Device for measuring the blood pressure of a subject

Abstract

An apparatus for determining a subject's blood pressure is presented. The apparatus has a pressure signal supply unit configured to supply a measured pressure signal of a subject over a period of time, the pressure signal indicating the pulsation of blood and having a plurality of pressure pulses. The apparatus further has a processor configured to determine a blood pressure determination curve indicating the dependence of the applied pressure of the pressure pulses based on the plurality of pressure pulses, apply a transformation to the blood pressure determination curve, and determine the blood pressure based on the result of the transformation. This makes it possible to determine the blood pressure more accurately.

Description

Technical Field

[0001] The present invention relates to an apparatus, a method, and a computer program for determining a subject's blood pressure.

Background Art

[0002] US 2021 / 0235996 A discloses a signal processing apparatus including a memory configured to store instructions and a processor. The processor is configured to execute instructions to acquire a signal, obtain a frequency band spectrum by applying a fast Fourier transform (FFT) to the acquired signal, and remove noise from the obtained spectrum by applying a first filter and a second filter different from each other to the obtained frequency band spectrum.

[0003] The paper by M. Forouzanfar et al. (“Oscillometric Blood Pressure Estimation: Past, Present, and Future”, IEEE Reviews in Biomedical Engineering, volume 8, pages 44 to 63 (2015)) discloses that the use of automated blood pressure (BP) monitoring is growing because it requires little expertise and can be performed by patients several times a day at home. This paper further discloses that oscillometry is one of the most common measurement methods used in automated BP monitors, and for example, derived oscillometry is described.

[0004] US 2022 / 0096017 A discloses a control device for controlling a blood pressure measurement system. The pressurizing unit (applicator) applies an increasing pressure to a subject's site during a measurement period, while the pressure on the skin of the subject's site having a plurality of pressure pulses is measured. For each of at least some of these plurality of pressure pulses, some features characterizing each pressure pulse are determined, and based on these features, an end measurement time point at which the measurement period is stopped at that time or afterwards is determined. When reaching or after reaching this end measurement time point, that is, when the measurement period stops, the applied pressure decreases and a period after a subsequent blood pressure measurement starts.

[0005] DE 10 2017 110 770 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 a person, and this tissue pressure signal has a sequence of tissue pressure pulse curves. At least two individual tissue pressure pulse curves are identified in this tissue pressure signal, and for each of these identified tissue pressure pulse curves, at least one amplitude parameter and one area parameter are determined. The amplitude parameter indicates the amplitude of the identified tissue pressure pulse curve, and the area parameter indicates at least one partial area enclosed by the tissue pressure pulse curve. For each of the identified tissue pressure pulse curves, a pulsation force parameter indicating the shape of the tissue pressure pulse curve is determined based on at least the amplitude parameter and the area parameter. A parameter function indicating the functional relationship between the determined pulsation force parameter of the tissue pressure pulse curve and the corresponding clamp pressure or measurement time in the pressure cuff is generated. Based on this parameter function, at least one blood pressure value is determined.

[0006] EP 3 430 992 A1 discloses a blood pressure measurement system configured to surround a body part of a subject, the blood pressure measurement system having pressurizing means for applying pressure to the body part and a kinking-proof shell. When the blood pressure measurement system surrounds the body part, the kinking-proof shell is arranged to be positioned between the pressurizing means and the body part. The blood pressure measurement system is capable of measuring blood pressure by continuously increasing the clamping pressure and stopping the increase above the systolic blood pressure. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0007] An object of the present invention is to provide an improved apparatus, method and computer program for determining blood pressure, which enables, for example, more accurate determination of blood pressure. MEANS FOR SOLVING THE PROBLEM

[0008] In a first aspect of the present invention, there is provided an apparatus for determining the blood pressure of a subject, the apparatus comprising a pressure signal supply unit configured to supply a measured pressure signal of the subject over a period of time, the pressure signal being a) a shell configured to enclose a site where the blood of the subject flows, b) a pressurizing part configured to apply pressure from the outside of the shell to the shell, thereby applying pressure to the enclosed part of the subject, and c) a pressure sensor configured to measure a pressure signal on the skin of the enclosed part of the subject measured by using a measurement device having, the pressurizing part increasing or decreasing the applied pressure while the pressure signal is being measured, the measured pressure signal indicating a pulsation of blood and having a plurality of pressure pulses, a pressure signal supply unit, and A processor configured to determine a blood pressure determination curve based on the plurality of pressure pulses, the blood pressure determination curve indicating the dependence of the pressure pulses on the applied pressure, the processor further configured to apply a transformation to the blood pressure determination curve and to determine a blood pressure based on the result of this transformation, and a processor having.

[0009] It has been found that the method of interpreting the measured pressure signal is important for determining the exact blood pressure value of the subject. Based on this finding, although the blood pressure determination curve already shows the dependence on the pressure applied by the pressurizing part of the pressure pulse, the blood pressure is not determined based on the blood pressure determination curve itself, but rather by applying a transformation to the blood pressure determination curve and determining the blood pressure based on the result of this transformation, it has been recognized that it can be determined more accurately.

[0010] A pressure sensor configured to measure the pressure on the skin of the wrapped part of the subject is arranged inside the shell. However, this pressure sensor can also be arranged in another way for measuring the pressure on the skin of the wrapped part of the subject. For example, a pressure sensor pad filled with fluid can be arranged inside the shell and connected via a fluid path, that is, via a tube filled with fluid, to a pressure sensor outside the shell to measure the pressure on the skin of the wrapped part of the subject.

[0011] The pressure signal supply unit can be, for example, a receiving unit configured to receive a pressure signal from a measuring device and supply the received pressure signal. However, this pressure signal supply unit can also be a storage device in which previously measured pressure signals are stored and can be retrieved to supply the stored pressure signals. The pressure signal supply unit can be a measuring device that measures the pressure signal or can have it.

[0012] While the pressure signal is being measured, the pressure applied to the shell by the pressurizing unit and thereby applied to the enclosed part of the subject can, for example, continuously increase or decrease during the measurement period, particularly with a constant gradient. The measured pressure signal is typically understood as a composition, particularly a sum, of a portion due to an increase or decrease in the applied pressure and a portion due to the pulsation of the blood in the part of the subject enclosed by the shell. Therefore, the measured pressure signal has pressure pulses, and specifically, these pressure pulses can be understood as indicating the pulsation of the blood.

[0013] The portion of the measured pressure signal due to the pulsation of the blood typically first increases when the applied pressure increases near or from below the diastolic blood pressure, and starts to decrease at a certain point when the applied pressure further increases towards or beyond the systolic pressure. This, on the one hand, provides the necessary coupling between the pulsation of the blood in the part of the subject enclosed by the shell and the pressure sensor, while on the other hand, the applied pressure tends to suppress this pulsation of the blood. Similarly, the portion of the measured pressure signal due to the pulsation of the blood typically increases when the applied pressure decreases near or from above the systolic pressure, and starts to increase at a certain point when the applied pressure further decreases towards or below the diastolic pressure. This dependence, which is the dependence of the pressure pulses in the measured pressure signal on the applied pressure signal, is also shown by the blood pressure determination curve determined by the processor. For example, the blood pressure determination curve can also increase during the measurement period and then start to decrease again, particularly regardless of whether the applied pressure increases or decreases. The dependence of the pressure pulses of the measured pressure signal on the applied pressure, that is, how the pressure pulses depend on the applied pressure, serves as an indicator of blood pressure. Since this dependence is shown by the blood pressure determination curve, this blood pressure determination curve also serves as an indicator of blood pressure.

[0014] The blood pressure determination curve configured to be determined by the processor based on a plurality of pressure pulses in the pressure signal is preferably a continuous curve, in particular, a curve differentiable at least once, more specifically a smooth curve, where the terms "continuous", "differentiable" and "smooth" can be understood to have an approximate meaning, or a "discretized" meaning, as known in numerical analysis. The blood pressure determination curve preferably corresponds to a function of the applied pressure, the mean measured pressure, or the measurement time. In fact, the processor is not necessarily configured to determine the actual graphical representation corresponding to the blood pressure determination curve. Instead, the blood pressure determination curve corresponds only to the pressure values, understood as blood pressure determination curve values, associated with respective values of the applied pressure, the mean measured pressure, or the measurement time, and is specifically composed of these pressure values.

[0015] The transformation applied to the blood pressure determination curve is predefined so that the region of the blood pressure determination curve showing a dependence on the applied pressure exceeding a predetermined intensity of the pressure pulse is detected more efficiently. It has been found that the region where the dependence of the pressure pulse on the applied pressure is strong can provide valuable information about blood pressure. Therefore, more efficient detection of such regions is facilitated by emphasizing these regions. Since the pressure applied by the pressurizing unit increases or decreases over time, the dependence of the blood pressure determination curve on the applied pressure corresponds to the rate of change of the blood pressure determination curve. Thus, the dependence of the blood pressure determination curve on the applied pressure at a given point of the blood pressure determination curve, i.e., its local intensity, can be measured, for example, with respect to the slope of the curve at that point. It is recognized that the regions of the blood pressure determination curve where the dependence on the applied pressure is weak, especially where it disappears, can also provide valuable information about blood pressure, but it is also known that this is not the only case. The relative terms "strong" and "weak", referring to the strength of the dependence of the blood pressure determination curve on the applied pressure, are understood to be defined with respect to one or more predetermined thresholds. Furthermore, the dependence of the blood pressure determination curve on the applied pressure, especially the slope of the curve, is considered with respect to its actual value, i.e., its sign or its absolute value.

[0016] Applying a transformation to the blood pressure determination curve refers to transforming at least a part of this blood pressure determination curve, particularly the whole. Thus, the result of applying a transformation to the blood pressure determination curve may be the transformed blood pressure determination curve. When this transformation is applied only to a part of the blood pressure determination curve, the transformed blood pressure determination curve may deviate from the blood pressure determination curve only in this part, or may correspond only to this deviating part. When the blood pressure determination curve is transformed only partially, the processor may be configured to determine the blood pressure based only on the transformed part of the blood pressure determination curve. The blood pressure determination curve may be transformed only partially if it is expected that any part of the blood pressure determination curve will be a good basis for determining the blood pressure after transformation. Limiting the applied transformation to a part of the blood pressure determination curve can save computational resources.

[0017] The result of applying the conversion to the blood pressure determination curve can be considered as the converted blood pressure determination curve, but the processor does not necessarily have to be configured to actually determine the converted blood pressure determination curve. Instead, for example, the processor can be configured to determine new pressure values based on the pressure values corresponding to the blood pressure determination curve and determine the blood pressure based on these new pressure values, where these new pressure values are referred to as converted blood pressure determination curve values. Applying the conversion to the blood pressure determination curve corresponds to determining new pressure values based on the pressure values corresponding to this blood pressure determination curve, so applying the conversion is also understood as applying a function to the blood pressure determination curve, i.e., the blood pressure determination curve values. However, it should be noted that this function is not necessarily a normal function such as an analytical function. Instead, the applied conversion can only be represented by an operator such as a differential operator. In a preferred embodiment, the conversion applied to the blood pressure determination curve refers to obtaining the derivative of the blood pressure determination curve. For example, the processor is configured to determine the blood pressure based on the derivative of the blood pressure determination curve. The derivative of the blood pressure determination curve has been found to indicate regions where the applied pressure of the blood pressure pulse has a strong dependence and is thus particularly useful for more accurately determining the blood pressure, while at the same time requiring an acceptable computational effort for the calculation. When the conversion is a derivative, it is understood that the blood pressure determination curve is determined such that the curve is differentiable.

[0018] Instead of determining a derivative that enables efficient detection of the region in the blood pressure determination curve that exhibits a strong dependence on the applied pressure of the pressure pulse, it is possible to determine the difference between points on the blood pressure determination curve. The term "difference" is to be understood in particular as referring to a difference that is finite beyond the extent considered in numerical analysis for approximating a derivative. However, alternatively, taking the difference between different points on the blood pressure determination curve may, as is known from numerical analysis, be understood as corresponding to determining a finite, i.e., discretized, version of the derivative. In either case, the determination of the difference may be understood as an application of a transformation to the blood pressure determination curve, which results in a map that maps the blood pressure determination curve, or a part thereof, to a new curve that can be regarded as the transformed blood pressure determination curve, since the determined difference is associated with the points of the blood pressure determination curve.

[0019] Preferably, the processor is configured to determine the position of the maximum value of the derivative of the blood pressure determination curve and to determine the blood pressure based on this determined position and the measured pressure. In particular, the processor is configured to determine the blood pressure based on the average of the measured pressure at the determined position of the maximum value. It has been found that determining the blood pressure based on the determined maximum value of the derivative of the blood pressure determination curve and depending on the pressure measured on the skin to be measured, i.e., depending on the tissue pressure, enables a particularly accurate determination of the blood pressure. When determining the blood pressure based on the maximum value of the derivative of the blood pressure determination curve, the processor is configured to determine the derivative of the blood pressure determination curve only for the region where the maximum value of the derivative is expected to exist. This expected region may be a fixed region determined in advance based on previous measurements.

[0020] The maximum value of the derivative preferably points in the direction from low applied pressure to high applied pressure. In other words, preferably, the derivative is considered in the direction from low applied pressure to high applied pressure regardless of whether the pressure applied while measuring the pressure signal used to determine the blood pressure is increased or decreased.

[0021] Preferably, the processor determines a first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of one of the peak values of the overall peak of the blood pressure determination curve, and determines the position of the maximum value of the derivative of the blood pressure determination curve before the determined first peak, so as to determine the position of the maximum value of the derivative of the blood pressure determination curve. The predetermined percentage of the overall peak can be determined in advance by calibration. In a preferred embodiment, the predetermined percentage is 90%. The determination of the first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of one of the peak values of the overall maximum peak of the blood pressure determination curve can be carried out by normalizing the blood pressure determination curve to one of the peak values of the overall maximum peak such that this peak value becomes 1 after normalization. At this time, the predetermined percentage is a fixed absolute number between 0 and 1, preferably 0.9. It has been found that restricting the region in which the maximum value of the derivative of the blood pressure determination curve is determined can thus further improve the accuracy of determining blood pressure.

[0022] Here, it should be noted that the word "before" refers to the direction from low applied pressure to high applied pressure. Therefore, when the pressure applied while measuring the pressure signal used to determine blood pressure increases, the word "before" also means earlier in time, and when the pressure applied while measuring the pressure signal used to determine blood pressure decreases, the word "before" means later in time.

[0023] If the blood pressure determination curve has only a single peak, this single peak is the overall maximum peak and is also the first peak having a peak value greater than a predetermined percentage of one of the peak values of this overall maximum peak.

[0024] Preferably, the applied pressure increases while measuring the pressure signal used to determine blood pressure. This is advantageous compared to decreasing the applied pressure while measuring the pressure signal used to determine blood pressure.

[0025] The processor can be further configured to determine the position of the maximum value of the blood pressure determination curve and to determine the blood pressure based on this further determined position and the measured pressure. In particular, the processor can be configured to determine the blood pressure further based on the determined further position, i.e., the average of the measured pressures at the determined position of the maximum value of the blood pressure determination curve. In addition to the determined maximum value of the derivative of the blood pressure determination curve, determining the blood pressure based on the determined maximum value of the blood pressure determination curve and depending on the measured pressure on the skin, i.e., depending on the tissue pressure, enables more accurate determination of the blood pressure even though the dependence of the applied pressure on the blood pressure determination curve at its maximum value is usually relatively weak or zero because the derivative of the blood pressure determination curve at its maximum value is zero. In fact, the processor can be configured to determine the position of the maximum value of the blood pressure determination curve by determining, based on its derivative, i.e., based on the transformed blood pressure determination curve, i.e., by determining where the derivative is zero. Alternatively, for example, the processor can be configured to determine the position of the maximum value of the blood pressure determination curve and / or its transformed version by comparing the points on the respective curves or the corresponding function values with each other, and each maximum value can be determined to be located where the respective curve or its corresponding function changes from increasing, i.e., rising, to decreasing, i.e., falling. Further, each maximum value can be determined while the pressure signal is being measured, in particular while a part of the pressure signal that gives rise to each maximum value in the respective curve is being measured.

[0026] In addition to the transformed version of the blood pressure determination curve, determining blood pressure based on the blood pressure determination curve, particularly based on the positions of the maxima of both of these curves, enables a more accurate determination of blood pressure, while determining blood pressure based only on the transformed version of the blood pressure determination curve, particularly based only on the position of the maximum of the derivative of the blood pressure determination curve, is computationally more efficient. Further, the derivative of the blood pressure determination curve typically reaches its maximum earlier than the blood pressure determination curve itself during the measurement period, which enables a faster blood pressure determination and thus enables reducing the discomfort of the subject.

[0027] In addition to, or instead of, determining blood pressure based on the position of the maximum of the derivative of the blood pressure determination curve, blood pressure can be determined based on the position of the minimum of the derivative of the blood pressure determination curve. This is particularly advantageous when the pressure applied by the pressurizing unit is increased or decreased and the measurement time during which the pressure signal is measured is relatively long.

[0028] As already described above, the blood pressure determination curve can particularly correspond to a function of the applied pressure or the average measured pressure. Thus, instead of the measured pressure, particularly its average, the applied pressure at each maximum can also be used to determine blood pressure. The applied pressure can refer to the pressure that the pressurizing unit is controlled to apply.

[0029] It is understood that it is still acceptable to use a pressure close to this pressure instead of accurately using each pressure value at the determined position of each maximum for determining blood pressure. In other words, it is acceptable if each maximum is not determined exactly but is determined with a predetermined sufficient accuracy.

[0030] In one embodiment, the processor is configured to determine blood pressure as a function of a) the average of the measured pressures at the determined positions of the maximum values of the derivative of the blood pressure determination curve, and b) the average of the measured pressures at the determined positions of the maximum value of the blood pressure determination curve, and the dependencies of the function on the average of the measured pressures at the two positions are determined in advance based on reference measurement values. In particular, the function can be a linear function in which the dependencies of the function on the average of the measured pressures at the two positions are represented by a linear coefficient, and this linear coefficient is determined in advance in a linear regression performed based on the reference measurement values. While general functions allow for even higher accuracy, linear functions keep the computational effort acceptable while still allowing for very high accuracy in determining blood pressure.

[0031] The reference measurement values, also referred to as calibration measurement values, preferably correspond to the evaluation of a calibration set consisting of pairs of a) invasively measured blood pressure values and b) non-invasive blood pressure values determined based on non-invasively measured pressure signals, where the non-invasively measured pressure signals are measured by the device defined above simultaneously with the invasive measurement. The calibration set is preferably collected from an appropriate number of people in different hemodynamic states. The non-invasive blood pressure values are determined by the device defined above, and the linear coefficient of the function shown above representing blood pressure with respect to the applied pressure, in particular the average of the measured pressures at the two positions shown above, is optimized such that the deviation between the invasive blood pressure value and the non-invasive blood pressure value is minimized. For example, linear regression using the least squares method can be performed.

[0032] It has been found that determining blood pressure based on the derivative of the blood pressure determination curve enables a very accurate determination of blood pressure, but other transformations applied to the blood pressure determination curve can also provide a good or even better basis for an accurate determination of blood pressure. For example, the processor is configured to determine the logarithm of the blood pressure determination curve and determine blood pressure based thereon.

[0033] Furthermore, the term "derivative" has been used above and is subsequently used to refer to the first derivative, although higher order derivatives can also be used as transformations applied to the blood pressure determination curve.

[0034] Preferably, the processor is configured to determine, for each of a plurality of pressure pulses, at least one feature characterizing each pressure pulse, and based on the at least one determined feature, for each of the pressure pulses, determine a blood pressure determination value such that several blood pressure determination values are determined for several pressure pulses existing at different times. The processor is configured to determine a blood pressure determination curve such that several blood pressure determination values determined for several pressure pulses, and thus for several times, form a blood pressure determination curve. In this case, the blood pressure determination curve used for blood pressure measurement can be considered to be composed of individual tissue pressure waveforms (TPW) such that this curve is abbreviated as the TPW_M-curve, whereas the blood pressure determination values can be considered to parameterize the tissue pressure waveform such that these values are abbreviated as the TPWP_M. It has been found that it is possible to accurately determine blood pressure even if a single feature is considered for determining the blood pressure determination value. Thus, it is possible to accurately determine blood pressure with a relatively low computational effort.

[0035] The at least one feature can directly characterize each pressure pulse or can indirectly characterize each pressure pulse. In the latter case, each pressure pulse is processed to determine a feature determination pulse, and at least one feature is determined based on the determined feature determination pulse. This will be explained in more detail below. The processor is configured to determine at least one feature characterizing each pressure pulse for all or only a part of the plurality of pressure pulses, for example, for at least 5 or at least 10 pressure pulses each.

[0036] The processor can be adapted to process several blood pressure determination values obtained for several pressure pulses in order to obtain a blood pressure determination curve. For example, interpolation can be applied, and optionally smoothing can also be applied. In this way, a continuous, at least once differentiable, or smooth blood pressure determination curve can be obtained.

[0037] In one embodiment, the processor is configured to supply a feature determination pulse based on each pressure pulse in order to determine at least one feature for each pressure pulse, and to determine at least one of the following features. The following features are: i) the difference (TPP) between the maximum systolic pressure (TPsys) of the feature determination pulse and the pressure (TPdia) of the feature determination pulse at the end-diastolic point, ii) the area (TPA+.top50) enclosed by the upper part of the feature determination pulse, where a) the upper end of the upper part is at the maximum systolic pressure (TPsys) of the feature determination pulse, b) the lower end of the upper part is between the maximum systolic pressure (TPsys) of the feature determination pulse and the pressure value corresponding to the average (TPcl) of the measured pressure (TP), iii) the duration (t(pulse)) of each feature determination pulse, iv) the area (TPA / TPA norm) of each feature determination pulse, and v) the half-value width (W50) of each feature determination pulse. It has been found that the determination of blood pressure is further improved by using at least one of these features.

[0038] The feature determination pulse for each pressure pulse can be obtained, for example, by subtracting the average measured pressure (TPcl) from each of these pressure pulses. However, the feature determination pulse for each pressure pulse can also be determined in another way. The feature determination pulse can be the direct pressure pulse of each, that is, each measured pressure pulse. When the feature determination pulse for each pressure pulse is obtained by subtracting the average measured pressure (TPcl) from each pressure pulse to determine the area TPA+.top50, the pressure value corresponding to the average (TPcl) of the measured pressure (TP) to be measured becomes zero.

[0039] The difference (TPP) between the maximum systolic pressure of the feature-determining pulse and the pressure of the feature-determining pulse at the end-diastolic point is preferably the difference between the measured pressure of the maximum value and the measured pressure of the minimum value of each pressure pulse, i.e., the tissue pressure (TP) of each of said pressure pulses at the maximum systolic point, i.e., the difference between the pressure measured on the skin and the tissue pressure (TP) at the end-diastolic point of each of said pressure pulses. The duration t(pulse) of each of said feature-determining pulses preferably corresponds to the time difference between the end-diastolic point for each of said pressure pulses and the next end-diastolic point. Further, the area TPA is preferably the area under the curve of each feature-determining pulse from the end-diastolic point to the next end-diastolic point. This area can be a normalized area and is named "TPA.norm". For example, the area TPA can be normalized by scaling this area by the difference between the maximum pressure and the minimum pressure of each feature-determining pulse to determine TPA.norm. The half-width W50 corresponds to the width of 50% of the difference between the maximum pressure and the minimum pressure of each feature-determining pulse. Therefore, it is the width at 50% of the difference between the pressure of the feature-determining pulse at the maximum systolic point and the pressure of the feature-determining pulse at the end-diastolic point.

[0040] In a preferred embodiment, the processor is configured to determine the area TPA+.top50 enclosed by the upper part of this feature-determining pulse such that the lower end of the upper part of the feature-determining pulse is at a pressure value corresponding to half of the pressure distance (TPP+) between the maximum systolic pressure (TPsys) of the feature-determining pulse and the pressure value corresponding to the average (TPcl) of the measured pressures (TP).

[0041] Furthermore, in a preferred embodiment, the processor determines a blood pressure determination value (TPWP_M) and thus is configured to form a blood pressure determination curve (TPW_M-curve) based only on a feature that is the difference (TPP) between the maximum systolic pressure (TPsys) of the feature determination pulse and the pressure of the feature determination pulse at the end-diastolic point (TPdia). Thus, in this embodiment, no other features among the above-described features are used to determine the blood pressure determination value in addition to TPP. It has been found that this makes it possible to further increase the accuracy of determining blood pressure with a relatively low computational effort.

[0042] In a further improved embodiment, the processor determines a blood pressure determination value (TPWP_M) and thus is configured to form a blood pressure determination curve (TPW_M-curve) based only on a) a feature that is the difference (TPP) between the maximum systolic pressure (TPsys) of the feature determination pulse and the pressure of the feature determination pulse at the end-diastolic point (TPdia), and b) a feature that is the area TPA+.top50 enclosed by the upper part of the feature determination pulse. Thus, in this embodiment, no other features among the above-described features are used to determine the blood pressure determination value in addition to TPP and TPA+.top50. It has been found that this makes it possible to further increase the accuracy of determining blood pressure while still keeping the computational effort relatively low.

[0043] Preferably, the processor receives at least one characteristic of each pressure pulse as an input, provides a function that outputs each blood pressure determination value, and determines a blood pressure determination curve formed by each blood pressure determination value, together with the blood pressure determination values determined for other pressure pulses. The function has at least one parameter determined by calibration, where the reference blood pressure value is determined very accurately by invasive means, and at least one parameter is determined such that the device provides the blood pressure value measured invasively very accurately with high statistical accuracy and precision. In particular, for calibration measurements, pairs of simultaneously recorded invasive and non-invasive blood pressure values from an appropriate number of humans with different hemodynamic states are used. It should be noted that calibration is preferably only carried out in the development stage, i.e., not during the actual blood measurement procedure. Calibration can be carried out separately for different shell sizes, i.e., preferably for different sizes of blood pressure cuff, or for different groups of shell sizes. For example, different parameters of the function can be determined by calibration for different shell sizes, or different groups of shell sizes, i.e., at least one parameter for each can be determined for each shell size or for each group of shell sizes.

[0044] For example, the processor is configured to determine a blood pressure determination value (TPWP_M) based on at least one determined feature by raising at least one feature for each pressure pulse to a predetermined exponent. This predetermined exponent can be predefined by calibration as described in the previous paragraph. Thus, this predetermined exponent can be a parameter of the function described in the previous paragraph, and the parameter, i.e., the predetermined exponent in this example, is predefined by calibration. The function can have the following structure. a) Multiply a predetermined coefficient by b) the result of the first power obtained by raising the first feature characterizing each pressure pulse to the first predetermined exponent. Optionally, c) further multiply by the result of the second power obtained by raising the second feature characterizing each pressure pulse to the second predetermined exponent. Optionally, d) further multiply by the result of the third power obtained by raising the third feature characterizing each pressure pulse to the third predetermined exponent, and so on. Here, in a preferred embodiment, the function has only a) and b), or only a), b) and c). Also, the predetermined coefficient can be predefined by calibration.

[0045] The processor is also configured to control the measured value of the pressure signal in accordance with the blood pressure value determined in some cases, i.e., the blood pressure value determined during the measurement. In one embodiment, the processor is configured to control the measurement device such that the applied pressure increases during the measurement period extending to the end measurement time point, and the applied pressure is decreased during the period after the next subsequent blood pressure measurement. The pressure sensor measures the pressure (TP) on the skin at least during the measurement period. The processor determines the end measurement time point at which the measurement period is stopped then or thereafter based on at least one characteristic determined for at least some of the plurality of pressure pulses, and when or after reaching the end measurement time point, decreases the applied pressure and is configured to control the pressurizing unit to start the period after the next subsequent blood pressure measurement. In particular, at least one characteristic determined for each of the pressure pulses can be used to determine the end measurement time point such that sufficient pressure data for an accurate determination of the blood pressure is measured despite the relatively short measurement period. This enables a reduction in blood pressure measurement time and tissue pressure, i.e., the clamping pressure applied to the skin of the body part during the measurement remains substantially below the systolic arterial pressure and ends.

[0046] Preferably, the processor is configured to: a) determine an end decision value for each of several pressure pulses based on at least one characteristic determined for each pressure pulse such that several end decision values are determined for several pressure pulses existing at different times, where the several end decision values determined for several pressure pulses, and thus for several times, form an end decision curve; and b) determine an end measurement time point based on the end decision curve. By using the end decision curve, the accuracy of determining the end measurement time point can be further enhanced. The processor is adapted to process several end decision values obtained for several pressure pulses in order to obtain a continuous end decision curve. Known mathematical techniques can be used to obtain the continuous curve based on the individual end decision values. For example, interpolation, a fitting procedure, a filtering method, etc. can be applied.

[0047] The processor preferably meets the following conditions a) the maximum value of the end decision curve occurs earlier in time than the maximum value of the blood pressure decision curve; b) the maximum value of the end decision curve occurs at or after the maximum value of the blood pressure decision curve in time, and the decrease after the maximum value of the end decision curve is steeper than the decrease after the maximum value of the blood pressure decision curve; and c) the end decision curve coincides with the blood pressure decision curve and is configured to determine the end decision curve such that it satisfies one of the above conditions. It has been found that when the end decision curve and the blood pressure decision curve have one of these relationships with each other, the end measurement time point can be determined more accurately.

[0048] In a preferred embodiment, the processor is configured to determine the end measurement time point further based on the blood pressure decision curve. It has also been found that when not only the end decision curve but also the blood pressure decision curve is used for determining the end measurement time point, the measurement time can be further shortened.

[0049] 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 passing through the maximum value; and b) when the blood pressure determination curve reaches or passes through the maximum value. The predetermined percentage of the maximum value is more preferably in the range of 40% to 95%. In particular, when both curves use this method to determine the end measurement time point, it has been found that this time point can be determined very accurately so that the blood pressure can be measured very accurately despite the relatively short blood pressure measurement time.

[0050] In one embodiment, the processor is configured to control the pressurizing unit such that the pressurizing unit increases the applied pressure at a first rate during a period before measurement and then increases the applied pressure at a second rate during a subsequent measurement period, where the first rate is greater than the second rate. Thus, it is possible to reach the applied pressure at which the measurement period should start relatively quickly, thereby further reducing the overall time required to measure blood pressure.

[0051] In one embodiment, the processor is configured to control the pressurizing unit such that at the end of the period before measurement, the measured pressure is within the range of 15 to 30 mmHg. This ensures that the pressure on the skin, i.e., the tissue pressure, is measured over a sufficiently wide pressure range during the measurement period, which enables an accurate and precise measurement of blood pressure.

[0052] If the previous diastolic arterial pressure obtained from a previous blood pressure measurement of the same subject is not used by the processor to control the pressurizing unit, a range of 15 to 30 mmHg is preferably applied. When the previous diastolic arterial pressure is used for controlling the pressurizing unit, the measured pressure at the end of the period before measurement may be higher. The control of the pressurizing unit depending on the previously obtained diastolic arterial pressure is described below.

[0053] Note that the pressure at the end of the period before the measurement is not the pressure applied between two subsequent blood pressure measurements, in particular the pressure applied before the start of this period before the measurement. This pressure is named "attachment pressure" and should not exceed 15 mmHg.

[0054] In one embodiment, the processor is configured to: a) store or receive the previous diastolic arterial pressure obtained by a previous blood pressure measurement; b) determine a first end measurement pressure that should exist at the end of the period before the measurement and can thus be regarded as the target pressure, depending on the previous diastolic arterial pressure such that the first end measurement pressure is less than the previous diastolic arterial pressure; and c) control the pressurizing unit such that the measured pressure at the end of the period before the measurement is less than or equal to the determined first end measurement pressure. Preferably, the processor is configured to determine the first end measurement pressure such that the pressure is 90% or less of the previous diastolic arterial pressure. In addition, this ensures that during the measurement period, the pressure on the skin, i.e., the tissue pressure, is measured over a range wide enough to accurately and precisely determine blood pressure.

[0055] In one embodiment, the processor is further configured to store or receive the time at which the previous diastolic arterial blood pressure was measured and to determine the first end measurement pressure depending on: i) the previous diastolic arterial pressure; and ii) the time distance to the blood pressure measurement at which the previous diastolic arterial pressure was measured, indicated by the stored time. The diastolic arterial pressure may change over time, where the first end measurement pressure can still be determined relatively accurately considering the time distance to the blood pressure measurement at which the previous diastolic arterial blood was measured. Thus, although there is this uncertainty regarding the change of the diastolic arterial pressure over time, the end of the period before the measurement can be determined such that during the subsequent measurement period, the pressure on the skin, i.e., the tissue pressure, is measured over a range wide enough to accurately and precisely determine blood pressure.

[0056] The processor can be further configured to: a) store or receive the previous pressure measured by the pressure sensor in the period from the end of the previous measurement period of the previous blood pressure measurement to the start of the pre-measurement period, and b) control the pressurizing unit so that the pressure measured at the start of the pre-measurement period is equal to or lower than a predetermined pressure value based on the stored or received previous measurement. The predetermined pressure value is preferably 15 mmHg or less, more preferably 10 mmHg or less.

[0057] The pressure measured at the start of the pre-measurement period can be regarded as the mounting pressure that exists during the measurement pause between two subsequent blood pressure measurements, i.e., the mounting pressure that exists before the start of each blood pressure measurement. This mounting pressure is preferably controlled to achieve a given or pre-set value, i.e., a predefined pressure value. This control is preferably carried out to adapt to changes in the volume of the body part, such as an increase caused by tissue edema (e.g., capillary leakage such as sepsis, increased circulating blood volume), or a decrease caused by the reduction of tissue edema or a decrease in circulating blood volume. This should in particular prevent venous congestion caused by venous reflux insufficiency due to compression of the veins at a tissue pressure higher than the venous pressure in each body part during the measurement pause, i.e., between two subsequent blood pressure measurements. In a preferred embodiment, the pressure on the skin, which is also regarded as the tissue pressure, is continuously measured throughout the procedure of performing one or more blood pressure measurements, and the pressurizing unit is controlled to prevent venous congestion during the measurement pause.

[0058] The shell is preferably an anti-kink shell. This anti-kink shell is preferably disposed (or sandwiched) between the pressurizing unit, i.e., for example, a fluid bag, and the part of the subject to be wrapped. A relatively rigid anti-kink shell prevents or at least significantly reduces the occurrence of wrinkles or kinks on the surface that compresses the pressurizing unit, particularly the fluid bag. As a result, there are no wrinkles that adversely affect the amplitude, shape, and reproducibility of the measurement signal, so the measurement accuracy can be improved.

[0059] The kink prevention shell preferably exhibits a rigidity significantly greater than that of the wall of the fluid bag when the pressurizing part has the above-mentioned fluid bag. Preferably, the rigidity of the kink prevention shell is selected to ensure that buckling of the kink prevention shell does not occur when pressure is applied to the wrapped part of the subject for measuring the blood pressure of the subject. At the same time, the kink prevention shell should be sufficiently flexible so that, for example, when pressure is applied by the pressurizing part by inflating the fluid bag of the pressurizing part, the kink prevention shell can reduce its inner diameter.

[0060] The kink prevention shell is a reinforcing component configured to ensure the rigidity of the measurement device for blood pressure measurement. The kink prevention shell may be the only reinforcing component of the measurement device, and this reinforcing component exhibits structural robustness or strength and is configured to provide rigidity against compressive forces during blood pressure measurement. In particular, the reinforced kink prevention shell may be pressed against the wrapped part of the subject without any further intervening reinforcing elements, that is, preferably, there are no further elements providing any reinforcing function between the reinforced kink prevention shell and the wrapped part of the subject.

[0061] Preferably, the kink prevention shell is a reinforced integral shell. Such a design makes it possible to provide sufficient rigidity in a direct way.

[0062] Preferably, the kink prevention shell is dimensioned to overlap when surrounding the subject's part. In other words, the kink prevention shell preferably completely surrounds the body part of the subject at least when pressure is applied by the pressurizing part. Thus, torsion or wrinkles can be prevented or at least significantly reduced along the entire circumference of the measurement device.

[0063] By applying the anti-kink shell, torsion or wrinkles are prevented or at least significantly reduced. Therefore, when the inner diameter of the shell decreases by supplying pressurized fluid, preferably air, for example, to the fluid bag of the pressurizing element, the overlapping portions of the shell, that is, the outer ends of the shell, should be capable of moving or sliding relative to each other. Thus, the measuring device, especially the anti-kink shell, is preferably designed such that the overlapping portions can slide easily relative to each other. For example, the surface portions of the shell that slide in direct contact with each other can exhibit a relatively low coefficient of friction by selecting the material and / or surface structure accordingly. The term "low coefficient of friction" in the present invention refers to the coefficient of friction between two flat surfaces that is less than 0.5, preferably less than 0.3, more preferably less than 0.2, and even more preferably less than 0.1.

[0064] In one example, the shell, especially the anti-kink shell, is made of metal and / or plastic, especially fiber-reinforced plastic. For example, the shell is made of a thermoplastic material, preferably polyurethane or polyolefin, more preferably made of polyethylene and / or polytetrafluoroethylene (PTFE), or made of or coated with a thermoplastic material coated with PTFE. For example, the shell may be made of a thermoplastic material that provides a surface on which an adhesive can be permanently adhered. When the shell has a fiber-reinforced plastic material, the fibers are natural fibers, organic fibers, or inorganic fibers.

[0065] In particular, when the shell is made of a plastic material, in one example, the shell exhibits a thickness in the range of 0.25 mm to 6 mm, more preferably in the range of 1 mm to 3 mm, and even more preferably in the range of 1.0 mm to 2.0 mm. For example, the shell can have a thickness of 1.5 mm, especially for adults. Or, the shell can have a thickness of 0.5 mm, especially for infants and young children. In a preferred embodiment, the shell is made of polyethylene (PE) with a thickness of 1.5 mm.

[0066] In one example, in order to prevent torsion on the one hand and allow a reduction in the inner diameter on the other hand, the kink prevention shell exhibits an elastic modulus exceeding 50 MPa, more preferably in the range of 100 MPa to 10 GPa, and even more preferably in the range of 200 MPa to 1 GPa.

[0067] The present invention also relates to an apparatus for determining a subject's blood pressure, the apparatus comprising a) a pressure signal supply unit configured to supply a measured non-invasive oscillometric pressure signal of a subject over a period of time, the measured pressure signal indicating the pulsation of the blood and having a plurality of pressure pulses, the pressure signal supply unit b) determining a blood pressure determination curve based on the plurality of pressure pulses, determining a first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of one of the peak values of the overall maximum peak of the blood pressure determination curve, determining the position of the maximum value of the derivative of the blood pressure determination curve that is before the determined first peak, determining the blood pressure based on the determined position of the maximum value of the derivative of the blood pressure determination curve and the measured pressure signal a processor configured as and having.

[0068] The non-invasive oscillometric pressure signal can be measured by using a measuring device comprising a cuff wrapped around a body part of the subject, such as the upper arm, forearm, or wrist of the subject, where the cuff does not necessarily have a shell. Also, other known non-invasive measuring devices for measuring the oscillometric pressure signal can be used. The pressure signal supply unit can be, for example, a receiving unit configured to receive a pressure signal from the measuring device and supply the received pressure signal. However, the pressure signal supply unit can also be a storage device in which a previously measured pressure signal is stored and this pressure signal is retrieved to supply the stored pressure signal. The pressure signal supply unit can be the measuring device for measuring the pressure signal or can have it.

[0069] The blood pressure determination curve can be the envelope of the non-invasive oscillometric pressure signal. This envelope can be formed, for example, as a peak-to-peak or baseline-to-peak envelope. In particular, the envelope can be determined as described in the paper "Oscillometric Blood Pressure Estimation: Past, Present, and Future" by M. Forouzanfar et al., IEEE Reviews in Biomedical Engineering, volume 8, pages 44 to 63 (2015), which is incorporated herein by reference, or by using other known techniques.

[0070] The processor can be configured to determine the blood pressure based on the average of the oscillometric measured pressure at the determined position of the maximum value. This average is an average curve that no longer contains vibrations. In other words, the vibrations of the measured pressure signal are around or near the average curve. The average can be determined, for example, by using a moving average filter that averages the pressure signal. In one embodiment, the processor is configured to determine the systolic blood pressure by multiplying the average of the oscillometric measured pressure at the determined position of the maximum value by a pre-defined coefficient, and the pre-defined coefficient can be pre-defined by calibration.

[0071] In another aspect of the present invention, a method for determining the blood pressure of a subject is presented, and this method includes A step of supplying a measured pressure signal (TP) of a subject over a period of time by a pressure signal supply unit, wherein the pressure signal (TP) comprises: a) a shell configured to wrap a site through which blood of the subject flows; b) a pressurizing unit configured to apply pressure from outside the shell to the shell, thereby applying pressure to the wrapped site of the subject; and c) a pressure sensor configured to measure a pressure signal on the skin of the wrapped site of the subject, wherein the pressurizing unit increases or decreases the applied pressure while the pressure signal is being measured, and the measured pressure signal indicates the pulsation of blood and is measured using a measuring device having a plurality of pressure pulses. A step of determining a blood pressure determination curve based on the plurality of pressure pulses, wherein the blood pressure determination curve indicates the dependence of the pressure pulses on the applied pressure. A step of applying a transformation to the blood pressure determination curve, and A step of determining the blood pressure based on the result of the transformation. It has.

[0072] The present invention also relates to a method for determining the blood pressure of a subject, the method comprising: A step of supplying a measured non-invasive oscillometric pressure signal of a subject over a period of time, wherein the measured pressure signal indicates the pulsation of blood and has a plurality of pressure pulses. A step of determining a blood pressure determination curve based on the plurality of pressure pulses, A step of determining a first peak of the blood pressure determination curve having a peak value greater than a predetermined ratio of one of the peak values of the overall maximum peaks of the blood pressure determination curve, A step of determining the position of the maximum value of the derivative of the blood pressure determination curve that is before the determined first peak, and A step of determining the blood pressure based on the determined position of the maximum value of the derivative of the blood pressure determination curve and the measured pressure signal. It has.

[0073] Here too, it should be noted that the maximum value of the derivative preferably points in the direction from a low applied pressure to a high applied pressure. In other words, preferably, the derivative is considered in the direction from a low applied pressure to a high applied pressure regardless of whether the applied pressure increases or decreases while measuring the pressure signal used to determine blood pressure.

[0074] It should also be noted here that the term "before" refers to the direction from a low applied pressure to a high applied pressure. Thus, when the applied pressure increases while measuring the pressure signal used to determine blood pressure, the term "before" also means temporally before, and when the applied pressure decreases while measuring the pressure signal used to determine blood pressure, the term "before" means temporally after.

[0075] As described above, when the blood pressure determination curve has only a single peak, this single peak is the overall maximum peak and is also the first peak having a peak value greater than a predetermined percentage of one of the peak values of this overall maximum peak.

[0076] In a further aspect of the invention, a computer program for determining blood pressure is presented, the computer program having program code means for causing an apparatus for determining blood pressure to execute the steps of the method for determining blood pressure.

[0077] The invention also relates to a computer program for determining blood pressure, where the computer program causes an apparatus for determining blood pressure to determine a pressure determination curve based on a plurality of pressure pulses of a supplied non-invasive oscillometric pressure signal of a subject over a period of time, where the measured pressure signal indicates the pulsation of the blood and has a plurality of pressure pulses, determine a first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of one of the peak values of the overall maximum peak of the blood pressure determination curve, Determine the position of the maximum value of the derivative of the blood pressure determination curve that is before the determined first peak, and determine the blood pressure based on the determined position of the maximum value of the derivative of the blood pressure determination curve and the measured pressure signal and has program code means for that.

[0078] The device, method, and computer program can be adapted to continuously determine blood pressure, i.e., such that several subsequent blood pressure measurements are performed, or to discontinuously determine blood pressure, i.e., for example, to determine it once.

[0079] It should be understood that the processor, method, and computer program have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0080] It should be understood that the preferred embodiments of the present invention can also be any combination of the dependent claims or the above embodiments with each independent claim.

[0081] These and other aspects of the present invention will become apparent from and be elucidated with reference to the embodiments described hereinafter.

Brief Description of the Drawings

[0082]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

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Figure 11

Figure 12

Figure 13

Figure 14

DETAILED DESCRIPTION OF THE INVENTION

[0083] Figure 1 schematically and exemplarily shows an apparatus 1 for determining a subject's blood pressure. The apparatus 1 has a shell 4 as seen in Figure 2, and this shell 4 is configured to enclose a site 5 through which the subject's blood flows. In this embodiment, the subject's site 5 is the subject's arm, and in Figure 2, the brachial artery 13 is shown within this arm 5, and the arrow within the brachial artery 13 indicates the direction of blood flow away from the heart. The apparatus 1 further has a pressure sensor 7 disposed inside the shell 4 and configured to measure the pressure on the outer skin of the enclosed arm 5 of the subject. The measured pressure can also be regarded as tissue pressure (TP). As shown in Figure 2, the pulse wave in the brachial artery 13 generates a pressure wave 12 that is transmitted to the pressure sensor 7 through the tissue of the arm 5. Thus, the measured pressure signal has a pressure pulse indicating the pulsation of the blood. For clarity reasons, the shell 4 is not shown in Figure 1.

[0084] The apparatus 1 further has a cuff 6 that can be inflated by using a pump 8 that surrounds the shell 4 and applies pressure to the shell 4 from the outside thereof, thereby applying pressure to the enclosed arm 5 of the subject. Since the cuff 6 and the pump 8 enable the application of pressure to the shell 4 and thereby to the enclosed arm 5 of the subject, the cuff 6 and the pump 8 can be regarded as forming a pressurizing part 6, 8. Further, the shell 4, the pressurizing part 6, 8, and the pressure sensor 7 can be regarded as components of a measuring device controlled by a processor 3. The shell 4 with the cuff 6 is preferably a kink-preventing shell cuff as described in WO 2014 / 121945 A1.

[0085] Processor 3 is configured to control the measuring device such that the pressurizing units 6, 8 increase the pressure applied during a measuring period that extends until the end measurement time point and then decrease the pressure applied during the period following the subsequent blood pressure measurement, and such that the pressure sensor 7 measures the pressure on the skin, i.e., the tissue pressure TP, at least during said measuring period. Further, the processor 3 is configured to control the pressurizing units 6, 8 such that the pressurizing units 6, 8 increase the applied pressure at a first rate during the period before measurement and then increase the applied pressure at a second rate during the subsequent measuring period, where the first rate is greater than the second rate. The control of the measuring device such that the cuff 6 expands and thus the applied pressure increases is shown in FIG. 1, i.e., the thick arrow indicates the situation of expansion.

[0086] The device 1 has a valve 20, and when the valve 20 is opened, the compressed air in the system is released from this system into the surrounding atmosphere, making it possible to contract the cuff. In FIG. 3, the situation of contraction in which the pump 8 is switched off is indicated by the thick arrow.

[0087] The processor 3 can be regarded as having a control unit 10 for controlling the pump 8 and the valve 20 and a processing unit 11 specifically configured to execute several calculations further described below. The device 1 can also have, for example, a display 22 for displaying the measured blood pressure value. In this embodiment, the processor 3 also controls the measurement, where the control unit 10 can determine how to control said measurement based on the output of the processing unit 11, but in other embodiments, the processor is not used to control the measurement and can instead be used, for example, to process the measurement data after the measurement is completed.

[0088] During a pre-measurement period that can also be regarded as a high-speed inflation period, the processor 3 controls the device 1 such 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 again controls the device 1 such 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. Thus, the measurement period can also be regarded as a low-speed inflation period.

[0089] Figure 4 schematically and illustratively shows the measured pressure TP with respect to time t. The first inflation in the pre-measurement period starts from the tissue pressure TP, which is the attachment pressure Patt measured in the non-inflated cuff 6. This attachment pressure Patt is, for example, in the range of 0 to 15 mmHg. It has been found that an attachment pressure Patt of 15 mmHg or less does not cause venous congestion for 12 hours or more, and as a result, the assembly of the cuff 6 and the shell 4 is suitable for longer-term monitoring. For this reason, it is preferable that the attachment pressure Patt is 15 mmHg or less. In Figure 4, the arrow 30 indicates the start of the pre-measurement period, that is, the start of the high-speed inflation period. During this pre-measurement period, the part of the overall tissue pressure range where there is no or almost no information for determining blood pressure should be passed through as quickly as possible. Therefore, during the pre-measurement period, the inflation rate is preferably as large as possible. For example, the inflation rate with respect to the tissue pressure TP is 8 mmHg / s or more. This pre-measurement period with a high inflation rate ends at the tissue pressure value indicated by "TPlow" in Figure 4.

[0090] The tissue pressure value TPlow also indicates the start of the measurement period at a slower second inflation rate. In FIG. 4, the start of this measurement period, which can also be regarded as the low-speed inflation period, is indicated by arrow 31. In one embodiment, the processor 3 is configured to control the pump 8 such that the measured pressure TPlow is within the range of 15 to 30 mmHg at the end of the period before measurement. Thus, in one embodiment, the tissue pressure TPlow can be predefined such that its pressure is a value of 15 to 30 mmHg. However, in a situation where the diastolic arterial pressure determined in the previous measurement (DAPprev) is available, the tissue pressure TPlow may depend on this diastolic arterial pressure, and the tissue pressure TPlow may be larger. This larger TPlow is schematically shown in FIG. 4. For example, the processor 3 can be configured to store (or access a memory storage device having it) the previous diastolic arterial pressure DAPprev. The previous diastolic arterial 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 be present at the end of the period before measurement, that is, at the end of the first inflation period, and thus can also be regarded as the first end measurement pressure. The tissue pressure TPlow is determined depending on the previous diastolic arterial pressure DAPprev such that this tissue pressure TPlow is smaller than the previous diastolic arterial pressure DAPprev. Preferably, the processor is configured to control the pump 8 such that the measured pressure at the end of the period before measurement is equal to the determined first end measurement pressure TPlow. In one embodiment, the processor 3 determines the tissue pressure TPlow at the end of the period before measurement such that the tissue pressure TPlow does not exceed a predetermined percentage of the previous diastolic arterial pressure DAPprev. This can ensure that all necessary tissue pressure pulse curves that enable accurate calculation of blood pressure can be recorded. The calculation of blood pressure based on the measured tissue pressure will be further described below. The predetermined percentage is preferably 90%.

[0091] Blood pressure can vary from measurement to measurement, for example, for clinically relevant events to occur in a subject. Diastolic arterial pressure (DAP) has been found to be able to drop by about 30% within one minute in the most severe situations of acute blood loss during surgery. To cope with these possible blood pressure changes, the processor 3 can be adapted to determine the tissue pressure TPlow depending on the previous diastolic arterial pressure DAPprev and the duration of the pause time between measurements. Thus, the processor 3 further stores (or accesses a memory storage device having it) the time at which the previous diastolic arterial pressure DAPprev was measured, and is configured to determine the first end-time measurement pressure TPlow depending on i) the previous diastolic arterial pressure DAPprev and ii) the time distance to the blood pressure measurement at which the previous diastolic arterial pressure DAPprev indicated by the stored time was measured. An exemplary specific equation for determining this first end-time measurement pressure TPlow is further shown below.

[0092] 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 most preferably 2.5 mmHg / s. It has been found that the second inflation rate within this range enables accurate blood pressure determination. Note that these rates refer to the change in the tissue pressure TP measured by the pressure sensor 7.

[0093] In one embodiment, the slow second inflation rate depends on the heart rate (HR) and / or the pulse pressure (PP), which is the difference between the systolic blood pressure and the diastolic blood pressure. For example, the second inflation rate can increase with an increase in the heart rate and an increase in the pulse pressure PP. This increase may be linear or may be represented by another functional relationship. In one embodiment, this functional relationship is such that the inflation rate of the tissue pressure is 1 mmHg / s when the heart rate HR is 40 beats per minute and the pulse pressure PP is 20 mmHg, and the inflation rate of the tissue pressure, i.e., the second slow inflation rate, is 10 mmHg / s when the heart rate HR is 80 beats per minute and the pressure pulse PP is 100 mmHg. The measurement period ends at the end measurement time point 32, and thereafter, since there is no need to collect tissue pressure data after this end measurement time point 32, preferably, immediate rapid contraction continues at the maximum possible reduction rate.

[0094] In FIG. 4, the time interval 40 indicates the inflation - contraction period from the start 30 of the high - speed inflation until the tissue pressure TP drops below 20 mmHg during the high - speed contraction to enable venous return. The period 41 indicates the cycle time, which is the time from the start of the measurement to the start of the next measurement, and the period 42 indicates the rest time, which is the difference between the inflation - contraction time 40 and the cycle time 41.

[0095] FIG. 4 shows the average pressure TPcl, which can be regarded as the tissue clamp pressure applied to the tissue when the cuff 6 is attached to the arm 5 of the subject, for example, the upper arm. The average pressure TPcl can be calculated by applying a low - pass filter to the tissue pressure TP, and this low - pass filter can be arranged within the processor 3. The low - pass filter is preferably set such that the average pressure TPcl includes only frequencies below the predicted minimum pulse rate (PRni). A preferred low - pass filter will be further described below. The processor 3 is preferably configured to determine the alternating component TPac of the tissue pressure by subtracting the average pressure TPcl from the measured tissue pressure TP (i.e., TPac = TP - TPcl). In FIG. 4, the TPac curve is shown enlarged by a factor of 2 for clarity.

[0096] During the low-expansion period, i.e., during the measurement period, the TP pulse curve and / or the TPac pulse curve are recorded, and these are analyzed simultaneously, i.e., online. The TP pulse curve and / or the TPac pulse curve have a tissue pressure waveform (TPW) that has information enabling the accurate determination of blood pressure. Since the blood pressure is measured non-invasively (although with an accuracy comparable to that of invasively measured blood pressure), it can be abbreviated as niBP, meaning "non-invasive blood pressure". In FIGS. 5 to 8, the TPac pulse curve is shown schematically and illustratively.

[0097] In what follows, the TPac pulse curve is used to determine the characteristics for the pressure pulse 9. Thus, the TPac pulse curve can be regarded as a characteristic determination pulse curve or a characteristic determination pulse. Thus, FIGS. 5 to 8 show the characteristic determination pulse curve or the characteristic determination pulse 29 that is the TPac pulse. In another embodiment, the characteristic determination pulse may be the direct TP pulse curve, i.e., the pressure pulse 9 can be used directly to determine the characteristics. The processor 3 is configured to determine at least one characteristic characterizing each of the pressure pulses of the plurality of pressure pulses 9. The characteristics determined for the pressure pulse 9 indicate the pressure pulse 9, i.e., for example, the shape of the pressure pulse 9 and / or the pressure value characterizing the pressure pulse 9.

[0098] In one embodiment, the processor 3 is configured to determine, as a characteristic for each pressure pulse, the difference TPP between the measured pressure of the maximum value of each characteristic determination pulse 29 and the measured pressure of the minimum value. This characteristic is described below with reference to FIG. 5.

[0099] The difference TPP is the difference 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, which is preferably the minimum pressure of each characteristic determination pulse. In FIG. 5, as well as in FIGS. 6 to 8, the terms "t.start" and "t.stop" indicate the start and end of each of the respective pulses 29.

[0100] The processor 3 is also configured to determine a pulse duration (t(Pulse)), which is the time difference between the end point of the expansion of the feature determination pulse 29 and the next end point of the expansion. This feature can also be defined as the time difference between the start (t.start) and the end (t.stop) of each pulse. This feature is shown in FIG. 6.

[0101] The processor 3 can be adapted to determine a pulse area (TPA) of each pulse 29, which is the area under each pulse curve within the time defined by t.start to t.stop and has a range from the pressure (TPdia) of the feature determination pulse at the end point of the expansion to the maximum systolic pressure (TPsys) of the feature determination pulse. Preferably, as shown in FIG. 6, the pulse area TPA is scaled to TPP = 1. This scaled pressure pulse area is called "TPA.norm".

[0102] The processor 3 is also adapted to determine a half-value pulse width (W50) of each pulse 29, as shown in FIG. 7.

[0103] Furthermore, as schematically shown in FIG. 8, the processor 3 is adapted to determine the area TPA+.top50 enclosed by the upper part of the feature determination pulse 29. The upper end of the area TPA+.top50 enclosed by this upper part is at the maximum systolic pressure TPsys of the feature determination pulse 29, and the lower end of the upper area TPA+.top50 is between the maximum systolic pressure TPsys of the feature determination pulse 29 and the pressure value corresponding to the average TPcl of the measured pressure TP. Since the feature determination pulse 29 is determined by subtracting the average TPcl from the measured pressure TP, the pressure value corresponding to the average TPcl of this measured pressure TP is zero. Preferably, the processor 3 is configured to determine the area TPA+.top50 enclosed by the upper part of the feature determination pulse such that the lower end of the upper part corresponds to the pressure value that is half of the pressure distance TPP+ between the maximum systolic pressure TPsys of the feature determination pulse and the pressure value corresponding to the average TPcl of the measured pressure TP.

[0104] FIGS. 5 to 8 show the TPac pulse curve, in this example, such that features are also defined based on the TPac pulse curve. However, as described above, it is also possible to define these or other features based on the TP pulse curve.

[0105] The processor 3 is further configured to determine a blood pressure determination value TPWP_M for each of several pressure pulses based on at least one determined feature such that several blood pressure determination values TPWP_M are determined for several pressure pulses existing at different times, where the processor 3 is configured to determine a blood pressure determination curve TPW_M-curve such that several blood pressure determination values TPWP_M determined for several pressure pulses and thus for several times form the blood pressure determination curve TPW_M-curve.

[0106] Processor 3 is configured to determine a blood pressure determination value TPWP_M based on the characteristics determined for the pressure pulse 9. Thus, similar to the characteristics determined for the pressure pulse 9, the blood pressure determination value TPWP_M also represents the pressure pulse 9. The blood pressure determination curve TPW_M-curve is formed by several blood pressure determination values TPWP_M determined for several pressure pulses 9 and thus for several times, where the applied pressure changes over time, so the blood pressure determination curve TPW_M-curve shows the dependence on the applied pressure of the pressure pulse 9.

[0107] Processor 3 is further configured to apply a transformation to the blood pressure determination curve TPW_M-curve and determine the blood pressure based on the result of this transformation, i.e., based on the transformed version TPW_M-curve' of the blood pressure determination curve TPW_M-curve, or if only a part of the blood pressure determination curve TPW_M-curve is transformed, based on the transformed part. In this embodiment, the transformation corresponds to taking the derivative, i.e., the first derivative, such that the result of this transformation, i.e., TPW_M-curve', is the first derivative of the blood pressure determination curve TPW_M-curve, but in other embodiments, this transformation may be something else, where a possible other transformation may correspond to applying a function such as a logarithm or a higher-order derivative to the blood pressure determination curve TPW_M-curve, for example. Generally, but not necessarily always, in this embodiment, processor 3 is configured to determine the blood pressure based on the blood pressure determination curve TPW_M-curve itself.

[0108] In particular, processor 3 is configured to determine the position of the maximum value (TPW_M-curve'.max) of the first derivative TPW_M-curve' of the blood pressure determination curve TPW_M-curve and in addition 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 two determined positions and the measured pressure TP. For example, processor 3 uses the following equation 1 SAPni = α·(TPcl@TPW_M - curve.max) + β·(TPcl@TPW_M - curve’.max) (1) According to this, it is configured to determine the systolic arterial pressure (SAPni) based on the average TPcl of the measured pressures TP at two determined positions.

[0109] Here, the parameters α and β can be determined in advance based on a linear regression with respect to a reference value of the systolic arterial pressure that is determined very accurately, and in some cases non - invasively, by calibration, in particular, for example, by using the least - squares method. Exemplary values of α and β determined during calibration using an exemplary data set are α = 1.43 and β = - 0.25.

[0110] The processor 3 can be configured to determine the first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of the peak value of the overall peak of the blood pressure determination curve, and to determine the position of the maximum value of the derivative of the blood pressure determination curve that is before the determined first peak, thereby determining the position of the maximum value of the first - order derivative of the blood pressure determination curve. The predetermined percentage of the overall peak can be determined in advance by calibration. In a preferred embodiment, the predetermined percentage is 90%. The determination of the first peak of the blood pressure determination curve having a peak value greater than a predetermined percentage of the peak value of one of the overall maximum peaks of the blood pressure determination curve can be performed by normalizing the blood pressure determination curve to the peak value of one of the overall maximum peaks such that this peak value becomes 1 after normalization. This predetermined percentage is a fixed absolute number between 0 and 1, preferably 0.9.

[0111] Preferably, the processor 3 is configured to provide a function that receives at least one characteristic of each pressure pulse as an input and outputs each blood pressure determination value TPWP_M that forms a blood pressure determination curve TPW_M-curve, together with the blood pressure determination value determined for other pressure pulses. This function has at least one parameter determined by calibration, where, by invasive means, a reference blood pressure value is determined very accurately, and at least one parameter is determined so that the device provides a very accurate invasively measured blood pressure value with high statistical accuracy and precision.

[0112] According to the above item 1, when the parameters α and β are determined in advance based on the reference measurement value, the systolic arterial pressure (SAPni) can also be regarded as being determined by a fixed function of two positions TPW_M-curve.max and TPW_M-curve’.max, where the linear dependence of this function on the two positions is represented by the pre-determined parameters α and β. Therefore, the processor 3 is efficiently configured to provide a first function for determining the blood pressure determination value TPWP_M from the blood pressure pulse 9 to form the blood pressure determination curve TPW_M-curve, and to provide a second function corresponding to item 1 for determining the blood pressure based on the TPW_M-curve and its transformation TPW_M-curve’.

[0113] In a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on a blood pressure determination value TPWP_M that depends only on a characteristic that is 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. Thus, in one embodiment, the function used to determine the blood pressure determination value TPWP_M, i.e., the first function, depends on TPP but not on any other characteristic of the pressure pulse. In this case, for example, the blood pressure determination value TPWP_M is given by the following equation 2 TPWP_M = c·TPP exp1 (2) It can be determined according to this. Here, c and exp1 are predetermined constants. For example, c and exp1 can be determined in advance by calibration. However, it has been found that c and exp1 can be selected to be equal to 1 together, for example, when TPWP_M = 1, that is, c = 1 = exp1.

[0114] Furthermore, in a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M - curve based on a blood pressure determination value TPWP_M that depends only on a) a feature that is the difference TPP between the maximum systolic pressure TPsys of the feature determination pulse and the pressure TPdia of the feature determination pulse at the end - diastolic point, and b) a feature that is the area TPA+.top50 surrounded by the upper part of the feature determination pulse. Thus, in one embodiment, the function used to determine the blood pressure determination value TPWP_M, which was called the first function above, depends on TPP and TPA+.top50 but does not depend on further features of the pressure pulse. In this case, for example, the blood pressure determination value TPWP_M is given by the following formula 3 TPWP_M = c·TPA+.top50 exp2 ·TPP exp1 (3) It can be determined according to this.

[0115] Here, c, exp1 and exp2 are predetermined constants. For example, c can be made equal to 1 again, that is, c = 1, and exp1 and exp2 can be determined in advance by calibration of Equation 3. However, it is also possible for the constant c to be determined by calibration. In a preferred embodiment, in Equation 3, c and exp1 are both equal to 1 (c = 1, exp1 = 1), and exp2 is equal to 0.7 (exp2 = 0.7).

[0116] Processor 3 is further configured to determine an end measurement time point 32 at which or after which the measurement period is stopped, preferably based on at least one characteristic determined for a plurality of pressure pulses 9. In particular, processor 3 can be configured to determine an end decision value TPWP_E for each pressure pulse based on at least one characteristic determined for each pressure pulse.

[0117] Preferably, the processor receives at least one characteristic of each pressure pulse as an input and outputs each end decision value TPWP_E that forms an end decision curve together with the end decision values determined for other pressure pulses, that is, is also configured to provide a further function. Also, this function has at least one parameter that can be determined by calibration. For example, the end decision value TPWP_E is given by the following formula 4 TPWP_E = c·TPP exp3 (4) or according to the following formula 5 TPWP_E = c·TPA +.top50 exp4 ·TPP exp3 (5) where c, exp3, and exp4 in formula 4 and formula 5 are predetermined constants, respectively. For example, set c equal to 1, that is, c = 1, while exp3 and, if possible, exp4 are determined in advance by calibration, and formula 4 and formula 5 can be determined respectively. In one embodiment, for either formula 4 or 5, the constant c can also be determined by calibration and can in particular be other than 1.

[0118] Note that constants such as c, exp1, exp2, and exp3 that appear in two or more mathematical expressions, as in the above examples, can generally have the same or different values in each different mathematical expression. Therefore, for example, these constants can also be called additional indices related to each mathematical expression, but are omitted in this specification. Nevertheless, for example, it should be understood that six exponential values are required to determine the above mathematical expressions 2 to 5.

[0119] Note that the end determination value TPWP_E can also be determined as follows.

[0120] Specifically, the processor 3 is configured to multiply a) the power of the determined pulse area TPA.norm at a predetermined seventh exponent (exp7) by b) the power of the determined difference TPP at a predetermined eighth exponent (exp8). Therefore, the end determination value TPWP_E is given by the following mathematical expression using predetermined exp7≠0 and exp8≠0. TPWP_E = TPA.norm exp7 ·TPP exp8 and can be calculated according to this.

[0121] The processor 3 is configured to determine the end determination value TPWP_E by dividing a) the power of the determined pulse area TPA.norm at a predetermined ninth exponent (exp9) by b) the power of the determined pulse duration t(pulse) at a predetermined tenth exponent (exp10), and then multiplying the resulting quotient by c) the power of the determined difference TPP at a predetermined eleventh exponent (exp11). This can be expressed by the following mathematical expression using predetermined exp9≠0, exp10≠0, and exp11≠0. TPWP_E = TPA.norm exp9 / t(pulse) exp10 ·TPP exp11 and can be represented as such.

[0122] The processor 3, for example, uses the mathematical formulas discussed in the two previous paragraphs TPWP_E = TPA.norm exp7 ·TPP exp8 and TPWP_E = TPA.norm exp9 / t(pulse) exp10 ·TPP exp11 is also configured to determine an end decision value for each pressure pulse based on multiplying the calculation result obtained by using one of them by the power of a further predetermined exponent of the half-value width (W50). For example, when the latter of the two mathematical formulas is multiplied by the half-value width W50, the mathematical formula, using predetermined exp12≠0, exp13≠0, exp14≠0, and exp15≠0, the mathematical formula is TPWE_E = TPA.norm exp12 / t(pulse) exp13 ·TPP exp14 ·W50 exp15 becomes

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

[0124] The exponents of the different mathematical formulas are determined in advance by calibration as described above. For example, in a preferred embodiment, the mathematical formula TPWP_E = TPA.norm exp9 / t(pulse) exp10 ·TPP exp11 It is used with exponents exp9 = 1.1, exp10 = 0.4, and exp11 = 0.5.

[0125] Processor 3 preferably meets the following conditions a) The maximum value of the end determination curve (TPW_E - curve.max) occurs earlier in time than the maximum value of the blood pressure determination curve (TPW_M - curve.max), b) The maximum value of the end determination curve (TPW_E - curve.max) occurs when or after the maximum value of the blood pressure determination curve (TPW_M - curve.max), and the decrease after the maximum value of the end determination curve TPW_E - curve is steeper than the decrease after the maximum value of the blood pressure determination curve TPW_M - curve, and c) The end determination curve TPW_E - curve coincides with the blood pressure determination curve TPW_M - curve is configured to determine the end determination curve TPW_E curve so as to satisfy one of the above. Therefore, the parameters of the function are preferably a) TPW_E - curve.max occurs earlier in time than TPW_M - curve.max, or b) TPW_E - curve.max occurs when or after TPW_M - curve.max, but the TPW_E - curve has a negative derivative with an absolute derivative value greater than the absolute derivative value of the negative derivative of the blood pressure determination curve TPW_M - curve after reaching the maximum value, or c) The TPW_E - curve coincides with the TPW_M - curve, that is, the end determination curve and the blood pressure determination curve coincide are predefined as follows.

[0126] In FIG. 9, the blood pressure determination curve TPW_M - curve and the end determination curve TPW_E - curve are exemplarily shown, where these curves are normalized so that their respective maximum values correspond to 100%.

[0127] To minimize the stress on the subject, it is desirable to complete each blood pressure measurement as quickly as possible. In this case, since the maximum value of the blood pressure determination curve TPW_M-curve is used for non-invasive blood pressure determination, in this case, as soon as the maximum value of the blood pressure determination curve TPW_M-curve is formed and thus can be fully determined, the blood pressure measurement can be terminated. Note that if only the maximum value of the derivative of the blood pressure determination curve TPW_M-curve', TPW_M-curve', is used, the blood pressure measurement can be terminated as soon as this maximum value is formed. Therefore, during the measurement period, the time when the end criterion that defines the end measurement point is reached is investigated, and here, preferably, the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve are used to determine when this end criterion is reached and thus to determine the end measurement point. For example, when the end determination curve TPW_E-curve forms a maximum value, for each newly measured TP pulse curve, that is, for each newly measured TP pulse, a) whether the end determination curve TPW_E-curve has decreased below a certain percentage of the maximum value of the end determination curve TPW_E-curve, where the percentage is preferably in the range of 40% to 95%, and b) whether the blood pressure determination curve TPW_M-curve has formed a maximum value, that is, whether it has reached its maximum value or passed its maximum value can be examined. The processor 3 can be configured to determine the end determination time point 32 as the point in time when both conditions a) and b) are satisfied.

[0128] To determine whether the blood pressure determination curve TPW_M-curve has successfully reached or passed its maximum value, it is possible to detect whether the blood pressure determination curve TPW_M-curve has dropped after its maximum value.

[0129] In one embodiment, both the blood pressure determination curve TPW_M-curve and its transformed version TPW_M-curve' can be smoothed curves such that the maximum value of either of these two curves is smoothed. The smoothing procedure used to smooth the blood pressure determination curve TPW_M-curve can include, for example, filtering and / or fitting, where the transformed blood pressure determination curve TPW_M-curve' is already smoothed because the transformation applied to the blood pressure determination curve itself and the blood pressure determination curve is smooth. For example, taking a derivative or applying a smooth function is a smooth transformation. Further, after each smoothed maximum value, several pressure pulses are considered to clearly detect the respective smoothed maximum value, where the number of these several pulses can be determined in advance or can depend on the heart rate of the subject. For example, this number increases with an increase in the heart rate. In one embodiment, this number is 3 for a heart rate of 60 beats per minute and 10 for a heart rate of 200 beats per minute.

[0130] To smooth the blood pressure determination curve TPW_M-curve, a moving average filter, in particular a variable moving average filter, can be used, which is applied to the blood pressure determination value TPWP_M determined for the pressure pulse. The window used for averaging can be fixed or variable, and in the latter case, the window preferably has a maximum duration of, for example, 8 seconds. The use of this filter causes a filter delay, and the minimum filter delay is the same length as the total duration of several pulses. Having a filter delay of the length of several pulses is sufficient to safely determine the maximum value of the descending smoothed blood pressure determination curve TPW_M-curve, and thus this blood pressure determination curve TPW_M-curve. This means that as soon as a decrease in the smoothed blood pressure determination curve TPW_M-curve is detected, the measurement period can be ended without the need to collect more pressure pulses. This is possible in this example, for instance, by smoothing the blood pressure determination curve TPW_M-curve twice using a relatively large variable moving average filtering window of up to 8 seconds (2×8 second filter) with at least 3 pressure pulses of TP, which can remove disturbing cardiorespiratory interactions in an estimated 95% of the measurements. These smoothing filtering windows can each be adapted to the respiratory rate and tidal volume, thereby making it possible to improve the exclusion of unwanted disturbances of the TPW_M-curve caused by cardiorespiratory interactions.

[0131] In FIG. 9, when the end determination curve TPW_E-curve falls below 90% of the maximum value of this end determination curve TPW_E-curve, both of the above-described conditions a) and b) are satisfied. Due to the filter delay, after both conditions a) and b) are satisfied, the measurement ends with several tissue pressure pulses.

[0132] The continuous TPW_E-curve and the continuous TPW_M-curve shown in FIG. 9 were obtained by filtering the values TPWP_E and TPWP_M determined for different pressure pulses, respectively. This filtering leading to a filter delay will be further described below. In FIG. 9, the filter delay results in two additional pressure pulses such that a rapid contraction of cuff 6 starts two pressure pulses after both conditions a) and b) are satisfied.

[0133] The end determination curve TPW_E-curve having a maximum value that occurs several seconds earlier in time than the maximum value of the blood pressure determination curve TPW_M-curve can shorten the measurement period, i.e., shorten the slow inflation time and enable reducing the amount of pressure applied to the subject. After reaching t(a_end), i.e., after the end determination curve TPW_E-curve reaches a point where it falls below a predetermined percentage of the maximum value of this 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 one embodiment, the measurement is continued until the next maximum value of the TPW_M-curve and the maximum value of the blood pressure determination curve (TPW_M-curve.max) are determined thereafter.

[0134] If the end determination curve TPW_E-curve having a maximum value occurring temporally before the maximum value of the blood pressure determination curve TPW_M-curve is not used, low-speed inflation needs to be continued until the blood pressure determination curve TPW_M-curve falls below a specific percentage of its maximum value. On average, by using the end point determination curve TPW_E-curve having a maximum value occurring temporally before the maximum value of the blood pressure determination curve TPW_M-curve, blood pressure measurement can end approximately 20 to 60 seconds later at TPcl within 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. Therefore, blood pressure measurement ends when the clamp pressure reaches approximately SAP + 20 mmHg. When using the device 1 described above with reference to FIG. 1, when the measurement ends, the tissue pressure TP drops to Patt as quickly as possible and remains there for a certain time, preferably for about 20% of the inflation - contraction period 40 shown in FIG. 4, before another measurement is started.

[0135] The processor 3 is configured to determine blood pressure based on the transformed blood pressure determination curve TPW_M-curve’, in particular based on the position of the maximum value of the derivative of the blood pressure determination curve TPW_M-curve, and in this case, further based on the blood pressure determination curve TPW_M-curve itself, in particular based on the position of the maximum value of the blood pressure determination curve TPW_M-curve itself. The processor 3 is adapted to make this determination of the blood pressure, which is the non-invasive blood pressure, as described above with respect to Equation 1. While determined by the processor 3, the curve TPW_M-curve’ is not included in FIG. 9. However, if the resulting transformation is selected to be the derivative, the TPW_M-curve’ can be estimated from the slope of the TPW_M-curve in FIG. 9. An example where the TPW_M-curve and TPW_M-curve’ are included in a single figure is shown by FIG. 11, which is further described below.

[0136] In one embodiment, the processor 3 is configured to determine the TPcl value at the time point t(TPW_M-curve’.max) when the derivative of the blood pressure determination curve TPW_M-curve’ has the maximum value (TPW_M-curve’.max), and the TPcl value at the time point t(TPW_M-curve.max) when the blood pressure determination curve TPW_M-curve has the maximum value (TPW_M-curve.max). Here, in FIG. 10, the TPcl values at the respective time points of these maximum values are shown as “TPcl@TPW_M-curve’.max” and “TPcl@TPW_M-curve.max”, respectively. Also in FIG. 10, the curve TPW_M-curve’ is not shown, but the time point t(TPW_M-curve’.max) at which the derivative TPW_M-curve’ of the TPW_M-curve has the maximum value can be estimated from the slope of the TPW_M-curve that itself has the maximum value at t(TPW_M-curve.max). These time points t(TPW_M-curve.max) and t(TPW_M-curve’.max) are also shown in FIG. 9.

[0137] The processor 3 is further 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 can be, for example, the same as the filter used to determine the blood pressure determination curve TPW_M-curve. The resulting curve is named “TPdia-curve” in FIG. 10. Further, the processor 3 can be configured to determine the upper envelope of the tissue pressure TP by applying a filter to the maximum of the systolic phase of the tissue pressure TP. Additionally, this filter can be, for example, the same as the filter used to generate the blood pressure determination curve TPW_M-curve. This curve is named “TPsys-curve” in FIG. 10.

[0138] Next, the processor 3 can be configured to determine the systolic arterial pressure value as a predetermined linear combination of TPcl@TPW_M-curve’.max and TPcl@TPW_M-curve.max, that is, a linear combination using predetermined coefficients α and β corresponding to the calibrated function as given by the above formula (1). The predetermined coefficients α and β can preferably be such that the linear combination results in a systolic arterial pressure value that can be expressed as a percentage (TPcl.s%) of TPcl@TPW_M-curve.max, and this percentage is preferably in the range of 100 to 150%, more preferably in the range of 110 to 150%. In FIG. 10, the non-invasive systolic arterial pressure is named “SAPni”, where the above formula (1) is shown again. In FIG. 10, the non-invasive systolic arterial pressure SAPni is about 134 mmHg.

[0139] The predetermined coefficients α and β can also be such that the non-invasive systolic arterial pressure SAPni is a predetermined percentage (TPsys.s%) of the TPsys curve at the time position where the blood pressure determination curve TPW_M-curve has its maximum value. This predetermined percentage is preferably in the range of 100 to 140%.

[0140] The processor 3 can also be configured to determine the non-invasive mean arterial pressure (MAPni) based on the transformed TPW_M-curve, particularly its derivative. For example, a formula such as the above formula (1), that is, MAPni = α’·(TPcl@TPW_M-curve.max)+β’·(TPcl@TPW_M-curve’.max) (6) can be reused using new predetermined, i.e., calibrated coefficients α' and β'. These predetermined coefficients α' and β' can be such that the determined non-invasive mean arterial pressure (MAPni) corresponds to the value of the TPsys-curve at time point t(bx) when the TPcl value, or alternatively the value of the TPdia-curve, or alternatively the blood pressure determination curve TPW_M-curve has a value bx representing a predetermined ratio to its maximum value. The predetermined coefficients α' and β' can be such that the non-invasive mean arterial pressure MAPni is a predetermined ratio (TPcl.m%) of TPcl at TPW_M-curve.max, where the predetermined ratio is preferably in the range of 80 to 110%. Exemplary values of α' and β' determined during calibration using an exemplary dataset are α' = 0.44 and β' = 0.46.

[0141] The processor 3 is also configured to determine the non-invasive diastolic arterial pressure DAPni based on the transformed TPW_M-curve, in particular its derivative. For example, equations such as equations 1 and 6 above, i.e., DAPni = α”·(TPcl@TPW_M-curve.max)+β”·(TPcl@TPW_M-curve’.max) (7) can be reused using new predetermined, i.e., calibrated coefficients α” and β”. These predetermined coefficients α” and β” can be such that the determined non-invasive diastolic arterial pressure (DAPni) corresponds to the value of the TPcl-curve at time point t(cx) when the TPdia-curve value, or alternatively the blood pressure determination curve TPW_M curve has a value cx representing a predetermined ratio to its maximum value. The predetermined coefficients α” and β” can be such that DAPni is a predetermined ratio (TPcl.d%) of TPcl@TPW_M-curve.max, where this predetermined ratio is preferably 60 to 80%. Exemplary values of α” and β” determined during calibration using an exemplary dataset are α” = -0.08 and β” = 0.88.

[0142] As described above, the parameters of the functions used to determine the end determination curve TPW_E-curve and to determine the blood pressure determination curve TPW_M-curve are determined by calibration. Therefore, these parameters are determined in advance so that during the calibration phase, the deviation between the invasively measured blood pressure value measured very accurately and the blood pressure value obtained by the device 1 is minimized and the time required for blood pressure measurement is relatively reduced. Preferably, thereby, one or more parameters of the function used to determine the blood pressure determination curve TPW_M-curve, i.e., one or more parameters of the function further called the first function above, are regarded as the first set of one or more parameters and are selected to achieve a good balance between, on the one hand, high-precision non-invasive blood pressure and, on the other hand, a low TP level at the end of the measurement, and thus a low measurement time. If the one or more parameters are selected such that they create a TPW_M-curve with a maximum value relatively early, the TP level and the measurement time at the end of the measurement are relatively reduced. However, at this time, the accuracy and position of the finally determined non-invasive blood pressure value also decrease. Therefore, the first set of the one or more parameters is preferably selected so that a desired balance is achieved between the measurement time and the accuracy of the non-invasive blood pressure value.

[0143] One or more parameters of the function used to determine the end determination curve TPW_E-curve, i.e., one or more parameters of the function further called a further function above, are regarded as forming a further set of one or more parameters and are preferably selected such that the maximum value of the end determination curve TPW_E-curve comes relatively early. In one embodiment, the first set of one or more parameters and the second set of one or more parameters may be the same so that the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve are also the same.

[0144] Describing systolic arterial pressure (SAPni), mean arterial pressure (SAPni), and diastolic arterial pressure (SAPni) in terms of the maximum value of the blood pressure determination curve and the position of its derivative, i.e., in the terms used above, calibration to derive predetermined values of the coefficients α, β, α’, β’, α”, and β” in the function, each of which is called a second function, preferably corresponds to the evaluation of a calibration set consisting of pairs of measured values of simultaneously recorded invasive and non-invasive blood pressure values from an appropriate number of humans with different hemodynamic states. The non-invasive blood pressure value is determined by the device 1 as described above, and parameters such as the coefficients α, β, α’, β’, α”, and β” are optimized such that the deviation between the invasive and non-invasive blood pressure values is minimized.

[0145] Figure 11 shows TP, TPcl, TPac, TPW_M-curve, and TPW_E-curve according to a further example. Thus, these curves are determined in the same way as those shown in FIGS. 9 and 10, but based on further measurements, they result in different measured pressure signals TP. Unlike FIGS. 9 and 10, FIG. 11 also shows the derivative TPW_M-curve’ of the TPW_M-curve used to determine blood pressure. The points in time t(TPW_M-curve.max) and t(TPW_M-curve’.max) at which the TPW_M-curve and TPW_M-curve’ respectively reach their maximum values are also shown in FIG. 11. Correspondingly, TPcl@TPW_M-curve.max and TPcl@TPW_M-curve’.max are also identified in this embodiment such that the blood pressure is determined again according to any of the above-mentioned mathematical formulas 1, 6, and 7.

[0146] The processor 3 is adapted to estimate the type of blood pressure value based on two other already measured types of blood pressure values. In particular, one of the blood pressure values MAPni, SAPni, and DAPni can be estimated based on the other blood pressure values of these blood pressure values. This can be done according to the following mathematical formula, and mathematical formula 8 uses c1=(0.2..0.7), c2=(2..6), c3=(-5..5), SAPni = c1·MAPni + c2·(MAPni - DAPni) - c3 mmHg (8) which gives Equation 9 as MAPni = c4·DAPni + c5·(SAPni - DAPni) - c6 mmHg (9) using c4 = (0.8..1.3), c5 = (0.25..0.5), c6 = (-5..5) MAPni = c4·DAPni + c5·(SAPni - DAPni) - c6 mmHg (9) which gives Equation 10 as DAPni = c7·MAPni - c8·(SAPni - MAPni) - c9 mmHg (10) using c7 = (0.6..1.1), c8 = (0.15..0.4), c9 = (-5..5) DAPni = c7·MAPni - c8·(SAPni - MAPni) - c9 mmHg (10) and so on.

[0147] The coefficients and constants of Equations 8, 9, and 10 are determined a priori by calibration based on a statistical evaluation of as large and as widely spread a set of clinical invasive blood pressure data as possible. Thus, very accurate invasive blood pressure values SAPi (invasive systolic arterial pressure), MAPi (invasive mean arterial pressure), and DAPi (invasive diastolic arterial pressure) are used, and when these very accurate invasive blood pressure values are given, the coefficients and constants of Equations 8, 9, and 10 are changed so that these equations are valid.

[0148] Blood pressure measurement is intended to be used quickly and continuously in a series of measurements to enable effective semi - continuous blood pressure monitoring such that the stress on the individual being monitored, i.e., the subject being monitored, is minimized. This series of rapid blood pressure measurements can also be regarded as non - invasive fast - mode cycle (FMC) measurements of blood pressure.

[0149] In one embodiment, the first blood pressure measurement starts a slow inflation, i.e., the measurement period, at a predetermined tissue pressure TPlow within the range of 15 to 30 mmHg because there is no information on the previous diastolic arterial pressure (DAP). Further, during this measurement period, the inflation rate is set to a medium value. This inflation rate can be defined as the rate at which TPcl increases over time, and this inflation rate can be selected, for example, to have a value of 1.9 mmHg / s. This corresponds to the measured value of a "normal" blood pressure value. At the end of the systolic phase, when TPcl reaches Patt, the blood pressure measurement preferably pauses for at least 2 seconds to enable reperfusion of the subject's body part enclosed by the shell 4. This pause time 42 preferably has a length within the range from more than 0% to about 50% of the preceding inflation - contraction period 40 that gives rise to the cycle 41. The next blood pressure measurement starts a slow inflation, i.e., the measurement period, at a higher TPlow, using the information on the diastolic arterial pressure (DAP) determined in the previous measurement (DAPprev) respectively, as shown in FIG. 12.

[0150] The TPlow value should not exceed 90% of the diastolic arterial pressure to ensure that all pulses necessary for blood pressure calculation are recorded. Further, as described above, the blood pressure may change during the time interval (t_inter) between the start of contraction and the start of the next slow inflation. Therefore, preferably, a function that models the blood pressure decrease depending on this time interval t_inter is applied. In clinical data from high - risk surgeries, it has been observed that the diastolic arterial pressure decreases by more than 28% within 1 minute. Therefore, TPlow is the following function TPlow = 90%DAPprev - 28%DAPprev·t_inter / 60 seconds (11) can be calculated by using a linear function like this. Here, "90%DAPprev" and "28%DAPprev" represent 90% and 28% of the previously measured diastolic arterial pressure DAPprev respectively.

[0151] TPlow can be determined by using a linear function that depends on the previous time interval between the start of contraction and the start of the subsequent low-speed expansion. This linear function has a negative slope such that TPlow decreases over time. The slope of the linear function and the positive constant of the linear function can be determined in advance by calibration. In Equation 11, 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.

[0152] In FIG. 12, according to Equation 11, it can be seen how TPlow adapts depending on t_inter. In particular, it can be seen that Measurements #2a and #2b have different TPlow values, where the time interval t_inter of Measurement #2b is larger than the time interval t_inter of Measurement #2a, so the TPlow value of Measurement #2b is smaller than the TPlow value of Measurement #2a. In FIG. 12, since PP is increasing before Measurement #2a, it can also be seen that the inflation rate of Measurement #3 is increasing. Furthermore, the TPlow of Measurement #3 is large compared to the previous measurement because the diastolic arterial pressure DAP is increasing before Measurement #2a. Note that in FIG. 12, interval 44 is the cycle period of the second Measurement #2a, interval 43 is the inflation-contraction period of the second Measurement #2a, and interval 45 is the rest time of the second Measurement #2a. Furthermore, it should be noted that the third Measurement #3 refers to the second Measurement #2a, and the additional second Measurement #2b is shown only to indicate an alternative to the second Measurement #2a.

[0153] FIG. 13 shows a further example for adapting the TPlow value depending on the time interval t_inter according to Equation 11. In this example, the inflation rate during the measurement period is decreasing in Measurement #3 due to the decrease in PP before Measurement #2a and the low TPlow value due to the decrease in DAP before Measurement #2a compared to the previous measurement.

[0154] As described above, filters are 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. Further, filters are also used to determine TPcl based on TP. Preferably, a low-pass filter is used as the filter. This low-pass filter can be, for example, a cascaded moving average filter with a variable window length up to 8 seconds, where the window lengths at the start and end of filtering can be shortened to minimize the filter settling time. For example, the filtering can include averaging twice within a moving window that contains at least three TP pressure pulse curve signals and has a maximum of 8 seconds (2×8 second filter). Optionally, signal padding can be applied before and / or after the signal to completely fill the filter window before filtering. For example, padding using the first pressure pulse value before the start and the last pressure pulse value at the end can be applied.

[0155] Due to filter delay, TPcl is extrapolated from previous values and becomes available for the last part of the measured signal. The filter is applied, for example, to extract TPcl from TP, form smooth TPW_E-curves and smooth TPW_M-curves without fluctuations due to blood pressure pulsations, and generate envelope functions over the systolic peak of TP (TPsys-curve) and the minimum at the end of diastole (TPdia-curve).

[0156] In the following, embodiments of a method for determining blood pressure are exemplarily described with reference to the flowchart shown in FIG. 14.

[0157] After initializing and starting the device in step 101, TPlow is determined in step 102. In the first measurement, TPlow can be set to a value between 15 mmHg and 30 mmHg. If blood pressure measurement has already been performed, in order to determine TPlow, for example, the previous systolic arterial pressure value can be used according to Equation 11.

[0158] In step 103, the cuff during the pre-measurement period is inflated at a relatively large first inflation rate until it reaches TPlow. Then, in step 104, the measurement period, i.e., the slow inflation period, starts, and during this measurement period, the blood pressure determination curve TPW_M-curve and the end determination curve TPW_E-curve are determined. Further, these curves are used to determine the end measurement time point, and when this end measurement time point is reached or passed, the slow inflation period is stopped, and in step 105, the cuff is deflated. After contraction and rest to enable venous return in step 106, the method continues with step 102. Therefore, this method can be implemented in a loop for continuously monitoring blood pressure over time in several measurement cycles. While steps 102 to 105 are being executed, the processor calculates the blood pressure value in parallel. The loop can be executed until an abort criterion is met. For example, when a doctor inputs a command corresponding to the device via an input unit such as a keyboard, computer mouse, touch pad, etc., the blood pressure monitoring is interrupted.

[0159] This device preferably enables non-invasive FMC measurement of blood pressure based on non-invasive high-fidelity tissue pressure TP recordings made using a kink prevention shell system, as described in WO 2014 / 121945 A1. This device preferably enables a statistical average maximum pressure inflation of about 85% or less of the systolic arterial pressure. A single blood pressure measurement using this device 1 takes about 20 to 60 seconds depending on the height of the arterial blood pressure and pulse pressure, and the reciprocal of the heart rate, and this device is preferably configured to provide non-invasive systolic arterial pressure SAPni, non-invasive mean arterial pressure MAPni, and non-invasive diastolic arterial pressure DAPni. The measurements are preferably performed with short breaks during which the cuff is not pressurized between successive measurements, allowing venous return. These short breaks are preferably in the range of 5 to 10 seconds. Since the clamp pressure preferably always remains below the SAP, arterial perfusion of the site wrapped by the shell, such as the upper arm or wrist of the subject, is preferably not completely interrupted during the measurement. Thus, compared to conventional oscillometric measurements, the measurement is less stressful for the subject.

[0160] For example, device 1 described above with reference to FIG. 1 provides a reliable method for quickly determining blood pressure using a clamp pressure that does not exceed the SAP. Due to the relatively short measurement time and relatively low maximum cuff pressure, this blood pressure measurement is very convenient for people and can, for example, reduce the likelihood of predicted complications such as thrombophlebitis, pain, petechial hemorrhage, limb edema, peripheral neuropathy, etc.

[0161] In one embodiment, TPlow can be the DAP or higher. TPlow defines the tissue pressure at the start of the measurement period, i.e., at the start of the low-speed inflation period, and the low-speed inflation can end when a specific end criterion is reached. This end criterion has been described above.

[0162] In the above-described embodiments, the features are determined by using the TPac pulse, but these features can also be determined by directly using the measured pressure pulse, i.e., the TP pulse. It is also possible to process the TP pulse in another way, i.e., without subtracting the average TP value for determining the TPac pulse. For example, for each measured pressure pulse, the pressure values at t.start and t.stop are connected by a straight line, and this straight line can be drawn from each measured pressure pulse to determine the feature determination pulse.

[0163] In the above-described embodiments, the TPW_M-curve and the TPW_E-curve are determined, but it is also possible that the TPW_M-curve is determined while the TPW_E-curve is not determined, where the conversion of the TPW_M-curve and, in some cases, the TPW_M-curve itself are used to determine blood pressure.

[0164] Other variations to the disclosed embodiments can be understood and implemented by those skilled in the art when practicing the claimed invention upon examination of the drawings, the disclosure, and the appended claims.

[0165] In the claims, the term "comprising" does not exclude other elements or steps, and does not exclude the possibility that there are a plurality of them even if it does not state that there are a plurality of them.

[0166] A single unit or device may perform the functions of several items recited in the claims. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used advantageously. The determination of the end measurement time point, the characteristics of the pulse, a specific curve and the transformation of that curve, and the calculation of blood pressure values, etc., performed by one or more units or devices can be performed by any other number of units or devices. The calculation and determination according to the method, and / or the control of the device can be implemented as computer program code means and / or as dedicated hardware.

[0167] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied 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 telecommunications systems.

[0168] Any reference signs in the claims shall not be construed as limiting the scope. In particular, letters such as TPP, TPA, etc., used within parentheses in the claims as reference signs shall not be construed as limiting the scope. For example, other features than those represented by the reference signs can also be used in accordance with the claims.

[0169] An apparatus for determining a subject's blood pressure is presented. The apparatus has a pressure signal supply unit configured to supply a measured pressure signal of the subject over a period of time, the pressure signal indicating the pulsation of the blood and having a plurality of pressure pulses. The apparatus further has a processor configured to determine a blood pressure determination curve indicating the dependence of the applied pressure of the pressure pulses based on the plurality of pressure pulses, apply a transformation to this blood pressure determination curve, and determine the blood pressure based on the result of this transformation. This makes it possible to determine the blood pressure more accurately.

Claims

1. A device for measuring the blood pressure of a subject, wherein the device is A pressure signal supply unit configured to supply a measured pressure signal of a subject over a certain period of time, wherein the pressure signal is a) A shell configured to enclose the area through which the subject's blood flows, b) A pressurizing unit configured to apply pressure to the shell from the outside of the shell, thereby applying pressure to the enclosed area of ​​the subject, and c) A pressure sensor configured to measure a pressure signal on the skin of the wrapped portion of the subject, wherein the pressurizing portion increases or decreases the applied pressure while the pressure signal is being measured, and the measured pressure signal indicates blood pulsation and has a plurality of pressure pulses. A pressure signal supply unit, which is measured using a measuring device having, A processor configured to determine a blood pressure determination curve based on the plurality of pressure pulses. It has, The blood pressure determination curve shows the dependence of the pressure pulse on the applied pressure. The processor is configured to determine at least one characteristic that characterizes each of the plurality of pressure pulses, and to determine a blood pressure determination value for each of the pressure pulses based on the determined at least one characteristic, such that several blood pressure determination values ​​are determined for several pressure pulses that exist at different times. The processor is configured to determine the blood pressure determination curve such that, for some pressure pulses, and therefore for some time, some blood pressure determination values ​​determined for some time form a blood pressure determination curve. The processor is further configured to apply a transformation to the blood pressure determination curve and determine the blood pressure based on the result of the transformation. The transformation applied to the blood pressure determination curve means finding the derivative of the blood pressure determination curve, and the processor is configured to determine the blood pressure based on the derivative of the blood pressure determination curve, and The processor is configured to determine the position of the maximum value of the derivative of the blood pressure determination curve, and to determine the blood pressure based on the determined position and the measured pressure. Device.

2. The apparatus according to claim 1, wherein 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 having a peak value greater than a predetermined proportion of the peak value of one of the overall maximum peaks of the blood pressure determination curve, and determining the position of the maximum value of the derivative of the blood pressure determination curve that is before the determined first peak, wherein "before" refers to the direction from low applied pressure to high applied pressure.

3. The apparatus according to claim 1 or 2, wherein the processor is configured to determine the blood pressure based on the average of the measured pressures at the determined position of the maximum value.

4. The apparatus according to claim 1 or 2, wherein the processor is further configured to determine the position of the maximum value of the blood pressure determination curve and to determine the blood pressure based on this further determined position and the measured pressure.

5. The apparatus according to claim 4, wherein the processor is configured to determine the blood pressure based on the average of the measured pressures at the further determined location.

6. The aforementioned processor, a) The average of the measured pressures at the determined position of the maximum value of the derivative of the blood pressure determination curve, and b) The average of the measured pressure at the determined position of the maximum value of the blood pressure determination curve. The blood pressure is configured to be determined as a function of, The apparatus according to claim 3, wherein the dependence of the function on the mean of the measured pressures at the two locations is predetermined based on a reference measurement.

7. The apparatus according to claim 6, wherein the function is a linear function in which the dependence of the measured pressures at the two locations on the mean is represented by linear coefficients, the linear coefficients being predetermined in a linear regression performed on the reference measurement values.

8. The processor, for each pressure pulse, supplies a feature determination pulse based on each pressure pulse in order to determine the at least one feature, and the following features, The difference between the maximum systolic pressure of the feature determination pulse and the pressure of the feature determination pulse at the end of diastole, The area enclosed by the upper part of the feature determination pulse, wherein a) the upper end of the upper part is at the maximum systolic pressure of the feature determination pulse, and b) the lower end of the upper part is between the maximum systolic pressure of the feature determination pulse and the pressure value corresponding to the average of the measured pressures, The duration of each of the feature determination pulses mentioned above, The area of ​​each of the feature determination pulses, and The full width at half maximum of each of the feature determination pulses mentioned above The apparatus according to claim 1 or 2, configured to determine at least one of the following.

9. The apparatus according to claim 8, wherein the processor is configured to determine the blood pressure determination value and thus form the blood pressure determination curve based solely on the feature which is the difference between the maximum systolic pressure of the feature determination pulse and the pressure of the feature determination pulse at the end of diastole, or based solely on a) the feature which is the difference between the maximum systolic pressure of the feature determination pulse and the pressure of the feature determination pulse at the end of diastole, and b) the feature which is the area enclosed by the upper part of the feature determination pulse.

10. The apparatus according to claim 1 or 2, wherein the processor is configured to determine the blood pressure determination value based on the determined at least one feature by raising each of the pressure pulses to the power of the at least one feature by a predetermined exponent.

11. A method for measuring the blood pressure of a subject, wherein the method is A pressure signal supply unit supplies a measured pressure signal of a subject over a period of time, wherein the pressure signal is: a) A shell configured to enclose the area through which the subject's blood flows, b) A pressurizing unit configured to apply pressure to the shell from the outside of the shell, thereby applying pressure to the enclosed area of ​​the subject, and c) A pressure sensor configured to measure the pressure signal on the skin of the wrapped portion of the subject, wherein the pressurizing portion increases or decreases the applied pressure while the pressure signal is being measured, and the measured pressure signal indicates blood pulsation and has a plurality of pressure pulses. Steps are measured by using a measuring device having A step of determining a blood pressure determination curve based on the plurality of pressure pulses, wherein the blood pressure determination curve shows the dependence of the pressure pulses on the applied pressure, and for each of the plurality of pressure pulses, at least one feature is determined that characterizes each pressure pulse, and for several pressure pulses existing at different times, several blood pressure determination values ​​are determined based on the determined at least one feature, and the blood pressure determination curve is determined such that the several blood pressure determination values ​​determined for several pressure pulses and therefore for several times form a blood pressure determination curve. The step of applying a transformation to the blood pressure determination curve, and A step of determining blood pressure based on the result of the transformation, wherein the transformation applied to the blood pressure determination curve means finding the derivative of the blood pressure determination curve, the blood pressure is determined based on the derivative of the blood pressure determination curve, the position of the maximum value of the derivative of the blood pressure determination curve is determined, and the blood pressure is determined based on the determined position and the measured pressure. A method for measuring the blood pressure of the subject, including the following.

12. A computer program for determining blood pressure, comprising program code for causing a device for determining blood pressure according to claim 1 or 2 to perform the steps described in claim 11.

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