Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2001-10-16
2003-06-24
Hindenburg, Max F. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S490000, C600S485000
Reexamination Certificate
active
06582374
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for automatically measuring a blood pressure of a living subject according to so-called oscillometric method.
2. Related Art Statement
The oscillometric blood-pressure measuring method is carried out as follows: A pressing pressure of an inflatable cuff which is wound around, e.g., an upper arm of a living subject, that is, a cuff pressure is slowly changed, and a blood pressure of the subject is determined based on the change of an oscillatory component occurring to the cuff during the changing of the cuff pressure (i.e., the change of respective amplitudes of respective heartbeat-synchronous pulses of a cuff pulse wave with respect to the change of cuff pressure). An automatic blood-pressure measuring apparatus which employs the oscillometric method can measure a blood pressure at a front neck, a finger, or an inferior limb of a living subject where it is difficult to measure a blood pressure according to a microphone-using method. In addition, the microphone-using method requires a microphone to be accurately positioned on an artery of the subject, whereas the oscillometric method just needs the cuff to be wound around a portion of the subject. Thus, the oscillometric method can be easily carried out by both skilled and non-skilled operators. Moreover, the oscillometric method can be carried out at a noisy place, or on a child or an in-shock patient who produces small Korotkoff sounds only. Thus, the oscillometric-type automatic blood-pressure measuring devices have come into wide use.
However, according to the oscillometric method, a blood pressure is determined based on the change of respective amplitudes of respective pulses of the cuff pulse wave occurring to the cuff during the slow changing of cuff pressure, on the assumption that the blood pressure of the subject does not change during the changing of cuff pressure. More specifically described, it is assumed that respective amplitudes A, and respective prescribed points, such as minimal values (i.e., diastolic pressures) or maximal values (i.e., systolic pressures), of respective pulses of a blood-pressure wave, shown in
FIG. 1A
, do not change during the changing of cuff pressure.
However, in an actual blood-pressure measurement, the cardiac output of the subject may change during the changing of cuff pressure, so that as shown in
FIG. 1B
, the respective amplitudes A of respective pulses of the blood-pressure wave may change, or so that as shown in
FIG. 1C
, the amplitudes A may not change but the blood pressure values may change. In some cases, both the amplitudes A and the blood pressure values may change. If the cardiac output or the blood pressure largely changes during the blood-pressure measurement, the envelope of respective amplitudes of respective pulses of the cuff pulse wave with respect to the cuff pressure deforms, which leads to determining an inaccurate blood pressure or even failing to determine a blood pressure.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus which automatically measures a blood pressure of a living subject with high accuracy.
The Inventor has carried out extensive studies and found the following facts: When amplitude of a blood-pressure waveform changes, amplitude of a volumetric pulse wave also changes. Therefore, if the same corrections to correct respective amplitudes of a volumetric pulse wave obtained during the changing of pressure of an inflatable cuff, to a predetermined value, are applied to respective amplitudes of a cuff pulse wave occurring to the cuff during the changing of the cuff pressure, an accurate blood pressure can be determined based on the thus corrected amplitudes of the cuff pulse wave. In addition, when blood pressure changes, pulse period also changes. Therefore, if blood pressure values are estimated based on pulse period values obtained during the changing of the cuff pressure, and the same corrections to correct the respective blood pressure values to a predetermined value, are applied to respective values of the cuff pressure at respective times of detection of the pulse period values, an accurate blood pressure can be determined based on the thus corrected values of the cuff pressure. Moreover, if those two inventions are combined, a more accurate blood pressure can be determined. Moreover, if a pulse pressure (i.e., an amplitude of a blood-pressure waveform) is estimated, based on two successive pulse period values obtained during the changing of the cuff pressure, according to a known technique, and the same corrections to correct respective pulse pressure values, determined based on respective pairs of successive pulse period values obtained during the changing of the cuff pressure, to a predetermined value, are applied to respective amplitudes of a cuff pulse wave occurring to the cuff during the changing of the cuff pressure, an accurate blood pressure can be determined based on the thus corrected amplitudes of the cuff pulse wave. Furthermore, if this invention is combined with the above-indicated second invention, a more accurate blood pressure can be determined.
The above object has been achieved by the present invention. According to the first invention, there is provided an apparatus for automatically measuring a blood pressure of a living subject, comprising an inflatable cuff which is adapted to be wound around a first portion of the subject, a cuff pulse wave including a plurality of heartbeat-synchronous pulses occurring to the cuff when a pressure in the cuff is changed; a volumetric-pulse-wave detecting device which is adapted to be worn on a second portion of the subject and which detects, from the second portion of the subject, a volumetric pulse wave including a plurality of heartbeat-synchronous pulses; a correction-factor determining means for iteratively determining, for each of the heartbeat-synchronous pulses of the volumetric pulse wave, a correction factor to correct an amplitude of the each heartbeat-synchronous pulse to a predetermined value; a corrected-cuff-pulse-wave-amplitude determining means for iteratively multiplying, by the correction factor determined by the correction-factor determining means for the each of the heartbeat-synchronous pulses of the volumetric pulse wave, an amplitude of one of the heartbeat-synchronous pulses of the cuff pulse wave that corresponds to the each heartbeat-synchronous pulse of the volumetric pulse wave, and thereby iteratively determining a corrected amplitude of the one heartbeat-synchronous pulse of the cuff pulse wave; and a blood-pressure determining means for determining a blood pressure of the subject based on a change of the respective corrected amplitudes of the respective heartbeat-synchronous pulses of the cuff pulse wave, with respect to the pressure of the cuff.
According to this invention, the correction-factor determining means iteratively determines, for each of the pulses of the volumetric pulse wave detected by the volumetric-pulse-wave detecting device, a correction factor to correct an amplitude of the each pulse to a predetermined value, and the corrected-cuff-pulse-wave-amplitude determining means iteratively multiplies, by the correction factor determined for the each of the pulses of the volumetric pulse wave, an amplitude of one of the pulses of the cuff pulse wave that corresponds to the each pulse of the volumetric pulse wave, and thereby iteratively determines a corrected amplitude of the one pulse of the cuff pulse wave. The thus determined corrected cuff-pulse-wave amplitudes are free of the influence of change of cardiac output of the subject during the changing of pressure of the cuff. And, the blood-pressure determining means determines a blood pressure of the subject based on a change of the respective corrected amplitudes of the respective pulses of the cuff pulse wave, with respect to the pressure of the cuff. Therefore, the thus determined blood pressure enjoys a high accuracy.
According to th
Colin Corporation
Hindenburg Max F.
Mallari Patricia C
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