METHOD FOR DETERMINING A PATIENT'S BLOOD PRESSURE VALUE, BLOOD PRESSURE MONITOR AND DIALYSIS SYSTEM

Description

Technical field

[0001] The present invention relates to a method for determining a patient's blood pressure and a corresponding blood pressure measuring device. The invention further relates to a dialysis system comprising such a blood pressure measuring device. State of the art

[0002] Dialysis devices for performing hemodialysis are known from the prior art, in which a patient's blood is passed through a dialyzer unit in an extracorporeal circuit and thus purified of unwanted substances and a reduction of body water is carried out.

[0003] In hemodialysis, substances and fluids are exchanged in the dialyzer unit along a semipermeable membrane, also called a dialyzer, by diffusion using respective concentration gradients between the patient's blood and a suitably designed dialysate.

[0004] Furthermore, dialysis devices for performing hemofiltration are known in which substances and fluid volume are removed from the blood in an extracorporeal circuit by means of a semipermeable membrane of the dialyzer subjected to a pressure gradient. To compensate for the increased removal of fluid volume, salts, and other substances from the blood after passing through the dialyzer, which is caused by the pore size of the membrane, a replacement fluid is typically added to the blood after it has passed through the dialyzer.

[0005] A combination of the two methods is also known, which is then called hemodiafiltration.

[0006] During dialysis, water, especially plasma water, is removed from the patient, which can affect the patient's cardiovascular system, particularly by reducing blood volume.

[0007] Intradialytic hypotension is considered one of the most frequent complications of hemodialysis. It can lead to nausea, vomiting, headache, dizziness, cramps, fatigue, pallor, cold sweats, and / or loss of consciousness, and requires appropriate nursing intervention. One cause can be excessive or rapid fluid removal from the patient's blood and / or insufficient refilling of replacement fluid into the bloodstream.

[0008] A decrease in systolic blood pressure and / or diastolic blood pressure and / or a decrease in mean arterial blood pressure can be used as an indicator of intradialytic hypotension.

[0009] In conventional dialysis machines, blood pressure values, particularly systolic blood pressure, are typically measured intermittently, especially hourly, using a cuff-based, non-invasive blood pressure monitor via oscillometric measurement. However, because this is a non-continuous method and an acute drop in blood pressure can occur rapidly, for example within 10 minutes, such a measurement method is not well-suited for the early and reliable detection of intradialytic hypotension.

[0010] From KACHUEE MOHAMMAD ET AL: "Cuffless Blood Pressure Estimation Algorithms for Continuous Health-Care Monitoring", IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, IEEE SERVICE CENTER, PISCATAWAY, NJ, USA, Vol. 64, No. 4, April 1, 2017 (2017-04-01), pages 859-869, XP011642867, ISSN: 0018-9294, DOI: 10.1109 / TBME.2016.2580904, a method for cuffless monitoring of a measured blood pressure is known, whereby physiological parameters are extracted from signals of a photoplethysmograph.

[0011] Direct blood pressure monitoring using a cuff is known from EP 3 427 651 A1. Furthermore, GB 2 552 455 A discloses a method for measuring blood pressure using a reflected pressure wave based on a dicrotic notch. WO 2015 / 092753 A1 also discloses a method for determining blood pressure based on pulse wave parameters. Description of the invention

[0012] Starting from the known state of the art, it is an object of the present invention to provide an improved method for determining a patient's blood pressure value, as well as a corresponding blood pressure measuring device for a dialysis system, which in particular enable continuous and sustained monitoring of the patient's blood pressure value and can be implemented cost-effectively.

[0013] The problem is solved by a method for determining a patient's blood pressure value with the features of claim 1, a blood pressure measuring device with the features of claim 8, and a dialysis system with the features of claim 11. Advantageous embodiments are described in the dependent claims, the description, and the figures.

[0014] Accordingly, a method for determining a patient's blood pressure is proposed, comprising a step of ascertaining the patient's pulse waveform, in particular a time-dependent pulse waveform, and a step of determining a reference point in the pulse waveform during a transition from systole to diastole of a cardiac cycle. The blood pressure value is then determined based on this determined reference point.

[0015] By determining blood pressure based on a measured pulse pattern, the proposed method allows for continuous blood pressure monitoring over extended periods, such as throughout an entire dialysis treatment. Furthermore, this method is less complex and requires less effort compared to the oscillometric measurement methods used in conventional dialysis devices, which employ cuff-based blood pressure monitors.

[0016] Determining a patient's blood pressure based on the pulse method is made possible by the proposed procedure of identifying a reference point within the pulse waveform, which allows for a clear and reliable correlation with a corresponding blood pressure value. In other words, a unique blood pressure value can be reliably determined based on this reference point.

[0017] More precisely, the determination of a reference point is proposed, which indicates a transition range from systole to diastole of a cardiac cycle of the patient.

[0018] Generally, the terms "systole" and "diastole" refer to different phases of the cardiac cycle. More precisely, systole is the phase in which the heart muscle contracts, pumping blood from the ventricles into the circulatory system. Diastole, on the other hand, describes the relaxation phase of the heart, during which blood flows into the ventricles. The transition between systole and diastole is also known as the incisura, which corresponds to the point at which the aortic valve, also called the semilunar valve, closes.

[0019] The time interval during which the aortic valve closes can be identified in a pulse waveform by observing a brief rise in the pulse waveform due to hydrodynamic effects such as the elasticity of the vessel walls or a Windkessel effect. In this way, the incisura can be detected in a healthy heart in the region between systole and diastole.

[0020] As previously described, the reference point to be determined lies in the transition zone between systole and diastole of a patient's cardiac cycle. The transition zone between systole and diastole is understood here as the area in the pulse waveform where the phase transition from systole to diastole of the patient's cardiac cycle occurs. In other words, this area contains the incisura of the cardiac cycle.

[0021] As its name suggests, the reference point provides a unique reference point for the pulse pattern of a cardiac cycle, enabling, in particular, a comparison of pulse patterns between different cardiac cycles of the same patient. Accordingly, the reference point can be a mathematically definable point in the pulse pattern, especially in the transition zone of the pulse pattern.

[0022] By placing the reference point in the transition zone between systole and diastole of the cardiac cycle, it can be ensured that the reference point is at least approximately aligned with, or connected to, the incisure. In other words, the reference point can be temporally located within the timeframe of the incisure of the cardiac cycle or coincide with it as closely as possible.

[0023] In the proposed method, the transition zone from systole to diastole of the patient's cardiac cycle is positioned between a local minimum and a local maximum in the pulse waveform. Specifically, the transition zone extends between the local minimum and the local maximum.

[0024] To define the transition region, the procedure can further include a step of determining the local minimum and the local maximum. This step can be performed depending on the rate of change of the determined pulse waveform. The rate of change of the pulse waveform corresponds to a first derivative of the pulse waveform, where the local minimum and the local maximum of the pulse waveform have a rate of change of zero. In other words, the local minimum and the local maximum in the pulse waveform can be determined by setting the rate of change to zero.

[0025] The method proposed here can be used to determine and monitor a patient's blood pressure during dialysis treatment, particularly during hemodialysis. Accordingly, the method can be used in conjunction with a dialysis machine. However, the proposed method is not limited to this application. Rather, it can be used in any application where determining a patient's blood pressure is necessary or required.

[0026] More precisely, the procedure may be designed to determine systolic blood pressure. Generally, "systolic blood pressure" refers to the maximum blood pressure value during one cardiac cycle.

[0027] Alternatively or additionally, the procedure can be designed to determine mean arterial pressure as the blood pressure value. The term "mean arterial pressure" generally refers to the average value of a blood pressure curve over time, particularly over a cardiac cycle.

[0028] Alternatively or additionally, the procedure can be used to determine diastolic blood pressure. Generally, "diastolic blood pressure" refers to the minimum blood pressure value during one cardiac cycle.

[0029] The blood pressure value to be determined can be an absolute value. Alternatively, the blood pressure value to be determined can be a relative value, specifically in relation to a reference blood pressure. By providing the blood pressure value to be determined in the form of a relative value, a change in the blood pressure value can be indicated by the procedure. The blood pressure reference value can, for example, correspond to a blood pressure value in a previous cardiac cycle. For instance, the blood pressure reference value can correspond to a blood pressure value at the start of monitoring or at the beginning of a medical treatment procedure, particularly a dialysis procedure.

[0030] As previously described, the procedure includes the step of determining the patient's time-dependent pulse pattern. Generally, the term "pulse" refers to the mechanical effects of the pressure and volume fluctuations in the body's circulatory system resulting from systolic blood ejection. These varying mechanical effects are reflected in the frequency, amplitude, and course of the pressure pulses. In this context, "pulse pattern" can be understood as the temporal progression of the pulse amplitude at a specific location on the body, for example, in the patient's arm.

[0031] The pulse pattern can be determined in such a way that it at least partially indicates one of the patient's cardiac cycles. Alternatively, the pulse pattern can be determined in such a way that it indicates at least one cardiac cycle, preferably several, especially consecutive, cardiac cycles. The determination of the pulse pattern can be continuous, particularly without interruptions. The pulse pattern determined by the method can accordingly depict a continuous and / or steady pulse, especially pulse amplitude. Alternatively or additionally, the determination of the pulse pattern can be intermittent, particularly in interrupted time intervals.

[0032] In a further development, the pulse pattern can be recorded based on time- and volume-dependent blood flow values ​​in a tissue segment of the patient. This can be done using photoplethysmography. The term "photoplethysmography" generally refers to an optical measurement technique for determining the volume change of an organ, a perfused tissue segment, or a blood vessel, which depends on the blood pressure wave occurring in the circulatory system. Typically, light in the red or infrared wavelength range is shone into living tissue using an emitter, and the degree of light absorption is measured by a detector, which provides a volume-dependent measurement based on the change in light absorption. In other words, the absorption rate of the tissue increases with systole and decreases with diastole, so that the measured light absorption allows for the measurement of the blood volume pulse.

[0033] Light absorption can be measured more precisely using a photoplethysmographic sensor, such as a pulse oximeter. A distinction can be made between sensors that determine light absorption using light transmitted through the tissue or light reflected from the tissue. This can be performed on a well-vascularized tissue section of the patient, for example, an arm (especially the forearm), a finger, a toe, or an earlobe.

[0034] In a further development, the pulse pattern can be normalized. For this purpose, the procedure can include an additional step of normalizing the determined or measured pulse pattern. This allows for an improvement in the accuracy of the blood pressure reading.

[0035] For example, the measured pulse waveform can be normalized based on an amplitude, particularly a maximum amplitude within a cardiac cycle. Accordingly, the pulse waveform can be an amplitude-normalized pulse waveform. In this way, the susceptibility of the measured pulse waveform to amplitude fluctuations can be minimized.

[0036] Alternatively or additionally, the pulse rate can be time-normalized. For example, the pulse rate can be normalized by a specific cardiac cycle duration or period. Time normalization by cardiac cycle duration can eliminate the effect of heart rate variation on determining the reference point.

[0037] As described above, the reference point can be a mathematically determinable, and in particular, uniquely determinable point in the pulse waveform. The rate of change of the pulse waveform can be used to determine the reference point. In other words, the reference point is determined based on the rate of change of the pulse waveform. Thus, the reference point will be determined depending on the previously described local minimum and maximum in the pulse waveform, which can be uniquely determined via the rate of change of the pulse waveform.

[0038] Alternatively or additionally, the reference point can be determined based on a derivative of the rate of change of the pulse waveform. The derivative of the rate of change corresponds to a second derivative of the pulse waveform.

[0039] According to the invention, the reference point is determined based on an inflection point in the pulse waveform and corresponds to the inflection point in the pulse waveform. Generally, an inflection point of a curve is understood to be a point at which the curve changes its curvature. To determine the inflection point, the second derivative of the pulse waveform can be set to zero, whereby the value of a third derivative of the pulse waveform at the inflection point must be non-zero. The inflection point corresponding to the reference point has a positive rate of change or slope to ensure that the reference point lies within the transition region extending between the local minimum and the local maximum.

[0040] The following section explains in more detail the step of determining the blood pressure value based on the reference point.

[0041] The step of determining the blood pressure value is based on a time point and the amplitude of the reference point. Specifically, the blood pressure value is determined by calculating the ratio of the time point to the amplitude.

[0042] Blood pressure is determined using a mathematical model or function. Accordingly, the procedure also includes a step of providing the mathematical model or function.

[0043] The mathematical model or function is designed to determine the blood pressure value as an output variable, depending on at least one input variable comprising the time and / or the amplitude of the reference point. Accordingly, the blood pressure value can be expressed as a function of the time and amplitude of the reference point according to at least one of the following equations: BD n = F 1 t RP _ n , BD n = F 2 h RP _ n , BD n = F 3 t RP _ n h RP _ n , where BD n displays the blood pressure value for the cardiac cycle n; F each refers to a mathematical model or a mathematical function; t RP_n the time of the reference point RP for the cardiac cycle n; and h RP_n indicates the amplitude of the reference point RP for the cardiac cycle n.

[0044] As described above, the blood pressure value is determined based on a quotient formed from the time and the amplitude. Accordingly, the blood pressure value can be expressed as a function of this quotient as follows: BD n = F t RP _ n h RP _ n

[0045] The mathematical function can, in particular, be a linear function. Accordingly, the above equations (1), (2) and (4) can be expressed as follows: BD n = c 1 + m 1 × t RP _ n , BD n = c + m 2 × h RP _ n , BD n = c + m 3 × t RP _ n h RP _ n , where c represents a shift constant of the linear functions; and m represents a slope of the linear functions.

[0046] Alternatively, the mathematical function can be a polynomial function, in particular a polynomial function of the second degree or a higher degree.

[0047] The step of providing the mathematical function can be used, in particular, to derive the mathematical function or model based on measured blood pressure values ​​and corresponding pulse curves, or to adapt an existing mathematical function or model. Such an adaptation of the mathematical function or model can also be referred to as calibration.

[0048] More precisely, the step of providing the mathematical function can include a sub-step of providing at least two data sets. Each data set can contain a measured blood pressure value and a corresponding time and / or amplitude of the reference point. The measured blood pressure value can, for example, be measured oscillometrically using a cuff-based, non-invasive blood pressure monitor and assigned to a determined reference point. The corresponding reference point can be based, in particular, on a pulse curve linked to the time of the blood pressure measurement. The measured blood pressure value and the corresponding reference point thus constitute a data set as described above and can be combined as such.

[0049] In a further step, the mathematical function can then be determined or derived based on the provided data sets. Determining or deriving the mathematical function based on the provided data sets can be done, in particular, by means of interpolation or regression, especially linear regression, or by means of any method for determining a polynomial function based on the corresponding data sets. Such methods for determining or deriving a mathematical function based on the corresponding data sets are known to those skilled in the art and are therefore not explained in more detail in this disclosure.

[0050] In a further development, the procedure can include a step of issuing a warning signal. In this step, the warning signal can be issued when the measured blood pressure reaches a predefined threshold. The predefined threshold can be set in relation to a blood pressure value from a previous cardiac cycle, particularly at the beginning of a medical treatment, such as dialysis. If the blood pressure value to be determined is a systolic blood pressure value, the threshold can be set by subtracting a value of approximately 15 or 20 mmHg from the blood pressure value of a previous cardiac cycle.

[0051] In the case that the blood pressure value to be determined is a diastolic blood pressure value, the cutoff value may be set by subtracting the blood pressure value of a preceding cardiac cycle with a value of essentially 15 or 20 mmHg.

[0052] In the case that the blood pressure value to be determined corresponds to a mean arterial pressure value, the cutoff value may be set by subtracting the blood pressure value of a preceding cardiac cycle with a value of essentially 7.5 or 10 mmHg.

[0053] Furthermore, a blood pressure measuring device for determining a patient's blood pressure is proposed. The blood pressure measuring device can be designed to perform the procedure described above. The technical features described in connection with the preceding procedure are therefore considered disclosed for the blood pressure measuring device, and vice versa.

[0054] The blood pressure monitor includes a measuring unit for determining the patient's pulse rate. Furthermore, the blood pressure monitor includes a control unit for determining a reference point in the pulse rate during the transition from systole to diastole of a cardiac cycle, and for determining the blood pressure value based on this determined reference point.

[0055] The blood pressure monitor may be intended for measuring blood pressure during dialysis treatment, but its use is not limited to this application. In particular, the blood pressure monitor may be integrated into a dialysis system and communicate with a dialysis machine. Accordingly, the blood pressure monitor may include an interface for communication with a dialysis machine or another device for the exchange, especially bidirectional, of information, particularly measured or specified values.

[0056] The basic structure and function of a dialysis machine or system are known to those skilled in the art and are not explained in detail in the present disclosure. Rather, the focus is on technical features of the blood pressure monitor that are related to the present invention.

[0057] The measuring unit of the blood pressure monitor may be designed to record the pulse rate based on time- and volume-dependent blood flow values ​​in a tissue segment of the patient, particularly by means of photoplethysmography. The measuring unit may therefore be a photoplethysmographic measuring unit, in particular a pulse oximeter. Furthermore, the measuring unit may be designed to be detachably attached to a well-perfused tissue segment of the patient. For example, the measuring unit may be designed to be attached to an arm, in particular the forearm, a finger, a toe, and / or an ear of a patient. Accordingly, the measuring unit may comprise a wristband, a finger clip, a toe clip, and / or an ear clip.

[0058] The blood pressure monitor can be designed for continuous monitoring of a patient's pulse. Based on this, the monitor can determine at least one blood pressure reading for each recorded cardiac cycle. This is done using a reference point determined by the control unit, which can be established for each recorded cardiac cycle. In this way, continuous blood pressure monitoring can be ensured, particularly during medical treatment.

[0059] To determine the blood pressure value based on a specific reference point, the blood pressure monitor can use a mathematical model or function that, using the reference point as input, outputs the blood pressure value. This mathematical model or function can be stored in a memory unit within the blood pressure monitor. The control unit can then access this memory unit and the stored mathematical model or function to calculate the blood pressure value based on the specific reference point.

[0060] In a further development, the control unit can be configured to determine the function to be stored in the memory unit and / or to adapt a function already stored in the memory unit. This can be done based on measurement data or data sets provided by the control unit. The data sets can each include a measured blood pressure value and a corresponding reference point, in particular a corresponding time and / or amplitude of the reference point. The data sets can be provided on a patient-specific basis. In this way, the determination of patient-specific mathematical models or functions for calculating the blood pressure value can be ensured. The data sets are preferably provided in such a way that the measured blood pressure values ​​were recorded at a predefined body part, in particular at the same body part of the patient each time.

[0061] In one embodiment, blood pressure values ​​measured on the patient can be transmitted to the control unit of the blood pressure monitor via the interface. Based on this, the control unit can be configured to assign a pulse waveform of a cardiac cycle and / or a reference point within the pulse waveform to each measured blood pressure value, in order to generate at least two data sets in which, in particular, measured blood pressure values ​​are assigned to corresponding reference points. Based on the data sets thus determined, the control unit can then calculate the mathematical function, in particular by means of an interpolation or regression method, for example, a linear regression method.

[0062] Alternatively, previously generated data sets can be transmitted to the blood pressure monitor via the interface. For example, the data sets can be generated by a device connected to the blood pressure monitor, such as a dialysis machine. In this case, the blood pressure monitor can transmit the time-dependent pulse curve to this device via the interface. The mathematical function itself can also be transferred to the blood pressure monitor and stored in its memory unit. Accordingly, the mathematical function can be provided or derived by the device connected to the blood pressure monitor.

[0063] To generate the measured blood pressure values, the device connected to the blood pressure monitor, such as a dialysis machine, may include a further blood pressure monitor specifically designed for measuring blood pressure. This further blood pressure monitor could, for example, be a cuff-based, non-invasive blood pressure monitor that oscillometrically measures a patient's blood pressure at regular intervals, such as every 10 minutes.

[0064] In a further development, the blood pressure monitor can include a warning signal unit that can be configured to issue a warning signal when the blood pressure reading determined by the control unit reaches a predefined limit. The warning signal can be a visual and / or audible signal, in particular an alarm signal. Specifically, the predefined limit can be set in relation to a blood pressure reading from a previous cardiac cycle, for example, at the start of medical treatment or dialysis. In this way, the blood pressure monitor can, for example, indicate intradialytic hypotension occurring during dialysis treatment.

[0065] Accordingly, the proposed blood pressure monitor can be configured to diagnose intradialytic hypotension. In response to the warning signal issued by the blood pressure monitor, the dialysis machine can counteract a further drop in the patient's blood pressure. To this end, the dialysis machine can stop ultrafiltration and thus further water removal from the patient's blood. Alternatively or additionally, the dialysis machine can position the patient in a stable position, for example, the so-called Tendelenburg position. Alternatively or additionally, in response to the warning signal, medical personnel can be informed and / or a blood pressure measurement can be initiated to validate the drop in blood pressure.

[0066] Furthermore, a dialysis system is proposed that includes a blood pressure monitor as described above. The technical features described above in connection with the blood pressure monitor are therefore also considered disclosed for the dialysis system. The dialysis system preferably further comprises a dialysis machine, in particular for performing hemodialysis, hemofiltration, or hemodiafiltration. Brief description of the characters

[0067] Preferred further embodiments of the invention are explained in more detail by the following description of the figures. These show: Figure 1: A dialysis system comprising a blood pressure monitor for determining a patient's blood pressure value based on a measured pulse waveform; Figure 2: A diagram illustrating the pulse waveform measured by the blood pressure monitor; Figure 3: A flowchart illustrating a procedure performed by the blood pressure monitor to determine the patient's blood pressure value; Figure 4: A diagram illustrating a normalized pulse waveform of one cardiac cycle of the patient; Figure 5: A diagram illustrating a correlation between measured blood pressure values ​​and determined reference points; and Figure 6: A diagram illustrating an average systolic blood pressure waveform of a patient during hemodialysis. Detailed description of preferred embodiments

[0068] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are designated with identical reference numerals, and repeated descriptions of these elements are sometimes omitted to avoid redundancy.

[0069] Figure 1 Figure 10 schematically shows a dialysis system 10 for performing hemodialysis on a patient. The dialysis system 10 comprises a dialysis machine 12 and a blood pressure monitor 14 for determining a patient's blood pressure based on a measured pulse rate.

[0070] The blood pressure monitor 14 includes a wristband 16 that can be detachably attached to the patient's forearm or upper arm during dialysis treatment. The wristband 16 is equipped with a measuring unit 18, a control unit 20, a storage unit 22, a warning signal unit 24, and a radio interface 26 for data exchange with a complementary radio interface 28 on the dialysis machine 12.

[0071] The measuring unit 18 is designed to measure the patient's pulse rate over time. Measuring unit 18 is intended for non-invasive pulse measurement. For example, measuring unit 18 can be a photoplethysmographic unit that uses photoplethysmography to measure time- and volume-dependent blood flow values ​​in a tissue section of the patient and uses this data to determine the patient's pulse rate.

[0072] A pulse pattern of the patient, determined using measuring unit 18, is shown in the Figure 2 The diagram shown illustrates the amplitude of a patient's pulse over the duration of three cardiac cycles. The abscissa of the diagram represents the duration and the ordinate the amplitude of a signal recorded by measuring unit 18.

[0073] The control unit 20 is configured to process the data measured by the measuring unit 18. More precisely, the control unit 20 is configured to determine a reference point RP in the pulse waveform during a transition zone ÜB between systole and diastole of a cardiac cycle of the patient and to determine a blood pressure value for the patient based on the determined reference point.

[0074] Alternatively or in addition to the arrangement of the photoplethysmographic measuring unit in the bracelet described here, the photoplethysmographic measuring unit can also be arranged in an ear clip, finger clip or toe clip.

[0075] The following describes a procedure for determining blood pressure values ​​carried out by the control unit 20 of the blood pressure measuring device 14 with reference to Figure 3 explained in more detail.

[0076] In a first step S1 of the procedure, a signal indicating the patient's pulse pattern is determined by the measuring unit 18 and transmitted to the control unit 20. To eliminate high-frequency interference, the control unit 20 first performs a low-pass filtering, for example for a frequency range of 20 Hz, in a step S2 to reduce the in Figure 2 to determine the pulse curve shown. Subsequently, the control unit 20 calculates a first and second derivative of the pulse curve in step S3, which is displayed in Figure 2 are illustrated and are used to determine the reference point RP.

[0077] In a further step S4, the control unit 20 is configured to identify pulse curves within the pulse history that are associated with different heart cycles or with different heart cycles, and to extract them for further processing. For this purpose, the control unit 20 can be configured to determine a start and an end point for each pulse curve.

[0078] The subsequent steps S5 to S7 are then performed for each detected pulse curve or for the pulse profile of each detected cardiac cycle.

[0079] In step S5, an offset elimination is performed for each individual pulse waveform before an amplitude- and time-dependent normalization of the individual pulse waveforms is carried out in step S6. For this purpose, a maximum amplitude and a cardiac cycle duration or cardiac period are first determined for each individual pulse waveform. Subsequently, the amplitude of an individual pulse waveform is normalized by the corresponding maximum and the width of the pulse waveform by the corresponding cardiac cycle duration, in order to generate a value for each of the detected cardiac cycles as described in [reference to relevant section]. Figure 4 to determine the illustrated standardized pulse pattern. More precisely, it shows Figure 4 a normalized pulse curve for a cardiac cycle, where the abscissa represents normalized duration values ​​and the ordinate represents normalized amplitude values.

[0080] In a further development, patient-dependent parameter determination can be performed. The patient-specific parameters to be used can be transferred to the control unit 20, for example from a patient file or a patient card, which can be recorded in particular using the dialysis machine 12 and transmitted to the control unit 20.

[0081] Starting with the standardized pulse waveform, a reference point RP is then determined in step S7 within the pulse waveform for each cardiac cycle. In this case, the reference point RP is a mathematically unique point in the pulse waveform within a transition zone ÜB between systole and diastole of a cardiac cycle of the patient. The transition zone is defined in Figure 4The reference point RP is illustrated and extends between a local minimum and a local maximum in the pulse waveform. More precisely, the reference point RP corresponds to an inflection point in the pulse waveform that exhibits a positive rate of change or slope. To determine the inflection point, the control unit 20 uses the calculated second derivative of the pulse waveform. In other words, the control unit 20 determines the reference point based on the second derivative of the pulse waveform. Specifically, the control unit 20 can be configured to determine a point between the local minimum and the local maximum for which the second derivative is zero.

[0082] For the specified reference point RP, a time of the reference point, an amplitude height and a quotient formed therefrom are then determined for each of the identified cardiac cycles, which are subsequently referred to as reference parameters.

[0083] In step S8, an average value for the reference parameters is then determined for the identified, consecutive cardiac cycles. This can be done continuously within the procedure. For example, the control unit 20 can be configured to determine an average value for the reference parameters based on three cardiac cycles.

[0084] In a next step, S9, the control unit 20 determines a systolic blood pressure value based on at least one of the following three linear functions: SBP = c + m 1 × t ¯ SBP = c 2 + m 2 × h ¯ , SBP = c + m 3 × t ¯ h ¯ , where SBP displays the systolic blood pressure value; c displays a shift constant of the linear functions; m displays a slope of the linear functions; t displays the averaged time of the reference point, for example over two to 20 cardiac cycles, preferably five to 20 cardiac cycles; and hThe average amplitude height of the reference point is displayed, for example, over two to 20 cardiac cycles, preferably five to 20 cardiac cycles.

[0085] It is also possible to work with a moving average, where a window size for the selected parameter is chosen depending on the desired or required accuracy of the procedure.

[0086] Alternatively, in step S9, the control unit 20 can determine a mean arterial blood pressure value based on the determined reference parameters using a mathematical function.

[0087] The linear functions are preferably stored in the memory unit 22 of the blood pressure monitor 14. Alternatively to the functions mentioned above, at least one second-degree or higher-degree polynomial function can be used to determine the blood pressure value.

[0088] In the dialysis system 10 shown here, the dialysis machine 12 is configured to derive and / or adjust the functions described above for calculating the patient's blood pressure during operation. Alternatively, the control unit 20 of the blood pressure monitor 14 can be configured to derive and / or adjust the functions described above for calculating the patient's blood pressure during operation. This is done on the basis of data sets provided by the dialysis machine, each containing a measured blood pressure value with an associated reference point, in particular the associated reference parameters.

[0089] To generate the measured blood pressure values, the dialysis machine 12 includes an additional blood pressure monitor 30. More precisely, the additional blood pressure monitor 30 is a cuff-based, non-invasive blood pressure monitor that oscillometrically measures a patient's blood pressure at regular intervals, for example, every 10 minutes or hourly, during dialysis treatment. For this purpose, a cuff 32 is attached to the patient's arm, using which the patient's systolic and / or diastolic blood pressure value is determined.

[0090] The dialysis machine 12 is configured to assign a corresponding reference point and the corresponding reference parameters of the reference point to each measured blood pressure value, thereby generating a data record. For this purpose, the control unit 20 is configured to transmit the corresponding reference parameters to the dialysis unit 12 at the respective times of the blood pressure measurements taken, using the additional blood pressure monitor 30. The data records generated in this way are stored in a further storage unit 34 within the dialysis machine 12.

[0091] Figure 5The diagram illustrates data sets generated in this way. The data sets comprise a measured blood pressure value and a corresponding calculated reference quotient, represented as points in the diagram. The reference quotient relates a time point to the amplitude of a reference point. Accordingly, the abscissa displays a value for the reference quotient and the ordinate a value for the measured blood pressure value.

[0092] Based on the data records stored in the further storage unit 34, the dialysis unit 12 is configured to perform the mathematical functions, in particular the coefficients c and m 1-3 of the above equations (8), (9) and (10) are to be determined using linear regression. With regard to equation (10), the result of this procedure step is to be expressed as a linear function in the Figure 5 The diagram shown illustrates this.

[0093] After the mathematical functions have been determined or adjusted, the coefficients c and m 1-3 of the above equations (8), (9) and (10) are transmitted via the radio interfaces 26 and 28 to the blood pressure monitor 14 and stored in its memory unit 22. In this way, it is ensured that the control unit 20 calculates the blood pressure values ​​based on the mathematical functions determined or adapted by the dialysis machine 12.

[0094] The dialysis machine 12 is set up to calibrate or adjust the mathematical functions, especially the coefficients, at regular and predefined intervals, for example every three or four weeks. c 1-3 and m 1-3. Furthermore, the dialysis machine 12 is configured to perform the determined coefficients. c 1-3 and m 1-3 , to be transmitted to the blood pressure monitor 14 before the start of dialysis treatment.

[0095] Alternatively or additionally, the mathematical functions can also be adapted and determined and transferred to the blood pressure monitor 14 during dialysis treatment. Figure 6 The diagram illustrates the average course of a patient's systolic blood pressure during hemodialysis. The x-axis represents the time course, and the y-axis represents the systolic blood pressure. It shows that the systolic blood pressure drops particularly sharply during the first 30 minutes of dialysis treatment. This provides an opportunity to collect suitable data sets at the beginning of dialysis treatment for the adaptation or derivation of mathematical functions. Based on this data, mathematical functions can then be adapted or provided, which can subsequently be used to determine blood pressure values ​​during the remainder of the treatment.

[0096] In an alternative configuration, the blood pressure monitor 14 and the additional blood pressure monitor 30 can be arranged in a single wristband or cuff. This ensures that both blood pressure monitors take measurements at the same location on the patient's body, thus improving patient comfort. The blood pressure monitor 14 can be configured to take a blood pressure reading before and after a measurement taken by the additional blood pressure monitor 30.

[0097] The blood pressure monitor 14 further includes the warning signal unit 24 for issuing a warning signal. The warning signal unit 24 is configured to issue the warning signal when the blood pressure value determined by the control unit 20 reaches or falls below a predetermined limit. More precisely, the warning signal unit 24 is configured to issue the warning signal when the control unit 20 determines that, during the course of dialysis treatment, a blood pressure measurement determined by the control unit 20 falls below a value determined or measured at the beginning of the dialysis treatment by at least 15 or 20 mmHg. In other words, in this configuration, the limit refers to an absolute change in the determined blood pressure measurement relative to the measurement at the beginning of the dialysis treatment. Alternatively, the limit can also refer to a relative change in the determined blood pressure measurement relative to the measurement at the beginning of the dialysis treatment.

[0098] The warning signal unit 24 is configured to issue a visual and an audible alarm in response to the generated warning signal. Furthermore, the warning signal unit 24 is configured to transmit the generated warning signal to the dialysis machine 12 via the radio interface 26. In response to the warning signal, the dialysis machine 12 may be configured to perform a blood pressure measurement using the additional blood pressure monitor 30. Alternatively or additionally, the dialysis machine may, in response to the warning signal, initiate a change in the patient's position, in particular into the so-called Tendelenburg position. Alternatively or additionally, the dialysis machine may, in response to the warning signal, request medical personnel. Alternatively or additionally, the dialysis machine 12 may, in response to the warning signal, interrupt the ultrafiltration process of the patient's blood.

[0099] In a further development, the warning signal unit 24 can be configured to issue a two-stage warning signal. In this configuration, the warning signal unit 24 can issue a first warning signal if the measured blood pressure falls below the blood pressure value determined or measured at the start of the dialysis treatment by a value between 15 and 20 mmHg. Furthermore, the warning signal unit 24 can issue a second warning signal if the measured blood pressure value determined during the dialysis procedure falls below the blood pressure value determined or measured at the start of the dialysis treatment by at least 20 mmHg.

[0100] In one embodiment, the dialysis machine 12 can be configured to first perform a measurement with the additional blood pressure monitor 30 upon receiving the warning signal. Only if this measurement also shows that the measured blood pressure value has reached the limit value is an alarm signal issued, in particular to the medical treatment staff, and / or the ultrafiltration is interrupted and / or a change in the patient's position is initiated.

[0101] In a further development, the dialysis machine 12 can be configured to control an ultrafiltration process performed by the dialysis machine 12 based on the blood pressure measurements determined by the blood pressure measuring unit 14 and transmitted to it via the radio interfaces 26, 28. The transmitted blood pressure measurements can serve as input for a closed control loop to regulate the ultrafiltration rate during the ultrafiltration process.

[0102] Where applicable, all individual features shown in the exemplary embodiments can be combined and / or exchanged without leaving the scope of the invention. Reference symbol list

[0103] 10 Dialysis system 12 Dialysis machine 14 Blood pressure monitor 16 Wristband 18 Measuring unit 20 Control unit 22 Storage unit 24 Warning signal unit 26 Wireless interface of the blood pressure monitor 28 Wireless interface of the dialysis machine 30 Additional blood pressure monitor 32 Cuff 34 Additional storage unit

Claims

1. Method for determining a blood pressure value of a patient, comprising the steps: - detecting a non-invasive measurement of a pulse of the patient and determining a pulse wave of the patient by means of a measuring unit (18); - determining, by means of a controller (20), a reference point (RP) in the pulse wave in a transitional region (ÜB) from the systole to the diastole of a cardiac cycle of the patient, wherein the reference point (RP) is a turning point having a positive rate of change or gradient between a local minimum and a local maximum; and - determining, by means of the controller (20), the blood pressure value on the basis of the determined reference point (RP), characterized in that the determining is performed based on a provided mathematical function which correlates a quotient formed from the time point (t) and the amplitude (h) of the reference point (RP) as the input variable to a blood pressure value as the output variable.

2. Method according to claim 1, wherein the blood pressure value corresponds to a systolic and / or a diastolic and / or an mean arterial blood pressure value.

3. Method according to claim 1 or 2, wherein the pulse wave is recorded on the basis of time and volume-dependent blood flow values in a tissue section of the patient, in particular by means of photoplethysmography.

4. Method according to any one of claims 1 to 3, wherein the pulse wave is normalized in amplitude and / or time, in particular normalized in cardiac cycle duration.

5. Method according to any one of the preceding claims, wherein the mathematical function is a linear function or a polynomial function.

6. Method according to any one of the preceding claims, wherein the step of providing the mathematical function comprises the following substeps: - providing at least two data sets, comprising a measured blood pressure value and an associated time point (t) and / or an associated amplitude (h) of a reference point (RP); and - determining the mathematical function on the basis of the provided data sets, in particular by means of an interpolation or regression method.

7. Method according to any one of the preceding claims, further comprising a step of outputting a warning signal, when the determined blood pressure value reaches a predetermined limit value, wherein in particular the predetermined limit value is set with respect to a blood pressure value of a preceding cardiac cycle, in particular at the beginning of a medical treatment.

8. Blood pressure measurement device (14) for determining a blood pressure value of a patient, comprising: - a measuring unit (18) for determining a pulse wave of the patient; and - a controller (20) for determining a reference point (RP) in the pulse wave in a transition region from the systole to the diastole of a cardiac cycle of the patient, and for determining the blood pressure value on the basis of the determined reference point (RP), wherein the controller (20) is configured to determine a turning point as a reference point (RP) that has a positive rate of change or gradient between a local minimum and a local maximum, characterized in that the control unit is configured to determine the blood pressure value further based on a provided mathematical function which correlates a quotient formed from the time point (t) and amplitude (h) of the reference point (RP) as the input variable to a blood pressure value as the output variable.

9. Blood pressure measurement device according to claim 8, further comprising an interface (26), via which blood pressure values measured in the patient are transmitted to the controller (20), wherein the controller (20) is configured to provide or adjust the mathematical function on the basis of the measured blood pressure values and an associated pulse wave.

10. Blood pressure measurement device according to claim 8 or 9, further comprising a warning signal unit (24), which is configured to output a warning signal when the blood pressure value determined by the control unit (22) reaches a predetermined limit value, wherein in particular the predetermined limit value is determined with reference to a blood pressure value of a preceding cardiac cycle, in particular at the start of a medical treatment.

11. Dialysis system (10), comprising a blood pressure measurement device (14) according to any one of claims 8 to 10.