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EP-4498902-B1 - APPARATUS FOR DETERMINING AN INDICATOR REPRESENTATIVE FOR A PHYSIOLOGICAL PARAMETER

EP4498902B1EP 4498902 B1EP4498902 B1EP 4498902B1EP-4498902-B1

Inventors

  • PFEIFFER, ULRICH
  • Stolze, Benjamin
  • REGH, Stephan Guido Maria
  • KIEFER, Antonia

Dates

Publication Date
20260506
Application Date
20230324

Claims (15)

  1. An apparatus (100) for determining an indicator that is representative for a physiological parameter, wherein the apparatus comprises: - a pulse signal providing unit (101) configured to provide a measured pulse signal of a patient over a time period corresponding to a plurality of subsequent respiratory cycles of the patient, wherein the pulse signal is a pressure signal that has been measured by using a pressure cuff with a pressure sensor being in contact with the outer skin of the patient, wherein pressure applied to the patient by the pressure cuff is increased or decreased, while the pressure sensor measures the pressure signal on the outer skin of the patient, and wherein the measured pressure is indicative of blood pulsations, - an indicator determination unit (102) configured to carry out a determination procedure adapted to determine an indicator that is representative for a physiological parameter based on the provided pulse signal, wherein the determination procedure includes a) determining a respiratory pulse variation signal (r0) corresponding to pulse variations caused by ventilation or respiration induced heart-lung interaction based on the provided measured pulse signal, characterised in that the determination procedure further includes b) determining a systolic part of the respiratory pulse variation signal (r0), which corresponds to a time period in which the increasing or decreasing applied pressure passed the systolic arterial pressure of the patient and which therefore is prone to comprising an artifact, c) modifying the respiratory pulse variation signal (r0) such that the determined systolic part of the respiratory pulse variation signal (r0) is corrected and d) determining the indicator based on the measured pulse signal and the modified respiratory pulse variation signal (r0).
  2. The apparatus (100) as defined by claim 1, wherein the indicator determination unit (102) is configured to correct the systolic part of the respiratory pulse variation signal (r0) by replacing at least a subpart of the systolic part by another part of the respiratory pulse variation signal (r0) and/or by removing at least a subpart of the systolic part.
  3. The apparatus (100) as defined by claim 1 or 2, wherein the indicator determination unit (102) is configured to represent the respiratory pulse variation signal (r0) as a respiratory pulse variation signal (r0) oscillating around an average value thereof and to determine the systolic part of the respiratory pulse variation signal (r0) such that it includes a lowest minimum and/or a highest maximum of the respiratory pulse variation signal (r0).
  4. The apparatus (100) as defined by claim 3, wherein the indicator determination unit (102) is configured to determine the systolic part of the respiratory pulse variation signal (r0) such that it includes a half wave of the respiratory pulse variation signal (r0) with a lowest minimum and/or a half wave of the respiratory pulse variation signal (r0) with a highest maximum and to modify the respiratory pulse variation signal (r0) by a) replacing the lowest minimum half wave and/or the highest maximum half wave by a half wave of another part the respiratory pulse variation signal (r0) and/or b) removing the lowest minimum half wave and/or the highest maximum half wave.
  5. The apparatus (100) as defined by claim 4, wherein the indicator determination unit (102) is configured to determine the systolic part of the respiratory pulse variation signal (r0) such that it includes at least one first half wave of the respiratory pulse variation signal (r0) adjacent the half wave of the respiratory pulse variation signal (r0) with the lowest minimum and/or at least one second half wave of the respiratory pulse variation signal (r0) adjacent the half wave of the respiratory pulse variation signal (r0) with the highest maximum and to modify the respiratory pulse variation signal (r0) by a) replacing the at least one first half wave and/or the at least one second half wave by a half wave of another part of the respiratory pulse variation signal (r0) and/or b) removing the at least one first half wave and/or the at least one second half wave.
  6. The apparatus (100) as defined by any of the preceding claims, wherein the indicator determination unit (102) is configured to determine the systolic part of the respiratory pulse variation signal (r0) as a part in which a maximum decrease position (10) is present, at which the respiratory pulse variation signal (r0) and/or an envelope signal curve (s0) of the pulse signal (p0) has its maximum decrease.
  7. The apparatus (100) as defined by claim 6, wherein the indicator determination unit (102) is configured to represent the respiratory pulse variation signal (r0) as a respiratory pulse variation signal (r0) oscillating around an average value thereof and to modify the respiratory pulse variation signal (r0) by a) replacing the half wave (h1), which comprises the maximum immediately before the maximum decrease position (10), and the half wave (h2), which comprises the minimum immediately behind the maximum decrease position (10), of the respiratory pulse variation signal (r0) by half waves (h3, h4) of another part the respiratory pulse variation signal and/or b) removing these half waves (h1, h2).
  8. The apparatus (100) as defined by any of the preceding claims, wherein the indicator determination unit (102) is configured to determine the systolic part of the respiratory pulse variation signal (r0) as a part in which a difference between two consecutive extrema of the respiratory pulse variation signal (r0) is largest.
  9. The apparatus (100) as defined by claim 8, wherein the indicator determination unit (102) is configured to represent the respiratory pulse variation signal (r0) as a respiratory pulse variation signal (r0) oscillating around an average value thereof and to modify the respiratory pulse variation signal (r0) by a) replacing the half waves, which comprise the consecutive extrema with the largest difference by half waves of another part the respiratory pulse variation signal and/or b) removing these half waves.
  10. The apparatus (100) as defined by any of the preceding claims, wherein the pulse signal providing unit (101) is configured to represent the measured pulse signal as pulse signal (p0) oscillating around an average value thereof, wherein the indicator determination unit (102) is configured to represent the respiratory pulse variation signal (r0) as a respiratory pulse variation signal (r0) oscillating around an average value thereof and to represent the modified respiratory pulse variation signal as a modified respiratory pulse variation signal oscillating around an average value thereof, and wherein the indicator determination unit (102) is configured such that - first data values (s0) are determined by determining an envelope signal curve for the pulse signal (p0), - in a first fitting, a provided first functional prototype, which depends on a first fit parameter to be modified during the first fitting, is fitted to the first data values (s0) such that a resulting fit envelope signal function (f0) represents an idealized curve progression of the envelope signal curve over the plurality of respiratory cycles without comprising pulse variations caused by ventilation or respiration induced heart-lung interaction, - second data values are determined by determining an absolute respiratory pulse variation curve for the modified respiratory pulse variation signal, - in a second fitting, a provided second functional prototype, which depends on a second fit parameter to be modified during the second fitting, is fitted to the second data values such that a resulting fit respiration function (g1, g2, g3) is indicative of an idealized progression in amplitude of the absolute respiratory pulse variation curve over the plurality of respiratory cycles, and - the indicator is determined based on the fit envelope signal function (f0) and the fit respiration function (g1, g2, g3).
  11. The apparatus (100) as defined by claim 10, wherein the indicator determination unit (102) is configured such that the determined respiratory pulse variation signal (r0) corresponds to a difference between the envelope signal curve (s0) and the fit envelope signal function (f0).
  12. The apparatus (100) as defined by any of claims 10 and 11, wherein the indicator determination unit (102) is configured to determine the indicator based on a first ratio (F1, F2, F3) of a maximum of the fit respiration function (g1, g2, g3) and the maximum of the fit envelope signal function (f0), which is named modified first ratio because of being based on the modified respiratory pulse variation signal, and/or based on a second ratio (S1, S2, S3) of a) the fit respiration function (g1, g2, g3) at the maximum of the fit envelope signal function (f0) and b) the maximum of the fit envelope signal function (f0), which is named modified second ratio because of being based on the modified respiratory pulse variation signal.
  13. The apparatus (100) as defined by any of claims 10 to 12, wherein the indicator determination unit (102) is configured to carry out the steps of determining the second data values and of fitting, in the second fitting, a provided second functional prototype as defined in claim 10 resulting in a fit respiration function (g0) for the unmodified respiratory pulse variation signal (r0) and to determine the indicator further based on a second ratio (S0) of a) the fit respiration function (g0), which has been determined based on the unmodified respiratory pulse variation signal, at the maximum of the fit envelope signal function (f0) and b) the maximum of the fit envelope signal function (f0), which is named unmodified second ratio because of being based on the unmodified respiratory pulse variation signal, and/or based on a first ratio (F0) of a maximum of the fit respiration function (g0), which has been determined based on the unmodified respiratory pulse variation signal, and the maximum of the fit envelope signal function (f0), which is named unmodified first ratio because of being based on the unmodified respiratory pulse variation signal.
  14. A method (200) for determining an indicator that is representative for a physiological parameter, wherein the method comprises: - providing (201) a measured pulse signal of a patient over a time period corresponding to a plurality of subsequent respiratory cycles of the patient by a pulse signal providing unit (101), wherein the pulse signal is a pressure signal that has been measured by using a pressure cuff with a pressure sensor being in contact with the outer skin of the patient, wherein pressure applied to the patient by the pressure cuff is increased or decreased, while the pressure sensor measures the pressure signal on the outer skin of the patient, and wherein the measured pressure is indicative of blood pulsations, - carrying out (202) a determination procedure adapted to determine an indicator that is representative for a physiological parameter based on the provided pulse signal by an indicator determination unit (102), wherein the determination procedure includes a) determining a respiratory pulse variation signal (r0) corresponding to pulse variations caused by ventilation or respiration induced heart-lung interaction based on the provided measured pulse signal, characterised in that the determination procedure further includes b) determining a systolic part of the respiratory pulse variation signal, which corresponds to a time period in which the increasing or decreasing applied pressure passed the systolic arterial pressure of the patient and which therefore is prone to comprising an artifact, c) modifying the respiratory pulse variation signal such that the determined systolic part of the respiratory pulse variation signal is corrected and d) determining the indicator based on the measured pulse signal and the modified respiratory pulse variation signal.
  15. A computer program for determining an indicator that is representative for a physiological parameter, the computer program comprising program code means for causing an apparatus (100) as defined by any of claims 1 to 13 to carry out the steps of the method (200) as defined in claim 14.

Description

FIELD OF THE INVENTION The invention relates to an apparatus, a method and a computer program for determining an indicator that is representative for a physiological parameter. BACKGROUND OF THE INVENTION EP 2 759 257 B1 discloses a method for determining an indicator that is representative for a patient's volume responsiveness. A pulse signal of a patient over a time period corresponding to a plurality of subsequent respiratory cycles of the patient is measured, wherein the measured pulse signal is detected by a non-invasive pulse measurement method using a pressure cuff, wherein the pressure applied in the pressure cuff is continuously increased or decreased in the course of a measurement period. The measured pulse signal is represented as pulse signal oscillating around an average value thereof, wherein an envelope signal curve for the pulse signal is determined. Moreover, a fit envelope signal function is determined based on the previously determined envelope signal curve, wherein the fit envelope signal function is determined based on a predetermined first functional prototype and represents an idealized curve progression of the envelope signal curve over the plurality of respiratory cycles without comprising pulse variations caused by ventilation or respiration induced heart-lung interaction. Then, a respiratory pulse variation signal is determined, which corresponds to the pulse variations caused by ventilation or respiration induced heart-lung interaction over the plurality of respiratory cycles, wherein the determined respiratory pulse variation signal corresponds to a difference between the envelope signal curve and the fit envelope signal function. As a next step, an envelope respiration curve is determined for the previously determined respiratory pulse variation signal and a fit envelope respiration function is determined based on the previously determined envelope respiration curve, wherein the fit envelope respiration function is determined based on a predetermined second functional prototype and represents an idealized curve progression of the envelope respiration curve over the plurality of respiratory cycles. Finally, the indicator that is representative for the patient's volume responsiveness is determined based on the fit envelope signal function and the fit envelope respiration function. SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus, a method and a computer program which allow for an improved determination of an indicator that is representative for a physiological parameter. In a first aspect of the present invention an apparatus for determining an indicator that is representative for a physiological parameter is presented, wherein the apparatus comprises: a pulse signal providing unit configured to provide a measured pulse signal of a patient over a time period corresponding to a plurality of subsequent respiratory cycles of the patient, wherein the pulse signal is a pressure signal that has been measured by using a pressure cuff with a pressure sensor being in contact with the outer skin of the patient, wherein pressure applied to the patient by the pressure cuff is increased or decreased, while the pressure sensor measures the pressure signal on the outer skin of the patient, and wherein the measured pressure is indicative of blood pulsations,an indicator determination unit configured to carry out a determination procedure adapted to determine an indicator that is representative for a physiological parameter based on the provided pulse signal, wherein the determination procedure includes a) determining a respiratory pulse variation signal corresponding to pulse variations caused by ventilation or respiration induced heart-lung interaction based on the provided measured pulse signal, b) determining a systolic part of the respiratory pulse variation signal, which corresponds to a time period in which the increasing or decreasing applied pressure passed the systolic arterial pressure of the patient and which therefore is prone to comprising an artifact, c) modifying the respiratory pulse variation signal such that the determined systolic part of the respiratory pulse variation signal is corrected and d) determining the indicator based on the measured pulse signal and the modified respiratory pulse variation signal. When the pressure applied to the patient by using the pressure cuff, which also might be regarded as being a clamping pressure, is increased or decreased, particularly continuously increased or decreased, it will pass the systolic arterial pressure of the patient at least once depending on the heart-lung interaction. If the heart-lung interaction is large leading to high systolic arterial pressure variation, there can be several passings of the clamping pressure with the systolic arterial pressure. During these passings of clamping pressure with systolic arterial pressure mostly a sudden, significant change in pressure pulses' ampli