System and method for determining fluid reactivity and hemodynamic parameters

Abstract

There is provided a system (100) for determining a fluid reactivity parameter FRP of a patient wherein the determined fluid reactivity parameter is a systolic pressure change (SPV) or a pulse pressure change (PPV), the system comprising units (101, 102, 103) for providing a respiratory rate, a heart rate, and a measured blood pulsation signal indicative of a series of blood pulses of the patient. The system further comprises a unit (104) for determining a first processed signal (envup) based on the blood pulsation signal and a second processed signal (envdown) based on the blood pulsation signal, where the first processed signal is indicative of an upper envelope of the blood pulsation signal and where the second processed signal is indicative of a lower envelope of the blood pulsation signal, and a unit (105) for determining the FRP by: a) identifying, based on the first and second processed signals, a first FRP determination signal (base up, base down) corresponding to the first and second processed signals in a spectral range up to the respiratory rate, and a second FRP determination signal (base up, base down) corresponding to the first and second processed signals in a spectral range up to the respiratory rate; and a second FRP determination signal (rippleup, rippledown) corresponding to the first and second processed signals under any harmonics of respiratory rate and up to heart rate, and b) determining the FRP based on the first and second FRP determination signals.

Description

Technical Field

[0001] The present invention relates to a system and method for determining fluid responsiveness parameters and a system and method for determining hemodynamic parameters. The present invention also relates to computer programs corresponding to said systems and methods. Background Art

[0002] US2011077532 A1 relates to a method and apparatus for dynamic estimation of fluid reactivity.

[0003] US2020260969 A1 relates to technology for predicting fluid responsiveness in critically ill patients.

[0004] US2008033306 A1 relates to a device and a method for determining a physiological parameter of a patient, wherein the parameter can be used to characterize volume responsiveness.

[0005] The fluid responsiveness of a patient refers to the increase in cardiac output after the administration of fluid. Knowing the fluid responsiveness of a patient may be very important for clinicians in a surgical setting in order to assess the amount of fluid in the patient's body and decide whether the patient requires additional fluid intake. In order to quantify the fluid responsiveness of a patient, several fluid responsiveness parameters (FRPs) are known. However, not all of these parameters are clinically accepted in all cases. For example, fluid responsiveness parameters such as pulse pressure variation (PPV) or the less certain systolic blood pressure variation (SPV) are currently clinically accepted only when assessed in a stable cardiac condition and a stable respiratory condition. These fluid responsiveness parameters can usually only be accurately estimated for patients who are ventilated at a fixed ventilation rate and do not have cardiac problems (e.g., ectopic beats or arrhythmias), because the assessment of the blood pressure measurement required for this becomes relatively complex and may become inaccurate due to several assumptions that need to be made in addition.

[0006] In addition to directly assisting the clinician in the surgical setting by providing the patient's fluid responsiveness parameters, such as via a display, the fluid responsiveness parameters may also be used to determine hemodynamic parameters in order to be able to interpret the provided fluid responsiveness parameters and take clinical measures based thereon, wherein these additional parameters may also assist the clinician. However, again, the fluid responsiveness parameters are generally only useful for accurately determining hemodynamic parameters under stable cardiac conditions. Furthermore, many of the hemodynamic parameters that can be determined based on the fluid responsiveness parameters are generally only useful for ventilated patients, i.e., under stable respiratory conditions.

[0007] Regardless of whether the fluid responsiveness parameters are used for direct interpretation by the clinician or for indirect interpretation via hemodynamic parameters determined based on the fluid responsiveness parameters, it is important to know when the fluid responsiveness parameters can be trusted. Assessment of the reliability of the estimated fluid responsiveness parameters can be challenging, particularly when the fluid responsiveness parameters are determined based on relatively short measurements, such as measurements covering only a few respiratory cycles. However, in some cases, short measurement durations may be necessary. For example, it may be necessary to estimate the fluid responsiveness of a patient during short duration maneuvers such as passive leg raising or during a field examination performed by a clinician using, for example, a measuring cuff.

[0008] For these reasons, there is a need for efficient determination of fluid responsiveness parameters, their reliability, and hemodynamic parameters that correlate with fluid responsiveness parameters. Summary of the invention

[0009] The object of the present invention is to allow efficient determination of a fluid responsiveness parameter. The present invention also relates to efficient determination of the reliability of the determined fluid responsiveness parameter and of a hemodynamic parameter related to the determined fluid responsiveness parameter, thereby meeting the above further needs.

[0010] The invention is defined in the independent claim. The dependent claims define advantageous embodiments.

[0011] In a first aspect, a system for determining a fluid responsiveness parameter of a patient is provided, wherein the system comprises i) a breathing rate providing unit configured to provide a breathing rate, ii) a heart rate providing unit configured to provide a heart rate, and iii) a blood pulsation signal providing unit configured to provide a blood pulsation signal, wherein the blood pulsation signal is a measurement signal indicating a series of blood pulses of the patient. The system further comprises iv) a processed signal determining unit configured to determine a processed signal based on the blood pulsation signal, wherein the processed signal indicates an envelope of the blood pulsation signal, and v) a fluid responsiveness parameter determining unit configured to determine the fluid responsiveness parameter by: a) identifying a first fluid responsiveness parameter determination signal based on the processed signal, wherein the first fluid responsiveness parameter determination signal corresponds to the processed signal in a frequency spectrum range up to the breathing rate, and identifying a second fluid responsiveness parameter determination signal based on the processed signal, wherein the second fluid responsiveness parameter determination signal corresponds to the processed signal at the breathing rate and any harmonics thereof up to the heart rate, and b) determining the fluid responsiveness parameter based on the first fluid responsiveness parameter determination signal and the second fluid responsiveness parameter determination signal.

[0012] It has been found that the second fluid responsiveness parameter determination signal can carry sufficient information about the effect of the patient's breathing on a series of blood pulses indicated by the measured blood pulsation signal, while the first fluid responsiveness parameter determination signal can carry sufficient additional information for determining the fluid responsiveness parameter. Therefore, the fluid responsiveness parameter can be efficiently determined. This is particularly advantageous in situations where the fluid responsiveness parameter needs to be determined quickly, i.e., it is not necessary to obtain a long series of blood pulses, such as for rapid spot checks during surgery. It has also been found that the determination of the fluid responsiveness parameter is robust, i.e., it shows good accuracy on a variety of different blood pulsation signals provided (in particular, signals for different patients and acquired using different measuring devices).

[0013] The first fluid responsiveness parameter determination signal preferably corresponds to the processed signal over the entire frequency spectrum range (i.e., all frequencies) up to the respiratory rate, and the second fluid responsiveness parameter determination signal preferably corresponds to the processed signal at the respiratory rate and all its harmonics up to the heart rate. The first fluid responsiveness parameter determination signal may in particular comprise a continuous frequency spectrum up to the respiratory rate, whereas the second fluid responsiveness parameter determination signal may comprise a discrete frequency spectrum consisting of the respiratory rate and its harmonics up to the heart rate.

[0014] The correspondence between signals within a spectral range or at a specific frequency (such as breathing rate) and its harmonics is preferably understood herein as referring to the correspondence, in particular the equality, of the corresponding spectral components of the signals, wherein the spectral components can be determined by spectral analysis. For example, a first signal corresponding to a second signal within a spectral range between frequency f1 and frequency f2 and additionally at frequency f3 should preferably be understood as making the spectrum of the first signal correspond to the spectrum of the second signal between f1 and f2 and additionally at f3. The frequency will preferably be understood herein as being equal to the rate. The harmonics of a frequency will preferably be understood herein as referring to integer multiples of the frequency.

[0015] The respiratory rate providing unit, the heart rate providing unit and the blood pulsation signal providing unit may each be a corresponding receiving unit configured to receive the corresponding quantity from, for example, a measuring device and to provide the received quantity. However, these providing units may also be storage devices in which previously measured corresponding quantities have been stored and from which the corresponding quantity may be retrieved to provide the corresponding quantity. The providing unit may also be or include a measuring device that measures the corresponding quantity.

[0016] The respiratory rate and heart rate may be provided specifically for the patient for whom the fluid responsiveness parameter is to be determined. For example, the respiratory rate may correspond to a constant ventilation rate at which the patient is ventilated, and the heart rate may correspond to a heart or pulse rate measured at a given time. Even though the patient's heart rate may vary over time, the variation may be slow enough to be negligible when the fluid responsiveness parameter is determined quickly, i.e., when using a blood pulsation signal that extends only over a relatively short time (e.g., less than ten, particularly less than five, or even only one or two respiratory cycles).

[0017] The blood pulsation signal can, for example, be a tissue pressure signal measured using a pressure sensor in contact with the patient's skin when a cuff around a limb is inflated to apply increased pressure to the limb. For example, such a system and a corresponding measurement method are described in EP3430992 A1 and WO2020 / 148137A1, the entire contents of which are incorporated herein by reference. However, the blood pulsation signal can also be derived from different measurements. For example, the blood pulsation signal can be measured in the pressure of an inflatable cuff that surrounds a limb and is inflated to apply increased pressure to the limb, can also be measured in a (photo) plethysmography measurement (PPG), or can be measured by displacement measurement using an inertial measurement unit (IMU).

[0018] In the case of tissue pressure (TP) measurement, the oscillatory component of the measured blood pulsation signal may be referred to as "TPac". The oscillatory component of the blood pulsation signal may also be referred to as the AC component and may be determined as the difference between the measured blood pulsation signal and its DC component, wherein the DC component of the measured blood pulsation signal may refer to, for example, an average value.

[0019] The processed signal determination unit may be configured to determine the processed signal based on the blood pulsation signal by first determining an oscillatory component of the blood pulsation signal and then determining the processed signal based on the oscillatory component. For example, the processed signal may correspond to an envelope signal (or simply envelope) of the oscillatory component. The processed signal, in particular the envelope, may be determined by applying a filter, in particular a nonlinear filter, to the oscillatory component. An exemplary filter that may be used for this purpose is given by the following equation:

[0020]

[0021] where x[i] refers to the input signal, i.e. the oscillatory component of the blood pulsation signal, which may be in particular the signal TPac in the case of tissue pressure measurement, where i is a discrete sample index, and y[i] refers to the calculated (i.e. filtered) output signal, and where

[0022]

[0023] and

[0024]

[0025] is the time constant T of the smoothing function that characterizes the filter up and T down Calculate the filter parameters, where the constant F s Corresponds to the sampling rate of the input signal. In order to determine the processed signal, the filter parameters can be selected as T up =T pulse / 2 and T down =T pulse 2, where T pulse 2 = 60 / PR, where PR corresponds to the measured pulse rate provided as heart rate by the heart rate providing unit, and where T up , T down , T pulse The SLE is measured in seconds and the PR is measured in beats or pulses per minute.

[0026] While the processed signal determination unit may be configured to obtain a processed signal by applying a filter to the oscillatory component of the blood pulsation signal, the fluid responsiveness parameter determination unit may be configured to determine a filtered fluid responsiveness parameter determination signal based on a second fluid responsiveness parameter determination signal and further application of the filter, and to determine the fluid responsiveness parameter based on the first fluid responsiveness parameter determination signal and the filtered fluid responsiveness parameter determination signal.

[0027] Thus, a filter may be used to obtain a processed signal, wherein when a filtered fluid responsiveness parameter determination signal is determined using a second fluid responsiveness parameter determination signal, the same or another filter may be applied, but the first fluid responsiveness parameter determination signal need not necessarily be further processed. In other words, starting from the blood pulsation signal, the filter may only need to be applied once to obtain the first fluid responsiveness parameter determination signal, while the same filter may be applied twice, or two different filters may be applied to obtain the filtered fluid responsiveness parameter determination signal.

[0028] For example, it may not be necessary to apply a filter having an averaging or smoothing effect to the first fluid responsiveness parameter determination signal, since the first fluid responsiveness parameter determination signal corresponds to a processed signal in the spectral range up to the breathing rate and therefore may only comprise relatively low frequencies and may not require any more averaging or smoothing in order to be used as a basis for the fluid responsiveness parameter determination. This is particularly the case if the filter that has been applied to obtain the processed signal based on which the first fluid responsiveness parameter determination signal is determined also has an averaging or smoothing effect.

[0029] Preferably, a filter is applied to determine a filtered fluid reactivity parameter determination signal based on the second fluid reactivity parameter determination signal, the filter again being described by equations (1) to (3) above, wherein the input x[i] now corresponds to the second fluid reactivity parameter determination signal or a signal comprising the second fluid reactivity parameter determination signal, and wherein the filter parameters are now selected to be T up =Tr esp / 4 and T dowm =T resp 4, where T resp =60 / VR and VR refers to the ventilation rate measured in breaths per minute.

[0030] In general, applying an appropriate filter to a signal such as a blood pulsation signal, its oscillatory component, or any signal derived therefrom (such as a second fluid reactivity parameter determination signal) can be an effective way to emphasize the corresponding signal attribute of interest. For example, in a signal including several pulses or oscillations as discussed herein, it may be interesting to see how the pulses or oscillations relate to or develop with each other. Therefore, a filter may be preferred that produces a corresponding filtered signal indicating how the pulses or oscillations in the input signal relate to or develop with each other. For example, a filter that produces an envelope of the corresponding input signal or a signal indicating the envelope may be preferred. The filter can be selected based on the respiratory rate and / or heart rate provided. Moreover, the filter can be designed so that it utilizes a reference point detection of the maximum value and applies interpolation between the detected values.

[0031] The fluid responsiveness parameter determination unit can be configured to determine the fluid responsiveness parameter based on the characteristic value of the first fluid responsiveness parameter determination signal and the filtered fluid responsiveness parameter determination signal. This can further improve the efficiency of the fluid responsiveness parameter determination because the entire signal does not need to be analyzed. The characteristic value can particularly refer to a global or local maximum value. For example, a characteristic position can be identified in one of the first fluid responsiveness parameter determination signal and the filtered fluid responsiveness parameter determination signal, wherein the value of the corresponding one of the signals at the position and the value of the other of the first fluid responsiveness parameter determination signal and the filtered fluid responsiveness parameter determination signal at the same position can then be identified, and the two identified values ​​can be used to determine the fluid responsiveness parameter. The position in the signal can correspond to a time point during the measurement of the corresponding signal. For example, if the blood pulsation signal is a tissue pressure signal measured using a pressure sensor that contacts the patient's skin when the cuff around the limb is inflated to apply increased pressure to the limb, the time point during the measurement can also correspond to the corresponding pressure applied by the cuff.

[0032] The processed signal determination unit may be configured to determine a first processed signal obtained by applying a filter to an oscillatory component of the blood pulsation signal and a second processed signal obtained by inverting the oscillatory component and applying the filter to the inverted oscillatory component, wherein the fluid responsiveness parameter determination unit may be configured to determine the fluid responsiveness parameter by: a') identifying a first fluid responsiveness parameter determination signal for each of the first processed signal and the second processed signal and combining the first fluid responsiveness parameter determination signals into a combined first fluid responsiveness parameter determination signal, identifying a second fluid responsiveness parameter determination signal for the first processed signal, determining the filtered fluid responsiveness parameter determination signal by applying a filter to the second fluid responsiveness parameter determination signal identified for the first processed signal, and b') determining the fluid responsiveness parameter based on the combined first fluid responsiveness parameter determination signal and the filtered fluid responsiveness parameter determination signal. In this case, the determined fluid responsiveness parameter may in particular be a systolic pressure variation (SPV).

[0033] In order to determine the systolic blood pressure change, the system may further include a blood pressure characteristic providing unit for providing a blood pressure characteristic, wherein the fluid responsiveness parameter determining unit is configured to determine the fluid responsiveness parameter further based on the blood pressure characteristic. The blood pressure characteristic may correspond to or be derived from a systolic arterial pressure (SAP) and / or a diastolic arterial pressure (DAP). However, the systolic blood pressure change may also be determined without reference to any blood pressure characteristic such as SAP or DAP.

[0034] In addition, the blood pressure characteristic providing unit may be a receiving unit configured to receive blood pressure characteristics from, for example, a measuring device and provide the received blood pressure characteristics, or a storage device in which previously measured blood pressure characteristics have been stored and can be retrieved therefrom to provide the blood pressure characteristics, or the blood pressure characteristic providing unit may be or include a measuring device for measuring the blood pressure characteristics.

[0035] Preferably, the systolic blood pressure change is determined according to the following equation:

[0036]

[0037] Wherein, baseline_sum corresponds to the sum of the two first fluid reactivity parameter determination signals, env_ripple_up corresponds to the filtered fluid reactivity parameter determination signal determined for the second fluid reactivity parameter determination signal, the index k corresponds to the maximum peak value in the signal baseline_sum, and N indicates the sampled signal length, for example expressed in the number of signal sampling points. As mentioned above, equation (4) can also be used alternatively without the factor (SAP-DAP) / SAP.

[0038] The processed signal determination unit may also be configured to determine a first processed signal obtained by applying a filter to an oscillatory component of the blood pulsation signal and a second processed signal obtained by inverting the oscillatory component and applying the filter to the inverted oscillatory component, wherein the fluid responsiveness parameter determination unit may be configured to determine the fluid responsiveness parameter by: a”) identifying a first fluid responsiveness parameter determination signal for each of the processed signals and combining them into a combined first fluid responsiveness parameter determination signal, identifying a second fluid responsiveness parameter determination signal for each of the processed signals and combining them into a combined second fluid responsiveness parameter determination signal, and determining a filtered combined second fluid responsiveness parameter determination signal by further applying a filter to the combined second fluid responsiveness parameter determination signal, and b”) determining the fluid responsiveness parameter based on the combined first fluid responsiveness parameter determination signal and the filtered combined second fluid responsiveness parameter determination signal. In this case, the fluid responsiveness parameter may in particular be a pulse pressure variation (PPV).

[0039] Combining two second fluid reactivity parameter determination signals, i.e. the second fluid reactivity parameter determination signal determined for the first processing signal and the second fluid reactivity parameter determination signal determined for the second processing signal, may specifically refer to the sum of these two signals. Therefore, the combined second fluid reactivity parameter determination signal may specifically refer to the sum of the second fluid reactivity parameter determination signal determined for the first processing signal and the second fluid reactivity parameter determination signal determined for the second processing signal. In case of using a nonlinear filter (which may be preferred), it may be advantageous to first determine the combined second fluid reactivity parameter determination signal and then, i.e., thereafter, apply the filter to obtain a filtered combined second fluid reactivity parameter determination signal, i.e., as opposed to first applying the filter and then combining the filtered signals.

[0040] Preferably, only the combined first fluid responsiveness parameter determination signal and the filtered combined second fluid responsiveness parameter determination signal are used to determine the PPV. Thus, no additional signals or data need to be considered, which can make the fluid responsiveness parameters more efficient. For example, the pulse pressure variation can be determined according to the following equation:

[0041]

[0042] Therein, baseline_sum corresponds to the sum of the two first fluid reactivity parameter determination signals, env_ripple_sum corresponds to the filtered sum of the two second fluid reactivity parameter determination signals, the index k corresponds to the maximum peak in the signal baseline_sum and N indicates the sampled signal length, for example expressed in the number of signal sampling points.

[0043] Determining the processed signal based on the blood pulsation signal by the processed signal determination unit may involve regularizing detected blood pulses in the blood pulsation signal due to ectopic beats. This may also make the assumption of a constant heart rate more applicable even in the case of heart problems or signal artifacts caused by other reasons. Regularization may refer, for example, to inserting artificial pulses at positions in a series of blood pulses where a pulse is expected but is not present or has an amplitude only below a predetermined threshold.

[0044] In an example, a system for determining the reliability of a fluid responsiveness parameter determined by a system as described above is proposed, wherein the system for determining the reliability of the determined fluid responsiveness parameter comprises: i) a breathing rate providing unit configured to provide a breathing rate based on which the fluid responsiveness parameter has been determined; ii) a heart rate providing unit configured to provide a heart rate based on which the fluid responsiveness parameter has been determined; iii) a processed signal providing unit configured to provide a processed signal based on which the fluid responsiveness parameter has been determined; and iv) a second fluid responsiveness parameter determination signal providing unit configured to provide a second fluid responsiveness parameter determination signal of the processed signal. In addition, the system for determining the reliability of the fluid responsiveness parameter comprises v) a reliability determination unit configured to determine the reliability of the determined fluid responsiveness parameter by: a) identifying a reliability determination signal based on the processed signal, wherein the reliability determination signal corresponds to the processed signal within a frequency spectrum between the breathing rate and the heart rate, and b) determining the reliability of the determined fluid responsiveness parameter based on the second fluid responsiveness parameter determination signal and the reliability determination signal.

[0045] It has been found that the reliability determination signal carries important information about the reliability of the determined fluid responsiveness parameter. Thus, together with the second fluid responsiveness parameter determination signal, it allows to efficiently determine the reliability of the determined fluid responsiveness parameter determination signal. In applications where the fluid responsiveness parameter is determined based on a relatively short series of blood pulses only, knowing the reliability of the determined fluid responsiveness parameter is particularly advantageous, since the determination is then particularly sensitive to irregularities in the series of blood pulses. Such irregularities may be caused by ectopic beats or correspond to other signal artifacts. For example, the reliability of the determined fluid responsiveness parameter may be measured according to a quality index, which takes values ​​between 0 and 100%. Different quality indices may be employed for different fluid responsiveness parameters.

[0046] Preferably, the quality index

[0047]

[0048] For SPV, and the quality index

[0049]

[0050] For PPV, wherein ripple_up corresponds to a second fluid responsiveness parameter determination signal determined for a first processed signal of an upper envelope indicating a blood pulsation signal, ripple_up2 corresponds to a reliability determination signal determined for the processed signal, ripple_sum corresponds to the sum of the second fluid responsiveness parameter determination signal determined for the processed signal and the second fluid responsiveness parameter determination signal determined for a processed signal of a lower envelope indicating a blood pulsation signal, ripple_sum2 corresponds to the sum of the reliability determination signal determined for the processed signal of the upper envelope indicating a blood pulsation signal and the reliability determination signal determined for the processed signal of the lower envelope indicating a blood pulsation signal, and K and N are defined for determining SPV and PPV, respectively.

[0051] Furthermore, a system for determining a hemodynamic parameter related to a fluid responsiveness parameter is proposed, wherein the system comprises i) the above-mentioned system for determining a fluid responsiveness parameter of a patient, ii) the above-mentioned system for determining the reliability of a fluid responsiveness parameter, iii) a first model providing unit configured to provide a first model of hemodynamic parameters, the first model depending on the fluid responsiveness parameter determined by the above-mentioned system for determining a fluid responsiveness parameter of a patient, iv) a second model providing unit configured to provide a second model of hemodynamic parameters, the second model not depending on the fluid responsiveness parameter. Furthermore, the system for determining a hemodynamic parameter related to a fluid responsiveness parameter comprises v) a combined model determining unit configured to determine a combined model based on the first model, the second model and the reliability of the fluid responsiveness parameter determined by the above-mentioned system for determining the reliability of a fluid responsiveness parameter, and v) a hemodynamic parameter determining unit configured to determine the hemodynamic parameter by applying the combined model.

[0052] Since the fluid responsiveness parameter can be effectively determined using the above-described system for determining the fluid responsiveness parameter, the hemodynamic parameters related to the fluid responsiveness parameter can also be effectively determined.

[0053] Preferably the hemodynamic parameter in relation to the fluid responsiveness parameter is understood such that a model can be found expressing the former in terms of the latter, wherein the model may refer to, for example, a function. The hemodynamic parameter may in particular be a stroke volume (SV). The combined model may in particular involve a weighting of the first model and the second model, wherein the weight depends on the reliability of the fluid responsiveness parameter, such that as the reliability of the fluid responsiveness parameter increases, the weight of the first model increases relative to the weight of the second model. Preferably, the sum of the weight of the first model and the weight of the second model is 1.

[0054] Another aspect relates to a computer-implemented method for determining a fluid responsiveness parameter of a patient, wherein the method comprises: i) providing a respiratory rate; ii) providing a heart rate; iii) providing a blood pulsation signal, wherein the blood pulsation signal is a measurement signal indicative of a series of blood pulses of the patient; iv) determining a processing signal based on the blood pulsation signal, wherein the processing signal indicates an envelope of the blood pulsation signal; and v) determining the fluid responsiveness parameter by the following steps: a) identifying a first fluid responsiveness parameter determination signal based on the processing signal, wherein the first fluid responsiveness parameter determination signal corresponds to the processing signal within a frequency spectrum up to the respiratory rate; and identifying a second fluid responsiveness parameter determination signal based on the processing signal at the respiratory rate and any harmonics thereof up to the heart rate; and b) determining the fluid responsiveness parameter based on the first fluid responsiveness parameter determination signal and the second fluid responsiveness parameter determination signal.

[0055] In addition, on the one hand, it relates to a method for determining the reliability of a fluid responsiveness parameter determined by the above-mentioned method for determining the fluid responsiveness parameter of a patient, wherein the method for determining the reliability of the determined fluid responsiveness parameter comprises: i) providing a breathing rate, based on which the fluid responsiveness parameter has been determined, ii) providing a heart rate, based on which the fluid responsiveness parameter has been determined, iii) providing a processing signal, based on which the fluid responsiveness parameter has been determined, iv) providing a second fluid responsiveness parameter determination signal of the processing signal, and v) determining the reliability of the determined fluid responsiveness parameter by: a) identifying a reliability determination signal based on the processing signal, wherein the reliability determination signal corresponds to the processing signal within a frequency spectrum between the breathing rate and the heart rate, and b) determining the reliability of the determined fluid responsiveness parameter based on the second fluid responsiveness parameter determination signal and the reliability determination signal.

[0056] On the other hand, a computer-implemented method for determining a hemodynamic parameter related to a fluid responsiveness parameter is provided, wherein the method comprises: i) determining the fluid responsiveness parameter of a patient by means of the above-mentioned method for determining the fluid responsiveness parameter of a patient, ii) determining the reliability of the determined fluid responsiveness parameter by means of the above-mentioned method for determining the reliability of the fluid responsiveness parameter, iii) providing a first model of the hemodynamic parameter that is dependent on the determined fluid responsiveness parameter, iv) providing a second model of the hemodynamic parameter that is independent of the fluid responsiveness parameter, v) determining a combined model based on the first model, the second model and the determined reliability of the determined fluid responsiveness parameter, and vi) determining the hemodynamic parameter by applying the combined model.

[0057] According to a further aspect, a computer program corresponding to the above-described system and method is provided.

[0058] Therefore, a computer program for determining a fluid responsiveness parameter of a patient is provided, wherein the program comprises instructions for causing a processor to perform the steps of the above-described method for determining a fluid responsiveness parameter of a patient when the program is run by the processor.

[0059] In addition, a computer program for determining the reliability of fluid responsiveness parameters determined by the above-mentioned method for determining fluid responsiveness parameters of a patient is provided, wherein the program includes instructions for causing a processor to execute the steps of the above-mentioned method for determining the reliability of fluid responsiveness parameters when the program is run by the processor.

[0060] Furthermore, a computer program for determining a hemodynamic parameter associated with a fluid responsiveness parameter is provided, wherein the program comprises instructions for causing a processor to perform the steps of the above-mentioned method for determining a hemodynamic parameter associated with a fluid responsiveness parameter when the program is run by the processor.

[0061] It shall be understood that the systems of claims 1 and 8, the methods of claims 9 and 10 and the computer programs of claims 11 and 12 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0062] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above embodiments with the respective independent claim.

[0063] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In the following drawings:

[0065] Figure 1A system for determining a fluid responsiveness parameter of a patient is schematically and exemplarily shown.

[0066] Figure 2 schematically and exemplarily shows a blood pulsation signal and DC and AC components of the blood pulsation signal,

[0067] Figure 3 schematically and exemplarily showing an oscillatory component of a blood pulsation signal and first and second processed signals determined based on the oscillatory component,

[0068] Figure 4A schematically and exemplarily showing a first fluid reactivity parameter determination signal, a second fluid reactivity parameter determination signal and a reliability determination signal determined based on a first processing signal,

[0069] Figure 4B schematically and exemplarily shows a first fluid reactivity parameter determination signal, a second fluid reactivity parameter determination signal and a reliability determination signal determined based on the second processing signal,

[0070] Figure 5 The method for determining the Figure 1 The reliability of the system for determining the fluid reactivity parameters is shown in the system.

[0071] Figure 6 Schematically and exemplarily shown from Figure 4A and 4B The first fluid reactivity parameter determination signal, the second fluid reactivity determination signal and the reliability determination signal are derived from the plurality of signals shown,

[0072] Fig. 7A The conventional definition of systolic blood pressure variation is shown schematically and exemplarily,

[0073] Figure 7B The conventional definition of pulse pressure variation is schematically and exemplarily shown,

[0074] Fig. 8A schematically and exemplarily shows a blood pulsation signal, which includes a pressure pulse due to an ectopic beat and an average value and an oscillation component of the blood pulsation signal,

[0075] Figure 8B Schematically and exemplarily shown Fig. 8A The oscillatory component of the blood pulsation signal shown, and the first and second processed signals determined based on the oscillatory component of the blood pulsation signal,

[0076] Figure 8C The schematic and exemplary method based on Figure 8BThe first processing signal shown determines a first fluid reactivity parameter determination signal, a second fluid reactivity parameter determination signal and a reliability determination signal,

[0077] Fig.8D The schematic and exemplary method based on Figure 8B The first fluid reactivity parameter determination signal, the second fluid reactivity parameter determination signal and the reliability determination signal determined by the second processing signal shown,

[0078] Fig. 8E Schematically and exemplarily shown from Figure 8C and 8D The first fluid reactivity parameter determination signal, the second fluid reactivity determination signal and the reliability determination signal are derived from the plurality of signals shown,

[0079] Fig. 9 A system for determining hemodynamic parameters is schematically and exemplarily shown,

[0080] Fig.10 A method for determining a fluid reactivity parameter is schematically and exemplarily shown,

[0081] Fig.11 Schematically and exemplarily, a method for determining the Fig.10 The method shown is a method of determining the reliability of the fluid reactivity parameters,

[0082] Fig.12 A method for determining a hemodynamic parameter is schematically and exemplarily shown,

[0083] Fig.13 Schematically and exemplarily illustrating the determination Figure 4A , 4B , 8C and 8D show specific details of the signals.

[0084] Fig.14A Schematically and exemplarily, by using Fig.13 The specific details of some of the signals identified to determine systolic blood pressure changes and their reliability are shown.

[0085] Fig. 14B Schematically and exemplarily, by using Fig.13 All signals identified are shown to determine pulse pressure variations and their reliability in detail, and

[0086] Fig.15 Specific details of determining the stroke volume SV are shown schematically and exemplarily. DETAILED DESCRIPTION

[0087] Figure 1A system 100 for determining a fluid responsiveness parameter (FRP) of a patient is schematically and exemplarily shown. The system 100 comprises a breathing rate providing unit 101 configured to provide a breathing rate and a heart rate providing unit 102 configured to provide a heart rate. The breathing rate providing unit 101 and the heart rate providing unit 102 may be part of or correspond to a single providing unit providing both the breathing rate and the heart rate. The provided breathing rate and / or heart rate may have values ​​that are assumed to be known a priori. For example, if a patient is in intensive care, he or she may receive external ventilation and the patient's pulse may be measured continuously. The provided breathing rate may then correspond to the ventilation rate, which will typically remain constant over an extended period of time, and the provided heart rate may correspond to the pulse rate measured at a given time. The heart or pulse rate may also be assumed to be constant, particularly for relatively short measurement times for acquiring any signal required to determine the fluid responsiveness parameter. The breathing rate and the heart rate may be provided by the providing unit based on previously received input, wherein the input may be provided automatically, for example based on control parameters of the ventilation system and pulse measurements, or may be provided manually, for example via a user interface of the system 100 .

[0088] The system 100 further includes a blood pulsation signal providing unit 103, which is configured to provide a blood pulsation signal, wherein the blood pulsation signal is a measurement signal indicating a series of blood pulses of the patient. For example, the blood pulsation signal can be provided based on the measurement results using a dedicated cuff system as described in EP3430992A1, and corresponds to, for example, a tissue pressure signal TP obtained as described in WO2020 / 148137A1. Figure 2 An example of a measured tissue pressure signal TP involved in the embodiments described later is shown. In other embodiments, other types of blood pulsation signals may be used. Figure 2 As shown, the tissue pressure signal TP includes a plurality of peaks, each peak indicating one of a series of blood pulses in the patient. Figure 2 The fact that the signal TP shown in φ generally increases over time is due to the measuring method according to which the pressure applied externally by the cuff system to the patient's skin increases continuously over the measuring time.

[0089] The system 100 also includes a processing signal determination unit 104, which is configured to determine two processing signals, referred to herein as env_up and env_down, based on the blood pulsation signal TP, wherein these processing signals indicate the respective envelopes of the blood pulsation signal TP. More specifically, the signal env_up is determined to indicate the upper envelope of the blood pulsation signal TP, and the signal env_down is determined to indicate the lower envelope of the blood pulsation signal TP. For example, based on the measured blood pulsation signal corresponding to the tissue pressure TP, its oscillation component TPac can be determined, for example by applying a high-pass filter to the blood pulsation signal TP. In this way, the blood pulsation signal TP can be decomposed into a DC component and an AC component, wherein the DC component corresponds to the clamping pressure TPcl applied externally to the patient's skin during the measurement and can be regarded as indicating the average value of the blood pulsation signal TP, and the AC component corresponds to the signal TPac. This decomposition is Figure 2 It is shown as an example in FIG.

[0090] exist Figure 3 In FIG. 1 , the signal component TPac is shown without the original signal TP and its DC component TPcl. Instead, Figure 3 In addition, the processing signal env_up and the inverted version of the processing signal env_down (which is positive itself) are shown in FIG. Figure 3 It is understood that the signal env_up, in particular its DC component, is similar to the upper envelope of the oscillating component TPac of the blood pulsation signal TP, while the signal env_down, in particular its DC component, is similar to the lower envelope of TPac before inversion. Therefore, the signals env_up and env_down can also be called "envelope" signals.

[0091] The system 100 further comprises a fluid responsiveness parameter determination unit 105, which is configured to determine the fluid responsiveness parameter FRP by: a) identifying two first fluid responsiveness parameter determination signals based on the processed signals env_up and env_down, the two first fluid responsiveness parameter determination signals corresponding to the "baseline" signals baseline_up and baseline_down in the illustrated embodiment, wherein the first fluid responsiveness parameter determination signals baseline_up and baseline_down correspond to the processed signals env_up and env_down in a frequency spectrum range up to the breathing rate (i.e., the breathing rate previously provided). Specifically, the signal baseline_up corresponds to the signal env_up in a frequency spectrum range up to the breathing rate, and the signal baseline_down corresponds to the signal env_down in a frequency spectrum range up to the breathing rate. Furthermore, the fluid responsiveness parameter determination unit 105 is configured to identify two second fluid responsiveness parameter determination signals based on the processed signals env_up and env_down, which correspond to the "ripple" signals ripple_up and ripple_down in the illustrated embodiment, wherein the second fluid responsiveness parameter determination signals ripple_up and ripple_down correspond to the processed signals env_up and env_down at the breathing rate and any harmonics thereof up to the heart rate (i.e., up to the previously provided heart rate). Specifically, the signal ripple_up corresponds to the signal env_up at the breathing rate and any harmonics thereof up to the heart rate, while the signal ripple_down corresponds to the processed signal env_down at the breathing rate and any harmonics thereof up to the heart rate. Thus, for example, the first fluid responsiveness parameter determination signals baseline_up and baseline_down may include a continuous spectrum of the corresponding envelope signals up to the breathing rate, while the second fluid responsiveness parameter determination signals ripple_up and ripple_down may include a discrete spectrum consisting of signal values ​​corresponding to the corresponding envelope signals at the breathing rate and harmonics thereof up to the heart rate.

[0092] The fluid reactivity parameter determination unit 105 is configured to determine the fluid reactivity parameter FRP based on the identified first fluid reactivity parameter determination signals baseline_up and baseline_down and the identified second fluid reactivity parameter determination signals ripple_up and ripple_down. However, as will be further exemplarily described below, for some fluid reactivity parameters, all of these fluid reactivity parameter determination signals may not be required.

[0093] Figure 4A and Figure 4B Schematically and exemplarily illustrated are first and second fluid reactivity parameter determination signals identified based on processing signals env_up and env_down, wherein: Figure 4A shows signals baseline_up and ripple_up identified based on signal env_up, and Figure 4B The signals baseline_down and ripple_down identified based on the signal env_down are shown. Figure 4A and Figure 4B Further signals ripple_up2 and ripple_down2 are shown respectively.

[0094] Signals ripple_up2 and ripple_down2 are examples of reliability determination signals identified based on the same processed signals env_up and env_down, based on which first and second fluid reactivity parameter determination signals are identified in order to determine the reliability of the fluid reactivity parameters determined by system 100 . For example, the system 100 may include a reliability determination unit, which is configured to determine the reliability Q of the fluid responsiveness parameter FRP determined by the fluid responsiveness parameter determination unit 105 in the following manner: a) identifying reliability determination signals ripple_up2 and ripple_down2 based on the processed signals env_up and env_down, in particular by identifying signal ripple_up2 based on signal env_up and identifying signal ripple_down2 based on signal env_down, wherein the reliability determination signals ripple_up2 and ripple_down2 correspond to the corresponding processed signals env_up, env_down in the frequency spectrum range between the breathing rate and the heart rate; and b) determining the reliability Q of the determined fluid responsiveness parameter FRP based on the second fluid responsiveness parameter determination signals ripple_up and ripple_down and the reliability determination signals ripple_up2 and ripple_down2. While the second fluid responsiveness parameter determination signals ripple_up and ripple_down may be considered as indicating a respiratory modulation, i.e. a typical ripple-like modulation of the pulse height in the measurement signal TP, the reliability determination signal may be considered as another ripple-like signal derived from the measurement signal TP and may therefore be considered as a further "ripple" signal. For example, the reliability determination signals ripple_up2 and ripple_down2 may comprise a continuous frequency spectrum of a corresponding envelope signal between the respiratory rate and the heart rate.

[0095] If the system 100 comprises a reliability determination unit, it may also, i.e. additionally, be regarded as a system for determining the reliability of a fluid reactivity parameter FRP. Preferably, the reliability determination unit corresponds to the fluid reactivity parameter determination unit 105, wherein, in particular, the system 100 may comprise a combined unit configured to perform the functions described above with respect to the fluid reactivity parameter determination unit 105 and the functions described above with respect to the reliability determination unit. On the other hand, for a system for determining the reliability of a given fluid reactivity parameter, the system itself does not necessarily determine the fluid reactivity parameter. Therefore, a system separate from the system 100 may also be provided for determining the reliability of the fluid reactivity parameter, as determined by the system 100. Such a system is Figure 5 It is shown schematically and exemplarily in FIG.

[0096] Figure 5 A system 500 for determining the reliability of a fluid responsiveness parameter FRP determined by the system 100 is shown. The system 500 includes a breathing rate providing unit 501, which is configured to provide a breathing rate based on which the fluid responsiveness parameter FRP has been determined. For example, the breathing rate providing unit 501 can correspond to the breathing rate providing unit 101, or directly or indirectly receive the breathing rate therefrom after storage. The system 500 also includes a heart rate providing unit 502, which is configured to provide a heart rate based on which the fluid responsiveness parameter FRP has been determined. For example, the heart rate providing unit 502 can correspond to the heart rate providing unit 102, or directly or indirectly receive the heart rate therefrom after storage.

[0097] The system 500 further comprises a processed signal providing unit 503, which is configured to provide processed signals env_up and env_down, based on which the fluid reactivity parameter FRP has been determined. The processed signal providing unit 503 may, for example, receive the processed signals env_up and env_down from the processed signal determining unit 104 after the processed signals env_up and env_down have been determined. Similarly, the system 500 comprises a second fluid reactivity parameter determination signal providing unit 504, which is configured to provide second fluid reactivity parameter determination signals ripple_up and ripple_down of the processed signals env_up and env_down (i.e., corresponding to the processed signals env_up and env_down), wherein the second fluid reactivity parameter determination signal providing unit 504 may, for example, receive the signals ripple_up and ripple_down directly or indirectly from the fluid reactivity parameter determining unit 105 after storage.

[0098] Furthermore, the system 500 comprises a reliability determination unit 505, which is configured to determine the reliability Q of the determined fluid responsiveness parameter FRP by: a) identifying the reliability determination signals ripple_up2 and ripple_down2 based on the processed signals env_up and env_down, in particular identifying the signal ripple_up2 based on the signal env_up and identifying the signal ripple_down2 based on the signal env_down, wherein the reliability determination signals ripple_up2 and ripple_down2 correspond to the processed signals env_up, env_down in the frequency spectrum between the breathing rate and the heart rate; and b) determining the reliability Q of the determined fluid responsiveness parameter FRP based on the second fluid responsiveness parameter determination signals ripple_up and ripple_down and the reliability determination signals ripple_up2 and ripple_down2. As will be further apparent below, all reliability determination signals may not be required in order to determine the reliability of some fluid responsiveness parameters.

[0099] from Figure 4A As can be seen in Figure 1, the signal ripple_up has less structure than ripple_up2. This is because ripple_up2 has more spectral content, in fact in this case ripple_up2 has all the spectral content between the breathing rate and the heart rate, while ripple_up only focuses on the breathing rate and its harmonics up to the heart rate. Figure 4B As can be seen in Figure 1, ripple_down has a smaller structure than ripple_down2 for the same reasons, now applied only to env_down.

[0100] In the illustrated embodiment, the processed signal determination unit 104 has obtained the processed signals env_up and env_down by applying a filter to the oscillatory component TPac of the blood pulsation signal TP, wherein the fluid responsiveness parameter determination unit 105 is configured to determine a filtered fluid responsiveness parameter determination signal env_ripple_up based on the second fluid responsiveness parameter determination signal ripple_up, and to determine another filtered fluid responsiveness parameter determination signal env_ripple_sum based on the second fluid responsiveness parameter determination signals ripple_up and ripple_down. Although both the filtered fluid responsiveness parameter determination signals env_ripple_up and env_ripple_sum are determined based on the further application of the filter, the signal env_ripple_up is determined by applying the filter to the second fluid responsiveness parameter determination signal ripple_up itself, so that the signal env_ripple_up can also be referred to as a filtered second fluid responsiveness parameter determination signal, however, in order to determine the signal env_ripple_sum, the filter is not applied to any of the second fluid responsiveness parameter determination signals ripple_up and ripple_down themselves, but to the signals derived therefrom, in particular their sum, as further described below. The fluid reactivity parameter determination unit 105 is configured to determine the fluid reactivity parameter FRP based on the first fluid reactivity parameter determination signals baseline_up and baseline_down and the filtered fluid reactivity parameter determination signals env_ripple_up and env_ripple_sum.

[0101] The filter applied to the oscillating component TPac to obtain the processed signals env_up and env_down and the filter used to determine the filtered fluid reactivity parameter determination signals env_ripple_up and env_ripple_sum can be the same or different from each other. The filter applied to the signal TPac to obtain the signals env_up and env_down can preferably be described according to the following equation:

[0102]

[0103] where x[i] refers to the input signal, ie in this case the signal TPac, where i is the discrete sample index, and y[i] refers to the calculated, ie filtered, output signal, and where

[0104]

[0105] and

[0106]

[0107] is the time constant T of the smoothing function that characterizes the filter up and T down Calculate the filter parameters, where the constant F s corresponds to the sampling rate at which the input signal is acquired. While env_up can be obtained by applying the filter directly to TPac, env_down is obtained by applying the filter to TPac only after multiplying TPac by a factor of -1 (ie, changing the sign of TPac).

[0108] The equation used above to describe the filter applied to obtain the signals env_up and env_down from TPac can be considered as a recursive averaging equation. The filter that can be implemented by this equation can be considered as an asymmetric filter because it has an upper limit prevalence, which means that the averaging is more targeted to positive values. In addition, the filter is non-linear. Since the signals env_up and env_down produced by the filtering can correspond to or be similar to the envelope of the input signal TPac, the processed signal determination unit 104 can be considered to include an "envelope detector", where the envelope detector can be a part of the processed signal determination unit 104, which implements the above recursive averaging equation for the filtering process. An exemplary choice of the time constant used when applying the filter to the oscillating component TPac to obtain the processed signals env_up and env_down is T up =T pulse / 2 and T down =T pulse 2, where T pulse =60 / PR, where PR corresponds to the measured pulse rate provided as heart rate by the heart rate providing unit 102, T up , T down , T pulse The AHR is measured in seconds, and the PR is measured in beats or pulses per minute.

[0109] The first fluid responsiveness parameter determination signal baseline_up, baseline_down and the second fluid responsiveness parameter determination signal ripple_up, ripple_down (also referred to as "baseline" and "ripple") can be identified by the fluid responsiveness parameter determination unit 105 based on the processed signals env_up and env_down (also referred to as "envelope") by spectrum analysis. It can also be said that the baseline and the ripple are "extracted" from the envelope, i.e., for example, by means of spectrum analysis. Specifically, the ventilation rate VR (which can have a value of 12 breaths per minute, for example) and the pulse rate PR (which can have a value of 52 heartbeats per minute, for example) can be converted into corresponding fundamental frequencies F0_vr and F0_pr, respectively, which can be provided by the corresponding providing units 101 and 102, wherein these fundamental frequencies can be used to extract corresponding parts of the spectrum corresponding to the signals env_up and env_down. Example values ​​for ventilation rate and pulse rate are VR=12 when measured in breaths / minute, and PR=52 when measured in beats / minute, wherein the values ​​of the corresponding fundamental harmonic frequencies would then be given by F0_vr=VR / 60=1 / 5 when measured in breaths / second and F0_pr=PR / 60=13 / 15 when measured in beats / second, respectively. As already indicated, extracting corresponding portions of the spectrum corresponding to the signals env_up and env_down may also be considered to correspond to or involve spectrum synthesis, wherein the result of the spectrum synthesis results in a baseline signal and a ripple signal, in accordance with the need to determine the signals baseline_up, baseline_down from the first fluid responsiveness parameter and the signals ripple_up, ripple_down from the second fluid responsiveness parameter.

[0110] The reliability determination unit may be configured to perform similar spectral analysis and / or synthesis based on the ventilation rate VR and the pulse rate PR to identify the reliability determination signals ripple_up2 and ripple_down2 in the signals env_up and env_down, respectively. For example, a single spectral analysis and / or synthesis may be performed by a unit combining the functions described above with respect to the fluid responsiveness parameter determination unit 105 and the reliability determination unit 505 to obtain all baseline signals and ripple signals, i.e., baseline_up, baseline_down, rippleup, ripple_down, ripple_up2, and ripple_down2.

[0111] The fluid reactivity parameter determination unit 105 and / or the reliability determination unit 505 are preferably configured to calculate the further signals baseline_sum, ripple_sum and ripple_sum2 according to the following equations:

[0112] baseline_sum=baseline_up+baseline_down, (11)

[0113] ripple_sum=ripple_up+ripple_down, (12)

[0114] ripple_sum2=ripple_up2+ripple_down2 (13)

[0115] Therefore, the "sum" signal on the left side of the above equation is calculated by adding the corresponding baseline signal and ripple signal. These "sum" signals baseline_sum, ripple_sum and ripple_sum2 and / or a subset thereof are used to determine the fluid reactivity parameter FRP and its reliability Q.

[0116] Specifically, the fluid reactivity parameter determination unit 105 may also be configured to calculate the signal env_ripple_sum from ripple_sum by applying a filter. As described above, the filter may correspond to the asymmetric filter described above for obtaining the envelope signals env_up and env_down, or may be a different filter. For example, the signal env_ripple_sum may be obtained by providing the signal ripple_sum or the absolute value of the signal ripple_sum as input to the filter described with respect to equation (8), where now T is used. up =T resp / 4 and T down =T resp 4 as the filter time constant, where T resp = 60 / VR and VR refers to the ventilation rate measured in breaths per minute. Take the signal ripple_sum or its absolute value and then apply the adapted filter - the output of this process is assumed to be the signal env_ripple_sum. Figure 6The "sum" signal and the signal env_ripple_sum are schematically and exemplarily shown. The fluid reactivity parameter determination unit 105 can also apply the same process as just described for calculating env_ripple_sum from ripple_sum to calculate the signal env_ripple_up from ripple_up. In particular, the same filter with the same parameters can be used, wherein the filter is then applied to ripple_up or its absolute value to obtain env_ripple_up. In a variant, the filters for calculating env_ripple_sum from ripple_sum and for calculating env_ripple_up from ripple_up can be different or completely different in terms of the choice of parameters.

[0117] As will be described later with reference to two specific exemplary fluid reactivity parameters, the fluid reactivity parameter determination unit 105 is configured to determine the fluid reactivity parameter based on characteristic values ​​of the first fluid reactivity parameter determination signals baseline_up and baseline_down (in particular their sum baseline_sum) and one of the filtered fluid reactivity parameter determination signals env_ripple_up and env_ripple_sum.

[0118] According to one example, the system 100 can be used to determine the systolic pressure variation SPV as a fluid responsiveness parameter. The parameter SPV is Fig. 7A It is schematically and exemplarily shown in FIG, which shows a series of measured blood pressure pulses, i.e. a signal similar to TPac, where the horizontal axis measures time in seconds and the vertical axis measures pressure in mmHg. SPV can generally be defined as

[0119]

[0120] Where SAPmin is the minimum arterial systolic pressure, and SAPmax is the maximum arterial systolic pressure, such as Fig. 7A Different definitions of SPV commonly used do not use a normalization of the mean SAP value (SAPmax+SAPmin) / 2. As suggested by these definitions, conventional methods for estimating fluid responsiveness via SPV use pressure pulses (measured invasively or non-invasively), and in particular several individual pressure pulses, to assess the variation of the pulse height of the pressure pulse due to a breathing cycle controlled, for example, via a ventilator.

[0121] In contrast, for the purpose of determining the systolic blood pressure change, the processed signal determination unit 104 is configured to determine the signal env_up as the first processed signal as described above, i.e. by applying the corresponding filter of equation (8) to the oscillatory component TPac of the blood pulsation signal TP, and to determine the signal env_down as the second processed signal as described above, i.e. by inverting the oscillatory component TPac and applying the filter of equation (8) to the inverted oscillatory component, where inversion refers to a change in sign. Furthermore, the fluid reactivity parameter determination unit 105 is configured to identify a second fluid reactivity parameter determination signal ripple_up for the first processing signal env_up by identifying a first fluid reactivity parameter determination signal baseline_up for the first processing signal env_up and another first fluid reactivity parameter determination signal baseline_down for the second processing signal env_down, combining the first fluid reactivity parameter determination signals baseline_up and baseline_down into a combined first fluid reactivity parameter determination signal baseline_sum by addition (as shown in equation (11)), and determine a filtered fluid reactivity parameter determination signal env_ripple_up by applying a corresponding filter of equation (8) (having the above parameters of the second fluid reactivity parameter determination signal ripple_up identified for the first processing signal env_up). Since the filter is specifically applied to the second fluid reactivity parameter determination signal ripple_up for the purpose of determining the SPV, the resulting specific filtered fluid reactivity parameter determination signal env_ripple_up may also be referred to as a filtered second fluid reactivity parameter determination signal. The fluid reactivity parameter determination unit 105 is configured to determine the SPV value based on the combined first fluid reactivity parameter determination signal baseline_sum and the filtered fluid reactivity parameter determination signal env_ripple_up (ie, the filtered second fluid reactivity parameter determination signal).

[0122] For the purpose of SPV determination, in this case, the system 100 also includes a blood pressure characteristic providing unit, which is used to provide blood pressure characteristics SAP and DAP, namely systolic pressure (SAP) and diastolic pressure (DAP), wherein the fluid responsiveness parameter determination unit is configured to further determine the SPV parameters based on these blood pressure characteristics SAP and DAP.

[0123] The SPV parameter is calculated by the fluid reactivity parameter determination unit 105 through the calculation of the modulation index, wherein the modulation index is calculated by detecting the time index k corresponding to the maximum peak in the signal baseline_sum and using the corresponding time index in the signal env_ripple_up (i.e., in the "envelope" of ripple_up). In particular, the SPV parameter is determined according to the following equation:

[0124]

[0125] Where N is the time window (in units of number of samples or sampling points), which can be, for example, several respiratory cycles long, so that multiple samples are used when determining the maximum value of the env_ripple_up signal, and where SAP is the mean systolic pressure and DAP is the mean diastolic pressure. The factor 2 enters the above equation because the signal env_ripple_up only represents the upper envelope of ripple_up. The factor (SAP-DAP) / SAP is needed because the use of "baseline" and "ripple" only reflects pulse pressure (PP) changes (PP=SAP-DAP), and the definition of SPV will need to be normalized using SAP. SAP and DAP values ​​can be obtained from non-invasive blood pressure (NIBP) measurements as described, for example, in WO2020 / 148137 A1, which is incorporated herein by reference in its entirety.

[0126] The system 100 can also be used to determine the pulse pressure variation PPV as a fluid responsiveness parameter, which constitutes a second example. To illustrate the clinical meaning of the PPV of the fluid responsiveness parameter, a PPV of 12% or greater is generally considered an indication that the patient will require more fluid. Figure 7B It is schematically and exemplarily shown in Figure 7B Again a series of measured blood pressure pulses is shown, i.e. a signal like TPac, where the horizontal axis measures time in seconds and the vertical axis measures pressure in mmHg. PPV is usually defined as

[0127]

[0128] Where PPmin is the minimum pulse height (pulse pressure), PPmax is the maximum pulse height, such as Figure 7B shown.

[0129] Thus, while SPV estimates FRP focusing on the maximum value of the pressure pulse, i.e., the arterial systolic pressure, PPV estimates fluid responsiveness based on the ratio between the pulse height variation due to breathing or ventilation and the mean pulse height. However, usually, a pressure pulse (invasively or non-invasively measured), in particular several pressure pulses, are used to assess the variation of the pulse height of the pressure pulse due to the respiratory cycle.

[0130] In contrast, for the purpose of determining PPV, the processed signal determination unit 104 is configured to determine the signal env_up as a first processed signal by applying the corresponding filter of equation (8) to the oscillatory component TPac of the blood pulsation signal TP as described above, and to determine the signal env_down as a second processed signal also as described above, i.e., by first inverting the oscillatory component TPac and applying the filter to the inverted oscillatory component. The fluid reactivity parameter determination unit 105 is configured to determine the PPV parameter by identifying a first fluid reactivity parameter determination signal for the first processing signal env_up and another first fluid reactivity parameter determination signal for the second processing signal env_down, and combining the two first fluid reactivity parameter determination signals into a combined first fluid reactivity parameter determination signal baseline_sum by addition, as shown in equation (11), wherein the fluid reactivity parameter determination unit 105 is also configured to identify a second fluid reactivity parameter determination signal ripple_up for the first processing signal env_up, identify another second fluid reactivity parameter determination signal ripple_down for the second processing signal env_down, and combine the two second fluid reactivity parameter determination signals ripple_up and ripple_down into a combined second fluid reactivity parameter determination signal ripple_sum by addition, as shown in equation (12), and also determine the filtered combined second fluid reactivity parameter determination signal env_ripple_sum by applying a corresponding filter to the combined second fluid reactivity parameter determination signal ripple_sum. The fluid reactivity parameter determination unit 105 is configured to determine the PPV parameter based on the combined first fluid reactivity parameter determination signal baseline_sum and the filtered combined second fluid reactivity parameter determination signal env_ripple_sum.

[0131] Furthermore, the PPV parameter is calculated by the fluid reactivity parameter determination unit 105 through the calculation of the modulation index, wherein, in this case, the modulation index is calculated by detecting the time index k corresponding to the maximum peak in the signal baseline_sum and using the corresponding time index in the signal env_ripple_sum (i.e., in the "envelope" of ripple_sum instead of ripple_up). Specifically, the PPV parameter is determined according to the following equation:

[0132]

[0133] where N is again the time window (in number of samples or sampling points), which may be, for example, several breathing cycles long, so that multiple samples are used when determining the maximum value of the env_ripple_sum signal.

[0134] The calculations performed to determine the SPV and PPV parameters therefore differ only in the additional factor (SAP-DAP) / SAP for SPV and in the choice between env_ripple_up and env_ripple_sum for determining the respective modulation index. In a variant, this additional factor may also be omitted for determining the SPV.

[0135] like Fig. 8A As schematically and exemplarily shown in FIG. 1 , the blood pulsation signal TP may include a blood pulse caused by an ectopic beat or a pressure pulse indicating a blood pulse. Such a pulse may be considered as an artifact in the signal. Fig. 8A In the embodiment, the pulse caused by the ectopic beat is indicated by PP_ect in the blood pulsation signal TP and its oscillation component TPac. The indicated pulse is attenuated by 50%. Figure 8B , 8C , 8D and 8E, the pulses due to ectopic beats may carry any signal derived from the blood pulsation signal TP, Figure 8B , 8C , 8D and 8E respectively show Figure 2 , Figure 3 , Figure 4A and 4B The signal corresponds to the signal shown in , but is based on the inclusion of Fig. 8A The pulsation signal TP of the pulse caused by the ectopic beat is determined instead of the Figure 2 The processing signal determination unit 104 may determine the processing signals env_up and env-down based on the blood pulsation signal TP shown without any pulses due to ectopic beats. Therefore, the accuracy of the determination of the fluid responsiveness parameter may be affected by whether there are pulses corresponding to ectopic beats in the blood pulsation signal TP. In order to reduce the adverse effects of ectopic beats on the accuracy of FRP determination, the processing signal determination unit 104 may determine the processing signals env_up and env-down based on the blood pulsation signal TP by also applying regularization to the detected blood pulses caused by ectopic beats in the blood pulsation signal TP. For example, the processing signal determination unit 104 may include a dedicated ectopic beat detection unit, which is configured to detect blood pulses caused by ectopic beats in the blood pulsation signal TP.

[0136] Regularization of the detected blood pulses due to ectopic beats (which can also be considered as repair or fixing of the blood pulsation signal TP) can ensure that the so-called respiratory adjustments are not taken into account when determining the fluid responsiveness parameters that are actually caused only by ectopic beats. Pulses due to ectopic beats can be detected based on time and amplitude information, wherein the corresponding missing or weak pulses can then be artificially filled based on previous or subsequent pulses in the signal. Some pulses caused by ectopic beats, especially like Fig. 8A Those pulses shown in that are not fully attenuated may require more effort to repair than other pulses. Preferably, only those pulses are detected as being due to ectopic beats and are thereafter regularized beyond a predetermined degree, i.e., only very weak pulses, since modification of pulses that are weakened only due to respiratory regulation should be avoided. In addition, any of the methods described in the article “Predicting fluid response with stroke volume variation despite multiple extrsysoles” by M. Cannesson et al. in Critical Care Medicine, Vol. 40, No. 1, pp. 193-198 (2012), which is incorporated herein by reference in its entirety, can be used to improve the situation of ectopic beats, in particular for the regularization of blood pulses detected in the blood pulsation signal due to ectopic beats, which article is incorporated herein by reference in its entirety.

[0137] Regularization of the pulses in the signal TP due to ectopic beats is optional, but it may ensure a stable pulse rate in the signal, i.e. this may be particularly advantageous for longer measurement times, i.e. if a blood pulsation signal is used for FRP determination that has been acquired over a relatively long time window. For patients whose heartbeats show true arrhythmias, regularization may be challenging or even impossible, in which case it may be preferable not to trust the determined fluid responsiveness parameters, i.e. to associate zero reliability with them. For example, as described in WO2019 / 211210 A1, the entire contents of which are incorporated herein by reference, a heart rate variability measure (such as a measure called PRvar) may be used to decide whether an arrhythmia is present. If this is the case, the estimated fluid responsiveness parameters may not be used to improve the SV estimate (instead assumed fluid responsiveness values ​​may be used).

[0138] More generally, as described above, the reliability determination unit 505 may be identical to or integrated with the fluid reactivity parameter determination unit 105, and the reliability determination unit 505 may be configured to determine the reliability of the determined SPV parameters and the determined PPV parameters according to the corresponding quality index QI. Specifically, the quality index of the determined SPV parameters (referred to herein as SPV QI) may be calculated according to the following equation:

[0139]

[0140] Wherein, k and N are defined as in the above formula (8) and are used to determine the SPV parameters.

[0141] Furthermore, a quality index (referred to herein as PPVQI) of the determined PPV parameters may be calculated according to the following equation:

[0142]

[0143] Wherein, k and N are defined as in the above formula (10) and are used to determine the PPV parameters.

[0144] Fig. 9 A system 1500 for determining a patient's stroke volume SV as a hemodynamic parameter associated with a fluid responsiveness parameter is schematically and exemplarily shown. The system 1500 includes a system 100 for determining a patient's fluid responsiveness parameters SPV and PPV, and a system 500 for determining the corresponding reliability of the fluid responsiveness parameters SPV and PPV determined by the system 100 according to the quality indexes SPV QI and PPV QI. The system 1500 also includes a first model providing unit 1510 configured to provide a first model of the stroke volume SV that depends on the SPV and PPV; and a second model providing unit 1520 configured to provide a second model of the stroke volume SV that does not depend on the SPV and PPV. In addition, the system 1500 includes: a combined model determining unit 1530 configured to determine a combined model based on the first model, the second model, and a corresponding one of the quality indexes SPV QI and PPV QI; and a hemodynamic parameter determining unit 1540 configured to determine the stroke volume SV by applying the combined model.

[0145] In particular, the pulse contour stroke volume (PCSV) may be used as a measure of the stroke volume SV. Thus, the first model may correspond to a first function SV1 that expresses the pulse contour stroke volume PCSV in terms of any one of SPV and PPV, and the second model may correspond to a second function SV that expresses the pulse contour stroke volume PCSV in terms of other quantities than SPV and PPV.

[0146] An example of a first model for calculating stroke volume using fluid responsiveness parameters is mentioned in equation (31) of WO2019 / 211210 A1, while an example of a second model for calculating stroke volume without using fluid responsiveness parameters is mentioned in equation (11) of WO2019 / 211210 A1. Alternatively, further examples of the second model are known from the Wessling Algorithm or alternative methods, see Table 1 in the contribution "The Effect of Signal Quality on Six Cardiac Output Estistators" by T. Chen et al., 36th Annual Conference on Computers in Cardiology, pp. 197-200 (2009), the entire contents of which are incorporated herein by reference.

[0147] Then, the combined model may correspond to a function expressing the pulse contour stroke volume PCSV according to the first function SV1, the second function SV2, and the mapping function w according to the following equation:

[0148] PCSV=w·SV1+(1-w)·SV2, (20)

[0149] The mapping function can have the following forms:

[0150] w=QI, (21)

[0151] Wherein if the selection of SV1 depends on SPV, the QI is the SPV QI, and if the selection of SV1 depends on PPV, the QI is the PPV QI. In addition, a combination of PPV and SPV is possible by applying a weighted combination of PPV and SPV parameters for SV1 and a weighted combination of PPV QI and SPV QI for w, similar to equation (16) of WO2019 / 211210 A1. Alternatively, other nonlinear mapping functions w may be used, such as a sigmoid function.

[0152] Thus, the corresponding FRP is used to estimate a first stroke volume SV1 represented by the first function, but there is a fallback case where the FRP is not used to estimate the stroke volume, and then a second stroke volume SV2 represented by the second function. The quality index determined by the system 500 for the respectively used FRP enters the stroke volume determination through a mapping function w, which can also be regarded as a weighting parameter for weighting SV1 and SV2 in order to calculate PCSV as the final stroke volume.

[0153] Fig.10A method 200 for determining a fluid responsiveness parameter of a patient is schematically and exemplarily shown. For example, the method 200 comprises a step 201 of providing a breathing rate for the patient, a step 202 of providing a heart rate for the patient, and a step 203 of providing a blood pulsation signal TP for the patient, wherein the blood pulsation signal TP is a measurement signal indicating a series of blood pulses of the patient, such as Figure 2 Schematically and exemplarily shown in . The method 200 also includes a step 204 of determining one or more processed signals based on the blood pulsation signal TP, wherein, as described in detail above, the processed signals indicate the corresponding envelope of the blood pulsation signal TP. In addition, the method 200 includes a step 205 of determining a fluid reactivity parameter. In this step 205, it can also be regarded as including several sub-steps, determining one or more first fluid reactivity parameter determination signals based on the one or more processed signals, wherein the one or more first fluid reactivity parameter determination signals each correspond to a corresponding one of the one or more processed signals in the frequency spectrum range up to the respiratory rate, and determining one or more second fluid reactivity parameter determination signals based on the one or more processed signals, wherein the one or more second fluid reactivity parameter determination signals each correspond to a corresponding one of the one or more processed signals at the respiratory rate and any harmonics thereof up to the heart rate. Then, during step 205, the fluid reactivity parameter is determined based on the one or more first fluid reactivity parameter determination signals and the one or more second fluid reactivity parameter determination signals.

[0154] Fig.11 The method for determining the Fig.10 The method 600 of determining the reliability of a fluid responsiveness parameter by the method shown. The method 600 comprises: step 601, providing a breathing rate based on which the fluid responsiveness parameter has been determined; step 602, providing a heart rate based on which the fluid responsiveness parameter has been determined; step 603, providing one or more processed signals based on which the fluid responsiveness parameter has been determined; and step 604, providing one or more second fluid responsiveness parameter determination signals corresponding to the one or more processed signals. In another step 605 of the method 600, which can also be regarded as comprising several sub-steps, determining the reliability of the determined fluid responsiveness parameter by identifying one or more reliability determination signals based on the one or more processed signals, wherein the one or more reliability determination signals correspond to a corresponding one of the one or more processed signals in the frequency spectrum range between the breathing rate and the heart rate, and determining the reliability of the determined fluid responsiveness parameter based on the one or more second fluid responsiveness parameter determination signals and the one or more reliability determination signals.

[0155] Fig.12 Schematically and exemplarily, a method for determining Fig.10Method 2600 for determining hemodynamic parameters associated with a fluid responsiveness parameter determined according to method 200 is shown. Method 2600 includes the steps of method 200 for determining a fluid responsiveness parameter for a patient, and the steps of method 600 for determining the reliability of the determined fluid responsiveness parameter. In addition, method 2600 includes a step 2610 of providing a first model of the hemodynamic parameters to be determined, wherein the first model depends on the fluid responsiveness parameter determined according to method 200, and a step 2620 of providing a second model of the hemodynamic parameters, wherein the second model differs from the first model in that the second model does not depend on the fluid responsiveness parameter. In addition, method 2600 includes a step 2630 of determining a combined model based on the first model, the second model and the reliability of the determined fluid responsiveness parameter (i.e., the reliability determined according to method 600). In another step 2640 of method 2600, the hemodynamic parameters are determined by applying the combined model.

[0156] Fig.13 It is schematically and exemplarily shown how to determine the "baseline" signal, baseline_up, baseline_down, the "ripple" signal, ripple_up, ripple_down and the "ripple 2" signal ripple_up2, ripple_down2, which are examples of the first and second fluid responsiveness parameter determination signal and the reliability determination signal, respectively, based on the pulse rate PR understood to be indicative of the heart rate, the provided ventilation rate VR controlling the patient's breathing rate and the processed "envelope" signals env_up and env_down ("env") determined based on the measured blood pulsation signal. The results show that the harmonics F0_pr and F0_vr of the pulse rate PR and the ventilation rate VR are determined, and a corresponding spectral analysis is performed on the processed signals in order to determine their spectral parts a below the ventilation rate, b) at the ventilation rate and their harmonics up to the pulse rate and c) between the ventilation rate and the pulse rate. Based on several spectral parts, the baseline signal and the ripple signal are determined by spectral synthesis, such as Fig.13 as shown in the rightmost box.

[0157] Fig.14A and 14B It is shown schematically and by way of example how the fluid reactivity parameters SPV and PPV and their respective reliability can be determined. Fig.14AAs shown, in order to determine the SPV and its reliability SPV QI, the signals env_up and env_down are determined based on the oscillation component TPac of the blood pulsation signal TP via a process which can also be referred to as an envelope detector, wherein based on the signals env_up and env_down, the signals baseline_up, ripple_up, ripple_up2 and baseline_down are determined instead of the signals ripple_down and ripple_down, because the latter two signals are not required for determining the SPV and its reliability SPV QI. The determination of the selected baseline signal and ripple signal can also be regarded as the extraction of the modulation of the pulses in the blood pulsation signal, as Fig.14A . It is also shown that the pulse rate PR and the ventilation rate VR enter the envelope detection and modulation extraction, for example via the parameters of the filter used for envelope detection and the selection of the spectrum part in the spectrum analysis performed for modulation extraction. It is worth noting that in this case, VR does not enter the detection of env_up and env_down.

[0158] The SPV parameters are then determined based on a signal baseline_sum formed by adding the signals baseline_up and baseline_down and by an envelope which is again determined by an envelope detector by using a filter on, for example, the ripple_up signal by determining a corresponding modulation index (optionally also depending on the systolic arterial pressure SAP and the diastolic arterial pressure DAP). The reliability of the SPV parameters is determined by depending on a corresponding quality index of the signals ripple_up and ripple_up2. Although in this case VR does not enter into the detection of env_up and env_down, PR does not enter into the detection of the envelope of ripple_up.

[0159] like Fig. 14B As shown, the determination of the PPV and its reliability is slightly different from the determination of the SPV and its reliability. In particular, ripple_down and ripple_down2 are also determined, and the corresponding "sum" signals ripple_sum and ripple_sum2 are determined by adding the corresponding ripple signals. The PPV is then determined based on the envelope detected for ripple_sum and further based on the signal baseline_sum, but without reference to SAP and DAP. The reliability of the PPV is determined based on the two "sum" ripple signals, rather than only on the signals ripple_up and ripple_up2. Although the VR does not enter the detection of env_up and env_down, in this case the PR does not enter the detection of the envelope of ripple_sum.

[0160] Fig.15 An example of how to determine the stroke volume SV as a hemodynamic parameter based on either of the fluid responsiveness parameters SPV and PPV is schematically and exemplarily shown. Since in the case where SPV is used as the fluid responsiveness parameter FRP, only the systolic arterial pressure and the diastolic arterial pressure are optionally required as input data, Fig.15 The corresponding arrows in are indicated by dashed lines as optional. Similarly, as described in further detail above, the detection of those pulses in the blood pulsation signal (i.e., the tissue pressure signal TP) due to, for example, ectopic beats and their regularization or repair is optional, even in the rather specific embodiment that has been shown, as shown in the frame of the corresponding box. Fig.15 , the oscillatory component of TP is determined by applying a high-pass filter. Then, as described above for Fig.13 as well as Fig.14A and Fig. 14B As described, the corresponding fluid responsiveness parameters and their reliability are determined. The mapping function w and the first model function SV1 and the second model function SV2 described further above are used to calculate the stroke volume SV.

[0161] The fluid responsiveness parameter (FRP) is an important clinical parameter in the surgical environment and is sometimes used as an intermediate parameter in stroke volume estimation algorithms (such as those used with the system described in EP3430992 A1). FRP estimation aims to measure the modulation index of the effect of breathing on cardiac pulsation. However, in situations where it is desired to provide the FRP to the clinician quickly (as in a spot check scenario), only a limited number of respiratory cycles can be utilized. Therefore, the implementation of FRP determination is extremely sensitive to artifacts and ectopic beats. Therefore, by using a priori inputs of respiratory rate (as shown by ventilation rate (VR)) and heart rate (as shown by pulse rate (PR)), a robust means is provided to calculate FRP with a quality index. It can be safely assumed that both VR and PR are constant, because for VR we always have a fixed rate in the surgical environment, and for PR we can detect and fix ectopic beats.

[0162] In other words, the systems and methods described herein can be used for short-duration measurements of fluid responsiveness parameters and corresponding quality indices, which are considered to be very important in surgical environments. It has been found that for short-duration measurements, the following fact can be utilized: there is a fixed / stable breathing rate and a fixed / stable heart rate in the corresponding short time window, at least to a sufficient degree. Such short-duration measurements can be applied to spot check scenarios (using the system described in EP3430992 A1 or a traditional air cuff). In addition, it can be applied to continuous measurements with, for example, arterial blood pressure (ABP) and (light) plethysmography (PPG), where it is necessary to obtain fluid responsiveness parameters to be tracked quickly, such as in actions such as passive leg raising. Therefore, in addition to the use case where the fluid responsiveness parameter (FRP) is provided to and interpreted by the clinician, it can also be used internally for algorithms, such as those used with the system known from EP3430992A1. As described above, these systems are particularly useful in surgical environments with ventilated patients. Estimated fluid responsiveness parameters such as PPV can be used to improve stroke volume (SV) estimation, but so far mainly in the setting of stable heart rate (ie, no arrhythmias).

[0163] In order to determine a good quality index corresponding to the quality or reliability of the determined fluid responsiveness parameter, a priori known values ​​of the breathing rate (such as VR (ventilation rate)) and the heart rate (as indicated by PR (pulse rate)) can be assumed, and these rates can be used in the spectral domain to estimate the so-called "respiratory ripple", which is the variation in pulse pressure height modulated by the patient's breathing (e.g., caused by the ventilator). The breathing rate can be used to extract the first and next harmonics from the spectrum that contribute to this ripple. The heart rate can be used to decide how many harmonics can be included in this ripple extraction, because otherwise the heart pulsation will start to affect the estimate of the ripple. The quality of the fluid responsiveness parameter can be evaluated by comparing the estimated pulsation (e.g., based on a single ventilator harmonic between VR and PR) with the pulsation estimated by using the entire spectrum between VR and PR.

[0164] The systems and methods described herein may be used with a measurement system as described in EP3430992 A1, and the embodiments shown above are also based on measurement data acquired using such a system, even though they may also be acquired using a different system. Since when using the system described in EP3430992 A1 one is generally interested in the reliability of the determined fluid responsiveness parameters, it is envisaged not only to present the FRP to the clinician, but also to provide a quality index of the FRP in order to decide how to use the FRP in stroke volume (SV) estimation.

[0165] The fluid responsiveness parameter (FRP) and its quality index may preferably be displayed on the patient monitor, as they will be beneficial to the clinician's assessment. In addition, the ventilation rate (VR) and pulse rate (PR) may also be shown on the patient monitor. In this case, the patient monitor may require corresponding input data streams.

[0166] Although the embodiments described in detail above relate to SPV and PPV as exemplary fluid responsiveness parameters and to an acquired blood pulsation signal used in a specific manner, in other embodiments, other fluid responsiveness parameters, corresponding reliabilities and related hemodynamic parameters may be determined, in particular also based on a blood pulsation signal acquired using a different measurement system, such as pressure via an inflated cuff for non-invasive blood pressure measurement or by (photo) plethysmography (PPG) or via displacement measurement using an inertial measurement unit (IMU). Furthermore, even for determining SPV and PPV, their reliabilities and SV based thereon, other equations than those given above may be found. For example, a filter of a different type than the one defined in equation (1) may be used.

[0167] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims.

[0168] In the claims, the word "comprising" does not exclude other elements or steps, and the indicative "a" or "an" does not exclude a plurality.

[0169] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0170] Processes such as providing a respiratory rate, heart rate, blood pulsation signal or any other signal may be performed by any other number of units, as well as any identification and determination of signals based on other signals, etc. performed by one or more units. These processes may be implemented as program code of a computer program and / or dedicated hardware.

[0171] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0172] Any reference signs in the claims should not be construed as limiting the scope.

[0173] A system for FRP determination is proposed, comprising a unit for providing a respiratory rate, a heart rate and a blood pulsation signal indicative of a measurement of a series of blood pulses of a patient. The system further comprises a unit for determining a processed signal indicative of an envelope of the blood pulsation signal based on the blood pulsation signal, and a unit for determining the FRP by: a) based on the processed signal, identifying a first FRP determination signal corresponding to the processed signal in a frequency spectrum range up to the respiratory rate, and a second FRP determination signal corresponding to the processed signal at the respiratory rate and any harmonics thereof up to the heart rate, and b) determining the FRP based on the first and second FRP determination signals.

Claims

1. A system (100) for determining a fluid responsiveness parameter of a patient, wherein: The determined fluid responsiveness parameter is systolic pressure variation (SPV) or pulse pressure variation (PPV), wherein the system comprises: A breathing rate (101) providing unit configured to provide a breathing rate, A heart rate providing unit (102) is configured to provide a heart rate, a blood pulsation signal providing unit (103), which is configured to provide a blood pulsation signal, wherein the blood pulsation signal is a measurement signal indicating a series of blood pulses of the patient, a processing signal determination unit (104) configured to determine a first processing signal (env_up) based on the blood pulsation signal and to determine a second processing signal (env_down) based on the blood pulsation signal, wherein the first processing signal indicates an upper envelope of the blood pulsation signal, wherein the second processing signal indicates a lower envelope of the blood pulsation signal, and A fluid reactivity parameter determination unit (105) is configured to determine the fluid reactivity parameter (SPV, PPV) by: a) identifying a first fluid responsiveness parameter determination signal (baseline_up, baseline_down) based on the first processed signal (env_up) and the second processed signal (env_down), wherein the first fluid responsiveness parameter determination signal corresponds to the first processed signal (env_up) and the second processed signal (env_down) within a frequency spectrum up to the breathing rate, and identifying a second fluid responsiveness parameter determination signal (ripple_up, ripple_down) based on the first processed signal (env_up) and the second processed signal (env_down), wherein the second fluid responsiveness parameter determination signal (ripple_up, ripple_down) corresponds to the first processed signal (env_up) and the second processed signal (env_down) at the breathing rate and any harmonics thereof up to the heart rate, and b) determining the fluid reactivity parameters (SPV, PPV) based on the first fluid reactivity parameter determination signal (baseline_up, baseline_down) and the second fluid reactivity parameter determination signal (ripple_up, ripple_down).

2. The system (100) according to claim 1, wherein: The processed signal determination unit (104) is configured to obtain the first processed signal (env_up) and the second processed signal (env_down) by applying a filter to the oscillatory component of the blood pulsation signal, wherein the fluid responsiveness parameter determination unit (105) is configured to determine a filtered fluid responsiveness parameter determination signal (env_ripple_up, env_ripple_sum) based on the second fluid responsiveness parameter determination signal (ripple_up, ripple_down) and further application of the filter, and to determine the fluid responsiveness parameters (SPV, PPV) based on the first fluid responsiveness parameter determination signal (baseline_up, baseline_down) and the filtered fluid responsiveness parameter determination signal (env_ripple_up, env_ripple_sum).

3. The system (100) according to claim 2, wherein: The fluid reactivity parameter determination unit (105) is configured to determine the fluid reactivity parameters (SPV, PPV) based on characteristic values ​​of the first fluid reactivity parameter determination signal (baseline_up, baseline_down) and the filtered fluid reactivity parameter determination signal (env_ripple_up, env_ripple_sum).

4. The system (100) according to any one of the preceding claims, wherein: The processed signal determination unit (104) is configured to determine a first processed signal (env_up) obtained by applying a filter to an oscillatory component of the blood pulsation signal and a second processed signal (env_down) obtained by inverting the oscillatory component and applying the filter to the inverted oscillatory component, and wherein the fluid responsiveness parameter determination unit (105) is configured to determine the fluid responsiveness parameter (SPV) by: a′) identifying a first fluid reactivity parameter determination signal for each of the first processed signal (env_up) and the second processed signal (env_down) and combining the first fluid reactivity parameter determination signals (baseline_up, baseline_down) into a combined first fluid reactivity parameter determination signal (baseline_sum), identifying a second fluid reactivity parameter determination signal (ripple_up) for the first processed signal (env_up), determining a filtered fluid reactivity parameter determination signal (env_ripple_up) by applying a filter to the second fluid reactivity parameter determination signal (ripple_up) identified for the first processed signal (env_up), and b') determining the fluid reactivity parameter (SPV) based on the combined first fluid reactivity parameter determination signal (baseline_sum) and the filtered fluid reactivity parameter determination signal (env_ripple_up).

5. The system (100) according to any one of the preceding claims, wherein: The system further comprises: a blood pressure characteristic providing unit for providing blood pressure characteristics (SAP, DAP), Wherein, the fluid responsiveness parameter determination unit (105) is configured to determine the fluid responsiveness parameter (SPV) further based on the blood pressure characteristics (SAP, DAP).

6. The system (100) according to any one of the preceding claims, wherein: The processed signal determination unit (104) is configured to determine a first processed signal (env_up) obtained by applying a filter to an oscillatory component of the blood pulsation signal and a second processed signal (env_down) obtained by inverting the oscillatory component and applying the filter to the inverted oscillatory component, and wherein the fluid responsiveness parameter determination unit (105) is configured to determine the fluid responsiveness parameter (PPV) by: a”) identifying a first fluid reactivity parameter determination signal for each of the processed signals (env_up, env_down) and combining them into a combined first fluid reactivity parameter determination signal (baseline_sum), identifying a second fluid reactivity parameter determination signal for each of the processed signals (env_up, env_down) and combining them into a combined second fluid reactivity parameter determination signal (ripple_sum), and determining a filtered combined second fluid reactivity parameter determination signal (env_ripple_sum) by further applying a filter to the combined second fluid reactivity parameter determination signal (ripple_sum), and b″) determining the fluid reactivity parameter (PPV) based on the combined first fluid reactivity parameter determination signal (baseline_sum) and the filtered combined second fluid reactivity parameter determination signal (env_ripple_sum).

7. The system (100) according to any one of the preceding claims, wherein: Determination of the first processed signal (env_up) and the second processed signal (env_down) by the processed signal determination unit based on the blood pulsation signal involves regularization of detected blood pulses (PP_ect) due to ectopic beats in the blood pulsation signal.

8. A system (1500) for determining a hemodynamic parameter (SV) related to a fluid responsiveness parameter (SPV, PPV), wherein: The system comprises: The system (100) according to any one of claims 1 to 7, a breathing rate providing unit (501) configured to provide a breathing rate, based on which the fluid responsiveness parameters (SPV, PPV) have been determined, a heart rate providing unit (502) configured to provide a heart rate, based on which the fluid responsiveness parameters (SPV, PPV) have been determined, a processing signal providing unit (503) configured to provide a first processing signal (env_up) and a second processing signal (env_down), based on which the fluid reactivity parameters (SPV, PPV) have been determined, a second fluid reactivity parameter determination signal providing unit (504) configured to provide a second fluid reactivity parameter determination signal (ripple_up, ripple_down) of the first processed signal (env_up) and the second processed signal (env_down), and A reliability determination unit (505) is configured to determine the reliability (QI) of the determined fluid reactivity parameter (SPV, PPV) by: a) identifying a first reliability determination signal (ripple_up2) based on the first processed signal (env_up), and identifying a second reliability determination signal (ripple_down2) based on the second processed signal (env_down), wherein the first reliability determination signal (ripple_up2) and the second reliability determination signal (ripple_down2) correspond to the first processed signal (env_up) and the second processed signal (env_down) within a frequency spectrum range between the breathing rate and the heart rate, and b) determining the reliability (QI) of the determined fluid reactivity parameter (SPV, PPV) based on the second fluid reactivity parameter determination signal (ripple_up, ripple_down) and the first reliability determination signal (ripple_up2) and the second reliability determination signal (ripple_down2), a first model providing unit (1510) configured to provide a first model of hemodynamic parameters, the first model of hemodynamic parameters being dependent on the fluid responsiveness parameters (SPV, PPV) determined by the system (100) according to any one of claims 1 to 7, a second model providing unit (1520) configured to provide a second model of hemodynamic parameters, the second model of hemodynamic parameters being independent of the fluid responsiveness parameters (SPV, PPV), and a combined model determining unit (1530) configured to determine a combined model based on the first model, the second model and the reliability (QI) of the fluid reactivity parameters (SPV, PPV), and A hemodynamic parameter determination unit (1540) is configured to determine the hemodynamic parameter by applying the combined model.

9. A computer-implemented method (200) for determining a fluid responsiveness parameter of a patient, wherein: The determined fluid responsiveness parameter is systolic pressure variation (SPV) or pulse pressure variation (PPV), wherein the method (200) comprises: providing (201) a breathing rate, providing (202) heart rate, providing (203) a blood pulsation signal, wherein the blood pulsation signal is a measurement signal indicative of a series of blood pulses of the patient, determining (204) a first processed signal (env_up) based on the blood pulsation signal and determining (204) a second processed signal (env_down) based on the blood pulsation signal, wherein the first processed signal indicates an upper envelope of the blood pulsation signal, wherein the second processed signal indicates a lower envelope of the blood pulsation signal, and The fluid reactivity parameters (SPV, PPV) are determined (205) by: a) identifying a first fluid responsiveness parameter determination signal (baseline_up, baseline_down) based on the first processed signal (env_up) and the second processed signal (env_down), wherein the first fluid responsiveness parameter determination signal corresponds to the first processed signal (env_up) and the second processed signal (env_down) within a frequency spectrum up to the breathing rate, and identifying a second fluid responsiveness parameter determination signal (ripple_up, ripple_down) based on the first processed signal (env_up) and the second processed signal (env_down), wherein the second fluid responsiveness parameter determination signal (ripple_up, ripple_down) corresponds to the first processed signal (env_up) and the second processed signal (env_down) at the breathing rate and any harmonics thereof up to the heart rate, and b) determining the fluid reactivity parameters (SPV, PPV) based on the first fluid reactivity parameter determination signal (baseline_up, baseline_down) and the second fluid reactivity parameter determination signal (ripple_up, ripple_down).

10. A computer-implemented method (2600) for determining a hemodynamic parameter (SV) related to a fluid responsiveness parameter (SPV, PPV), wherein: The method (2600) comprises: Determining a fluid responsiveness parameter (SPV, PPV) of a patient by a method (200) according to claim 9, The reliability (QI) of the determined fluid reactivity parameters (SPV, PPV) is determined by: providing (601) a breathing rate, based on which the fluid responsiveness parameters (SPV, PPV) have been determined, providing (602) a heart rate, based on which the fluid responsiveness parameters (SPV, PPV) have been determined, providing (603) a first processed signal (env_up) and a second processed signal (env_down), based on which the fluid reactivity parameters (SPV, PPV) have been determined, providing (604) a second fluid reactivity parameter determination signal (ripple_up, ripple_down) of the first processed signal (env_up) and the second processed signal (env_down), and The reliability (QI) of the determined fluid reactivity parameters (SPV, PPV) is determined (605) by: a) identifying a first reliability determination signal (ripple_up2) based on the first processed signal (env_up) and identifying a second reliability determination signal (ripple_down2) based on the second processed signal (env_down), wherein the first reliability determination signal and the second reliability determination signal correspond to the first processed signal (env_up) and the second processed signal (env_down) within a frequency spectrum range between the breathing rate and the heart rate, and b) determining the reliability (QI) of the determined fluid reactivity parameter (SPV, PPV) based on the second fluid reactivity parameter determination signal (ripple_up, ripple_down) and the first reliability determination signal (ripple_up2) and the second reliability determination signal (ripple_down2), The method (2600) for determining a hemodynamic parameter (SV) related to a fluid responsiveness parameter (SPV, PPV) further comprises: providing (2610) a first model of hemodynamic parameters that are dependent on the determined fluid responsiveness parameters (SPV, PPV), providing (2620) a second model of hemodynamic parameters that is independent of the fluid responsiveness parameters (SPV, PPV), determining (2630) a combined model based on the first model, the second model and the determined reliabilities (QI) of the determined fluid reactivity parameters (SPV, PPV), and The hemodynamic parameters are determined (2640) by applying the combined model.

11. A computer program for determining a patient's fluid responsiveness parameters (SPV, PPV), wherein: The program comprises instructions which, when the program is run by a processor, cause the processor to perform the steps of the method (200) according to claim 9.

12. A computer program for determining a hemodynamic parameter (SV) related to a fluid responsiveness parameter (SPV, PPV), wherein: The program includes instructions that cause a processor to perform the steps of the method (2600) according to claim 10 when the program is executed by the processor.

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