System and method for estimating cardiac output
First Claim
1. A method for estimating blood output through a flow region of a patient'"'"'s body, comprising the following steps:
- A) injecting an indicator as an indicator input signal having an input signal profile and a period into an upstream position in the flow region;
B) sensing the presence of the indicator at a downstream position in the flow region to determine an indicator output signal;
C) estimating as a predetermined function of the input signal profile and the indicator output signal both a local blood output value over a local estimation time, and a trend blood output value over a trend estimation time, in which the trend estimation time is longer than the local estimation time, thereby providing estimated blood output values corresponding to both relatively fast and slow changes in blood output.
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Abstract
Cardiac output CO is separately estimated in a local estimator and a trend estimator to provide CO values. A thermal signal is injected preferably according to a pseudo-random binary sequence signal profile at an upstream position in a blood flow region of a patient'"'"'s body and is sensed as an indicator output signal at a downstream position. Low-frequency noise is preferably removed from the sensed indicator output signal. The local and trend estimations are based on measured frequency-domain transfer function values between the sensed and input indicator signal in relation to a pre-determined transfer function model, which is preferably a lagged normal model. The trend estimator is preferably a Kalman filter. The local estimator preferably forms its estimate based on non-recursive optimization of a cost function. The local estimator preferably provides initial values to start the trend estimator.
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Citations
24 Claims
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1. A method for estimating blood output through a flow region of a patient'"'"'s body, comprising the following steps:
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A) injecting an indicator as an indicator input signal having an input signal profile and a period into an upstream position in the flow region; B) sensing the presence of the indicator at a downstream position in the flow region to determine an indicator output signal; C) estimating as a predetermined function of the input signal profile and the indicator output signal both a local blood output value over a local estimation time, and a trend blood output value over a trend estimation time, in which the trend estimation time is longer than the local estimation time, thereby providing estimated blood output values corresponding to both relatively fast and slow changes in blood output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for estimating blood output through a flow region of a patient'"'"'s body, comprising the following steps:
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A) injecting a thermal indicator as an indicator input signal having a pseudo-random binary sequence (PRBS) input signal profile and a period into an upstream position in the flow region; B) sensing the presence of the indicator at a downstream position in the flow region to determine an indicator output signal; C) removing any low-frequency noise trend from the indicator output signals; D) selecting state parameters of a predetermined transfer function model relating the indicator output signal to the indicator input signal; E) determining an autocorrelation value Cxx of the input signal and converting the autocorrelation value Cxx to the frequency domain; F) determining a cross-correlation value Cxy between the indicator input signal and the indicator output signal and converting the cross-correlation value Cxy to the frequency domain; G) computing measured transfer function values as a predetermined function of the quotient between the frequency-converted cross-correlation and autocorrelation values; H) determining optimal local state parameters as a predetermined optimization function of the transfer function model and the measured transfer function values, and estimating a local blood output value as a predetermined output function of at least one of the optimal local state parameters; and I) recursively estimating optimal trend state parameters by Kalman filtering the measured transfer function values, and estimating a trend blood output value as the predetermined output function of at least one of the optimal local state parameters.
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13. A system for estimating blood output through a flow region of a patient'"'"'s body, comprising:
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A) injection means for injecting an indicator as an indicator input signal having an input signal profile and a period into an upstream position in the flow region; B) indicator sensing means for sensing the presence of the indicator at a downstream position in the flow region to determine an indicator output signal; C) estimation means including a local estimator for estimating over a local estimation time a local blood output value as a predetermined function of the input signal profile and the indicator output signal, and a trend estimator for estimating a trend blood output value over a trend estimation time, in which the trend estimation time is longer than the local estimation time, thereby providing estimated blood output values corresponding to both relatively fast and slow changes in blood output. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A system for estimating blood output through a flow region of a patient'"'"'s body, comprising:
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A) indicator injection means for injecting a thermal indicator having a pseudo-random binary sequence (PRBS) input signal profile into an upstream position in the flow region as an indicator input signal; B) thermistor means for sensing the presence of the indicator at a downstream position in the flow region to determine an indicator output signal; C) pre-filter means for removing any low-frequency noise trend from the indicator output signals; D) transfer function measuring means; 1) for computing an autocorrelation value Cxx of the input signal and converting the autocorrelation value Cxx to the frequency domain; 2) for computing a cross-correlation value Cxy between the indicator input signal and the indicator output signal and converting the cross-correlation value Cxy to the frequency domain; 3) for computing measured transfer function values as a predetermined function of the quotient between the frequency-converted cross-correlation and autocorrelation values; E) local estimation means for determining optimal local state parameters as a predetermined optimization function of the transfer function model and the measured transfer function values, and estimating a local blood output value as a predetermined output function of at least one of the optimal local state parameters; and F) trend estimation means for recursively estimating optimal trend state parameters by Kalman filtering the measured transfer function values, and estimating a trend blood output value as the predetermined output function of at least one of the optimal local state parameters.
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Specification