Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-11-18
2001-05-22
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C128S899000
Reexamination Certificate
active
06234973
ABSTRACT:
Reference is hereby made to commonly assigned, co-pending U.S. Patent Application Serial No filed on even date herewith BAROMETRIC PRESSURE SENSOR FOR USE WITH IMPLANTABLE ABSOLUTE PRESSURE SENSOR by Robert T. Taepke.
FIELD OF THE INVENTION
The present invention relates to an implantable barometric pressure sensor coupled with an implantable medical device (IMD) for providing a barometric pressure related, reference pressure value for use in combination with an absolute physiologic pressure value, e.g. a cardiac pressure value, measured by an implantable absolute pressure sensor coupled to the IMD, and particularly to the fabrication of various embodiments of the barometric pressure sensor and the periodic calibration thereof.
BACKGROUND OF THE INVENTION
A great many IMDs for cardiac monitoring and/or therapy comprising sensors located in a blood vessel or heart chamber coupled with an implantable monitor or therapy delivery device have been proposed or implemented. For example, such cardiac systems include implantable heart monitors and therapy delivery devices including pacemakers, cardioverter/defibrillators, heart pumps cardiomyostimulators, ischemia treatment devices, and drug delivery devices. Most of these cardiac systems include electrodes for sensing and sense amplifiers for recording and/or deriving sense event signals from the intracardiac or remote electrogram (EGM). In current cardiac IMDs providing a therapy, the sense event signals are utilized to control the delivery of the therapy in accordance with an operating algorithm and at least selected EGM signal segments and sense event histogram data or the like are stored in internal RAM for telemetry out to an external programmer at a later time. In the MEDTRONIC® Reveal™ implantable loop recorder, a 42 minute segment of EGM is recorded when the patient feels the effects of an arrhythmic episode and activates the recording function by applying a magnet over the site of implantation, but this device provides no therapy.
Efforts have also been underway for many years to develop implantable physiologic signal transducers and sensors for temporary or chronic use in a body organ or vessel usable with such IMDs for monitoring a physiologic condition other than or in addition to the EGM to derive and store data and/or to control a therapy delivered by the IMD. A comprehensive listing of implantable therapy delivery devices are disclosed in conjunction with implantable sensors for sensing a wide variety of cardiac physiologic signals in U.S. Pat. No. 5,330,505, incorporated herein in its entirety by this reference.
Blood pressure and temperature signal values respond to changes in cardiac output that may be caused by a cardiac failure, e.g., fibrillation or high rate tachycardia, or that may reflect a change in the body's need for oxygenated blood. In the former case, monitoring of a substantial drop in blood pressure in a heart chamber, particularly the right ventricle, alone or in conjunction with an accelerated or chaotic EGM, was proposed more than thirty years ago as an indicia of fibrillation or tachycardia sufficient to trigger automatic delivery of defibrillation or cardioversion shock. More recently, it has been proposed to monitor the changes in blood pressure (dP/dt) that accompany normal heart contraction and relaxation and blood pressure changes that occur during high rate tachycardia and fibrillation or flutter.
A number of cardiac pacing systems and algorithms for processing the monitored mean and dP/dt blood pressure have been proposed and, in some instances employed clinically, for treating bradycardia. Such systems and algorithms are designed to sense and respond to mean or dP/dt changes in blood pressure to change the cardiac pacing rate in a rate range between an upper and a lower pacing rate limit in order to control cardiac output. Similarly, a number of cardiac pacing systems have been proposed, e.g., the system disclosed in U.S. Pat. No. 4,436,092, incorporated herein by reference, and, in some instances employed clinically, that sense and respond to changes in blood temperature to change the cardiac pacing rate in a rate range between an upper and a lower pacing rate limit in order to control cardiac output.
With respect to cardiac monitoring, it has been proposed to sense and record such additional physiologic signals including blood pressure in or adjoining blood vessels and heart chambers during the cardiac cycle, blood temperature, blood pH, to and a variety of blood gases. Implantable heart monitors and blood pressure and temperature sensors that derive absolute blood pressure signals and temperature signals are disclosed in commonly assigned U.S. Pat. Nos. 5,368,040, 5,535,752 and 5,564,434, and in U.S. Pat. No. 4,791,931, all incorporated by reference herein.
The leads and circuitry disclosed in the above-incorporated, commonly assigned, '752 and '434 patents can be employed to record the EGM and absolute blood pressure values for certain intervals. The recorded data is periodically telemetered out to a programmer operated by the physician in an uplink telemetry transmission during a telemetry session initiated by a downlink telemetry transmission and receipt of an interrogation command.
Certain of the measured physiologic signals derived from the heart or blood in the circulatory system are affected by ambient conditions that cannot be separately measured by the above-described IMDs and physiologic sensors. Specifically, blood pressure and temperature signal values derived by a wholly implantable system are affected by atmospheric pressure acting on the patient and ambient temperature or by a fever afflicting the patient, respectively. In addition, certain implantable blood pressure sensors, e.g., those disclosed in the above-incorporated, commonly assigned '434 and '752 patents, are also affected by blood temperature changes
Changes in ambient conditions other than weather changes can also influence the measurement of absolute blood pressure changes, including both mean or average blood pressure and dP/dt pressure changes, by implantable pressure sensors. For example, when a patient in which such an implantable blood pressure sensing medical device is implanted changes elevation by ascending or descending in an elevator in a tall building or in an airplane, the change in barometric pressure changes the absolute blood pressure sensed in the body by an amount that can mask changes that are sought to be measured. In the context of an implantable rate responsive pacemaker operating under a rate control algorithm, the pressure change caused by the elevation change itself may exceed the blood pressure change that reflects a change in exercise level of the patient and be mis-interpreted as meriting a change in pacing rate to the upper or lower pacing rate limit, which can, at least, be uncomfortable to the patient. The barometric pressure effect can similarly have a negative effect on operating and detection functions of other IMDs reliant on accurately sensing cardiac blood pressure changes that truly reflect a cardiac function or requirement for cardiac output.
The effect of barometric pressure on cardiac blood pressure measurements has been noted. In commonly assigned U.S. Pat. No. 4,407,296, a micro-machined pressure sensor is disposed at the distal end of a lead in an oil filled chamber on one side of a pressure sensor element that is closed by a flexible membrane that is perpendicular to the lead body axis. The membrane is disposed behind a protective grill at the distal tip of the lead within which blood fluids can contact the exposed side of the membrane. Blood pressure changes deflect the membrane, and the deflection is transmitted through the oil to the micro-machined pressure sensor element which is deflected to produce a pressure signal value change proportional to the blood pressure change acting on the membrane. The blood pressure change reflects both the blood pumping action of the heart and the ambient atmospheric pressure acting on the patient's bod
Halperin Louis E.
Meador John T.
Miesel Keith A.
Stylos Lee
Taepke, II Robert T.
Atlass Michael B.
Carter Ryan
Medtronic Inc.
O'Connor Cary
Patton Harold R.
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