Method for Determining a Blood Pressure Value of a Patient, Blood Pressure Monitor and Dialysis System

Abstract

The present disclosure relates to a method for determining a blood pressure value of a patient. The method comprises a step of determining a pulse course of the patient; a step of determining a reference point in the pulse course within a transition area from systole to diastole of a cardiac cycle of the patient; and a step of determining the blood pressure value based on the determined reference point.

Claims

1-16. (canceled)

17. A method for determining a blood pressure value of a patient, the method comprising: determining a pulse course of the patient; determining a reference point in the pulse course within a transition area from systole to diastole of a cardiac cycle of the patient; and determining the blood pressure value based on the reference point.

18. The method according to claim 17, wherein the transition area is disposed between a local minimum and a local maximum of the pulse course.

19. The method according to claim 17, wherein the blood pressure value corresponds to a systolic blood pressure value and/or a diastolic blood pressure value and/or a mean arterial blood pressure value.

20. The method according to claim 17, wherein the pulse course is determined based on time-based and volume-based blood flow values in a tissue section of a patient.

21. The method according to claim 20, wherein the pulse course is determined by photoplethysmography.

22. The method according to claim 17, wherein the pulse course is normalized using an amplitude and/or time as a measure of scale.

23. The method according to claim 22, wherein the time is a duration of the cardiac cycle.

24. The method according to claim 17, wherein the reference point is determined based on a rate of change of the pulse course.

25. The method according to claim 17, wherein the reference point corresponds to a point of inflection in the pulse course, and wherein at the point of inflection, the pulse course has a positive rate of change or slope.

26. The method according to claim 17, wherein the blood pressure value is determined based on a time and/or an amplitude of the reference point.

27. The method according to claim 26, further comprising providing a mathematical function for determining the blood pressure value as a function of time and/or amplitude of the reference point.

28. The method according to claim 27, wherein the mathematical function is a linear function or polynomial function which correlates, as an input variable, the time and/or the amplitude of the reference point to the blood pressure value as an output value.

29. The method according to claim 28, wherein the mathematical function correlates a quotient formed by the time and/or the amplitude of the reference point to the blood pressure value.

30. The method according to claim 27, wherein providing the mathematical function comprises: providing at least two data sets, each of which comprises a measured blood pressure value and an associated time and/or amplitude of the reference point; and determining the mathematical function on the basis of the provided data sets by an interpolation method or a regression analysis method.

31. The method according to claim 17, further comprising outputting a warning signal when the determined blood pressure value has reached a predetermined threshold value, wherein the predetermined threshold value is determined with respect to a blood pressure value of a preceding cardiac cycle at the beginning of a medical treatment.

32. A blood pressure monitor for determining a blood pressure value of a patient, comprising: a measuring unit for determining a pulse course of the patient; and a control unit for determining a reference point in the pulse course within a transition area from systole to diastole of a cardiac cycle of the patient and for determining the blood pressure value based on the determined reference point.

33. The blood pressure monitor according to claim 32, further comprising an interface, via which measured blood pressure values are transmitted to the control unit, wherein based on the measured blood pressure values, the control unit is configured for providing or adjusting a mathematical function by which the blood pressure value is determined based on the determined reference point.

34. The blood pressure monitor according to claim 33, wherein the blood pressure value is determined based on a time and/or an amplitude of the reference point.

35. The blood pressure monitor according to claim 32, further comprising an alarm unit configured for outputting a warning signal when the blood pressure value determined by the control unit has reached a predetermined threshold value, wherein the predetermined threshold value is determined with respect to a blood pressure value of a preceding cardiac cycle at the beginning of a medical treatment.

36. A dialysis system comprising a blood pressure monitor according to claim 32.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

[0067] FIG. 1 is a schematic view of a dialysis system comprising a blood pressure monitor for determining a blood pressure value of a patient on the basis of a measured pulse course;

[0068] FIG. 2 shows a diagram illustrating a pulse course measured by the blood pressure monitor;

[0069] FIG. 3 shows a flow diagram illustrating a method performed by the blood pressure monitor for determining the blood pressure value of the patient;

[0070] FIG. 4 shows a diagram illustrating a normalized pulse course of a patient's cardiac cycle;

[0071] FIG. 5 shows a diagram illustrating a correlation between measured blood pressure values and determined reference points; and

[0072] FIG. 6 shows a diagram illustrating an average course of a patient's systolic blood pressure during a hemodialysis treatment.

DETAILED DESCRIPTION

[0073] In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

[0074] FIG. 1 schematically shows a dialysis system 10 configured for performing a hemodialysis treatment on a patient. The dialysis system 10 comprises a dialysis device 12 and a blood pressure monitor 14 for determining a blood pressure value of the patient on the basis of a measured pulse course or pulse profile.

[0075] The blood pressure monitor 14 comprises a wristband 16 configured for being detachably attached to a patient's forearm or upper arm during the dialysis treatment. The wristband 16 is equipped with a measuring unit 18, a control unit 20, a memory unit 22, an alarm unit 24 and a wireless interface 26. The wireless interface 26 is configured for exchanging data with a complementary designed wireless interface 28 provided at the dialysis device 12.

[0076] The measuring unit 18 is configured to measure or determine a time-dependent pulse course of the patient. Specifically, the measuring unit 18 is configured to measure the pulse course in a non-invasive manner. For example, the measuring unit 18 may be provided in the form of a photoplethysmographic measuring unit which uses photoplethysmography to measure time- and volume-based blood flow values on a tissue section of the patient, based on which it determines the patient's pulse course.

[0077] A pulse course of the patient determined by the measuring unit 18 is illustrated in the diagram depicted in FIG. 2. Specifically, the diagram depicted in FIG. 2 illustrates the course of amplitude level of the patient's pulse over a time range of three cardiac cycles. The abscissa of the diagram depicts the time and the ordinate depicts the associated amplitude level of a signal acquired by the measuring unit 18.

[0078] The control unit 20 is configured for processing the signal and data measured by the measuring unit 18. More specifically, the control unit 20 is configured to determine a reference point RP in the pulse course, wherein the reference point RP is disposed within a transition area TA of the pulse course indicating a transition phase from systole to diastole of a cardiac cycle of the patient. Further, the control unit 20 is configured to determine a blood pressure value of the patient based on the determined reference point.

[0079] Alternatively or additionally to the shown configuration, in which the photoplethysmographic measuring unit 18 is provided in the wristband 16, the photoplethysmographic measuring unit 18 may be provided in an ear clip, a finger clip or a toe clip.

[0080] In the following, a method performed by the control unit 20 for determining blood pressure values is specified.

[0081] In a first step S1 of the method, the measuring unit 18 detects or determines a signal being indicative of the pulse course of the patient which is transmitted to the control unit 20. In a second step S2, the control unit 20 performs low-pass filtering, e.g. for a frequency in the range of 20 Hz, in order to eliminate high-frequency distortions. As a result, the pulse course or pulse curve depicted in FIG. 2 is determined. Subsequently, in a third step S3, the control unit 20 calculates a first and a second derivative or derivation of the pulse course, which are depicted in FIG. 2 and which are used for determining the reference point RP.

[0082] In a further step S4, the control unit 20 is configured to determine individual cardiac cycles or individual pulse curves associated to different cardiac cycles in the pulse course and to extract them for further processing. For doing so, the control unit 20 may be configured to determine a starting point and an end point for each pulse curve.

[0083] The subsequent steps S5 to S7 are then performed for each one of the detected pulse curves or, in other words, for the pulse curve for each one of the detected cardiac cycles.

[0084] In step S5, an offset elimination is performed for each one of the pulse curves before, in step S6, an amplitude-based and time-based normalization of the pulse curves is performed. For doing so, at first, a maximum amplitude and a cardiac cycle duration or cardiac period are determined for each one of the pulse curves. Then, the amplitude of each one of the pulse curves is normalized using the associated maximum amplitude as a measure of scale and the width of the pulse curve is normalized using the associated cardiac cycle duration as a measure of scale. In this way, a normalized pulse course is determined for each one of the cardiac cycle. Such a normalized pulse course is depicted in FIG. 4. Specifically, FIG. 4 shows a diagram illustrating a normalized pulse course for one cardiac cycle, wherein the abscissa shows normalized time duration values and the ordinate shows normalized amplitude values.

[0085] In a further development, patient-specific parameters may be determined. The patient-specific parameters may be transmitted to the control unit 20, for example, from a patient file or patient card which, e.g., may be obtained by the dialysis device 12 and may be transmitted to the control unit 20.

[0086] In the step S7, based on the normalized pulse course, a reference point RP is determined in the pulse course for each cardiac cycle. Specifically, the reference point RP refers to a mathematically definable point in the pulse course within a transition area TA being indicative of a transition phase from systole to diastole of the cardiac cycle. The transition area TA is depicted in FIG. 4 and extends between a local minimum and a local maximum of the pulse course. More specifically, the reference point RP corresponds to a point of inflection in the pulse course, at which the pulse curve has a positive rate of change or slope. For determining the point of inflection, the control unit 20 makes use of the determined second derivative of the pulse course. In other words, the control unit 20 determines the reference point RP on the basis of the second derivative of the pulse course. Specifically, for doing so, the control unit 20 may be configured to determine a point of the pulse course in an area between the local minimum and the local maximum, at which the second derivative of the pulse course equals to zero.

[0087] Then, based on the determined reference point RP, a point in time of the reference point RP, an amplitude level of the reference point RP and a quotient or ratio formed by the point in time and amplitude of the reference point RP are determined for each one of the identified cardiac cycles. Hereinafter, these parameters are referred to as reference parameters.

[0088] Thereafter, in a further step S8, an average value for each reference parameter is calculated for successive cardiac cycles. This may be performed continuously during the method. For example, the control unit 20 may be configured to calculate the average value for the reference parameters among the cardiac cycles on the basis of three successive cardiac cycles.

[0089] In the a step S9, the control unit 20 determines a systolic blood pressure value on the basis of at least one of the following three linear functions:

[00003]$\begin{array}{cc}\mathrm{SBP}=c_1+m_1\times \stackrel{\_}{t}& \left(8\right)\\ \mathrm{SBP}=c_2+m_2\times \stackrel{\_}{h},& \left(9\right)\\ \mathrm{SBP}=c_3+m_3\times \frac{\stackrel{\_}{t}}{\stackrel{\_}{h}},& \left(10\right)\end{array}$

wherein SBP refers to a systolic blood pressure value; c refers to an intercept constant of the linear functions; m refers to a slope of the linear functions; t refers to an average value of the point in time of the reference point over, for example, 2 to 20, i.e., 5 to 20, cardiac cycles; h refers to an average value of the amplitude level of the reference point over, for example, 2 to 20, i.e., 5 to 20, cardiac cycles.

[0090] Further, a moving average may be used, wherein a window size for each one of the considered parameters may be selected in dependence on a desired or required accuracy.

[0091] Alternatively, in step S9, the control unit 20 may determine a mean arterial blood pressure value on the basis of the determined reference parameters by means of a corresponding mathematical function.

[0092] The linear functions are preferably stored in a memory unit 22 of the blood pressure monitor 14. Alternatively, as regards the above described linear functions, at least one polynomial function, e.g., a polynomial of degree two or of a higher degree, may be used for determining the blood pressure values.

[0093] In the shown dialysis system 10, the dialysis device 12 is configured to derive the above described linear functions for determining the patient's blood pressure values and/or to adapt the linear functions during operation. Alternatively, the control unit 20 of the blood pressure monitor 14 may be configured to derive the above described linear functions for determining the patient's blood pressure values and/or to adapt the linear functions during operation. This may be performed on the basis of data sets provided by the dialysis device 12. Each of the data sets comprises a measured blood pressure value and an associated reference point, e.g., associated reference parameters.

[0094] In order to generate the measured blood pressure values, the dialysis device 12 comprises a further blood pressure monitor 30. Specifically, the further blood pressure monitor 30 is a cuff-based, non-invasive blood pressure monitor, which is configured to oscillometrically measure patient's blood pressure values at regular intervals during the dialysis treatment, for example every 10 minutes or hourly. For doing so, a cuff 32 of the blood pressure monitor 30 is fixed to an arm of the patient, via which a systolic and/or diastolic blood pressure value of the patient is measured.

[0095] The dialysis device 12 is configured to assign to each one of the measured blood pressure values a corresponding reference point and the corresponding reference parameter of the reference point. In this way, the data sets are generated. Specifically, the control unit 20 is configured to transmit to the dialysis device 12 the determined reference parameters which correspond to blood pressure values determined by means of the further blood pressure monitor 30. The thus generated data sets are stored in a further memory unit 34 in the dialysis device 12.

[0096] FIG. 5 shows a diagram illustrating data sets which are generated in such a way. Each one of the data sets comprises a measured blood pressure value and a corresponding reference quotient. In the diagram, the data sets are represented in the form of dots. The reference quotient refers to a ratio in which the point in time of a reference point is divided by its amplitude level. Accordingly, the abscissa of the diagram shows a value of the reference quotient and the ordinate quantifies the measured blood pressure value.

[0097] The dialysis device 12 is configured to determine the mathematical functions, i.e., the coefficients c.sub.1-3 and m.sub.1-3 of the above equations (8), (9) and (10), based on the data sets stored in the further memory unit 34 by applying a linear regression analysis method. With regards to equation (10), the result of this method step is illustrated in the diagram depicted in FIG. 5 in the form of a linear function.

[0098] Once the mathematical functions have been determined or adapted, the coefficients c.sub.1-3 and m.sub.1-3 of the above equations (8), (9) and (10) are transmitted to the blood pressure monitor 14 via the interfaces 26, 28 and stored in the memory unit 22. In this way, it can be ensured that the control unit 20 calculates the blood pressure values on the basis of the mathematical functions determined or adapted by the dialysis device 12.

[0099] The dialysis device 12 is configured to calibrate or adjust the mathematical functions, e.g., the coefficients c.sub.1-3 and m.sub.1-3, at regular and predefined intervals, for example every three or four weeks. Further, the dialysis device 12 is configured to transmit the determined coefficients c.sub.1-3 and m.sub.1-3 to the blood pressure monitor 14 before starting a dialysis treatment.

[0100] Alternatively or additionally, the step of determining and adjusting the mathematical functions as well as the step of transmitting the same to the blood pressure monitor 14 may be performed during the dialysis treatment. FIG. 6 depicts a diagram which illustrates an average course of the patient's systolic blood pressure during a hemodialysis treatment. The abscissa of the diagram shows the time and the ordinate shows the systolic blood pressure. As can be gathered from the diagram, the systolic blood pressure rapidly drops within the first 30 minutes of the dialysis treatment. Based on this finding, it may be advantageous to acquire data sets used for adapting or deriving the mathematical functions at the beginning of the dialysis treatment. These data sets then may be used to adapt or provide the mathematical functions, based on which, in the further course of the treatment, blood pressure values may be determined.

[0101] In an alternative configuration, the blood pressure monitor 14 and the further blood pressure monitor 30 may be accommodated in a single wristband or cuff. In this way, it may be ensured that both blood pressure monitors perform measurements at the same part of the patient's body. This may improve patient's comfort. Further, the blood pressure monitor 14 may be configured to determine a blood pressure value before and after a measurement performed by the further blood pressure monitor 30.

[0102] The blood pressure monitor 14 further comprises the alarm unit 24 configured for outputting a warning signal. The alarm unit 24 is configured to output the warning signal when the blood pressure value determined by the control unit 20 reaches or falls below a threshold value. More specifically, the alarm unit 24 is configured to output the warning signal when the control unit 20 determines that a blood pressure value determined by the control unit 20 during the dialysis treatment falls at least 15 or 20 mmHg below a blood pressure value determined or measured at the beginning of the dialysis treatment. In other words, in this configuration, the threshold value refers to an absolute value change of the determined blood pressure value with respect to a measurement of the blood pressure value at the beginning of the dialysis treatment. Alternatively, the threshold value may refer to a relative value change of the determined blood pressure value with respect to a measurement of the blood pressure value at the beginning of the dialysis treatment.

[0103] The alarm unit 24 is configured to generate an optical or acoustic alarm in response to the generated warning signal. Further, the alarm unit 24 is configured to transmit the generated warning signal to the dialysis device 12 via the interface 26. The dialysis device 12 may be configured to carry out a blood pressure measurement in response to the received warning signal by means of the further blood pressure monitor 30. Alternatively or additionally, the dialysis device 12 may be configured to initiate repositioning of the patient, i.e., into the so-called Tendelenburg position, in response to the received warning signal. Alternatively or additionally, the dialysis device 12 may be configured to request medical staff in response to the received warning signal. Alternatively or additionally, the dialysis device 12 may be configured to interrupt an ultrafiltration treatment in response to the received warning signal.

[0104] In a further development, the alarm unit 24 may be configured to output a two-level warning signal. In this configuration, the alarm unit 24 may be configured to output a first warning signal when the determined blood pressure value falls below the initial blood pressure value determined or measured at the beginning of the dialysis treatment by a value between 15 and 20 mmHg. Further, the alarm unit 24 may be configured to output a second warning signal when the blood pressure value determined during the dialysis treatment falls at least 20 mmHg below the initial blood pressure value determined or measured at the beginning of the dialysis treatment.

[0105] In one configuration, the dialysis device 12 may be configured to, in response to the warning signal, at first, carry out a measurement using the further blood pressure monitor 30. Only if this measurement indicates that the measured blood pressure value has reached the threshold value, an alarm signal, i.e., directed to the medical staff, is output and/or the ultrafiltration treatment is interrupted and/or a change of the patient's position is initiated.

[0106] In the further development, the dialysis device 12 may be configured to control an ultrafiltration treatment carried out by the dialysis device 12 on the basis of the blood pressure values determined by means of the blood pressure monitor 14 and transmitted thereto via the interfaces 26, 28. For doing so, the thus transmitted blood pressure values may be used as input values for a closed loop control circuit for controlling an ultrafiltration rate in the ultrafiltration treatment.

[0107] It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

List of Reference Numerals

[0108] 10 Dialysis system

[0109] 12 Dialysis device

[0110] 14 Blood pressure monitor

[0111] 16 Wristband

[0112] 18 Measuring unit

[0113] 20 Control unit

[0114] 22 Memory unit

[0115] 24 Alarm unit

[0116] 26 Wireless interface of the blood pressure monitor

[0117] 28 Wireless interface of the dialysis device

[0118] 30 Further blood pressure monitor

[0119] 32 Cuff

[0120] 34 Further memory unit