Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-07-11
2002-02-12
Nasser, Robert L. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S485000, C600S494000
Reexamination Certificate
active
06346083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blood-pressure measuring apparatus which includes an inflatable cuff adapted to be worn on a body portion of a living subject and measures a blood pressure of the subject according to oscillometric method, and particularly to such an apparatus which additionally includes, for improving the accuracy of blood-pressure measurement, a pulse-wave detecting device for detecting a pulse wave propagated to a downstream-side portion of the cuff as seen in a direction of flow of blood in an artery of the body portion and determines a blood pressure of the subject based on the pulse wave detected by the pulse-wave detecting device.
2. Related Art Statement
Generally, an oscillometric-type blood-pressure (“BP”) measuring apparatus increases a pressing pressure of an inflatable bag accommodated in a cuff adapted to be wound around a body portion of a living subject, up to a predetermined pressure at which the bag can completely stop the flow of blood in an artery of the body portion under the cuff, subsequently slowly decreases the pressing pressure of the bag while continuously detecting the pressure in the bag, extracts a pulse wave from the continuously detected pressure of the bag, specifies a pressure of the bag at a rising point where respective amplitudes of respective heartbeat-synchronous pulses of the extracted pulse wave significantly largely changes, and determines the specified pressure of the bag as a systolic BP value of the subject.
However, the above BP measuring apparatus may not measure an accurate systolic BP value because the apparatus may not specify an accurate rising point of the pulse amplitudes of the pulse wave. More specifically described, even if the pressing pressure of the cuff may be higher than the systolic BP value of the subject, the pulsation of the artery may be transmitted to an upstream-side portion of the cuff as seen in the direction of flow of blood in the artery. In particular, in the case where the cuff is worn on a certain body portion (e.g., an ankle) of the subject where it is difficult for the cuff to completely stop the blood flow in the artery, a considerably great pulse wave may be transmitted to the upstream-side portion of the cuff while the pressing pressure of the cuff is higher than the systolic BP value of the subject. Accordingly, the pulse amplitudes of the pulse wave show an unclear rising point.
To solve the above problem, it has been proposed to provide a pulse-wave detecting device inside a downstream-side portion of an inflatable bag of a cuff and determine a BP value based on pulse amplitudes detected by the pulse-wave detecting device. For example, the pulse-wave detecting device may be one which includes a pulse-wave-detecting inflatable bag which is independent of the artery-pressing inflatable bag and is provided inside the downstream-side portion of the artery-pressing bag, and a pressure sensor which detects the pressure in the pulse-wave-detecting bag. In this case, a BP value is determined based on pulse amplitudes of a pulse wave transmitted to the pulse-wave-detecting bag. While the pressing pressure of the artery-pressing bag is higher than the systolic BP value of the subject, the pulsation of the artery may be propagated to the artery-pressing bag, but is not directly propagated to the pulse-wave-detecting bag provided inside the downstream-side portion of the artery-detecting bag. Thus, the pulse amplitudes of the pulse wave detected by the pulse-wave detecting device show a clearer rising point, which leads to determining a more accurate BP value.
However, in some cases, even pulse amplitudes of a pulse wave detected by the pulse-wave detecting device do not show a clear rising point. In particular, in the case where the cuff is worn on, e.g., an ankle where it is difficult for the cuff to completely stop the blood flow in the artery, the pulse amplitudes of a pulse wave detected by the pulse-wave detecting device may not show a clear rising point. In this case, while the pressing pressure of the artery-pressing bag is higher than the systolic BP value of the subject, the pulsation of the artery is, indeed, not directly propagated to the pulse-wave-detecting bag provided inside the downstream-side portion of the artery-detecting bag. However, the pulsation may be indirectly propagated to the pulse-wave-detecting bag via the artery-pressing bag. That is, even if the pressing pressure of the artery-pressing bag may be higher than the systolic BP value of the subject, a pulse wave is produced from an artery located on an upstream side of the cuff, and this pulse wave is propagated to an upstream-side portion of the artery-pressing bag of the cuff, and this pulse wave is detected by the pulse-wave sensor via the pulse-wave-detecting bag. Therefore, a BP value determined based on pulse amplitudes of a pulse wave detected by the pulse-wave detecting device may not be accurate.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a blood-pressure measuring apparatus which measures an accurate blood pressure.
The Applicants have carried out their extensive studies to achieve the above object, and found that it is possible to measure an accurate blood pressure by subtracting, from respective amplitudes of heartbeat-synchronous pulses of a pulse wave detected by a pulse-wave sensor, the influence of respective amplitudes of heartbeat-synchronous pulses of a pulse wave propagated to an inflatable bag employed for pressing an arterial vessel of a living subject, and thereby clearly showing a rising point of the former pulse amplitudes. The present invention has been developed based on this finding.
(1) According to a first feature of the present invention, there is provided a blood-pressure measuring apparatus comprising an inflatable cuff which is adapted to be wound around a body portion of a living subject and which includes a first inflatable bag which is inflatable to press an arterial vessel of the body portion and stop flow of blood in the arterial vessel; a first pulse-wave detecting device which detects a first pulse wave which is produced from the arterial vessel and is propagated to the first inflatable bag of the cuff wound around the body portion, the first pulse wave including a plurality of heartbeat-synchronous pulses; a second pulse-wave detecting device which detects a second pulse wave which is produced from the arterial vessel and is propagated to a downstream-side portion of the cuff wound around the body portion as seen in a direction in which the blood flows in the arterial vessel, the second pulse wave including a plurality of heartbeat-synchronous pulses; amplitude correcting means for correcting at least one of (a) a first group of respective amplitudes of the heartbeat-synchronous pulses of the first pulse wave detected by the first pulse-wave detecting device and (b) a second group of respective amplitudes of the heartbeat-synchronous pulses of the second pulse wave detected by the second pulse-wave detecting device, so that at least one amplitude of the first group that corresponds to at least one heartbeat-synchronous pulse of the first pulse wave that is detected by the first pulse-wave detecting device while the flow of the blood in the arterial vessel is stopped by the first inflatable bag is substantially equal to at least one amplitude of the second group that corresponds to at least one heartbeat-synchronous pulse of the second pulse wave that is detected by the second pulse-wave detecting device while the flow of the blood in the arterial vessel is stopped by the first inflatable bag; amplitude-difference determining means for determining a difference between each of the amplitudes of the first group and a corresponding one of the amplitudes of the second group after the at least one of the first and second groups is corrected by the amplitude correcting means; and blood-pressure determining means for determining a blood pressure of the subject based on the differe
Nishibayashi Hideo
Nunome Tomohiro
Carter Ryan
Colin Corporation
Nasser Robert L.
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