Pressure sensor with increased sensitivity for use with an implantable medical device
First Claim
1. A method of obtaining pressure data of a body fluid using a pressure sensor, the pressure sensor comprising a measurement capacitor responsive to changes in body fluid pressure, the method comprising:
- charging, during a first charge period of an integration cycle, the measurement capacitor at a first charge rate;
charging, during a second charge period of the integration cycle, the measurement capacitor at a second charge rate; and
producing, using the length of the first charge period and the second charge period of the measurement capacitor, a signal indicative of a pressure change of the body fluid imparted to the measurement capacitor.
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Accused Products
Abstract
An apparatus and method for obtaining pressure data using a body implantable pressure sensor includes a measurement capacitor which is responsive to pressure changes of a body fluid. Non-constant, multiple current source charging of the measurement capacitor provides for a significant increase in sensitivity to conditions of pressure of a body fluid. Pressure data is obtained by charging the measurement capacitor at a first charge rate during a first charge period of an integration cycle and, during a second charge period of the integration cycle, charging the measurement capacitor at a second charge rate. The first charge rate is preferably greater than the second charge rate. The duration of the first and second charge periods may be varied. A signal indicative of a pressure change of a body fluid imparted to the measurement capacitor is produced by the pressure sensor. The signal may be a signal indicative of a change in a time of integration. The signal, indicative of a time of integration, has a sensitivity to pressure changes which is greater than a mechanical capacitive sensitivity of the measurement capacitor to such pressure changes. The signal may alternatively be a signal indicative of a change in capacitance of the measurement capacitor, such as a voltage signal, or a signal having a duty cycle indicative of the pressure change. The pressure sensor may be implemented in a pacemaker, a pacemaker/cardioverter/defibrillator (PCD) or a hemodynamic monitor.
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Citations
34 Claims
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1. A method of obtaining pressure data of a body fluid using a pressure sensor, the pressure sensor comprising a measurement capacitor responsive to changes in body fluid pressure, the method comprising:
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charging, during a first charge period of an integration cycle, the measurement capacitor at a first charge rate;
charging, during a second charge period of the integration cycle, the measurement capacitor at a second charge rate; and
producing, using the length of the first charge period and the second charge period of the measurement capacitor, a signal indicative of a pressure change of the body fluid imparted to the measurement capacitor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
charging the measurement capacitor at the first charge rate comprises charging the measurement capacitor using a first current source; and
charging the measurement capacitor at the second charge rate comprises charging the measurement capacitor using a second current source.
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8. The method of claim 7, further comprising switching connectivity of the measurement capacitor from the first current source to the second current source in response to a switch signal.
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9. The method of claim 8, wherein the switch signal is produced by a timing circuit.
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10. The method of claim 8, wherein the pressure sensor further comprises a reference capacitor substantially insensitive to conditions of pressure, further wherein the switch signal is produced by the reference capacitor or a timing circuit.
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11. The method of claim 1, wherein the first charge rate is greater than the second charge rate.
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12. The method of claim 1, further comprising varying a duration of the first charge period or a duration of the second charge period.
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13. A circuit for detecting a pressure change of a body fluid, comprising:
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a pressure sensor comprising a measurement capacitor responsive to pressure changes of the body fluid;
a switch coupled to the measurement capacitor;
a first current source coupled to the switch;
a second current source coupled to the switch; and
a timing circuit, the switch coupling the first current source to the measurement capacitor for charging the measurement capacitor at a first charge rate during a first charge period of an integration cycle, and the switch, in response to a switch signal produce by the timing circuit, coupling the second current source to the measurement capacitor for charging the measurement capacitor at a second charge rate during a second charge period of the integration cycle, the pressure sensor producing a signal indicative of a pressure change of the body fluid imparted to the measurement capacitor. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21)
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22. A body implantable pressure sensing apparatus, comprising:
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an implantable medical device;
a lead coupled to the implantable medical device; and
a pressure sensor provided on the lead, the pressure sensor, comprising;
a measurement capacitor responsive to pressure changes of a body fluid;
a switch coupled to the measurement capacitor;
a first current source coupled to the switch;
a second current source coupled to the switch; and
a timing circuit, the switch coupling the first current source to the measurement capacitor for charging the measurement capacitor at a first charge rate during a first charge period of an integration cycle, and the switch, in response to a switch signal produce by the timing circuit, coupling the second current source to the measurement capacitor for charging the measurement capacitor at a second charge rate during a second charge period of the integration cycle, the pressure sensor producing a signal indicative of a pressure change of the body fluid imparted to the measurement capacitor. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30)
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31. A method of obtaining physiologic data of a body tissue using a capacitive pickoff sensor, the capacitive pickoff sensor comprising a measurement capacitor responsive to conditions of a physiologic condition, the method comprising:
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charging, during a first charge period of an integration cycle, the measurement capacitor at a first charge rate;
charging, during a second charge period of the integration cycle, the measurement capacitor at a second charge rate; and
producing, using the lengths of the first and second charge periods of the measurement capacitor, a signal indicative of physiologic condition of the body fluid imparted to the measurement capacitor. - View Dependent Claims (32, 33)
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34. A body implantable physiologic condition sensing apparatus, comprising:
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an implantable medical device;
a sensor housing coupled to the implantable medical device; and
a capacitive pickoff sensor provided in the or housing, the sensor, comprising;
a measurement capacitor responsive to physiologic condition of a body tissue;
a switch coupled to the measurement capacitor;
a first current source coupled to the switch;
a second current source coupled to the switch; and
a timing circuit, the switch coupling the first current source to the measurement capacitor for charging the measurement capacitor at a first charge rate during a first charge period of an integration cycle, and the switch, in response to a switch signal produce by the timing circuit, coupling the second current source to the measurement capacitor for charging the measurement capacitor at a second charge rate during a second charge period of the integration cycle, the physiologic condition sensor producing a signal indicative of a physiologic condition of the body tissue imparted to the measurement capacitor.
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Specification