Continuous blood pressure measuring system and method

Abstract

Systems and methods for measuring blood pressure make flow velocity measurements from arterial locations and blood vessel diameter measurements from the same arterial location using an ultrasound system. Arterial wave velocities are obtained from blood flow velocities and vessel diameters, and then blood pressure changes are tracked. Continuous blood pressure estimation is made by intermittent cuff measurements along with tracking variations in blood pressure between those intermittent measurements.

Description

Technical Field

[0001] The present invention relates to a method and a computer program for measuring blood pressure, a blood pressure analysis system and a blood pressure measurement system, and in particular to continuous but non-invasive blood pressure measurement. Background Art

[0002] Continuous blood pressure (BP) monitoring is an important aspect of patient management in the perioperative setting. Continuous BP can only be obtained invasively using an arterial line. However, this carries risks, such as the risk of nosocomial infection. In addition, there is a drive to shorten the period of using invasive BP monitoring. The main obstacle to this drive is the absence of suitable alternatives for continuous assessment of BP.

[0003] An alternative to an arterial line is an inflatable pressure cuff. However, a pressure cuff may provide measurements only during intermittent periods of time (e.g., after a preprogrammed time interval set by the clinician, such as after every 5 or 10 minutes). In this approach, dynamic changes in BP that occur between such measurements may be missed.

[0004] Continuous BP monitoring is essential for many perioperative procedures, such as assessment of hemodynamic instability, and for identifying and differentiating types of shock.

[0005] US2005 / 0143640 discloses a system that uses ultrasound data in combination with pressure measurements from an inflatable pressure cuff to provide blood pressure estimates. Ultrasound is used to analyze the propagation waveform at multiple locations along the artery and derive the pulse wave velocity. This is used to derive the blood pressure measurement.

[0006] US2010 / 0106016 also describes non-invasive continuous blood pressure measurement by combining blood pressure cuff measurements with ultrasound analysis to monitor the size, shape and appearance of arteries. This arterial information is used to create a mechanical model of the artery from which blood pressure can be estimated.

[0007] These methods are complex to implement and / or inaccurate. There remains a need for a simple and accurate way to continuously and non-invasively monitor blood pressure.

[0008] US2006 / 211942 discloses the use of ultrasound to determine blood flow rate and blood vessel diameter. A transmission line model is used to relate blood vessel measurements to electrical components. The method uses two sensors or sensor arrays to obtain two different measurements. Summary of the invention

[0009] The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

[0010] According to one aspect of the present invention, there is provided a method for measuring blood pressure, the method comprising:

[0011] receiving ultrasonic blood flow velocity measurements from an arterial location; and

[0012] receiving ultrasound vessel diameter measurements from the same arterial location using the same single ultrasound system;

[0013] Arterial wave velocity is determined from the diameter-velocity cycle related to blood flow velocity and vessel diameter;

[0014] tracking blood pressure changes based on the arterial wave velocity and blood flow velocity measurements;

[0015] obtaining intermittently measured blood pressure from a cuff; and

[0016] A continuous blood pressure estimate is derived from the intermittent measurements and the tracked blood pressure changes between those intermittent measurements.

[0017] The method uses ultrasound to continuously obtain velocity and diameter measurements from arterial locations and converts this information to track relative changes in blood pressure. Ultrasound information can be obtained from a wearable ultrasound system. By combining information from a blood pressure cuff, absolute pressure can be continuously tracked. Analysis can be performed with the aid of closed-loop calculations that can be used in real time.

[0018] The method may include:

[0019] receiving pulsed wave Doppler ultrasound blood flow velocity measurements from an arterial location; and receiving B-mode ultrasound blood vessel diameter measurements from the same arterial location.

[0020] M-mode ultrasound may alternatively be used to derive vessel diameter measurements.

[0021] Thus, a single ultrasound system at a single arterial location may be used.

[0022] The method may include obtaining the arterial wave velocity based on the rate of change of blood flow velocity with respect to the logarithm of the diameter. The derivative relationship between blood flow velocity and diameter produces the arterial wave velocity.

[0023] The method may include setting the timing of the next cuff measurement based on the level of change in arterial wave velocity. In this way, when cuff measurements are not required, the number of cuff measurements can be reduced, thereby saving power and discomfort. When it can be determined that the blood pressure has not changed significantly, cuff measurements are not required.

[0024] The method may include identifying a change in arterial wave velocity that is a predetermined factor greater than a threshold level of hemodynamic change. For example, the threshold level relates to changes in blood pressure due to breathing or due to the action of taking a cuff pressure measurement.

[0025] The method may further comprise estimating cardiac output from the blood flow velocity measurements and the vessel diameter measurements.Thus, both BP and cardiac output may be tracked continuously and non-invasively.

[0026] The present invention also provides a blood pressure analysis system, comprising:

[0027] A single ultrasound system; and

[0028] A processor, the processor being configured to:

[0029] receiving a blood flow velocity measurement from an arterial location acquired by an ultrasound system;

[0030] receiving a blood vessel diameter measurement obtained by an ultrasound system from the same arterial location;

[0031] Arterial wave velocity is determined from the diameter-velocity cycle related to blood flow velocity and vessel diameter;

[0032] tracking blood pressure changes based on the arterial wave velocity and blood flow velocity measurements;

[0033] receiving intermittently measured blood pressure from a cuff; and

[0034] A continuous blood pressure estimate is derived from the intermittent measurements and the tracked blood pressure changes between those intermittent measurements.

[0035] The analysis system includes a processor for executing the above method.

[0036] For example, the processor is configured to set the timing of the next cuff measurement based on the level of change in arterial wave velocity. For example, the processor is further configured to identify a change in arterial wave velocity that is a predetermined factor greater than a threshold level of hemodynamic change. The processor may also estimate cardiac output based on the blood flow velocity measurement results and the vessel diameter measurement results.

[0037] The present invention also provides a blood pressure measurement system, comprising:

[0038] A single ultrasound system configured to:

[0039] obtaining blood flow velocity measurements from an arterial location; and

[0040] Obtain vessel diameter measurements from the same arterial location;

[0041] a blood pressure cuff; and

[0042] The blood pressure analysis system described above.

[0043] For example, the ultrasound system includes an ultrasound patch. This provides a comfortable wearable system for continuous blood pressure monitoring.

[0044] For example, the ultrasound system of the blood pressure measurement system is configured as follows:

[0045] Obtaining arterial diameter measurements using B-mode ultrasound imaging; and

[0046] Blood velocity measurements were obtained by pulsed-wave Doppler ultrasound.

[0047] The present invention also provides a computer program product comprising a computer program, wherein the computer program is configured to execute the above method when the program is run on a processor of the above blood pressure analysis system.

[0048] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] For a better understanding of the invention, and to more clearly show how it may be put into practice, reference will now be made to the accompanying drawings, in which:

[0050] Figure 1 A method and system for measuring blood pressure are shown;

[0051] Figure 2 A graph showing the natural logarithm of the blood vessel diameter (i.e., lnD) versus the blood velocity U;

[0052] Figure 3 The velocity waveform is shown over time, and the systolic foot and end diastole are shown;

[0053] Figure 4 shows the relationship between pressure P and blood flow velocity U; and

[0054] Figure 5 One method for determining when there is a change in arterial wave velocity to trigger a new cuff measurement is shown. DETAILED DESCRIPTION

[0055] The present invention will be described with reference to the accompanying drawings.

[0056] It should be understood that the detailed description and specific examples are intended for illustrative purposes only while indicating exemplary embodiments of the device, system and method, and are not intended to limit the scope of the invention. These and other features, aspects and advantages of the device, system and method of the present invention will be better understood through the following description, the appended claims and the accompanying drawings. It should be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar components.

[0057] The present invention provides a system and method for measuring blood pressure. The system uses an ultrasound system to make flow velocity measurements from an arterial location and to make vessel diameter measurements from the same arterial location. Arterial wave velocity is obtained from the blood flow velocity and vessel diameter measurements, and then blood pressure changes are tracked. Continuous blood pressure estimation is performed based on intermittent cuff measurements together with the tracked blood pressure changes between those intermittent measurements.

[0058] Figure 1 A method 100 of measuring blood pressure is shown. Hardware components for performing the method steps are shown as dashed boxes.

[0059] Ultrasonic blood flow velocity U measurements are obtained from an arterial location in step 102. Ultrasonic blood vessel diameter D measurements are obtained from the same arterial location in step 104. Ultrasonic measurements are obtained by ultrasound system 101 .

[0060] In step 106, the relationship between the logarithm of the blood vessel diameter (ie, lnD) and the blood flow velocity U is analyzed.

[0061] This enables the arterial wave velocity C to be determined in step 108 .

[0062] A numerical estimator is used in step 110 to solve equations relating vessel diameter D, flow velocity U, arterial wave velocity C and pressure (explained further below). This enables tracking of blood pressure changes in step 112 based on previous arterial wave velocity and blood flow velocity measurements.

[0063] Intermittently measured blood pressure is received from a cuff 115 in step 114. In step 116, a continuous blood pressure estimate is derived from the intermittent measurements and the tracked changes in blood pressure between those intermittent measurements.

[0064] Steps 106, 108, 110, 112, and 116 are performed by processor 118, which processes the received ultrasound data (pulsed mode Doppler ultrasound blood flow velocity measurements and B-mode ultrasound vessel diameter measurements) and the received cuff pressure measurements and derives continuous BP values.

[0065] Thus, the core of the invention utilizes velocity and diameter measurements using ultrasound in the arteries to calculate arterial wave velocity C, and thereafter uses C (in conjunction with blood pressure measurements) to track blood pressure changes. Combined with BP measured intermittently using a cuff, BP can be estimated continuously and non-invasively.

[0066] Velocity and diameter measurements may be obtained using an ultrasound patch, and cuff measurements may be obtained using a standard blood pressure cuff. The method may be operated in real time.

[0067] For example, a wearable ultrasound patch can be applied to the carotid artery to continuously acquire arterial diameter D via B-mode ultrasound imaging and local blood velocity U measurements via pulsed wave Doppler (PWD). These D and U measurements can be used to estimate arterial wave velocity C as follows:

[0068]

[0069] Figure 2 A plot of the natural logarithm of the vessel diameter (ie, lnD) versus the blood flow velocity U is shown. The relationship forms a cycle during each heartbeat cycle. The diameter-velocity cycle involves the blood flow velocity and the vessel diameter (specifically, the logarithm of the vessel diameter in this example).

[0070] The start and end of each heartbeat at the location on the artery where the patch is applied can be determined based on identifying the systolic foot and the end diastolic phase from either or both of the D and U waveforms.

[0071] As an example, Figure 3 The velocity waveform is shown over time, and the systolic foot and end-diastolic phase of the first two pulses are shown.

[0072] The change in speed (dU) can be written as a positive (dU + ) and negative speed (dU - ). Positive and negative velocities refer to the forward and backward velocity components of a traveling wave.

[0073] A similar explanation applies to the diameter D.

[0074] Equation 1 above describes the linear relationship between U and lnD for a unidirectional wave. Since during the early part of contraction, reflected waves are unlikely to occur or their effects are minimal, by fitting a straight line to the lnD vs. U loop (e.g. Figure 2 As shown) we obtain 1 / 2C and therefore C can be derived.

[0075] Thus, a tangent line in the initial portion of the cycle (e.g., at a position corresponding to before or near the peak systolic velocity) is used to derive the arterial wave velocity C. From a computational perspective, C can be calculated by using an overall average lnD vs.U cycle acquired over multiple heartbeats, or equivalently (i.e., by averaging multiple lnD vs.U cycles), C can be calculated for each heartbeat and then averaged. When multiple beats are used, a quality check can be included, for example, the D and U values ​​from each individual beat should remain within a certain range, such as two standard deviations or less.

[0076] For further explanation, refer to J Feng et al., “Determination of wave speed and waveseparation in the arteries using diameter and velocity”, J. Biomech. 2010 Feb 10, 43(3): pp. 455-462.

[0077] As described in that article, when only unidirectional waves are present, this relationship results in a straight line in the early part of the cycle when the wave is most likely running in the forward direction. Using knowledge of the wave speed, a set of equations are derived to separate the forward and backward waves from the measured D and U waveforms. Once the forward and backward waveforms for D and U are established, the energy carried by the forward and backward waves is determined.

[0078] A similar relationship exists between pressure, arterial wave velocity, and blood flow velocity:

[0079]

[0080] Figure 4 The relationship between pressure P and blood flow velocity U is shown. Again, this relationship forms a cycle for each heartbeat cycle.

[0081] Since C is known, and p is the blood density (constant), the change in pressure P can be estimated after each heartbeat or after taking an average over a set of heartbeats.

[0082] The value C has been calculated according to equation 1 and the velocity dU is obtained by ultrasonic measurement ± Therefore, Equation 2 can be rearranged to calculate the change in pressure, ΔP.

[0083] The above method effectively tracks blood pressure changes. Combined with the intermittent measurement of blood pressure P using a cuff, it is possible to non-invasively and continuously track the absolute pressure P+ΔP.

[0084] Thus, the present invention is able to measure BP using a single sensor and measuring at a single location using equations 1 and 2. The simplicity of the equations means that BP measurement can be achieved in real time and using an ultrasound sensor that can be placed at a location different from (and possibly remote from) the cuff location. For example, the ultrasound sensor can be placed at the carotid artery or the femoral artery (or both), while the cuff is placed on one of the arms.

[0085] As mentioned above, using only cuff measurements means that dynamic changes that occur in BP between such measurements may be missed. Furthermore, if BP remains stable, a new BP cuff measurement is redundant, but makes the measurement uncomfortable for the patient. Thus, obtaining cuff-based BP measurements at a predetermined frequency is associated with two disadvantages:

[0086] (i) BP is a dynamic signal, and obtaining only intermittent point measurements can lead to missed clinical insights, especially for trend information. For example, a patient with intermittent hypotension may show two normal consecutive BP measurements, between which a hypotensive episode occurs. This situation may lead to false clinical confidence in the patient's BP stability.

[0087] (ii) For example, cuff inflation is uncomfortable for the patient and may interfere with sleep and recovery.

[0088] An optional additional feature is for dynamically triggering cuff inflation so that it only occurs when there is confidence that the underlying BP has changed to a meaningful degree from the last cuff measurement.

[0089] This dynamic method of triggering cuff-based measurements will not only provide richer data and more insight into the patient's BP stability, but also lead to a better patient experience due to improved comfort.

[0090] Thus, ultrasound analysis as described above can be used to non-invasively and continuously assess that the underlying BP has changed a significant amount from the last cuff-based measurement, and this information can be used to trigger cuff reinflation and a new BP measurement.Thus, pressure changes can be used to change the timing of the cuff-based measurement.

[0091] This is Figure 1 This is indicated by arrow 120 .

[0092] Equation 2 above shows that significant changes in arterial wave velocity C may be associated with significant changes in pressure P. Therefore, by quantifying significant changes in C, it can be determined when a cuff measurement should be taken.

[0093] It is known from the literature that cuff inflation can lead to a clinically insignificant increase in BP (e.g., <10 mm Hg). Similarly, respiratory modulation of BP is a well-known phenomenon. These changes in BP will correlate with changes in C.

[0094] By utilizing these conventionally accessible changes in C, levels at which changes in C are significant can be determined. For example, a change in C can be determined to be significant when the change in C differs by a predetermined factor from normal hemodynamic changes due to breathing or changes due to inflation of a blood pressure cuff. In this way, significant changes in C can be determined, which will reflect significant underlying changes in BP. This determination can then be used to (re)trigger the BP cuff to obtain a new BP measurement.

[0095] There are various methods for determining what constitutes a meaningful change in C, thereby performing a new BP measurement.

[0096] The first method is to use several heartbeats before cuff inflation and average their lnD vs. U curves to calculate C avg The overall average value of the cuff inflation C cuff During this time a new value C is calculated. Cuff inflation changes BP and thus also C, but only to clinically insignificant values ​​(<10 mm Hg) as described above.

[0097] This is reported, for example, in V. Sheshadri et al., “Accuracy in blood pressure monitoring: The effect of noninvensive blood pressure cuff inflation on intra-arterial blood pressure values” Anesth Essay Res., vol. 11, no. 1, p. 169, 2017.

[0098] As long as the overall value C avg With C cuff If the difference is a predetermined factor (e.g. 10%), the cuff can be triggered to re-inflate. Then, C cuff .

[0099] exist Figure 5 This method is shown in .

[0100] In step 200, ultrasound measurements are performed as described above.

[0101] In step 202, the mean arterial wave velocity C is calculated. avg In step 204, during the previous cuff inflation period, the average C avgThe results of the arterial wave velocity measurement C cuff If the difference exceeds the threshold, the cuff is re-inflated in step 206 and C is obtained. cuff In step 208, continuous BP measurement is continued.

[0102] An alternative second method is to exploit the fact that respiratory modulation also changes BP and thus the C value for the heartbeat corresponding to the respiratory cycle. The standard deviation of C over one or more respiratory cycles, i.e., C resp-sd . Similarly, you can use the same resp-sd The change of C by a different predetermined factor triggers the cuff inflation. Afterwards, C can be recalculated. resp-sd .

[0103] The slope of the DU cycle can be used to generate a trigger, as is clear from the example above. However, additional triggers can be used, such as the area under the curve of the DU cycle, the shape of the DU cycle (i.e., aspect ratio), etc. These triggers can be generic (e.g., using defined thresholds) or patient specific (e.g., based on triggers exceeding standard deviations observed in a particular patient), or via contextual information from a patient monitor (such as the presence of a ventilator and its settings).

[0104] The system can be enhanced with additional functionality. One option is to estimate cardiac output.

[0105] WO2021 / 250234 discloses a method for deriving hemodynamic parameters based on blood velocity and arterial diameter measurements (i.e., parameters obtained by the above-mentioned systems and methods). Specifically, stroke volume and cardiac output can be obtained. Thus, it has been shown that velocity and diameter estimates from the carotid artery can be used to estimate cardiac output (CO). Therefore, in combination with the above-mentioned blood pressure monitoring system, both BP and CO can be tracked continuously and non-invasively.

[0106] Cuff inflation can affect hemodynamics and CO estimation, so the period corresponding to cuff inflation should not be used for CO estimation. Cuff inflation acts as a triggering event that impedes blood flow by increasing arterial resistance over the limb. The corresponding dilation of the common carotid artery during this period can also be used as a template for the patient if the patient has fluid overload.

[0107] The system can also be used to derive pulse contours or external hemodynamic parameters. Pulse contour analysis requires estimates of arterial compliance and resistance determined from arterial pressure waveforms typically measured at peripheral sites. These estimates change over time as the patient's condition changes. Pulse wave velocity estimates performed at the carotid arteries can also be used to estimate (local) arterial compliance. Due to the anatomical location of the carotid arteries closer to the central aorta, they are more sensitive to changes in central hemodynamic parameters (e.g., resistance and compliance).

[0108] Therefore, the pulse wave velocity measurement can be used as a trigger to update the hemodynamic parameters of the pulse profile analysis system.Alternatively, changes in the peripheral pressure waveform can be used to trigger the update of the carotid pulse wave velocity.

[0109] As described above, the pulse wave velocity in the carotid artery is determined from the initial linear portion of the velocity-diameter cycle. This is performed based on the assumption that the velocity and diameter waveforms are not affected by reflections from peripheral sites (i.e., no reflections). Therefore, the transition from the linear region to the non-linear region can be used to determine that there is (increased) reflection and therefore that the vascular tone has changed.

[0110] Variations of the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention, based on a study of the drawings, the present disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0111] The functions implemented by a processor may be implemented by a single processor or by multiple separate processing units, which may be collectively considered to constitute a “processor.” In some cases, such processing units may be remote from each other and communicate with each other in a wired or wireless manner.

[0112] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0113] The computer program may be stored / distributed on suitable media such as optical storage media or solid-state media supplied together with or as part of other hardware, but may also be distributed in other forms such as via the Internet or other wired or wireless telecommunications systems.

[0114] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A method for measuring blood pressure, the method comprising: receiving (102) ultrasonic blood flow velocity measurements from an arterial location; and receiving (104) ultrasound vessel diameter measurements from the same arterial location using the same single ultrasound system; Determine (108) arterial wave velocity based on the diameter-velocity cycle related to blood flow velocity and vessel diameter; tracking (112) blood pressure changes based on the arterial wave velocity and the blood flow velocity measurements; obtaining (114) intermittently measured blood pressure from a cuff; as well as A continuous blood pressure estimate is derived (116) based on the intermittent measurements and the tracked blood pressure changes between those intermittent measurements.

2. The method according to claim 1, comprising: receiving a pulsed wave Doppler ultrasound blood flow velocity measurement from the arterial location; as well as A B-mode ultrasound vessel diameter measurement is received from the same arterial location.

3. The method according to claim 1 or 2, comprising obtaining the arterial wave velocity based on the rate of change of blood flow velocity with respect to the logarithm of the diameter.

4. A method according to any one of claims 1 to 3, comprising setting the timing of the next cuff measurement based on the level of change of the arterial wave velocity.

5. The method of claim 4, comprising identifying a change in arterial wave velocity that is a predetermined factor greater than a threshold level of hemodynamic change.

6. The method of any one of claims 1-5, further comprising estimating cardiac output based on the blood flow velocity measurements and vessel diameter measurements.

7. A blood pressure analysis system, comprising: Single ultrasound system; as well as a processor (118), Wherein, the processor is configured to: receiving (102) blood flow velocity measurements from an arterial location acquired by the ultrasound system; receiving (104) a blood vessel diameter measurement obtained by the ultrasound system from the same arterial location; Determine (108) arterial wave velocity based on the diameter-velocity cycle related to blood flow velocity and vessel diameter; tracking (112) blood pressure changes based on the arterial wave velocity and the blood flow velocity measurements; receiving (114) intermittently measured blood pressure from a cuff; as well as A continuous blood pressure estimate is derived (116) based on the intermittent measurements and the tracked blood pressure changes between those intermittent measurements.

8. The blood pressure analysis system according to claim 7, wherein: The processor is configured to set the timing of a next cuff measurement based on the level of change in the arterial wave velocity.

9. The blood pressure analysis system according to claim 8, wherein: The processor is configured to identify a change in arterial wave velocity that is a predetermined factor greater than a threshold level of hemodynamic change.

10. The blood pressure analysis system according to any one of claims 7 to 9, wherein: The processor is configured to estimate cardiac output based on the blood flow velocity measurements and the blood vessel diameter measurements.

11. The blood pressure analysis system according to any one of claims 7 to 10, wherein: The processor is configured to obtain the arterial wave velocity based on a rate of change of blood flow velocity with respect to a logarithm of the diameter.

12. A blood pressure measurement system, comprising: A single ultrasound system (101) configured to: obtaining blood flow velocity measurements from an arterial location; and Obtain vessel diameter measurements from the same arterial location; a blood pressure measuring cuff (115); and A blood pressure analysis system (118) according to any one of claims 7-11.

13. The blood pressure measurement system according to claim 12, wherein: The ultrasound system includes an ultrasound patch.

14. The blood pressure measurement system according to any one of claims 11 to 13, wherein: The ultrasound system is configured to: Obtaining the blood vessel diameter measurement result by B-mode ultrasound imaging; and The blood flow velocity measurements were obtained by pulsed wave Doppler ultrasound.

15. A computer program product comprising a computer program, the computer program being configured to perform the method according to any one of claims 1-6 when the program is run on the processor of the blood pressure analysis system according to any one of claims 7-11.

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