Device for determining blood pressure of subject

Abstract

The invention relates to determining the blood pressure of a subject on the basis of a pressure signal which has been measured by using a measuring device comprising a) a housing enclosing a portion of the subject through which blood flows, b) a pressure applicator applying pressure to the housing, thereby applying pressure to the enclosed portion of the subject, and c) a pressure sensor that measures a pressure signal on the skin of the wrapped portion of the subject. For several pressure pulses of the pressure signal, a respective characteristic characterizing the respective pressure pulse is determined, and a respective blood pressure determination value is determined on the basis of the respective characteristic, thereby forming a blood pressure determination curve (TPWM-curve) for determining the blood pressure. This allows the blood pressure to be determined with a relatively low computational effort.

Description

Technical Field

[0001] The present invention relates to an apparatus, a method and a computer program for determining the blood pressure of a subject. Background Art

[0002] EP 3818929 A1 discloses a control device for controlling a blood pressure measurement system. An applicator applies increasing pressure to a subject part during a measurement time period while measuring the pressure on the subject part skin, the pressure comprising a plurality of pressure pulses. For each pressure pulse of at least some of the plurality of pressure pulses, several features characterizing the respective pressure pulse are determined, wherein an end measurement time point at which the measurement time period is to be stopped or thereafter is determined based on these features, and wherein when or after the end measurement time point is reached, i.e. when the measurement time period is to be stopped, the applied pressure is reduced to start a subsequent blood pressure post-measurement time period.

[0003] DE 102017110770 B3 discloses a method for non-invasively determining at least one blood pressure value from a tissue pressure signal using a pressure cuff applied to an individual, the tissue pressure signal having a series of tissue pressure pulse curves. At least two separate tissue pressure pulse curves are identified in the tissue pressure signal, and at least one amplitude parameter and an area parameter are determined for each identified tissue pressure pulse curve, the amplitude parameter indicating the amplitude of the identified tissue pressure pulse curve, and the area parameter indicating at least one partial area surrounded by the tissue pressure pulse curve. For each identified tissue pressure pulse curve, a pulsating power parameter is determined, which indicates the shape of the tissue pressure pulse curve based at least on the amplitude parameter and the area parameter. A parameter function is generated, which indicates the functional relationship between the pulsating power parameter of the determined tissue pressure pulse curve and the corresponding clamping pressure at the pressure cuff or the measurement time. At least one blood pressure value is determined based on the parameter function.

[0004] EP 3430992 A1 discloses a blood pressure measurement system configured to surround a subject's body part, wherein the blood pressure measurement system comprises a pressurizing device for applying pressure to the body part and an anti-kink housing. When the blood pressure measurement system surrounds the body part, the anti-kink housing is arranged to be located between the pressurizing device and the body part. The blood pressure measurement system allows blood pressure to be measured by continuously increasing the clamping pressure and stopping when the increase exceeds the systolic blood pressure. Summary of the invention

[0005] It is an object of the present invention to provide an improved device, method and computer program for determining blood pressure which allow, for example, blood pressure to be determined more accurately and / or with a reduced computational effort.

[0006] In a first aspect of the present invention, a device for determining the blood pressure of a subject is provided, wherein the device comprises:

[0007] A pressure signal providing unit, configured to provide a measured pressure signal of an object over a period of time, wherein the pressure signal has been measured by using a measuring device, the measuring device comprising: a) a housing, b) a pressure applicator, and c) a pressure sensor, wherein the housing is configured to enclose a portion of the object through which blood flows, the pressure applicator is configured to apply pressure to the housing, preferably from outside the housing, thereby applying pressure to the enclosed portion of the object, the pressure sensor is configured to measure the pressure signal on the skin of the enclosed portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal indicates blood pulsation and includes a plurality of pressure pulses,

[0008] A processor configured to: determine at least one feature characterizing a corresponding pressure pulse among the multiple pressure pulses; determine a blood pressure determination value for the corresponding pressure pulse based on the determined at least one feature, so that several blood pressure determination values ​​are determined for several pressure pulses existing at different times, wherein a blood pressure determination curve is formed for the several pressure pulses and therefore the several blood pressure determination values ​​determined for several times; and determine the blood pressure based on the blood pressure determination curve.

[0009] It has been found that even if a single feature is considered to determine the blood pressure determination value, the blood pressure can be accurately determined. Therefore, the blood pressure can be accurately determined with a relatively low calculation workload.

[0010] The at least one characteristic may directly characterize the corresponding pressure pulse or indirectly characterize the corresponding pressure pulse. In the latter case, the corresponding pressure pulse is processed to determine a characteristic determination pulse, and at least one characteristic is determined based on the determined characteristic determination pulse. This will be explained in further detail below. The processor can be configured to determine at least one characteristic characterizing the corresponding pressure pulse for each pressure pulse of all or only some (e.g., at least 5 or at least 10) of the plurality of pressure pulses.

[0011] The pressure signal providing unit may be a receiving unit configured to receive a pressure signal from, for example, a measuring device and provide the received pressure signal. However, the pressure signal providing unit may also be a memory having previously measured pressure signals stored therein and may retrieve the pressure signal from the memory to provide the pressure signal. The pressure signal providing unit may also be or include a measuring device for measuring the pressure signal.

[0012] The processor may be adapted to process several blood pressure determination values ​​obtained for several pressure pulses to obtain a continuous blood pressure determination curve. For example, interpolation and optionally also smoothing may be applied.

[0013] In an embodiment, the processor is configured to provide a characteristic determination pulse based on the corresponding pressure pulse in order to determine at least one characteristic for the corresponding pressure pulse, and determine at least one of the following characteristics: i) the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end-diastolic point, ii) the area (TPA+.top) enclosed by the first upper part of the characteristic determination pulse, wherein a) the upper end of the first upper part is at the maximum systolic pressure (TPsys) of the characteristic determination pulse, and b) the lower end of the first upper part is at the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure corresponding to the measured pressure. The invention relates to a method for determining blood pressure by using a second upper portion of the characteristic determination pulse, wherein a) the upper end of the second upper portion is at the maximum systolic pressure (TPsys) of the characteristic determination pulse, and b) the lower end of the second upper portion is between the pressure value corresponding to the average value (TPcl) of the measured pressure (TP) and the pressure (TPdia) of the characteristic determination pulse at the end diastolic point. It has been found that by using at least one of these features, the determination of blood pressure can be further improved.

[0014] For example, the characteristic determination pulse for the corresponding pressure pulse can be obtained by subtracting the average measured pressure (TPcl) from the corresponding pressure pulse. However, the characteristic determination pulse for the corresponding pressure pulse can also be determined in another way. It can also be directly the corresponding pressure pulse, i.e. the corresponding measured pressure pulse. If the characteristic determination pulse for the corresponding pressure pulse has been obtained by subtracting the average measured pressure (TPcl) from the corresponding pressure pulse, then in order to determine the area TPA+.top, the pressure value corresponding to the average value (TPcl) of the measured pressure (TP) will be zero.

[0015] The difference (TPP) between the maximum systolic pressure of the characteristic determination pulse and the pressure of the characteristic determination pulse at the end-diastolic point is preferably the difference between the maximum measured pressure and the minimum measured pressure of the corresponding pressure pulse, that is, the difference between the tissue pressure (TP) of the corresponding pressure pulse at the maximum contraction point (that is, the measured pressure on the skin) and the tissue pressure (TP) of the corresponding pressure pulse at the end-diastolic point. The duration t(pulse) of the corresponding characteristic determination pulse preferably corresponds to the time difference between the end-diastolic point and the next end-diastolic point of the corresponding pressure pulse. In addition, the area TPA is preferably the area under the curve of the corresponding characteristic determination pulse from the end-diastolic point to the next end-diastolic point. The area can be a normalized area and then named "TPA.norm". For example, the area TPA can be normalized by scaling the area TPA to the difference between the maximum pressure and the minimum pressure of the corresponding characteristic determination pulse to determine TPA.norm. The full width at half maximum W50 corresponds to the width at 50% of the difference between the maximum pressure and the minimum pressure of the corresponding characteristic determination pulse. It is therefore the width at which 50% of the difference between the pressure of the characteristic pulse at the point of maximum contraction and the pressure of the characteristic pulse at the point of end-diastole.

[0016] In a preferred embodiment, the processor is configured to determine the area (TPA+.top) enclosed by the first upper portion of the characteristic determination pulse such that the lower end of the first upper portion is at a pressure value corresponding to half the pressure distance (TPP+) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure value corresponding to the average value (TPcl) of the measured pressure (TP). In this case, the area enclosed by the first upper portion is named TPA+.top50.

[0017] Furthermore, in a preferred embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M) based only on the following feature, and thus form a blood pressure determination curve (TPW_M curve): a feature of the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) at the end diastolic point of the characteristic determination pulse. Therefore, in this embodiment, in addition to TPP, no other of the above features are used to determine the blood pressure determination value. It has been found that this allows to further improve the accuracy of determining the blood pressure with a relatively low computational workload.

[0018] Furthermore, in a preferred embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M) and thus form a blood pressure determination curve (TPW_M-curve) based on only one feature from the following list of features: i) the area of ​​the corresponding feature determination pulse (TPA / TPA.norm), ii) the area enclosed by the first upper part of the feature determination pulse (TPA+.top), and iii) the area enclosed by the second upper part of the feature determination pulse (TPA.top). Therefore, in this embodiment, in addition to TPA or TPA.norm or TPA+.top or TPA.top, no other of the above features are used to determine the blood pressure determination value. It has been found that this also allows to even further improve the accuracy of determining the blood pressure, wherein the computational workload may still be relatively low.

[0019] In a further improved embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M) and thus form a blood pressure determination curve (TPW_M-curve) based only on the following features: a) a feature as the difference TPP between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end diastolic point, and b) a feature as the area TPA+.top enclosed by the first upper part of the characteristic determination pulse. Therefore, in this embodiment, in addition to TPP and TPA+.top, in particular in addition to TPP and TPA+.top50, no other of the above features are used to determine the blood pressure determination value. It has been found that this allows to even further improve the accuracy of the determination of the blood pressure, wherein the computational workload may still be relatively low.

[0020] In a further improved embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M) and thus form a blood pressure determination curve (TPW_M-curve) based only on the following features: a) a feature as the difference TPP between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end diastolic point, and b) a feature as the area TPA.top enclosed by the second upper part of the characteristic determination pulse. Thus, in this embodiment, apart from TPP and TPA.top, none of the above features are used to determine the blood pressure determination value. It has been found that this allows to even further improve the accuracy of determining the blood pressure, wherein the computational workload may still be relatively low.

[0021] Preferably, the processor is configured to determine the position of the maximum of the blood pressure determination curve (TPW_M-curve) and determine the blood pressure based on the determined position and the measured pressure (TP). In particular, the processor can be configured to determine the blood pressure based on the average value (TPcl) of the measured pressure (TP) at the position of the determined maximum. Determining the blood pressure based on the maximum of the determined blood pressure determination curve and according to the measured pressure on the skin (i.e., according to the tissue pressure) allows to further improve the accuracy of determining the blood pressure.

[0022] As an alternative or in addition to the maximum value of the blood pressure determination curve (i.e., the curve itself), the maximum value of the derivative of the blood pressure determination curve may also be used. That is, the processor may be configured to determine a first position of the maximum value of the blood pressure determination curve and / or a second position of the derivative of the blood pressure determination curve, and determine the blood pressure based on the determined first position and / or second position, respectively, and based on the measured pressure (TP). In particular, the processor may be configured to determine the blood pressure based on an average value (TPcl) of the measured pressure (TP) at the determined first position and / or second position.

[0023] In an example, the processor is configured to determine the position of the maximum value of the derivative of the blood pressure determination curve by determining a first peak of the blood pressure determination curve (the peak value of the first peak is greater than a predetermined percentage of the peak value of the total peak of the blood pressure determination curve) and by determining the position of the maximum value of the derivative of the blood pressure determination curve (which is before the determined first peak). The predetermined percentage of the total peak value can be predetermined by calibration. In a preferred embodiment, the predetermined percentage is 90%. The determination of the first peak of the blood pressure determination curve can be achieved by normalizing the blood pressure determination curve to the peak value of the total maximum peak, the peak value of the first peak being greater than a predetermined percentage of the peak value of the total maximum peak of the blood pressure determination curve, so that the peak value is 1 after normalization. Then, the predetermined percentage is a fixed absolute value between 0 and 1, preferably 0.9. It has been found that limiting the area for determining the maximum value of the derivative of the blood pressure determination curve allows the accuracy of determining the blood pressure to be further improved in this way.

[0024] The maximum value of the derivative preferably refers to the direction from low applied pressure to high applied pressure. In other words, preferably, when measuring the pressure signal for determining the blood pressure, the derivative is considered in the direction from low applied pressure to high applied pressure, regardless of whether the applied pressure is increasing or decreasing.

[0025] Note that the word "before" here refers to the direction from low applied pressure to high applied pressure. Therefore, if the applied pressure increases when measuring the pressure signal for determining blood pressure, the word "before" also means before in time, and if the applied pressure decreases when measuring the pressure signal for determining blood pressure, the word "before" means after in time.

[0026] If the blood pressure determination curve has only a single peak, the single peak is the total maximum peak, and it is also the first peak whose peak value is greater than a predetermined percentage of the peak value of the total maximum peak.

[0027] Preferably, the applied pressure is increased when measuring the pressure signal for determining the blood pressure. This is advantageous compared to reducing the applied pressure when measuring the pressure signal for determining the blood pressure.

[0028] Preferably, the processor is configured to provide a function that receives at least one feature of the corresponding pressure pulse as input and outputs a corresponding blood pressure determination value, which together with the blood pressure determination values ​​determined for other pressure pulses forms a blood pressure determination curve. The function has at least one parameter that can be determined by calibration, wherein a reference blood pressure value is determined very accurately in an invasive manner, and at least one parameter is determined so that the device produces a very accurately invasively measured blood pressure value with high statistical precision and accuracy. In particular, for calibration, measurement pairs of invasive and non-invasive blood pressure values ​​recorded simultaneously from a sufficient number of individuals under different hemodynamic conditions are used. It should be noted that calibration is preferably performed only during the development phase, i.e. not during the actual blood measurement process. Calibration can be performed separately for different housing sizes (i.e., preferably for different blood pressure cuff sizes) or for different groups of housing sizes. For example, for different housing sizes or different groups of housing sizes, different parameters of the function can be determined by calibration, i.e., for each housing size or for each group of housing sizes, a corresponding at least one parameter can be determined.

[0029] For example, the processor may be configured to determine the blood pressure determination value (TPWP_M) based on the at least one feature for the corresponding pressure pulse by raising the determined at least one feature to the power of a predefined exponent. The predefined exponent may be predefined by calibration as described in the previous paragraph. Thus, the predefined exponent may be a parameter of the function mentioned in the previous paragraph, wherein the parameter (i.e., the predefined exponent in this example) is predefined by calibration. The function may have the following structure: a) a predefined factor multiplied by b) a result of a first exponential operation that raises a first feature characterizing the corresponding pressure pulse to the power of a first predefined exponent, optionally further multiplied by c) a result of a second exponential operation that raises a second feature characterizing the corresponding pressure pulse to the power of a second predefined exponent, optionally further multiplied by d) a result of a third exponential operation that raises a third feature characterizing the corresponding pressure pulse to the power of a third predefined exponent, and so on, wherein, in a preferred embodiment, the function includes only a) and b) or only a), b) and c). The predefined factor may also be predefined by calibration. In the example, the predefined factor is 1.

[0030] In an embodiment, a pressure sensor is arranged within the housing, the pressure sensor being configured to measure the pressure on the skin of the wrapped portion of the subject. However, the pressure sensor may also be arranged in another manner for measuring the pressure on the skin of the wrapped portion of the subject. For example, a pressure sensor pad filled with a fluid may be arranged inside the housing and connected to a pressure sensor outside the housing via a fluid path (i.e., via a pipe filled with a fluid) to measure the pressure on the skin of the wrapped portion of the subject.

[0031] In an embodiment, the processor is configured to control the measuring device such that the applied pressure is increased during a measuring time period extending to an end measurement time point and the applied pressure is reduced during a subsequent post-blood pressure measurement time period, wherein the pressure sensor measures the pressure (TP) on the skin at least during the measuring time period, wherein the processor is configured to determine an end measurement time point based on at least one feature determined for at least some of the plurality of pressure pulses, at or after which the measuring time period will stop, and to control the pressure applicator such that it reduces the applied pressure to start a subsequent post-blood pressure measurement time period when or after the end measurement time point has been reached. In particular, the at least one feature determined for each of these pressure pulses can be used to determine the end measurement time point such that the measuring time period is relatively short and sufficient pressure data has still been measured, which allows an accurate determination of the blood pressure. This allows a reduction in the blood pressure measurement time and tissue pressure, i.e. the clamping pressure applied to the skin of the body part during the measurement is kept substantially below the arterial systolic pressure.

[0032] Preferably, the processor is configured to: a) determine, for the respective pressure pulse, an end determination value based on at least one feature that has been determined for the respective pressure pulse, so that for several pressure pulses present at different times, several end determination values ​​are determined, wherein the several end determination values ​​determined for the several pressure pulses and therefore for the several times form an end determination curve, and b) determine the end measurement time point based on the end determination curve. By using the end determination curve, the accuracy of determining the end measurement time point can be further improved. The processor can be adapted to process several end determination values ​​obtained for several pressure pulses to obtain a continuous end determination curve. In order to obtain a continuous curve based on different end determination values, known mathematical techniques can be used. For example, interpolation, fitting processes, filtering processes, etc. can be applied.

[0033] The processor is preferably configured to determine the end determination curve such that it satisfies one of the following conditions: a) the maximum of the end determination curve occurs temporally before the maximum of the blood pressure determination curve, b) the maximum of the end determination curve occurs temporally at or after the maximum of the blood pressure determination curve, and the decrease of the end determination curve after its maximum is steeper than the decrease of the blood pressure determination curve after its maximum, and c) the end determination curve is identical to the blood pressure determination curve. It has been found that if the end determination curve and the blood pressure determination curve have one of these relationships relative to each other, the end measurement time point can be determined more accurately.

[0034] In a preferred embodiment, the processor is configured to determine the end measurement time point further based on the blood pressure determination curve. It has also been found that the measurement time can be even further reduced if not only the end determination curve but also the blood pressure determination curve is used to determine the end measurement time point.

[0035] Preferably, the processor is configured to determine the end measurement time point by determining a) when the end determination curve drops to a value equal to or less than a predetermined percentage of the maximum value after exceeding its maximum value and b) when the blood pressure determination curve reaches or exceeds its maximum value. Further preferably, the predetermined percentage of the maximum value is in the range of 40% to 95%. It has been found in particular that if two curves are used in this way to determine the end measurement time point, the time point can be determined very accurately, so that the blood pressure measurement time is relatively short and the blood pressure is still measured very accurately.

[0036] In an embodiment, the processor is configured to control the pressure applicator so that it increases the applied pressure at a first rate in a preceding measurement period, the preceding measurement period being followed by a measurement period, and increases the applied pressure at a second rate in the measurement period, wherein the first rate is greater than the second rate. Thus, the applied pressure at which the measurement period should start can be reached relatively quickly, thereby allowing the total time required to measure blood pressure to be further reduced.

[0037] In an embodiment, the processor is configured to control the pressure applicator so that at the end of the previous measurement period, the measured pressure is in the range of 15 to 30 mmHg. This ensures that the pressure on the skin, i.e. the tissue pressure, is measured in a sufficiently large pressure range during the measurement period, which allows accurate and precise measurement of blood pressure.

[0038] If the processor does not use a previous arterial diastolic pressure obtained by a previous blood pressure measurement of the same subject to control the pressure applicator, the range of 15 to 30 mmHg is preferentially applied. If the previous arterial diastolic pressure is used to control the pressure applicator, the measured pressure at the end of the previous measurement period may also be higher. The control of the pressure applicator according to the previously obtained arterial diastolic pressure will be explained below.

[0039] It should be noted that the pressure at the end of the previous measurement time is not the pressure applied between two subsequent blood pressure measurements, in particular before the start of the previous measurement period. This pressure may be named "subordinate pressure" and should not exceed 15 mmHg.

[0040] In an embodiment, the processor is configured to a) store or receive a previous arterial diastolic pressure obtained by a previous blood pressure measurement, b) determine a first end measurement pressure based on the previous arterial diastolic pressure, which first end measurement pressure should exist at the end of the previous measurement period and can therefore also be regarded as a target pressure, so that the first end measurement pressure is less than the previous arterial diastolic pressure, and c) control the pressure applicator so that the measured pressure at the end of the previous measurement period is equal to or less than the determined first end measurement pressure. Preferably, the processor is configured to determine the first end measurement pressure so that it is 90% or less of the previous arterial diastolic pressure. In addition, this ensures that during the measurement period, the pressure on the skin, i.e. the tissue pressure, is measured over a sufficiently large range to accurately and precisely determine the blood pressure.

[0041] In an embodiment, the processor is configured to further store or receive a time at which a previous arterial diastolic pressure was measured, and to determine a first end measurement pressure based on i) the previous arterial diastolic pressure and ii) a time distance to the blood pressure measurement, as indicated by the stored time, at which time distance the previous arterial diastolic pressure was measured. The arterial diastolic pressure may vary over time, wherein the first end measurement pressure may still be determined relatively accurately if the time distance of the blood pressure measurement at which the previous arterial diastolic pressure was measured is taken into account. Thus, despite this uncertainty regarding the variation of the arterial diastolic pressure over time, the end of the previous measurement time period may be determined such that during the subsequent measurement time period, the pressure on the skin, i.e., the tissue pressure, is measured over a sufficiently large range to accurately and precisely determine the blood pressure.

[0042] The processor may also be configured to a) store or receive a previous pressure measured by the pressure sensor during a period between the end of a previous measurement time period of a previous blood pressure measurement and the beginning of a previous measurement time period, and b) control the pressure applicator so that the pressure measured at the beginning of the previous measurement time period is equal to or less than a predetermined pressure value based on the stored or received previous measurement. The predetermined pressure value is preferably equal to or less than 15 mmHg, and further preferably equal to or less than 10 mmHg.

[0043] The pressure measured at the beginning of the preceding measurement time period can be regarded as an auxiliary pressure present during the measurement pause between two subsequent blood pressure measurements (i.e. before the start of the respective blood pressure measurement), wherein the auxiliary pressure is preferably controlled to achieve a given or preset value, i.e. a predetermined pressure value. This control is preferably performed to adapt to changes in the volume of the body part, such as an increase caused by tissue edema (capillary leakage, e.g. in sepsis, hypervolemia) or a decrease caused by a reduction in tissue edema or hypovolemia. This should in particular avoid venous congestion during the measurement pause (i.e. between two subsequent blood pressure measurements), which venous congestion is impaired venous return caused by venous compression, wherein the tissue pressure is higher than the venous pressure in the respective body part. In a preferred embodiment, the pressure on the skin (which can also be regarded as tissue pressure) is measured continuously during the entire process of performing one or more blood pressure measurements, and the pressure applicator is controlled such that venous congestion is avoided during the measurement pause.

[0044] The housing is preferably an anti-kink housing. The anti-kink housing is preferably located (or sandwiched) between the pressure applicator (i.e., for example, the fluid bag) and the wrapped portion of the object. The anti-kink housing is relatively rigid and avoids or at least significantly reduces the generation of wrinkles or kinks at the compression action surface of the pressure applicator (in particular, the fluid bag). Therefore, the measurement accuracy can be improved because there is no wrinkling that negatively affects the amplitude, form and reproducibility of the measurement signal.

[0045] If the pressure applicator includes such a fluid bag, the anti-kink housing preferably exhibits a stiffness that is significantly greater than the stiffness of the fluid bag wall. Preferably, the stiffness of the anti-kink housing is selected to ensure that the anti-kink housing does not buckle when pressure is applied to the wrapped portion of the subject to measure the subject's blood pressure. At the same time, the anti-kink housing should be sufficiently flexible to allow the anti-kink housing to reduce its inner diameter when pressure is applied by the pressure applicator (e.g., by expanding the fluid bag of the pressure applicator).

[0046] The anti-kink housing is a reinforcing component configured to ensure the stiffness of the measuring device for pressure measurement. The anti-kink housing may be the only reinforcing component of the measuring device, which reinforcing component exhibits structural solidity or strength and is configured to provide stiffness against compressive forces during pressure measurement. In particular, the reinforced anti-kink housing may be pressed against the wrapped part of the object without the need to insert any other reinforcing elements, i.e., between the reinforced anti-kink housing and the wrapped part of the object, preferably no other elements providing any reinforcing function.

[0047] Preferably, the anti-kink housing is a reinforced one-piece housing. This design allows providing sufficient rigidity in a straightforward manner.

[0048] Preferably, the anti-kink housing is dimensioned to overlap when surrounding the portion of the subject. In other words, the anti-kink housing preferably completely surrounds the subject's body part, at least from the time the pressure applicator applies pressure. Thus, kinks or wrinkles along the entire circumference of the measuring device may be avoided or at least significantly reduced.

[0049] Due to the accommodation of the anti-kink housing, kinks or wrinkles are avoided or at least significantly reduced, so that when the inner diameter of the housing is reduced due to the supply of pressurized fluid (preferably air) to a fluid bag of, for example, a pressure applying element, the overlapping parts of the housing (i.e. the lateral ends of the housing) should be able to move or slide relative to each other. Therefore, the measuring device, in particular the anti-kink housing, is preferably designed so that the overlapping parts can easily slide relative to each other. For example, the surface parts of the housing that are in direct sliding contact with each other can exhibit a relatively low friction coefficient, for example by correspondingly selecting the material and / or surface structure. In the context of the present invention, the term "low friction coefficient" means that the friction coefficient of two flat surfaces is less than 0.5, preferably less than 0.3, more preferably less than 0.2, and even more preferably less than 0.1.

[0050] In examples, the housing, in particular the anti-kink housing, is made of metal and / or plastic, in particular fiber reinforced plastic. For example, the housing can be made of a thermoplastic material or coated with a thermoplastic material, preferably made of polyurethane or polyolefin, more preferably made of polyethylene and / or polytetrafluoroethylene (PTFE) or coated with PTFE. For example, the housing can be made of a thermoplastic material that provides a surface to which the adhesive can adhere durably. If the housing comprises a fiber reinforced plastic material, the fibers can be natural fibers, organic fibers or inorganic fibers.

[0051] In particular, if the housing is made of a plastic material, in an example, the thickness of the housing is in the range of 0.25 mm to 6 mm, more preferably in the range of 1 mm to 3 mm, even more preferably in the range of 1.0 mm to 2.0 mm. For example, the housing may have a thickness of 1.5 mm, particularly for adults. Or the housing may have a thickness of 0.5 mm, particularly for infants and young children. In a preferred embodiment, the housing is made of polyethylene (PE) having a thickness of 1.5 mm.

[0052] In an example, to avoid kinking on the one hand and allow reducing the inner diameter on the other hand, the elastic modulus of the kink housing is greater than 50 MPa, more preferably in the range of 100 MPa to 10 GPa, even more preferably in the range of 200 MPa to 1 GPa.

[0053] In another aspect of the present invention, a method for determining blood pressure of a subject is provided, wherein the method comprises:

[0054] A measured pressure signal (TP) of an object over a period of time is provided by a pressure signal providing unit, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising: a) a shell, b) a pressure applicator, and c) a pressure sensor, wherein the shell is configured to wrap a portion of the object through which blood flows; the pressure applicator is configured to preferably apply pressure to the shell from outside the shell, thereby applying pressure to the wrapped portion of the object; the pressure sensor is configured to measure a pressure signal on the skin of the wrapped portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal indicates blood pulsation and includes a plurality of pressure pulses,

[0055] determining, by the processor, for a corresponding pressure pulse in the plurality of pressure pulses, at least one feature characterizing the corresponding pressure pulse,

[0056] determining, by the processor, for each pressure pulse, a blood pressure determination value (TPWP_M) based on the determined at least one characteristic, such that for a number of pressure pulses present at different times, a number of blood pressure determination values ​​(TPWP_M) are determined, wherein the number of blood pressure determination values ​​(TPWP_M) determined for a number of pressure pulses and therefore for a number of times form a blood pressure determination curve (TPW_M-curve), and

[0057] The blood pressure is determined by the processor based on the blood pressure determination curve (TPW_M-curve).

[0058] In another aspect of the present invention, a computer program for determining blood pressure is provided, wherein the computer program comprises a program code module for causing an apparatus for determining blood pressure to perform the steps of the method for determining blood pressure.

[0059] The device, the method and the computer program may be adapted to determine the blood pressure continuously, ie performing several subsequent blood pressure measurements, or to determine the blood pressure discontinuously, ie for example once.

[0060] It shall be understood that the processor of claim 1, the 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.

[0061] It should be understood that a preferred embodiment of the present invention may also be any combination of the dependent claims or the above embodiments with the corresponding independent claim.

[0062] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In the following figures:

[0064] Figure 1 Schematically and exemplarily an embodiment of an apparatus for determining the blood pressure of a subject with a blood pressure cuff of the measuring device inflated is shown, the apparatus comprising a measuring device,

[0065] Figure 2 schematically and exemplarily shows a housing of a measuring device wrapped around the upper arm of a subject,

[0066] Figure 3 The device is shown schematically and exemplarily with a deflated blood pressure cuff,

[0067] Figure 4 Measured tissue pressure and other values ​​derived from the tissue pressure measurements are shown schematically and exemplarily,

[0068] Figures 5 to 8 Calculation of different characteristics of the pressure pulse of the measured tissue pressure is shown,

[0069] Fig. 9 schematically and exemplarily showing an end determination curve and a blood pressure determination curve,

[0070] Fig.10 The determination of a blood pressure value by using a blood pressure determination curve is schematically and exemplarily illustrated,

[0071] Fig.11 Several examples of continuous blood pressure measurements are schematically shown,

[0072] Fig.12 Another example of several continuous blood pressure measurements is shown schematically and exemplarily, and

[0073] Fig.13 A flow chart illustrating an embodiment of a method for determining blood pressure of a subject is shown. DETAILED DESCRIPTION

[0074] Figure 1 Schematically and exemplarily, a device 1 for determining the blood pressure of a subject is shown. The device 1 comprises a housing 4 which can be Figure 2 and is configured to wrap around a portion 5 of the subject through which blood flows. In this embodiment, the portion 5 of the subject is the subject's arm, wherein Figure 2 5 shows a brachial artery 11 in the arm 5, and wherein the arrow in the brachial artery 11 indicates the direction of blood flow away from the heart. The device 1 also includes a pressure sensor 7, which is arranged inside the housing 4 and is configured to measure the pressure on the skin of the wrapped arm 5 of the subject. The measured pressure can also be regarded as tissue pressure (TP). Figure 2As shown, the pulse wave in the brachial artery 11 causes a pressure wave 12, which is transmitted to the pressure sensor 7 via the tissue of the arm 5. For clarity, Figure 1 The housing 4 is not shown.

[0075] The device 1 further comprises a cuff 6 which surrounds the housing 4 and can be inflated by applying pressure to the housing 4 and thereby to the subject's wrapped arm 5 from outside the housing 4 using a pump 8. Since the cuff 6 and the pump 8 together are capable of applying pressure to the housing 4 and thereby to the subject's wrapped arm 5, they can be considered to form a pressure applicator 6, 8. Furthermore, the housing 4, the pressure applicator 6, 8 and the pressure sensor 7 can be considered to be parts of a measuring device controlled by the processor 3. The housing 4 with the cuff 6 is preferably an anti-kink housing cuff as described in WO2014 / 121945A1.

[0076] The processor 3 is configured to control the measuring device so that the pressure applicators 6, 8 increase the applied pressure during a measuring time period extending to the end measurement time point and reduce the applied pressure during a subsequent blood pressure measurement post-time period, and the pressure sensor 7 measures the pressure on the skin, i.e., the tissue pressure TP, at least during the measuring time period. In addition, the processor 3 is configured to control the pressure applicators 6, 8 so that they increase the applied pressure at a first rate during a preceding measuring time period, which is followed by a measuring time period, and increase the applied pressure at a second rate during the measuring time period, wherein the first rate is greater than the second rate. Figure 1 , the control of the measuring device is shown such that the cuff 6 is inflated and the applied pressure thus increases, ie the thick arrow indicates the inflation.

[0077] The device 1 includes a valve 20 which, when open, allows compressed air within the system to leave the system and enter the surrounding atmosphere, thereby deflating the cuff. Figure 3 In FIG. 1 , this deflation situation with the pump 8 switched off is indicated by a thick arrow.

[0078] The processor 3 may be seen as comprising a control part 10 for controlling the pump 8 and the valve 20 and a processing part 11 which is in particular configured to perform some calculations as will be explained further below. The device 1 may also comprise a display 22 for displaying, for example, measured blood pressure values.

[0079] In the preceding measurement period (which may also be considered a fast inflation period), the processor 3 controls the device 1 so that the valve 20 is closed and the pump 8 inflates the cuff 6 at a larger first rate. In the subsequent measurement period, the processor 3 also controls the device 1 so that the valve 20 is closed, but the pump 8 is controlled so that the inflation of the cuff 6 continues at a lower second rate. Therefore, the measurement period may also be considered a slow inflation period.

[0080] Figure 4 The relationship between the measured pressure TP and the time t is shown schematically and exemplarily. The first inflation in the previous measurement time period starts with a tissue pressure TP, i.e., an accessory pressure Patt, which is the tissue pressure measured in the uninflated cuff 6. For example, the accessory pressure Patt can be in the range of 0 to 15 mmHg. An accessory pressure Patt of up to 15 mmHg has been shown not to cause venous congestion for more than 12 hours, making the assembly of the shell 4 and the cuff 6 most suitable for long-term monitoring. For this reason, it is preferred that the accessory pressure Patt is not greater than 15 mmHg. Figure 4 In FIG. 1 , arrow 30 indicates the beginning of the pre-measurement period, i.e. the beginning of the rapid inflation period. During this pre-measurement period, the portion of the entire tissue pressure range that has no or substantially no information for determining the blood pressure should be passed as quickly as possible. Therefore, during the pre-measurement period, the inflation rate is preferably as large as possible. For example, the inflation rate relative to the tissue pressure TP may be equal to or greater than 8 mmHg / s. This pre-measurement period with a rapid inflation rate is Figure 4 The test ends at the tissue pressure value indicated by “TPlow” in the flow chart.

[0081] The tissue pressure value TPlow also indicates the beginning of a measurement period having a second, slower inflation rate. Figure 4 , this start of the measurement time period (which can also be regarded as a slow inflation period) is indicated by an arrow 31. In an embodiment, the processor 3 is configured to control the pump 8 so that at the end of the previous measurement time period, the measured pressure TPlow is in the range of 15 to 30 mmHg. Therefore, in an embodiment, the tissue pressure TPlow can be predefined as a value between 15 and 30 mmHg. However, in case an arterial diastolic pressure (DAPprev) determined in a previous measurement is available, the tissue pressure TPlow can depend on this arterial diastolic pressure and the tissue pressure TPlow can also be larger. This larger TPlow Figure 4Schematically shown in . For example, the processor 3 can be configured to store (or access a memory to store) a previous arterial diastolic pressure DAPprev. The previous arterial diastolic pressure DAPprev has been obtained by a previous blood pressure measurement and can be used to determine the tissue pressure TPlow. The tissue pressure TPlow should appear at the end of the previous measurement time period, that is, at the end of the first inflation period, and can therefore also be regarded as the first end measurement pressure. The tissue pressure TPlow is determined based on the previous arterial diastolic pressure DAPprev so that the tissue pressure TPlow is less than the previous arterial diastolic pressure DAPprev. Preferably, the processor is configured to control the pump 8 so that the measured pressure at the end of the previous measurement time period is equal to the determined first end measurement pressure TPlow. In an embodiment, the processor 3 determines the tissue pressure TPlow at the end of the previous measurement time period so that it is not higher than a predetermined percentage of the previous arterial diastolic pressure DAPprev. This can ensure that all necessary tissue pressure pulse curves are recorded, thereby accurately calculating the blood pressure. The calculation of blood pressure based on the measured tissue pressure will be further explained below. The predetermined percentage is preferably 90%.

[0082] For example, blood pressure may change between measurements due to clinically relevant events occurring to the subject. It has been found that in the most severe cases of acute blood loss during surgery, the diastolic arterial pressure (DAP) may drop by about 30% within one minute. In order to cope with these possible changes in blood pressure, the processor 3 may be adapted to determine the tissue pressure TPlow based on the previous diastolic arterial pressure DAPprev and based on the duration of the interruption time between measurements. Therefore, the processor 3 may be configured to further store (or access a memory to store) the time at which the previous diastolic arterial pressure DAPprev was measured, and determine the first end measurement pressure TPlow based on i) the previous diastolic arterial pressure DAPprev and ii) the time distance to the blood pressure measurement, as indicated by the stored time, at which the previous diastolic arterial pressure DAPprev was measured. An exemplary specific equation for determining the first end measurement pressure TPlow will be further given below.

[0083] The second inflation rate applied during the measurement period is preferably in the range of 1 mmHg / s to 6 mmHg / s, the lowest inflation rate is preferably 1.5 mmHg / s, and the highest inflation rate is preferably 2.5 mmHg / s. It has been found that the second inflation rate within this range can accurately determine the blood pressure. It should be noted that these rates refer to the changes in the tissue pressure TP measured by the pressure sensor 7.

[0084] In an embodiment, the slower second inflation rate depends on the heart rate (HR) and / or pulse pressure (PP), which is the difference between systolic and diastolic pressure. For example, the second inflation rate can increase with an increase in heart rate and an increase in pulse pressure PP. This increase can be linear or can be described by another functional relationship. In an embodiment, the functional relationship is such that at a heart rate HR of 40 / min and a pulse pressure PP of 20mmHg, the tissue pressure inflation rate is 1mmHg / s, and at a heart rate HR of 80 / min and a pulse pressure PP of 100mmHg, the tissue pressure inflation rate, i.e., the second slow inflation rate is 10mmHg / s. The measurement time period ends at the end measurement time point 32, after which immediate rapid deflation is preferentially performed at the maximum possible reduction rate, because tissue pressure data does not need to be collected after the end measurement time point 32.

[0085] exist Figure 4 , time interval 40 indicates the inflation / deflation time period from the start of rapid inflation 30 to the time when the tissue pressure TP drops below 20 mmHg during rapid deflation to allow venous return. Time period 41 indicates the cycle time, i.e., the time between the start of a measurement and the start of the next measurement, and time period 42 indicates the break period, i.e., the difference between the inflation / deflation time period 40 and the cycle time 41.

[0086] Figure 4 Also shown is an average pressure TPcl, which can be viewed as the tissue clamping pressure affecting the tissue when the cuff 6 is attached to the subject's arm 5 (e.g., upper arm). The average pressure TPcl can be calculated by applying a low-pass filter to the tissue pressure TP, wherein the low-pass filter can be located within the processor 3. The size of the low-pass filter is preferably set so that the average pressure TPcl only includes frequencies below the expected minimum pulse rate (PRni). The preferred low-pass filter will be further described below. The processor 3 is preferably configured to determine the AC component TPac of the tissue pressure by subtracting the average pressure TPcl from the measured tissue pressure TP, that is, TPac=TP-TPcl. Figure 4 In the figure, the TPac curve is magnified 2 times to improve the visibility of the curve.

[0087] During slow inflation, i.e. during the measuring period, a TP pulse curve and / or a TPac pulse curve is recorded which can be analyzed simultaneously, i.e. online, wherein the TP pulse curve and / or the TPac pulse curve has a tissue pressure waveform (TPW) comprising information allowing an accurate determination of the blood pressure. Since the blood pressure is measured non-invasively (although its accuracy is comparable to that of invasively measured blood pressure), it can be abbreviated to niBP, meaning "non-invasive blood pressure". Figures 5 to 8 The TPac pulse curve is shown schematically and exemplarily in FIG.

[0088] In the following, the TPac pulse curve is used to determine the characteristics of the pressure pulse 9. Therefore, the TPac pulse curve can be regarded as a characteristic determining pulse curve or a characteristic determining pulse. Figures 5 to 8 Therefore, it is shown that the characteristic determination pulse curve or the characteristic determination pulse 29 is a TPac pulse. In another embodiment, the characteristic determination pulse can also be directly a TP pulse curve, that is, the pressure pulse 9 can be directly used to determine the characteristics. The processor 3 is configured to determine at least one feature characterizing the corresponding pressure pulse for a corresponding pressure pulse in the plurality of pressure pulses 9.

[0089] In an embodiment, the processor 3 is configured to determine the difference TPP between the maximum measured pressure and the minimum measured pressure of the corresponding characteristic determination pulse 29 as the characteristic of the corresponding pressure pulse. Figure 5 Describe the feature.

[0090] The difference TPP is the difference between the maximum systolic pressure (TPsys) of the characteristic-determining pulse and the pressure (TPdia) at the end-diastolic point of the characteristic-determining pulse, TPdia being preferably the minimum pressure of the corresponding characteristic-determining pulse. Figure 5 as well as Figures 6 to 8 In FIG. 2 , the terms “t.start” and “t.stop” indicate the start and end of the corresponding pulse 29 , respectively.

[0091] The processor 3 may also be configured to determine a pulse duration (t(Pulse)), which is the time difference between the end-diastolic point of a characteristic determining pulse 29 and the next end-diastolic point. The characteristic may also be defined as the time difference between the start (t.start) of the corresponding pulse and the end (t.stop) of the corresponding pulse. The characteristic is Figure 6 Shown in.

[0092] The processor 3 may also be adapted to determine the pulse area (TPA) of the corresponding pulse 29, the pulse area (TPA) being the area under the curve of the corresponding pulse within the time defined by t.start to t.stop and ranging from the pressure at the end-diastolic point of the characteristic-determining pulse (TPdia) to the maximum systolic pressure (TPsys) of the characteristic-determining pulse. Figure 6 As shown, the pulse area TPA is scaled to TPP = 1. This scaled pressure pulse area is named "TPA.norm".

[0093] The processor 3 may also be adapted to determine the pulse half-width (W50) of the corresponding pulse 29, such as Figure 7 shown.

[0094] Furthermore, the processor 3 may be adapted to determine the area TPA+.top enclosed by the first upper part of the characteristic determination pulse 29, such as Figure 8 . The upper end of the area TPA+.top enclosed by the first upper part is at the maximum systolic pressure TPsys of the characteristic determination pulse 29, and the lower end of the area TPA+.top of the first upper part is between the maximum systolic pressure TPsys of the characteristic determination pulse 29 and the pressure value corresponding to the average value TPcl of the measured pressure TP. Since the characteristic determination pulse 29 has been determined by subtracting the average value TPcl from the measured pressure TP, the pressure value corresponding to the average value TPcl of the measured pressure TP is zero. Preferably, the processor 3 is configured to determine the area TPA+.top enclosed by the first upper part of the characteristic determination pulse so that the lower end of the first upper part is at a pressure value corresponding to half of the pressure distance TPP+ between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure value corresponding to the average value TPcl of the measured pressure TP. The corresponding area is then named TPA+.top50.

[0095] Figures 5 to 8 The TPac pulse curve is shown so that in this example also features are defined based on the TPac pulse curve. However, as described above, these or other features may also be defined based on the TP pulse curve.

[0096] The processor 3 is also configured to determine a blood pressure determination value TPWP_M for the corresponding pressure pulse based on at least one determined feature, so that for several pressure pulses present at different times, several blood pressure determination values ​​TPWP_M are determined, wherein the several blood pressure determination values ​​TPWP_M determined for several pressure pulses and therefore for several times form a blood pressure determination curve TPW_M-curve. The processor 3 is configured to determine the blood pressure based on the blood pressure determination curve TPW_M-curve, for example, as explained in WO2018 / 210931Al. Specifically, the processor 3 is configured to determine the position of the maximum value (TPW_M-curve.max) of the blood pressure determination curve TPW_M-curve, and determine the blood pressure based on the determined position and the measured pressure TP. For example, the processor 3 is configured to determine the arterial systolic blood pressure (SAPni) based on the average TPcl of the measured pressure TP at the position of the determined maximum value (TPWM-curve.max) according to the following equation:

[0097] SAPni=α · (TPcl@TPW_M-curve.max), (1)

[0098] The parameter α can be predetermined by calibration.

[0099] In practice, the processor 3 may be configured to determine the position of the maximum value of the blood pressure determination curve TPW_M-curve and / or the position of the derivative (such as the first-order derivative) of the blood pressure determination curve TPW_M-curve, and determine the blood pressure based on one or both of the determined position and the measured pressure TP. For example, the processor 3 may be configured to determine the arterial systolic blood pressure based on the average value TPcl of the measured pressure TP at one or two of the determined positions according to SAPni=α'·(TPcl@TPW_M-curve.max)+β'·(TPcl@TPW_M-curve.max), wherein TPW_M-curve' refers to the derivative of TPW_M-curve, and wherein the parameters α' and β' may be predetermined by calibration.

[0100] Preferably, the processor is configured to provide a function that receives as input at least one characteristic of a corresponding pressure pulse and outputs a corresponding blood pressure determination value, which together with blood pressure determination values ​​determined for other pressure pulses forms a blood pressure determination curve. The function has at least one parameter that can be determined by calibration, wherein a reference blood pressure value is determined very accurately in an invasive manner, and the at least one parameter is determined such that the device produces very accurate invasively measured blood pressure values ​​with high statistical precision and accuracy.

[0101] In a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M, which depends only on the characteristics of the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia at the end-diastolic point of the characteristic determination pulse. Therefore, in an embodiment, the function used to determine the blood pressure determination value TPWP_M depends on TPP, but does not depend on any other characteristics of the pressure pulse. In particular, the blood pressure determination value TPWP_M can be determined according to the following equation:

[0102] TPWP_M = d1 · TPP exp1 , (2)

[0103] Wherein, dl and expl are predetermined constants. For example, dl and expl can be predetermined by calibration. However, it has been found that they can also be selected to be equal to 1, that is, dl=l=expl, so that TPWP_M=TPP.

[0104] Furthermore, in a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M, which depends only on a) a feature of the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia of the characteristic determination pulse at the end-diastolic point, and b) a feature of the area TPA+.top50 enclosed by the first upper part of the characteristic determination pulse. Therefore, in an embodiment, the function for determining the blood pressure determination value TPWP_M depends on TPP and TPA+.top50, but does not depend on other features of the pressure pulse. In particular, the blood pressure determination value TPWP_M can be determined according to the following equation:

[0105] TPWP_M = d2 · TPA+.top50 exp2 TPP exp3 , (3)

[0106] Wherein, d2, exp2 and exp3 are predetermined constants. For example, d2 may be equal to 1, i.e., d2=1, wherein exp2 and exp3 may be predetermined by calibration. However, the constant d2 may also be determined by calibration. In a preferred embodiment, d2 and exp3 are both equal to 1 (d2=1, exp3=1), and exp2 is equal to 0.7 (exp2=0.7).

[0107] Preferably, the processor 3 is further configured to determine an end measurement time point 32 based on at least one feature determined for the plurality of pressure pulses 9, at or after which the measurement time period is stopped. Specifically, the processor 3 may be configured to determine, for each pressure pulse, an end determination value TPWP_E based on at least one feature that has been determined for the corresponding pressure pulse.

[0108] Preferably, the processor is configured to further provide a function that receives at least one feature of the corresponding pressure pulse as input and outputs a corresponding end determination value TPWP_E, which together with the end determination values ​​determined for other pressure pulses forms an end determination curve. The function also has at least one parameter that can be determined by calibration. Specifically, the end determination value TPWP_E can be determined according to the following formula:

[0109] TPWP_E = d3 · TPP exp4 , (4)

[0110] or according to

[0111] TPWP_E=d4·TPA+.top50 exp5 TPP exp6 , (5)

[0112] Wherein, d3, d4, exp5 and exp6 are predetermined constants. For example, d3 and / or d4 may be equal to 1, i.e., d3=1 and d4=1, and exp4, exp5 and exp6 may be predetermined by calibration. In an embodiment, constant d3 and / or constant d4 may also be determined by calibration, and in particular not be 1.

[0113] The end determination value TPWP_E may also be determined as follows.

[0114] In particular, the processor 3 may be configured to multiply a) the determined pulse area TPA.norm to a power of a predetermined seventh exponent (exp7) by b) the determined difference TPP to a power of a predetermined eighth exponent (exp8). Thus, the end determination value TPWP_E may be calculated according to the following equation:

[0115] TPWP_E=TPA.norm exp7 TPP exp8 , (6)

[0116] Among them, the predetermined exp7≠0, exp8≠0.

[0117] The processor 3 may also be configured to determine the end determination value TPWP_E by dividing a) the determined pulse area TPa.norm to a power of a predetermined ninth exponent (exp9) by b) the determined pulse duration t(pulse) to a power of a predetermined tenth exponent (exp10), and multiplying the quotient by c) the determined difference TPP to a power of a predetermined eleventh exponent (exp1). This may be represented by the following equation:

[0118] TPWP_E=TPA.norm exp9 / t(Pulse) Exp10 TPP exp11 , (7)

[0119] Among them, the predetermined exp9≠0, exp10≠0, exp11≠0.

[0120] The processor 3 may also be configured to determine the end determination value of the corresponding pressure pulse based on multiplying the calculation result obtained by using, for example, equation (6) or equation (7) by another predetermined exponent of the half-maximum full width (W50). For example, if equation (7) is multiplied by the half-maximum full width W50, the following equation (8) is generated:

[0121] TPWP_E=TPA.norm exp12 / t(Pulse) Exp13 TPP exp14 ·W50 exp15 , (8)

[0122] Among them, the predetermined exp12≠0, exp13≠0, exp14≠0, exp15≠0.

[0123] Therefore, in this embodiment, based on at least TPP and TPA.norm of the corresponding pulse curve, TPWP_E reflecting the characteristic value of the corresponding pulse curve can be calculated by combining and weighting the amplitude and area parameters, wherein any TPWP_E can be expanded by multiplying by the power of the corresponding exponent of W50.

[0124] As mentioned above, the exponents of the different equations are predetermined by calibration. For example, in a preferred embodiment, equation (7) is used, where the exponents exp9=1.1, Exp10=0.4, exp11=0.5.

[0125] The processor 3 is preferably configured to determine the end determination curve TPW_E-curve so that it satisfies one of the following conditions: a) the maximum value (TPW_E-curve.max) of the end determination curve occurs in time before the maximum value (TPW_M-curve.max) of the blood pressure determination curve, b) the maximum value (TPW_E-curve.max) of the end determination curve occurs in time at or after the maximum value (TPW_M-curve.max) of the blood pressure determination curve, and the decrease of the end determination curve TPW_E-curve after its maximum value is steeper than the decrease of the blood pressure determination curve TPW_M-curve after its maximum value, and c) the end determination curve TPW_E-curve is the same as the blood pressure determination curve TPW_M-curve. Therefore, the parameters of the function are preferably predefined so that a) TPW_E-curve.max occurs before TPW_M-curve.max in time, or b) TPW_E-curve.max occurs at or after TPW_M-curve.max in time, but TPW_E-curve has a negative derivative whose absolute derivative value is greater than the absolute derivative value of the negative derivative of the blood pressure determination curve TPW_M-curve after its maximum value, or c) TPW_E-curve can be the same as TPW_M-curve, that is, the end determination curve and the blood pressure determination curve can be the same.

[0126] exist Fig. 9 , a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve are shown by way of example, wherein these curves have been normalized so that the respective maximum values ​​correspond to 100%.

[0127] It is desirable to terminate each blood pressure measurement as quickly as possible to minimize the stress on the subject (i.e. the subject). Once the maximum value of the blood pressure determination curve TPW_M-curve has been formed, the blood pressure measurement can be terminated, so that the blood pressure measurement can be completely determined, because the maximum value of the blood pressure determination curve TPW_M-curve is used for non-invasive blood pressure determination. Therefore, during the measurement period, it is checked when the end criterion defining the end measurement time point is reached, wherein, in order to determine when the end criterion is reached and thus determine the end measurement time point, the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve are preferentially used. For example, when the end determination curve TPW_E-curve has formed its maximum value, it can be checked with each newly measured TP pulse curve (i.e., with each newly measured TP pulse) whether a) the end determination curve TPW_E-curve has fallen below a percentage of the maximum value of the end determination curve TPW_E-curve, wherein the percentage is preferably in the range from 40% to 95%, and whether b) the blood pressure determination curve TPW_M-curve has formed its maximum value, i.e. has reached or exceeded its maximum value. The processor 3 may be configured to determine the end measurement time point 32 as a time point that satisfies both conditions a) and b).

[0128] In order to safely determine whether the blood pressure determination curve TPW_M-curve reaches or exceeds its maximum value, it may be detected whether the blood pressure determination curve TPW_M-curve drops after its maximum value.

[0129] In an embodiment, the blood pressure determination curve TPW_M-curve may be a smoothed curve such that the maximum of the blood pressure determination curve is also smoothed. The smoothing process for smoothing the blood pressure determination curve may include, for example, filtering and / or fitting. In addition, after smoothing the maximum value, several pressure pulses may be considered to explicitly detect the smoothed maximum value, wherein the number of these several pulses may be predetermined or may depend on the heart rate of the subject. For example, the number may increase as the heart rate increases. In an embodiment, for a heart rate of 60 / min, the number is 3, and for a heart rate of 200 / min, the number is 10.

[0130] In order to smooth the blood pressure determination curve TPW_M-curve, a moving average filter, in particular a variable moving average filter, applied to the blood pressure determination values ​​TPWP_M determined for the pressure pulses can be used. The window for averaging can be fixed or variable, wherein, in the latter case, it preferably has a maximum duration of, for example, 8s. The use of this filter results in a filter delay, wherein the minimum filter delay is as long as the duration of several pulses added together. A filter delay with a length of several pulses is sufficient to safely determine the falling smoothed blood pressure determination curve TPW_M-curve and, therefore, the maximum value in the blood pressure determination curve TPW_M-curve. This means that once a decrease in the smoothed blood pressure determination TPW_M-curve is detected, the measurement period will be terminated without the need to collect more pressure pulses. This is possible because, in this example, the blood pressure determination curve TPW_M-curve is smoothed with a relatively large variable moving average filter window with, for example, at least three TP pressure pulses and a maximum of 8s twice (2×8s filter), eliminating an estimated 95% of disturbing cardiopulmonary interactions in the measurement. These smoothing filter windows can be adapted to the breathing rate or ventilation rate, allowing better elimination of unwanted TPW_M-curve disturbances caused by cardiopulmonary interactions.

[0131] exist Fig. 9 In the embodiment, both conditions a) and b) are satisfied when the end determination curve TPW_E-curve drops below 90% of the maximum value of the end determination curve TPW_E-curve. Due to the filter delay, the measurement is terminated a few tissue pressure pulses after both conditions a) and b) are satisfied.

[0132] Fig. 9 The continuous TPW_E-curve and the continuous TPW_M-curve shown in are obtained by filtering the TPWP_E and TPWP_M values ​​determined for different pressure pulses, respectively. This filtering, which results in a filter delay, will be further explained below. Fig. 9 In , the filter delay results in two additional pressure pulses, so that the two pressure pulses after conditions a) and b) are met start a rapid deflation of the cuff 6 .

[0133] An end determination curve TPW_E-curve having a maximum value that occurs a few seconds earlier in time than the maximum value of the blood pressure determination curve TPW_M-curve allows shortening the measurement period, i.e., shortening the slow inflation time and reducing the amount of pressure applied to the subject. After reaching t(a_end), i.e., after reaching a point in time at which the end determination curve TPW_E-curve has fallen below a predetermined percentage of the maximum value of the TPW_E-curve, if the TPW_M-curve has several maximum values, the largest maximum value of the blood pressure determination curve TPW_M-curve found so far is the absolute maximum value (TPW_M-curve.max) of the blood pressure determination curve TPW_M-curve, if the blood pressure determination curve TPW_M-curve is decreasing at time t(a_end). Otherwise, in an embodiment, the measurement will continue until the next maximum value of the TPW_M-curve, after which the maximum value (TPW_M-curve.max) of the blood pressure determination curve will be determined.

[0134] Without using an end determination curve TPW_E-curve having a maximum value that occurs before the maximum value of the blood pressure determination curve TPW_M-curve in time, it will be necessary to continue slow inflation until the blood pressure determination curve TPW_M-curve has fallen below a certain percentage of its maximum value. On average, by using an end determination curve TPW_E-curve having a maximum value that occurs before the maximum value of the blood pressure determination curve TPW_M-curve in time, the blood pressure measurement can be terminated after about 20 to 60 seconds at TPcl in the range of 70% to 95% of the systolic arterial pressure (SAP). This is significantly lower than the end pressure level of conventional oscillometric niBP measurement. The blood pressure measurement is terminated when the clamping pressure reaches about SAP+20 mmHg. When using the above reference Figure 1 When the device 1 is used, and when the measurement is terminated, the tissue pressure TP drops as quickly as possible to Patt, where it stays for a period of time, preferably before another measurement is started. Figure 4 Within about 20% of the inflation and deflation time period 40 indicated in .

[0135] The processor 3 is configured to determine the blood pressure based on the blood pressure determination curve TPW_M-curve and / or its derivative, in particular based on the maximum value of the blood pressure determination curve TPW_M-curve and / or its derivative. The processor 3 can be suitable for performing such a determination of the blood pressure, which is a non-invasive blood pressure, as described in WO2018 / 210931A1.

[0136] In an embodiment, the processor 3 is configured to determine the TPcl value at a time point when the blood pressure determination curve TPW_M-curve reaches its maximum value (TPW_M-curve.max), wherein Fig.10 The value of TPcl at the time point of the maximum value is indicated as "TPcl@TPW_M-curve.max". The processor 3 is also configured to determine the lower envelope of the tissue pressure TP by applying a filter to the end-diastolic point of the tissue pressure TP. The filter may be the same as the filter used to determine, for example, the blood pressure determination curve TPW_M-curve. The resulting curve is Fig.10 In the embodiment of the invention, the processor 3 is named "TPdia-curve". Furthermore, the processor 3 can be configured to determine the upper envelope of the tissue pressure TP by applying a filter to the systolic maximum of the tissue pressure TP. Furthermore, the filter can be similar to the filter used, for example, to generate the blood pressure determination curve TPW_M-curve. The curve is in Fig.10 It is named “TPsys-curve” in the paper.

[0137] Then, the processor 3 may be configured to determine the arterial systolic pressure value as a predetermined percentage (TPcl.s%) of TPcl@TPW_M-curve.max. The predetermined percentage is preferably in the range of 100% to 150%, and further preferably in the range of 110% to 150%. Fig.10 In the , non-invasive systolic pressure is named "SAPni" and the predetermined percentage is expressed as "TPcl.s% (TPcl@TPW_M-curve.max)". Fig.10 In the study, the non-invasive arterial systolic blood pressure SAPni was approximately 134 mmHg.

[0138] The processor 3 may also be adapted to determine the non-invasive systolic pressure SAPni as a predetermined percentage (TPsys.s%) of the TPsys-curve at the time position at which the blood pressure determination curve TPW_M-curve reaches its maximum value. The predetermined percentage is preferably in the range of 100% to 140%.

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

[0140] The processor 3 may also be configured to determine the non-invasive diastolic pressure DAPni as the value of TPdia-curve or TPcl-curve at a time point t(cx), which is a time point at which the blood pressure determination curve TPW_M-curve has a value cx representing a predetermined percentage of its maximum value. The processor 3 may also be configured to alternatively determine DAPni as a predetermined percentage (TPcl.d%) of TPcl@TPW_M-curve.max, wherein the predetermined percentage is preferably in the range of 60% to 80%.

[0141] As described above, the parameters of the function for determining the end determination curve TPW_E-curve and for determining the blood pressure determination curve TPW_M-curve are determined by calibration. The percentage for determining the blood pressure value is also determined by calibration. Therefore, these parameters and percentages are predetermined so that during the calibration phase, the deviation between the invasive blood pressure value measured very accurately and the blood pressure value obtained by the device is minimized, and the time required for the blood pressure measurement is relatively low. Therefore, preferably, one or more parameters of the function for determining the blood pressure determination curve TPW_M-curve (which can be regarded as a first set of one or more parameters) are selected in such a way that a good balance is achieved between high-precision non-invasive blood pressure and a low TP level at the end of the measurement, thereby shortening the measurement time. If one or more parameters are selected so that it creates a TPW_M-curve with a relatively early maximum value, the TP level at the end of the measurement and the measurement time will be relatively low. However, the accuracy and position of the non-invasive blood pressure value finally determined will also be reduced. Therefore, it is preferred to select the first set of one or more parameters to achieve an ideal balance between the measurement time and accuracy of the non-invasive blood pressure value.

[0142] Preferably, one or more parameters of the function for determining the end determination curve TPW_E-curve are selected, which can be regarded as forming a second set of one or more parameters, so that the maximum value of the end determination curve TPW_E-curve is relatively early. In an embodiment, the first set of one or more parameters and the second set of one or more parameters can also be the same, so that the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve can also be the same.

[0143] The values ​​of TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d%, bx, cx are preferably calibrated by statistically evaluating a calibration set consisting of measurement pairs of invasive blood pressure values ​​and non-invasive blood pressure values ​​recorded simultaneously from a sufficient number of individuals under different hemodynamic conditions as described in WO2018 / 210931A1. As described above, non-invasive blood pressure values ​​are determined by device 1, and parameters such as the values ​​TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d% can be optimized so that the deviation between the invasive blood pressure values ​​and the non-invasive blood pressure values ​​is minimized.

[0144] The processor 3 may be adapted to estimate a blood pressure value based on two other already measured blood pressure values. In particular, one of the blood pressure values ​​MAPni, SAPni and DAPni may be estimated based on another of these blood pressure values. This may be done according to the following equation:

[0145] SAPni=cl·MAPni+c2·(MAPni-DAPni)-c3mmHg (9)

[0146] Among them, cl = (0.2..0.7), c2 = (2..6), c3 = (-5..5),

[0147] MAPni=c4·DAPni+c5·(SAPni-DAPni)-c6mmHg (10)

[0148] Among them, c4=(0.8..1.3), c5=(0.25..0.5), c6=(-5..5),

[0149] DAPni=c7·MAPni-c8·(SAPni-MAPni)-c9mmHg (11)

[0150] Among them, c7=(0.6..1.1), c8=(0.15..0.4), c9=(-5..5).

[0151] The coefficients and constants of equations (9), (10) and (11) are predetermined by calibration based on statistical evaluation of a clinical invasive blood pressure data set that is as large as possible and sufficiently extensive. Therefore, very accurate invasive blood pressure values ​​SAPi (invasive systolic pressure), MAPi (invasive mean arterial pressure) and DAPi (invasive diastolic pressure) are used, wherein, given these very accurate invasive blood pressure values, the coefficients and constants of equations (9), (10) and (11) are modified so that these equations are valid.

[0152] Blood pressure measurements are intended to be taken in rapid succession in a series of measurements to allow effective semi-continuous blood pressure monitoring, minimizing stress on the individual being monitored (i.e., the subject being monitored). This rapid sequence of pressure measurements can also be considered a non-invasive fast mode cycle (FMC) measurement of blood pressure.

[0153] In an embodiment, the initial blood pressure measurement has no information about the previous diastolic arterial pressure (DAP), and therefore slow inflation, i.e., a measuring time period, is started at a predetermined tissue pressure TPlow in the range of 15 to 30 mmHg. In addition, during this measuring time period, the inflation rate is set to an intermediate value. The inflation rate can be defined as the rate at which TPcl increases over time, wherein the inflation rate can be selected so that it has a value of, for example, 1.9 mmHg / s. This would correspond to the measurement of a "normal" blood pressure value. At the end of the deflation phase, when TPcl has reached Patt, the blood pressure measurement is preferentially interrupted for at least 2 s in order to allow reperfusion of the subject's body part wrapped by the shell 4. The interruption time 42 preferably has a length in the range of greater than 0% to about 50% of the previous inflation / deflation time period 40, resulting in a cycle 41. The following blood pressure measurement will use the information of the diastolic arterial pressure (DAP) determined in the corresponding previous measurement (DAPprev) to start slow inflation, i.e., a measuring time period, with a higher TPlow, such as Fig.11 shown.

[0154] The TPlow value should not be higher than 90% of the diastolic blood pressure to ensure that all pulses required for the blood pressure calculation are recorded. In addition, as mentioned above, the blood pressure can change in the time interval (t_inter) between the start of deflation and the start of the next slow inflation. Therefore, preferably, a function that models the decrease in blood pressure according to the time interval t_inter is applied. It has been observed in clinical data from high-risk surgery that the diastolic blood pressure can decrease by more than 28% in one minute. Therefore, TPlow can be calculated by a linear function using the following function:

[0155] TPlow=90%DAPprev-28%DAPprev·t_inter / 60s, (12)

[0156] Here, "90% DAPprev" and "28% DAPprev" respectively represent 90% and 28% of the previously measured arterial diastolic pressure DAPprev.

[0157] TPlow can be determined by using a linear function that depends on the previous time interval between the start of deflation and the start of the next slow inflation, wherein the linear function has a negative slope so that TPlow decreases over time. The slope of the linear function and the positive constant of the linear function can be predetermined by calibration. In equation (12), the positive constant is 90% DAPprev and the negative slope is -28% DAPprev. The positive constant and the negative slope can also have other values. For example, the negative slope can be -30% DAPprev.

[0158] exist Fig.11 In , it can be seen how TPlow is adjusted according to t_inter according to equation (12). In particular, it can be seen that measurements #2a and #2b have different TPlow values, where the TPlow value of measurement #2b is smaller than the TPlow value of measurement #2a because the time interval t_inter for measurement #2b is larger than that for measurement #2a. Fig.11 It can also be seen that the inflation rate for measurement #3 increases due to the increase in PP prior to measurement #2a. In addition, for measurement #3, TPlow is greater than the previous measurements because the diastolic arterial pressure DAP has increased prior to measurement #2a. It should be noted that Fig.11 , interval 44 is the cycle period of the second measurement #2a, interval 43 is the inflation and deflation period of the second measurement #2a, and interval 45 is the interruption time of the second measurement #2a. In addition, it should be noted that the third measurement #3 refers to the second measurement #2a, and another second measurement #2b is shown only to illustrate an alternative to the second measurement #2a.

[0159] Fig.12 Another example of adjusting the TPlow value according to the time interval t_inter according to equation (12) is shown. In this example, the inflation rate in the measurement time period of measurement #3 is reduced compared to the previous measurement due to the decrease in PP before measurement #2a and the decrease in TPlow value due to the decrease in DAP before measurement #2a.

[0160] As described above, a filter is used to determine the end determination curve TPW_E-curve, the blood pressure determination curve TPW_M-curve, and the envelope curves TPsys-curve and TPdia-curve. In addition, a filter is used to determine TPcl based on TP. As a filter, a low-pass filter is preferably used. The low-pass filter can be, for example, a cascaded moving average filter with a variable window length of up to 8s, wherein the window length can be shorter at the beginning and end of the filtering to minimize the filter settling time. For example, filtering can include averaging within a moving window of a signal containing at least three TP pressure pulse curves and a maximum of 8s twice (2x8s filter). Optionally, signal filling can be applied before and / or after the start of the signal to completely fill the filter window before filtering. For example, the first pressure pulse value before the start and the last pressure pulse value after the end can be applied for filling.

[0161] Due to the filter delay, TPcl is extrapolated from its previous value to the last part of the signal available for measurement. The filter can be applied, for example, to extract TPcl from TP, to form a smoothed TPW_E-curve and a smoothed TPW_M-curve without variations caused by blood pressure pulsations, and to create an envelope function on the systolic peak (TPsys-curve) and the end-diastolic minimum (TPdia-curve) of TP.

[0162] In the following, reference will be made to Fig.13 An embodiment of a method for determining blood pressure is exemplarily described with reference to the flowchart shown in FIG.

[0163] After initialization and startup of the device in step 101, TPlow is determined in step 102. For a first measurement it may be a value from 15 mmHg to 30 mmHg. If a blood pressure measurement has already been performed, TPlow may be determined using a previous diastolic blood pressure value, for example according to equation (12).

[0164] In step 103, in the pre-measurement time period, the cuff is inflated at a relatively large first inflation rate until TPlow is reached. Then, in step 104, a measurement time period is started, i.e., a slow inflation period, during which a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve are determined. In addition, these curves are used to determine an end measurement time point, wherein when the end measurement time point has been reached or exceeded, the slow inflation period is stopped, and in step 105, the cuff is deflated. After deflation and pausing to allow venous return in step 106, the method continues with step 102. Therefore, the method can be performed in a loop for continuous monitoring of blood pressure changes over time in several measurement cycles. When executing steps 102 to 105, the processor calculates blood pressure values ​​in parallel. The loop can be performed until the termination criterion is met. For example, if the physician has entered a corresponding command into the device via an input unit such as a keyboard, a computer mouse, a touch pad, etc., the monitoring of blood pressure is interrupted.

[0165] The device allows non-invasive FMC blood pressure measurement based on non-invasive high-fidelity tissue pressure TP recordings preferably recorded with an anti-kink shell system described in WO2014 / 121945Al. The device preferably allows inflation of a statistically averaged maximum pressure of about 85% or less of the arterial systolic pressure. Depending on the height of the arterial blood pressure, the pulse pressure and the inverse of the heart rate, a single blood pressure measurement using device 1 may take about 20 to 60 seconds, wherein the device is preferably configured to provide non-invasive systolic pressure SAPni, non-invasive mean arterial pressure MAPni and non-invasive arterial diastolic pressure DAPni. Preferably, a short break is taken with an unpressurized cuff between consecutive measurements to allow venous return. These short interruptions are preferably in the range of 5 to 10 seconds. During the measurement, the arterial perfusion of the part wrapped by the shell (such as the upper arm or wrist of the subject) is preferably never completely interrupted because the clamping pressure is preferably permanently kept below SAP. Therefore, compared with conventional oscillometric measurements, the measurement is less stressful on the subject.

[0166] The above references are for example Figure 1 The described device 1 provides a reliable method for quickly determining blood pressure without clamping pressure exceeding SAP. Due to the relatively short measurement time and relatively low maximum cuff pressure, the blood pressure measurement is very convenient for the individual and can reduce the possibility of potential complications (such as thrombophlebitis, pain, subcutaneous hematoma, limb edema, peripheral neuropathy, etc.).

[0167] In an embodiment, TPlow may be at or above DAP. TPlow defines the tissue pressure at the beginning of the measurement period, ie the tissue pressure at the beginning of the slow inflation period, wherein the slow inflation may be terminated when a certain end criterion is reached. The end criterion has been described above.

[0168] Although in the above-described embodiment, the feature is determined by using the TPac pulse, the feature can also be determined by directly using the measured pressure pulse (i.e., the TP pulse). The TP pulse can also be processed in another way, i.e., the TPac pulse is not determined by subtracting the average TP value. For example, for the corresponding measured pressure pulse, the pressure values ​​at t.start and t.stop can be connected by a straight line, and the straight line can be subtracted from the corresponding measured pressure pulse to determine the feature determination pulse.

[0169] Although the TPW_M-curve and the TPW_E-curve have been determined in the above-described embodiment, the TPW_M-curve may be determined instead of the TPW_E-curve, wherein the TPW_M-curve is used to determine the blood pressure.

[0170] Although in the above-described embodiment, the processor 3 is configured to form the blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M that depends only on the following feature, which is the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia at the end-diastolic point of the characteristic determination pulse, in another embodiment, the blood pressure determination curve TPW_M-curve can be formed based on the blood pressure determination value TPWP_M that depends only on another feature. For example, the blood pressure determination curve TPW_M-curve can be formed based on the blood pressure determination value TPWP_M that depends only on the area TPA or TPA.norm of the corresponding characteristic determination pulse or only on the area TPA+.top surrounded by the first upper part of the characteristic determination pulse, in particular, on the area TPA+.top50, or only on the area TPA.top surrounded by the second upper part of the characteristic determination pulse, wherein a) the upper end of the second upper part is at the maximum systolic pressure TPsys of the characteristic determination pulse, and b) the lower end of the second upper part is between the pressure value corresponding to the average value TPcl of the measured pressure TP and the pressure TPdia at the end-diastolic point of the characteristic determination pulse. Therefore, in an embodiment, the function for determining the blood pressure determination value TPWP_M depends on the area TPA or TPA.norm of the corresponding characteristic determination pulse or the area TPA+.top surrounded by the first upper part of the characteristic determination pulse, in particular TPA+.top50 or the area TPA.top surrounded by the second upper part of the characteristic determination pulse, but does not depend on any other characteristics of the pressure pulse. For example, the blood pressure determination value TPWP_M can be determined according to one of the following equations:

[0171] TPWP_M=d5·TPA exp16 , (13)

[0172] TPWP_M=d6·TPA+.top exp17 , (14) and

[0173] TPWP_M=d7·TPA.top exp18 , (15)

[0174] Wherein, d5, d6, d7, exp16, exp17, exp18 are predetermined constants. For example, they can be predetermined by calibration. In an embodiment, d5=1, d6=1, d7=1, wherein the exponents are determined when calibrating the device.

[0175] In another preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M, which depends only on a) the characteristics of the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia of the characteristic determination pulse at the end-diastolic point, and b) the characteristics of the area (TPA.top) enclosed by the second upper part of the characteristic determination pulse or the area (TPA / TPA.norm) of the corresponding characteristic determination pulse. Therefore, in an embodiment, the function for determining the blood pressure determination value TPWP_M depends on a) TPP and b) TPA.top or TPA or TPA.norm, but does not depend on further characteristics of the pressure pulse. In particular, the blood pressure determination value TPWP_M can be determined according to one of the following equations:

[0176] TPWP_M=d8·TPA.top exp19 TPP exp20 ,(16)

[0177] TPWP_M=d9·TPA.top exp21 TPP exp22 ,(17) and

[0178] TPWP_M=d10·TPA·norm exp23 TPP exp24 , (18)

[0179] Wherein, d8, d9, d10, exp19, exp20, exp21, exp22, exp23, exp24 are predetermined constants. For example, they can be predetermined by calibration. In one embodiment, d8=1, d9=1, d10=1, wherein the exponents are determined when calibrating the device.

[0180] The equations which have been described above for TPWP_M can be used correspondingly for TPWP_E. The structure of the equations is the same, only other constants determined by calibration are used.

[0181] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims.

[0182] In the claims, the word "comprising" does not exclude other elements or steps, and the indicative "a" or "an" does not exclude a plurality.

[0183] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0184] Calculations such as determining the end measurement time point, pulse characteristics, certain curves, blood pressure values, etc., performed by one or more units or devices can be performed by any other number of units or devices. The calculations and determinations and / or control of the device according to the method can be implemented as program code modules of a computer and / or dedicated hardware.

[0185] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0186] Any reference signs in the claims should not be construed as limiting the scope. In particular, the use of letters such as TPP, TPA, etc. in brackets in the claims as reference signs should not be construed as limiting the scope. For example, according to the claims, in addition to the features indicated by the reference signs, other features may also be used.

[0187] The invention relates to determining the blood pressure of a subject based on a pressure signal that has been measured by using a measuring device, the measuring device comprising a) a housing enclosing a part of the subject through which blood flows, b) a pressure applicator for applying pressure to the housing and thereby to the enclosed part of the subject, and c) a pressure sensor for measuring the pressure signal on the skin of the enclosed part of the subject. For several pressure pulses of the pressure signal, respective features characterizing the respective pressure pulses are determined, wherein respective blood pressure determination values ​​are determined based on the respective features, thereby forming a blood pressure determination curve for determining the blood pressure. This allows the blood pressure to be determined with a relatively low computational effort.

Claims

1. An apparatus for determining the blood pressure of a subject, the apparatus comprising: A pressure signal providing unit, configured to provide a measured pressure signal (TP) of an object over a period of time, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising a) a housing, b) a pressure applicator, and c) a pressure sensor, the housing being configured to wrap around a portion of the object through which blood flows, the pressure applicator being configured to apply pressure to the housing, thereby applying pressure to the wrapped portion of the object, the pressure sensor being configured to measure the pressure signal on the skin of the wrapped portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal indicates blood pulsation and comprises a plurality of pressure pulses (9), A processor configured to: determine at least one feature characterizing a corresponding pressure pulse among the multiple pressure pulses (9); determine a blood pressure determination value (TPWP_M) for the corresponding pressure pulse based on the determined at least one feature, so that for several pressure pulses existing at different times, several blood pressure determination values ​​(TPWP_M) are determined, wherein a blood pressure determination curve (TPW_M-curve) is formed for the several pressure pulses and therefore the several blood pressure determination values ​​(TPWP_M) determined for several times; and determine the blood pressure based on the blood pressure determination curve (TPW_M-curve).

2. The device according to claim 1, wherein: The processor is configured to: in order to determine the at least one characteristic for the corresponding pressure pulse, provide a characteristic determination pulse (29) based on the corresponding pressure pulse, and determine at least one of the following characteristics: the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) at the end-diastolic point of the characteristic determination pulse, the area (TPA+.top) enclosed by a first upper portion of the characteristic determination pulse, wherein a) the upper end of the first upper portion is at the maximum systolic pressure (TPsys) of the characteristic determination pulse, and b) the lower end of the first upper portion is between the maximum systolic pressure (TPsys) of the characteristic determination pulse and a pressure value corresponding to the average value (TPcl) of the measured pressure (TP), The corresponding characteristics determine the duration (t(pulse)) of the pulse (29), The corresponding characteristic determines the area of ​​the pulse (29) (TPA / TPA.norm), The corresponding characteristic determines the full width at half maximum (W50) of the pulse (29), and The area enclosed by the second upper part of the characteristic determining pulse (TPA.top), wherein a) the upper end of the second upper part is at the maximum systolic pressure (TPsys) of the characteristic determining pulse, and b) the lower end of the second upper part is between the pressure value corresponding to the average value (TPcl) of the measured pressure (TP) and the pressure (TPdia) of the characteristic determining pulse at the end-diastolic point.

3. The device according to claim 2, wherein: The processor is configured to determine an area (TPA+.top50) enclosed by the first upper part of the characteristic determination pulse so that the lower end of the first upper part is at a pressure value corresponding to half the pressure distance (TPP+) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure value corresponding to the average value (TPcl) of the measured pressure (TP).

4. The device according to any one of claims 2 and 3, wherein: The processor is configured to determine the blood pressure determination value (TPWP_M) and thereby form the blood pressure determination curve (TPW_M-curve) based on only one feature in the following list of features: the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) at the end-diastolic point of the characteristic determination pulse, The corresponding characteristic determines the area of ​​the pulse (29) (TPA / TPA.norm), determining the area enclosed by said first upper portion of the pulse from said characteristic (TPA+.top), and The area enclosed by the second upper portion of the pulse (TPA.top) is determined from the characteristics.

5. The device according to any one of claims 2 and 3, wherein: The processor is configured to determine the blood pressure determination value (TPWP_M) and thereby form the blood pressure determination curve (TPW_M-curve) based only on the following characteristics: a) as a characteristic of the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) at the end-diastolic point of the characteristic determination pulse, and b) as a characteristic of the area enclosed by the first upper part of the characteristic determination pulse (TPA+.top), or as a characteristic of the area enclosed by the second upper part of the characteristic determination pulse (TPA.top).

6. A device according to any one of the preceding claims, wherein: The processor is configured to determine a position of a maximum of the blood pressure determination curve (TPW_M-curve) and to determine the blood pressure based on the determined position and the measured pressure (TP).

7. The device according to claim 6, wherein: The processor is configured to determine the blood pressure based on an average value (TPcl) of the measured pressures (TP) at the determined locations of the maximum values.

8. Apparatus according to any one of the preceding claims, wherein: The processor is configured to control the measuring device so that the applied pressure is increased during a measuring time period extending to an end measuring time point (32) and the applied pressure is reduced during a subsequent post-blood pressure measurement time period, and wherein the pressure sensor (7) measures the pressure (TP) on the skin at least during the measuring time period, wherein the processor is configured to determine an end measuring time point (32) based on the at least one characteristic determined for at least some of the plurality of pressure pulses (9), at or after which the measuring time period is to be stopped, and to control the pressure applicator (6, 8) so that when or after the end measuring time point (32) has been reached, the pressure applicator reduces the applied pressure to start the subsequent post-blood pressure measurement time period.

9. The device according to claim 8, wherein: The processor is configured to: determining, for a respective pressure pulse, an end determination value (TPWP_E) based on the at least one feature that has been determined for the respective pressure pulse, such that for several pressure pulses present at different times, several end determination values ​​(TPWP_E) are determined, wherein the several end determination values ​​(TPWP_E) determined for the several pressure pulses and therefore for the several times form an end determination curve (TPW_E), The end measurement time point (32) is determined based on the end determination curve (TPW_E-curve).

10. The device according to claim 9, wherein: The processor is configured to determine the end determination curve (TPW_E-curve) such that it satisfies one of the following conditions: The maximum value of the end determination curve (TPW_E-curve) occurs before the maximum value of the blood pressure determination curve (TPW_M-curve) in terms of time, the maximum value of the end determination curve (TPW_E-curve) occurs in time at or after the maximum value of the blood pressure determination curve (TPW_M-curve), and the decline of the end determination curve (TPW_E-curve) after reaching its maximum value is steeper than the decline of the blood pressure determination curve (TPW_M-curve) after reaching its maximum value, and The end determination curve (TPW_E-curve) is the same as the blood pressure determination curve (TPW_M-curve).

11. The device according to any one of claims 9 and 10, wherein: The processor is configured to determine the end measurement time point (32) further based on the blood pressure determination curve (TPW_M-curve).

12. The device according to claim 11, wherein The processor is configured to determine the end measurement time point (32) by determining a) when the end determination curve (TPW_E-curve) drops to a value equal to or less than a predetermined percentage of the maximum value after exceeding its maximum value and b) when the blood pressure determination curve (TPW_M-curve) reaches or exceeds its maximum value.

13. A method for determining the blood pressure of a subject, wherein: The method comprises: A measured pressure signal (TP) of an object over a period of time is provided by a pressure signal providing unit, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising a) a housing, b) a pressure applicator, and c) a pressure sensor, wherein the housing is configured to wrap a portion of the object through which blood flows, the pressure applicator is configured to apply pressure to the housing, thereby applying pressure to the wrapped portion of the object, the pressure sensor is configured to measure the pressure signal on the skin of the wrapped portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal indicates blood pulsation and includes a plurality of pressure pulses (9), determining, by the processor, for a corresponding pressure pulse in the plurality of pressure pulses (9), at least one feature characterizing the corresponding pressure pulse, determining, by the processor, for the respective pressure pulses, a blood pressure determination value (TPWP_M) based on the determined at least one characteristic, such that for a number of pressure pulses present at different times, a number of blood pressure determination values ​​(TPWP_M) are determined, wherein the number of blood pressure determination values ​​(TPWP_M) determined for the number of pressure pulses and therefore for the number of times form a blood pressure determination curve (TPW_M-curve), and The blood pressure is determined by the processor based on the blood pressure determination curve (TPW_M-curve).

14. A computer program for determining blood pressure, the computer program comprising: A program code module for causing the device for determining blood pressure according to any one of claims 1 to 12 to execute the steps of claim 13.

Images