Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-06-30
2001-06-12
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S500000
Reexamination Certificate
active
06245022
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to systems and devices for measuring arterial blood pressure. In particular, the invention relates to an improved method and device for measuring arterial blood pressure in a non-invasive manner while reducing the effects of motion artifacts using a constant gain adjustment during pressure pulses.
There has been a continuing need for devices which will measure blood pressure non-invasively, with accuracy comparable to invasive methods. Medwave, Inc. the assignee of the present invention, has developed non-invasive blood pressure measurement devices which are described in the following United States patents: U.S. Pat. No. 5,649,542 entitled CONTINUOUS NONINVASIVE BLOOD PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,450,852 entitled CONTINUOUS NON-INVASIVE PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,640,964 entitled WRIST MOUNTED BLOOD PRESSURE SENSOR; U.S. Pat. No. 5,720,292 entitled BEAT ONSET DETECTOR; U.S. Pat. No. 5,738,103 entitled SEGMENTED ESTIMATION METHOD; U.S. Pat. No. 5,722,414 entitled CONTINUOUS NON-INVASIVE BLOOD PRESSURE MONITORING SYSTEM; U.S. Pat. No. 5,642,733 entitled BLOOD PRESSURE SENSOR LOCATOR; and U.S. Pat. No. 5,797,850 entitled METHOD AND APPARATUS FOR CALCULATING BLOOD PRESSURE OF AN ARTERY. Further description of these devices is found in United States patent application Ser. No. 08/912,139 filed Aug. 15, 1997, entitled HAND-HELD NON-INVASIVE BLOOD PRESSURE MEASUREMENT DEVICE.
As described in these patents and the pending patent application, the Medwave non-invasive blood pressure measurement device and method determines blood pressure by sensing pressure waveform data derived from an artery. A pressure sensing device includes a sensing chamber with a diaphragm which is positioned over the artery. A transducer coupled to the sensing chamber senses pressure within the chamber. A flexible body conformable wall is located adjacent to (and preferably surrounding) the sensing chamber. The wall is isolated from the sensing chamber and applies force to the artery while preventing pressure in a direction generally parallel to the artery from being applied to the sensing chamber.
As varying pressure is applied to the artery by the sensing chamber, pressure waveforms are sensed by the transducer to produce sensed pressure waveform data. The varying pressure may be applied automatically in a predetermined pattern, or may be applied manually in a somewhat random fashion.
The sensed pressure waveform data is analyzed to determine waveform parameters which relate to the shape of the sensed pressure waveforms. One or more blood pressure values are derived based upon the waveform parameters. The Medwave blood pressure measurement devices include both automated devices for continuously monitoring blood pressure (such as in a hospital setting) and hand-held devices which can be used by a physician, or by a patient when desired. These devices represent an important improvement in the field of non-invasive blood pressure measurement. Still further improvements, of course, are highly desirable.
BRIEF SUMMARY OF THE INVENTION
The present invention is an improvement to a non-invasive blood pressure sensing device and method of the type having a fluid filled sensing chamber and a flexible body conformable wall proximate to and isolated from the sensing chamber which applies force to the artery. The present invention is an improvement which minimizes effects of motion artifacts on the blood pressure measurement while maintaining accuracy of blood pressure readings using a constant gain adjustment during pressure pulses.
In the present invention, the flexible body conformable wall includes a chamber which is separate from the sensing chamber. A first transducer senses pressure within the sensing chamber, while a second transducer senses pressure within the chamber which is a part of the flexible body conformable wall.
The signals from the first and second transducers are processed and used to derive pressure waveform data from which blood pressure values are derived. Part of the processing includes the use of an adjusted gain that is substantially constant during heart beats, but that may vary from beat to beat. Signal values obtained from the second transducer are multiplied by the adjusted gain and then subtracted from the signal values obtained from the first transducer. The use of signals from both the first and the second transducers eliminates fluctuations in the signal from the first transducer which are the result of motion artifacts.
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Archibald G. Kent
Curran Timothy G.
Danielson Orland H.
Poliac Marius O.
Thede Roger C.
Kinney & Lange , P.A.
Medwave, Inc.
Nasser Robert L.
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