Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
1999-09-16
2001-02-13
O'Connor, Cary (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S485000, C600S494000, C600S500000, C600S520000
Reexamination Certificate
active
06186954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood-pressure monitoring apparatus which monitors a blood pressure of a living subject based on information relating to propagation of a pulse wave through an arterial vessel of the subject.
2. Related Art Statement
As information relating to a pulse wave which propagates through an arterial vessel of a living subject, there are known a pulse-wave-propagation time DT and a pulse-wave-propagation velocity V
M
(m/s). The pulse-wave-propagation time DT is a time which is needed by a pulse wave to propagate between two different positions of the arterial vessel. Additionally, it is known that the above pulse-wave-propagation-relating information is, within a predetermined range, substantially proportional to the blood pressure (“BP”, mmHg) of the living subject. Therefore, there has been proposed a BP monitoring apparatus which determines, in advance, coefficients &agr;, &bgr; in the following expression: EBP=&agr;(DT)+&bgr; (where &agr; is a negative constant and &bgr; is a positive constant), or EBP=&agr;(V
M
)+&bgr; (where &agr; and &bgr; are positive constants), based on two measured BP values of the subject and two measured pulse-wave-propagation time values (DT) or two measured pulse-wave-propagation velocity values (V
M
), iteratively determines an estimated BP value EBP of the subject, based on each piece of subsequently obtained pulse-wave-propagation-relating information, according to the above-indicated first or second expression, and starts a BP measurement using an inflatable cuff when an estimated BP value EBP is judged as being abnormal.
Meanwhile, at least two measured BP values and at least two pieces of obtained pulse-wave-propagation-relating information are needed for determining a relationship between pulse-wave-propagation-relating information and estimated BP value EBP represented by the first or second expression, because each of the first and second expressions includes two unknown constants. In order to determine an accurate relationship, it is desirable that the two measured BP values have the greatest possible difference. However, the conventional BP monitoring device carries out the second BP measuring operation using the inflatable cuff, irrespective of what BP value the subject currently has. Accordingly, the accuracy of the determined relationship may be insufficient. If many BP measuring operations each using the cuff are repeated till two BP values having a sufficiently great difference are obtained, it takes a long time and results in giving an unnecessary load to the subject.
SUMMERY OF THE INVENTION
It is therefore an object of the present invention to provide a blood-pressure monitoring apparatus which determines an estimated blood-pressure value of a living subject based on information relating to propagation of a pulse wave through an arterial vessel of the subject and which accurately and efficiently determines a relationship between pulse-wave-propagation-relating information and estimated blood-pressure value.
The Inventor has carried out various studies and has found that as a blood vessel of a living subject becomes harder, the velocity of a pulse wave which propagates through the blood vessel becomes faster and that as the blood vessel becomes softer, the velocity becomes slower. That is, the Inventor has found that the slope of a linear relationship between pulse-wave-propagation-relating information and estimated BP value EBP is proportional to the hardness of the blood vessel. The present invention has been developed based on this finding, and is directed to the art of determining the slope of the linear relationship based on the hardness of the blood vessel.
The present invention provides a blood-pressure monitoring apparatus which has one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (16). Any technical feature which includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that technical feature.
(1) According to a first feature of the present invention, there is provided a blood-pressure monitoring apparatus comprising a measuring device which includes an inflatable cuff adapted to apply a pressing pressure to a body portion of a living subject and which measures at least one blood-pressure value of the living subject by changing the pressing pressure of the inflatable cuff, a pulse-wave-propagation-relating-information obtaining device which iteratively obtains a piece of pulse-wave-propagation-relating information relating to propagation of a pulse wave through an arterial vessel of the living subject, estimating means for iteratively estimating a blood-pressure value, EBP, of the living subject, based on each piece of pulse-wave-propagation-relating information, PWPI, obtained by the pulse-wave-propagation-relating-information obtaining device, according to a linear relationship between pulse-wave-propagation-relating information and blood pressure, the linear relationship being defined by a following linear expression, EBP=&agr;(PWPI)+&bgr;, where &agr; is a slope and &bgr; is an intercept; index-value calculating means for calculating, based on the blood-pressure value of the living subject measured by the measuring device, an index value indicative of a hardness of a blood vessel of the living subject, slope determining means for determining, based on the calculated index value, the slope &agr; of the linear expression, and intercept determining means for determining the intercept &bgr; of the linear expression, based on the blood-pressure value measured by the measuring device, the piece of pulse-wave-propagation-relating information obtained by the pulse-wave-propagation-relating-information obtaining device when the blood-pressure value is measured by the measuring device, and the slope &agr; determined by the slope determining means. The present BP monitoring apparatus can determine a relationship between pulse-wave-propagation-relating information and (estimated) blood pressure, based on a single measured BP value and a single piece of obtained pulse-wave-propagation-relating information.
(2) According to a second feature of the present invention, there is provided a blood-pressure monitoring apparatus comprising a measuring device which includes an inflatable cuff adapted to apply a pressing pressure to a first body portion of a living subject and which measures at least one blood-pressure value of the living subject by changing the pressing pressure of the inflatable cuff, a pulse-wave-propagation-relating-information obtaining device which iteratively obtains a piece of pulse-wave-propagation-relating information relating to propagation of a pulse wave through an arterial vessel of the living subject, estimating means for iteratively estimating a blood-pressure value, EBP, of the living subject, based on each piece of pulse-wave-propagation-relating information, PWPI, obtained by the pulse-wave-propagation-relating-information obtaining device, according to a linear relationship between pulse-wave-propagation-relating information and blood pressure, the linear relationship being defined by a following linear expression, EBP=&agr;(PWPI)+&bgr;, where &agr; is a slope and &bgr; is an intercept, a pulse-wave detecting device which detects a peripheral pulse wave including a plurality of heartbeat-synchronous pulses, from a second body portion of the living subject, peripheral-pulse-wave-relating-value calculating means for iteratively calculating a peripheral-pulse-wave-relating value relating to each of the heartbeat-synchronous pulses of the peripheral pulse wave detected by the pulse-wave detecting device, index-value calculating means for iteratively calculating, based on each of the iteratively calculated peripheral-pulse-wave-relating values, an index value indicative of a hardness of a blood vessel of the living subject, and
Carter Ryan
Colin Corporation
O'Connor Cary
Oliff & Berridg,e PLC
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