Control device for controlling a measuring system for measuring blood pressure

Abstract

The invention relates to a control device for controlling a measuring system for measuring a blood pressure and optionally a hemodynamic parameter of a subject. In a first measuring time period T1, for a measured pressure pulse, a feature is determined which characterizes the respective pressure pulse. On the basis of the feature, a starting value is determined and, on the basis of the starting value, a starting curve TPW_F-curve is formed. The measuring system is controlled such that, after the starting curve has reached a first maximum, a second measuring time period subsequently occurs, in which a blood pressure value is determined on the basis of a pressure measured in the second measuring time period. It has been found that, by using the maximum in the first measuring time period for defining a starting point for the actual blood pressure measurement, the blood pressure value and optionally the hemodynamic parameter of the subject can be determined very accurately and quickly.

Description

TECHNICAL FIELD

[0001] The present invention relates to a control device for controlling a measurement system for measuring blood pressure of a subject. The present invention further relates to a measurement system for measuring blood pressure of a subject, as well as a control method and a computer program for controlling the measurement system. BACKGROUND

[0002] DE 10 2017 110 770 B3 discloses a method for non-invasively determining a blood pressure value from a tissue pressure signal by means of a pressure cuff applied to an individual. The tissue pressure signal has a series of tissue pressure pulse curves, wherein at least two individual tissue pressure pulse curves are identified in the tissue pressure signal. For each identified tissue pressure pulse curve, an amplitude parameter and an area parameter are determined, wherein the amplitude parameter is indicative of an amplitude of the respective identified tissue pressure pulse curve and the area parameter is indicative of at least one partial area enclosed by the respective tissue pressure pulse curve. Furthermore, for each identified tissue pressure pulse curve, a pulsatility power parameter describing the respective tissue pressure pulse curve is determined based on the amplitude parameter and the area parameter. A parameter function is generated which describes a functional relationship between the determined pulsatility power parameters of the tissue pressure pulse curves and a clamping pressure assigned at a pressure cuff or a measurement time, wherein the blood pressure value is determined based on the parameter function.

[0003] US 2011 / 0152650 A1 discloses a method of operating a non-invasive blood pressure monitor having a blood pressure cuff. During operation of the non-invasive blood pressure monitor, the blood pressure cuff is initially inflated at a fast inflation rate. Once the blood pressure cuff reaches a first pressure, the inflation rate of the blood pressure cuff is reduced from the fast inflation rate to a measurement inflation rate. The blood pressure cuff continues to be inflated at the measurement inflation rate while the non-invasive blood pressure monitor receives signals from the patient. Based on the signals received from the patient, the non-invasive blood pressure monitor calculates an "initial inflation pressure" at which the blood pressure cuff is inflated to the calculated initial inflation pressure and then terminates inflation. In this way, the signals received from the patient during inflation are used to calculate the initial inflation pressure to shorten the amount of time required to take a blood pressure measurement.

[0004] EP 3 430 992 A1 discloses a blood pressure measurement system configured to surround a body part of a subject, wherein the blood pressure measurement system comprises a pressurizing device for applying pressure to the body part and an anti-twist housing. The anti-twist housing is arranged to be located between the pressurizing device and the body part when the blood pressure measurement system surrounds the body part. The blood pressure measurement system allows for a very precise measurement of blood pressure by continuously increasing the tightening pressure and stopping the rise above the systolic pressure, but it is desirable to shorten the time required for performing blood pressure measurements and optionally other measurements such as blood flow dynamics measurements. SUMMARY

[0005] It is an object of the present invention to provide a control device for controlling a measurement system for measuring a blood pressure and optionally a hemodynamic parameter of a subject, which allows to shorten the measurement time. It is a further object of the present invention to provide a measurement system for measuring a blood pressure of a subject comprising a control device, and a control method and a computer program for controlling a measurement system.

[0006] In a first aspect of the present invention, a control device for controlling a measurement system for measuring a blood pressure of a subject is presented, wherein the measurement system comprises: a) a housing configured to enclose a portion of the subject through which blood flows; b) a pressure applicator configured to apply a pressure to the housing from outside the housing, thereby applying a pressure to the enclosed portion of the subject; and c) a pressure sensor configured to measure a pressure on the skin of the enclosed portion of the subject, wherein the control device is configured to control the measurement system such that

[0007] the pressure applicator increases the applied pressure over time in a first measurement time period having a first slope and in a second measurement time period having a second slope, wherein the first measurement time period and the second measurement time period are arranged in this order in time,

[0008] the pressure sensor measures the pressure on the skin during the first measurement time period and during the second measurement time period, wherein the measured pressure comprises a plurality of pressure pulses,

[0009] wherein the control device is further configured to

[0010] determine, in the first measurement time period, for each pressure pulse of the plurality of pressure pulses at least one feature characterizing the respective pressure pulse,

[0011] determine, for the respective pressure pulse, based on the at least one feature that has been determined for the respective pressure pulse, a starting value to be used for determining the start of the second measurement time period, such that for several pressure pulses occurring at different times, several starting values are determined,

[0012] form, based on the several starting values, a starting curve to be used for determining the start of the second measurement time period,

[0013] and, after the starting curve has reached a first maximum value, control the measurement system such that the second measurement time period subsequently succeeds,

[0014] determine a blood pressure value based on the pressure measured in the second measurement time period.

[0015] It has been found that by controlling the measurement system such that after the starting curve has reached a first maximum value, a second measurement time period subsequently occurs, it is possible to very accurately define the starting point of the second measurement time period in which the blood pressure value is determined, such that this is reached relatively quickly, and the measurement within the second measurement time period allows a very accurate determination of the blood pressure value. Thus, it is possible to very accurately and quickly determine the blood pressure value and optionally the hemodynamic parameters of the subject.

[0016] The pressure on the skin of the wrapped part of the subject can be measured directly or indirectly, wherein in the latter case the skin of the wrapped part of the subject can be provided with a sock-like material and the pressure on the skin of the wrapped part of the subject can be measured through this material. This can also be regarded as a measurement of the pressure on the skin covered with a material which can be a fabric.

[0017] The at least one feature can directly characterize the respective pressure pulse or indirectly characterize the respective pressure pulse. In the latter case, the respective pressure pulse is processed to determine a feature-determining pulse and the at least one feature is determined based on the determined feature-determining pulse. This will be explained in further detail below.

[0018] In embodiments, the pressure sensor configured to measure the pressure on the skin of the wrapped part of the subject is arranged inside the housing. However, the pressure sensor can also be arranged in another way for measuring the pressure on the skin of the wrapped part of the subject. For example, a fluid-filled pressure sensor pad can be arranged inside the housing and connected via a fluid path, i.e. via a fluid-filled tube, to a pressure sensor outside the housing in order to measure the pressure on the skin of the wrapped part of the subject.

[0019] Preferably, the control device is further configured to control the measurement system such that

[0020] - the pressure applicator also increases the applied pressure over time within a zeroth measurement time period with a zeroth slope, wherein the zeroth measurement time period is arranged in time before the first measurement time period, wherein the first slope is smaller than or equal to the zeroth slope,

[0021] - the pressure sensor also measures the pressure on the skin during the zeroth measurement time period, wherein the measured pressure comprises at least one pressure pulse,

[0022] wherein the control device is further configured to

[0023] - determine a heart rate value indicative of the heart rate of the subject based on the at least one pressure pulse of the measured pressure in the zeroth measurement time period, and, after determining the heart rate value, determine the first slope based on the determined heart rate value and control the measurement system such that the first measurement time period subsequently occurs at least initially with the determined first slope.

[0024] In particular, the second slope is also smaller or equal to the zeroth slope. Preferably, the zeroth slope is the largest slope among the zeroth slope, the first slope and the second slope. The relatively large zeroth slope allows to pass through the zeroth measurement time period relatively fast, thereby allowing to further increase the speed of measuring blood pressure values and, optionally, also to measure blood hemodynamic parameters. Furthermore, by basing the first slope on the determined heart rate value, it is even possible to further increase the accuracy of determining the start of the second measurement time period in which the actual blood pressure measurement and, optionally, the measurement of blood hemodynamic parameters is performed.

[0025] The control device can be configured to determine a heart rate value also during the first measurement time period and to correct the first slope based on the heart rate value determined during the first measurement time period. By determining a heart rate value also during the first measurement time period and by correcting the first slope based on the heart rate value determined during the first measurement time period, it is possible to further increase the accuracy of determining the start of the second measurement time period in which the actual blood pressure measurement and, optionally, the measurement of blood hemodynamic parameters is performed.

[0026] Preferably, the control device is configured to control the measurement system such that in the zeroth measurement time period the measured pressure comprises at least two subsequent pressure pulses. In particular, the control device is configured to control the measurement system such that in the zeroth measurement time period the measured pressure comprises exactly two subsequent pressure pulses. Thus, after having measured two subsequent pressure pulses, the zeroth measurement time period can be stopped and the first measurement time period can be started. Two subsequent pressure pulses are a good compromise between passing through the zeroth measurement time period as fast as possible and making the determination of the heart rate value accurate enough. For example, based on each of the two subsequent pressure pulses, it is possible to determine a respective heart rate value and it is possible to average these heart rate values in order to determine a heart rate value for determining the first slope. It is also possible to determine the heart rate value, for example, based on the time required to measure the two subsequent pressure pulses. In an embodiment, the zeroth slope used in the zeroth measurement time period can be, for example, 8 mmHg / s. It has been found that this zeroth slope eventually leads to a fast and accurate measurement of blood pressure values and, optionally, blood hemodynamic parameters.

[0027] In an embodiment, the first slope is larger than the second slope. The relatively large first slope allows to reach the start of the second measurement time period faster. Furthermore, the determined heart rate value indicates a time pulse width, i.e. a width of a pressure pulse, wherein preferably the control device is configured to control the measurement system such that the first slope is equal to or larger than 4 mmHg / PW, wherein PW is the time pulse width indicated by the heart rate value. It has been found that this allows a further improved determination of the start of the second measurement time period.

[0028] The control device is further configured to determine, in the first measurement time period, a first blood pressure value on the basis of the starting curve, to determine a second slope on the basis of the determined first blood pressure value, and to control the measurement system such that the second measurement time period occurs at least initially with the determined second slope after the starting curve reaches the first maximum value. In particular, the control device is configured to determine the systolic arterial blood pressure as the first blood pressure value. Determining the second slope on the basis of the determined first blood pressure value, which is preferably the systolic arterial blood pressure, allows for further improving the measurement in the second measurement time period.

[0029] In embodiments, the second slope can be determined by providing a maximum mean pressure value to be reached at the end of the second measurement time period, by providing a length of the second measurement time period, and by a) the difference between the provided maximum mean pressure value and the mean pressure value at the end of the first measurement time period divided by b) the provided length of the second time period. As mentioned above, the determined second slope can be only an initial slope, i.e. the second slope can be corrected during the second measurement time period, which will be explained further below. Similarly, the provided length of the second measurement time period for determining the second slope, which can be only an initial second slope, can also be only an initial length of the second measurement time period. Thus, the actual length of the second measurement time period can be greater or smaller than the provided length of the second measurement time period, wherein the actual length can depend on the measurements performed during the second measurement time period, as will also be described below. Furthermore, the provided maximum mean pressure value for determining the second slope, which can be an initial second slope, can be an initial maximum mean pressure value, wherein the maximum mean pressure value can be corrected based on the measurements performed during the second measurement time period. However, it is also possible that the initially determined second slope is used throughout the second measurement time period, so that no correction can be performed. Thus, in embodiments, it is also possible that the determined second slope is constant and does not change during the second measurement time period. In this case, the provided length of the second measurement time period and the provided maximum mean pressure value can also be constant.

[0030] To provide the maximum mean pressure value, the control device can comprise assignments between the first blood pressure value and the maximum mean pressure value, wherein these assignments can be pre-determined by a calibration. In particular, these assignments can be determined by the calibration such that they result in very precise blood pressure measurements, wherein the length of the second measurement time period is relatively small, in particular as small as possible. For example, during the calibration process, the assignments can be determined such that a deviation between the determined blood pressure value and a blood pressure value of a known invasive measurement, which is used as a gold standard and which has been measured at the same time, is smaller than a predefined deviation threshold, and the length of the second measurement time period is as small as possible.

[0031] The kind and / or the assignment of the first blood pressure value is preferentially dependent on the type of the blood pressure value to be finally determined. Furthermore, the assignment can be a functional assignment, wherein during the calibration process parameters of the functional assignment are determined such that the respective blood pressure value is calculated very accurately by using a relatively short second measurement time period. For example, the respective calibration function can comprise a linear calibration function with two parameters a and b (e.g. maximum mean pressure value = b + a • first blood pressure value), wherein the parameters a and b can be determined by the calibration. In an embodiment, in the second measurement time period the systolic arterial blood pressure or the mean arterial blood pressure shall be determined, wherein in this case the parameter a can be 1 and the parameter b can for example be equal to or less than 10 mmHg and preferably equal to or less than 5 mmHg. In this case, preferably, the first blood pressure value is also the systolic arterial blood pressure.

[0032] In an embodiment, the control device can also be configured to determine a blood hemodynamic monitoring parameter, like the pulse pressure variation, based on the pressure measured in the second measurement time period, wherein in this case the parameter a can be 1 and the parameter b can be 20 mmHg. Furthermore, in this example the first blood pressure value can also be the systolic arterial blood pressure. Preferably, if the pulse pressure variation shall be determined and also preferably if another blood hemodynamic monitoring parameter shall be determined, the parameter b is used which is larger than the parameter b which can be used for determining the systolic arterial blood pressure or the mean arterial blood pressure based on the pressure measured in the second measurement time period.

[0033] The parameter b can also be a percentage of the first blood pressure value. Thus, in an embodiment the maximum mean pressure value can be defined by the function (1 + x) • first blood pressure value, wherein the first blood pressure value is here also preferably the systolic arterial blood pressure. This function can also be used for determining the maximum mean pressure value if for example the systolic arterial blood pressure, the mean arterial blood pressure or the pulse pressure variation shall be determined based on the pressure measured in the second measurement time period. Corresponding to what has been explained above, if the pulse pressure variation shall be determined, the parameter x is preferably larger than the parameter x which is used for determining the systolic arterial blood pressure or the mean arterial blood pressure based on the pressure measured in the second measurement time period.

[0034] The length of the second measurement period provided for determining the second slope can be a predetermined length, wherein the predetermined length can depend on the type of blood pressure value that shall be determined based virtually on the pressure to be measured in the second measurement period, i.e. different predetermined lengths can be provided for different types of blood pressure values to be measured. Furthermore, the predetermined length of the second measurement period can be determined beforehand by calibration, so that the desired blood pressure value can be determined very accurately based on the pressure measured in the second measurement period, wherein the length of the second measurement period provided is still relatively small. It is also possible that the length provided depends on a heart rate (HR) value and / or a respiration rate (RR) value. The HR value and / or the RR value can be measured during the first measurement period or can have been measured beforehand. The length of the second measurement period can be provided so that it covers a predefined number of pulses and / or a predefined number of breathing or ventilation cycles defined by the HR value, wherein ventilation cycles can also be defined by a ventilator. For example, the length of the second measurement period can be provided so that it covers at least five or six pulses or 3.5 breathing or ventilation cycles. Furthermore, the length, i.e. how many pulses and / or breathing or ventilation cycles shall be covered, can depend on the desired type of blood pressure value or hemodynamic monitoring parameter type determined based on the pressure measured in the second measurement period. As explained above, the length provided for determining the second slope can be an initial length that can be shortened or lengthened during the second measurement period.

[0035] The control device can further comprise direct assignments between the first blood pressure value and the second slope, wherein these direct assignments can also be determined by calibration, in particular by determining parameters of a corresponding calibration function. In embodiments, these calibration functions are a combination of the calibration functions for determining the maximum mean pressure value and the length of the second measurement period for determining the second slope as described above. Thus, the calibration function can correspond to a division of a) the difference between the maximum mean pressure value at the end of the first measurement period and the mean pressure value by b) the length of the second measurement period, wherein the maximum mean pressure and the length of the second measurement period can be determined as described above.

[0036] In embodiments, the control device is configured to determine the starting value during the first measurement period for the respective pressure pulse by exponentiating at least one feature with a predetermined exponent. If several features are used for determining the starting value for the respective pressure pulse, each of these multiple features is exponentiated with a respective predetermined exponent and the exponentiated features are combined, in particular multiplied.

[0037] Preferably, the control device is configured such that forming the starting curve on the basis of the number of starting values comprises a low-pass filtering of the number of starting values. The low-pass filtering is preferably a moving average filtering, wherein the filter window can have a length of e.g. 4 seconds. The filter window is preferably centered in time to the average value to be determined at present.

[0038] In embodiments, the control device is configured to, for determining the at least one feature for the respective pressure pulse, provide a feature determination pulse on the basis of the respective pressure pulse and to determine at least one of the following features:

[0039] - a difference between the maximum systolic pressure of the feature determination pulse and the pressure of the feature determination pulse at the end of diastole point,

[0040] - a duration of the respective feature determination pulse,

[0041] - an entire area under the respective feature determination pulse,

[0042] - a width at half maximum of the respective feature determination pulse, and

[0043] - an upper area under the upper portion of the respective feature determination pulse.

[0044] The duration of the respective pressure pulse preferably corresponds to the time difference between the end of diastole point and a subsequent end of diastole point for the respective feature determination pulse. Further, the entire area is preferably the entire area under the curve of the respective feature determination pulse from the end of diastole point to the subsequent end of diastole point. The area can be a normalized area. For example, the area can be normalized by scaling the area to the difference between the maximum pressure and the minimum pressure of the respective feature determination pulse. The width at half maximum corresponds to the width at 50% of the difference between the maximum pressure and the minimum pressure of the respective feature determination pulse. It is thus the width at 50% of the difference between the pressure of the feature determination pulse at the maximum systolic point and the pressure of the feature determination pulse at the end of diastole point. The upper area is the upper portion of the entire area under the feature determination pulse. The upper area can be a normalized upper area, wherein the upper area under the feature determination pulse can be normalized to the difference between the maximum systolic pressure of the feature determination pulse and the pressure of the feature determination pulse at the end of diastole point. The upper area can be more sensitive to waveform changes, i.e. to changes of the feature determination pulse, under applied pressures close to the systolic arterial blood pressure, which can lead to an improved accuracy of determining the systolic arterial blood pressure.

[0045] For example, the feature-determining pulse for the respective pressure pulse can be obtained by subtracting the average measured pressure from the respective pressure pulse. However, the feature-determining pulse for the respective pressure pulse can also be determined in another way. It can also be the respective pressure pulse directly, i.e. the respective measured pressure pulse.

[0046] In embodiments, the control device is configured to determine the starting value for the respective pressure pulse based on at least one of the following calculations:

[0047] - multiplying a) the determined overall area with a power of a predetermined first exponent by b) the determined difference with a power of a predetermined second exponent,

[0048] - dividing a) the determined area with a power of a predetermined third exponent by b) the determined duration with a power of a predetermined fourth exponent, and multiplying the quotient by c) the determined difference with a power of a predetermined fifth exponent.

[0049] In embodiments, the control device is configured to determine the starting value for the respective pressure pulse based on further multiplication with the width at half the maximum value with a power of a further predetermined exponent. Thus, in embodiments, the above calculations are extended by multiplication with the width at half the maximum value with a power of a further predetermined exponent. These different exponents are preferably predefined and can be determined beforehand by a calibration measurement, wherein reference blood pressure values are determined very precisely by an invasive device and the exponents are determined such that the measurement system controlled by the control device produces very accurate invasive measurement blood pressure values with high statistical precision and accuracy. Specifically, for the calibration measurement, pairs of invasive and non-invasive blood pressure values from a sufficient number of individuals recorded simultaneously under different hemodynamic conditions are used. It should be noted that the calibration is preferably only performed in the development phase, i.e. not during actual blood measurements. The calibration can be performed separately for different housing sizes, i.e. preferably for different blood pressure cuff sizes, or for different size groups of housings. For example, for different housing sizes or size groups of housings, different sets of exponents can be determined by the calibration, i.e. for each housing size or for each size group of housings a respective set of exponents can be determined. The calculations for determining the starting value can also be used to determine the blood pressure determination value.

[0050] In embodiments, the control device is further configured to determine a respiration rate value indicative of a respiration rate based on the pressure measured in the second measurement time period and / or to receive a respiration rate value from another device. Specifically, the control device can be configured to determine the respiration rate value online, i.e. while still measuring the pressure in the second measurement time period. Further, the other device can be a ventilator, for example, which provides the respiration rate value to the control device, which can then also be considered a ventilation cycle.

[0051] In embodiments, the control device is configured to stop the second measurement time period as soon as the respiration rate value indicates that the second measurement time period covers 3.5 respiratory or ventilation cycles and / or a predetermined maximum measurement time period has been reached and / or a maximum mean pressure value has been reached. This allows to control the measurement during the second measurement time period such that the total measurement time is not unnecessarily long, allowing to further shorten the total measurement time. The mean pressure value can be calculated by e.g. averaging the measured pressure over a predefined moving time interval. It can also be calculated by applying a low pass filter to the measured tissue pressure. The low pass filter is preferably dimensioned such that the mean pressure only includes frequencies below a minimum expected pulse rate. A preferred low pass filter will be further described below. The mean pressure value can also be regarded as a non-oscillatory DC component of the measured tissue pressure, which increases with increasing inflation.

[0052] The predetermined maximum measurement time period preferably corresponds to 3.5 times an expected maximum respiratory or ventilation cycle duration. The expected maximum respiratory or ventilation cycle duration can be e.g. 7.5 s, which corresponds to a respiration rate value of 8 respiratory or ventilation cycles per minute. The maximum mean pressure value is preferably larger than the systolic arterial blood pressure, in particular larger than 20 mmHg. Here, the systolic arterial blood pressure is preferably the first blood pressure value or a blood pressure value determined based on pulses measured during the second measurement time period, wherein in the latter case the maximum mean pressure value is corrected during the second measurement time period. Thus, in embodiments, the control device is configured to correct the second slope depending on the maximum mean pressure value and / or based on the respiration rate value determined during the second measurement time period. If the maximum mean pressure value changes during the second measurement time period, since it is e.g. the systolic arterial blood pressure plus 20 mmHg, and because the systolic arterial blood pressure is measured during the second time period and the measured systolic arterial blood pressure changes, the second slope can be changed depending on the measured systolic arterial blood pressure during the second measurement time period and optionally depending on the respiration rate value. This can allow to further improve the measurement of the final blood pressure value and optionally of the hemodynamic parameters. Overall, the determination of the respiratory or ventilation cycles and / or the blood pressure while the measurement is performed in the second measurement time period allows to accurately and quickly determine when one of the following respective stop criteria is met, a) the second measurement time period covers 3.5 respiratory or ventilation cycles and / or b) the predetermined maximum measurement time period has been reached and / or c) the maximum mean pressure value has been reached. It can also be used to manipulate the pressure application in the second measurement time period via a respective correction of the slope such that at least one of the stop criteria is reached accurately and quickly. In particular, the second slope can be controlled such that the second measurement time period covers 3.5 respiratory or ventilation cycles or corresponds to the predetermined maximum measurement time period when the mean pressure has reached a value equal to the measured systolic arterial pressure plus a predetermined blood pressure value, like 20 mmHg.

[0053] The control device can be configured to determine:

[0054] - for a respective pressure pulse measured in the second measurement time period, a blood pressure determination value based on at least one of the at least one determined features, such that a number of blood pressure determination values is determined for a number of pressure pulses occurring at different times, wherein the number of blood pressure determination values determined for the number of pressure pulses and thus for the number of times forms a blood pressure determination curve,

[0055] - determining a blood pressure value based on the blood pressure determination curve.

[0056] In particular, a number of features can be determined for a respective pressure pulse measured in the second measurement time period, wherein the blood pressure determination value can be determined by combining at least two of the determined features, such that a number of blood pressure determination values is determined for a number of pressure pulses occurring at different times, wherein the number of blood pressure determination values determined for the number of pressure pulses and thus for the number of times forms a blood pressure determination curve. By determining the blood pressure using this blood pressure determination curve, the blood pressure can be determined even more accurately. Preferably, the control device is configured to determine a maximum of the blood pressure determination curve and to determine the blood pressure based on the determined maximum and the measured pressure.

[0057] The control device can be adapted to process the number of blood pressure determination values obtained for the number of pressure pulses to obtain a continuous blood pressure determination curve. For example, interpolation and / or smoothing can be applied. In particular, the control device is configured such that forming the blood pressure determination curve based on the number of blood pressure determination values comprises low-pass filtering the number of blood pressure measurements. Further, the low-pass filtering here is preferably a moving average filter, which is preferably centered on the time for which the average is currently to be determined.

[0058] Preferably, the control device is configured such that the low-pass filtering of the number of starting values and the low-pass filtering of the number of blood pressure determination values both use a filter window, wherein the filter window used for the low-pass filtering of the number of starting values has a window length that is smaller than the filter window used for the low-pass filtering of the number of blood pressure determination values. For example, the window length used for the low-pass filtering of the number of blood pressure determination values can be twice the window length used for the low-pass filtering of the number of starting values. In an embodiment, the window length used for the low-pass filtering of the number of blood pressure determination values is 8s, while the window length used for the low-pass filtering of the number of starting values is 4s. Furthermore, in an embodiment, the number of blood pressure determination values is low-pass filtered a number of times, preferably twice, while the number of starting values can only be low-pass filtered once. This results in a stronger low-pass filtering of the measurement results obtained in the second measurement time period compared to the filtering of the measurement values obtained in the first measurement time period, which in turn allows for a more accurate determination of the blood pressure based on the blood pressure determination curve. The low-pass filtering is preferably performed such that the cardiopulmonary interaction is eliminated in the blood pressure determination curve in order to allow for a high quality blood pressure determination. For the starting curve, it is not necessarily required to eliminate the cardiopulmonary interaction, as a rough estimate of the blood pressure and the ability to detect the maximum of the starting curve is sufficient. In an embodiment, the respiratory rate value is determined using the cardiopulmonary interaction detectable on the starting curve even in the second measurement time period.

[0059] In an embodiment, the control device is configured to determine the blood pressure determination values for the respective pressure pulses during the second measurement time period by exponentiating at least one feature with a predetermined exponent. If a number of features is used to determine the blood pressure determination values for the respective pressure pulses, these number of features are each exponentiated with a respective predetermined exponent, and the exponentiated features are combined, in particular multiplied.

[0060] The control device is preferably configured to determine the blood flow hemodynamic monitoring parameters, i.e. the blood flow hemodynamic parameters, based on the pressures measured in the second measurement time period as well. In particular, the control device is configured to determine at least one of a fluid responsiveness parameter (FRP), a cardiac output (CO), a systemic arterial resistance (SAR) and a cardiac power output (CPO) as the blood flow hemodynamic monitoring parameter. The control device can also be adapted to determine, for example, a pulse pressure variation (PPV), a systolic pressure variation (SPV) or a stroke volume variation (SPF) as the fluid responsiveness parameter (FRP) based on the pressures measured in the second measurement time period.

[0061] In another aspect of the application, a measurement system for measuring a blood pressure of a subject is presented, wherein the measurement system comprises:

[0062] a housing configured to enclose a portion of the subject through which blood flows,

[0063] - a pressure applicator configured to apply a pressure to the casing from outside the casing, thereby applying a pressure to the wrapped part of the subject,

[0064] - a pressure sensor configured to measure the pressure on the skin of the wrapped part of the subject, and

[0065] - the control device of any one of claims 1 to 11.

[0066] In another aspect of the application, a control method for controlling a measurement system as claimed in claim 12 is presented, wherein the control method comprises:

[0067] - increasing the applied pressure over time in a first measurement time period having a first slope and in a second measurement time period having a second slope by using the pressure applicator, wherein the first measurement time period and the second measurement time period are arranged in this order in time,

[0068] - measuring the pressure on the skin during the first measurement time period and the second measurement time period by using the pressure sensor, wherein the measured pressure comprises a plurality of pressure pulses,

[0069] wherein the method further comprises

[0070] - determining, in the first measurement time period, for each pressure pulse of at least some of the plurality of pressure pulses, at least one feature characterizing the respective pressure pulse,

[0071] determining, for the respective pressure pulse, based on the at least one feature that has been determined for the respective pressure pulse, a starting value to be used for determining the onset of the second measurement time period, such that for several pressure pulses occurring at different times, several starting values are determined,

[0072] forming a starting curve of the starting values to be used for determining the onset of the second measurement time period based on the several starting values,

[0073] and, after the starting curve has reached a first maximum value, controlling the measurement system such that the second measurement time period subsequently occurs,

[0074] - determining a blood pressure value based on the pressure measured in the second measurement time period.

[0075] wherein the method further comprises, in the first measurement time period, determining a first blood pressure value based on the starting curve, determining the second slope based on the determined first blood pressure value, and, after the starting curve has reached the first maximum value, controlling the measurement system such that the second measurement time period subsequently occurs with the determined second slope.

[0076] In another aspect of the application, a computer program for controlling a measurement system as defined in claim 12 is presented, the computer program comprising program code means for causing the measurement system to perform the steps of claim 13 when the computer program is run on a control device of the measurement system.

[0077] The control device, method and computer program are preferably adapted to continuously control the measurement system to perform several subsequent blood pressure measurements while being attached to the subject.

[0078] It is to be understood that the control device of claim 1, the measurement system of claim 12, the control method of claim 13 and the computer program of claim 14 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0079] It is to be understood that the preferred embodiments of the present application can also be any combination of the dependent claims or the above-mentioned embodiments with the corresponding independent claims.

[0080] These and other aspects of the present application will be apparent from the following description of embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0081] In the following drawings:

[0082] Figure 1 An embodiment of a measurement system for measuring the blood pressure of a subject is schematically and exemplarily shown in a situation in which the blood pressure cuff of the measurement system is inflated,

[0083] Figure 2 A housing of a measurement system is schematically and exemplarily shown wrapped around the upper arm of a subject,

[0084] Figure 3 The measurement system is schematically and exemplarily shown in a situation in which the blood pressure cuff is deflated,

[0085] Figure 4 Measured tissue pressure and other values derived from the tissue pressure measurement are schematically and exemplarily shown,

[0086] Figure 5 Measured tissue pressure and other values derived from the tissue pressure measurement according to an embodiment of the present application are schematically and exemplarily shown,

[0087] Figures 6 to 9 A calculation of several features of a pressure pulse for the measured tissue pressure is shown,

[0088] Figure 10 A flow chart exemplarily illustrating an embodiment of a control method for controlling a measurement system for measuring the blood pressure of a subject is shown,

[0089] Figure 11 The measured tissue pressure and other values derived from the tissue pressure measurement according to another embodiment of the application are schematically and exemplarily shown. DETAILED DESCRIPTION

[0090] Figure 1 A measurement system 1 for measuring the blood pressure of a subject is schematically and exemplarily shown. The measurement system 1 comprises a housing 4, which in Figure 2 It can be seen in that the housing 4 is configured to enclose a part 5 of the subject through which blood flows. In this embodiment, the part 5 of the subject is the arm of the subject, wherein, in Figure 2 The brachial artery 21 is shown within the arm 5, and wherein the arrow within the brachial artery 21 indicates the direction of blood flow away from the heart. The measurement system 1 further comprises a pressure sensor 7 arranged within the housing 4 and configured to measure the pressure on the outer skin of the enclosed arm 5 of the subject. The measured pressure can also be regarded as tissue pressure (TP). As Figure 2 The pulse wave within the brachial artery 21 causes a pressure wave 12, which is transmitted via the tissue of the arm 5 to the pressure sensor 7. For the sake of clarity, Figure 1 The housing 4 is not shown in

[0091] The measurement system 1 further comprises a cuff 6, which encloses the housing 4 and which is inflatable by using a pump 8 to apply pressure from the outside of the housing 4 to the housing 4, and thus to the enclosed arm 5 of the subject. Since the cuff 6 and the pump 8 together can apply pressure to the housing 4, and thus to the enclosed arm 5 of the subject, they can be regarded as forming a pressure applicator 6, 8. The housing 4 with the cuff 6 is preferably a twist-proof housing cuff as described in WO 2014 / 121945 Al.

[0092] The measurement system 1 further comprises a control device 3 configured to control the measurement system 1 such that the pressure applicator 6, 8 increases the applied pressure in a pressure increase time period and decreases the applied pressure in a subsequent pressure decrease time period, and such that the pressure sensor 7 measures the pressure on the skin, i.e. the tissue pressure TP, at least in the pressure increase time period. Figure 1 The control of the measurement system 1 is shown in that the cuff 6 is inflated, thereby increasing the applied pressure, i.e. the bold arrow indicates the inflation.

[0093] The measurement system 1 comprises a valve 20, which, when opened, allows compressed air within the system to exit the system into the surrounding atmosphere to deflate the cuff. In Figure 3 This deflation situation, in which the pump 8 is closed, is indicated with a bold arrow.

[0094] The control device 3 can be seen as comprising the actual controller 10 for controlling the pump 8 and the valve 20 as well as a processor 11 which is specifically configured to perform some calculations which will be further explained below. The measurement system 1 can further comprise a display 22 for displaying e.g. measured blood pressure values.

[0095] The measured pressure TP has a pressure pulse 9 which will be explained below with respect to Figure 4 It should be noted that Figure 4 is only used to illustrate aspects of the present application, like the pressure pulse 9, but it does not show an embodiment of the present application which requires that within the first measurement time period a start determination curve is determined, wherein a maximum of the start determination curve is used to determine the start of the second measurement time period as will be explained below with specific reference to Figure 5 .

[0096] As can be seen in Figure 4 , the measured pressure TP has a pressure pulse 9 with respect to time t as explained above. In Figure 4 , the zeroth inflation starts at a tissue pressure TP which is the attachment pressure Patt, i.e. the measured tissue pressure in the uninflated cuff 6. The attachment pressure Patt can range from 0 to 15 mmHg. An attachment pressure Patt of up to 15 mmHg has proven not to cause venous congestion for more than 12 hours, thus making the assembly of the housing 4 and the cuff 6 most suitable for long-term monitoring. Therefore, preferably, the attachment pressure Patt is not more than 15 mmHg. In Figure 4 , the arrow 30 indicates the start of the zeroth inflation. During the zeroth inflation, the part of the entire tissue pressure range without or substantially without information for the determination of the blood pressure should be passed as quickly as possible. Therefore, during the zeroth inflation, the inflation rate is preferentially as large as possible. For example, the inflation rate with respect to the tissue pressure TP can be equal to or more than 8 mmHg / s. The zeroth inflation period with the fast inflation rate ends in Figure 4 , at the tissue pressure value indicated by "TPlow". The tissue pressure value TPlow also indicates the start of the first inflation time period with the slower first inflation rate. In Figure 4 , the start of the first inflation time period is indicated by the arrow 31, which first inflation time period can also be considered as a slow inflation period.

[0097] In Figure 4 , the time interval 40 indicates the inflation-deflation time period from the start 30 of the fast inflation until the tissue pressure TP has dropped below 20 mmHg during the fast deflation to allow venous return. The time period 41 indicates the cycle time which is the time between the start of a measurement and the start of the subsequent measurement, and the time period 42 indicates the interruption period which is the difference between the inflation-deflation time period and the cycle time 41.

[0098] As mentioned above, Figure 4 For illustration of aspects of the application only, embodiments of the application require that a start determination curve is determined in a first measurement time period, wherein a maximum of the start determination curve is used for determining a start of a second measurement time period. Embodiments of the application are illustrated Figure 5 .

[0099] As can be seen in Figure 5 , the control device 3 is preferably configured to control the measurement system 1 such that the pressure applicator 6, 8 increases the applied pressure over time in a zeroth measurement time period To with a zeroth slope, in a first measurement time period Ti with a first slope and in a second measurement time period T2 with a second slope, wherein the zeroth measurement time period To, the first measurement time period Ti and the second measurement time period T2 are arranged in this order in time. The multiple pressure increases within the different measurement time periods can be regarded as different ramps, as illustrated in Figure 5 with ramp 0, ramp 1 and ramp 2. The pressure sensor 7 measures the pressure TP on the skin during the zeroth measurement time period, the first measurement time period and the second measurement time period, wherein the measured pressure TP comprises multiple pressure pulses. The corresponding inflation phases are indicated with reference sign 55 in Figure 5 .

[0100] In the zeroth measurement time period To, which can also be regarded as a fast inflation phase, the control device 3 controls the measurement system 1 such that the valve 20 is closed and the pump 8 inflates the cuff 6 with a zeroth rate, i.e. with a zeroth slope. In the subsequent first measurement time period Ti, the control device 3 further controls the measurement system 1 such that the valve 20 is closed, but the pump 8 is controlled such that the inflation of the cuff 6 continues with a first rate, i.e. with a first slope which is smaller than the zeroth slope. In the subsequent second measurement time period T2, the control device 3 still controls the measurement system 1 such that the valve 20 is closed, but the pump 8 is controlled such that the inflation of the cuff 6 continues with a second rate, i.e. with a second slope which is also smaller than the zeroth slope. Preferably, the first slope is larger than the second slope.

[0101] The control device 3 is also configured to control the measurement system 1 such that the measured pressure TP includes at least one pressure pulse during a zero measurement time period T0, and to determine a heart rate value HR of the indicated object based on at least one pressure pulse of the pressure TP measured during the zero measurement time period T0. After determining the heart rate value HR, a first slope is determined based on the determined heart rate value HR, and the measurement system 1 controls the measurement system 1 such that a first measurement time period T1 and the determined first slope subsequently occur. The control device 3 can also be configured to determine the heart rate value HR during the first measurement time period T1 and to correct the first slope based on the heart rate value HR determined during the first measurement time period.

[0102] The pressure pulse is caused by the pulsating heart, and the heart rate value can be determined, for example, based on the width of the corresponding pressure pulse or based on the number of pressure pulses over a period of time. The determined heart rate value preferably indicates the time pulse width, i.e., the width of the pressure pulse, wherein the control device 3 can be configured to control the measurement system 1 such that a first slope is equal to or greater than 4 mmHg / PW, where PW is the time pulse width indicated by the heart rate value.

[0103] In this embodiment, the control device 3 is configured to control the measurement system 1 such that, during the zero measurement time period T0, the measured pressure TP includes at least two subsequent pressure pulses, preferably exactly two. Therefore, the control device 3 is preferably configured to determine the heart rate value based on the pressure pulses of the pressure TP measured during the zero measurement time period once two subsequent pressure pulses have been measured. Specifically, the heart rate value is determined based on the first two measured subsequent pressure pulses, after which measurements are performed during the first measurement time period.

[0104] In addition, the zeroth measurement time period, as referenced above. Figure 4 The zero inflation period can begin at an attachment pressure Patt ranging from, for example, 0 to 15 mmHg, i.e., preferably not greater than 15 mmHg. During the zero measurement period, the portion of the entire tissue pressure range for which there is little or no information for determining blood pressure should be traversed as quickly as possible, while still gathering sufficient information to measure the heart rate value HR. Therefore, during this zero measurement period T0, the zero inflation rate is preferably as large as possible, while still allowing for sufficiently accurate determination of the heart rate. For example, the zero slope relative to tissue pressure TP can be equal to or greater than 8 mmHg / s, but it can also have other values.

[0105] The control device 3 is further configured to determine, in the first measurement time period T1, for each of at least some of the plurality of pressure pulses at least one feature characterizing the respective pressure pulse. Preferably, several features are determined for each pressure pulse. This will be explained in the following.

[0106] Figure 4 Also shown is an average pressure TPc1 which can be seen as a tissue clamping pressure affecting the tissue when the cuff 6 is attached to the arm 5 of the subject, e.g. the upper arm. The average pressure TPc1 can be calculated by applying a low pass filter to the tissue pressure TP, wherein the low pass filter can be located within the control device 3, in particular within the processor 11 of the control device 3. The low pass filter is preferably dimensioned such that the average pressure TPc1 only includes frequencies below the lowest expected pulse rate (PRni). A preferred low pass filter will be further described in the following. The control device 3 is preferably configured to determine an alternating component of the tissue pressure TPac by subtracting the average pressure TPc1 from the measured tissue pressure TP, i.e. TPac = TP - TPc1. In Figure 4 In Fig. 6, the TPac curve is shown with a 2-fold amplification in order to improve the visibility of this curve.

[0107] During the zero measurement time period, the first measurement time period and the second measurement time period, the TP pulse curve and / or the TPac pulse curve can be analyzed and at the same time parameters are calculated, i.e. parameters are calculated on-line, wherein the TP pulse curve or the TPac pulse curve has a tissue pressure waveform (TPW) which includes information allowing an accurate measurement of the blood pressure. Since the blood pressure is measured non-invasively, although with an accuracy comparable to the accuracy of invasively measured blood pressure, it can be abbreviated as niBP, meaning “non-invasively measured blood pressure”. The TPac pulse curve is schematically and exemplarily shown in Figures 6 to 9 Fig. 6.

[0108] In the following, the TPac pulse curve is used for determining features of the pressure pulses. The TPac pulse curve can thus be seen as a feature determination pulse curve or a feature determination pulse. Figures 6 to 9 A feature determination pulse curve or a feature determination pulse 29 as a TPac pulse is thus shown. In another embodiment, the feature determination pulse can also be directly the TP pulse curve, i.e. the pressure pulse can be directly used for determining the features.

[0109] It has been observed that when increasing the clamping pressure, i.e. when increasing the pressure applied via the cuff 6 to the arm 5, the diastolic tissue pressure pulse form changes from a rather sharp shape to a flat diastolic shape when crossing the mean arterial pressure (MAP), as shown in Fig. 2 of WO 2018 / 210931 A1. Figure 7As can be seen in Fig. 7A, 7B, 7C. This behavior can be modeled by changes in several TPW parameters. The TPW parameters can be extracted from the TP pulse curve as described in document WO 2018 / 210931 A1.

[0110] In embodiments, the control device 3 is configured to determine a TPP difference between a maximum measured pressure and a minimum measured pressure of the respective feature determination pulse 29 as a feature for the respective pressure pulse, i.e. a TPW parameter. This feature, i.e. the TPW parameter, will be described in the following with reference to Figure 6 .

[0111] The difference TPP is the difference between the maximum systolic pressure of the feature determination pulse TPsys and the pressure of the feature determination pulse at the point of the end of diastole (TPdia), which is preferably the minimum pressure of the respective feature determination pulse. In Figure 6 , and in Figure 7 and Figure 8 , the terms “t.start” and “t.stop” indicate the start and the end of the respective pulse 29, respectively.

[0112] The control device 3 can also be configured to determine a pulse duration (t(pulse)), which is the time difference between the point of the end of diastole and the subsequent point of the end of diastole of the feature determination pulse 29. This feature can also be defined as the time difference between the start of the respective pulse (t.start) and the end of the respective pulse (t.stop). This feature is illustrated in Figure 7 .

[0113] The control device 3 can also be adapted to determine a total pulse area (TPA) of the respective pulse 29, which is the total area under the respective pulse curve in the time defined by t.start to t.stop, ranging from the pressure of the feature determination pulse at the point of the end of diastole (TPdia) to the maximum systolic pressure of the feature determination pulse (TPsys). Preferably, as illustrated in Figure 7 , the total pulse area TPA is scaled to TPP = 1. This scaled pressure pulse area is named “TPA.norm”.

[0114] As illustrated in Figure 8 , the control device 3 can also be adapted to determine a pulse width at half maximum (W50) of the respective pulse 29.

[0115] Furthermore, the control device 3 can be adapted to determine a pulse area (TPA.top) of the respective pulse 29, which is the area under the respective pulse curve in the time defined by t.start to t.stop, ranging from the pressure of the feature determination pulse at the point of the end of diastole (TPdia) to the maximum systolic pressure of the feature determination pulse (TPsys). Preferably, as illustrated in Figure 9the upper pulse area TPA.top. The lower boundary of the upper pulse area TPA.top is defined by a predetermined percentage of the difference TPP. For example, the percentage value can be determined with reference to a determination of a predefined exponent during an initial training phase, wherein the percentage value, the exponent and other parameters are determined such that the difference between a) the non-invasive blood pressure determined by using the present method and b) the invasively measured blood pressure value is minimized. For more details regarding the features, in particular regarding the upper pulse area TPA.top, reference is made to DE 10 2017 110 770 B3.

[0116] Figures 6 to 9 The TPac pulse curve is shown such that in this example, the feature, i.e. the TPW parameter, has also been defined based on the TPac pulse curve. However, as mentioned above, it is also possible to define these or other features based on the TP pulse curve.

[0117] The control device 3 is further configured to determine, in the first measurement time period T1, for the respective pressure pulse, a start value TPWP_F to be used for determining the start of the second measurement time period based on the several features that have been determined for the respective pressure pulse such that for several pressure pulses occurring at different times, several start values TPWP_F are determined. In particular, the control device 3 is configured to determine, during the first measurement time period T1, for the respective pressure pulse, the start value TPWP_F by exponentiating the features with a predetermined exponent and by multiplying the exponentiated features with each other. This will be explained further below.

[0118] The control device 3 is further configured to form, in the first measurement time period T1, a start curve TPW_F-curve for determining the start of the second measurement time period T2 based on the several start values TPWP_F and, after the start curve TPW_F-curve has reached a first maximum value, to control the measurement system 1 such that the second measurement time period T2 subsequently occurs. Preferably, the start curve TPW_F-curve is formed based on the several start values TPWP_F by low-pass filtering the several start values TPWP_F. The low-pass filtering is preferably a moving average filtering, wherein the filter window can have a length of e.g. 4 seconds. The filter window is preferably centered at the time for which the average value is currently to be determined.

[0119] In particular, the control device 3 can be configured to determine the start value TPWP_F for each pressure pulse in the first measurement time period T1 by combining at least two of the features that have been determined for the respective pressure pulse. In particular, the control device 3 can be configured to multiply a) the determined pulse area TPA.norm with a predetermined first exponent (exp1) to the power and b) the determined difference TPP with a predetermined second exponent (exp2) to the power. Thus, the start value TPWP_F can be calculated according to the following formula:

[0120] TPWP_F = TPA.norm expl • TTP exp2 (1)

[0121] wherein the predefined exp1 ≠ 0, exp2 ≠ 0.

[0122] The control device 3 can further be configured to determine the starting value TPWP_F by dividing a) the determined pulse area TPA.norm by b) the determined pulse duration t(pulse) raised to a predetermined fourth exponent (exp4), and multiplying the resulting quotient by c) the determined difference TPP raised to a predetermined fifth exponent (exp5). This can be expressed by the following formula:

[0123] TPWP_F = TPA.norm exp3 / t(pluse) exp4 • TPP exp5 (2)

[0124] wherein the predetermined exp3 ≠ 0, exp4 ≠ 0, exp5 ≠ 0.

[0125] The control device 3 can further be configured to determine the starting value for a respective pressure pulse based on multiplying the calculation result obtained by using, for example, formula (1) or formula (2) with the width at half maximum (W50) raised to a further predetermined exponent. For example, if formula (2) is multiplied with the width at half maximum W50, the following formula (3) results:

[0126] TPWP_F = TPA.norm exp6 / t(pulse) exp7 • TPP exp8 • W50 exp9 (3)

[0127] wherein the predetermined exp6 ≠ 0, exp7 ≠ 0, exp8 ≠ 0, exp9 ≠ 0.

[0128] Thus, in this embodiment, TPWP_F reflecting a characteristic value for a respective pulse curve can be calculated based on at least the TPP and TPA.norm for the respective pulse curve by combining and weighting the amplitude and area parameters, wherein TPWP_F can be extended by multiplying W50 with the respective exponent. The exponents of the different formulas are predetermined, preferably in a manner as will be further explained below.

[0129] The determined starting value TPWP_F is used to form a starting curve TPWP_F in the first measurement time period T1. However, as Figure 5 indicated, it is also possible to determine a starting value TPWP_F for the second measurement time period T2, thereby determining a starting curve TPWP_F-curve.

[0130] The control device 3 is further configured to determine, in the first measurement time period T1, a first blood pressure value based on the starting curve TPWP_F-curve, to determine a second slope based on the determined first blood pressure value, and to control the measurement system 1 such that the second measurement time period T2 occurs subsequently with the determined second slope after the starting curve TPWP_F-curve has reached a first maximum value. The first blood pressure value is preferably a systolic arterial blood pressure value (SAPni). The control device 3 is further configured to determine a final blood pressure value based on the measured pressure TP in the second measurement time period T2.

[0131] The control device 3 is further configured to determine a respiratory rate value RR indicative of a respiratory rate based on the measured pressure TP in the second measurement time period, or to receive the respiratory rate value RR from another device. In particular, the control device 3 can be configured to determine the respiratory rate value RR online, i.e. while still measuring the pressure TP in the second measurement time period. Further, the other device can be a breathing machine, for example, which provides the respiratory rate value to the control device. Further, the control device 3 is preferably configured to stop the second measurement time period as soon as the respiratory rate value RR indicates that the second measurement time period covers 3.5 respiratory or ventilation cycles and / or a predetermined maximum measurement time period has been reached and / or a maximum mean pressure value has been reached. The predetermined maximum measurement time period preferably corresponds to 3.5 times an expected maximum respiratory or ventilation cycle duration. This expected maximum respiratory or ventilation cycle duration can be, for example, 7.5 s, corresponding to a respiratory rate value RR of 8 respiratory or ventilation cycles per minute. The maximum mean pressure value is preferably greater than the systolic arterial blood pressure. In particular, it is the systolic arterial blood pressure plus 20 mmHg. Here, the systolic arterial blood pressure is preferably the first blood pressure value or a blood pressure value determined based on the pulses measured during the second measurement time period, wherein in the latter case the maximum mean pressure value is corrected during the second measurement time period.

[0132] The control device 3 can be configured to correct the second slope based on the respiratory rate value RR determined during the second measurement time period and / or in dependence on the maximum mean pressure value. Thus, if the maximum mean pressure value changes during the second measurement time period, since it is, for example, the systolic arterial blood pressure plus 20 mmHg, and since the systolic arterial blood pressure is measured during the second time period, the second slope can change in dependence on the respiratory rate value and the systolic arterial blood pressure measured during the second measurement time period.

[0133] In order to determine a blood pressure value on the basis of the measured pressure in the second measurement time period T2, the control device 3 is configured to determine, for a respective pressure pulse measured within the second measurement time period T2, a blood pressure determination value TPWP S on the basis of a combination of at least two of the determined features, such that a number of blood pressure determination values TPWP S is determined for a number of pressure pulses existing at different times, wherein the number of blood pressure determination values TPWP S determined for the number of pressure pulses and thus for the number of times forms a blood pressure determination curve TPW S-curve.

[0134] Thus, a number of features can be determined for a respective pressure pulse measured in the second measurement time period T2, wherein a blood pressure determination value TPWP S can be determined by combining at least two of the determined features, such that a number of blood pressure determination values TPWP S is determined for a number of pressure pulses existing at different times, wherein the number of blood pressure determination values TPW S determined for the number of pressure pulses and thus for the number of times forms a blood pressure determination curve TPW S-curve.

[0135] The control device 3 is configured such that the blood pressure determination curve TPW S - curve comprising the number of blood pressure determination values TPWP S is formed based on a low pass filtering of the number of blood pressure determination values TPWP S. Here, the low pass filtering is preferably also a moving average filtering, which is preferably centered on the time for which the average is to be determined. In particular, the control device 3 is configured such that the low pass filtering of the number of starting values TPWP F and the low pass filtering of the number of blood pressure determination values TPWP S both use a filter window, wherein the filter window used for the low pass filtering of the number of starting values TPWP F has a window length which is smaller than the filter window used for the low pass filtering of the number of blood pressure determination values TPWP S. For example, the window length used for the low pass filtering of the number of blood pressure determination values TPWP S can be twice the window length used for the low pass filtering of the number of starting values TPWP F. In an embodiment, the window length used for the low pass filtering of the number of blood pressure determination values TPWP S is 8s, while the window length used for the low pass filtering of the number of starting values TPWP F is 4s. Furthermore, in an embodiment, the low pass filtering of the number of blood pressure determination values TPWP S is performed several times, preferably twice, while the low pass filtering of the number of starting values TPWP F can be performed only once. This results in a stronger low pass filtering of the measurement values obtained in the second measurement time period T2 compared to the filtering of the measurement values obtained in the first measurement time period T1, which in turn allows a more accurate determination of the blood pressure based on the blood pressure determination curve TPW S - curve. The low pass filtering is preferably performed such that the cardiopulmonary interaction is eliminated in the blood pressure determination curve TPW S - curve in order to allow a high quality blood pressure determination. For the starting curve, it is not necessarily required to eliminate the cardiopulmonary interaction, since a rough estimate of the blood pressure and the ability to detect the maximum of the starting curve TPW F - curve is sufficient. In an embodiment, the respiratory rate value RR is determined even in the second measurement time period using the cardiopulmonary interaction which is detectable on the starting curve in the second measurement time period. Thus, the starting curve TPW F - curve can also be determined in the second measurement time period based on the pressure pulses measured in the second measurement time period, as Figure 5 indicated in Fig. 1.

[0136] In an embodiment, the blood pressure determination curve TPW S - curve is determined as explained in WO 2018 / 210931 Al. In particular, determining the arterial blood pressure based on the determined maximum of the blood pressure determination curve and depending on the pressure applied on the skin, i.e. the tissue pressure, allows for a relatively short measurement time. In general, the tissue pressure depends on the height of the arterial blood pressure, the height of the arterial pulse pressure and the inverse of the heart rate.

[0137] As described in WO 2018 / 210931 A1, in an embodiment, the control device 3 is configured to determine the TPcl value at the time point at which the blood pressure determination curve TPW_S-curve has its maximum (TPW_S-curve.max), wherein the TPcl value at the time of this maximum can be denoted as "TPcl@TPW_S-curve.max". The control device 3 is further configured to determine a lower envelope of the tissue pressure TP by applying a filter to the end diastolic point of the tissue pressure TP. The filter can be the same as the filter used for determining e.g. the blood pressure determination curve TPW_S-curve. The generated curve can be denoted as "TPdia-curve". Furthermore, the control device 3 can be configured to determine an upper envelope of the tissue pressure TP by applying a filter to the systolic maximum of the tissue pressure TP. And, this filter can be similar to the filter used for e.g. generating the blood pressure determination curve TPW_S-curve. This curve can be denoted as "TPsys-curve". Then, the control device 3 can be configured to determine the systolic arterial pressure value as a predetermined percentage (TPcl.s%) of TPcl@TPW_S-curve.max. This predetermined percentage is preferably in the range of 100% to 150%, further preferably in the range of 110% to 150%. The non-invasive systolic arterial pressure can be denoted as "SAPni" and the predetermined percentage can be denoted as "TPcl.s% (TPcl@TPW_S-curve.max)".

[0138] The control device 3 can further be adapted to determine the non-invasive systolic arterial pressure SAPni as a predetermined percentage (TPsys.s%) of the TPsys-curve at the time position at which the blood pressure determination curve TPW_S-curve has its maximum. This predetermined percentage is preferably in the range of 100% to 140%.

[0139] The control device 3 can be configured to determine the non-invasive mean arterial pressure (MAPni) as the TPcl value or alternatively the value of the TPdia-curve or alternatively the value of the TPsys-curve at the time point t(bx) which is the time point at which the blood pressure determination curve TPW_S-curve has a value bx representing a predetermined percentage relative to its maximum. The control device 3 can further be adapted to alternatively determine the non-invasive mean arterial pressure MAPni as a predetermined percentage (TPcl.m%) of TPcl on the TPW_S-curve, wherein the predetermined percentage is preferably in the range of 80% to 110%.

[0140] The control device 3 can further be configured to determine the non-invasive diastolic arterial pressure DAPni at a time point t(cx) as the value of the TPdia-curve or alternatively of the TPcl-curve, which time point t(cx) is the time point at which the blood pressure determination curve TPW_S-curve has a value cx representing a predetermined percentage of its maximum value. The control device 3 can further be configured to determine DAPni alternatively as a predetermined percentage of TPcl@TPW_S-curve.max, wherein the predetermined percentage is preferably in the range of 60% to 80%. Preferably, the control device 3 is configured to determine the first blood pressure values based on the starting curve TPW_F-curve in the same way, i.e. in the way as described above with respect to the TPW_S-curve, wherein possibly a different determination of the first blood pressure values based on the parameters (like percentage values) of the TPW_F-curve than for the determination of the blood pressure values based on the TPW_S-curve is used. Further, the parameters for determining the first blood pressure values based on the starting curve TPW_F-curve can be determined beforehand by calibration.

[0141] As described above, the indices for determining the starting curve TPW_F-curve and for determining the blood pressure determination curve TPW_S-curve are determined by calibration. The percentages for determining the blood pressure values are also determined by calibration. Thus, these parameters are determined beforehand such that the deviation between the very precisely measured invasive blood pressure values and the blood pressure values obtained by the measurement system is minimized during the calibration phase and the time required for the blood pressure measurement is relatively low.

[0142] The values TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d%, bx, cx are preferably calibrated as described in WO 2018 / 210931 A1 by statistical evaluation of a calibration set consisting of simultaneously recorded measurement values from a sufficient number of individuals under different hemodynamic conditions from invasive blood pressure values and non-invasive blood pressure values. The non-invasive blood pressure values are determined by the measurement system 1 as described above and the parameters such as the values TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d% can be optimized such that the deviation between the invasive blood pressure values and the non-invasive blood pressure values is minimized.

[0143] The control device 3, in particular the processor 11 of the control device 3, can be adapted to estimate one blood pressure value based on two other already measured blood pressure values. In particular, one of the blood pressure values MAPni, SAPni and DAPni can be estimated based on the other one of these blood pressure values. This can be done according to the following formula:

[0144] SAPni = c1 · MAPni + c2 · (MAPni - DAPni) - c3 mmHg (4)

[0145] wherein cl = (0.2..0.7), c2 = (2..6), c3 = (-5..5),

[0146] MAPni = c4 DAPni + c5 (SAPni - DAPni) - c6 mmHg (5)

[0147] wherein c4 = (0.8..1.3), c5 = (0.25..0.5), c6 = (-5..5),

[0148] DAPni = c7 MAPni - c8 (SAPni - MAPni) - c9 mmHg (6)

[0149] wherein c7 = (0.6..1.1), c8 = (0.15..0.4), c9 = (-5..5),

[0150] The coefficients and constants of the formulas (4), (5) and (6) are predetermined by calibration based on statistical evaluation of as large and as sufficiently widely distributed as possible clinical invasive blood pressure data sets. Thus, very accurate invasive blood pressure values SAPi (invasive systolic arterial pressure), MAPi (invasive mean arterial pressure) and DAPi (invasive diastolic arterial pressure) are used, wherein given these very accurate invasive blood pressure values, the coefficients and constants of the formulas (4), (5) and (6) are corrected so that these formulas are valid.

[0151] The blood pressure measurement is intended to be used in a fast successive measurement sequence to allow an efficient semi-continuous blood pressure monitoring so that the stress for the monitored individual (i.e. the monitored subject) is minimized. This fast stress measurement sequence can also be regarded as a non-invasive fast mode cyclic measurement of the blood pressure.

[0152] The control device 3 can be configured to determine a blood pressure determination value TPWP S for the respective pressure pulse based on multiplying a) the determined area TPA or TPA.norm by a predetermined power of a tenth exponent exp10 and b) the determined difference TPP by a predetermined power of an eleventh exponent exp11. For example, the blood pressure determination value TPWP S can be calculated for the respective pressure pulse according to the following formula:

[0153] TPWP S = TPA.norm exp10 · TPP exp11 (7)

[0154] wherein the predetermined exp10 ≠ 0, exp11 ≠ 0.

[0155] The control device 3 can further be configured to determine a blood pressure determination value TPWP_S for the respective pressure pulse by dividing a) the determined area TPA or TPA.norm by b) the determined duration (t(pulse)) to the power of a predetermined twelfth exponent (exp12) and multiplying the resulting quotient by c) the determined difference TPP to the power of a predetermined fourteenth exponent (exp14). For example, the blood pressure determination value TPWP_S can be calculated according to the following formula:

[0156] TPWP_S = TPA.norm exp12 / t(pulse) exp13 • TPP exp14 (8)

[0157] wherein the predetermined exp12≠0, exp13≠0, exp14≠0.

[0158] The control device 3 can further be configured to determine a blood pressure determination combined value TPWP_S for the respective pressure pulse by further multiplying the width W50 at half the maximum value by the power of a further predetermined exponent. For example, the blood pressure determination combined value TPWP_S can be calculated according to the following formula:

[0159] TPWP_S = TPA.norm exp15 / t(pulse) exp16 • TPP exp17 • W50 exp18 (9)

[0160] wherein the predetermined exp15≠0, exp16≠0, exp17≠0, exp18≠0.

[0161] The control device 3 is configured to determine the blood pressure based on the blood pressure determination curve TPW_S-curve. Preferably, the control device 3 is configured to determine a maximum value of the blood pressure determination curve TPW_S-curve and to determine the blood pressure based on the determined maximum value and the measured pressure.

[0162] The different indices are preferably predefined and can be predetermined by a calibration measurement, wherein by the invasive device a reference blood pressure value is determined very precisely and the indices are determined such that the measurement system controlled by the control device produces very precisely non-invasive measured blood pressure values with high precision and accuracy. Specifically, for the calibration a simultaneous recorded measurement pair of invasive and non-invasive blood pressure values from a sufficient number of individuals under different hemodynamic conditions is used. It should be noted that the calibration is preferably only carried out in the development phase, i.e. not during actual blood measurement. The calibration can be carried out individually for different housing sizes, i.e. preferably for different blood pressure cuff sizes or for different housing size groups. For example, for different housing sizes or housing size groups a different set of indices can be determined by the calibration, i.e. for each housing size or each housing size group a respective set of indices can be determined.

[0163] The control device 3 is configured to determine further hemodynamic monitoring parameters based on the pressure measured in the second measurement time period T2. Specifically, the control device 3 is configured to determine at least one of a fluid response parameter FRP, a cardiac output CO, a systemic arterial resistance SAR and a cardiac power output CPO as a hemodynamic monitoring parameter. As fluid response parameter FRP, a pulse pressure variation PPV, a systolic pressure variation SPV or a stroke volume variation SPV can be determined based on the pressure measured in the second measurement time period T2. For determining one or several hemodynamic monitoring parameters, i.e. one or several hemodynamic parameters, based on the pressure measured in the second measurement time period T2, known algorithms can be used, like the algorithms disclosed in EP 2 759 257 B1 and WO 2019 / 211210 A1, which are incorporated herein by reference.

[0164] As described above, for determining the starting curve TPW_F-curve, the blood pressure determination curve TPW_S-curve and the envelope curves TPsys-curve and TPdia-curve, filters are used. Further, for determining TPcl based on TP, filters are used as well. As filters, preferably low pass filters are used. For example, the low pass filter can be a cascaded moving average filter with a window length of up to 8s, wherein the window length can be shorter at the beginning and end of the filter to minimize the filter settling time. For example, the filtering can comprise averaging over a moving window containing at least three TP pressure pulse curves and a signal of maximum 8s and applying a two times moving average filter (2x8s filter). Optionally, signal padding can be applied before the start and / or after the end of the signal to fill the filter window completely before filtering. For example, padding with the first pressure pulse value before the start and with the last pressure pulse value after the end can be applied.

[0165] In an embodiment, due to the filter delay, TPcl is extrapolated from its previous value to the last part of the signal available for the measurement. The filter enables to apply, for example, to extract TPcl from TP, to form a smoothed TPW_F-curve and a smoothed TPW_S-curve, free of changes caused by blood pressure pulsations, and to create an envelope function on the systolic peak (TPsys-curve) and the diastolic minimum (TPdia-curve). However, the smoothing is preferably such that the TPW_F-curve still shows the cardiopulmonary interaction.

[0166] In an embodiment, for defining the blood pressure determination curve TPW_S-curve, the formula (8) is used with the following exponents exp12=0.7, exp13=0.4, exp14=1.0. By using these exponents with formula (8), a very good precision and accuracy can be obtained for blood pressure values validated with a statistical evaluation of non-invasive blood pressure values determined by the measurement system 1 with simultaneously (specifically in the range of 20 to 60 seconds of the inhalation-exhalation time period) acquired invasive blood pressure reference values. The following set of exponents with formula (7) leads to a higher precision and accuracy, but also to a measurement time of several seconds longer: exp10=1.0, exp11=1.21. In an embodiment, for determining the starting curve TPW_F-curve, formula (2) is used with the following exponents: exp3=1.1, exp4=0.4, exp5=0.5.

[0167] In the following, embodiments of a control method for controlling the measurement system 1 will be exemplarily described with reference to the flowchart shown in Figure 10 Fig. 2.

[0168] After initializing and starting the system in step 101, in step 102, the pressure applicators 6, 8 increase the applied pressure over time with a zeroth slope in a zeroth measurement time period To. During the zeroth measurement time period To, the pressure sensor 7 measures the pressure TP on the skin, wherein the measured pressure TP comprises several pressure pulses. Further, still in step 102, a heart rate value HR indicative of the heart rate of the subject is determined based on at least one pressure pulse of the measured pressure TP in the zeroth measurement time period To, and after determining the heart rate value HR, a first slope is determined based on the determined heart rate value HR. Specifically, after having detected two subsequent pressure pulses and using them for determining the heart rate value HR, in step 103, a first measurement time period T1 occurs with the determined first slope.

[0169] In step 103, in the first measurement time period T1, for each of at least some of the plurality of pressure pulses, a number of features characterizing the respective pressure pulse is determined, and, for the respective pressure pulse, based on a combination of at least two of the features that have been determined for the respective pressure pulse, a starting value TPWP_F for determining the start of the second measurement time period T2 is determined, such that for a number of pressure pulses occurring at different times a number of starting values TPWP_F are determined. Further, still in step 103, based on the number of starting values TPWP_F, a starting curve TPW_F-curve for determining the start of the second measurement time period T2 is formed, wherein the second measurement time period T2 occurs subsequently after the starting curve TPW0_F-curve has reached a first maximum value.

[0170] In step 104, the second measurement time period T2 is performed, wherein based on the pressure measured in the second measurement time period a blood pressure value is determined.

[0171] After the second measurement time period T2, in step 105, the cuff is deflated. After the deflation and pause in step 106 to allow venous return, the method continues to step 102. Thus, the control method can be performed in a loop for a number of measurement cycles continuously monitoring the blood pressure over time. While steps 102 to 105 are performed, the control device calculates the blood pressure value in parallel. The loop can be performed until a termination criterion is met. For example, if the physician has input a respective command to the measurement system via an input unit, e.g. a keyboard, a computer mouse, a touchpad, etc., the blood pressure monitoring is interrupted.

[0172] The measurement system 1 provides a heart rate value HR and a non-invasive blood pressure niBP adaptive method to shorten the measurement time with a high-fidelity oscillometric blood pressure cuff, which results in less strain on the measured limb and less stress for the patient. The time-optimized adaptive clamping pressure control is divided into three parts, namely a zeroth measurement time period TO that prioritizes maximum fast pre-inflation, a first measurement time period T1 that prioritizes fast inflation related to the heart rate value HR, and a second measurement time period T2 that prioritizes slow inflation related to the niBP.

[0173] The measurement system can be adapted such that the measurement starts with a maximum possible TPcl increase rate which allows to detect at least two subsequent pressure pulses TP below TPcl = MAP. For example, in this zeroth measurement time period To, the increase rate, i.e. the zeroth slope, can be 8 mmHg / s. The control device can then be configured to determine a heart rate value HR as soon as two subsequent pressure pulses TP have been detected. Then, a switch to a first measurement time period Ti can be made, in which a TPcl increase rate related to the heart rate value HR is used preferentially. This increase rate, i.e. the first slope, can be for example 4 mmHg / PW, where PW indicates the width of the respective pulse. The measurement is performed during the first measurement time period Ti such that enough pressure pulses TP can be collected which allows to provide a first estimate of the blood pressure value niBP, where TPcl can be close to MAP. In particular, in the first measurement time period Ti, a fast tissue pressure waveform curve TPW_F-curve, i.e. a start determination curve TPW-F-curve, is recorded based on start values TPWP_F determined from characteristics and statistical predetermined indices of the pressure pulses. The start values TPWP_F are filtered by using a moving average filter with a window length of 4 s, which results in a filter delay of 2 s for example. The window length is preferably chosen such that a good balance between the minimum filter delay and an acceptable accuracy of the first estimate of the blood pressure value niBP for further inflation control is achieved. As shown in Fig. 3, the filtering, i.e. smoothing, can be performed such that the cardiopulmonary interaction can still be seen in the resulting TPW_F-curve. Figure 5

[0174] After a first maximum of the TPW_F-curve has been detected, a first blood pressure value niBP estimate can be calculated based on the TPW_F-curve as described above with reference to the TPW_S-curve. The TPWP_F-curve can be formed based on TPWP_F values defined by equations (1), (2) or (3) for example. However, it is also possible to determine the TPWP_F values by using other combinations of the indexed characteristics. For example, the TPWP_F values can be determined from a determination of TPWP_S values as described in equations (4), (5) or (6) for example. It is also possible to determine the TPWP_S values and / or the TPW_F values according to the following equations:

[0175] TPWP = TPA.top exp19 / t(pulse) exp20 • TPP exp21 • W50 exp22 (10).

[0176] It is also possible to determine the TPWP_F and TPW_S values according to the following equations: ​

[0177] TPWP = TPA.top.norm exp23 / t(pulse) exp24 • TPP exp25 • W50 exp26 (11).

[0178] The feature TPA.top.norm is normalized to the TPPd area TPA.top. As described above, the exponents in equations (10) and (11) are determined by calibration. If MAPni, i.e. the non-invasive mean arterial pressure, shall be determined, then equations (1), (2) and (3) are preferred, since TPA.norm is relatively sensitive to waveform changes, i.e. pressure pulse changes, at lower TP pulse areas, when TPcl crosses the mean arterial pressure. If SAPni, i.e. the non-invasive systolic arterial pressure, shall be determined, then equations (10) and (11) can be preferred, since TPA.top and TPA.top.norm are more sensitive to TP pulse waveform changes near TPsys at TPcl close to SAP. It is also possible to determine TPWP-F and / or TPWP-S values according to the following equations:

[0179] TPWP = TPA.top exp27 • TPA.top.norm exp28 • TPA.norm exp29 / t(pulse) exp30 • TPP exp31 • W50 exp32 (12)

[0180] Furthermore, the exponents for equation (12) can be obtained by calibration, wherein in equation (12) as well as in other equations, different sets of exponents can be used, depending for example on whether SAPni or MAPni shall be determined. It is also possible to determine several niBP values in different ways and then to combine these niBP values in a weighted manner. For example, a DAPni value can be determined based on a TPW-curve, i.e. based on a TPW_F-curve and / or a TPW_S-curve, and this DAPni value can be combined in a weighted manner with other DAPni values which have been determined based on an estimation formula similar to equation (6). It is also possible to determine several TPW curves, i.e. for example several TPW_S-curves, by using different combinations of determined features as described in the above equations, to determine for each TPW curve a respective blood pressure value similar to a SAPni or MAPni value, and to combine the several blood pressure values determined for the several TPW-curves in a weighted manner. The weighted combination of the several blood pressure values can for example simply be an average.

[0181] After the first maximum of the TPW_F-curve has been detected and the first blood pressure value has been determined based on the TPW_F-curve as the first SAPni value, the second measurement time period T2 starts with a slower TPcl increase rate, i.e. with a second slope which is smaller than the first slope. The second slope is preferably chosen such that it allows to record at least 3.5 ventilation or breathing cycles until TPcl = SAPni + 20 mmHg for calculating the fluid responsiveness parameter FRP. Depending on the degree of fluid responsiveness, the breathing rate RR can be already detected online during the measurement by using the TPWP values, i.e. a combination of features which are sensitive to the heart-lung interaction, as shown in Figure 5 In an embodiment, the second measurement time period T2 can be terminated as soon as 3.5 breathing or ventilation cycles have been identified. Otherwise, the second slope can be set according to a maximum expected ventilation or breathing cycle duration of 7.5 s corresponding to a breathing rate of 8 / min.

[0182] In the second measurement time period T2, a relatively slower TPW_S-curve for a more accurate niBP estimation is recorded compared to the niBP estimation made based on the pressures measured in the first measurement time period T1. The TPWP_S values are filtered by using, for example, an adaptive moving average over two windows each of up to 8 s, wherein the window length of the window over which the average is taken is longer compared to the window length used for the TPWP_F values. Specifically, the filtering, i.e. smoothing, of the TPWP_S values is such that the heart-lung interaction is eliminated, whereas the filtering of the TPW_F values is such that the heart-lung interaction is still visible, as shown in Figure 5 Correspondingly, the TPW_S-curve does not show any heart-lung interaction anymore, which facilitates a more accurate final blood pressure measurement.

[0183] When measuring the pressures in the second measurement time period T2, the second slope can be continuously adjusted based on the blood pressure values determined during the second measurement time period T2, which are determined based on the TPW_S-curve formed during the measurement. The second slope can also be continuously corrected based on the breathing rate detected online, which can be obtained from other devices or which can be obtained from the heart-lung interaction visible in the TPW_F-curve formed during the second measurement time period T2.

[0184] After the second measurement time period T2 has stopped, a final non-invasive blood pressure value and advanced hemodynamic monitoring parameters can be determined. For example, the control device can be configured to determine at least one of a fluid responsiveness parameter (FRP), a cardiac output (CO), a systemic arterial resistance (SAR) and a cardiac power output (CPO) as a hemodynamic monitoring parameter. The control device can be adapted to determine, for example, a pulse pressure variation (PPV), a systolic pressure variation (SPV) or a stroke volume variation (SPF) as a fluid responsiveness parameter (FRP) based on the pressure measured in the second measurement time period. The cardiac power output CPO can be determined by multiplying the mean arterial pressure with the cardiac output CO.

[0185] In other embodiments, the control device 3 is configured such that the second measurement time period ends after the TPW_S-curve has reached its maximum value, as Figure 11 is schematically and exemplarily shown. If no FRP is required, this is particularly preferred. If only a blood pressure value shall be measured, this is also preferred. The cycle time can then be shortened, which also reduces the maximum necessary TPcl to a level below the SAP. Thus, the perfusion at the measurement site of the subject is never completely interrupted. Furthermore, the measurement time is significantly shortened, which leads to a reduction of the physical stress of the subject. This is important for long-term monitoring, especially in septic patients with altered skin, for example. After the maximum value of the TPW_S-curve has been detected, a blood pressure value, such as the SAPni or the DAPni, can be determined based on the maximum value of the TPW_S-curve as described above. It is also possible to determine the parameters SV, CO, SAR and CPO as described above.

[0186] Although in the above described embodiments the features are determined by using the TPac pulse, it is also possible to determine the features by directly using the measured pressure pulse, i.e. the TP pulse. It is also possible to process the TP pulse in another way, i.e. not by subtracting the mean TP value to determine the TPac pulse. For example, the pressure values at t.start and t.stop can be connected by a straight line for the respective measured pressure pulse, and this straight line can be subtracted from the respective measured pressure pulse in order to determine the feature determining pulse.

[0187] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0188] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality.

[0189] A single unit or device can implement the functionality of several items listed 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.

[0190] The determination of similar pulse characteristics, certain curves, blood pressure values, etc. performed by one or several units or devices can be performed by any other number of units or devices. The calculation and / or control of the measurement system according to the control method can be implemented as program code means of a computer and / or as dedicated hardware.

[0191] A computer program can be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state storage medium supplied together with other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0192] Any reference signs in the claims should not be construed as limiting the scope. In particular, any references to a method should not be construed as limiting the scope to the specific steps of the method. Specific features of the method may, for example, be implemented in the form of computer program code units and / or dedicated hardware.

[0193] The present invention relates to a control device for controlling a measurement system for measuring a blood pressure and optionally a hemodynamic parameter of a subject. In a first measurement time period, for a measured pressure pulse, a feature is determined which characterizes the respective pressure pulse. Based on the feature, a starting value is determined and based on the starting value a starting curve TPW_F-curve is formed. The measurement system is controlled such that after the starting curve has reached a first maximum value, a second measurement time period occurs subsequently, wherein based on a pressure measured in the second measurement time period a blood pressure value is determined. It has been found that by using the maximum value in the first measurement time period to define a starting point for the actual blood pressure measurement, the blood pressure value and optionally the hemodynamic parameter of the subject can be determined very accurately and quickly.

Claims

1. A control device for controlling a measurement system (1) for measuring the blood pressure of a subject, wherein, The measuring system (1) includes a) a housing (4) configured to enclose the portion (5) through which blood flows of the object, b) pressure applicators (6, 8) configured to apply pressure from the outside of the housing (4) to the housing (4), thereby applying pressure to the enclosed portion (5) of the object, and c) a pressure sensor (7) configured to measure the pressure (TP) on the skin of the enclosed portion (5) of the object, wherein the control device (3) is configured to control the measuring system (1) such that The pressure applied by the pressure applicators (6, 8) increases over time during a first measurement time period (T1) with a first inclination and during a second measurement time period (T2) with a second inclination, wherein the first measurement time period (T1) and the second measurement time period (T2) are arranged in this temporal order. The pressure sensor (7) measures the pressure (TP) on the skin during the first measurement time period and the second measurement time period, wherein the measured pressure (TP) includes a plurality of pressure pulses (9). The control device (3) is further configured to: during the first measurement time period (T1), for each pressure pulse of at least some of the plurality of pressure pulses (9), determine at least one feature characterizing the pressure pulse (9); for the pressure pulse (9), based on the at least one feature already determined for the pressure pulse (9), determine an initial value (TPWP_F) to be used to determine the start of the second measurement time period, such that for a plurality of pressure pulses (9) occurring at different times, a plurality of initial values ​​(TPWP_F) are determined; based on the plurality of initial values ​​(TPWP_F), form an initial curve (TPW_F-curve) to be used to determine the start of the second measurement time period; and, after the initial curve (TPW_F-curve) has reached a first maximum value, control the measurement system (1) so that the second measurement time period subsequently occurs. - The blood pressure value (niBP) is determined based on the pressure (TP) measured during the second measurement time period (T2). The control device (3) is further configured to determine a first blood pressure value based on the initial curve (TPW-F-curve) during the first measurement time period (T1); determine a second slope based on the determined first blood pressure value; and control the measurement system (1) after the initial curve (TPW-F-curve) has reached a first maximum value, so that the second measurement time period (T2) subsequently appears with the determined second slope.

2. The control device as described in claim 1, wherein, The control device (3) is also configured to control the measurement system (1), such that The pressure applicators (6, 8) also increase the applied pressure over time during a zero measurement time period (T0) with a zero slope, wherein the zero measurement time period (T0) is arranged temporally before the first measurement time period (T1), and wherein the first slope is less than or equal to the zero slope. The pressure sensor (7) also measures the pressure (TP) on the skin during the zeroth measurement time period, wherein the measured pressure (TP) includes at least one pressure pulse (9). The control device (3) is further configured to determine a heart rate value (HR) indicating the heart rate of the object based on at least one pressure pulse (9) of the pressure (TP) measured in the zero measurement time period (T0), and after determining the heart rate value (HR), determine the first slope based on the determined heart rate value (HR), and control the measurement system (1) such that the first measurement time period (T1) subsequently occurs with the determined first slope.

3. The control device as described in claim 2, wherein, The control device (3) is configured to also determine the heart rate value (HR) during the first measurement time period (T1) and correct the first slope based on the heart rate value (HR) determined during the first measurement time period.

4. The control device according to any one of claims 1-3, wherein, The control device (3) is configured such that forming the initial curve (TPW_F-curve) based on the plurality of initial values ​​(TPWP_F) includes low-pass filtering of the plurality of initial values ​​(TPWP_F).

5. The control device according to any one of claims 1-3, wherein, The control device (3) is configured to provide a feature determination pulse (29) based on the pressure pulse in order to determine the at least one feature for the pressure pulse, and to determine at least one of the following features: - The feature determines the difference (TPP) between the maximum systolic pressure (TPsys) of the pulse and the pressure (TPdia) of the pulse at the end of diastole. -The feature determines the duration (t(pulse)) of the pulse (29). -The features determine the entire area (TPA, TPA.norm) of the pulse (29). -The feature determines the width (W50) at half the maximum value of the pulse (29), and -The upper area (TPA.top, TPA.top.norm) below the upper part of the pulse (29) as determined by the feature.

6. The control device according to any one of claims 1-3, wherein, The control device (3) is configured to stop the second measurement period once the provided respiratory rate value (RR) indicates that the second measurement period covers 3.5 respiratory or ventilation cycles (VC) and / or has reached the predetermined maximum measurement period and / or has reached the maximum mean pressure value.

7. The control device as described in claim 6, wherein, The control device (3) is configured to correct the second slope based on the respiratory rate (RR) value determined during the second measurement time period and / or based on the maximum mean pressure value.

8. The control device according to any one of claims 1-3, wherein, The control device (3) is configured as follows: - For a pressure pulse measured during the second measurement time period, a blood pressure determination value (TPWP_S) is determined based on at least one of the at least one determined features, such that for a plurality of pressure pulses occurring at different times, a plurality of blood pressure determination values ​​(TPWP_S) are determined, wherein a blood pressure determination curve (TPWP_S-curve) is formed for the plurality of pressure pulses and therefore for the plurality of blood pressure determination values ​​(TPWP_S) determined for the plurality of times. - The blood pressure value is determined based on the blood pressure determination curve (TPW_S-curve).

9. The control device as claimed in claim 8, wherein, The control device (3) is configured such that forming the blood pressure determination curve (TPW_S-curve) based on the plurality of blood pressure determination values ​​(TPWP_S) includes low-pass filtering of the plurality of blood pressure determination values ​​(TPWP_S).

10. The control device as claimed in claim 9, wherein, The control device (3) is configured such that forming the initial curve (TPW_F-curve) based on the plurality of initial values ​​(TPWP_F) includes low-pass filtering of the plurality of initial values ​​(TPWP_F), and the control device (3) is configured such that both the low-pass filtering of the plurality of initial values ​​(TPWP_F) and the low-pass filtering of the plurality of blood pressure determination values ​​(TPWP_S) use a filter window, wherein the window length of the filter window used for low-pass filtering of the plurality of initial values ​​(TPWP_F) is smaller than the window length of the filter window used for low-pass filtering of the plurality of blood pressure determination values ​​(TPWP_S).

11. The control device according to any one of claims 1-3, wherein, The control device (3) is configured to also determine hemodynamic monitoring parameters based on the pressure measured during the second measurement time period.

12. A measurement system for measuring the blood pressure of a subject, wherein, The measurement system (1) includes: - A shell (4), which is configured to enclose the portion (5) through which the blood of the object flows. - Pressure applicators (6, 8), configured to apply pressure from the outside of the housing (4) to the housing (4), thereby applying pressure to the enclosed portion (5) of the object. - A pressure sensor (7) configured to measure the pressure (TP) on the skin of the wrapped portion (5) of the object, and - The control device as claimed in any one of claims 1 to 11.

13. A control method for controlling the measurement system as described in claim 12, wherein, The control method includes: - By using the pressure applicators (6, 8), the applied pressure is increased over time in a first measurement time period (T1) with a first inclination and in a second measurement time period (T2) with a second inclination, wherein the first measurement time period (T1) and the second measurement time period (T2) are arranged in this temporal order. - The pressure (TP) on the skin is measured during the first measurement time period and the second measurement time period using the pressure sensor (7), wherein the measured pressure (TP) includes a plurality of pressure pulses (9). The method further includes - During the first measurement time period (T1), for each pressure pulse of at least some of the plurality of pressure pulses (9), at least one feature characterizing the pressure pulse (9) is determined; for the pressure pulse (9), based on the at least one feature already determined for the pressure pulse (9), a starting value (TPWP_F) to be used to determine the start of the second measurement time period is determined, such that for a plurality of pressure pulses (9) occurring at different times, a plurality of starting values ​​(TPWP_F) are determined; based on the plurality of starting values ​​(TPWP_F), a starting curve (TPW_F-curve) to be used to determine the start of the second measurement time period is formed; and after the starting curve (TPW_F-curve) has reached a first maximum value, the measurement system (1) is controlled so that the second measurement time period subsequently occurs. - The blood pressure value (niBP) is determined based on the pressure (TP) measured during the second measurement time period (T2). The method further includes determining a first blood pressure value based on the initial curve (TPW-F-curve) during the first measurement time period (T1); determining a second slope based on the determined first blood pressure value; and controlling the measurement system (1) after the initial curve (TPW-F-curve) has reached a first maximum value, so that the second measurement time period (T2) subsequently appears with the determined second slope.

14. A computer-readable medium storing a computer program for controlling a measurement system as claimed in claim 12, the computer program including program code units that, when the computer program is run on the control device (3) of the measurement system (1), cause the measurement system (1) to perform the steps as claimed in claim 13.

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