Telemetric intracranial pressure monitoring system
First Claim
1. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
- passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including an inductor-capacitor circuit having a resonant frequency;
probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and
interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor, the interrogation circuit means including;
a probe drive circuit generating an RF signal whose frequency varies in a predetermined manner throughout an operating frequency range encompassing the resonant frequency of the sensor means, the RF signal generated by the probe drive circuit being output to the probe;
a frequency counting circuit means receiving the RF signal generated by the probe drive circuit for selectively counting the number of cycles of the RF signal for a predetermined time;
a coincidence detector means receiving the signal output by the probe means for triggering the frequency counting circuit means to begin counting the number of cycles of the RF signal received by the frequency counting circuit means for a predetermined time, thereby generating the signal proportional to the pressure sensed by the sensor means.
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Accused Products
Abstract
The present invention relates to an apparatus for monitoring the intracranial pressure of a patient. The apparatus includes an implantable sensor implanted in the skull of a patient. The implantable sensor senses pressure and outputs a signal indicative of the pressure in the patient'"'"'s skull. The apparatus further includes a probe receiving the signal output by the implantable sensor when the probe is positioned near the implantable sensor. The probe outputs a signal indicative of the pressure sensed by the implantable sensor. An interrogation circuit is provided for receiving the signal output by the probe and automatically outputting a digital signal proportional to the pressure sensed by the implantable sensor.
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Citations
34 Claims
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1. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
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passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including an inductor-capacitor circuit having a resonant frequency; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor, the interrogation circuit means including; a probe drive circuit generating an RF signal whose frequency varies in a predetermined manner throughout an operating frequency range encompassing the resonant frequency of the sensor means, the RF signal generated by the probe drive circuit being output to the probe; a frequency counting circuit means receiving the RF signal generated by the probe drive circuit for selectively counting the number of cycles of the RF signal for a predetermined time; a coincidence detector means receiving the signal output by the probe means for triggering the frequency counting circuit means to begin counting the number of cycles of the RF signal received by the frequency counting circuit means for a predetermined time, thereby generating the signal proportional to the pressure sensed by the sensor means. - View Dependent Claims (2, 3, 11, 12)
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4. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including; a housing adapted to be disposed within at least a portion of the skull of the patient, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber including; a bellows having an open upper end, a closed lower end plate portion defining the second capacitance plate, an elastomeric sidewall extending generally between the open upper end and the closed lower end plate portion, and an upper flange portion extending a distance outwardly from the sidewall; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency, the coil means including an upper end, a lower end and a length extending generally between the upper and lower ends of the coil means, the flange portion and the first capacitance plate being fixed a distance apart less than the length of the coil means; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frecuency of the inductor-capacitor resonant circuit is varied in response to a chance in pressure sensed by the pressure responsive means; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor. - View Dependent Claims (5, 6, 7, 8, 9)
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10. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including; a housing adapted to be disposed within at least a portion of the skull of the patient, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber further including; an aperture communicating with the gas receiving cavity of the pressure sensitive chamber, the aperture having an upper tapered portion and a lower cylindrical portion; and a tapered pin disposed in the aperture for sealing the pressure reference gas within the gas receiving cavity, the tapered pin having a taper less than the taper of the upper tapered portion of the aperture; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor.
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13. An implantable sensor for sensing pressure within a cavity in a living entity, the implantable sensor comprising:
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a housing adapted to be disposed within at least a portion of the cavity in the living entity, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber including; a bellows having an open upper end, a closed lower end Plate portion defining the second capacitance plate, an elastomeric sidewall extending generally between the open upper end and the closed lower end, and an upper flange portion extending a distance outwardly from the sidewall; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency, the coil means having an upper end, a lower end and a length extending generally between the upper and lower ends of the coil means, the upper flange portion and the first capacitance Plate being fixed a distance apart less than the length of the coil means; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means. - View Dependent Claims (14, 15, 16, 17, 18)
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19. An implantable sensor for sensing pressure within a cavity in a living entity, the implantable sensor comprising:
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a housing adapted to be disposed within at least a portion of the cavity in the living entity, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber including; an aperture communicating with the gas receiving cavity of the pressure sensitive chamber, the aperture having a tapered upper portion and a cylindrical lower portion; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means; and a tapered pin disposed in the aperture for sealing the pressure reference gas within the gas receiving cavity wherein the tapered pin has a taper less than the taper of the upper tapered portion of the aperture.
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20. A pressure sensitive capacitor comprising:
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a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, the pressure sensitive chamber having a portion defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate wherein the pressure sensitive chamber further defines; an aperture communicating with the gas receiving cavity of the pressure sensitive chamber, the aperture having an upper tapered portion and a lower cylindrical portion; a tapered pin disposed in the aperture for sealing the pressure reference gas within the gas receiving cavity wherein the tapered Pin has a taper less than the taper of the upper tapered portion of the aperture; and wherein actual pressure surrounding the pressure sensitive chamber opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the capacitance of the pressure sensitive capacitor is varied based on the actual pressure surrounding the pressure sensitive chamber.
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21. An interrogation circuit for outputting RF signals to a probe which is electrically coupled to an implantable sensor having a resonant frequency and being implanted in a cavity within a patient, the interrogation circuit comprising:
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a probe drive circuit means for generating RF signals whose frequency varies in a predetermined manner throughout an operating frequency range, the RF signals generated by the probe drive circuit means being output to the probe; a frequency counting circuit means receiving the RF signal output by the probe drive circuit means for selectively counting the number of cycles of the RF signal for a predetermined time; and a coincidence detector means for receiving a signal output by the probe, the signal output by the probe being indicative of the pressure sensed by the implantable sensor and the coincidence detector means outputting a trigger signal to be received by the frequency counting circuit means for triggering the frequency counting circuit means to begin counting the number of cycles of the RF signal output by the probe drive circuit means for a predetermined time so as to generate a signal proportional to the pressure sensed by the implantable sensor. - View Dependent Claims (22)
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23. A method for forming an implantable sensor for sensing the pressure within a cavity within a living entity, the method comprising the steps of:
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disposing an implantable sensor and a quantity of fluid within a sealed container, the implantable sensor having a housing defining a chamber and the implantable sensor having a pressure reference disposed within the chamber of the housing; drawing a vacuum within the sealed container; submerging the implantable sensor within the quantity of fluid; releasing the vacuum in the sealed container back to atmospheric pressure for allowing a quantity of fluid to migrate into the implantable sensor through an aperture formed through the housing of the implantable sensor; exchanging the quantity of fluid within the implantable sensor with a quantity of fluid substantially saturated with gas at a temperature substantially equal to standard body temperature; and sealing the implantable sensor, whereby the implantable sensor has a calibration baseline that remains substantially constant throughout the life of the implantable sensor. - View Dependent Claims (24)
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25. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including; a housing adapted to be disposed within at least a portion of the skull of the patient, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; and a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means, the pressure responsive means of the sensor means including; a flexible membrane connected to a portion of the housing such that the flexible membrane communicates with the chamber formed in the housing whereby the flexible membrane communicates the cranial pressure to the chamber of the housing; a quantity of fluid disposed within the housing of the sensor means, the fluid serving to transmit deformations of the flexible membrane into compression of the pressure sensitive chamber, wherein the fluid is substantially saturated with gas at a temperature substantially equal to standard body temperature; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor.
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26. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
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passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including; a housing adapted to be disposed within at least a portion of the skull of the patient, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber including; a bellows having a sidewall constructed of alternating layers of a first metal and a second metal wherein the sidewall has at least 3 layers of the first metal and at least 2 layers of the second metal; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal proportional to the pressure sensed by the implantable sensor. - View Dependent Claims (27)
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28. An implantable sensor for sensing pressure within a cavity in a living entity, the implantable sensor comprising:
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a housing adapted to be disposed within at least a portion of the cavity in the living entity, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means, the pressure responsive means including; a flexible membrane connected to a portion of the housing such that the flexible membrane communicates with the chamber formed in the housing wherein the flexible membrane communicates the cranial pressure to the chamber of the housing; and a quantity of fluid disposed within the housing of the implantable sensor, the fluid serving to transmit deformations of the flexible membrane into compression of the bellows wherein the fluid is substantially saturated with gas at a temperature substantially equal to standard body temperature.
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29. An implantable sensor for sensing pressure within a cavity in a living entity, the implantable sensor comprising:
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a housing adapted to be disposed within at least a portion of the cavity in the living entity, the housing defining a chamber; a pressure sensitive capacitor disposed within the chamber of the housing, the pressure sensitive capacitor comprising; a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, a portion of the pressure sensitive chamber defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, the pressure sensitive chamber including; a bellows having a sidewall constructed of alternating layers of a first metal and a second metal wherein the sidewall has at least 3 layers of the first metal and at least 2 layers of the second metal; coil means electrically connected to a portion of both the pressure sensitive chamber and the first capacitance plate for forming an inductor-capacitor resonant circuit having a resonant frequency; pressure responsive means for communicating the actual pressure within the cavity in the living entity to the pressure sensitive chamber such that the pressure within the cavity in the living entity opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the resonant frequency of the inductor-capacitor resonant circuit is varied in response to a change in pressure sensed by the pressure responsive means. - View Dependent Claims (30)
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31. A pressure sensitive capacitor comprising:
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a first capacitance plate; a pressure sensitive chamber constructed of a gas impermeable substance, the pressure sensitive chamber defining a gas receiving cavity filled with a gas which forms a pressure reference, the pressure sensitive chamber having a portion defining a second capacitance plate spaced a distance from the first capacitance plate and being movable relative to the first capacitance plate, wherein the pressure sensitive chamber further comprises; a bellows having a sidewall constructed of alternating layers of a first metal and a second metal wherein the sidewall has at least 3 layers of the first metal and at least 2 layers of the second metal; and wherein actual pressure surrounding the pressure sensitive chamber opposes the pressure sensitive chamber and varies the distance between the first and second capacitance plates, whereby the capacitance of the pressure sensitive capacitor is varied based on the actual pressure surrounding the pressure sensitive chamber. - View Dependent Claims (32)
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33. An apparatus for monitoring the intracranial pressure of a patient, the apparatus comprising:
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passive sensor means adapted to be implanted in the skull of a patient for sensing pressure and outputting a signal indicative of the pressure in the patient'"'"'s skull, the sensor means including an inductor-capacitor circuit having a resonant frequency; probe means receiving the sensor means output signal when the probe means is positioned near the sensor means for outputting a signal indicative of the pressure sensed by the sensor means; and interrogation circuit means receiving the probe means output signal for automatically outputting a signal relative to the pressure sensed by the implantable sensor, the interrogation circuit means including; a probe drive circuit generating an RF signal whose frequency varies in a predetermined manner throughout an operating frequency range encompassing the resonant frequency of the sensor means, the RF signal generated by the probe drive circuit being output to the probe; a frequency counting circuit means receiving the RF signal generated by the probe drive circuit for selectively counting the number of cycles of the RF signal for a predetermined time; a coincidence detector means receiving the signal output by the probe means for triggering the frequency counting circuit means to begin counting the number of cycles of the RF signal received by the frequency counting circuit means for a predetermined time, thereby generating the signal relative to the pressure sensed by the sensor means.
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34. An interrogation circuit for outputting RF signals to a probe which is electrically coupled to an implantable sensor having a resonant frequency and being implanted in a cavity within a patient, the interrogation circuit comprising:
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a probe drive circuit means for generating RF signals whose frequency varies in a predetermined manner throughout an operating frequency range, the RF signals generated by the probe drive circuit means being output to the probe; a frequency counting circuit means receiving the RF signal output by the probe drive circuit means for selectively counting the number of cycles of the RF signal for a predetermined time; and a coincidence detector means for receiving a signal output by the probe, the signal output by the probe being indicative of the pressure sensed by the implantable sensor and the coincidence detector means outputting a trigger signal to be received by the frequency counting circuit means for triggering the frequency counting circuit means to begin counting the number of cycles of the RF signal output by the probe drive circuit means for a predetermined time so as to generate a signal relative to the pressure sensed by the implantable sensor.
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Specification