operating response for the transducer; determining a plurality of calibration parameters based on the determined operating response; storing data representative of the calibration parameters within the storage device; and calibrating the transducer during operation based at least in part on the stored calibration parameters. In one embodiment, the transducer element comprises a silicon strain beam pressure transducer and the calibration parameters comprise reference voltage and temperature values, linearity, sensitivity, and shunted resistor values calculated using a series of predetermined functional relationships. These calibration parameters are stored in the EEPROM previously described at time of manufacture. When used during normal operation, the output of the pressure transducer is calibrated by the host system using the pre-stored calibration parameters taken directly from the EEPROM during each individual use.
In a seventh aspect of the invention, an improved method of ensuring the condition of limited (e.g., single) use components within a blood pressure monitoring device is disclosed. The method generally comprises providing a blood pressure monitoring device including a removable sensor assembly; measuring at least one parameter of a living subject using the device and sensor assembly to obtain first data; storing the first data relating to the at least one parameter; measuring the at least one parameter at a second time to obtain second data; comparing the stored first data to the second data using a predetermined criterion; and disabling the blood pressure measuring device if the criterion is not satisfied. In one embodiment, the sensor assembly comprises a pressure transducer and one or more ultrasonic transducers, which are collectively used to gather parametric data relating to the blood pressure within the radial artery of the subject. The parametric data is stored within the EEPROM, and compared with subsequent measurements taken with the same device using a comparison algorithm. In this fashion, significant differences between the parametric data obtained in successive readings is detected, which indicates that the caregiver has used the device on different patients. If certain acceptance criteria are exceeded, the system generates a disable signal which prevents completion of the analysis and display of the current measurement, as well as any subsequent measurements, until the pressure transducer (and optionally ultrasonic transducers) is/are replaced.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference is now made to the drawings, in which like numerals refer to like parts throughout. For purposes of clarity, the following description of the subject invention is cast in the context of arterial blood pressure measuring systems utilizing the principle of arterial tonometry and ultrasonic wave analysis. Such blood pressure monitoring systems are disclosed, for example, in co-pending U.S. patent application Ser. No. 09/342,549, entitled “Method and Apparatus for the Non-Invasive Determination of Arterial Blood Pressure”, filed Jun. 29, 1999, which is assigned to the assignee hereof, and incorporated herein by reference in its entirety. Alternatively, the methods and apparatus described in co-pending U.S. patent application Ser. No. 09/534,900 entitled “Method and Apparatus for Assessing Hemodynamic Parameters Within the Circulatory System of a Living Subject” filed Mar. 23, 2000, also incorporated herein by reference in its entirety, may be used in conjunction with the present invention. Other methods and apparatus, regardless of theory or principles of operation, may also be substituted.
It is also noted that while the invention is described herein in terms of a method and apparatus for assessing the hemodynamic parameters of the circulatory system via the radial artery (i.e., wrist) of a human subject, the invention may also be embodied or adapted to monitor such parameters at other locations on the human body, as well as monitoring these parameters on other warm-blooded species. All such adaptations and alternate embodiments are considered to fall within the scope of the claims appended hereto.
The present invention generally comprises a “smart” blood pressure sensor assembly which is used in conjunction with blood pressure system and host device in order to provide the enhanced functionality of the invention. This functionality includes, inter alia, (i) the ability to pre-store data relating to the manufacture, configuration, and calibration of the sensor assembly prior to use; (ii) the ability to use the pre-stored data to calibrate and enable/disable the sensor assembly during use, based on certain parameters and analyses conducted when the sensor assembly is connected to the host device; and (iii) the ability to store data obtained by the sensors or designated by the subject or caregiver within the sensor assembly and/or the host device during use. Each of these aspects in one fashion or another enhances the accuracy and reliability of blood pressure measurements taken with the system, as described in greater detail in the following paragraphs.
Sensor Assembly and Housing
Referring now to
The housing 104 and cover 102 of the illustrated embodiment are fabricated from a high strength, low cost polymer such as polycarbonate to provide the desired mechanical and electrical properties while still making the disposal of the assembly 100 economically feasible. Other materials (both polymeric and not) may be substituted depending on the properties and attributes desired.
The main housing 104 and cover 102 enclose a number of components, including a printed circuit board (PCB) 108, sensors in the form of a pressure transducer chip 110 and ultrasonic transducer (e.g., PZT) 112, bonding ring 114 for the pressure transducer chip 110, and storage device 116. In the embodiment of
The aforementioned EEPROM is easily accommodated within the sensor housing 104 on the PCB 108. Connections are made in the present embodiment by wire bonding or alternate methods at the same time the pressure transducer is connected 110, although other assembly and bonding methods may be used. A gel cup (not shown) or other means may optionally be used to protect the EEPROM 116 from electrostatic discharge or other electrical or physical trauma. Electrical signals are transferred in and out of the sensor assembly 100 using a plurality of electrical conductors (not shown) of the type well known in the art. Essentially any configuration of electrical connector or coupling may be substituted depending on the needs of the particular application.
Referring now to
The housing elements 202, 204 are formed from a low-cost thermoplastic such as polycarbonate although it will be recognized that other materials such as ethylene tetrafluoroethylene (i.e., Tefzel®), Teflon®, PVC, ABS, or even non-polymers may be substituted depending on the desired material and physical properties (such as rigidity, tensile strength, compatibility with certain chemical agents, ultrasonic transmission at certain wavelengths, etc.).
As in the embodiment of
In the illustrated embodiment, the second housing element 204 “snaps” into a channel 220 formed in the first housing element 202 such that the contact surfaces 222, 224 of each the first housing element and that of the pressure transducer 225 are in substantial planar alignment. In this fashion, the contact surfaces 222, 224, 225 each contact the skin (or interposed coupling medium) of the subject concurrently, allowing for ready coupling of each of the transducers to the subject. The snap functionality previously described is accomplished using a series of transverse ridges 226 formed on exterior lateral surfaces 228a, 228b the first housing element coupled with the extending inner edges 230a, 230b of the removal tabs 232 formed on the corresponding sides of the second housing element 204, although it will be appreciated that any other types of arrangements for retaining the second housing element 204 in a given physical relationship with the first housing element 202 may be utilized, such arrangements being well understood by those of ordinary skill in the mechanical arts. For example, other types of snap arrangements (such as one or more raised pins or protrusions, coupled with a complementary detent) may be used. Alternatively, a frangible construction may be employed. As yet another alternative, an adhesive such as a non-permanent silicone-based adhesive, or a frictional interference construction may be used to retain the second housing element 204 within the first 202.
The removal tabs 232 of the second housing element 204 are constructed such that when the tabs are grasped by the user (such as between the thumb and forefinger) and compressed slightly, the extending inner edges 230a, 230b of the tabs 232 disengage slightly from the transverse ridges 226, thereby allowing the second housing element 204 to be removed from the first 202 by pulling it vertically there from. The sidewalls 240a, 240b of the second housing element are designed to allow sufficient flexibility such that when the tabs 232 are compressed, the sidewalls flex and disengage the inner edges 230a, 230b from their respective ridges 226.
The first and second housing elements are also provided with a groove 234 and vertical ridge 236 formed on corresponding mating surfaces of the two components which act to align the second housing element properly, and in one orientation only, within the first housing element. Hence, it will be apparent that the second housing element 204 may only be received within the first element 202 in one orientation, such that the transducer elements 210, 212, 216 are in proper alignment when the assembly 200 is properly assembled.
The first housing element 202 is further equipped with a pair of pivot pins 250a, 250b which are disposed linearly and parallel to the longitudinal axis 252 of the first element 202. The pivot pins 250 are received within respective bores (not shown) formed in a first support element 254 of the gimbal assembly 256 as shown in
Additionally, it will be appreciated that while the embodiment of the sensor assembly 200 of
Apparatus for Physiologic Assessment
Referring now to
The apparatus 400 of
Further included in the apparatus 400 are a pressure transducer 416 for measuring blood pressure from the radial artery tonometrically; an applanation device 407 coupled to the transducer 416 for varying the degree of applanation (compression) on the artery; two ultrasonic transducers 410, 412 for generating ultrasonic emissions and reflections thereof, these ultrasonic emissions being used to derive blood velocity (and kinetic energy); a signal processor 420 operatively connected to the pressure and ultrasonic transducers 416, 410, 412 for analyzing the signals generated by these transducers and generating a calibration function based thereon; a signal generator/receiver 422 used to generate ultrasonic signals for transmission into the artery, and receive signals from the ultrasonic transducers 410, 412; and a controller 426 operatively coupled to the applanation device 407 and the signal processor 420 for controlling the degree of applanation pressure applied to the artery. The pressure and ultrasonic transducers 416, 410, 412 are arranged within the sensor assembly 200 previously described with respect to
The local controller assembly 444 further includes portions of the logic circuit (as described below with respect to
The analysis and display unit 446 comprises display, data analysis, user control, and data storage functions for the apparatus 400 including the display of raw data sensed by the transducer elements, display of parameters calculated based on the raw data by the processor and associated signal processing algorithms, equipment status indications, display of information stored within the storage device 218 of the sensor assembly (such as pressure transducer manufacture date/location, calibration parameters, etc.), name/SSN of the subject being monitored, etc. In one embodiment, the analysis and display station comprises a dedicated device having a CRT, TTT/LCD, LED, or plasma display coupled with a variety of pre-specified control and data storage functions. Alternatively, a laptop or handheld computer having software adapted for performing each of the foregoing functions, or those specifically chosen by the user, may be substituted. It will be recognized that each of the foregoing display, storage, and user control functions are well known to those of ordinary skill in the electronic arts, and accordingly are not described further. Analysis of the signals derived from the sensor assembly 200 is described in the foregoing U.S. patent applications previously incorporated herein.
The signal generator/receiver 422 generates electrical signals or pulses which are provided to the ultrasonic transducers 410, 412 and converted into ultrasonic energy radiated into the blood vessel. This ultrasonic energy is reflected by various structures within the artery, including blood flowing therein, as well as tissue and other bodily components in proximity to the artery. These ultrasonic reflections (echoes) are received by the ultrasonic transducers and converted into electrical signals which are then converted by the signal generator/receiver 422 to a digital form (using, e.g., an ADC) and sent to the signal processor 420 for analysis. In the present embodiment, the signal processor comprises a microprocessor unit and a digital signal processor (DSP) unit (not shown) in order to facilitate, inter alia, rapid data processing and the control functionality previously described, although it will be recognized that the processor 420 may configured in other ways if desired. Depending on the type of ultrasonic analysis technique and mode employed, the signal processor 420 utilizes its program (either embedded or stored in an external storage device) to analyze the received signals. For example, if the system is used to measure the maximum blood velocity, then the received echoes are analyzed for, inter alia, Doppler frequency shift. Alternatively, if the arterial diameter (area) is measured, then an analysis appropriate to the aforementioned A-mode is employed. U.S. patent applications Ser. No. 09/342,549 filed Jun. 29, 1999 and 09/534,900 filed Mar. 23, 2000, previously incorporated by reference herein, describe adaptations of the apparatus 400 for time-frequency and hemodynamic parameter blood pressure measurement, respectively.
In the configuration of
Referring now to
As shown in
Next, in step 606, a series of conversion algorithms are applied to the “raw” tranducer response data obtained in step 604 to convert the response data to calibration parameters useful for calibrating the pressure transducer in-situ during operation. Allowable ranges for the resulting calibration parameters are also specified. Table 2 illustrates an exemplary set of calibration parameters, allowable ranges, and conversion algorithms for a typical silicon strain beam pressure transducer element.
where:
-
- Eref=Reference voltage used by vendor at measurement (V)
- Tref=Reference temperature used by vendor (degree C)
- Th=“High” temperature used by vendor during raw data measurement (degrees C)
- Vos=Offset voltage of transducer (bridge) at zero applied pressure and Tref (mV)
- VosTC=Temperature correction factor for offset voltage of bridge (mV/degree C)
- Eb0=Bridge voltage at Tref (V)
- Eb0TC=Temperature correction factor for bridge voltage (mV/degree C)
- Sens=Sensitivity of bridge to pressure change (uV/mmHg)
- Lin Error=Linearity error on non-linearity (%)
- Ecal=Shunted output voltage of bridge (mV)
The conversion algorithms of Table 2 are derived based on the definition of the various calibration parameters (Table 3. below), and the raw transducer response data. For example, in the case of the temperature correction factor for the bridge voltage (Eb0TC), the bridge voltage taken at the reference temperature T0 and zero pressure, or Eb0, is subtracted from the bridge voltage taken at the “hot” temperature “Th” and zero pressure (Eb4), the resultant of which is divided by the difference between the hot temperature and the reference temperature (i.e., Th minus T0) to produce Eb0TC. The derivation of the other conversion algorithms is generally analogous, and easily determined by those of ordinary skill in the electronic arts.
Next, in step 608, the calculated calibrations parameters (Table 3 below) are stored within the storage device (e.g., EEPROM) of the transducer element for later recall during calibration/operation (step 610). Appendix I illustrates exemplary code useful for extracting the calibration parameters of Table 3 for a pressure transducer element from the EEPROM associated therewith.
Referring now to
In the embodiment of
In the illustrated embodiment, the span compensating resistor Ra 720, value is chosen to be 1000 ohms based on the bridge impedance, span TC, and reference voltage Eref 703, which is chosen to be 5 V. It will be recognized, however, that a range of values for Ra are possible from a few hundred ohms to several thousand ohms. Reference voltages other than 5 V may also be used. The main functions of resistor Ra 720, are to temperature compensate the span sensitivity of the transducer to temperature, and to provide signal Eb, which provides an output which is a function of the temperature of the bridge. The calibration and functionality of the transducer and the system can be checked by periodically turning on the analog switch 770, which shunts one side of the bridge with precision resistor Rcal 780. In one embodiment, this operation is initially performed at the time of manufacture, and the result is stored in the EEPROM as Ecal. The resistor 780 is selected to have a near zero TC, and a precise value that gives a response approximately equal to the equivalent of 100 mmHg. When the disposable transducer element is first connected, the system processor turns on the switch 770 and reads the output of the circuit 700. It then compares the value obtained with Ecal, which is stored in the EEPROM. If the results match within specified limits, then system accuracy is ensured. Note that this calibration verification generally is performed when the sensor is off the wrist of the subject. Since the system can control and sense the applanation of the sensor, this condition is ensured, and calibration will typically be checked prior to a blood pressure measurement interval.
During operation, the bridge voltage Eb of the circuit 700 is sampled at an interval of once per second, and the input value to the DAC recalculated in order to continually update the DAC output provided to the second stage amplifier 708. In this fashion, the output of the bridge (transducer element) is continually compensated for temperature.
In a second embodiment of the logic circuit 800 shown in
Appendix II hereto illustrates various exemplary applications of the smart sensor assembly of the invention, including storing data that enhances sensor and system performance and reliability. It is noted that the applications described in Appendix II are not exhaustive, but rather merely illustrative of the broader concept of the invention disclosed herein.
Referring to Appendix II, Items 1 through 17 therein represent exemplary data that is encoded on the EEPROM during sensor manufacturing according to the present embodiment. Each of these items is described in greater detail below with reference to Appendix I. Note that each of these Items can be considered optional, and furthermore that other configurations (such as different coding schemes, ranges/bits assigned to each parameter, etc.) may be used consistent with the invention. he blood pressure readings obtained from a subject.
Referring again to Appendix II, Items 18 through 35 therein represent exemplary data that the exemplary ultrasonic blood pressure measuring system used in conjunction with the sensor of the present invention writes to the EEPROM 116 during the time that the sensor assembly is connected to the host system. These items are described in greater detail below.
It is noted that the sensor replacement and error codes previously described (Items 23 and 30) are useful for service issues. In one possible scenario, failure analysis may be performed on one or more subsets of a given sensor population (such as those sensors which failed during use over a given period of time at a given health care facility). The contents of the sensor's EEPROM may be downloaded to allow analysis of the individual failures. For example, if a large percentage of the aforementioned sensor failures occurred when the sensors were connected to a particular mechanism, the likely source of the failures, i.e., the common mechanism, could be divined as uniquely identified by its EEPROM serial number. Other scenarios are possible, all considered to be within the scope of the present invention.
Items 36 through 39 of Appendix II illustrate additional data which may optionally be recorded within the storage device according to the present invention. These items can be configured by the health care provider/physician if desired. For example, the hospital name and care unit as well as the patient name and attending may be entered into the storage device(s) of the sensor and/or measurement system. If the hospital staff wanted to be sure that a sensor was only used on one patient, or only on a particular individual, or only within a specific ward or department (such as the Operating Room or Intensive Care Unit), the system may be configured to facilitate this. If use outside of the allowed parameters was detected, the sensor would be rejected, and the appropriate replacement code stored in the sensor's EEPROM.
It is also noted that since the present embodiment stores data in the sensor itself, the utilization of the sensor can be controlled across multiple mechanisms, systems, and power down events. Additional protection may also be gained by downloading a write authorization code to the sensor. For example, if attempts were made to write to the sensor to reset its run time, and the correct write authorization code was not utilized, the system would reject the sensor. The 32-bit encryption algorithm previously described further thwarts such attempts. Other security or cryptographic techniques well known in the art may be used to implement this protective functionality as well.
Method of Operation
Referring now to
Referring now to
As shown in
Referring now to
Lastly, in step 1110, the collected data (including for example mean pressure, heart rate, peak blood flow at mean pressure, kinetic energy, arterial diameter at mean pressure, and transform peak values) are stored in the EEPROM or other storage device previously described. This data collectively (or subsets thereof) comprises a characteristic signature for a given sensor assembly and patient.
Referring now to
It is noted that many variations of the methods described above may be utilized consistent with the present invention. Specifically, certain steps are optional and may be performed or deleted as desired. Similarly, other steps (such as additional data sampling, processing, filtration, calibration, display, or mathematical analysis for example) may be added to the foregoing embodiments. Additionally, the order of performance of certain steps may be permuted, or performed in parallel (or series) if desired Hence, the foregoing embodiments are merely illustrative of the broader methods of the invention disclosed herein.
While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the invention. The foregoing description is of the best mode presently contemplated of carrying out the invention. This description is in no way meant to be limiting, but rather should be taken as illustrative of the general principles of the invention. The scope of the invention should be determined with reference to the claims.
Claims
1-36. cancel
37. A method of operating a device used for measuring at least one parameter associated with a living subject, said device comprising a host system and a detachable sensor assembly with associated storage device having a first plurality of data stored therein, the method comprising:
- placing said sensor assembly in data communication with said host system, said host system having a second plurality of data associated therewith;
- reading at least a portion of said first plurality of data from said storage device;
- evaluating said at least portion of said first plurality of data and at least a portion of said second plurality of data; and
- determining whether said sensor assembly is enabled for measuring said at least one parameter based at least in part on said act of evaluating.
38. The method of claim 37, further comprising reading said second plurality of data from a storage device.
39. The method of claim 38, wherein the act of storing a first plurality of data comprises storing said data within an electrically erasable programmable read-only memory (EEPROM).
40. The method of claim 37, wherein said at least portion of said first plurality of data comprises data relating to the date of manufacture of said sensor assembly, and said at least portion of said second data comprises another date which is later than that of said date of manufacture.
41. The method of claim 37, wherein said at least portion of said first plurality of data comprises data relating to the duration of use of said sensor assembly, and said at least portion of said second data comprises a parameter relating to a maximum allowed duration.
42. The method of claim 37, wherein said at least portion of said first plurality of data comprises data relating to the user of said sensor assembly, and said at least portion of said second data comprises a parameter relating to said user.
43. The method of claim 37, wherein said act of evaluating comprises determining if said sensor assembly is compatible with said host system.
44. The method of claim 43, wherein said act of determining if said sensor assembly is compatible with said host system comprises comparing a first multi-bit hexadecimal value in said at least portion of said first data with a corresponding value of said second data.
45. The method of claim 37, wherein said device comprises a device adapted to measure a hemodynamic parameter, and said act of placing comprises physically mating said detachable sensor assembly to a substantially movable portion of said device.
46. The method of claim 37, further comprising calibrating said sensor assembly based at least in part on said first data.
47. The method of claim 45, wherein said enabling for measurement comprises a condition precedent to said act of calibrating said sensor.
48. The method of claim 37, wherein said at least portion of said first data comprises cryptographic data which is uniquely related to complementary cryptographic data of said at least portion of said second data.
49. A method of operating a device used for measuring at least one parameter associated with a living subject, said device comprising a host system and a detachable sensor assembly with associated storage device having a first plurality of data stored therein, the method comprising:
- placing said sensor assembly in data communication with said host system;
- reading at least a portion of said first plurality of data from said storage device;
- creating a test condition within said sensor assembly;
- determining at least one value relating to the operation of said sensor assembly relating to said test condition; and
- determining whether said sensor assembly is enabled for measuring said at least one parameter based at least in part on said act of measuring.
50. The method of claim 49, wherein said sensor assembly comprises a bridge circuit, and said portion of said first data comprises data relating to the electrical output of said sensor assembly during a shunted condition of said bridge circuit, and said act of determining at least one value comprises:
- creating substantially the same shunted condition within said sensor assembly; and
- obtaining second data relating to the electrical output of said sensor assembly.
51. A method of recording data, comprising:
- collecting first data relating to at least one parameter associated with a living subject;
- analyzing said first data to generate a first estimate of said at least one parameter;
- collecting second data relating to said at least one parameter;
- analyzing said second data to generate a second estimate of said at least one parameter;
- comparing said first estimate and said second estimate using at least one acceptance criterion; and
- storing at least either said first data or said second data in a storage device if said at least one criterion is met.
52. The method of claim 51, wherein the acts of collecting said first and second data each comprise collecting pressure data derived from a tonometric pressure sensor, and said first and second estimates comprise estimates of a blood pressure.
53. The method of claim 51, wherein the acts of analyzing said first and second data comprise determining a time-frequency representation for each.
54. The method of claim 51, wherein the acts of analyzing said first and second data comprise:
- measuring a first hemodynamic parameter from a blood vessel of said subject;
- measuring a second parameter from said blood vessel;
- deriving a calibration function based at least in part on said second parameter; and
- calibrating the first hemodynamic parameter using said calibration function.
55. The method of claim 54, wherein the act of measuring a first hemodynamic parameter comprises measuring blood velocity.
56. The method of claim 51, further comprising:
- obtaining third and fourth data relating to the identity of an individual during at least a portion of said acts of collecting said first and second data, respectively; and
- comparing said third and fourth data to verify that said identity relating to each is the same.
57. A method of ensuring the adequacy of a sensor assembly used in measuring at least parameter associated with a living subject, comprising:
- encoding first data within said sensor assembly, said first data being representative of a first time;
- placing said sensor assembly in data communication with a host system;
- measuring a second time using said host system;
- comparing said first and second times using an acceptance criterion; and
- disabling said sensor assembly from further use if said criterion is not satisfied.
58. The method of claim 57, wherein the act of comparing comprises calculating the difference between said first and second times, and comparing said difference to said acceptance criterion.
59. A method of ensuring the condition of a degradable component within a medical device, comprising:
- providing a degradable component, said degradable component being adapted to measure at least one physical parameter associated with a living subject;
- measuring said at least one parameter of a living subject using said degradable component to obtain first data;
- storing said first data relating to said at least one parameter within a storage device;
- measuring said at least one parameter a second time using said degradable component to obtain second data;
- comparing said first data to the second data using at least one predetermined criterion; and
- disabling said medical device if said at least one criterion is not satisfied.
60. The method of claim 59, wherein the act of measuring comprises measuring pressure.
61. The method of claim 60, wherein said at least one predetermined criterion comprises a difference in pressure.
62. The method of claim 59, further comprising deriving first and second estimates of arterial blood pressure based at least in part on said acts of measuring said at least one parameter at said first and second times, respectively.
63. A method of operating a blood pressure measuring device comprising a host system and a detachable pressure sensor assembly with associated storage device having a first plurality of data stored within, the method comprising:
- placing said sensor assembly in data communication with said host system, said host system having a second plurality of data associated therewith;
- reading at least a portion of said first plurality of data from said storage device;
- comparing said at least portion of said first plurality of data to at least a portion of said second plurality of data; and
- determining whether said sensor assembly is enabled for measuring blood pressure based at least in part on said act of comparing.
64. A method of evaluating the performance of a plurality of replaceable sensor assemblies each having a storage device associated therewith, and first data adapted to differentiate each sensor from at least a portion of said plurality, the method comprising:
- operating each of said plurality of sensor assemblies;
- generating second data resulting from said act of operating;
- storing said second data; and
- analyzing said second data from at least a portion of said plurality of sensor assemblies based at least in part on said first data associated therewith.
65. The method of claim 64, wherein said act of operating comprises:
- attaching each of said replaceable sensors to a host device; and
- performing at least one verification of each of said sensor assemblies based at least in part on data stored in said storage device.
66. The method of claim 64, wherein said act of generating second data comprises generating at least one of a plurality of possible error failure codes for said sensor assembly.
67. The method of claim 66, wherein said act of storing said second data comprises storing said second data within said storage device for that sensor assembly.
68. The method of claim 66, wherein said act of storing said second data comprises storing said second data within a storage device associated with a host device to which that sensor assembly is connected.
69. The method of claim 68, further comprising aggregating second data from a plurality of ones of said host devices in order to perform said analyzing.
70. The method of claim 66, wherein said second data comprises failure or error codes, and said act of analyzing comprises identifying one or more commonalities in said codes across multiple ones of said sensor assemblies.
71. Replaceable sensor apparatus adapted for measuring at least one parameter associated with a living subject in concert with a host device, said detachable sensor assembly further comprising a storage device having a first plurality of data stored therein, said sensor assembly further being adapted for qualification according to the method comprising:
- placing said sensor assembly in data communication with said host system;
- reading at least a portion of said first plurality of data from said storage device;
- creating a test condition within said sensor assembly;
- determining at least one value relating to the operation of said sensor assembly relating to said test condition; and
- determining whether said sensor assembly is qualified for measuring said at least one parameter based at least in part on said act of measuring.
72. Replaceable sensor apparatus adapted for use with a host device and configured to prevent use thereof beyond a prescribed period of time according to the method comprising:
- encoding first data within said sensor apparatus, said first data being representative of a first time;
- placing said sensor apparatus in data communication with said host system;
- measuring a second time using said host system;
- comparing said first and second times using an acceptance criterion; and
- disabling said sensor apparatus from further use if said criterion is not satisfied.
73. Replaceable tonometric sensor apparatus adapted to preserve data integrity according to the method comprising:
- collecting first data relating to at least one parameter associated with a living subject using said sensor apparatus;
- analyzing said first data to generate a first estimate of said at least one parameter;
- collecting second data relating to said at least one parameter using said sensor apparatus;
- analyzing said second data to generate a second estimate of said at least one parameter;
- comparing said first estimate and said second estimate using at least one acceptance criterion; and
- storing at least one of said first data and said second data in a storage device if said at least one criterion is met.
74. Tonometric disposable medical sensor apparatus adapted for use with a host device and having at least one pressure sensor and storage device associated therewith, said storage device containing both identifying and parametric information, said identifying and parametric information being used in cooperation by said sensor apparatus and host device to ensure that (i) said sensor apparatus is compatible with said host device; (ii) said sensor apparatus is functioning properly, and (iii) said sensor apparatus has not expired.
75. The apparatus of claim 74, wherein said apparatus is further adapted to verify use on only one patient.
Type: Application
Filed: Jan 9, 2004
Publication Date: Mar 3, 2005
Inventors: Ronald Conero (San Diego, CA), Stuart Gallant (San Diego, CA)
Application Number: 10/754,414