Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-08-09
2004-06-08
Schaetzle, Kennedy (Department: 3762)
Surgery
Diagnostic testing
Cardiovascular
C600S506000, C600S547000
Reexamination Certificate
active
06748262
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a heartbeat synchronous information acquiring apparatus for determining heartbeat synchronous information based on an impedance pulse wave of a living body. The present information also relates to a pulse wave propagation velocity related information acquiring apparatus, a blood pressure monitoring apparatus and a preejection period measuring apparatus adapted to utilize the acquired heartbeat synchronous information. As far as this patent application is concerned, the expression “heartbeat synchronous information” refers to a predetermined part of a heartbeat synchronous pulse wave.
2. Detailed Description of the Related Art
The impedance between two bodily positions with the heart interposed between them involves changes in the impedance attributable to expansions and contractions of the heart that are expressed in the form of an impedance pulse wave composed of heartbeat synchronous components. Apparatus for acquiring various pieces of bio-information by utilizing the heartbeat synchronous information determined as a function of the impedance pulse wave have been proposed to date.
For instance, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142597 an apparatus for determining heartbeat synchronous information as a function of the impedance pulse wave of a living body and measuring the pulse wave propagation velocity at which a pulse wave propagates in a living body by utilizing the obtained heartbeat synchronous information. Additionally, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142596 a blood pressure monitoring apparatus for determining heartbeat synchronous information as a function of the impedance pulse wave of a living body, continually computing the pulse wave propagation velocity at which the pulse wave propagates in a living body by utilizing the obtained heartbeat synchronous information and then monitoring a blood pressure based on the obtained pulse wave propagation velocity. Furthermore, the applicant of the present patent application has proposed in Japanese Patent Application No. 8-142598 a preejection period measuring apparatus for computing a preejection period from a time lag between a predetermined part of an induced electro-cardiac wave and a corresponding predetermined part of the impedance pulse wave (or heartbeat synchronous information) of a living body.
When acquiring various pieces of bio-information by utilizing the heartbeat synchronous information determined as a function of the impedance pulse wave of a living body, it is absolutely essential that the heartbeat synchronous information is determined accurately. However, the impedance of a living body is in fact a micro-signal that needs to be amplified by about 10,000 times (to about 80 dB) when it is to be perceived as a signal. As the micro-signal is amplified, induction noise surrounding a subject and radiation noise from unrelated devices become apparent making the signal less recognizable. Additionally, the blood of the subject moving through blood vessels can give rise to noise along with the impedance pulse wave. Furthermore, the impedance can change as the subject moves, which in turn moves electrodes fitted to the subject. Therefore, the noise detected along with the impedance pulse wave can sometimes make it impossible to accurately determine the heartbeat synchronous information of the subject. For instance, when determining the heartbeat synchronous information from consecutive peaks of heartbeats in the impedance pulse wave, the amplitudes of the peaks of high noise can be greater than those of the peaks of the heartbeats. Consequently, noise which shows a large amplitude can be determined as heartbeat synchronous information.
SUMMARY OF THE INVENTION
In view of the above identified circumstances, the object of the present invention is to provide a heartbeat synchronous information acquiring apparatus that can accurately determine heartbeat synchronous information as well as a pulse wave propagation velocity related information acquiring apparatus, a blood pressure monitoring apparatus, and a preejection period measuring apparatus adapted to utilize the acquired heartbeat synchronous information.
As a result of intensive research efforts carried but to achieve the above object, the inventor of the present invention has found that it is possible to accurately determine the heartbeat synchronous information by extracting an impedance pulse wave for a predetermined period, which is a time span long enough to generate such heartbeat synchronous information, out of a continuously detected impedance pulse wave. This is done by using an induced electro-cardiac wave adapted to produce a signal greater than a signal of an impedance of a living body, and hence less affected by noise. The heartbeat synchronous information is then determined from an extracted partial impedance pulse wave because the heartbeat synchronous information is not affected by noise other than that of the extracted part. This invention is based on this finding.
The First Aspect of the Invention
In the first aspect of the invention, there is provided a heartbeat synchronous information acquiring apparatus provided with an impedance pulse wave detector for detecting an impedance pulse wave of a living body, containing heartbeat synchronous components, between a pair of electrodes fitted to predetermined positions of the living body with the heart interposed between them. This is done in order to acquire the heartbeat synchronous information, generated synchronously with heartbeats of the living body, based on the impedance pulse wave. The apparatus is composed of (a) an induced electro-cardiac wave detection device for continuously detecting an induced electro-cardiac wave of the living body, and (b) a gate means for extracting a partial impedance pulse wave from the impedance pulse wave by taking in the impedance pulse wave for an intake period based on a time of detection of a predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device. There is also (c) a heartbeat synchronous information determining means for determining a periodically appearing predetermined part of the partial impedance pulse wave extracted by the gate means as heartbeat synchronous information.
Advantages the First Aspect of the Invention
With the above described arrangement, the partial impedance pulse wave is extracted by the gate means from the impedance pulse wave. The partial impedance pulse wave is detected by the impedance pulse wave detector by taking in the impedance pulse wave for the intake period based on the time of detection of the predetermined part of the induced electro-cardiac wave. The periodically appearing predetermined part of the partial impedance pulse wave extracted by the gate means is determined as heartbeat synchronous information by the heartbeat synchronous information determining means. Thus, it is now possible to accurately acquire heartbeat synchronous information.
Other Modes of Carrying out the Invention in the First Aspect
Preferably, the intake period of the gate means is from the end of a predetermined first time period starting from the time of detection of the predetermined part of the induced electro-cardiac wave by the electro-cardiac wave detection device to the end of a predetermined second time period starting from the time of detection of the predetermined part. The second time period is longer than the first time period. With this arrangement, the intake period is determined only based on a part of the induced electro-cardiac wave that is less affected by noise so that the intake period can be determined accurately, and it is no longer necessary to provide an additional device for determining the intake period. It will be appreciated that, if the intake period is not determined accurately, the partial impedance pulse wave may contain unnecessary parts, or may not contain the ne
Harada Chikao
Kawaguchi Keizoh
Narimatsu Kiyoyuki
Yokozeki Akihiro
Colin Medical Technology Corporation
Droesch Kristen
Schaetzle Kennedy
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