Device for determining blood pressure of subject

Abstract

An apparatus for determining a blood pressure of a subject is presented. The apparatus comprises a pressure signal providing unit configured to provide a measured pressure signal (TP) of the subject over a period of time, where the pressure signal is indicative of a blood pulsation and comprises a plurality of pressure pulses. The apparatus further includes a processor configured to: determine a blood pressure determination curve (TPWM-curve) based on the plurality of pressure pulses, the blood pressure determination curve indicating a dependency of the pressure pulses on an applied pressure; applying the transformation to the blood pressure determination curve; and determining the blood pressure based on a result of the transformation. This allows for a more accurate determination of blood pressure.

Description

Technical Field

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

[0002] US 2021 / 0235996 A1 discloses a signal processing device, including a processor and a memory for storing instructions. The processor is configured to execute the instructions to obtain a signal, obtain a frequency band spectrum by applying a fast Fourier transform (FFT) to the obtained signal, and remove noise from the obtained frequency band spectrum by applying a first filter and a second filter different from each other to the obtained frequency band spectrum.

[0003] The article "Oscillometric Blood Pressure Estimation: Past, Present, and Future" IEEE Reviews in Biomedical Engineering, volume 8, pages 44 to 63 (2015) by M. Forouzanfar et al. discloses that the use of automatic blood pressure (BP) monitoring is growing because it does not require much expertise and can be performed several times a day by patients at home. It also discloses that the oscillometric method is one of the most common measurement methods used in automatic BP monitors, wherein, for example, the derivative oscillometric method is described.

[0004] US 2022 / 0096017 A1 discloses a control device for controlling a blood pressure measurement system. An applicator applies increasing pressure to a portion of an object during a measurement time period while measuring the pressure on the skin of the portion of the object, the pressure comprising a plurality of pressure pulses. For each pressure pulse of at least some of the plurality of pressure pulses, several features characterizing the corresponding pressure pulse are determined, wherein an end measurement time point at or after which the measurement time period is to be stopped is determined based on these features, and wherein when or after the end measurement time point is reached, i.e., when the measurement time period is to be stopped, the applied pressure is reduced to start a subsequent blood pressure post-measurement time period.

[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 an individual, the tissue pressure signal having a series of tissue pressure pulse curves. At least two individual tissue pressure pulse curves are identified in the tissue pressure signal, and at least one amplitude parameter and an area parameter are determined for each identified tissue pressure pulse curve, the amplitude parameter indicating the amplitude of the identified tissue pressure pulse curve, and the area parameter indicating at least one partial area enclosed by the tissue pressure pulse curve. For each identified tissue pressure pulse curve, a pulsating power parameter is determined, the pulsating power parameter indicating the shape of the tissue pressure pulse curve based at least on the amplitude parameter and the area parameter. A parameter function is generated, which indicates the functional relationship between the pulsating power parameter of the determined tissue pressure pulse curve and the corresponding clamping pressure at the pressure cuff or the measurement time. At least one blood pressure value is determined based on the parameter function.

[0006] EP 3 430 992 A1 discloses a blood pressure measurement system, which is configured to surround a body part of a subject, wherein the blood pressure measurement system comprises a pressurizing device for applying pressure to the body part and an anti-kink housing. When the blood pressure measurement system surrounds the body part, the anti-kink housing is arranged to be located between the pressurizing device and the body part. The blood pressure measurement system allows blood pressure to be measured by continuously increasing the clamping pressure and stopping the increase above the systolic pressure. Summary of the invention

[0007] It is an object of the present invention to provide an improved device, method and computer program for determining blood pressure which allow, for example, a more accurate determination of blood pressure.

[0008] In a first aspect of the present invention, a device for determining the blood pressure of a subject is provided, wherein the device comprises:

[0009] - a pressure signal providing unit configured to provide a measured pressure signal of an object over a period of time, wherein the pressure signal has been measured by using a measuring device, the measuring device comprising: a) a shell configured to enclose a portion of the object through which blood flows; b) a pressure applicator configured to apply pressure to the shell and thereby to the enclosed portion of the object from the outside of the shell; and, c) a pressure sensor configured to measure the pressure signal on the skin of the enclosed portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal is indicative of blood pulses and comprises a plurality of pressure pulses,

[0010] - a processor configured to determine a blood pressure determination curve based on the plurality of pressure pulses, wherein the blood pressure determination curve indicates a dependency of the pressure pulses on an applied pressure, and wherein the processor is further configured to apply a transformation to the blood pressure determination curve and to determine the blood pressure based on a result of the transformation.

[0011] It has been found that the way in which the measured pressure signal is interpreted is critical for determining the accurate blood pressure value of the subject. Based on this finding, it has been realized that the blood pressure can be determined more accurately by determining in the following way: not only based on the blood pressure determination curve itself (even though it already indicates the dependence of the pressure pulses on the pressure applied by the pressure applicator), but by applying a transformation to the blood pressure determination curve and determining the blood pressure based on the result of the transformation.

[0012] A pressure sensor configured to measure the pressure on the skin of the wrapped portion of the subject may be arranged inside the housing. However, the pressure sensor may also be arranged in another way to measure the pressure on the skin of the wrapped portion of the subject. For example, a pressure sensor pad filled with a fluid may be arranged inside the housing and connected to a pressure sensor outside the housing via a fluid path (i.e., via a pipe filled with a fluid) to measure the pressure on the skin of the wrapped portion of the subject.

[0013] The pressure signal providing unit may be a receiving unit configured to receive a pressure signal from, for example, a measuring device and to provide the received pressure signal. However, the pressure signal providing unit may also be a memory in which a previously measured pressure signal has been stored and from which the pressure signal may be retrieved to provide the pressure signal. The pressure signal providing unit may also be or include a measuring device for measuring the pressure signal.

[0014] For example, when measuring the pressure signal, the pressure applied by the pressure applicator to the shell and thereby to the enclosed part of the object can be continuously (in particular with a constant gradient) increased or decreased during the measuring time period. The measured pressure signal can generally be understood as a composition, in particular the sum, of a part due to increasing or decreasing the applied pressure and a part due to blood pulsation in the part of the object enclosed by the shell. Therefore, the measured pressure signal includes pressure pulses, wherein, in particular, the pressure pulses can be understood as indicating blood pulsation.

[0015] The portion of the measured pressure signal due to blood pulsation will generally first increase when the applied pressure increases from close to the diastolic pressure or even below, and will begin to decrease at a certain point when the applied pressure increases further towards the systolic pressure or even above the systolic pressure, because, on the one hand, the applied pressure provides the necessary coupling between the blood pulsation in the part of the object enclosed by the housing and the pressure sensor, while on the other hand, the applied pressure tends to suppress the blood pulsation. Similarly, the portion of the measured pressure signal due to blood pulsation will generally also increase when the applied pressure decreases from close to the systolic pressure or even above the systolic pressure, and will begin to decrease at a certain point when the applied pressure decreases further towards the diastolic pressure or even below the diastolic pressure. This correlation (which is the correlation of the pressure pulses in the measured pressure signal to the applied pressure) is also indicated by the blood pressure determination curve, which is determined by the processor. For example, the blood pressure determination curve can also increase and thereafter begin to decrease again within the measurement time period, in particular regardless of whether the applied pressure is increasing or decreasing. The dependence of the pressure pulses in the measured pressure signal on the applied pressure (i.e., how the pressure pulses depend on the applied pressure) indicates the blood pressure. Since this correlation is indicated by the blood pressure determination curve, the blood pressure determination curve will also indicate the blood pressure.

[0016] The blood pressure determination curve that the processor is configured to determine based on a plurality of pressure pulses in the pressure signal is preferably a continuous curve, in particular a differentiable curve at least once, more particularly a smooth curve, wherein it is understood that the terms "continuous", "differentiable" and "smooth" may have an approximate or "discretized" meaning, as known in numerical analysis. Preferably, the blood pressure determination curve corresponds to a function of the applied pressure, the average measured pressure or the measurement time. In practice, the processor is not necessarily configured to determine an actual graphical representation corresponding to the blood pressure determination curve. On the contrary, for example, the blood pressure determination curve may correspond only to pressure values, in particular consist of pressure values, which may be understood as blood pressure determination curve values ​​associated with corresponding values ​​of the applied pressure, the average measured pressure or the measurement time.

[0017] The transformation applied to the blood pressure determination curve can be predefined so that areas of the blood pressure determination curve indicating the dependence of the blood pressure pulse on the applied pressure exceeding a predetermined intensity are detected more effectively than in the blood pressure determination curve itself. It has been found that areas where the dependence of the blood pressure pulse on the applied pressure is strong can provide valuable information about the blood pressure. Therefore, more effective detection of such areas can be promoted by emphasizing these areas. Since the pressure applied by the pressure applicator 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. Therefore, the dependence of the blood pressure determination curve on the applied pressure at a given point of the curve (i.e., its local intensity) can be measured, for example, its slope at this point. It should be recognized that areas in the blood pressure determination curve with a weak (especially vanishing) dependence on the applied pressure can also provide valuable information about the blood pressure, but it has been found that they are not the only information. The relative terms "strong" and "weak" relate to the intensity of the dependence of the blood pressure determination curve on the applied pressure, which is understood to be defined relative to one or more predetermined thresholds. Furthermore, the dependence of the blood pressure determination curve on the applied pressure (in particular the slope of the curve) can be considered either in terms of its actual value (ie including the sign) or in terms of its absolute value.

[0018] Applying a transformation to the blood pressure determination curve involves transforming at least a portion of the blood pressure determination curve, in particular the entire blood pressure determination curve. Thus, the result of applying the transformation to the blood pressure determination curve may be a transformed blood pressure determination curve, wherein, if the transformation is applied to only a portion of the blood pressure determination curve, the transformed blood pressure determination curve may deviate from the blood pressure determination curve only in that portion, or may correspond only to the deviated portion. If the blood pressure determination curve is only partially transformed, the processor may be configured to determine the blood pressure based only on the transformed portion of the blood pressure determination curve. The blood pressure determination curve may be only partially transformed in cases where it can be expected which portion of the blood pressure determination curve is a good basis for determining the blood pressure after being transformed. Limiting the applied transformation to a portion of the blood pressure determination curve may save computing resources.

[0019] Although the result of applying the transformation to the blood pressure determination curve can be considered to be a transformed blood pressure determination curve, the processor is not necessarily configured to actually determine the transformed 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, wherein these new pressure values ​​can be referred to as transformed blood pressure determination curve values, and the blood pressure is determined based on the new pressure values. Since applying the transformation to the blood pressure determination curve can correspond to determining new pressure values ​​based on the pressure values ​​corresponding to the blood pressure determination curve, applying the transformation can also be 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 the function is not necessarily an ordinary function, such as an analytical function. Instead, the applied transformation can be expressed by only an operator such as a differential operator. In a preferred embodiment, the transformation applied to the blood pressure determination curve involves taking the derivative of the blood pressure determination curve, so that the processor is configured to determine the blood pressure based on the derivative of the blood pressure determination curve. It has been found that the derivative of the blood pressure determination curve is particularly helpful in indicating areas of strong dependence of the blood pressure pulse on the applied pressure, and therefore helps to more accurately determine the blood pressure while requiring computationally acceptable computational effort. It will be appreciated that when the transformation is a derivative, the blood pressure determination curve is determined such that it is differentiable.

[0020] Instead of determining the derivative, which allows effectively detecting areas in the blood pressure determination curve indicating a strong dependence of the pressure pulse on the applied pressure, it is also possible to determine the differences between the points of the blood pressure determination curve. The term "difference" may in particular be understood as relating to differences that are finite beyond the extent considered in the numerical analysis for approximating the derivative. However, alternatively, taking the differences between different points of the blood pressure determination curve may also be understood as corresponding to determining a finite (i.e., discretized) version of the derivative, as known from the numerical analysis. In any case, the determination of the differences may also be understood as a transformation applied to the blood pressure determination curve, since the determined differences may be understood as being associated with points of the blood pressure determination curve, thereby producing a graph that maps the blood pressure determination curve or a portion thereof to a new curve, which new curve may be regarded as a transformed blood pressure determination curve.

[0021] Preferably, the processor is configured to determine the position of the maximum of the derivative of the blood pressure determination curve, and to determine the blood pressure based on the determined position and the measured pressure. In particular, the processor may be configured to determine the blood pressure based on the average value of the measured pressure at the position of the determined maximum. It has been found that determining the blood pressure based on the maximum of the derivative of the determined blood pressure determination curve and according to the measured pressure on the skin (i.e. according to the tissue pressure) allows the blood pressure to be determined particularly accurately. When the blood pressure is determined based on the maximum of the derivative of the blood pressure determination curve, the processor may be configured to determine the derivative of the blood pressure determination curve only for the area where the maximum of the derivative is expected to be located. The expected area may be a fixed area predetermined based on previous measurements.

[0022] The maximum value of the derivative preferably relates to the direction from low applied pressure to high applied pressure. In other words, preferably, when measuring the pressure signal for determining the blood pressure, the derivative is considered in the direction from low applied pressure to high applied pressure, regardless of whether the applied pressure is increasing or decreasing.

[0023] Preferably, 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 predefined percentage of the peak value of the total peaks of the blood pressure determination curve and by determining the position of the maximum value of the derivative of the blood pressure determination curve that precedes the determined first peak. The predefined percentage of the total peak can be predetermined by calibration. In a preferred embodiment, the predefined percentage is 90%. The determination of the first peak of the blood pressure determination curve can be achieved by normalizing the blood pressure determination curve to the peak value of the total maximum peak, so that the peak value is 1 after normalization, and the first peak has a peak value greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve. The predefined percentage is then a fixed absolute value between 0 and 1, and is preferably 0.9. It has been found that limiting the area in which the maximum value of the derivative of the blood pressure determination curve is determined in this way allows the accuracy of the blood pressure determination to be further increased.

[0024] Note that the word "before" here refers to the direction from low applied pressure to high applied pressure. Therefore, if the pressure applied when measuring the pressure signal for determining blood pressure is increased, the word "before" also means before in time, and if the pressure applied when measuring the pressure signal for determining blood pressure is reduced, the word "before" means after in time.

[0025] If the blood pressure determination curve has only a single peak, the single peak is the total maximum peak, and it is also the first peak having a predefined percentage of peaks greater than the total maximum peak.

[0026] Preferably, the applied pressure is increased when measuring the pressure signal for determining the blood pressure. This is advantageous compared to reducing the applied pressure when measuring the pressure signal for determining the blood pressure.

[0027] The processor may also be configured to determine the position of the maximum of the blood pressure determination curve and to determine the blood pressure further based on the further determined position and the measured pressure. In particular, the processor may be configured to determine the blood pressure further based on the average value of the measured pressure at the further determined position (i.e. the position of the determined maximum of the blood pressure determination curve). Determining the blood pressure based on the determined maximum of the blood pressure determination curve and the determined maximum of its derivative and according to the measured pressure on the skin (i.e. according to the tissue pressure) allows a more accurate determination of the blood pressure, even though the dependence of the blood pressure determination curve on the applied pressure at its maximum would normally be considered to be relatively weak or even vanishing, since the derivative of the blood pressure determination curve vanishes at its maximum. In practice, the processor may be configured to determine the position of the maximum of the blood pressure determination curve based on the derivative of the blood pressure determination curve (i.e. also based on the transformed blood pressure determination curve, i.e. by determining where the derivative is zero). Alternatively, for example, the processor may be configured to determine the position of the maximum of the blood pressure determination curve and / or its transformed version by comparing points on the respective curves or corresponding function values ​​with each other, wherein it may be determined that the respective maximum located on the respective curve or its corresponding function changes from rising or increasing to falling or decreasing. Furthermore, the respective maximum value can be determined when measuring the pressure signal, in particular when measuring the portion of the pressure signal which produces the respective maximum value in the respective curve.

[0028] Although determining the blood pressure based on the blood pressure determination curve in addition to the transformed version of the blood pressure determination curve (in particular, based on the positions of the maxima of both curves) may allow a more accurate determination of the blood pressure, determining the blood pressure based only on the transformed version of the blood pressure determination curve (in particular, based only on the positions of the maxima of the derivative of the blood pressure determination curve) may be computationally more efficient. Furthermore, since the derivative of the blood pressure determination curve will generally present its maximum value earlier within the measurement time period than the blood pressure determination curve itself, this also allows a faster blood pressure determination and therefore less discomfort for the subject.

[0029] In addition to or alternatively to determining the blood pressure based on the position of the maximum value of the derivative of the blood pressure determination curve, the blood pressure can be determined based on the position of the minimum value of the derivative of the blood pressure determination curve. This can be particularly advantageous in the case where the pressure applicator increases or decreases the applied pressure and the measurement time of the measured pressure signal is relatively long.

[0030] As already indicated above, the blood pressure determination curve may correspond in particular to a function of the applied pressure or the measured mean pressure. Thus, instead of measuring the pressure, in particular its mean value, the applied pressure at the corresponding maximum value may also be used to determine the blood pressure. The applied pressure relates to the pressure applied by the control pressure applicator.

[0031] It should be understood that it is still acceptable to determine the blood pressure using a pressure close to the pressure rather than the exact corresponding pressure value at the determined position of the corresponding maximum value. In other words, it may be acceptable if the corresponding maximum value is determined not precisely but with a predetermined sufficient accuracy.

[0032] In one embodiment, the processor is configured to determine the blood pressure as a function of a) the average value of the measured pressure at the location of the maximum value of the derivative of the determined blood pressure determination curve and b) the average value of the measured pressure at the location of the maximum value of the determined blood pressure determination curve, wherein the dependence of the function on the average value of the measured pressure at the two locations is predetermined based on the reference measurement results. In particular, the function can be a linear function, whose dependence on the average value of the measured pressure at the two locations is represented by a linear coefficient, wherein the linear coefficient is predetermined in a linear regression performed based on the reference measurement results. Even though a general function can allow a higher accuracy, a linear function keeps the computational effort acceptable while still allowing a very high accuracy in determining the blood pressure.

[0033] The reference measurement (which may also be referred to as calibration measurement) preferably corresponds to the evaluation of a calibration set consisting of pairs of: a) invasively measured blood pressure values ​​and b) non-invasively measured blood pressure values ​​determined based on a non-invasively measured pressure signal, wherein the non-invasively measured pressure signal is measured simultaneously with the invasive measurement by a device as defined above. Preferably, the calibration set is collected from a sufficient number of individuals and under different hemodynamic conditions. The non-invasive blood pressure values ​​are determined by a device as defined above, and the linear coefficients of the above-mentioned function expressing the blood pressure as a function of the applied pressure, in particular the average value of the measured pressures at the above-mentioned two positions, can be optimized so that the deviation between the invasive blood pressure values ​​and the non-invasive blood pressure values ​​is minimized. For example, a linear regression using the least squares method can be performed.

[0034] Although it has been found that it allows a very accurate determination of blood pressure to determine blood pressure based on the derivative of the blood pressure determination curve, other transformations applied to the blood pressure determination curve may also result in a good or even better basis for accurately determining blood pressure. For example, the processor may be configured to determine the logarithm of the blood pressure determination curve and determine blood pressure based thereon.

[0035] Furthermore, although the term "derivative" has been used above and will also be used subsequently to refer to first-order derivatives, higher derivatives may also be used as the transformation to be applied to the blood pressure determination curve.

[0036] Preferably, the processor is configured to: determine at least one feature characterizing the corresponding pressure pulse for a corresponding pressure pulse among the plurality of pressure pulses; determine a blood pressure determination value for the corresponding pressure pulse based on the determined at least one feature, so that several blood pressure determination values ​​are determined for several pressure pulses present at different times, wherein the processor is configured to determine a blood pressure determination curve, so that several blood pressure determination values ​​determined for several pressure pulses and therefore for several times form a blood pressure determination curve. The blood pressure determination curve used for blood pressure measurement in this case can be considered to be constructed from a single tissue pressure waveform (TPW), so that it can be abbreviated as TPW_M-curve, and the blood pressure determination values ​​can be considered to parameterize the tissue pressure waveform, so that they can be abbreviated as TPWP_M. It has been found that the blood pressure can be accurately determined even if a single feature is taken into account to determine the blood pressure determination value. Therefore, it is possible to accurately determine the blood pressure with relatively low computational effort.

[0037] The at least one characteristic may directly characterize the corresponding pressure pulse or indirectly characterize the corresponding pressure pulse. In the latter case, the corresponding pressure pulse is processed to determine a characteristic determination pulse, and at least one characteristic is determined based on the determined characteristic determination pulse. This will be explained in more detail further below. The processor may be configured to determine at least one characteristic characterizing the corresponding pressure pulse for each pressure pulse of all or only some (e.g., at least 5 or at least 10) of the plurality of pressure pulses.

[0038] The processor may be adapted to process several blood pressure determination values ​​obtained for several pressure pulses to obtain a blood pressure determination curve. For example, interpolation and optionally also smoothing may be applied. In this way, a continuous, at least once differentiable or even smooth blood pressure determination curve may be obtained.

[0039] In an embodiment, the processor is configured to: provide a characteristic determination pulse based on the corresponding pressure pulse in order to determine at least one feature for the corresponding pressure pulse, and determine at least one of the following features: i) the difference (TPP) between the maximum systolic pressure (TPSys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end diastolic point, ii) the area (TPA+.top50) enclosed by the upper part of the characteristic determination pulse, wherein a) the upper end of the upper part is at the maximum systolic pressure (TPSys) of the characteristic determination pulse, and b) the lower end of the upper part is between the maximum systolic pressure (TPSys) of the characteristic determination pulse and the pressure value corresponding to the average value (TPcl) of the measured pressure (TP), iii) the duration of the corresponding characteristic determination pulse (t(pulse)), iv) the area of ​​the corresponding characteristic determination pulse (TPA / TPA.norm), and v) the half-peak full width (W50) of the corresponding characteristic determination pulse. It has been found that by using at least one of these features, the determination of blood pressure can be further improved.

[0040] The characteristic determination pulse for the corresponding pressure pulse can be obtained, for example, by subtracting the measured average pressure (TPcl) from the corresponding pressure pulse. However, the characteristic determination pulse for the corresponding pressure pulse can also be determined in another way. It can also be the corresponding pressure pulse directly, that is, the corresponding measured pressure pulse. If the characteristic determination pulse for the corresponding pressure pulse has been obtained by subtracting the measured average pressure (TPcl) from the corresponding pressure pulse, then for determining the area TPA+.top50, the pressure value corresponding to the average value (TPcl) of the measured pressure (TP) will be zero.

[0041] The difference (TPP) between the maximum systolic pressure of the characteristic determination pulse and the pressure of the characteristic determination pulse at the end-diastolic point is preferably the difference between the maximum measured pressure and the minimum measured pressure of the corresponding pressure pulse, that is, the difference between the tissue pressure (TP) of the corresponding pressure pulse at the maximum contraction point (that is, the measured pressure on the skin) and the tissue pressure (TP) at the end-diastolic point of the corresponding pressure pulse. The duration t(pulse) of the corresponding characteristic determination pulse preferably corresponds to the time difference between the end-diastolic point and the next end-diastolic point for the corresponding pressure pulse. In addition, the area TPA is preferably the area under the curve of the corresponding characteristic determination pulse from the end-diastolic point to the next end-diastolic point. The area can be a normalized area and then named "TPA.norm". For example, the area TPA can be normalized by scaling the area TPA to the difference between the maximum pressure and the minimum pressure of the corresponding characteristic determination pulse in order to determine TPA.norm. The full width at half maximum W50 corresponds to the width at 50% of the difference between the maximum pressure and the minimum pressure of the corresponding characteristic determination pulse. It is therefore the width at which 50% of the difference between the pressure of the characteristic pulse at the point of maximum contraction and the pressure of the characteristic pulse at the point of end-diastole.

[0042] In a preferred embodiment, the processor is configured to determine an area TPA+.top50 enclosed by the upper part of the characteristic determination pulse so that the lower end of the upper part is at a pressure value that is half the pressure distance (TPP+) between the pressure value corresponding to the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure value corresponding to the average value (TPcl) of the measured pressure (TP).

[0043] Furthermore, in a preferred embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M) based only on the feature of the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure at the end diastolic point (TPdia) of the characteristic determination pulse, and thus form a blood pressure determination curve (TPW_M-curve). Therefore, in this embodiment, in addition to TPP, no other above-mentioned features are used to determine the blood pressure determination value. It has been found that this allows to further increase the accuracy of determining the blood pressure with relatively low computational effort.

[0044] In a further improved embodiment, the processor is configured to determine the blood pressure determination value (TPWP_M), and thus form a blood pressure determination curve (TPW_M-curve), only based on: a) a feature as the difference TPP between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end diastolic point; and, b) a feature as the area TPA+.top50 enclosed by the upper part of the characteristic determination pulse. Thus, in this embodiment, in addition to TPP and TPA+.top50, none of the above features are used to determine the blood pressure determination value. It has been found that this allows an even further increased accuracy of determining the blood pressure, wherein the computational effort may be relatively low.

[0045] Preferably, the processor is configured to provide a function that receives at least one feature of the corresponding pressure pulse as input and outputs a corresponding blood pressure determination value, and determines a blood pressure determination curve so that the blood pressure determination curve is formed by the corresponding blood pressure determination value together with the blood pressure determination values ​​determined for other pressure pulses. The function has at least one parameter that can be determined by calibration, wherein a reference blood pressure value is determined very accurately in an invasive manner, and at least one parameter is determined so that the device produces very accurate invasively measured blood pressure values ​​with high statistical precision and accuracy. In particular, for the calibration measurement, pairs of invasive and non-invasive blood pressure values ​​recorded simultaneously from a sufficient number of individuals under different hemodynamic conditions are used. It should be noted that calibration is preferably performed only in the development phase, i.e. not during the actual blood measurement process. Calibration can be performed separately for different housing sizes (i.e., preferably for different blood pressure cuff sizes) or for different combinations of housing sizes. For example, for different housing sizes or housing size combinations, different parameters of the function can be determined by calibration, i.e., for each housing size or for each group of housing sizes, a corresponding at least one parameter can be determined.

[0046] For example, the processor may be configured to determine the blood pressure determination value (TPWP_M) based on the determined at least one feature for the corresponding pressure pulse by raising the at least one feature to the power of a predefined exponent. The predefined exponent may be predefined by calibration as described in the previous paragraph. Thus, the predefined exponent may be a parameter of the function mentioned in the previous paragraph, wherein the parameter (i.e., the predefined exponent in this example) is predefined by calibration. The function may have the following structure: a) a predefined factor multiplied by b) a result of raising the first feature characterizing the corresponding pressure pulse to the first power of the power of the first predefined exponent, optionally further multiplied by c) a result of raising the second feature characterizing the corresponding pressure pulse to the second power of the power of the second predefined exponent, optionally further multiplied by d) a result of raising the third feature characterizing the corresponding pressure pulse to the third power of the power of the third predefined exponent, and so on, wherein, in a preferred embodiment, the function includes only a) and b) or only a), b) and c). The predefined factor may also be predefined by calibration.

[0047] The processor may also be configured to control the measurement of the pressure signal, possibly in dependence on the determined blood pressure value (i.e., the blood pressure value determined during the measurement). In an embodiment, the processor is configured to control the measuring device such that the applied pressure increases during a measurement time period extending to an end measurement time point and the applied pressure decreases during a subsequent blood pressure post-measurement time period, wherein the pressure sensor measures the pressure (TP) on the skin at least during the measurement time period, wherein the processor is configured to determine the end measurement time point based on at least one feature determined for at least some of the plurality of pressure pulses, stop the measurement time period at or after the end measurement time point, and control the pressure applicator such that when the end measurement time point is reached or after the end measurement time point, it reduces the applied pressure to start a subsequent blood pressure post-measurement time period. In particular, at least one feature determined for the pressure pulses, respectively, may be used to determine the end measurement time point such that the measurement time period is relatively short and sufficient pressure data has still been measured, which allows an accurate determination of the blood pressure. This allows a reduced blood pressure measurement time and tissue pressure, i.e., the clamping pressure applied to the skin of the body part during the measurement is maintained and ends substantially below the systolic arterial pressure.

[0048] Preferably, the processor is configured to: a) determine, for the respective pressure pulse, an end determination value based on at least one feature that has been determined for the respective pressure pulse, so that for several pressure pulses present at different times, several end determination values ​​are determined, wherein the several end determination values ​​determined for the several pressure pulses and therefore for the several times form an end determination curve, and b) determine the end measurement time point based on the end determination curve. By using the end determination curve, the accuracy of determining the end measurement time point can be further improved. The processor can be adapted to process several end determination values ​​obtained for several pressure pulses to obtain a continuous end determination curve. In order to obtain a continuous curve based on different end determination values, known mathematical techniques can be used. For example, interpolation, fitting processes, filtering processes, etc. can be applied.

[0049] The processor is preferably configured to determine the end determination curve such that it satisfies one of the following conditions: a) the maximum of the end determination curve occurs temporally before the maximum of the blood pressure determination curve, b) the maximum of the end determination curve occurs temporally at or after the maximum of the blood pressure determination curve, and the decrease of the end determination curve after its maximum is steeper than the decrease of the blood pressure determination curve after its maximum, and c) the end determination curve is identical to the blood pressure determination curve. It has been found that if the end determination curve and the blood pressure determination curve have one of these relationships relative to each other, the end measurement time point can be determined more accurately.

[0050] In a preferred embodiment, the processor is configured to determine the end measurement time point further based on the blood pressure determination curve. It has also been found that if not only the end determination curve but also the blood pressure determination curve is used to determine the end measurement time point, the measurement time can be further reduced.

[0051] Preferably, the processor is configured to determine the end measurement time point by determining when a) the end determination curve has dropped to a value equal to or less than a predefined percentage of the maximum value after having exceeded its maximum value and b) the blood pressure determination curve has reached or exceeded its maximum value. Further preferably, the predefined percentage of the maximum value is in the range of 40% to 95%. It has been found in particular that if two curves are used in this way to determine the end measurement time point, the time point can be determined very accurately, so that the blood pressure measurement time is relatively short and the blood pressure is still measured very accurately.

[0052] In an embodiment, the processor is configured to control the pressure applicator so that it increases the applied pressure at a first rate in a preceding measurement period, the preceding measurement period being followed by a measurement period, during which the applied pressure increases at a second rate, wherein the first rate is greater than the second rate. Thus, the applied pressure at which the measurement period should start can be reached relatively quickly, thereby allowing the total time required to measure the blood pressure to be further reduced.

[0053] In an embodiment, the processor is configured to control the pressure applicator so that at the end of the previous measurement period, the measured pressure is in the range of 15 to 30 mmHg. This ensures that the pressure on the skin, i.e. the tissue pressure, is measured in a sufficiently large pressure range during the measurement period, which allows accurate and precise measurement of blood pressure.

[0054] If the previous diastolic arterial pressure obtained by the previous blood pressure measurement of the same subject is not used by the processor to control the pressure applicator, the range of 15 to 30 mmHg is preferably applied. If the previous diastolic arterial pressure is used for the control of the pressure applicator, the measured pressure at the end of the previous measurement period can also be higher. The control of the pressure applicator according to the previously obtained diastolic arterial pressure will be explained below.

[0055] It should be noted that the pressure at the end of the previous measurement time is not the pressure applied between two subsequent blood pressure measurements, in particular before the start of the previous measurement period. This pressure can be named "attachment pressure" and should not exceed 15 mmHg.

[0056] In an embodiment, the processor is configured to a) store or receive a previous diastolic arterial pressure obtained by a previous blood pressure measurement, b) determine a first end measurement pressure based on the previous diastolic arterial pressure, which first end measurement pressure should exist at the end of the previous measurement period and can therefore also be regarded as a target pressure, so that the first end measurement pressure is less than the previous diastolic arterial pressure, and c) control the pressure applicator so that the measured pressure at the end of the previous measurement period is equal to or less than the determined first end measurement pressure. Preferably, the processor is configured to determine the first end measurement pressure so that it is 90% or less of the previous diastolic arterial pressure. In addition, this ensures that the pressure on the skin, i.e. the tissue pressure, is measured over a sufficiently large range during the measurement period to accurately and precisely determine the blood pressure.

[0057] In an embodiment, the processor is configured to further store or receive a time at which a previous diastolic arterial pressure has been measured, and to determine a first end measurement pressure as a function of i) the previous diastolic arterial pressure at which the previous diastolic arterial pressure has been measured and ii) the time distance to the blood pressure measurement, as indicated by the stored time. The diastolic arterial pressure may vary over time, wherein the first end measurement pressure may still be determined relatively accurately if the time distance to the blood pressure measurement at which the previous diastolic arterial pressure has been measured is taken into account. Thus, despite this uncertainty regarding the variation of the diastolic arterial pressure over time, the end of the previous measurement time period may be determined such that during the subsequent measurement time period, the pressure on the skin, i.e. the tissue pressure, is measured over a sufficiently large range to accurately and precisely determine the blood pressure.

[0058] The processor may also be configured to a) store or receive a previous pressure measured by the pressure sensor during a time period between the end of a previous measurement time period of a previous blood pressure measurement and the beginning of a previous measurement time period, and b) control the pressure applicator so that the measured pressure at the beginning of the previous measurement time period is equal to or less than a predefined pressure value based on the stored or received previous measurement. The predetermined pressure value is preferably equal to or less than 15 mmHg, and further preferably equal to or less than 10 mmHg.

[0059] The measured pressure at the start of the preceding measurement time period can be regarded as the attachment pressure present during the measurement pause between two subsequent blood pressure measurements (i.e. before the start of the respective blood pressure measurement), wherein the attachment pressure is preferably controlled to achieve a given or preset value, i.e. a predetermined pressure value. The control is preferably performed to adapt to changes in the volume of the body part, such as an increase caused by tissue edema (e.g. capillary leak in sepsis, hypervolemia) or a decrease by contracting tissue edema or by hypovolemia. This should in particular avoid venous congestion during the measurement pause (i.e. between two subsequent blood pressure measurements), which venous congestion is caused by impaired venous return caused by venous compression due to a tissue pressure that is higher than the venous pressure in the respective body part. In a preferred embodiment, the pressure on the skin (which can also be regarded as tissue pressure) is measured continuously during the entire process of performing one or several blood pressure measurements, and the pressure applicator is controlled such that venous congestion is avoided during the measurement pause.

[0060] The housing is preferably an anti-kink housing. The anti-kink housing is preferably located (or sandwiched) between the pressure applicator (i.e. the fluid bag) and the wrapped part of the object. The relatively rigid anti-kink shell avoids or at least significantly reduces the generation of wrinkles or kinks at the compression action surface of the pressure applicator (in particular the fluid bag). Therefore, the measurement accuracy can be improved because there is no wrinkle that negatively affects the amplitude, form and reproducibility of the measurement signal.

[0061] If the pressure applicator includes such a fluid bag, the anti-kink housing preferably exhibits a stiffness that is significantly greater than the stiffness of the walls of the fluid bag. Preferably, the stiffness of the anti-kink housing is selected to ensure that buckling of the anti-kink housing does not occur when pressure is applied to the wrapped portion of the subject to measure the subject's blood pressure. At the same time, the anti-kink housing should be sufficiently flexible to allow the anti-kink housing to reduce its inner diameter when pressure is applied by the pressure applicator (e.g., by inflating the fluid bag of the pressure applicator).

[0062] The anti-kink housing is a reinforcing component, which is configured to ensure the stiffness of the measuring device for pressure measurement. The anti-kink housing may be the only reinforcing component of the measuring device, said reinforcing component exhibiting structural solidity or strength and being configured to provide stiffness against compressive forces during pressure measurement. In particular, the reinforced anti-kink housing may be pressed against the wrapped part of the object without any further reinforcing elements being interposed, i.e. between the reinforced anti-kink housing and the wrapped part of the object, preferably no further elements providing any reinforcing function are present.

[0063] Preferably, the anti-kink housing is a reinforced one-piece housing. This design allows providing sufficient rigidity in a straightforward manner.

[0064] Preferably, the anti-kink housing is dimensioned to overlap when surrounding the part of the subject. In other words, the anti-kink housing preferably completely surrounds the body part of the subject, at least from the time the pressure is applied by the pressure applicator. Thus, kinks or wrinkles can be avoided or at least significantly reduced along the entire circumference of the measuring device.

[0065] Since kinks or wrinkles are prevented or at least significantly reduced by the accommodating kink housing, the overlapping parts of the housing (i.e. the lateral ends of the housing) should be able to move or slide relative to each other when the inner diameter of the housing is reduced due to the supply of pressurized fluid (preferably air) to a fluid bag of, for example, a pressure applying element. Therefore, the measuring device (especially the anti-kink housing) is preferably designed so that the overlapping parts can easily slide relative to each other. For example, the surface parts of the housing that are in direct sliding contact with each other can exhibit a relatively low friction coefficient, for example by correspondingly selecting the material and / or surface structure. In the context of the present invention, the term "low friction coefficient" relates to a friction coefficient of 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.

[0066] In examples, the housing, in particular the anti-kink housing, is made of metal and / or plastic, in particular fiber reinforced plastic. For example, the housing can be made of a thermoplastic material or coated with a thermoplastic material, preferably made of polyurethane or polyolefin, more preferably made of polyethylene and / or polytetrafluoroethylene (PTFE) or coated with PTFE. For example, the housing can be made of a thermoplastic material that provides a surface to which the adhesive can be durably adhered. If the housing comprises a fiber reinforced plastic material, the fibers can be natural fibers, organic fibers or inorganic fibers.

[0067] In particular, if the housing is made of a plastic material, the housing exhibits a thickness in the range of 0.25 mm to 6 mm, more preferably in the range of 1 mm to 3 mm, even more preferably in the range of 1.0 mm to 2.0 mm, in one example. For example, the housing may have a thickness of 1.5 mm, in particular for adults. Alternatively, the housing may have a thickness of 0.5 mm, in particular for newborns and young children. In a preferred embodiment, the housing is made of polyethylene (PE) having a thickness of 1.5 mm.

[0068] In an example, to avoid kinking on the one hand and to allow a reduction in the inner diameter on the other hand, the anti-kink housing exhibits an elastic modulus greater than 50 MPa, more preferably in the range of 100 MPa to 10 GPa, even more preferably in the range of 200 MPa to 1 GPa.

[0069] The present invention also relates to an apparatus for determining blood pressure of a subject, the apparatus comprising: a) a pressure signal providing unit configured to provide a measured non-invasive oscillometric pressure signal of the subject over a period of time, wherein the measured pressure signal is indicative of blood pulsation and comprises a plurality of pressure pulses; and b) a processor configured to:

[0070] - determining a blood pressure determination curve based on the plurality of pressure pulses,

[0071] - determining a first peak of the blood pressure determination curve, the peak value of the first peak being greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve,

[0072] - determining the position of the maximum of the derivative of the blood pressure determination curve before the determined first peak,

[0073] - The blood pressure is determined based on the position of the maximum of the derivative of the determined blood pressure determination curve and the measured pressure signal.

[0074] A non-invasive oscillometric pressure signal can be measured using a measuring device having a cuff that is wrapped around a body part of the subject, such as the subject's upper arm, forearm or wrist, wherein the cuff does not need to include a housing. Other known non-invasive measuring devices for measuring oscillometric pressure signals may also be used. The pressure signal providing unit may be a receiving unit configured to receive a pressure signal from, for example, a measuring device and to provide the received pressure signal. However, the pressure signal providing unit may also be a memory in which previously measured pressure signals have been stored and from which the pressure signal can be retrieved to provide the pressure signal. The pressure signal providing unit may also be or include a measuring device for measuring the pressure signal.

[0075] The blood pressure determination curve may be an envelope of the non-invasive oscillometric pressure signal. For example, the envelope may be formed as a peak-to-peak or baseline-to-peak envelope. In particular, the envelope may be determined as described in the article "Oscillometric Blood Pressure Estimation: Past, Present, and Future" by M. Fouzanfar et al., IEEE Reviews in Biomedical Engineering, Vol. 8, pp. 44-63 (2015), which is incorporated herein by reference or by using another known technique.

[0076] The processor may be configured to determine the blood pressure based on an average value of the oscillometric pressure at the location of the determined maximum value. The average value is the average curve that no longer includes oscillations. In other words, the oscillations of the measured pressure signal are near or in the vicinity of the average curve. The average value may be determined by using, for example, a moving average filter that averages the pressure signal. In an embodiment, the processor is configured to determine the systolic blood pressure by multiplying the average value of the oscillometric pressure at the location of the determined maximum value by a predefined factor, wherein the predefined factor may be predefined by calibration.

[0077] In another aspect of the present invention, a method for determining blood pressure of a subject is provided, wherein the method comprises:

[0078] - providing a measured pressure signal (TP) of the object over a period of time by a pressure signal providing unit, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising: a) a shell configured to enclose a portion of the object through which blood flows; b) a pressure applicator configured to apply pressure to the shell and thereby to the enclosed portion of the object from outside the shell; and, c) a pressure sensor configured to measure the pressure signal on the skin of the enclosed portion of the object, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal is indicative of blood pulsation and comprises a plurality of pressure pulses,

[0079] - determining a blood pressure determination curve based on the plurality of pressure pulses, wherein the blood pressure determination curve indicates a dependency of the pressure pulses on the applied pressure,

[0080] - applying a transformation to said blood pressure determination curve, and

[0081] - Determining the blood pressure based on the result of said transformation.

[0082] The invention also relates to a method for determining the blood pressure of a subject, the method comprising:

[0083] - providing a measured non-invasive oscillometric pressure signal of the subject over a period of time, wherein the measured pressure signal is indicative of blood pulsation and comprises a plurality of pressure pulses,

[0084] - determining a blood pressure determination curve based on the plurality of pressure pulses,

[0085] - determining a first peak of the blood pressure determination curve, the first peak having a peak value that is greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve,

[0086] - determining the position of the maximum of the derivative of the blood pressure determination curve before the determined first peak,

[0087] - The blood pressure is determined based on the position of the maximum of the derivative of the determined blood pressure determination curve and the measured pressure signal.

[0088] Note again that the maximum value of the derivative preferably relates to the direction from low applied pressure to high applied pressure. In other words, preferably, when measuring the pressure signal for determining blood pressure, the derivative is considered in the direction from low applied pressure to high applied pressure, regardless of whether the applied pressure is increasing or decreasing.

[0089] It should also be noted that the word "before" here relates to the direction from low applied pressure to high applied pressure. Therefore, if the applied pressure increases when measuring the pressure signal for determining blood pressure, the word "before" also means before in time, and if the applied pressure decreases when measuring the pressure signal for determining blood pressure, the word "before" means after in time.

[0090] As described above, if the blood pressure determination curve has only a single peak, the single peak is the total maximum peak and is also the first peak having a peak value greater than a predefined percentage of the peak value of the total maximum peak.

[0091] In another aspect of the present invention, a computer program for determining blood pressure is provided, wherein the computer program comprises program code means for causing an apparatus for determining blood pressure to perform the steps of the method for determining blood pressure.

[0092] The invention also relates to a computer program for determining blood pressure, wherein the computer program comprises program code means for causing an apparatus for determining blood pressure to:

[0093] - determining a blood pressure determination curve based on a plurality of pressure pulses of a provided non-invasive oscillometric pressure signal of the subject over a period of time, wherein the measured pressure signal is indicative of blood pulsation and comprises the plurality of pressure pulses,

[0094] - determining a first peak of the blood pressure determination curve, the first peak having a peak value that is greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve,

[0095] - determining the position of the maximum of the derivative of the blood pressure determination curve before the determined first peak,

[0096] - The blood pressure is determined based on the position of the maximum of the derivative of the determined blood pressure determination curve and the measured pressure signal.

[0097] The apparatus, the method and the computer program may be adapted to determine the blood pressure continuously, ie performing several subsequent blood pressure measurements, or to determine the blood pressure discontinuously, ie for example once.

[0098] It shall be understood that the processor, the method and the computer program have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0099] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above embodiments with the respective independent claim.

[0100] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] In the following figures:

[0102] Figure 1 An embodiment of an apparatus for determining the blood pressure of a subject with an inflated blood pressure cuff of the measuring device is schematically and exemplarily shown, the apparatus comprising a measuring device,

[0103] Figure 2 A housing of a measuring device wrapped around the upper arm of a subject is schematically and exemplarily shown;

[0104] Figure 3 The device is shown schematically and exemplarily with a deflated blood pressure cuff.

[0105] Figure 4 Schematically and exemplarily shown are measured tissue pressure and other values ​​derived from the tissue pressure measurement,

[0106] Figures 5 to 8 illustrates the calculation of different characteristics of the pressure pulse that measures tissue pressure,

[0107] Fig. 9 schematically and exemplarily showing an end determination curve and a blood pressure determination curve,

[0108] Fig.10 The determination of a blood pressure value by using a blood pressure determination curve is schematically and exemplarily illustrated,

[0109] Fig.11 schematically and exemplarily showing a plurality of curves for blood pressure determination, including a curve corresponding to a derivative of a blood pressure determination curve,

[0110] Fig.12 Several examples of continuous blood pressure measurements are shown schematically and exemplarily,

[0111] Fig.13 Another example of several continuous blood pressure measurements is shown schematically and exemplarily, and

[0112] Fig.14 A flow chart illustrating an embodiment of a method for determining blood pressure of a subject is shown. DETAILED DESCRIPTION

[0113] Figure 1 Schematically and exemplarily, a device 1 for determining the blood pressure of a subject is shown. The device 1 comprises a housing 4 which can be Figure 2 and is configured to wrap around a portion 5 of the subject through which blood flows. In this embodiment, the portion 5 of the subject is the subject's arm, wherein Figure 25 shows a brachial artery 13 in the arm 5, and wherein the arrow in the brachial artery 13 indicates the direction of blood flow away from the heart. The device 1 also includes a pressure sensor 7, which is arranged inside the housing 4 and is configured to measure the pressure on the skin of the wrapped arm 5 of the subject. The measured pressure can also be regarded as tissue pressure (TP). Figure 2 As shown, the pulse wave in the brachial artery 13 causes a pressure wave 12, which is transmitted to the pressure sensor 7 via the tissue of the arm 5. Therefore, the measured pressure signal will include pressure pulses indicating blood pulsation. For clarity, Figure 1 The housing 4 is not shown.

[0114] The device 1 further comprises a cuff 6 which surrounds the housing 4 and can be inflated by applying pressure to the housing 4 and thereby to the subject's wrapped arm 5 from outside the housing 4 using a pump 8. Since the cuff 6 and the pump 8 together are capable of applying pressure to the housing 4 and thereby to the subject's wrapped arm 5, they can be considered to form a pressure applicator 6, 8. Furthermore, the housing 4, the pressure applicator 6, 8 and the pressure sensor 7 can be considered to be parts of a measuring device controlled by the processor 3. The housing 4 with the cuff 6 is preferably an anti-kink housing cuff as described in WO2014 / 121945A1.

[0115] The processor 3 is configured to control the measuring device so that the pressure applicators 6, 8 increase the applied pressure during a measuring time period extending to the end measurement time point and reduce the applied pressure during a subsequent blood pressure measurement post-time period, and the pressure sensor 7 measures the pressure on the skin, i.e., the tissue pressure TP, at least during the measuring time period. In addition, the processor 3 is configured to control the pressure applicators 6, 8 so that they increase the applied pressure at a first rate during a preceding measuring time period, which is followed by a measuring time period, and increase the applied pressure at a second rate during the measuring time period, wherein the first rate is greater than the second rate. Figure 1 , the control of the measuring device is shown such that the cuff 6 is inflated and the applied pressure thus increases, ie the thick arrow indicates the inflation.

[0116] The device 1 includes a valve 20 which, when open, allows compressed air within the system to leave the system and enter the surrounding atmosphere, thereby deflating the cuff. Figure 3 In FIG. 1 , this deflation situation with the pump 8 switched off is indicated by a thick arrow.

[0117] The processor 3 may be seen as comprising a control part 10 for controlling the pump 8 and the valve 20 and a processing part 11, which is in particular configured to perform some calculations as will be explained further below. The apparatus 1 may also comprise a display 22 for displaying, for example, the measured blood pressure value. Although in this embodiment the processor 3 also controls the measurement, wherein the control part 10 may determine how to control the measurement based on the output of the processing part 11, in other embodiments the processor may not be used to control the measurement, but rather to process the measurement data, for example after the measurement has been completed.

[0118] In the preceding measurement period (which may also be considered a fast inflation period), the processor 3 controls the device 1 so that the valve 20 is closed and the pump 8 inflates the cuff 6 at a larger first rate. In the subsequent measurement period, the processor 3 also controls the device 1 so that the valve 20 is closed, but the pump 8 is controlled so that the inflation of the cuff 6 continues at a lower second rate. Therefore, the measurement period may also be considered a slow inflation period.

[0119] Figure 4 The relationship between the measured pressure TP and the time t is shown schematically and exemplarily. The first inflation in the previous measurement time period starts with a tissue pressure TP, i.e., an accessory pressure Patt, which is the tissue pressure measured in the uninflated cuff 6. For example, the accessory pressure Patt can be in the range of 0 to 15 mmHg. An accessory pressure Patt of up to 15 mmHg has been shown not to cause venous congestion for more than 12 hours, making the assembly of the shell 4 and the cuff 6 most suitable for long-term monitoring. For this reason, it is preferred that the accessory pressure Patt is not greater than 15 mmHg. Figure 4 In FIG. 1 , arrow 30 indicates the beginning of the pre-measurement period, i.e. the beginning of the rapid inflation period. During this pre-measurement period, the portion of the entire tissue pressure range that has no or substantially no information for determining the blood pressure should be passed as quickly as possible. Therefore, during the pre-measurement period, the inflation rate is preferably as large as possible. For example, the inflation rate relative to the tissue pressure TP may be equal to or greater than 8 mmHg / s. This pre-measurement period with a rapid inflation rate is Figure 4 The test ends at the tissue pressure value indicated by “TPlow” in the flow chart.

[0120] The tissue pressure value TPlow also indicates the beginning of a measurement period having a second, slower inflation rate. Figure 4, this start of the measurement time period (which can also be regarded as a slow inflation period) is indicated by an arrow 31. In an embodiment, the processor 3 is configured to control the pump 8 so that at the end of the previous measurement time period, the measured pressure TPlow is in the range of 15 to 30 mmHg. Therefore, in an embodiment, the tissue pressure TPlow can be predefined as a value between 15 and 30 mmHg. However, in case an arterial diastolic pressure (DAPprev) determined in a previous measurement is available, the tissue pressure TPlow can depend on this arterial diastolic pressure and the tissue pressure TPlow can also be larger. This larger TPlow Figure 4 Schematically shown in . For example, the processor 3 can be configured to store (or access a memory to store) a previous arterial diastolic pressure DAPprev. The previous arterial diastolic pressure DAPprev has been obtained by a previous blood pressure measurement and can be used to determine the tissue pressure TPlow. The tissue pressure TPlow should appear at the end of the previous measurement time period, that is, at the end of the first inflation period, and can therefore also be regarded as the first end measurement pressure. The tissue pressure TPlow is determined based on the previous arterial diastolic pressure DAPprev so that the tissue pressure TPlow is less than the previous arterial diastolic pressure DAPprev. Preferably, the processor is configured to control the pump 8 so that the measured pressure at the end of the previous measurement time period is equal to the determined first end measurement pressure TPlow. In an embodiment, the processor 3 determines the tissue pressure TPlow at the end of the previous measurement time period so that it is not higher than a predetermined percentage of the previous arterial diastolic pressure DAPprev. This can ensure that all necessary tissue pressure pulse curves are recorded, thereby accurately calculating the blood pressure. The calculation of blood pressure based on the measured tissue pressure will be further explained below. The predetermined percentage is preferably 90%.

[0121] For example, blood pressure may change between measurements due to clinically relevant events occurring to the subject. It has been found that in the most severe cases of acute blood loss during surgery, the diastolic arterial pressure (DAP) may drop by about 30% within one minute. In order to cope with these possible changes in blood pressure, the processor 3 may be adapted to determine the tissue pressure TPlow based on the previous diastolic arterial pressure DAPprev and based on the duration of the interruption time between measurements. Therefore, the processor 3 may be configured to further store (or access a memory to store) the time at which the previous diastolic arterial pressure DAPprev was measured, and determine the first end measurement pressure TPlow based on i) the previous diastolic arterial pressure DAPprev and ii) the time distance to the blood pressure measurement, as indicated by the stored time, at which the previous diastolic arterial pressure DAPprev was measured. An exemplary specific equation for determining the first end measurement pressure TPlow will be further given below.

[0122] The second inflation rate applied during the measurement period is preferably in the range of 1 mmHg / s to 6 mmHg / s, the lowest inflation rate is preferably 1.5 mmHg / s, and the highest inflation rate is preferably 2.5 mmHg / s. It has been found that the second inflation rate within this range can accurately determine the blood pressure. It should be noted that these rates are related to the changes in the tissue pressure TP measured by the pressure sensor 7.

[0123] In an embodiment, the slower second inflation rate depends on the heart rate (HR) and / or the pulse pressure (PP), which is the difference between the systolic pressure and the diastolic 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 can be linear, or it can be described by another functional relationship. In an embodiment, the functional relationship is such that at a heart rate HR of 40 / min and a pulse pressure PP of 20mmHg, the tissue pressure inflation rate is 1mmHg / s, and at a heart rate HR of 80 / min and a pulse pressure PP of 100mmHg, the tissue pressure inflation rate, i.e., the second slow inflation rate is 10mmHg / s. The measurement time period ends at the end measurement time point 32, after which immediate rapid deflation is preferentially performed at the maximum possible reduction rate, because tissue pressure data does not need to be collected after the end measurement time point 32.

[0124] exist Figure 4 , time interval 40 indicates the inflation / deflation time period from the start of rapid inflation 30 to the time when the tissue pressure TP drops below 20 mmHg during rapid deflation to allow venous return. Time period 41 indicates the cycle time, i.e., the time between the start of a measurement and the start of the next measurement, and time period 42 indicates the break period, i.e., the difference between the inflation / deflation time period 40 and the cycle time 41.

[0125] Figure 4 Also shown is an average pressure TPcl, which can be viewed as the tissue clamping pressure affecting the tissue when the cuff 6 is attached to the subject's arm 5 (e.g., upper arm). The average pressure TPcl can be calculated by applying a low-pass filter to the tissue pressure TP, wherein the low-pass filter can be located within the processor 3. The size of the low-pass filter is preferably set so that the average pressure TPcl only includes frequencies below the expected minimum pulse rate (PRni). The preferred low-pass filter will be further described below. The processor 3 is preferably configured to determine the AC component TPac of the tissue pressure by subtracting the average pressure TPcl from the measured tissue pressure TP, that is, TPac=TP-TPcl. Figure 4 In the figure, the TPac curve is magnified 2 times to improve the visibility of the curve.

[0126] During slow inflation, i.e. during the measuring period, a TP pulse curve and / or a TPac pulse curve is recorded which can be analyzed simultaneously, i.e. online, wherein the TP pulse curve and / or the TPac pulse curve has a tissue pressure waveform (TPW) comprising information allowing an accurate determination of the blood pressure. Since the blood pressure is measured non-invasively (although its accuracy is comparable to that of invasively measured blood pressure), it can be abbreviated to niBP, meaning "non-invasive blood pressure". Figures 5 to 8 The TPac pulse curve is shown schematically and exemplarily in FIG.

[0127] In the following, the TPac pulse curve is used to determine the characteristics of the pressure pulse 9. Therefore, the TPac pulse curve can be regarded as a characteristic determining pulse curve or a characteristic determining pulse. Figures 5 to 8 Therefore, it is shown that the characteristic determination pulse curve or the characteristic determination pulse 29 is a TPac pulse. In another embodiment, the characteristic determination pulse can also be directly a TP pulse curve, that is, the pressure pulse 9 can be used directly to determine the characteristics. The processor 3 is configured to determine at least one feature characterizing the corresponding pressure pulse for a corresponding pressure pulse in the plurality of pressure pulses 9. The feature determined for the pressure pulse 9 indicates the pressure pulse 9, that is, for example, indicates the shape of the pressure pulse 9 and / or characterizes the pressure value of the pressure pulse 9.

[0128] In an embodiment, the processor 3 is configured to determine the difference TPP between the maximum measured pressure and the minimum measured pressure of the corresponding characteristic determination pulse 29 as the characteristic of the corresponding pressure pulse. Figure 5 Describe the feature.

[0129] The difference TPP is the difference between the maximum systolic pressure (TPsys) of the characteristic-determining pulse and the pressure (TPdia) at the end-diastolic point of the characteristic-determining pulse, TPdia being preferably the minimum pressure of the corresponding characteristic-determining pulse. Figure 5 as well as Figures 6 to 8 In FIG. 2 , the terms “t.start” and “t.stop” indicate the start and end of the corresponding pulse 29 , respectively.

[0130] The processor 3 may also be configured to determine a pulse duration (t(Pulse)), which is the time difference between the end-diastolic point of a characteristic determining pulse 29 and the next end-diastolic point. The characteristic may also be defined as the time difference between the start (t.start) of the corresponding pulse and the end (t.stop) of the corresponding pulse. The characteristic is Figure 6 Shown in.

[0131] The processor 3 may also be adapted to determine a pulse area (TPA) of the corresponding pulse 29, the pulse area (TPA) being the area under the curve of the corresponding pulse within the time defined by t.start to t.stop and ranging from the pressure at the end-diastolic point of the characteristic-determining pulse (TPdia) to the maximum systolic pressure (TPsys) of the characteristic-determining pulse. Figure 6 As shown, the pulse area TPA is scaled to TPP = 1. This scaled pressure pulse area is named "TPA.norm".

[0132] The processor 3 may also be adapted to determine the pulse half-width (W50) of the corresponding pulse 29, such as Figure 7 shown.

[0133] Furthermore, the processor 3 may be adapted to determine the area TPA+.top50 enclosed by the upper part of the characteristic determination pulse 29, such as Figure 8 . The upper end of the area TPA+.top50 enclosed by the upper part is at the maximum systolic pressure TPsys of the characteristic determination pulse 29, and the lower end of the area TPA+.top50 of the upper part is between the maximum systolic pressure TPsys of the characteristic determination pulse 29 and the pressure value corresponding to the average value TPcl of the measured pressure TP. Since the characteristic determination pulse 29 has been determined by subtracting the average value TPcl from the measured pressure TP, the pressure value corresponding to the average value TPcl of the measured pressure TP is zero. Preferably, the processor 3 is configured to determine the area TPA+.top50 enclosed by the upper part of the characteristic determination pulse so that the lower end of the upper part is at a pressure value corresponding to half of the pressure distance TPP+ between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure value corresponding to the average value TPcl of the measured pressure TP.

[0134] Figures 5 to 8 The TPac pulse curve is shown so that in this example also features are defined based on the TPac pulse curve. However, as described above, these or other features may also be defined based on the TP pulse curve.

[0135] The processor 3 is also configured to determine a blood pressure determination value TPWP_M for a corresponding pressure pulse based on at least one determined feature, so that several blood pressure determination values ​​TPWP_M are determined for several pressure pulses existing at different times, wherein the processor 3 is configured to determine a blood pressure determination curve TPW_M-curve, so that several blood pressure determination values ​​TPWP_M determined for several pressure pulses and therefore for several times form a blood pressure determination curve TPW_M-curve.

[0136] The processor 3 is configured to determine the blood pressure determination value TPWP_M based on the characteristics determined for the pressure pulse 9. Therefore, similarly to the characteristics determined for the pressure pulse 9, the blood pressure determination value TPWP_M also indicates the pressure pulse 9. Since 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 therefore for several times, wherein the applied pressure varies over time, the blood pressure determination curve TPW_M-curve indicates the dependency of the pressure pulse 9 on the applied pressure.

[0137] The processor 3 is also configured to apply a transformation to the blood pressure determination curve TPW_M-curve and determine the blood pressure based on the result of the 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 a derivative, i.e., a first-order derivative, so that the result of the transformation (i.e., TPW_M-curve') is the first-order derivative of the blood pressure determination curve TPW_M-curve, but in other embodiments, the transformation may be a different transformation, wherein the possible different transformations may correspond to applying a function such as a logarithm or a higher derivative to the blood pressure determination curve TPW_M-curve. Although this is not necessarily the case in general, in this embodiment, the processor 3 is configured to determine the blood pressure also based on the blood pressure determination curve TPW_M-curve itself.

[0138] Specifically, the processor 3 is configured to determine the position of the maximum value (TPW_M-curve.max) of the derivative TPW_M-curve' of the blood pressure determination curve TPW_M-curve, and additionally determine the position of the maximum value (TPW_M-curve.max) of the blood pressure determination curve TPW_M-curve, and determine the blood pressure based on the two determined positions and the measured pressure TP. For example, the processor 3 is configured to determine the systolic arterial blood pressure (SAPni) based on the average value TPcl of the measured pressures TP at the two determined positions according to the following equation:

[0139] SAPni=α·(TPcl@TPW_M-curve.max)

[0140] +β·(TPcl@TPW_M-curve'.max)(1)

[0141] Therein, the parameters α and β can be predetermined by calibration (in particular based on linear regression) as reference values ​​for very accurately, possibly non-invasively determined systolic arterial blood pressure, such as by using the method of least squares. Exemplary values ​​of α and β that have been determined during calibration using an exemplary data set are α=1.43 and β=-0.25.

[0142] The processor 3 may be configured to determine the position of the maximum of the first 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 predefined percentage of the peak value of the total peaks of the blood pressure determination curve and by determining the position of the maximum of the derivative of the blood pressure determination curve that precedes the determined first peak. The predefined percentage of the total peak may be predetermined by calibration. In a preferred embodiment, the predefined percentage is 90%. The determination of the first peak of the blood pressure determination curve may be achieved by normalizing the blood pressure determination curve to the peak value of the total maximum peak, the first peak having a peak value greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve, such that the peak value is 1 after normalization. The predefined percentage is then a fixed absolute value between 0 and 1, and is preferably 0.9.

[0143] Preferably, the processor 3 is configured to provide a function that receives as input at least one feature of the respective pressure pulse and outputs a respective blood pressure determination value TPWP_M, which together with the blood pressure determination values ​​determined for the other pressure pulses forms a blood pressure determination curve TPW_M-curve. The function has at least one parameter that can be determined by calibration, wherein a reference blood pressure value is determined very accurately in an invasive manner, and the at least one parameter is determined such that the device produces very accurate invasively measured blood pressure values ​​with high statistical precision and accuracy.

[0144] According to the above equation (1), once the parameters α and β have been predetermined based on the reference measurement results, the systolic arterial blood pressure (SAPni) can also be considered to be determined by a fixed function of the two positions TPW_M-curve.max and TPW_M-curve'.max, wherein the linear dependence of the function on the two positions is represented by the predetermined parameters α and β. Therefore, the processor 3 is effectively configured to provide a first function for determining the blood pressure determination value TPWP_M from the pressure pulse 9 so as to form a blood pressure determination curve TPW_M-curve, and to provide a second function corresponding to equation (1) for determining the blood pressure based on TPW_M-curve and its transformation TPW_M-curve'.

[0145] In a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M, and the blood pressure determination value TPWP_M depends only on the characteristics of the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia at the end-diastolic point of the characteristic determination pulse. Therefore, in an embodiment, the function (i.e., the first function) for determining the blood pressure determination value TPWP_M depends on TPP, but does not depend on any other characteristics of the pressure pulse. In this case, for example, the blood pressure determination value TPWP_M can be determined according to the following equation:

[0146] TPWP_M=c·TPP exp1 ,(2)

[0147] Wherein c and exp1 are predetermined constants. For example, c and exp1 may be predetermined by calibration. However, it has been found that they may also be selected to be equal to 1, ie, c=1=exp1, so that TPWP_M=TPP.

[0148] Furthermore, in a preferred embodiment, the processor 3 is configured to form a blood pressure determination curve TPW_M-curve based on the blood pressure determination value TPWP_M, which depends only on a) a feature of the difference TPP between the maximum systolic pressure TPsys of the characteristic determination pulse and the pressure TPdia of the characteristic determination pulse at the end of diastole, and b) a feature of the area TPA+.top50 enclosed by the upper part of the characteristic determination pulse. Therefore, in an embodiment, the function for determining the blood pressure determination value TPWP_M (which is referred to as the above-mentioned first function) depends on TPP and TPA+.top50, but does not depend on other features of the pressure pulse. In this case, for example, the blood pressure determination value TPWP_M can be determined according to the following equation:

[0149] TPWP_M=c·TPA+.top50 exp2 TPP exp1 , (3)

[0150] Wherein c, exp1 and exp2 are predetermined constants. For example, c can be equal to 1 again, i.e. c=1, wherein exp1 and exp2 can be predetermined by calibration for equation (3). However, the constant c can also 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).

[0151] Preferably, the processor 3 is further configured to determine an end measurement time point 32 based on at least one feature determined for the plurality of pressure pulses 9, at or after which the measurement time period is stopped. Specifically, the processor 3 may be configured to determine, for each pressure pulse, an end determination value TPWP_E based on at least one feature that has been determined for the corresponding pressure pulse.

[0152] Preferably, the processor is configured to further provide a function, i.e., another function, which receives at least one feature of the corresponding pressure pulse as input and outputs a corresponding end determination value TPWP_E, which together with the end determination values ​​determined for other pressure pulses forms an end determination curve. The function also has at least one parameter that can be determined by calibration. For example, the end determination value TPWP_E can be determined according to the following formula:

[0153] TPWP_E=c·TPP exp3 , (4)

[0154] or according to

[0155] TPWP_E=c·TPA+.top50 exp4 TPP exp3 , (5)

[0156] Wherein, c, exp3 and exp4 are predetermined constants of equations (4) and (5), respectively. For example, c may be equal to 1, i.e., c=1, and exp3 and possibly exp4 may be predetermined by calibration, respectively, to fix equations (4) and (5). In an embodiment, for any one of equations (4) and (5), the constant c may also be determined by calibration instead of 1.

[0157] It should be noted that constants such as c, exp1, exp2 and exp3 (appearing in more than one equation as in the above case) can generally have the same or different values ​​in the respective different equations. Thus, for example, these constants can also be referred to by additional indices associated with the respective equations, which are however omitted here. However, it should be understood that, for example, in order to fix the above equations (2) to (5), six index values ​​are required.

[0158] The end determination value TPWP_E may also be determined as follows.

[0159] In particular, the processor 3 may be configured to multiply a) the determined pulse area TPA.norm raised to a predetermined seventh exponential (exp7) power by b) the determined difference TPP raised to a predetermined eighth exponential (exp8) power. Thus, the difference TPP may be calculated according to the equation TPWP_E=TPA.norm. exp7 TPP exp8(wherein, exp7≠0, exp8≠0 is predetermined) to calculate the end determination value TPWP_E.

[0160] The processor 3 may also be configured to determine the end determination value TPWP_E by dividing a) the determined pulse area TPa.norm to a predetermined ninth exponential (exp9) power by b) the determined pulse duration t(pulse) to a predetermined tenth exponential (exp10) power, and multiplying the quotient by c) the determined difference TPP to a predetermined eleventh exponential (exp11) power. This can be expressed as TPWP_E=TPA.norm exp9 / t(Pulse) exp10 TPP exp11 To express, where it is predetermined that exp9≠0, exp10≠0, exp11≠0.

[0161] The processor 3 may also be configured to calculate the value of the TPWP_E based on the equation discussed in the previous two paragraphs, for example, by using TPWP_E = TPA.norm exp7 TPP exp8 and TPWP_E = TPA.norm exp9 / t(Pulse) exp10 TPP exp11 The calculation result obtained by one of the equations is multiplied by another predetermined exponent of the half-width (W50) to determine the end determination value of the corresponding pressure pulse. For example, if the former of the two equations is multiplied by the half-width W50, then the equation TPWP_E = TPA.norm exp12 / t(Pulse) exp13 TPP exp14 ·W50 exp15 Generates a result, where it is predetermined that exp6≠0, exp7≠0, exp8≠0, exp9≠0.

[0162] Therefore, in this embodiment, based on at least TPP and TPA.norm for the corresponding pulse curve, TPWP_E reflecting the characteristic value for the corresponding pulse curve can be calculated by combining and weighting the amplitude and area parameters, wherein any TPWP_E can be expanded by multiplying by the power of the corresponding exponent of W50.

[0163] As described above, the exponents of the different equations are predetermined by calibration. For example, in a preferred embodiment, the formula TPWP_E = TPA.norm is used. exp9 / t(Pulse) exp10 TPP exp11 , where exponents exp9=1.1, exp10=0.4, and exp11=0.5.

[0164] The processor 3 is preferably configured to determine the end determination curve TPW_E-curve so that it satisfies one of the following conditions: a) the maximum value (TPW_E-curve.max) of the end determination curve occurs in time before the maximum value (TPW_M-curve.max) of the blood pressure determination curve, b) the maximum value (TPW_E-curve.max) of the end determination curve occurs in time at or after the maximum value (TPW_M-curve.max) of the blood pressure determination curve, and the decrease of the end determination curve TPW_E-curve after its maximum value is steeper than the decrease of the blood pressure determination curve TPW_M-curve after its maximum value, and c) the end determination curve TPW_E-curve is the same as the blood pressure determination curve TPW_M-curve. Therefore, the parameters of the function are preferably predefined so that a) TPW_E-curve.max occurs before TPW_M-curve.max in time, or b) TPW_E-curve.max occurs at or after TPW_M-curve.max in time, but TPW_E-curve has a negative derivative whose absolute derivative value is greater than the absolute derivative value of the negative derivative of the blood pressure determination curve TPW_M-curve after its maximum value, or c) TPW_E-curve can be the same as TPW_M-curve, that is, the end determination curve and the blood pressure determination curve can be the same.

[0165] exist Fig. 9 , a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve are shown by way of example, wherein these curves have been normalized so that the respective maximum values ​​correspond to 100%.

[0166] It is desirable to terminate each blood pressure measurement as quickly as possible to minimize the stress on the subject (i.e., the object). The blood pressure measurement can be terminated once the maximum value of the blood pressure determination curve TPW_M-curve has been formed, and the blood pressure measurement can therefore be completely determined, because in this case, the maximum value of the blood pressure determination curve TPW_M-curve is used for non-invasive blood pressure determination. It should be noted that only the maximum value of the derivative TPW_M-curve' of the blood pressure determination curve is used, and the blood pressure measurement has been terminated once this maximum value is formed. Therefore, during the measurement time period, it is checked when the end criterion defining the end measurement time point is reached, wherein, in order to determine when the end criterion is reached and thus determine the end measurement time point, the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve are preferentially used. For example, when the end determination curve TPW_E-curve has formed its maximum value, it can be checked with each newly measured TP pulse curve (i.e. with each newly measured TP pulse) whether a) the end determination curve TPW_E-curve has fallen below a percentage of the maximum value of the end determination curve TPW_E-curve, wherein the percentage is preferably in the range from 40% to 95%, and whether b) the blood pressure determination curve TPW_M-curve has formed its maximum value, i.e. has reached or exceeded its maximum value. The processor 3 can be configured to determine the end measurement time point 32 as a time point that satisfies both conditions a) and b).

[0167] In order to safely determine whether the blood pressure determination curve TPW_M-curve reaches or exceeds its maximum value, it may be detected whether the blood pressure determination curve TPW_M-curve drops after its maximum value.

[0168] In an embodiment, either of the blood pressure determination curve TPW_M-curve and its transformed version TPW_M-curve' may be a smooth curve, so that any maximum of the two curves is also smooth. The smoothing process for smoothing the blood pressure determination curve TPW_M-curve may include, for example, filtering and / or fitting, wherein the transformed blood pressure determination curve TPW_M-curve' may have been smoothed because the blood pressure determination curve itself and the transformation applied thereto are smooth. For example, taking a derivative or applying a smoothing function is a smooth transformation. In addition, after the corresponding smooth maximum value, several pressure pulses may be considered to explicitly detect the corresponding smooth maximum value, wherein the number of these several pulses may be predetermined, or may depend on the heart rate of the subject. For example, the number may increase with increasing heart rate. In an embodiment, for a heart rate of 60 / min, the number is 3, and for a heart rate of 200 / min, the number is 10.

[0169] In order to smooth the blood pressure determination curve TPW_M-curve, a moving average filter, in particular a variable moving average filter, applied to the blood pressure determination values ​​TPWP_M determined for the pressure pulses can be used. The window for averaging can be fixed or variable, wherein, in the latter case, it preferably has a maximum duration of, for example, 8s. The use of this filter results in a filter delay, wherein the minimum filter delay is as long as the duration of several pulses added together. A filter delay with a length of several pulses is sufficient to safely determine the falling smoothed blood pressure determination curve TPW_M-curve and, therefore, the maximum value in the blood pressure determination curve TPW_M-curve. This means that once a decrease in the smoothed blood pressure determination TPW_M-curve is detected, the measurement period will be terminated without the need to collect more pressure pulses. This is possible because, in this example, the blood pressure determination curve TPW_M-curve is smoothed with a relatively large variable moving average filter window with, for example, at least three TP pressure pulses and a maximum of 8s twice (2×8s filter), eliminating an estimated 95% of disturbing cardiopulmonary interactions in the measurement. These smoothing filter windows can be adapted to the breathing rate or ventilation rate, allowing better elimination of unwanted TPW_M-curve disturbances caused by cardiopulmonary interactions.

[0170] exist Fig. 9 In the embodiment, both conditions a) and b) are satisfied when the end determination curve TPW_E-curve drops below 90% of the maximum value of the end determination curve TPW_E-curve. Due to the filter delay, the measurement is terminated a few tissue pressure pulses after both conditions a) and b) are satisfied.

[0171] Fig. 9 The continuous TPW_E-curve and the continuous TPW_M-curve shown in are obtained by filtering the TPWP_E and TPWP_M values ​​determined for different pressure pulses, respectively. This filtering, which results in a filter delay, will be further explained below. Fig. 9 In , the filter delay results in two additional pressure pulses, so that the two pressure pulses after conditions a) and b) are met start a rapid deflation of the cuff 6 .

[0172] An end determination curve TPW_E-curve having a maximum value that occurs a few seconds earlier in time than the maximum value of the blood pressure determination curve TPW_M-curve allows shortening the measurement period, i.e., shortening the slow inflation time and reducing the amount of pressure applied to the subject. After reaching t(a_end), i.e., after reaching a point in time at which the end determination curve TPW_E-curve has fallen below a predefined percentage of the maximum value of the TPW_E-curve, if the TPW_M-curve has several maximum values, the largest maximum value of the blood pressure determination curve TPW_M-curve found so far is the absolute maximum value (TPW_M-curve.max) of the blood pressure determination curve TPW_M-curve, if the blood pressure determination curve TPW_M-curve is decreasing at time t(a_end). Otherwise, in an embodiment, the measurement will be continued until the next maximum value of the TPW_M-curve, after which the maximum value (TPW_M-curve.max) of the blood pressure determination curve will be determined.

[0173] Without using an end determination curve TPW_E-curve having a maximum value that occurs before the maximum value of the blood pressure determination curve TPW_M-curve in time, it will be necessary to continue slow inflation until the blood pressure determination curve TPW_M-curve has fallen below a certain percentage of its maximum value. On average, by using an end determination curve TPW_E-curve having a maximum value that occurs before the maximum value of the blood pressure determination curve TPW_M-curve in time, the blood pressure measurement can be terminated after about 20 to 60 seconds at TPcl in the range of 70% to 95% of the systolic arterial pressure (SAP). This is significantly lower than the end pressure level of conventional oscillometric niBP measurement. The blood pressure measurement is terminated when the clamping pressure reaches about SAP+20 mmHg. When using the above reference Figure 1 When the device 1 is used, and when the measurement is terminated, the tissue pressure TP drops as quickly as possible to Patt, where it stays for a period of time, preferably before another measurement is started. Figure 4 Within about 20% of the inflation and deflation time period 40 indicated in .

[0174] The processor 3 is configured to determine the blood pressure based on the transformed blood pressure determination curve TPW_M-curve, in particular based on the position of the maximum 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 of the blood pressure determination curve TPW_M-curve itself. The processor 3 may be adapted to perform such a determination of the blood pressure (which is non-invasive) as described above with respect to equation (1). Although determined by the processor 3, the curve TPW_M-curve′ is not included in Fig. 9 However, in the case where the transformation obtained from it is chosen as the derivative, it can be obtained from Fig. 9 TPW_M-curve' is derived from the slope of TPW_M-curve in . Fig.11 An example is shown in which the TPW_M-curve and the TPW_M-curve' are included in a single figure, which will be further described below.

[0175] In an embodiment, the processor 3 is configured to determine the TPcl value at which the derivative TPW_M-curve' of the blood pressure determination curve has its maximum value (TPW_M-curve'.max) at the time point t (TPW_M-curve'.max) and the TPcl value at which the blood pressure determination curve TPW_M-curve has its maximum value (TPW_M-curve.max) at the time point t (TPW_M-curve.max), wherein Fig.10 In the example, the TPcl values ​​at the corresponding times of the maximum values ​​are represented as "TPcl@TPW_M-curve'.max" and "TPcl@TPW_M-curve.max", respectively. Fig.10 The curve TPW_M-curve' is also not shown, but from the slope of TPW_M-curve itself having its maximum value at t(TPW_M-curve.max), it can be inferred that the derivative TPW_M-curve' of TPW_M-curve has its maximum value at time t(TPW_M-curve'.max). The time points t(TPW_M-curve.max) and t(TPW_M-curve'.max) are also Fig. 9 Shown in.

[0176] 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 may be the same as the filter used to determine, for example, the blood pressure determination curve TPW_M-curve. The resulting curve is Fig.10In the embodiment of the invention, the processor 3 is named "TPdia-curve". Furthermore, the processor 3 can be configured to determine the upper envelope of the tissue pressure TP by applying a filter to the systolic maximum of the tissue pressure TP. Furthermore, the filter can be similar to the filter used, for example, to generate the blood pressure determination curve TPW_M-curve. The curve is in Fig.10 It is named “TPsys-curve” in the paper.

[0177] Then, 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 with predetermined coefficients α and β corresponding to the calibration function given by the above equation (1). The predetermined coefficients α and β preferably make the linear combination produce a systolic arterial pressure value that can be expressed as a percentage (TPcl.s%) of TPcl@TPW_M-curve.max, wherein the percentage is preferably in the range of 100% to 150%, and further preferably in the range of 110% to 150%. Fig.10 In, the non-invasive systolic arterial pressure is named "SAPni", where the above equation (1) is shown again. Fig.10 The non-invasive systolic arterial pressure SAPni was approximately 134 mmHg.

[0178] The predetermined coefficients α and β may 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. The predetermined percentage is preferably in the range of 100% to 140%.

[0179] The processor 3 may also be configured to determine the non-invasive mean arterial pressure (MAPni) based on the transformed TPW_M-curve (particularly its derivative). For example, an equation similar to equation (1) above may be used again, namely

[0180] MAPni=α′·(TPcl@TPW_M-curve.max)+β'·(TPcl@TPW_M-curve'.max), (6)

[0181] New predetermined (i.e. respectively calibrated) coefficients α' and β' are used. The predetermined coefficients α' and β' can make the determined non-invasive mean arterial pressure (MAPni) correspond to the TPcl value, or alternatively the value of the TPdia curve, or alternatively the value of the TPsys curve, at the time point t(bx), wherein the time point t(bx) is the time point at which the blood pressure determination curve TPW_M-curve has a value bx representing a predetermined percentage relative to its maximum value. The predetermined coefficients α' and β' can make the non-invasive mean arterial pressure MAPni a predetermined percentage (TPcl.m%) of TPcl@TPW_M-curve.max, wherein the predetermined percentage is preferably in the range of 80% to 110%. Exemplary values ​​of α' and β' that have been determined during calibration using an exemplary data set are α'=0.44 and β'=0.46.

[0182] The processor 3 may also be configured to determine the non-invasive diastolic arterial pressure DAPni based on the transformed TPW_M-curve (particularly its derivative). For example, an equation similar to the above equations (1) and (6) may be used again, namely

[0183] DAPni=α″·(TPcl@TPW_M-curve.max)+β”·(TPcl@TPW_M-curve'.max), (7)

[0184] New predetermined (i.e. respectively calibrated) coefficients α" and β". are used. The predetermined coefficients α" and β". can make the determined non-invasive diastolic arterial pressure (DAPni) correspond to the value of the TPdia curve or alternatively the value of the TPcl curve at the time point t(cx), which is the time point at which the blood pressure determination curve TPW_M-curve has a value cx representing a predetermined percentage of its maximum value. The predetermined coefficients α" and β". can make DAPni a predefined percentage (TPcl.d%) of TPcl@TPW_M-curve.max, wherein the predetermined percentage is preferably in the range from 60% to 80%. Exemplary values ​​of α" and β", which have been determined during calibration using an exemplary data set, are α"=-0.08 and β"=0.88.

[0185] As described above, the parameters of the function for determining the end determination curve TPW_E-curve and for determining the blood pressure determination curve TPW_M-curve are determined by calibration. Therefore, these parameters are predetermined so that during the calibration phase, the deviation between the very accurately measured invasive blood pressure value and the blood pressure value obtained by the device 1 is minimized, and the time required for the blood pressure measurement is relatively short. Preferably, one or several parameters in the function for determining the blood pressure determination curve TPW_M-curve (i.e., the function further referred to as the first function above, which can be considered as a first set of one or several parameters) are selected so as to achieve a good balance between high-precision non-invasive blood pressure and a low TP level at the end of the measurement on the one hand, and a short measurement time on the other hand. If one or several parameters are selected so that they create a TPW_M-curve with a relatively early maximum value, the TP level at the end of the measurement and the measurement time will be relatively low. However, the accuracy and position of the non-invasive blood pressure value finally determined are also reduced. Therefore, preferably a first set of one or several parameters is selected so that the desired balance between the measurement time and the accuracy of the non-invasive blood pressure value is achieved.

[0186] Preferably, one or several parameters of the function for determining the end determination curve TPW_E-curve (i.e. the function further referred to as another function above, which can be regarded as forming another set of one or several parameters) are selected so that the maximum value of the end determination curve TPW_E-curve is relatively early. In an embodiment, the first set of one or several parameters and the second set of one or several parameters may also be the same, so that the end determination curve TPW_E-curve and the blood pressure determination curve TPW_M-curve may also be the same.

[0187] The calibration leading to predetermined values ​​of the coefficients α, β, α′, β′, α″ and β″ in the functions describing the systolic arterial blood pressure (SAPni), the mean arterial blood pressure (SAPni) and the diastolic arterial blood pressure (SAPni) with respect to the positions of the maxima of the blood pressure determination curve and its derivative (i.e., functions thereof may each be referred to as second functions in the terminology used further above) preferably corresponds to an evaluation of a calibration set consisting of simultaneously recorded measurement pairs of invasive blood pressure values ​​and non-invasive blood pressure values ​​from a sufficient number of individuals under different hemodynamic conditions. The non-invasive blood pressure values ​​are determined by the device 1 as described above, and parameters such as the coefficients α, β, α′, β′, α″ and β″ may be optimized such that the deviation between the invasive and non-invasive blood pressure values ​​is minimized.

[0188] Fig.11The curves TP, TPcl, TPac, TPW_M-curve and TPW_E-curve according to another example are shown. Therefore, these curves are like Fig. 9 and Fig.10 is determined like its counterpart shown in , but based on further measurements, results in a different measured pressure signal TP. Fig. 9 and 10 different, Fig.11 The derivative TPW_M-curve' of the TPW_M-curve is also shown, which is used to determine the blood pressure. Fig.11 The time points t(TPW_M-curve.max) and t(TPW_M-curve'.max) at which TPW_M-curve and TPW_M-curve' have their respective maximum values ​​are indicated in FIG. Accordingly, in this example, TPcl@TPW_M-curve.max and TPcl@TPW_M-curve'.max can also be identified, so that the blood pressure can also be determined according to any of the equations (1), (6) and (7) discussed above.

[0189] The processor 3 may be adapted to estimate a blood pressure value based on two other already measured blood pressure values. In particular, one of the blood pressure values ​​MAPni, SAPni and DAPni may be estimated based on another of these blood pressure values. This may be done according to the following equation:

[0190] SAPni=c1·MAPni+c2·(MAPni-DAPni)-c3 mmHg (8)

[0191] Among them, c1=(0.2..0.7), c2=(2..6), c3=(-5..5),

[0192] MAPni=c4·DAPni+c5·(SAPni-DAPni)-c6 mmHg (9)

[0193] Among them, c4=(0.8..1.3), c5=(0.25..0.5), c6=(-5..5),

[0194] DAPni=c7·MAPni-c8·(SAPni-MAPni)-c9 mmHg (10)

[0195] Among them, c7=(0.6..1.1), c8=(0.15..0.4), c9=(-5..5).

[0196] The coefficients and constants of equations (8), (9) and (10) are predetermined by calibration based on statistical evaluation of a clinical invasive blood pressure data set that is as large as possible and sufficiently extensive. Therefore, very accurate invasive blood pressure values ​​SAPi (invasive systolic pressure), MAPi (invasive mean arterial pressure) and DAPi (invasive diastolic pressure) are used, wherein, given these very accurate invasive blood pressure values, the coefficients and constants of equations (8), (9) and (10) are modified so that these equations are valid.

[0197] Blood pressure measurements are intended to be taken in rapid succession in a series of measurements to allow effective semi-continuous blood pressure monitoring, minimizing stress on the individual being monitored (i.e., the subject being monitored). This rapid sequence of pressure measurements can also be considered a non-invasive fast mode cycle (FMC) measurement of blood pressure.

[0198] In an embodiment, the initial blood pressure measurement has no information about the previous diastolic arterial pressure (DAP), and therefore slow inflation, i.e., a measuring time period, is started at a predetermined tissue pressure TPlow in the range of 15 to 30 mmHg. In addition, during this measuring time period, the inflation rate is set to an intermediate value. The inflation rate can be defined as the rate at which TPcl increases over time, wherein the inflation rate can be selected so that it has a value of, for example, 1.9 mmHg / s. This would correspond to the measurement of a "normal" blood pressure value. At the end of the deflation phase, when TPcl has reached Part, the blood pressure measurement is preferentially interrupted for at least 2 s in order to allow reperfusion of the subject's body part wrapped by the shell 4. The interruption time 42 preferably has a length in the range of greater than 0% to about 50% of the previous inflation / deflation time period 40, resulting in a cycle 41. The following blood pressure measurement will use the information of the diastolic arterial pressure (DAP) determined in the corresponding previous measurement (DAPprev) to start slow inflation, i.e., a measuring time period, with a higher TPlow, such as Fig.12 shown.

[0199] The TPlow value should not be higher than 90% of the diastolic blood pressure to ensure that all pulses required for the blood pressure calculation are recorded. In addition, as mentioned above, the blood pressure can change in the time interval (t_inter) between the start of deflation and the start of the next slow inflation. Therefore, preferably, a function that models the decrease in blood pressure according to the time interval t_inter is applied. It has been observed in clinical data from high-risk surgery that the diastolic blood pressure can decrease by more than 28% in one minute. Therefore, TPlow can be calculated by a linear function using the following function:

[0200] Tplow=90%DAPprev-28%DAPprev·t_inter / 60s, (11)

[0201] Here, "90% DAPprev" and "28% DAPprev" respectively represent 90% and 28% of the previously measured arterial diastolic pressure DAPprev.

[0202] TPlow can be determined by using a linear function that depends on the previous time interval between the start of deflation and the start of the next slow inflation, wherein the linear function has a negative slope so that TPlow decreases over time. The slope of the linear function and the positive constant of the linear function can be predetermined by calibration. In equation (12), the positive constant is 90% DAPprev and the negative slope is -28% DAPprev. The positive constant and the negative slope can also have other values. For example, the negative slope can be -30% DAPprev.

[0203] exist Fig.12 In , it can be seen how TPlow is adjusted according to t_inter according to equation (12). In particular, it can be seen that measurements #2a and #2b have different TPlow values, where the TPlow value of measurement #2b is smaller than the TPlow value of measurement #2a because the time interval t_inter for measurement #2b is larger than that for measurement #2a. Fig.12 It can also be seen that the inflation rate for measurement #3 increases due to the increase in PP prior to measurement #2a. In addition, for measurement #3, TPlow is greater than the previous measurements because the diastolic arterial pressure DAP has increased prior to measurement #2a. It should be noted that Fig.12 , interval 44 is the cycle period of the second measurement #2a, interval 43 is the inflation and deflation period of the second measurement #2a, and interval 45 is the interruption time of the second measurement #2a. In addition, it should be noted that the third measurement #3 is related to the second measurement #2a, and another second measurement #2b is only shown to illustrate an alternative to the second measurement #2a.

[0204] Fig.13 Another example of adjusting the TPlow value according to the time interval t_inter according to equation (12) is shown. In this example, the inflation rate in the measurement time period of measurement #3 is reduced compared to the previous measurement due to the decrease in PP before measurement #2a and the decrease in TPlow value due to the decrease in DAP before measurement #2a.

[0205] As described above, a filter is used to determine the end determination curve TPW_E-curve, the blood pressure determination curve TPW_M-curve, and the envelope curves TPsys-curve and TPdia-curve. In addition, a filter is used to determine TPcl based on TP. As a filter, a low-pass filter is preferably used. The low-pass filter can be, for example, a cascaded moving average filter with a variable window length of up to 8s, wherein the window length can be shorter at the beginning and end of the filtering to minimize the filter settling time. For example, filtering can include averaging within a moving window of a signal containing at least three TP pressure pulse curves and a maximum of 8s twice (2x8s filter). Optionally, signal filling can be applied before and / or after the start of the signal to completely fill the filter window before filtering. For example, the first pressure pulse value before the start and the last pressure pulse value after the end can be applied for filling.

[0206] Due to the filter delay, TPcl is extrapolated from its previous value to the last part of the signal available for measurement. The filter can be applied, for example, to extract TPcl from TP, to form a smoothed TPW_E-curve and a smoothed TPW_M-curve without variations caused by blood pressure pulsations, and to create an envelope function on the systolic peak (TPsys-curve) and the end-diastolic minimum (TPdia-curve) of TP.

[0207] In the following, reference will be made to Fig.14 An embodiment of a method for determining blood pressure is exemplarily described with reference to the flowchart shown in FIG.

[0208] After initialization and startup of the device in step 101, TPlow is determined in step 102. For a first measurement it may be a value from 15 mmHg to 30 mmHg. If a blood pressure measurement has already been performed, TPlow may be determined using a previous diastolic blood pressure value, for example according to equation (12).

[0209] In step 103, in the pre-measurement time period, the cuff is inflated at a relatively large first inflation rate until TPlow is reached. Then, in step 104, a measurement time period is started, i.e., a slow inflation period, during which a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve are determined. In addition, these curves are used to determine an end measurement time point, wherein when the end measurement time point has been reached or exceeded, the slow inflation period is stopped, and in step 105, the cuff is deflated. After deflation and pausing to allow venous return in step 106, the method continues with step 102. Therefore, the method can be performed in a loop for continuous monitoring of blood pressure changes over time in several measurement cycles. When executing steps 102 to 105, the processor calculates blood pressure values ​​in parallel. The loop can be performed until the termination criterion is met. For example, if the physician has entered a corresponding command into the device via an input unit such as a keyboard, a computer mouse, a touch pad, etc., the monitoring of blood pressure is interrupted.

[0210] The device allows non-invasive FMC blood pressure measurement based on non-invasive high-fidelity tissue pressure TP recordings preferably recorded with an anti-kink shell system described in WO2014 / 121945Al. The device preferably allows inflation of a statistically averaged maximum pressure of about 85% or less of the arterial systolic pressure. Depending on the height of the arterial blood pressure, the pulse pressure and the inverse of the heart rate, a single blood pressure measurement using device 1 may take about 20 to 60 seconds, wherein the device is preferably configured to provide non-invasive systolic pressure SAPni, non-invasive mean arterial pressure MAPni and non-invasive arterial diastolic pressure DAPni. Preferably, a short break is taken with an unpressurized cuff between consecutive measurements to allow venous return. These short interruptions are preferably in the range of 5 to 10 seconds. During the measurement, the arterial perfusion of the part wrapped by the shell (such as the upper arm or wrist of the subject) is preferably never completely interrupted because the clamping pressure is preferably permanently kept below SAP. Therefore, compared with conventional oscillometric measurements, the measurement is less stressful on the subject.

[0211] The above references are for example Figure 1 The described device 1 provides a reliable method for quickly determining blood pressure without clamping pressure exceeding SAP. Due to the relatively short measurement time and relatively low maximum cuff pressure, the blood pressure measurement is very convenient for the individual and can reduce the possibility of potential complications (such as thrombophlebitis, pain, subcutaneous hematoma, limb edema, peripheral neuropathy, etc.).

[0212] In an embodiment, TPlow may be at or above DAP. TPlow defines the tissue pressure at the beginning of the measurement period, ie the tissue pressure at the beginning of the slow inflation period, wherein the slow inflation may be terminated when a certain end criterion is reached. The end criterion has been described above.

[0213] Although in the above-described embodiment, the feature is determined by using the TPac pulse, the feature can also be determined by directly using the measured pressure pulse (i.e., the TP pulse). The TP pulse can also be processed in another way, i.e., the TPac pulse is not determined by subtracting the average TP value. For example, for the corresponding measured pressure pulse, the pressure values ​​at t.start and t.stop can be connected by a straight line, and the straight line can be subtracted from the corresponding measured pressure pulse to determine the feature determination pulse.

[0214] Although in the above-described embodiment TPW_M-curve and TPW_E-curve have been determined, TPW_M-curve may also be determined instead of TPW_E-curve, wherein a transformation of the TPW_M-curve and possibly also the TPW_M-curve itself is used to determine the blood pressure.

[0215] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims.

[0216] In the claims, the word "comprising" does not exclude other elements or steps, and the indicative "a" or "an" does not exclude a plurality.

[0217] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0218] Calculations such as determination of the end measurement time point, pulse characteristics, certain curves and their transformations, blood pressure values, etc., performed by one or more units or devices may be performed by any other number of units or devices. The calculations and determinations and / or control of the device according to the method may be implemented as program code modules of a computer and / or dedicated hardware.

[0219] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0220] Any reference signs in the claims should not be construed as limiting the scope. In particular, the use of letters such as TPP, TPA, etc. in brackets in the claims as reference signs should not be construed as limiting the scope. For example, according to the claims, in addition to the features indicated by the reference signs, other features may also be used.

[0221] An apparatus for determining the blood pressure of an object is proposed. The apparatus comprises a pressure signal providing unit configured to provide a measured pressure signal of the object over a period of time, wherein the pressure signal indicates blood pulsation and comprises a plurality of pressure pulses. The apparatus further comprises a processor configured to: determine a blood pressure determination curve indicating the dependence of the pressure pulses on an applied pressure based on the plurality of pressure pulses; apply a transformation to the blood pressure determination curve; and determine the blood pressure based on a result of the transformation. This allows a more accurate determination of the blood pressure.

Claims

1. A device (1) for determining the blood pressure of a subject, the device comprising: - a pressure signal providing unit, configured to provide a measured pressure signal (TP) of an object over a period of time, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising: a) a shell (4) configured to enclose a portion (5) of the object through which blood flows; b) a pressure applicator (6, 8) configured to apply pressure to the shell (4) and thereby to the enclosed portion (5) of the object from outside the shell (4); and, c) a pressure sensor (7) configured to measure the pressure signal (TP) on the skin of the enclosed portion (5) of the object, wherein when measuring the pressure signal (TP), the pressure applicator (6, 8) increases or decreases the applied pressure, and wherein the measured pressure signal (TP) indicates blood pulsation and comprises a plurality of pressure pulses (9), and - a processor (3) configured to determine a blood pressure determination curve (TPW_M-curve) based on the plurality of pressure pulses (9), wherein the blood pressure determination curve (TPW_M-curve) indicates the dependence of the pressure pulses (9) on the applied pressure, and wherein the processor is further configured to apply a transformation to the blood pressure determination curve (TPW_M-curve) and to determine the blood pressure based on a result of the transformation.

2. The device (1) according to claim 1, wherein: The transformation applied to the blood pressure determination curve (TPW_M-curve) involves taking a derivative (TPW_M-curve') of the blood pressure determination curve (TPW_M-curve), such that the processor (3) is configured to determine the blood pressure based on the derivative (TPW_M-curve') of the blood pressure determination curve (TPW_M-curve).

3. The device (1) according to claim 2, wherein: The processor (3) is configured to determine the position of a maximum of the derivative (TPW_M-curve') of the blood pressure determination curve (TPW_M-curve) and to determine the blood pressure based on the determined position and the measured pressure (TP).

4. The device (1) according to claim 3, wherein: The processor (3) is configured to determine the position of the maximum value of the derivative (TPW_M-curve') of the blood pressure determination curve (TPW_M-curve) by determining a first peak of the blood pressure determination curve (TPW_M-curve) and by determining the position of the maximum value of the derivative (TPW_M-curve') of the blood pressure determination curve (TPW_M-curve) before the determined first peak, the first peak having a peak value that is greater than a predefined percentage of the peak value of the total maximum peak of the blood pressure determination curve (TPW_M-curve).

5. The device (1) according to any one of claims 3 and 4, wherein: The processor (3) is configured to determine the blood pressure based on an average value (TPcl) of the measured pressures (TP) at the determined locations of the maximum values.

6. The device (1) according to any one of claims 3 to 5, wherein: The processor (3) is further configured to determine a position of a maximum of the blood pressure determination curve (TPW_M-curve) and to determine the blood pressure further based on the further determined position and the measured pressure (TP).

7. The device (1) according to claim 6, wherein: The processor (3) is configured to determine the blood pressure further based on an average value (TPcl) of the measured pressures (TP) at the further determined locations.

8. The device (1) according to any one of claims 5 to 7, wherein: The processor (3) is configured to determine the blood pressure as a function of a) the average value (TPcl) of the measured pressure (TP) at the location of the maximum value of the derivative (TPW_M-curve') of the determined blood pressure determination curve (TPW_M-curve) and b) the average value (TPcl) of the measured pressure (TP) at the location of the maximum value of the determined blood pressure determination curve (TPW_M-curve), Therein, the dependence of the function on the average value (TPcl) of the measured pressures (TP) at two locations is predetermined based on reference measurement results.

9. The device (1) according to claim 8, wherein: The function is a linear function, whose dependence on the average value (TPcl) of the measured pressures (TP) at the two positions is represented by a linear coefficient, wherein the linear coefficient is predetermined in a linear regression performed based on the reference measurement results.

10. The device (1) according to any one of the preceding claims, wherein The processor (3) is configured to: determine at least one feature characterizing a corresponding pressure pulse among the multiple pressure pulses (9); determine a blood pressure determination value (TPWP_M) for the corresponding pressure pulse based on the determined at least one feature, so that for several pressure pulses existing at different times, several blood pressure determination values ​​(TPWP_M) are determined, wherein the processor (3) is configured to determine the blood pressure determination curve (TPW_M-CURVE), so that the several blood pressure determination values ​​(TPWP_M) determined for the several pressure pulses and therefore for several times form the blood pressure determination curve (TPW_M-CURVE).

11. The device (1) according to claim 10, wherein: The processor (3) is configured to: in order to determine the at least one characteristic for the corresponding pressure pulse, provide a characteristic determination pulse (29) based on the corresponding pressure pulse, and determine at least one of the following characteristics: the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) at the end-diastolic point of the characteristic determination pulse, the area enclosed by the upper part of the characteristic determination pulse (TPA+.top50), wherein a) the upper end of the upper part is at the maximum systolic pressure (TPsys) of the characteristic determination pulse, and b) the lower end of the upper part is between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure value corresponding to the average value (TPcl) of the measured pressure (TP), The corresponding characteristics determine the duration (t(pulse)) of the pulse (29), The corresponding characteristic determines the area (TPA / TPA.norm) of the pulse (29), and The corresponding characteristic determines the full width at half maximum (W50) of the pulse (29).

12. The device (1) according to claim 11, wherein: The processor (3) is configured to determine the blood pressure determination value (TPWP_M) based only on the feature of the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end-diastolic point, or based only on a) the feature of the difference (TPP) between the maximum systolic pressure (TPsys) of the characteristic determination pulse and the pressure (TPdia) of the characteristic determination pulse at the end-diastolic point and b) the feature of the area (TPA+.top50) enclosed by the upper part of the characteristic determination pulse, and thereby form the blood pressure determination curve (TPW_M-curve).

13. The device (1) according to any one of claims 10 to 12, wherein: The processor (3) is configured to determine, for the corresponding pressure pulse, the blood pressure determination value (TPWP_M) based on at least one characteristic determined by raising the at least one characteristic to the power of a predefined exponent.

14. A method for determining the blood pressure of a subject, wherein: The method comprises: - providing a measured pressure signal (TP) of the subject over a period of time by a pressure signal providing unit, wherein the pressure signal (TP) has been measured by using a measuring device, the measuring device comprising: a) a shell configured to enclose a portion of the subject through which blood flows; b) a pressure applicator configured to apply pressure to the shell and thereby to the enclosed portion of the subject from outside the shell; and, c) a pressure sensor configured to measure the pressure signal on the skin of the enclosed portion of the subject, wherein when measuring the pressure signal, the pressure applicator increases or decreases the applied pressure, and wherein the measured pressure signal indicates blood pulsation and comprises a plurality of pressure pulses (9), - determining a blood pressure determination curve (TPW_M-curve) based on the plurality of pressure pulses (9), wherein the blood pressure determination curve (TPW_M-curve) indicates the dependency of the pressure pulses (9) on the applied pressure, - applying a transformation to the blood pressure determination curve (TPW_M-curve), and - determining said blood pressure based on a result of said transforming.

15. A computer program for determining blood pressure, the computer program comprising program code means for causing the device for determining blood pressure according to any one of claims 1 to 13 to perform the steps according to claim 14.

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