US 5,392,781 A · Blood pressure monitoring in noisy environments

Abstract

Several techniques are provided for aiding in the discrimination of detected biological signals indicative of blood pressure from detected signals not indicative of blood pressure (e.g., noise). A threshold, based predominantly on a level of noise, is developed and used in the discrimination. A second threshold, based predominantly on levels of previously detected biological signals, is developed and additionally used to help discriminate the biological signals from noise. The biological signals are detected during a selected portion of a cardiac cycle, and additional signals detected outside of the selected portion of the cycle are applied to the detected signals. Another threshold may be developed based predominantly on a level of signals sensed by a transducer positioned to preferentially sense noise; the transducer is positioned so that the noise that it detects is related to noise that is detected during the detection of the biological signals. Blood pressure is measured during periodically scheduled measurement cycles, and a measurement cycle is suspended if noise exceeds a predetermined level. The times at which the detected signals (i.e., the signals indicative of blood pressure and the signals not indicative of blood pressure) are processed during a given cardiac cycle are selected based at least in part on the pressure of the cuff. The biological signals indicative of blood pressure that are detected during a current measurement cycle are used to at least in part determine the times at which the detected signals will be processed during a succeeding measurement cycle.

Claims121

Dependent claims

A method for use in measuring blood pressure, comprising

detecting a plurality of mixed signals, each of which includes biological signals indicative of blood pressure and signals not indicative of blood pressure,
separating said signals not indicative of blood pressure from said biological signals to develop a threshold, said separating including combining said plurality of mixed signals with each other so as to reinforce said signals not indicative of blood pressure and attenuate said biological signals so that said threshold is based predominantly on a level of said signals not indicative of blood pressure that have been separated from said biological signals, and
using said threshold to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure.

A procedure for use in measuring the blood pressure of a subject by detecting a plurality of mixed signals, each of which includes biological signals indicative of blood pressure and signals not indicative of blood pressure, comprising

a) inflating a cuff to a predetermined pressure and then decreasing said pressure in successive portions of a cardiac cycle while performing said detecting, and
b) processing said detected signals during each portion of the cardiac cycle, said processing including
separating said signals not indicative of blood pressure from said biological signals to develop a first threshold, said separating including combining said plurality of mixed signals with each other so as to reinforce said signals not indicative of blood pressure and attenuate said biological signals so that said first threshold is based predominantly on a level of said signals not indicative of blood pressure detected during said current portion of the cardiac cycle and that have been separated from said biological signals,
deriving a current candidate blood pressure signal based predominantly on said signals indicative of blood pressure detected during a current portion of the cardiac cycle,
deriving a second threshold based predominantly on candidate blood pressure signals detected during previous portions of the cardiac cycle,
comparing said first threshold and said second threshold to said current candidate blood pressure signal to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure,
determining that a validated blood pressure signal has occurred in the current portion of the cardiac cycle if said current candidate blood pressure signal exceeds said first threshold and said second threshold,
determining that an ambiguous signal has occurred in the current portion of the cardiac cycle if said first threshold exceeds said current candidate blood pressure signal, and
determining that an insignificant signal has occurred in the current portion of the cardiac cycle if said second threshold exceeds said current candidate blood pressure signal.

6 more elements

A procedure for measuring the blood pressure of a subject by detecting a plurality of mixed signals, each of which includes biological signals indicative of blood pressure and signals not indicative of blood pressure, comprising

a) inflating a cuff to a predetermined pressure and then decreasing said pressure in successive portions of a cardiac cycle while performing said detecting,
b) processing said detected signals during each portion of the cardiac cycle, said processing including
deriving a current candidate blood pressure signal based predominantly on said signals indicative of blood pressure detected during a current portion of the cardiac cycle,
developing a first threshold by combining said plurality of mixed signals with each other so as to reinforce said signals not indicative of blood pressure and attenuate said biological signals so that said first threshold is based predominantly on a level of said signals not indicative of blood pressure detected during said current portion of the cardiac cycle,
deriving a second threshold based predominantly on candidate blood pressure signals detected during previous portions of the cardiac cycle,
comparing said first threshold and said second threshold to said current candidate blood pressure signal to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure,
determining that a validated blood pressure signal has occurred in the current portion of the cardiac cycle if said current candidate blood pressure signal exceeds said first threshold and said second threshold,
determining that an ambiguous signal has occurred in the current portion of the cardiac cycle if said first threshold exceeds said current candidate blood pressure signal, and
determining that an insignificant signal has occurred in the current portion of the cardiac cycle if said second threshold exceeds said current candidate blood pressure signal,
c) storing candidate blood pressure signals and corresponding pressures of said cuff for each portion of said cardiac cycle during which a validated blood pressure signal is determined to have occurred, and incrementally decreasing said pressure and repeating said processing during a subsequent portion of the cardiac cycle,
d) determining a systolic pressure and a diastolic pressure of the subject from said stored candidate blood pressure signals and corresponding pressures, and
e) rejecting said systolic pressure if it is not within a predetermined range of pressures based on previously measured systolic pressures for the subject.

9 more elements

A procedure for measuring the blood pressure of a subject by detecting biological signals indicative of blood pressure and signals not indicative of blood pressure, comprising

a) inflating a cuff to a predetermined pressure and then decreasing said pressure in successive cardiac cycles while performing said detecting,
b) processing said detected signals during each cardiac cycle, said processing including
deriving a current candidate blood pressure signal based predominantly on said signals indicative of blood pressure detected during a current cardiac cycle,
developing a first threshold based predominantly on a level of said signals not indicative of blood pressure detected during said current cardiac cycle,
deriving a second threshold based predominantly on candidate blood pressure signals detected during previous cardiac cycles,
comparing said first threshold and said second threshold to said current candidate blood pressure signal to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure,
determining that a validated blood pressure signal has occurred in the current cardiac cycle if said current candidate blood pressure signal exceeds said first threshold and said second threshold, and, if a validated blood pressure signal is determined to have occurred, storing said candidate blood pressure signal and a corresponding pressure of said cuff during said cardiac cycle, and incrementally decreasing said pressure and repeating said processing during a subsequent cardiac cycle,
determining that an ambiguous signal has occurred in the current cardiac cycle if said first threshold exceeds said current candidate blood pressure signal, and
determining that an insignificant signal has occurred in the current cardiac cycle if said second threshold exceeds said current candidate blood pressure signal,
c) storing candidate blood pressure signals and corresponding pressures of said cuff for each said cardiac cycle during which a validated blood pressure signal is determined to have occurred,
d) determining a systolic pressure and a diastolic pressure of the subject from said stored candidate blood pressure signals and corresponding pressures,
e) determining whether a current heart rate of the subject differs from a previous heart rate, and
f) rejecting said systolic pressure if said systolic pressure has changed from a previously measured systolic pressure in a direction opposite to that in which said current heart rate has changed from said previous heart rate.

10 more elements

a) inflating a cuff to a predetermined pressure and then decreasing said pressure in successive portions of a cardiac cycle while performing said detecting,
b) processing said detected signals during each portion of the cardiac cycle, said processing including
deriving a current candidate blood pressure signal based predominantly on said signals indicative of blood pressure detected during a current portion of the cardiac cycle,
developing a first threshold by combining said plurality of mixed signals with each other so as to reinforce said signals not indicative of blood pressure and attenuate said biological signals so that said first threshold is based predominantly on a level of said signals not indicative of blood pressure detected during said current portion of the cardiac cycle,
deriving a second threshold based predominantly on candidate blood pressure signals detected during previous portions of the cardiac cycle,
comparing said first threshold and said second threshold to said current candidate blood pressure signal to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure,
determining that a validated blood pressure signal has occurred in the current portion of the cardiac cycle if said current candidate blood pressure signal exceeds said first threshold and said second threshold,
determining that an ambiguous signal has occurred in the current portion of the cardiac cycle if said first threshold exceeds said current candidate blood pressure signal, and
determining that an insignificant signal has occurred in the current portion of the cardiac cycle if said second threshold exceeds said current candidate blood pressure signal,
c) storing candidate blood pressure signals and corresponding pressures of said cuff for each portion of said cardiac cycle during which a validated blood pressure signal is determined to have occurred, and incrementally decreasing said pressure and repeating said processing during a subsequent portion of the cardiac cycle,
d) determining a systolic pressure and a diastolic pressure of the subject from said stored candidate blood pressure signals and corresponding pressures, and
e) said step of determining diastolic pressure comprises identifying a stored candidate blood pressure signal determined to have occurred in a given portion of the cardiac cycle which was followed by a predetermined number of cardiac cycles in which said insignificant signals are determined to have occurred, and designating the stored pressure that corresponds to said identified blood pressure signal as said diastolic pressure.

9 more elements

A procedure for measuring the blood pressure of a subject by detecting biological signals indicative of blood pressure and signals not indicative of blood pressure, comprising

a) inflating a cuff to a predetermined pressure and then decreasing said pressure in successive cardiac cycles while performing said detecting,
b) processing said detected signals during each cardiac cycle, said processing including
deriving a current candidate blood pressure signal based predominantly on said signals indicative of blood pressure detected during a current cardiac cycle,
developing a first threshold based predominantly on a level of said signals not indicative of blood pressure detected during said current cardiac cycle,
deriving a second threshold based predominantly on candidate blood pressure signals detected during previous cardiac cycles,
comparing said first threshold and said second threshold to said current candidate blood pressure signal to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure,
determining that a validated blood pressure signal has occurred in the current cardiac cycle if said current candidate blood pressure signal exceeds said first threshold and said second threshold, and, if a validated blood pressure signal is determined to have occurred, storing said candidate blood pressure signal and a corresponding pressure of said cuff during said cardiac cycle, and incrementally decreasing said pressure and repeating said processing during a subsequent cardiac cycle,
determining that an ambiguous signal has occurred in the current cardiac cycle if said first threshold exceeds said current candidate blood pressure signal, and
determining that an insignificant signal has occurred in the current cardiac cycle if said second threshold exceeds said current candidate blood pressure signal,
c) storing candidate blood pressure signals and corresponding pressures of said cuff for each said cardiac cycle during which a validated blood pressure signal is determined to have occurred,
d) determining a systolic pressure and a diastolic pressure of the subject from said stored candidate blood pressure signals and corresponding pressures by:
comparing a third threshold to said stored candidate blood pressure signals and designating as systolic pressure a highest stored pressure having a corresponding stored candidate blood pressure signal that exceeds said third threshold,
identifying a stored candidate blood pressure signal determined to have occurred in a given cardiac cycle which was followed by a predetermined number of cardiac cycles in which said insignificant signals are determined to have occurred,
designating the stored pressure that corresponds to said identified blood pressure signal as said diastolic pressure, and
increasing said third threshold if said signals not indicative of blood pressure exceed a predetermined level, and changing said designated systolic pressure and said designated diastolic pressure based on increases in said third threshold.

12 more elements

A computer assisted method of measuring the blood pressure of a subject, comprising

scheduling periodic measurement cycles;
measuring blood pressure during each measurement cycle by:
a) simultaneously detecting a plurality of mixed signals, each of which includes biological signals indicative of blood pressure and signals not indicative of blood pressure, and
b) processing said detected signals to determine said blood pressure, said processing including:
(1) separating said signals not indicative of blood pressure from said biological signals indicative of blood pressure during each measurement cycle to develop a first threshold, said separating including combining said plurality of mixed signals with each other so as to reinforce said signals not indicative of blood pressure and attenuate said biological signals so that said first threshold is based predominantly on a level of said signals not indicative of blood pressure that have been separated from said biological signals, and determining a second threshold based on said first threshold;
and
(2) using said first threshold to aid in discriminating said signals indicative of blood pressure from said signals not indicative of blood pressure;
and
suspending said measuring during one of said measurement cycles if said second threshold exceeds a predetermined level during said cycle.

6 more elements

Dependencies are inferred from the claim text.

Blood pressure monitoring in noisy environments

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Blood pressure monitoring in noisy environments

Life of this patent

Abstract

Claims121