Measurement system for measuring subject's blood pressure, and control device, control method, and computer program for controlling said measurement system

Abstract

The present invention relates to a control device for controlling a blood pressure measurement system. While a pressure applying unit applies increasing pressure to a part of the subject's body during a measurement period, a pressure TP including a plurality of pressure pulses 9 on the skin of the part of the subject's body is measured. For at least some of the pressure pulses, several characteristics characterizing the pressure pulse are determined. Based on these characteristics, a measurement end point 32 is determined, which is the point at which the measurement period is stopped or will be stopped later. When the measurement end point 32 is reached (i.e., when the measurement period is stopped), the applied pressure is reduced and a subsequent post-blood pressure measurement period is initiated. This allows for a shorter blood pressure measurement time and a lower maximum tissue pressure on the skin.

Description

[Technical field]

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

[0002] EP 3 430 992 A1 discloses a blood pressure measuring system arranged to surround a body part of a subject. The blood pressure measuring system comprises a pressure means for applying pressure to the body part and a kinking-proof shell. When the blood pressure measuring system surrounds the body part, the kink-proof shell is arranged between the pressure means and the body part. Although the blood pressure measuring system is able to measure blood pressure very accurately by continuously increasing the clamping pressure and stopping the increase above the systolic blood pressure, it is desirable to reduce the time required to perform a blood pressure measurement and the maximum clamping pressure that can be applied to the body part during the measurement. Summary of the Invention

[0003] It is an object of the present invention to provide a control device for controlling a measurement system for measuring the blood pressure of a subject, which enables a reduction in measurement time and a maximum clamping pressure applied to the subject. It is a further object of the present invention to provide a measurement system for measuring the blood pressure of a subject, which includes the control device, and a control method and a computer program for controlling the measurement system.

[0004] In a first aspect of the present invention, there is provided a control device for controlling a measurement system for measuring the blood pressure of a subject, the measurement system comprising: a) a shell that encases a part of the subject through which blood flows; b) a pressure applying unit that applies pressure to the shell from the outside of the shell, thereby applying pressure to the encased part of the subject; and c) a pressure sensor that measures the pressure on the skin of the encased part of the subject, and the control device controls the measurement system to: The pressure applying unit increases the applied pressure during a measurement period and decreases the applied pressure during a subsequent post-blood pressure measurement period; The pressure sensor measures the pressure on the skin at least during a measurement period; Here, the measured pressure includes a plurality of pressure pulses, and the control device determines, for each of at least some of the plurality of pressure pulses, several features characterizing the pressure pulse, and determines a measurement end point at which the measurement period is stopped based on the features determined for at least some of the plurality of pressure pulses, and controls the pressure applying unit to reduce the applied pressure to start a subsequent post-blood pressure measurement period when or after the measurement end point is reached.

[0005] It has been found that by using the determined characteristics of the pressure pulse to determine the end measurement time, it is possible to measure a relatively short period of time while still measuring enough pressure data to accurately determine blood pressure, thereby shortening the blood pressure measurement time and reducing tissue pressure, i.e., the clamping pressure on the skin of the body part, which remains significantly lower than the systolic arterial pressure during the measurement and terminates.

[0006] These features may directly characterize each pressure pulse or may indirectly characterize each pressure pulse, in which case each pressure pulse is processed to determine a characterizing pulse and the features are determined based on the determined characterizing pulse, as will be described in more detail below. The controller may be configured to determine for each pressure pulse, for example for each of at least 5 or 10 pressure pulses of the plurality of pressure pulses, a number of features characterizing the respective pressure pulse. The controller may also be configured to determine for each pressure pulse of the plurality of pressure pulses a number of features characterizing the respective pressure pulse.

[0007] In one embodiment, a pressure sensor configured to measure the pressure on the skin of the wrapped portion of the subject is disposed inside the shell. However, the pressure sensor may be disposed in another manner to measure the pressure on the skin of the wrapped portion of the subject. For example, a fluid-filled pressure sensor pad may be disposed inside the shell and connected via a fluid path, i.e., via a fluid-filled tube, to a pressure sensor outside the shell to measure the pressure on the skin of the wrapped portion of the subject.

[0008] Preferably, the control device a) determines several end determination combined values ​​for several pressure pulses present at different times by determining an end determination combined value by combining at least two of the multiple features determined for each pressure pulse, whereby several end determination combined values ​​determined for several pressure pulses and thus for several times form an end determination curve, and the control device further b) determines the measurement end time based on the end determination curve. By using the end determination curve, the accuracy of determining the measurement end time can be further increased. The control device may be configured to obtain a continuous end determination curve by processing several end determination combined values ​​obtained for several pressure pulses. To obtain a continuous curve based on several different end determination combined values, known mathematical methods may be used. For example, interpolation, fitting, filtering, etc. may be applied.

[0009] The control device is also preferably configured to provide a characterization pulse based on each pressure pulse to determine several features for each pressure pulse, and to determine at least one of the following features: a) the difference between the maximum systolic pressure of the characterization pulse and the pressure of the characterization pulse at the end diastolic point, b) the duration of each characterization pulse, c) the area of ​​each characterization pulse, and d) the half-width of each characterization pulse. The difference between the maximum and minimum measured pressure of each pressure pulse preferably corresponds to the difference between the tissue pressure (i.e. the measured pressure on the skin) of each pressure pulse at the maximum systolic point and the tissue pressure at the end diastolic point of each pressure pulse. The duration of each pressure pulse preferably corresponds to the time difference between the end diastolic point of each pressure pulse and the next end diastolic point. Furthermore, the area is preferably the area under the curve of each characterization pulse from the end diastolic point to the next end diastolic point. The area may be a normalized area. For example, the area may be normalized by scaling the area to the difference between the maximum and minimum pressure of each characterization pulse. The half-width corresponds to the width at 50% of the difference between the maximum and minimum pressure of each characterization pulse. The half-width is therefore the width at 50% of the difference between the pressure of the characterization pulse at the maximum systolic point and the pressure of the characterization pulse at the end diastolic point. It has been found that by using these characteristics, the determination of the measurement end point can be further improved. The characterization pulse of each pressure pulse can be obtained, for example, by subtracting the average measured pressure from each pressure pulse. However, the characterization pulse of each pressure pulse can also be determined in a different way. The characterization pulse can also be directly each pressure pulse, i.e. each measured pressure pulse.

[0010] In a preferred embodiment, the control device is configured to determine the end determination combined value for each pressure pulse based on at least one of the following calculations: i) a) multiplying the determined area to a first predetermined exponent by b) multiplying the determined difference to a second predetermined exponent; and ii) dividing the determined area to a third predetermined exponent by b) multiplying the determined duration to a fourth predetermined exponent and multiplying the quotient obtained from this division by c) multiplying the determined difference to a fifth predetermined exponent. The control device is also preferably configured to determine the end determination combined value for each pressure pulse based on further multiplication of the half-width to another predetermined exponent. Thus, in one embodiment, the calculation i) and / or the calculation ii) are extended by multiplication of the half-width to another predetermined exponent. Each exponent is preferably predefined and may be predefined by a calibration measurement. The reference blood pressure value is determined very accurately by invasive means, and the index is determined such that the measurement system controlled by the control device provides very accurate invasively measured blood pressure values ​​with high statistical accuracy and precision, while the blood pressure measurement time is significantly shorter than that of a conventional oscillometric non-invasive blood pressure measurement under the same conditions (e.g., blood pressure height, pulse pressure height, inverse heart rate). In particular, for the calibration measurement, pairs of invasive and non-invasive blood pressure values ​​recorded simultaneously from a sufficient number of individuals of different genders, reasonable height, weight, and age ranges in various hemodynamic states are used. Note that the calibration is preferably performed only in the development phase, i.e. not during the actual blood measurement procedure. The calibration may be performed separately for different shell sizes, i.e., preferably for each blood pressure cuff size or for each group of shell sizes. For example, a different set of indexes may be determined by calibration for different shell sizes or groups of shell sizes, i.e., a set of indexes may be determined for each shell size or group of shell sizes.

[0011] Preferably, the control device further determines several blood pressure determination combined values ​​for several pressure pulses present at different times by a) determining a blood pressure determination combined value for each pressure pulse by combining at least two of the determined features, where the determined several blood pressure determination combined values ​​for several pressure pulses, and therefore for several times, form a blood pressure determination curve, and the control device further determines the blood pressure based on the blood pressure determination curve. By determining the blood pressure using this blood pressure measurement curve, the blood pressure can be determined very accurately. Preferably, the control device is configured to determine a maximum value of the blood pressure determination curve, and determine the blood pressure based on the determined maximum value and the measured pressure. By determining the blood pressure based on the determined maximum value of the blood pressure determination curve and the measured pressure applied to the skin, i.e., tissue pressure, the accuracy of the blood pressure measurement can be further improved.

[0012] The control device may be configured to obtain a continuous blood pressure determination curve by processing several combined blood pressure determination values ​​obtained for several pressure pulses, for example, an interpolation may be applied and optionally further smoothing may be applied.

[0013] Preferably, the control device is configured to determine the blood pressure determination combined value for each pressure pulse based on at least one of the following calculations: i) a) multiplying the determined area to a power of a predetermined tenth exponent by b) multiplying the determined difference to a power of a predetermined eleventh exponent, and ii) a) dividing the determined area to a power of a predetermined twelfth exponent by b) multiplying the determined duration to a power of a predetermined thirteenth exponent and multiplying the quotient obtained from this division by c) multiplying the determined difference to a power of a predetermined fourteenth exponent. Also, the control device is preferably configured to determine the blood pressure determination combined value for each pressure pulse based on further multiplication of the half-width to a power of another predetermined exponent. Thus, in one embodiment, the above calculation i) and / or the above calculation ii) are extended by multiplication of the half-width to a power of another predetermined exponent. Also, each exponent is preferably predefined and may be predefined by a calibration measurement. The reference blood pressure value is determined very accurately by invasive means, and the index is determined in such a way that the measurement system controlled by the control device provides very accurate invasively measured blood pressure values ​​with high statistical accuracy and precision, while the blood pressure measurement time is significantly shorter than that of a conventional oscillometric non-invasive blood pressure measurement under the same conditions (e.g. blood pressure height, pulse pressure height, inverse heart rate). In particular, for the calibration measurement, pairs of invasive and non-invasive blood pressure values ​​recorded simultaneously from a sufficient number of individuals in various hemodynamic states are used. Again, the calibration is preferably performed only in the development phase, i.e. not during the actual blood measurement procedure. In this case as well, the calibration may be performed separately for different shell sizes, i.e. preferably for each blood pressure cuff size or for each group of shell sizes. For example, a different set of indexes may be determined by calibration for different shell sizes or groups of shell sizes, i.e. a set of indexes may be determined for each shell size or group of shell sizes.

[0014] The control device is preferably configured to determine the end determination curve so as to satisfy one of the following conditions: a) the maximum value of the end determination curve occurs before the maximum value of the blood pressure determination curve, b) the maximum value of the end determination curve occurs simultaneously with or after the maximum value of the blood pressure determination curve and the decrease of the end determination curve after the maximum value is steeper than the decrease of the blood pressure determination curve after the maximum value, c) the end determination curve coincides with the blood pressure determination curve. It has been found that the measurement end time can be determined more accurately when the end determination curve and the blood pressure determination curve have any of these relationships to each other.

[0015] In a preferred embodiment, the control device is further configured to determine the measurement end time based on the blood pressure determination curve. It has also been found that the measurement time can be further reduced by determining the measurement end time using the blood pressure measurement curve as well as the end measurement curve.

[0016] Preferably, the control device is configured to determine the end measurement time by determining a) when the end determination curve, after passing through the maximum value of the end determination curve, falls to a value below a predetermined percentage of the maximum value, and b) when the blood pressure determination curve reaches or passes through the maximum value of the blood pressure determination curve. It is also preferred that the predetermined percentage of the maximum value is within the range of 40% to 95%. In particular, it has been found that when using both curves in this way to determine the measurement end time, the measurement end time can be determined very accurately so that the blood pressure measurement time is relatively short, and at the same time the blood pressure can be measured very accurately.

[0017] In one embodiment, the control device is configured to control the pressurizer such that the pressurizer increases the applied pressure at a first rate during a pre-measurement period and then increases the applied pressure at a second rate during a measurement period, where the first rate is greater than the second rate. Thus, the pressure to be applied at the start of the measurement period can be reached relatively quickly, which can further reduce the overall time required to measure blood pressure.

[0018] In one embodiment, the control device is configured to control the pressure applying unit so that the pressure measured at the end of the pre-measurement period is within a range of 15 to 30 mmHg, thereby ensuring that the pressure on the skin, i.e., tissue pressure, is measured within a sufficiently large pressure range during the measurement period, making it possible to accurately measure blood pressure.

[0019] The range of 15 to 30 mmHg is preferably applied when the previous diastolic arterial pressure obtained by a previous blood pressure measurement of the same subject is not used by the control device for controlling the pressurizing unit. If the previous diastolic arterial pressure is used for controlling the pressurizing unit, the pressure measured at the end of the pre-measurement period may be higher. The control of the pressurizing unit according to the previously obtained diastolic arterial pressure will be described later.

[0020] It should be noted that the pressure at the end of the pre-measurement period is not the pressure applied between two successive blood pressure measurements, specifically the pressure applied before the start of the pre-measurement period: this pressure is called the "attachment pressure" and should not exceed 15 mmHg.

[0021] In one embodiment, the control device is configured to: a) store or receive a previous diastolic arterial pressure obtained by a previous blood pressure measurement; b) determine a first end measured pressure based on the previous diastolic arterial pressure such that the first end measured pressure to be present at the end of the pre-measurement period (and thus may also be considered as a target pressure) is smaller than the previous diastolic arterial pressure; and c) control the pressure applying unit so that the pressure measured at the end of the pre-measurement period is equal to or smaller than the determined first end measured pressure. The control device is preferably configured to determine the first end measured pressure to be equal to or smaller than 90% of the previous diastolic arterial pressure. This ensures that the pressure on the skin, i.e., tissue pressure, is measured in a sufficiently large pressure range during the measurement period, making it possible to accurately determine blood pressure.

[0022] In one embodiment, the control device is further configured to store or receive a time at which the previous diastolic arterial pressure was measured, and determine the first ending measured pressure based on i) the previous diastolic arterial pressure, and ii) the distance in time to the blood pressure measurement at which the previous diastolic arterial pressure was measured, as indicated by the stored time. Although the diastolic arterial pressure may change over time, the first ending measured pressure can be determined relatively accurately given the distance in time to the blood pressure measurement at which the previous diastolic arterial pressure was measured. Thus, despite this uncertainty regarding the change in diastolic arterial pressure over time, the end of the pre-measurement period can be determined such that during the subsequent measurement period, pressure on the skin, i.e., tissue pressure, can be measured over a range large enough to accurately determine blood pressure.

[0023] The control device may further be configured to a) store or receive a previous pressure measured by the pressure sensor within a period from the end of a previous measurement period of a previous blood pressure measurement to the start of a pre-measurement period, and b) control the pressure applying unit such that the pressure measured at the start of the pre-measurement period is equal to or less than a predetermined pressure value based on the stored or received previous measured pressure, the predetermined pressure value being preferably equal to or less than 15 mmHg, and more preferably equal to or less than 10 mmHg.

[0024] The pressure measured at the beginning of the pre-measurement period can be considered as the attachment pressure present during the measurement pause between two successive blood pressure measurements, i.e. before the start of each blood pressure measurement. The attachment pressure is preferably controlled to achieve a given or preset value, i.e. a predetermined pressure value. This control is preferably performed to accommodate changes in the volume of the body part, for example an increase due to tissue edema (e.g. capillary leakage in sepsis, hypervolemia, etc.) or a decrease due to a reduction in tissue edema or hypovolemia. This should in particular prevent venous congestion during the measurement pause, i.e. between two successive blood pressure measurements, due to a decrease in venous return due to tissue pressures higher than the venous pressure at the body part compressing the veins. In a preferred embodiment, the pressure on the skin (which can also be considered as tissue pressure) is continuously measured throughout the procedure of performing one or more blood pressure measurements, and the pressure unit is controlled in such a way that venous congestion during the measurement pause is avoided.

[0025] In a further aspect of the invention, a measurement system is provided for measuring a blood pressure of a subject, the measurement system comprising: a shell that encases the part of the subject through which blood flows; a pressure applying unit that applies pressure to the shell from the outside of the shell, thereby applying pressure to the wrapped part of the subject; a pressure sensor for measuring pressure on the skin of the subject at the wrapped area; and a control device according to any one of claims 1 to 19.

[0026] In another aspect of the invention there is provided a control method for controlling a measurement system as claimed in claim 20, the control method comprising the steps of: increasing the applied pressure during a measurement period by using the pressure unit, and then decreasing the applied pressure during a post-blood pressure measurement period; measuring the pressure on the skin during at least a measurement period by using a pressure sensor disposed inside the shell; Here, the measured pressure includes a plurality of pressure pulses, and for each of at least some of the plurality of pressure pulses, several features characterizing the pressure pulse are obtained, and based on the features obtained for at least some of the plurality of pressure pulses, a measurement end point at which the measurement period is stopped or is subsequently stopped is determined, and when or after the measurement end point is reached, the pressure applying unit is controlled to reduce the applied pressure to start a subsequent post-blood pressure measurement period.

[0027] In another aspect of the invention there is presented a computer program for controlling a measurement system according to claim 19. The computer program comprises program code means for causing the measurement system to carry out the steps of claim 20 when the computer program is executed on a control device of the measurement system.

[0028] The control device, the method and the computer program are preferably configured to continuously control the measurement system to perform several successive blood pressure measurements while attached to a subject.

[0029] It is to be understood that the control device according to claim 1, the measuring system according to claim 20, the control method according to claim 21 and the computer program according to claim 22 have similar and / or identical preferred embodiments, in particular as set out in the dependent claims.

[0030] It is to be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above embodiments with the independent claims.

[0031] These and other aspects of the invention will be elucidated and elucidated with reference to the embodiments described hereinafter. [Brief description of the drawings]

[0032] [Figure 1]FIG. 1 shows a schematic and exemplarily diagrammatic embodiment of a measurement system for measuring the blood pressure of a subject in a situation where a blood pressure cuff of the measurement system is inflated. [Diagram 2] FIG. 2 shows a schematic and exemplary shell of the measurement system that envelops the upper arm of a subject. [Diagram 3] FIG. 3 shows a schematic and exemplary illustration of the measurement system in the situation where the blood pressure cuff is deflated. [Figure 4] FIG. 4 illustrates, in a schematic and exemplary manner, measured tissue pressures and other values ​​derived from tissue pressure measurements. [Diagram 5] FIG. 5 shows the calculation of a first characteristic of the pressure pulse of the measured tissue pressure. [Figure 6] FIG. 6 shows the calculation of other characteristics of the pressure pulse of the measured tissue pressure. [Figure 7] FIG. 7 shows the calculation of other characteristics of the pressure pulse of the measured tissue pressure. [Figure 8] FIG. 8 shows a schematic and exemplary diagram of a termination decision curve and a blood pressure decision curve. [Figure 9] FIG. 9 shows a schematic and exemplary illustration of the determination of a blood pressure value using a blood pressure determination curve. [Figure 10] FIG. 10 shows, in a schematic and illustrative manner, an example of several successive blood pressure measurements. [Figure 11] FIG. 11 shows, diagrammatically and exemplarily, a further example of several successive blood pressure measurements. [Figure 12] FIG. 12 shows a flowchart exemplarily illustrating an embodiment of a control method for controlling a measurement system for measuring the blood pressure of a subject. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] FIG. 1 shows, in a schematic and exemplary manner, a measurement system 1 for measuring the blood pressure of a subject. The measurement system 1 comprises a shell 4 (see FIG. 2) configured to surround a part 5 of the subject through which blood flows. In this embodiment, the part 5 of the subject is the subject's arm, and in FIG. 2 a brachial artery 11 in the arm 5 is shown. An arrow in the brachial artery 11 indicates the blood flow direction away from the heart. The measurement system 1 further comprises a pressure sensor 7 arranged inside the shell 4 and configured to measure pressure on the skin of the surrounded arm 5 of the subject. The measured pressure may also be considered as tissue pressure (TP). As shown in FIG. 2, a pulse wave in the brachial artery 11 causes a pressure wave 12 that is transmitted through the tissue of the arm 5 to the pressure sensor 7. For clarity, the shell 4 is not shown in FIG. 1.

[0034] The measurement system 1 further comprises a cuff 6 which surrounds the shell 4 and is inflatable by means of a pump 8. By inflating the cuff, pressure is applied to the shell 4 from outside the shell 4 and thereby also to the wrapped arm 5 of the subject. The cuff 6 and the pump 8 may be considered as forming a pressure part 6, 8, since they cooperate to make it possible to apply pressure to the shell 4 and to the wrapped arm 5 of the subject. The shell 4 around which the cuff 6 is wrapped is preferentially an anti-kink shell cuff as described in WO2014 / 121945A1.

[0035] The measurement system 1 further comprises a control device 3 configured to control the measurement system 1 such that the pressurizing units 6, 8 increase the applied pressure during a measurement period and decrease the applied pressure during a subsequent post-blood pressure measurement period, and such that the pressure sensor 7 measures the pressure on the skin, i.e. the tissue pressure TP, at least during the measurement period. The control device 3 is further configured to control the pressurizing units 6, 8 such that the pressurizing units 6, 8 increase the applied pressure at a first rate during a pre-measurement period and increase the applied pressure at a second rate during a subsequent measurement period, where the first rate is greater than the second rate. In Fig. 1, the control of the measurement system 1 to increase the applied pressure by inflating the cuff 6 is shown, i.e. the thick arrow indicates the inflation situation.

[0036] The measurement system 1 comprises a valve 20. When the valve 20 is opened, the compressed air in the system is released from the system to the surrounding atmosphere, and the cuff is deflated. In Fig. 3, the deflation situation is shown by the thick arrow with the pump 8 turned off.

[0037] The control device 3 may be considered to comprise an actual controller 10 for controlling the pump 8 and the valves 20 and a processor 11 arranged in particular to carry out certain calculations which will be described below. The measurement system 1 may also comprise a display 22 for displaying, for example, the measured blood pressure values.

[0038] In the pre-measurement period (which may also be considered a fast inflation period), the controller 3 controls the measurement system 1 such that the valve 20 is closed and the pump 8 inflates the cuff 6 at a high, first rate. In the subsequent measurement period, the controller 3 also controls the measurement system 1 such that the valve 20 is closed, but the pump 8 is controlled such that inflation of the cuff 6 continues at a low, second rate. Thus, the measurement period may also be considered a slow inflation period.

[0039] FIG. 4 shows a schematic and exemplary representation of the measured pressure TP versus time t. The first inflation of the pre-measurement period starts with a tissue pressure TP, which is the attachment pressure Patt, which is the tissue pressure measured in the uninflated cuff 6. This attachment pressure Patt may be, for example, in the range of 0-15 mmHg. An attachment pressure Patt of 15 mmHg or less did not cause venous congestion for more than 12 hours, making the shell 4 and cuff 6 assembly suitable for long-term monitoring. For this reason, an attachment pressure Patt of 15 mmHg or less is preferred. In FIG. 4, arrow 30 indicates the start of the pre-measurement period, i.e. the start of the fast inflation period. During this pre-measurement period, the part of the overall tissue pressure range where there is no or substantially no information for determining the blood pressure should be passed as quickly as possible. Therefore, it is preferred that the inflation rate during the pre-measurement period is as large as possible. For example, the inflation rate for the tissue pressure TP may be 8 mmHg / s or more. This pre-measurement period with a fast inflation rate ends at a tissue pressure value indicated in FIG. 4 by "TPlow".

[0040] The tissue pressure value TPlow also indicates the start of a measurement period with a slower second inflation rate. In FIG. 4, the start of the measurement period (which may also be considered as a slow inflation period) is indicated by an arrow 31. In one embodiment, the control device 3 is configured to control the pump 8 such that the pressure TPlow measured at the end of the pre-measurement period is in the range of 15-30 mmHg. Thus, in one embodiment, the tissue pressure TPlow may be predefined to be a value of 15-30 mmHg. However, if a diastolic arterial pressure (DAPprev) determined in a previously performed measurement is available, the tissue pressure TPlow may depend on this diastolic arterial pressure and the tissue pressure TPlow may be larger. Such a larger TPlow is shown diagrammatically in FIG. 4. For example, the control device 3 may be configured to store (or access a memory storage) a previous diastolic arterial pressure DAPprev. The previous diastolic arterial pressure DAPprev was obtained by a previous blood pressure measurement and may be used to determine the tissue pressure TPlow. The tissue pressure TPlow should be present at the end of the pre-measurement period, i.e. at the end of the first inflation period, and therefore may also be considered as the first end measured pressure. The tissue pressure TPlow is determined based on the previous diastolic arterial pressure DAPprev, such that the tissue pressure TPlow is less than the previous diastolic arterial pressure DAPprev. Preferably, the control device is configured to control the pump 8 such that the pressure measured at the end of the pre-measurement period is equal to the determined first end measured pressure TPlow. In one embodiment, the control device 3, in particular the processor 11 of the control device 3, determines the tissue pressure TPlow at the end of the pre-measurement period such that it does not exceed a predetermined percentage of the previous diastolic arterial pressure DAPprev. This ensures that all tissue pressure pulse pressure curves necessary for an accurate calculation of the blood pressure can be recorded. The calculation of the blood pressure based on the measured tissue pressure is described in more detail below. The predetermined percentage is preferably 90%.

[0041] Blood pressure may vary from measurement to measurement, for example, due to a clinically relevant event occurring in the subject. It has been found that the diastolic arterial pressure (DAP) may fall by approximately 30% within one minute in the most severe cases of acute blood loss during surgery. To address such possible blood pressure changes, the control device 3 may be configured to determine the tissue pressure TPlow based on the previous diastolic arterial pressure DAPprev and the length of the rest period between measurements. Thus, the control device 3 may be further configured to store (or access a memory storage) the time at which the previous diastolic arterial pressure DAPprev was measured, and to determine the first end measured pressure TPlow based on i) the previous diastolic arterial pressure DAPprev and ii) the temporal distance to the blood pressure measurement at which the previous diastolic arterial pressure DAPprev was measured, as indicated by the stored time. An example of a specific formula for determining the first end measured pressure TPlow is described below.

[0042] The second inflation rate applied during the measurement period is preferably in the range of 1 mmHg / sec to 6 mmHg / sec, with the lowest inflation rate being preferably 1.5 mmHg / sec and the highest inflation rate being preferably 2.5 mmHg / sec. It has been found that applying a second inflation rate within this range allows accurate blood pressure measurement. Note that these rates refer to the change in tissue pressure TP measured by pressure sensor 7.

[0043] In one 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 and diastolic blood pressures. For example, the second inflation rate may increase with increasing heart rate and increasing pulse pressure PP. This increase may be linear or may be expressed by other functional relationships. In one embodiment, the functional relationship is such that when the heart rate HR is 40 / min and the pulse pressure PP is 20 mmHg, the tissue pressure inflation rate is 1 mmHg / sec, and when the heart rate HR is 80 / min and the pulse pressure PP is 100 mmHg, the tissue pressure inflation rate (i.e., the second slower inflation rate) is 10 mmHg / sec. The measurement period ends at the end of measurement time 32, after which an immediate fast deflation is performed, preferably with the largest possible rate of decrease, since it is not necessary to collect tissue pressure data after the end of measurement time 32. The measured pressure TP includes a plurality of pressure pulses 9. The control device 3 is configured to determine, for each of at least some of the multiple pressure pulses 9, several features characterizing each pressure pulse, and based on the features determined for the multiple pressure pulses 9, determine a measurement end point 32 at which the measurement period is stopped or is subsequently stopped, and control the pressurizing units 6, 8 so that when or after the measurement end point 32 is reached, the pressurizing units 6, 8 reduce the applied pressure to start a post-blood pressure measurement period in which a fast contraction is performed.

[0044] 4, time interval 40 indicates the inflation-deflation period from the start of fast inflation 30 until the tissue pressure TP falls below 20 mmHg during fast deflation to allow venous return. Period 41 indicates the cycle time, which is the time between the start of one measurement and the start of the next measurement, and period 42 indicates the rest period, which is the difference between inflation-deflation period 40 and cycle time 41.

[0045] FIG. 4 also shows the mean pressure TPcl, which may be considered to be the tissue clamping pressure applied to the tissue when the cuff 6 is attached to the subject's arm 5 (e.g., upper arm). The mean pressure TPcl may be calculated by applying a low pass filter to the tissue pressure TP. The low pass filter may be located in the control device 3, specifically in the processor 11 of the control device 3. The low pass filter is preferably set so that the mean pressure TPcl includes only frequencies below the lowest expected pulse rate (PRni). A preferred low pass filter is further described below. The control device 3 is preferably configured to determine an alternating component of the tissue pressure TPac by subtracting the mean pressure TPcl from the measured tissue pressure TP (i.e., TPac=TP-TPcl). In FIG. 4, the TPac curve is shown enlarged by a factor of two for ease of viewing.

[0046] During the slow inflation period, i.e., during the measurement period, the TP pulse curve and / or the TPac pulse curve are recorded, and the recorded curves can be simultaneously (i.e., online) analyzed and parameters calculated. Here, the TP pulse curve and / or the TPac pulse curve have a tissue pressure waveform (TPW) that contains information that allows blood pressure to be accurately determined. Since blood pressure is measured non-invasively (but with an accuracy comparable to that of invasive blood pressure measurement), it can be abbreviated to niBP, which stands for "noninvasive blood pressure". TPac pulse curves are shown diagrammatically and exemplarily in Figs. 5-7.

[0047] In the following, the TPac pulse curve is used to determine the characteristics of the pressure pulse 9. The TPac pulse curve may therefore be considered as a characterization pulse curve or a characterization pulse. Thus, Figures 5 to 7 show a characterization pulse curve or a characterization pulse 29 which is a TPac pulse. In another embodiment, the characterization pulse may be directly the TP pulse curve, i.e. the pressure pulse 9 may be directly used to determine the characteristics.

[0048] The control device 3 is configured to determine, for each of the plurality of pressure pulses 9, certain features characterizing each pressure pulse and to determine a measurement end point 32, at which point in time the measurement period is stopped or thereafter, based on the determined features for the plurality of pressure pulses 9. The determination of certain features of each pressure pulse, which may also be considered as TPW parameters, is described below.

[0049] As shown in Figures 7A, 7B and 7C of WO2018 / 210931A1, it was observed that when increasing the clamping pressure, i.e. increasing the pressure applied to the arm 5 via the cuff 6, the morphology of the diastolic tissue pressure pulse changes from a peaked shape to a flat diastolic shape when crossing the mean arterial pressure (MAP). This behavior can be modeled by the change of several TPW parameters. As described in the same document WO2018 / 210931A1, the TPW parameters can be extracted from the TP pulse curve.

[0050] In one embodiment, the control device 3 is configured to determine as a characteristic of each pressure pulse the TPP difference between the maximum and minimum measured pressure of each characterization pulse 29. This characteristic, i.e. this TPW parameter, is explained below with reference to FIG.

[0051] The differential TPP is the difference between the maximum systolic pressure TPsys of the characterization pulse and the pressure of the characterization pulse at the end diastolic point (TPdia) (preferably the minimum pressure of each characterization pulse). In Figures 5 and 6 and 7, "t.start" and "t.stop" indicate the start and end of each pulse 29, respectively.

[0052] The controller 3 may also be configured to determine the pulse duration (t(Pulse)), which is the time difference between the end-diastolic point of a characteristic pulse 29 and the next end-diastolic point. This characteristic may also be defined as the time difference between the start of each pulse (t.start) and the end of each pulse (t.stop). This characteristic is shown in FIG. 6.

[0053] The controller 3 may also be configured to determine the pulse area (TPA) of each pulse 29, which is the area under each pulse curve within the time defined by t.start to t.stop, ranging from the pressure of the characterizing pulse at the end diastolic point (TPdia) to the maximum systolic pressure of the characterizing pulse (TPsys). Preferably, the pulse area TPA is scaled to TPP=1 as shown in Figure 6. This scaled pressure pulse area is called "TPA.norm".

[0054] The controller 3 may also be configured to determine the half maximum pulse width (W50) of each pulse 29, as shown in FIG.

[0055] 5-7 show TPac pulse curves, and in this example the features, i.e., TPW parameters, are also defined based on the TPac pulse curves, although as mentioned above it is also possible to define these or other features based on the TP pulse curves.

[0056] The control device 3 is further configured to determine, for each pressure pulse, a termination decision combined value TPWP_E (which may also be called a "pulsation power parameter") by combining at least two of the features determined for each pressure pulse. In particular, the control device 3 may be configured to multiply a) the result of raising the determined pulse area TPA.norm to a first predetermined exponent (exp1) and b) the result of raising the determined difference TPP to a second predetermined exponent (exp2). The termination decision combined value TPWP_E can thus be calculated according to the following formula:

number

number

[0057] The control device 3 may also be configured to determine the termination decision combined value TPWP_E by: a) dividing the determined pulse area TPA.norm by a third predetermined exponent (exp3), b) dividing the determined pulse duration t(pulse) by a fourth predetermined exponent (exp4), and multiplying the quotient obtained from this division by c) dividing the determined difference TPP by a fifth predetermined exponent (exp5), which can be expressed as:

number

number

[0058] The control device 3 may also be configured to determine the end determination combined value of each pressure pulse by multiplying the calculation result obtained using, for example, formula (1) or formula (2) by the result of raising the half-width (W50) to a predetermined exponent. For example, when formula (2) is multiplied by the half-width W50, the following formula (3) is obtained.

number

number

[0059] Therefore, in this embodiment, based on at least the TPP and TPA.norm of each pulse curve, a TPWP_E reflecting the characteristic value of each pulse curve can be calculated by combining and weighting the amplitude and area parameters. Here, TPWP_E may be expanded by multiplying the result of raising W50 to a certain exponent. The exponent in each formula is a predetermined value, preferably predetermined in a manner further described below.

[0060] When the end decision combination value TPWP_E for each pressure pulse is determined by combining at least two of the features determined for each pressure pulse, several end decision combination values ​​TPWP_E become available for several pressure pulses and thus for several different times, in other words, a curve TPW_E-curve is obtained (which may also be called the "end decision curve"), since the control device 3 is configured to determine the measurement end time 32 based on this curve TPW_E-curve.

[0061] The control device 3 is further configured to determine a blood pressure determination combined value TPWP_M for each pressure pulse by combining at least two of the determined features, such that several blood pressure determination combined values ​​TPWP_M are determined for several pressure pulses present at different times. Here, several blood pressure determination combined values ​​TPWP_M determined for several pressure pulses, and thus for several times, form a blood pressure determination curve TPW_M-curve. The control device 3, in particular the processor 11 of the control device 3, is configured to determine the blood pressure based on the blood pressure determination curve TPW_M-curve. In one embodiment, the blood pressure determination curve TPW_M-curve is determined as described in WO2018 / 219031A1. In particular, by determining the arterial blood pressure based on the maximum value of the determined blood pressure determination curve and the pressure applied to the skin, i.e. the tissue pressure, a relatively short measurement time can be achieved. In general, the tissue pressure depends on the height of the arterial blood pressure, the height of the arterial pulse pressure, and the inverse of the heart rate.

[0062] The control device 3 may be configured to determine a combined blood pressure determination value TPWP_M for each pressure pulse based on a) multiplying the determined area TPA or TPA.norm by a predetermined tenth power (exp10) and b) multiplying the determined difference TPP by a predetermined eleventh power (exp11). For example, the combined blood pressure determination value TPWP_M for each pressure pulse may be calculated according to the following formula:

number

number

[0063] The control device 3 may also be configured to determine for each pressure pulse a) the determined area TPA or TPA.norm raised to a twelfth predetermined exponent (exp12), b) by dividing the determined duration (t(Pulse)) raised to a thirteenth predetermined exponent (exp13), and multiplying the quotient obtained from this division by c) the determined difference TPP raised to a fourteenth predetermined exponent (exp14). For example, the blood pressure determination combined value TPWP_M may be calculated according to the following formula:

number

number

[0064] The control device 3 may also be configured to determine a blood pressure determination combination value TPWP_M for each pressure pulse by further multiplying the result of raising the half-width W50 by a predetermined exponent. For example, the blood pressure determination combination value TPWP_M may be calculated according to the following formula:

number

number

[0065] The control device 3 is preferably configured to determine the termination decision curve TPW_E-curve to satisfy one of the following conditions: a) the maximum value of the termination decision curve (TPW_E-curve.max) occurs before in time the maximum value of the blood pressure determination curve (TPW_M-curve.max); b) the maximum value of the termination decision curve (TPW_E-curve.max) occurs simultaneously with or after in time the maximum value of the blood pressure determination curve (TPW_M-curve.max) and the decrease in the termination decision curve TPW_E-curve after the maximum value is steeper than the decrease in the blood pressure determination curve TPW_M-curve after the maximum value; c) the termination decision curve TPW_E-curve coincides with the blood pressure determination curve TPW_M-curve. Therefore, the index is preferably predefined such that a) TPW_E-curve.max occurs before TPW_M-curve.max, or b) TPW_E-curve.max occurs simultaneously with or after TPW_M-curve.max and the absolute value of the differential value of the negative derivative of the blood pressure determination curve of the TPW_E-curve after the maximum value is greater than the absolute value of the differential value of the negative derivative of the blood pressure determination curve TPW_M-curve, or c) the TPW_E-curve may be identical to the TPW_M-curve (i.e. the end determination curve may be identical to the blood pressure measurement curve).

[0066] FIG. 8 exemplarily shows a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve, where these curves are normalized so that their respective maximum values ​​correspond to 100 percent.

[0067] It is desirable to finish each blood pressure measurement as quickly as possible in order to minimize the stress of the subject. Since the maximum value of the blood pressure measurement curve TPW_M-curve is used for the non-invasive blood pressure determination, the blood pressure measurement can be ended as soon as the maximum value of the blood pressure measurement curve TPW_M-curve is formed and thus completely determinable. Thus, during the measurement period, it is checked whether a termination criterion has been reached, which defines the measurement end point. To determine whether this termination criterion has been reached, and thus to determine the measurement end point, preferably the termination decision curve TPW_E-curve and the blood pressure measurement curve TPW_M-curve are used. For example, when the termination decision curve TPW_E-curve has formed a maximum value, it is checked for each newly measured TP pulse curve, i.e. for each newly measured TP pulse, whether a) the termination decision curve TPW_E-curve has decreased below a certain percentage of the maximum value of the termination decision curve TPW_E-curve (this percentage is preferably within the range of 40% to 95%) and b) whether the blood pressure measurement curve TPW_M-curve has already formed a maximum value, i.e. has reached or passed the maximum value. The control device 3 may be configured to determine the measurement end point 32 as the point in time when both conditions a) and b) are met.

[0068] To determine whether the blood pressure measurement curve TPW_M-curve has safely reached or passed the maximum value, it may be detected whether the blood pressure measurement curve TPW_M-curve drops after the maximum value. In one embodiment, the blood pressure determination curve TPW_M-curve may be a smoothed curve such that the maximum value of the blood pressure determination curve is also smoothed. The smoothing process used to smooth the blood pressure determination curve may include, for example, filtering and / or fitting. Furthermore, to unambiguously detect the smoothed maximum value, several pressure pulses after the smoothed maximum value may be considered. The number of these several pulses may be predetermined or may depend on the subject's heart rate. For example, this number may increase with increasing heart rate. In one embodiment, this number is 3 for a heart rate of 60 / min and 10 for a heart rate of 200 / min.

[0069] To smooth the blood pressure determination curve TPW_M-curve, a moving average filter, in particular a variable moving average filter, may be applied to at least some of the pressure pulses. The window used for averaging may be fixed or variable. If variable, it preferably has a maximum duration, for example 8 seconds. The use of this filter results in a filter delay, the minimum filter delay being of the order of magnitude of the total duration of several pulses. With a filter delay of several pulses, a descending smoothed blood pressure determination curve TPW_M-curve and thus the maximum value of the blood pressure determination curve TPW_M-curve can be safely determined. That is, as soon as a drop in the smoothed blood pressure measurement TPW_M-curve is detected, the measurement period is 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 filtering window, in this example a maximum of 8 seconds, for example of at least 3 TP pressure pulses, and the application of the moving average filtering twice (2 x 8 seconds filter) removes disturbing heart-lung interactions in an estimated 95% of the measurements. These smoothing filter windows may be adapted to the respiratory rate, ventilation rate. This allows for improved removal of unwanted TPW_M-curve disturbances caused by heart-lung interactions.

[0070] In Figure 8, conditions a) and b) are both met when the termination decision curve TPW_E-curve falls below 90% of the maximum value of the termination decision curve TPW_E-curve. Due to the filter delay, both conditions a) and b) are met and the measurement is terminated after several tissue pressure pulses.

[0071] The continuous TPW_E-curve and the continuous TPW_M-curve shown in Fig. 8 were obtained by filtering the values ​​TPWP_E and TPWP_M determined for the different pressure pulses, respectively. This filtering, which produces a filter delay, will be explained further below. In Fig. 8, two additional pressure pulses occur due to the filter delay, and the fast deflation of the cuff 6 starts after both conditions a) and b) are met and two pressure pulses have occurred.

[0072] If the maximum of the end decision curve TPW_E-curve occurs a few seconds before the maximum of the blood pressure measurement curve TPW_M-curve, the measurement period can be shortened, i.e., the slow inflation time can be shortened and the amount of pressure applied to the subject can be reduced. If there are several maximum values ​​in the TPW_M-curve after t(a_end) is reached, i.e., after the end decision curve TPW_E-curve reaches a point in time below a predetermined percentage of the maximum value of the TPW_E-curve, the largest maximum value of the blood pressure decision curve TPW_M-curve is the absolute maximum value of the blood pressure decision curve TPW_M-curve (TPW_M-curve.max) if the blood pressure decision curve TPW_M-curve is decreasing at the time t(a_end). Otherwise, in one embodiment, the measurement continues until the next maximum value of the TPW_M-curve and the maximum value of the blood pressure decision curve (TPW_M-curve.max) are determined.

[0073] If a termination decision curve TPW_E-curve whose maximum occurs before the maximum of the blood pressure determination curve TPW_M-curve is not used, the slow inflation must continue until the blood pressure determination curve TPW_M-curve falls below a certain percentage of its maximum value. On average, by using a termination decision curve TPW_E-curve whose maximum occurs before the maximum of the blood pressure measurement curve TPW_M-curve, the blood pressure measurement can be terminated after about 20 to 60 seconds at a TPcl within 70 to 95% of the systolic arterial pressure (SAP). This is significantly below the termination pressure level of conventional oscillometric niBP measurements. In that case, the blood pressure measurement is terminated when the clamping pressure reaches about SAP+20 mmHg. When using the measurement system 1 described above with reference to FIG. 1, when the measurement is terminated, the tissue pressure TP falls to Patt as quickly as possible and remains there for some time before a new measurement is started, preferably for about 20 percent of the inflation-deflation period 40 shown in FIG. 4.

[0074] The control device 3, in particular the processor 11 of the control device 3, is configured to determine the blood pressure based on the blood pressure determination curve TPW_M-curve, in particular based on the maximum value of the blood pressure determination curve TPW_M-curve. The control device 3 may be adapted to perform this blood pressure (non-invasive blood pressure) determination as described in WO2018 / 210931A1.

[0075] In one embodiment, the control device 3 is configured to determine the TPcl value at the time point when the blood pressure determination curve TPW_M-curve has a maximum value (TPW_M-curve.max). Here, in FIG. 9, the TPcl value at the time point of this maximum value is shown as "TPcl@TPW_M-curve.max". The control device 3 is further configured to determine a lower envelope of the tissue pressure TP by applying a filter to the end-diastolic point of the tissue pressure TP. The filter may for example be the same as the filter used to determine the blood pressure measurement curve TPW_M-curve. The curve obtained is marked in FIG. 9 as "TPdia-curve". The control device 3 is further configured to determine an upper envelope of the tissue pressure TP by applying a filter to the systolic maximum of the tissue pressure TP. This filter may for example be the same as the filter used to determine the blood pressure measurement curve TPW_M-curve. This curve is marked in FIG. 9 as "TPsys-curve".

[0076] The control device 3 may then be configured to determine the systolic arterial pressure value as a predefined percentage (TPcl.s%) of TPcl@TPW_M-curve.max. This predefined percentage is preferably in the range of 100-150 percent, more preferably in the range of 110-150 percent. In FIG. 9, the non-invasive systolic arterial pressure is labeled "SAPni" and the predefined percentage is indicated as "TPcl.s%(TPcl@TPW_M-curve.max)". In FIG. 9, the non-invasive systolic arterial pressure SAPni is approximately 134 mmHg.

[0077] The control device 3 may also be adapted to determine the non-invasive systolic arterial pressure SAPni as a predetermined percentage (TPsys.s%) of the TPsys curve at the time position where the blood pressure determination curve TPW_M-curve is maximum, said predetermined percentage preferably being within the range of 100 to 140 percent.

[0078] The control device 3 may be configured to determine the non-invasive mean arterial pressure (MAPni) as the TPcl value, or the value of the TPDia-curve, or the value of the TPsys-curve, at a time t(bx) when the blood pressure determination curve TPW_M-curve has a value bx representing a predetermined percentage of its maximum value. The control device 3 may also be configured to determine the non-invasive mean arterial pressure MAPni as a predetermined percentage (TPcl.m%) of TPcl at TPW_M-curve.max, where the predetermined percentage is preferably within the range of 80-110%.

[0079] The control device 3 may also be configured to determine the non-invasive diastolic arterial pressure DAPni as the value of the TPdia-curve or the value of the TPcl-curve at a time t(cx) at which the blood pressure determination curve TPW_M-curve has a value cx representing a predetermined percentage of its maximum value. The control device 3 may also be configured to determine DAPni as a predetermined percentage (TPcl.d%) of TPcl@TPW_M-curve.max, where the predetermined percentage is preferably within the range of 60-80%.

[0080] As mentioned above, the indices used to determine the end determination curve TPW_E-curve and to determine the blood pressure determination curve TPW_M-curve are determined by calibration. The ratios used to determine the blood pressure value are also determined by calibration. These parameters are therefore pre-determined during the calibration phase so that the difference between the very accurately measured invasive blood pressure value and the blood pressure value obtained by the measurement system is minimized and the time required for blood pressure measurement is relatively short. Preferably, the set of indices used to determine the blood pressure determination curve TPW_M-curve (which may be considered as the first set of indices) is selected so that a good balance is achieved between a high accuracy of the non-invasive blood pressure and a low TP level at the end of the measurement (and therefore a short measurement time). If the indices are selected to 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 small. However, the accuracy and position of the finally determined non-invasive blood pressure value will also be reduced in that case. Therefore, the first set of indices is preferably selected so that a desired balance is achieved between the measurement time and the accuracy of the non-invasive blood pressure value.

[0081] The indices used to determine the termination decision curve TPW_E-curve (which may be considered to constitute a second set of indices) are preferably selected such that the maximum value of the termination decision curve TPW_E-curve is relatively early. In one embodiment, the first set of indices and the second set of indices may be the same, and as a result, the termination decision curve TPW_E-curve and the blood pressure decision curve TPW_M-curve may also be the same.

[0082] The values ​​TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d%, bx, cx are preferably calibrated by statistical evaluation of a calibration set of measurement pairs of invasive and non-invasive blood pressure values ​​recorded simultaneously from an appropriate number of people in different hemodynamic states, as described in WO2018 / 210931A1. The non-invasive blood pressure values ​​are determined by the measurement system 1 as described above, and parameters such as the values ​​TPcl.s%, TPsys.s%, TPcl.m%, TPcl.d% can be optimized such that the difference between the invasive and non-invasive blood pressure values ​​is minimized.

[0083] The control device 3, in particular the processor 11 of the control device 3, may be configured to estimate a type of blood pressure value based on two other types of already measured blood pressure values. In particular, one of the blood pressure values ​​MAPni, SAPni and DAPni may be estimated based on the remaining one of these blood pressure values. This may be done according to the following formula: SAPni=c1·MAPni+c2·(MAPni-DAPni)-c3 mmHg (7) where c1=(0.2 .. 0.7), c2=(2 .. 6), c3=(-5 .. 5). MAPni=c4·DAPni+c5·(SAPni-DAPni)-c6 mmHg (8) where c4=(0.8 .. 1.3), c5=(0.25 .. 0.5), c6=(-5 .. 5). DAPni=c7·MAPni-c8·(SAPni-MAPni)-c9 mmHg (9) where c7=(0.6 .. 1.1), c8=(0.15 .. 0.4), c9=(-5 .. 5).

[0084] The coefficients and constants of equations (7), (8), and (9) are pre-determined by calibration based on statistical evaluation of a clinical invasive blood pressure data set that is as large as possible and sufficiently wide. Thus, highly accurate invasive blood pressure values ​​SAPi (invasive systolic arterial pressure), MAPi (invasive mean arterial pressure), and DAPi (invasive diastolic arterial pressure) are used. Based on these highly accurate invasive blood pressure values, the coefficients and constants of equations (7), (8), and (9) are modified so that these equations are valid.

[0085] The blood pressure measurements are intended to be used in a sequence of measurements that are rapidly succeeding one another to allow for effective semi-continuous blood pressure monitoring with minimal stress on the monitored individual, i.e. the monitored subject. This rapid blood pressure measurement sequence may also be considered as a non-invasive fast mode cycling (FMC) measurement of blood pressure.

[0086] In one embodiment, the initial blood pressure measurement has no information about the previous diastolic arterial pressure (DAP), and therefore starts a slow inflation, i.e. measurement period, at a predefined tissue pressure TPlow in the range of 15-30 mmHg. Also, in this measurement period, the inflation rate is set to a moderate value. The inflation rate can be defined as the rate at which TPcl increases over time and may be selected to have a value of, for example, 1.9 mmHg / s. This corresponds to the measurement of a "normal" blood pressure value. When TPcl reaches Patt at the end of the contraction phase, the blood pressure measurement is interrupted, preferably for at least 2 seconds, to allow reperfusion of the part of the subject's body enclosed in the shell 4. This pause 42 preferably has a length in the range of greater than 0% and less than or equal to about 50% of the preceding inflation-deflation period 40, resulting in a cycle 41. In the subsequent blood pressure measurements, using the information of the diastolic arterial pressure (DAP / DAPprev) determined in each previous measurement, a slow inflation, i.e. measurement period, starts at a higher TPlow, as shown in FIG. 10.

[0087] To ensure that all pulses necessary for the calculation of blood pressure are recorded, the TPlow value must not exceed 90% of the diastolic arterial pressure. Furthermore, as mentioned above, blood pressure may change in the time interval (t_inter) between the start of contraction and the start of the next slow inflation. Therefore, preferably, a function is applied that models the blood pressure drop as a function of the time interval t_inter. Clinical data from high-risk surgeries confirmed that the diastolic arterial pressure may drop by more than 28% within one minute. Therefore, TPlow may be calculated using a linear function such as the following function: TPlow=90%DAPprev-28%DAPprev·t_inter / 60s (10) Here, "90%DAPprev" and "28%DAPprev" respectively indicate 90% and 28% of the previously measured diastolic arterial pressure DAPprev.

[0088] TPlow may be determined using a linear function that depends on the previous time interval from the start of deflation to the start of the next slow inflation, where the linear function has a negative slope such that TPlow decreases over time. The slope of the linear function and the positive constant of the linear function may be predetermined by calibration. In equation (10), the positive constant is 90% DAPprev and the negative slope is -28% DAPprev. The positive constant and the negative slope may have other values. For example, the negative slope may be -30% DAPprev.

[0089] In FIG. 10, it can be seen how TPlow is adapted depending on t_inter according to equation (10). In particular, it can be seen that the TPlow values ​​of measurement #2a and measurement #2b are different. The TPlow value of measurement #2b is smaller than the TPlow value of measurement #2a, since the time interval t_inter of measurement #2b is larger than the time interval of measurement #2a. Also, in FIG. 10, it can be seen that the inflation rate of measurement #3 is increased due to the increase in PP before measurement #2a. Furthermore, for measurement #3, TPlow is larger compared to the measurement before measurement #3, since the diastolic arterial pressure DAP has increased before measurement #2a. Note that in FIG. 10, interval 44 is the cycle period of the second measurement #2a, interval 43 is the inflation-deflation period of the second measurement #2a, and interval 45 is the rest time of the second measurement #2a. Also, the third measurement #3 refers to the second measurement #2a, and the further second measurement #2b is only displayed to show the substitution of the second measurement #2a.

[0090] Figure 11 shows a further example for adapting the TPlow value as a function of the time interval t_inter according to equation (10). In this example, the inflation rate during the measurement period is decreased in measurement #3 compared to the previous measurement. This is due to the decrease in PP before measurement #2a and the lower TPlow value due to the decrease in DAP before measurement #2a.

[0091] As described above, filters are used to determine the end determination curve TPW_E-curve, the blood pressure determination curve TPW_M-curve, and the envelopes TPsys-curve and TPdia-curve. Also, filters are used to determine TPcl based on TP. The filter is preferably a low-pass filter. The low-pass filter may be, for example, a cascaded moving average filter with a variable window length of 8 seconds or less. The window length may be shortened at the beginning and end of filtering to minimize filter settling time. For example, filtering may include averaging within a moving window that includes the signals of at least three TP pressure pulse curves and is 8 seconds or less, and applying moving average filtering twice (2 x 8 seconds filter). Optionally, signal padding may be applied before the start and / or after the end of the signal to completely fill the filter window before filtering. For example, padding may be applied with the value of the first pressure pulse before the start and the value of the last pressure pulse after the end.

[0092] Due to the filter delay, TPcl is extrapolated from previous values ​​to make it available at the end of the measurement signal. Filters may be applied, for example, to extract TPcl from TP, to form a smooth TPW_E-curve and a smooth TPW_M-curve that are free of fluctuations due to blood pressure pulsations, and to create envelope functions (TPsys-curve and TPdia-curve) on the systolic peaks and end-diastolic minima of TP.

[0093] In a preferred embodiment, equation (5) is used with exponents exp12=0.7, exp13=0.4, and exp14=1.0 to determine the blood pressure determination curve TPW_M-curve. By using these exponents with equation (5) for inflation-deflation periods in the range of 20-60 seconds, very good accuracy and precision can be obtained, which was confirmed by statistical evaluation of the non-invasive blood pressure values ​​determined by the measurement system 1 against simultaneously obtained invasive blood pressure reference values. Even higher accuracy and precision can be obtained by combining exponents exp10=1.0, exp11=1.21 with equation (4), but the measurement time will also increase by a few seconds.

[0094] In one embodiment, to determine the termination determination curve TPW_E-curve, equation (2) is used with exponents exp3=1.1, exp4=0.4, and exp5=0.5. It has been found that by using these exponents, it is possible to determine a relatively early termination of the slow inflation period, i.e., a relatively early measurement termination point, for inflation-deflation periods in the range of 20 to 60 seconds.

[0095] Next, an embodiment of a control method for controlling the measurement system 1 will be described by way of example with reference to the flowchart shown in FIG.

[0096] After initializing and starting the system in step 101, TPlow is determined in step 102. For the first measurement, TPlow may be set to a value between 15 mmHg and 30 mmHg. If a blood pressure measurement has already been performed, the previous diastolic arterial blood pressure value may be used to determine TPlow, for example according to equation (10).

[0097] In step 103, during the pre-measurement period, the cuff is inflated with a relatively large first inflation rate until TPlow is reached. Then, in step 104, the measurement period, i.e. the slow inflation period, is started. During the measurement period, a blood pressure determination curve TPW_M-curve and an end determination curve TPW_E-curve are determined. Furthermore, these curves are used to determine the end measurement time point. When the end measurement time point is reached or the end measurement time has elapsed, the slow inflation period is stopped and the cuff is deflated in step 105. After the deflation ends and a pause to allow venous return in step 106, the method continues with step 102. Thus, the control method can be implemented as a loop for continuously monitoring the blood pressure over time over several measurement cycles. While executing steps 102-105, the control device calculates blood pressure values ​​in parallel. The loop may be executed until an interruption criterion is met. For example, blood pressure monitoring is interrupted when the physician enters a corresponding command into the measurement system via an input unit such as a keyboard, a computer mouse, a touchpad, etc.

[0098] The measurement system allows non-invasive FMC measurement of blood pressure based on non-invasive, high fidelity tissue pressure TP recordings, preferably recorded with an anti-kink shell system as described in WO2014 / 121945A1. The measurement system preferably allows a statistical mean maximum pressure inflation of about 85 percent or less of the systolic arterial pressure. A single blood pressure measurement with the measurement system 1 typically takes about 20-60 seconds and depends on the height of the arterial pressure and pulse pressure, and the inverse of the heart rate. The measurement system is preferably configured to provide a non-invasive systolic arterial pressure SAPni, a non-invasive mean arterial pressure MAPni, and a non-invasive diastolic arterial pressure DAPni. The measurements are preferably performed with short pauses during which the cuff is not pressurized between successive measurements to allow venous return. These short pauses are preferably 5-10 seconds. Since the clamping pressure preferably remains below SAP at all times, it is preferred that the arterial perfusion of the subject's shell-covered areas (such as the upper arm and wrist) is not completely interrupted during the measurements. Therefore, the measurement places less stress on the subject than in conventional oscillometric measurements.

[0099] Conventional oscillometric noninvasive blood pressure measurements determine blood pressure using either continuous deflation or step-deflation techniques. The blood pressure cuff is inflated to a target clamping pressure above SAP, and then deflation is performed either continuously or stepwise. Conventional devices determine whether the actual SAP has been exceeded by slowly deflating, and if a proprietary algorithm determines that the deflation has not begun sufficiently above, at or below SAP, the deflation is stopped and inflation is performed to a higher target pressure well above SAP and deflated again.

[0100] Nihon Kohden uses a non-invasive blood pressure measurement called iNIBP, in which blood pressure is measured during blood pressure cuff inflation using an algorithm that detects blood pressure oscillations. SAP is detected and the measurement is terminated if the clamping pressure exceeds SAP. If blood pressure cannot be measured during inflation, a stepwise deflation is performed after inflation.

[0101] However, the article "Validation of inflationary noninvasive blood pressure monitoring in the emergency room" by J. Sasaki et al., Blood Pressure Monitoring, pp. 325-329 (2015) states that stepwise deflation after inflation is often required for iNIBP blood pressure measurement in the emergency room. Specifically, stepwise deflation was required in addition to inflation in more than 30% of the cases investigated. Therefore, the measurement time may be relatively long. Furthermore, increasing the clamping pressure to a high level above SAP may cause discomfort and pain in the awake subject. In contrast, the measurement system 1 described above, for example with reference to FIG. 1, provides a reliable method for quickly determining blood pressure with a clamping pressure that does not exceed SAP. Due to the relatively short measurement time and the relatively low maximum cuff pressure, this blood pressure measurement is very convenient for the subject and can reduce the risk of potential complications such as thrombophlebitis, pain, ecchymosis, limb edema, peripheral neuropathy, etc.

[0102] In one embodiment, TPlow may be equal to or greater than DAP. TPlow defines the tissue pressure at the beginning of the measurement period, i.e., the beginning of the slow inflation period, which may be terminated when certain termination criteria are reached. The termination criteria are described above.

[0103] Although in the above embodiment the features are determined by using the TPac pulse, the features may also be determined by directly using the measured pressure pulse, i.e. the TP pulse. It is also possible to process the TP pulse in a different way to determine the TPac pulse, i.e. other than by subtracting the average TP value. For example, for each measured pressure pulse, a line may be connected between the pressure value at t.start and the pressure value at t.stop, and this line may be subtracted from each measured pressure pulse to determine the feature determination pulse.

[0104] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art to which the claimed invention is directed, from the drawings, the disclosure, and the appended claims.

[0105] In the claims, the term "comprising" does not exclude other elements or steps, and the singular does not exclude a plurality.

[0106] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that several measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0107] The calculations performed by one or more units or devices, e.g. determination of measurement end time, pulse characteristics, curves, blood pressure values, etc. may be performed by any number of other units or devices. The calculations and determinations and / or the control of the measurement system according to the control method can be implemented as computer program code means and / or as dedicated hardware.

[0108] The computer program may be stored and / or distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, or may be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0109] Any reference signs in the claims should not be construed as limiting the scope. In particular, letters such as TPP and TPA used as reference signs in parentheses in the claims should not be construed as limiting the scope. For example, features other than those represented by the reference signs may be used in accordance with the claims.

[0110] The present invention relates to a control device for controlling a blood pressure measurement system. While a pressure applying unit applies increasing pressure to a part of a subject during a measurement period, pressure including a plurality of pressure pulses is measured on the skin of the part of the subject. For at least some of the pressure pulses, some features characterizing the pressure pulse are determined, and a measurement end point, which is a timing at which the measurement period is stopped or is subsequently stopped, is determined based on these features. When the measurement end point is reached (i.e., when the measurement period is stopped), the applied pressure is reduced and a subsequent post-blood pressure measurement period is started. This allows the blood pressure measurement time to be shortened or the maximum tissue pressure on the skin to be reduced.

Claims

1. A control device for controlling a measurement system for measuring the blood pressure of a subject, the measurement system comprising: a) a shell that encases a part of the subject through which blood flows; b) a pressure applying unit that applies pressure to the shell from the outside of the shell, thereby applying an applied pressure to the encased part of the subject; and c) a pressure sensor that measures the pressure on the skin of the encased part of the subject, wherein the control device controls the measurement system to: The pressurizing unit increases the applied pressure during a measurement period and decreases the applied pressure during a subsequent post-blood pressure measurement period; the pressure sensor measures the pressure on the skin during at least the measurement period; the pressure to be measured includes a plurality of pressure pulses, and the control device determines, for at least a portion of the plurality of pressure pulses, a number of features characterizing the pressure pulse, determines a measurement end point based on the features determined for the at least a portion of the plurality of pressure pulses, and controls the pressurizing unit to terminate the measurement period and reduce the applied pressure to start a subsequent post-blood pressure measurement period when or after the measurement end point is reached; The controller provides a characterization pulse based on each pressure pulse to determine a characteristic for the each pressure pulse; the difference between the peak systolic pressure of the characterizing pulse and the pressure of the characterizing pulse at the end diastolic point; the duration of said characterization pulse; the area of ​​the characterization pulse, and determining at least one characteristic of a half-width of said characterization pulse; Control device.

2. The control device includes: determining, for each pressure pulse, a termination decision combination value by combining at least two of said features determined for each pressure pulse, and determining several termination decision combination values ​​for several pressure pulses present at different times, wherein said several termination decision combination values ​​determined for said several pressure pulses, and thus for several times, form a termination decision curve; determining the measurement end point based on the end determination curve; The control device according to claim 1 .

3. The control device includes: a) multiplying the result of raising the determined area by a predetermined first exponent by b) multiplying the result of raising the determined difference by a predetermined second exponent; and a) dividing the result of raising the determined area to a third predetermined exponent, b) dividing the result of raising the determined duration to a fourth predetermined exponent, and multiplying the quotient obtained from this division by c) dividing the result of raising the determined difference to a fifth predetermined exponent; determining a termination decision combination value for each pressure pulse based on at least one of: the first predetermined index, the second predetermined index, the third predetermined index, the fourth predetermined index, and the fifth predetermined index are predetermined by a calibration measurement; The control device according to claim 2.

4. The control device of claim 3, wherein the control device determines an end determination combined value for each pressure pulse based on further multiplying the half-width by another predetermined exponent previously determined by a calibration measurement.

5. The control device includes: determining a blood pressure determination combined value for each pressure pulse by combining at least two of the determined plurality of features, thereby determining a number of blood pressure determination combined values ​​for a number of pressure pulses present at different times, wherein the determined number of blood pressure determination combined values ​​for the number of pressure pulses, and thus for the number of times, form a blood pressure determination curve; determining the blood pressure based on the blood pressure determination curve; A control device according to any one of claims 1 to 4.

6. The control device according to claim 5 , wherein the control device determines a maximum value of the blood pressure determination curve and determines the blood pressure based on the determined maximum value and the measured pressure.

7. The control device includes: a) multiplying the result of raising the determined area by a predetermined tenth power, and b) multiplying the result of raising the determined difference by a predetermined eleventh power; a) dividing the result of raising the determined area to a predetermined twelfth power, b) dividing the result of raising the determined duration to a predetermined thirteenth power, and multiplying the quotient obtained from this division by c) dividing the result of raising the determined difference to a predetermined fourteenth power; determining a blood pressure determining combination value for each pressure pulse based on at least one of: the predetermined tenth index, the predetermined eleventh index, the predetermined twelfth index, the predetermined thirteenth index, and the predetermined fourteenth index are predetermined by a calibration measurement; The control device according to claim 5 or 6.

8. The control device of claim 7, wherein the control device determines a combined blood pressure determination value for each pressure pulse based on further multiplying the half-width by another predetermined exponent previously determined by a calibration measurement.

9. The control device includes: the maximum of the end determination curve occurs prior in time to the maximum of said blood pressure determination curve; a maximum value of the end determination curve occurs simultaneously or later in time with a maximum value of the blood pressure determination curve, and a decrease in the end determination curve after the maximum value of the end determination curve is steeper than a decrease in the blood pressure determination curve after the maximum value of the blood pressure determination curve; and The termination decision curve is the same as the blood pressure decision curve. The termination decision curve is determined so as to satisfy one of the following conditions: The control device according to claim 7 which relies on claim 6, or claim 7 which relies on claim 6.

10. The control device further determines the measurement end point based on the blood pressure determination curve, as described in claim 6 which recites claim 5 which recites claim 2, claim 7 which recites claim 5 which recites claim 2, claim 8 which recites claim 5 which recites claim 2, or claim 9 which recites claim 5 which recites claim 2.

11. 11. The control device of claim 10, wherein the control device determines the measurement end time by determining: a) when the end determination curve, after passing through the maximum value of the end determination curve, falls to a value below a predetermined percentage of the maximum value; and b) when the blood pressure determination curve reaches or passes through the maximum value of the blood pressure determination curve.

12. The control device of claim 11, wherein the predetermined percentage of the maximum value is in the range of 40% to 95%.

13. 13. The control device of claim 1, wherein the control device controls the pressurizing unit to increase the applied pressure at a first rate during a pre-measurement period and then at a second rate during the measurement period, the first rate being greater than the second rate.

14. The control device according to claim 13, wherein the control device controls the pressure applying unit so that the pressure measured at the end of the pre-measurement period is within a range of 15 to 30 mmHg.

15. The control device includes: storing or receiving a previous diastolic arterial pressure obtained from a previous blood pressure measurement; determining the first end measured pressure based on the previous diastolic arterial pressure such that the first end measured pressure to be present at the end of the pre-measurement period is less than the previous diastolic arterial pressure; controlling the pressurizing unit so that the pressure measured at the end of the pre-measurement period becomes equal to or less than the first end-time measured pressure; A control device according to claim 13 or 14.

16. The control device of claim 15 , wherein the control device determines the first ending pressure measurement to be less than or equal to 90% of the previous diastolic arterial pressure.

17. 17. The control device of claim 15 or 16, further comprising: a controller that stores or receives a time at which the previous diastolic arterial pressure was measured; and determines the first ending measured pressure based on i) the previous diastolic arterial pressure and ii) a temporal distance to the blood pressure measurement at which the previous diastolic arterial pressure was measured as indicated by the stored time.

18. 1. A measurement system for measuring a blood pressure of a subject, the measurement system comprising: a shell that encases the part of the subject through which blood flows; a pressure unit that applies pressure to the shell from the outside of the shell, thereby applying pressure to the enclosed area of ​​the subject; a pressure sensor for measuring pressure on the skin of the subject at the wrapped area; and a control device according to any one of claims 1 to 17. Measurement system.

19. 20. A method of operating a measurement system according to claim 18, comprising the steps of: The control device increases the applied pressure during a measurement period by using the pressure unit, and then decreases the applied pressure during a post-blood pressure measurement period; the control device measuring the pressure on the skin at least during the measurement period by using the pressure sensor; wherein the measured pressure includes a plurality of pressure pulses; The controller further includes determining, for each of at least some of the pressure pulses, a number of features that characterize the pressure pulse; determining, by the controller, based on the determined characteristics of the at least some of the pressure pulses of the plurality of pressure pulses, a measurement end point at which the measurement period is or will subsequently be stopped; The control device further includes a step of controlling the pressure applying unit to reduce the applied pressure when or after the measurement end point is reached to end the measurement period and start the subsequent post-blood pressure measurement period, the controller providing a characterization pulse based on each pressure pulse to determine some of the characteristics for each pressure pulse; the difference between the peak systolic pressure of the characterizing pulse and the pressure of the characterizing pulse at the end diastolic point; the duration of said characterization pulse; the area of ​​the characterization pulse, and The half-width of the characterizing pulse Find at least one feature of How the measurement system works.

20. 20. A computer program for controlling a measurement system according to claim 18, said computer program comprising program code means for causing, when said computer program is executed on the control device of the measurement system, to carry out the steps of the method for operating a measurement system according to claim 19.

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