JP4700209B2 - Passive biotelemetry - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for wireless transfer of information about physiological variable values, in particular such information determined by invasive measurements.
[0002]
[Prior art]
There is a general need to invasively measure physiological variables. For example, when examining cardiovascular disease, it is highly desirable to obtain local measurements of blood pressure and blood flow in order to assess the condition of the subject. Accordingly, methods and devices have been developed for placing small sensors at locations where measurements are to be made and for communicating with the small sensors.
[0003]
For example, a system and method for measuring body fluid pressure in a living body is described in US Pat. No. 3,853,117. A sensor for intracranial implantation is formed as a mechanical resonant structure whose resonant frequency is a function of body fluid pressure. By applying sonic energy from an external source and receiving the response resonance signal, it is possible to detect the resonance frequency and consequently determine the body fluid pressure.
[0004]
Another example of a known intracranial pressure monitor is known through US Pat. No. 4,026,276, which describes a device with a passive resonant circuit having a natural frequency that is affected by atmospheric pressure. Local pressure is measured by observing the frequency at which energy from an electromagnetic field located outside the skull is absorbed.
[0005]
Devices based on acoustic as well as electromechanical interactions have been developed to communicate the indications of measured physiological variables. In both cases, the sensor comprises a resonant element. Its resonant frequency is a function of the physiological variable to be determined. Energy is radiated from an external transmitter of acoustic waves or electromagnetic waves toward the resonant element. The frequency of the transmitted energy is swept through a preselected range and recorded by the monitoring unit. Since the drop in the transmitted energy being monitored occurs at this resonant frequency, the recording unit detects the resonant frequency of the resonant element during the frequency sweep.
[0006]
Both of the above examples of known devices that measure physiological variables invasively are examples of passive systems. That is, the in-vivo sensor does not require an energy source such as electricity provided via a battery or electrical lead.
[0007]
It is known to mount a small sensor at the distal end of a guidewire or catheter to guide the sensor to a specific point of measurement during cardiovascular disease testing. A guide wire or a catheter is inserted into a blood vessel such as a femoral artery and guided to a local site in the cardiovascular system suspected of malfunction by fluoroscopy.
[0008]
The development of miniature sensors or microsensors for a number of physiological variables including pressure, flow, temperature, etc. constitutes a historic landmark.
However, the assembly of sensors and their associated cables and connectors is difficult to do cost-effectively due to the small physical dimensions, the required mechanical accuracy, and the uncompromising demands on patient safety. . More specifically, it is estimated that about half, or more than half of the total manufacturing cost of such devices is due to connectors and cables.
[0009]
As a result, devices that perform these functions are still expensive and their spread of use is limited to areas with the highest clinical priority. The cost aspect is further emphasized by the fact that the device for invasive treatment must be regarded as a disposable item due to the risk of transmitting an infectious disease. Great savings are possible if the cost of cables and connectors can be minimized and even eliminated.
[0010]
Another problem with passive sensors of the type disclosed in U.S. Pat. No. 4,026,276 is undesirable electromagnetic coupling between one transmitter / receiver and the other sensor. This coupling is due to the fact that power and signal transmission are not functionally separated. The implication of this problem is that the output signal of the system is affected by the position of the sensor, which is clearly an undesirable attribute.
[0011]
This problem can be overcome by adding to the sensor an active electronic circuit with a local transmitter that operates at a frequency other than that used to provide power to the sensor and circuit. This decouples the function of the wireless power supply from the signal transmission power supply, so that the output signal should not be affected by the position of the sensor. Such a solution can be found in “Linking sensors with telemetry: Impact on the system design” by R. Puers (8th Int. Conf. Solid State Sensors and Actuators, Minutes of Transducers-95, Stockholm Sweden, June 25-29, 1995, Vol. 1, pp47-50). However, a drawback of this solution is that it is difficult to downsize to the desired size for medical use with a guidewire. Furthermore, this type of broadband system is susceptible to electromagnetic interference and interference.
[0012]
[Problems to be solved by the invention]
Accordingly, there is a need for an improved communication system that is less sensitive to the location of the sensor as well as electromagnetic interference to communicate with a sensor located in a subject's body to invasively measure physiological variables.
[0013]
[Means for Solving the Problems]
The object of the present invention is to provide an apparatus for overcoming the above-mentioned problems. This object is achieved with a passive biotelemetry system according to claim 1 of the claims.
[0014]
In accordance with the present invention, it can be integrated on a single silicon die of extremely small dimensions and within the available space of a guide wire having an outer diameter of 0.4 mm or on a separate plate for implantation. An electronic circuit is provided that forms a transponder unit that requires only a few individual components that can be housed and packaged. Alternatively, the transponder unit may be inserted into the living body as an implant. Since the system operates with a narrow bandwidth, it is not sensitive to electromagnetic interference. It is not sensitive to position or to precise control of the transmission characteristics of the medium. In addition, the system eliminates the need for cables and connectors to connect the sensor to the in vitro environment.
[0015]
Further scope of the applicability of the present invention will become apparent from the detailed description set forth below. However, the detailed description and specific examples are given by way of illustration only, while illustrating preferred embodiments of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. The present invention will become more fully understood from the detailed description given herein, including the accompanying drawings, which are given by way of illustration only and are not limiting of the invention.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an electronic device outside a living body in which a transponder unit disposed in a human body or an animal body does not use a signal carrying cable or a physical connector and reduces sensitivity to electromagnetic interference. Present system architecture that enables communication. This is achieved using a novel principle of communicating an indication of the physiological variable to be measured, which reduces the sensitivity to the exact position of the microsensor circuit.
[0017]
In the system according to the present invention, narrow bandwidth high frequency power is radiated from the in vitro source of the subject and partially absorbed and used as a power source to the transponder unit. The transponder unit comprises a modulator unit and a sensor unit and is placed in the subject's body. The modulator unit is designed to change the electromagnetic field absorption according to a pattern controlled by the sensor unit in response to the measured physiological variable, thereby representing the physiological variable. The system includes a receiver unit which is disposed outside the living body and is effective for recording the electromagnetic field absorption.
[0018]
The transponder unit according to the present invention is applicable to a range of invasive measurements such as intravascular measurement (for example, for heart disease diagnosis), intraocular pressure measurement, intracerebral and peripheral brain measurement, aortic aneurysm measurement, etc. Useful. The transponder unit may be attached to an elongated member such as a guide wire or cannula or may be an implantable self-contained unit.
[0019]
The sensor unit of the transponder unit is not new per se, but “An IC Piezoresistive Pressure Sensor for Biomedical Instrumentation” (Samann, KD Wise, JD Angell, IEEE Trans. Biomed, Eng. Vol BME-20 (1973), pp101-109) or “A Monolithic Capacitive Pressure Sensor with Pulse-Period Output” (CS Sander, JW Knutti, JD Meindl, IEEE Trans. Electron. Devices Vol. ED-27 (1980), pp927- 930) and any other suitable sensor device may be included.
[0020]
The modulator unit of the transponder unit monitors the output from the sensor unit and performs modulation that temporally encodes the absorbed power based on the output from the sensor unit. That is, the degree of modulation is made temporally according to a signal representing the sensor state. This temporal modulation, performed according to a preselected algorithm, represents the encoded information of the physiological variable that is sensed by the sensor unit and transferred to the time domain. This modulation is detected outside the subject's body and the algorithm used is known so that the information is easily converted into a value representing the level of the physiological variable.
[0021]
Referring to FIG. 1, one embodiment of a communication system according to the present invention comprises a transmitter unit 1, a transponder unit 2 and a receiver unit 3. The transmitter unit 1 includes a narrow band oscillator 4, an amplifier 5, and an antenna 6. A high-frequency wave 101 having a substantially constant amplitude and frequency is emitted by the antenna 6 at the operating frequency of the oscillator 4.
[0022]
In order to control and maintain the oscillation frequency at a constant or controllable frequency, an appropriate control means such as the quartz crystal plate 17 is included. By using crystal, 10 ^-6 It is possible to guarantee the above frequency stability. This is important both for the immunity of the system to electromagnetic interference and to prevent unwanted interference induced from the system to other electronic equipment.
[0023]
The system is usually designed to radiate about 0.1-10 W of high frequency power 101 depending on the operating geometric distance, accuracy requirements, etc. The operating frequency is in the range of 100 MHz to 10 GHz and can typically be about 400 MHz. The schematic of FIG. 2 shows the transmitted high frequency voltage non-scalar as a function of time.
[0024]
The transponder unit 2 of FIG. 1 comprises means for converting the power generated by the transmitter unit 1 into a local voltage. If a ground electrode at a potential different from the potential of the transponder antenna 7 can be defined, a single wire or transponder antenna 7 can act as a conversion means when it receives power capacitively. As soon as there is a net potential gradient in the transmission medium, a voltage difference is created between the transponder antenna and the ground electrode. Therefore, a single wire, such as a part of the core wire of the guide wire, can function as a conversion element for electromagnetic waves together with the ground electrode, particularly at a high frequency corresponding to the same digit wavelength as the wire length.
[0025]
The voltage appearing between the terminal of the antenna 7 and the neutral ground 18 is applied to the rectifier 9, for example a Schottky diode for very high frequencies or a PN-type semiconductor for moderate frequencies. Entered. The rectified voltage passes through the low-pass filter 10 and serves as a supply voltage for the microsensor 11 and the modulator 12. The signal 102 between the low pass filter 10 and the microsensor 11 is schematically illustrated in FIG. 3 which shows a constant rectified voltage 102 as a function of time.
[0026]
The microsensor 11 is responsive to physiological variables such as pressure, flow, temperature to be measured and provides an output signal corresponding to the variables. It can operate on resistive, capacitive, piezoelectric, pyroelectric or optical operating principles according to a well-established implementation of the sensor design.
[0027]
The modulator 12 converts the output signal of the microsensor 11 into a temporally encoded signal according to a specific method or algorithm, for example, pulse width modulation (PWM), frequency modulation (FM), or the like. The modulation is fed back to the transponder antenna 7 via the switch 8. The output signal 103 from the modulator 12 is shown schematically in FIG. As shown in FIG. 4, the output signal is off until time T1. Between times T1 and T2, the output signal is on and then turns off again. It turns on again at time T3, and so on.
[0028]
Thus, the power absorbed by the transponder unit 2 is affected by the action of the switch 8 so that the absorption is different when the switch is in the on or off state. This difference in power absorption is also shown as a variation in the electromagnetic field emanating from the transmitter unit 1 as detected by the receiver unit 3. Therefore, the high-frequency voltage 104 detected by the receiver unit 3 shows a high level HL in the period between T1 and T2, as shown in FIG. 5, and the period before T1 and between T2 and T3. Indicates a low level LL.
[0029]
This makes it possible to extract information on the variable under measurement superimposed on the transmitted electromagnetic field by the demodulator of the receiver unit. As a result, as shown in FIG. 6, a signal 105 having substantially the same temporal characteristics as the output signal 103 from the modulator 12 in the transponder unit is generated. That is, for the signal 103 from the modulator 12 and the signal 105 from the demodulator 15, changes from “high” to “low” occur at substantially the same time. Thereby, temporal information included in the signal can be extracted.
[0030]
Note that the schematic wave in FIG. 5 is not a scalar. Typically, the transponder unit 2 absorbs 0.1-1% of the total energy radiated by the transmitter unit 1, of which the modulation range provided via the switch 8 is typically Specifically, it is 1 to 10%.
[0031]
Any useful algorithm may be selected for converting the measurement of the physiological variable into a characteristic value represented by one or several intervals of high or low absorption of the radio frequency voltage. For example, the modulator 12 may be configured to close the switch 8 during a period that is directly proportional to the variable under measurement. Of course, the variable can be measured repeatedly at selected intervals, with the modulator initialized for each measurement and the switch closed for an appropriate length of time. Alternatively, the measurement may be frequency encoded such that the modulator 12 closes the switch 8 a selected number of times over a given period of time, corresponding to a predetermined level of the measurement variable.
[0032]
The modulator 12 typically comprises a digital logic sequential circuit that is preferably designed in CMOS (complementary metal oxide semiconductor) technology for low power consumption. The switch 8 may be a single transistor that is a bipolar transistor or a field effect transistor, depending on the modulation type, operating frequency, and the like.
[0033]
The transponder unit 2 is physically miniaturized and can be one or a few components of very small dimensions. For example, the microsensor 11 may be a capacitive pressure sensor manufactured with a silicon surface process and having dimensions of less than 100 × 100 × 100 microns. The electronic circuit including rectifier 9, low pass filter 10, modulator 12, and switch 8 can be integrated on a separate silicon die having approximately the same dimensions as the microsensor.
[0034]
The transponder antenna 7 is preferably integrated with a core wire 51 having a guide wire structure as will be described later with reference to FIG. 11, but may be attached to an implant as will be described later with reference to FIG. Wire connections or “flip-flop” connections can effectively make electrical connections between components.
[0035]
The receiver 3 includes a receiver antenna 13, an amplifier 14, and a demodulator 15. The demodulator 15 converts the time or frequency encoded signal into a sensor signal according to an algorithm reverse to the algorithm of the modulator 12. The receiver 3 also comprises means 16 for processing and presenting the signal.
[0036]
The amplifier 14 is preferably of the type known in the literature as a phase sensitive, phase tracking or synchronous amplifier. The bandwidth of such an amplifier can be extremely small. The system according to the invention preferably operates with an extremely small bandwidth in order to minimize the effects of electromagnetic interference.
[0037]
FIG. 8 shows a detailed circuit of one embodiment of a transponder unit 72 comprising a transponder antenna 71, a rectifier 73 with a diode and a capacitor, a capacitive sensor 75, three inverters 76, 77, 78 and a resistor 74. An example of the figure is shown. The circuit forms a square wave generator that operates at a period given by R × C. Where R is the resistance of the resistor 74 in ohms, and C is the capacitance of the sensor 75 in farads. Thus, the period corresponds to the value of the measured physiological variable. When implemented in CMOS technology, this circuit has extremely low current consumption. In fact, the main power consumption occurs at the short moment of switching. Because this transient increases power consumption, this moment can be detected remotely by an external demodulator described below.
[0038]
FIG. 9 shows yet another implementation of a transponder unit 82 comprising a resistance sensor 85, a rectifier 87 having a diode and a capacitor, an operational amplifier 81, two other resistors 83, 84, a capacitor 86 and a transponder antenna 88. A detailed circuit diagram of the embodiment is shown. Similar to the circuit described with reference to FIG. 8, the circuit in FIG. 9 generates a square wave whose period is determined by the resistance of a passive component of the circuit, for example, sensor 85.
[0039]
FIG. 7 shows a second embodiment of a communication system according to the present invention. The transponder unit 22 corresponds to the transponder unit 2 of FIG. 1, and includes a transponder antenna 28, a rectifier 29, a low-pass filter 30, a microsensor 31, a modulator 32, and a switch 33.
[0040]
The transceiver unit 21 of FIG. 7 operates as a transmitter of high frequency power and as a receiver of sensor signals provided as passive modulation of the power absorbed by the transponder unit 22. For this reason, the transmitter / receiver unit 21 includes an oscillator 23, a crystal crystal plate 34, an amplifier 24, and an antenna 25, similarly to the transmitter unit 1 of FIG. Further, the transceiver unit 21 also comprises a demodulator 27 and means for processing and presenting the signal, similar to the receiver unit 3 of FIG.
[0041]
The demodulator 27 is used to detect small and time-dependent fluctuations in the antenna 25 impedance. If there is a variation in the power absorption caused by the modulator 32 and the switch 33, the variation of the antenna impedance is derived according to well-established reversible network principles.
[0042]
FIG. 10 shows one embodiment of a transponder unit 42 of a communication system according to the present invention that can continuously measure and transmit several physiological variables. Although not shown in FIG. 10, a transmitter unit and a receiver unit corresponding to those described with reference to FIG. 1 or a transceiver described with reference to FIG. 7 are also included in this communication system. It is.
[0043]
A selected number of microsensors 41, 43, 47 are provided, each responding to one or several physiological variables under investigation (FIG. 10 shows three as an example, with additional microsensors indicated by dotted lines) Show). Each sensor 41, 43, 47 provides a signal representative of at least one physiological variable to a multiplexer 44, which multiplexes each sensor with a modulator 45 and a switch 46, either sequentially or according to some other predetermined rule. Connect to. The operation principle of the modulator 45 and the switch 46 is the same as that of the modulator 12 and the switch 8 shown in FIG. The order in which the individual sensors 41, 43, 47 are connected to the modulator 45 may be based on a free-running oscillator (not shown) included in the modulator and sensor unit 42, or on the transmitter unit May be triggered by an addressing routine embedded in the power radiation from, e.g., modulation of the frequency or amplitude of the power radiation. Thus, many configurations are possible to control the transmission of monitoring values from the sensor, and common to all such configurations is that a microcontroller 47 is connected to the multiplexer 44 to provide digital control of the addressing routine. Is to do.
[0044]
As shown in FIG. 11, the transponder unit 151 including the microsensor 52 and the power conversion / modulation circuit 53 as described above is attached to the distal end of the guide wire 50. The core wire 51 extends along the length of the guide wire. The core 51, which can consist of a single wire or multiple strands, typically has a reduced diameter section 55 to ensure reduced bending stiffness to reduce the risk of ruptured blood vessels during positioning. Is provided. For the same reason, the guidewire tip 56 is typically rounded. A coil 57 covers the reduced diameter section 55 and provides the distal end of the guide wire having a substantially uniform outer diameter.
[0045]
The transponder unit 151 is mounted in the groove 153 in the section 55 of the core wire and is electrically connected 154 to the core wire 51 to provide ground potential to the transponder unit via the core wire.
[0046]
A coil wire section 54 of radiopaque material, such as platinum, is spirally wrapped around a portion of the guide wire section 55 to cover the transponder unit 151 and at the same time as the coil 57, Form part of the outer surface of the distal end of the guidewire. The coil wire 54 is insulated from the core wire 51 by the insulating layer 155 and connected to the transponder unit, and functions as power conversion means as described with reference to the power conversion transponder antenna 7 of FIG. Accordingly, since the core wire 51 and the wire 54 occupy spatially different places, if an electric field gradient exists as in the case where the transmitter or the transceiver unit described above is activated, a voltage is generated between the core wire 51 and the wire 54. Arise.
[0047]
FIG. 12 shows an example of the use of the system according to the invention in which a subject 62 is examined using a transponder unit 61 mounted on a guide wire 66. Guide wire 66 is surgically inserted into the femoral artery and advanced until transponder unit 61 is placed in the heart and local cardiovascular measurements are possible. A transmitter / receiver unit 63 including an antenna 64 is placed outside the subject 62. The transceiver unit 63 is connected to the signal processing and presentation unit 65. The signal processing and presentation unit 65 may be any suitable multipurpose device, such as a personal computer with appropriate interface circuitry, as will be apparent to those skilled in the art.
[0048]
Instead of being attached to the guide wire, the transponder unit may be attached to a substrate 162 that is inserted into the living body as an implant 160 as shown in FIG. The implant is covered with a protective encapsulant 164 such as silicone resin that protects the circuitry as well as the biological tissue surrounding the implant. As described for the different embodiments of the transponder antenna, a transponder antenna 167 connected to the transponder unit and made from a biocompatible material penetrates the encapsulating material. Of course, the substrate transponder unit, including the sensor, may be any of those described herein.
[0049]
The implant 160 is placed at the measurement site and fixed by an appropriate attachment means. An example of such attachment means is shown in FIG. 13 as a hole through the implant, which is used to suture and hold the implant. Such other attachment means may be a clamp or a hook-like protrusion.
[0050]
Thus, according to the present invention, the physiological variable information is determined using a constant pre-selected carrier frequency, as opposed to conventional systems that use a frequency sweep to determine the resonant frequency indicative of the physiological variable. Is done. Instead, the information is superimposed on a constant carrier frequency in the form of time or frequency modulation.
[0051]
In accordance with the present invention, a carrier frequency is provided to a transponder unit located in a living body by an alternating electromagnetic field that also provides energy for the operation of the transponder unit. The transponder unit interacts with the applied electromagnetic field as determined by at least one physical parameter at the sensor site. Interactions that can be observed as changes in electromagnetic field strength due to patterns representing physical parameter values are monitored in vitro and interpreted by the demodulation unit. In this way, the measured parameter values are communicated wirelessly, eliminating the need for connectors and wires along the guidewire.
[0052]
The present invention provides many advantages. Thus, the necessary electronic circuitry can be integrated on a single silicon die of extremely small dimensions, requiring only a few individual components. All the necessary components can be housed and packaged in an available space in a guide wire having an outer diameter of 0.4 mm or less. Also, the system operates with a narrow bandwidth and is not sensitive to electromagnetic interference. Furthermore, it is not sensitive to the position of the transmitter or to precise control of the transmission characteristics of the medium.
[0053]
The present invention may be varied in many ways with respect to the above detailed description. Such variations are not to be regarded as a departure from the spirit and scope of the invention, but are intended to be included within the scope of the claims as would be apparent to one skilled in the art.
[Brief description of the drawings]
FIG. 1 is a block diagram of a first embodiment of a communication system according to the present invention.
FIG. 2 is a schematic diagram of high frequency power transmitted from a transmitter of a communication system according to the present invention.
FIG. 3 is a schematic diagram of the rectified voltage in the transponder unit of the communication system according to the present invention.
FIG. 4 is a schematic diagram of an output signal from a modulator in a transponder unit of a communication system according to the present invention.
FIG. 5 shows a schematic diagram of the high frequency power received by the receiver unit of the communication system according to the present invention.
FIG. 6 is a schematic diagram of a demodulated output signal.
FIG. 7 is a block diagram of a second embodiment of a communication system according to the present invention.
FIG. 8 is a circuit diagram of one embodiment of a transponder unit of a communication system according to the present invention.
FIG. 9 is a circuit diagram of another embodiment of a transponder unit of a communication system according to the present invention.
FIG. 10 is a block diagram of one embodiment of a transponder unit of a communication system according to the present invention that can continuously measure and transmit several physiological variables.
FIG. 11 is a cross-sectional view of the distal end of a guidewire with a transponder unit.
FIG. 12 is a schematic diagram of the system according to the present invention in use.
FIG. 13 is a schematic cross-sectional view of an implant according to the present invention.

Claims (9)

A guide wire (50) provided with a transponder unit (2, 22, 72, 82) at its end and adapted to be inserted into a living body ,
The transponder unit is
A sensor (11, 52) sensitive to physiological variables;
A modulator unit (12; 32; 45; 74, 76, 77, 78; 81, 83, 84) for controlling the high frequency energy absorption of the transponder unit according to a time sequence representative of the physiological variable;
And a transponder antenna (7, 28, 71, 88) , at least a part of the antenna being integrated with a core wire of the guide wire.   The guidewire according to claim 1, wherein the transponder unit further comprises a rectifier (9, 29, 73, 87), wherein the antenna and the rectifier form a power source to the sensor and the modulator unit. .   The guidewire of claim 1, wherein the transponder unit (82) comprises a resistance sensor (85).   The guide wire of claim 1, wherein the transponder unit (72) comprises a capacitive sensor (75).   The guide wire of claim 1, wherein the transponder unit comprises a rectifier (73), a capacitive sensor (75), an inverter (76, 77, 78) and a resistor (74).   The guide wire according to claim 1, wherein the transponder unit comprises a resistance sensor (85), a rectifier (87), an operational amplifier (81), resistors (83, 84) and a capacitor (86). A high-frequency energy transmitter (1) disposed outside the living body, a high-frequency energy receiver (3) disposed outside the living body, and the guide wire according to any one of claims 1 to 6. A biotelemetry system for measuring physiological variables in a living body. The transmitter includes a narrowband oscillator (4, 23) that provides a substantially constant output frequency and amplitude,
The receiver includes a narrowband amplifier (14) that operates at the same frequency as the transmitter;
The biotelemetry system according to claim 7.   The biotelemetry system according to claim 8, wherein the narrowband amplifier is a synchronous amplifier.

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