Systems and methods for energy-efficient pulsing in ultrasound-based blood pressure sensor implants

Abstract

Disclosed are systems and methods for energy-efficient pulsing in ultrasound-based blood pressure sensor implants. In some embodiments, disclosed methods comprise conducting ultrasound sampling of a target vessel for blood pressure measurement only during defined time windows correlated to one or more characteristic features of the vessel during a cardiac cycle representing maximum and minimum diameters of the target vessel. In some embodiments, time windows are predicted by synchronizing ultrasound pulsing with a patient's electrocardiogram (ECG). In other embodiments, time windows are predicted by conducting limited periodic sampling and fitting the resulting limited measurements to a mathematical function that describes the waveform of vessel diameter over a cardiac cycle. In yet other embodiments, maximum and minimum diameter may be computed directly from the mathematical function.

Description

SYSTEMS AND METHODS FOR ENERGY-EFFICIENT PULSING IN ULTRASOUND-BASED BLOOD PRESSURE SENSOR IMPLANTSRELATED APPLICATION DATA

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 63 / 743,509, filed on January 9, 2025, and titled “Systems and Methods for Energy-Efficient Pulsing In Ultrasound-Based Blood Pressure Sensors,” which is incorporated by reference herein in its entirety.FIELD OF THE DISCLOSURE

[0002] The present disclosure relates to ultrasound-based blood pressure measurement with implantable devices and, more specifically, to systems and methods for energy-efficient pulsing in ultrasound-based blood pressure sensor implants.BACKGROUND

[0003] Energy saving is important for ultrasound-based blood pressure measurement devices, as it bears on both battery size (and therefore overall device size) and longevity. Device size and longevity are particularly important problems for implanted devices. Energy consumption is a significant limitation to be overcome for more widespread adoption of implantable ultrasound-based devices.

[0004] In pulse-echo blood pressure measurement, ultrasound pulses are directed at an artery, and reflections take place off both the near and far walls of the inner lumen of that artery. The timing difference between the return of these reflections is a measure of the diameter of the artery, and blood pressure is calculated from the differences in arterial diameter over a cardiac cycle. A transfer function between artery diameter and blood pressure is described in U.S. Patent No. 11,452,497, filed on October 4, 2021, and titled, “Injectable Hemodynamic Monitoring Devices, Systems and Methods”, which is incorporated herein by reference in its entirety for all purposes.

[0005] In such ultrasound-based blood pressure measurement devices, a function that often consumes the most power is the ultrasound measurement, which entails transmission of ultrasound pulses, amplifying and recording the reflected signals, and considerable data processing. The maximum and minimum values are important measurements, as these correspond to the systolic and diastolic pressure, respectively. Conventional ultrasound-based blood pressure measurement devices 1 Atorney Docket No. 17961-007WOU1are not synchronized to a patient’s heartbeat and instead involve sending out a repetitive set of pulses at a relatively high rate (for example, -50-1000 pulses per second), lasting from one to several heartbeats. Thus, hundreds to thousands of pulses are delivered for a single blood pressure measurement in conventional systems, even though as few as two pulses would be needed, if timed as described in the present disclosure to capture the maximum and minimum values.

[0006] Conventional ultrasound-based blood pressure measurement techniques thus can present significant power demands that render devices employing such techniques less than ideal as implantable devices in many cases. A need thus persists in the art for more energy-efficient techniques for ultrasound-based blood pressure measurement more well-suited to implantable devices and methods of use.SUMMARY OF THE INVENTION

[0007] In one implementation, the present disclosure is directed to a blood pressure measurement system. The system includes an implantable device comprising an implantable housing, at least one processor within the implantable housing, and an ultrasound pulser within the implantable housing and in communication with the processor; and a non-transient data store in communication with the at least one processor, the non-transient data store containing an instruction set comprising machine-executable instructions that, when executed by the processor (i) cause the ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement only during defined time windows correlated to one or more characteristic features of the vessel during a cardiac cycle representing maximum and minimum diameters of the target vessel, (ii) determine maximum and minimum diameters for the target vessel, and (iii) calculate blood pressure using the determined maximum and minimum diameters.

[0008] In another implementation, the present disclosure is directed to a method for calculating blood pressure. The method includes conducting an electrocardiogram (ECG) for a patient; determining a first triggering feature of the ECG at a first time; determining a first measurement window based on the first triggering feature at the first time; conducting ultrasound measurements of vessel diameter during the first measurement window; and calculating blood pressure of the patient using the ultrasound measurements of vessel diameter.

[0009] In yet another implementation, the present disclosure is directed to a method for calculating blood pressure. The method includes conducting limited ultrasound sampling on a patient by administering between 1 and 50 pulses per cardiac cycle for at least one cardiac cycle;2 Attorney Docket No. 17961-007WOU1estimating a function based on data from the limited ultrasound sampling, wherein the function represents vessel diameter over a cardiac cycle; computing a maximum diameter of the function and a minimum diameter of the function; and calculating blood pressure of the patient using the maximum diameter and the minimum diameter.

[0010] In still another implementation, the present disclosure is directed to a method for calculating blood pressure. The method includes conducting ultrasound sampling on a patient to determine a function, wherein the function represents vessel diameter over a cardiac cycle; storing the function to a stored library of functions; retrieving the function from the stored library of functions; predicting a first time window associated with a maximum diameter of the function and a second time window associated with a minimum diameter of the function; conducting ultrasound sampling during the first time window and the second time window; determining the maximum diameter during the first time window and determining the minimum diameter during the second time window; and calculating blood pressure of the patient using the maximum diameter and the minimum diameter.

[0011] In another implementation, the present disclosure is directed to a blood pressure measurement system. The system includes an implantable device comprising an implantable housing, at least one processor within the implantable housing, and at least one ultrasound pulser within the implantable housing and in communication with the processor; and a non-transient data store in communication with the at least one processor, the non-transient data store containing an instruction set comprising machine-executable instructions that, when executed by the processor (i) cause the at least one ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement by pulsing between 1 and 50 times per cardiac cycle for at least one cardiac cycle, (ii) estimate a function representing vessel diameter over cardiac cycle based on data from the ultrasound sampling; (iii) determine maximum and minimum diameters for the target vessel, and (iv) calculate blood pressure using the determined maximum and minimum diameters.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For the purpose of illustrating the disclosure, the drawings show aspects of one or more embodiments of the disclosure. However, it should be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:FIG. l isa flow diagram showing an example method of timing ultrasound measurement windows to coincide with systole and diastole;3 Atorney Docket No. 17961-007WOU1FIG. 2 is a graph showing an example ECG signal including a systole period and a diastole period; FIG. 3 is a system diagram showing an example energy -efficient blood pressure management system according to aspects of the present disclosure;FIG. 4 is an example ultrasound M-mode image showing the change in arterial diameter over several heartbeats;FIG. 5 is a graph showing an example wave shape for the pressure in a blood vessel;FIG. 6A is a flow diagram showing an example method of calculating blood pressure using limited ultrasound sampling and waveform fitting; andFIG. 6B is a flow diagram showing another example method of calculating blood pressure using limited ultrasound sampling and waveform fitting.DETAILED DESCRIPTION

[0013] Systems and methods of the present disclosure solve the above problems in the prior art by decreasing the number of pulses needed for a blood pressure measurement using an ultrasoundbased blood pressure measurement device, which saves energy, allows batteries and overall devices to be smaller, and allows devices to last longer. This reduction in device size and increase in longevity is particularly beneficial for implanted devices. Systems and methods described herein make blood pressure measurements with relatively fewer ultrasound pulses than the hundreds to thousands of pulses in conventional systems and methods.

[0014] In some embodiments, methods for energy-efficient pulsing comprise anticipating the timing of minimum and maximum pressure at a point in a blood vessel by synchronizing ultrasound pulsing with the patient’s electrocardiogram (ECG). In other embodiments, methods for energyefficient pulsing comprise conducting limited periodic sampling (“limited” meaning, for example, about 3 to 20 pulses per cardiac cycle) and fitting the resulting limited measurements to a mathematical function that describes the waveform of vessel diameter over a cardiac cycle.

[0015] In some embodiments, blood pressure measurement systems comprise an implantable device comprising an implantable housing, at least one processor within the implantable housing, and at least one ultrasound pulser within the implantable housing and in communication with the processor. In some embodiments, the ultrasound pulser comprises an ultrasound controller and at least one transducer. In some embodiments, blood pressure measurement systems further comprise a nontransient data store in communication with the at least one processor, the non-transient data store 4 Attorney Docket No. 17961-007WOU1containing an instruction set comprising machine-executable instructions that, when executed by the processor (i) cause the ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement only during defined time windows correlated to one or more characteristic features of the vessel during a cardiac cycle representing maximum and minimum diameters of the target vessel, (ii) determine maximum and minimum diameters for the target vessel, and (iii) calculate blood pressure using the determined maximum and minimum diameters.I. ECG Synchronization

[0016] Continuous sampling and classification of ECG signals are generally not as energetically costly as continuous ultrasound sampling. Systems and methods of the present disclosure leverage use of ECG signals in a new context to increase the efficiency of ultrasound sampling. Tn particular, ECG signals can inform optimum times to transmit ultrasound to capture the maximum and minimum levels, atributed to systole and diastole respectively, or any other levels of interest, and significantly reduce the number of ultrasound pulses needed by eliminating the need to transmit pulses during times that would not capture levels of interest. FIG. 1 shows an example algorithm 10 for using a patient’s ECG to choose ultrasound sampling windows according to the present disclosure. At step 12, ECG is measured and classified. An example ECG signal is shown in FIG. 2, which is discussed in more detail below. At step 14, it is determined whether an R-wave has been classified. While the embodiment shown in FIG. 1 involves detecting R-waves and / or T-waves, in other embodiments, other features of the ECG signal are used, such as, but not limited to, P-waves, Q-waves, and / or S-waves.

[0017] If an R-wave is detected at step 14, then the algorithm 10 moves to step 16, where there is a delay for the pressure pulse waveform to reach the vessel target. Notably, electrical signals transmit through the body more rapidly than do pressure pulses through a blood vessel. As a consequence, at any distance on a vessel away from the heart, a feature of the ECG signal will reach that point before the corresponding feature of the pressure waveform. To state this another way, there is a phase delay in the pressure waveform with respect to the ECG. It can be beneficial to know this phase delay for a given patient and / or device, so that it can be compensated for in the algorithm 10. In some embodiments, phase delay is determined in situ, such as by using a device to measure both ECG and pressure simultaneously and measuring the distance in arrival time of the two. This quantity is known in the art as pulse transit-time (PTT). In other embodiments, PTT is estimated through certain patient5 Atorney Docket No. 17961-007WOU1information (such as measured or inferred distance from the ultrasound transducer to the patient’s heart, the patient’s age, the patient’s size and / or weight, degree of vessel calcification, etc.).

[0018] After the delay, the algorithm 10 then proceeds to step 18, where it proceeds with ultrasound measurement of vessel diameter by sampling for a predetermined time. On the other hand, if an R-wave is not detected at step 14, then at step 20, it is determined whether a T-wave has been classified. If a T-wave is detected at step 20, then the algorithm 10 moves to step 16 and step 18 as described above. If a T-wave is not detected at step 20, then the algorithm 10 returns to step 12, where ECG is measured and classified. Similarly, step 12 may also be repeated after step 18.

[0019] An example ECG signal 22 is shown in FIG. 2. The ECG signal 22 comprises an R-wave 24 and a T-wave 26. The R-wave 24 indicates systole and the T-wave 26 indicates diastole. More specifically, the systole is identified from half of the maximum amplitude of the R-wave 24 until the maximum of the T-wave 26, and the diastole is indicated from half of the maximum amplitude of the T-wave 26 until half of the maximum amplitude of the following R-wave. As explained above, the algorithm 10 picks up on a feature of the ECG, namely, an R-wave 24 or a T-wave 26, inserts a delay to account for PTT, and starts sampling for a predetermined time. While picking up on one feature of the ECG is adequate to set the algorithm 10, in some embodiments, both an R-wave 24 and a T-wave 26 are used. In these embodiments, an R-wave 24 is detected, a delay is inserted, and sampling is done, then a T-wave 26 is detected, a delay is inserted, and sampling is done. This allows for two sampling windows — one that is around the maximum and one that is around the minimum. In other embodiments, other prominent features of the ECG are used as triggering events besides the R-waves 24 and T-waves 26. In some embodiments, sampling begins immediately after a prominent feature of the ECG is detected, rather than inserting a delay.

[0020] In some embodiments, energy-efficient blood pressure management systems comprise a single measurement device. In other embodiments, energy-efficient blood pressure management systems comprise multiple devices, such as an ECG measurement device and a blood pressure measurement device. In embodiments comprising multiple measurement devices, the measurement devices may be housed together or separately. In embodiments where measurement devices are housed separately, they may be in communication with each other by wires or means of intra-body telemetry (e.g., RF, induction, vibration including sonic and ultrasonic, electric fields, emission and detection of light, etc.).6 Atorney Docket No. 17961-007WOU1

[0021] FIG. 3 shows an example energy-efficient blood pressure management system 28 according to aspects of the present disclosure, which includes a simplified hardware configuration for the purposes of illustration. In one alternative, system 28 may be embodied as implantable device 28A including just the ultrasound components within an implantable housing. In another alternative, system 28 may be embodied as implantable device 28B, with ultrasound and ECG components within an implantable housing.

[0022] Embodiments of energy-efficient blood pressure management systems 28 comprise an ultrasound transducer 30 that is in proximity to a patient’s artery 32, a first ECG electrode 34 that is in proximity to the patient’s heart 36, and a second ECG electrode 38 that is in proximity to the artery 32. The ultrasound transducer 30 may comprise a single ultrasound transducer or an array of ultrasound transducers. The energy-efficient blood pressure management system 28 further comprises an ultrasound processor 40, an ultrasound controller 42, an ECG amplifier 44, and an ECG processor 46. The ultrasound controller 42 governs generation and reception of ultrasound waveforms. In some embodiments, the ultrasound processor 40 receives ultrasound waveforms from the ultrasound controller and makes computations to convert the received ultrasound waveforms into blood pressure measurements. Embodiments of energy-efficient blood pressure management systems 28 comprise an ultrasound pulser comprising the ultrasound transducer 30 and the ultrasound controller 42. As described in more detail below, the ultrasound pulser may be configured to conduct ultrasound pulsing for blood pressure measurement that is synchronized to a patient’s ECG.

[0023] Power is supplied by battery 41 , which may be configured as a power supply with a battery management system, or the battery management system may be configured in ultrasound controller 42. The ultrasound controller 42 is in communication with the ECG processor 46 and ultrasound processor 40. Processors 40 and 46 are configured to execute stored instructions for implementing energy efficient blood pressure measurement processes as described herein. Instructions may be stored in a non-transient data store communicating with the processors. In some embodiments, the non-transient data store is within the implantable device. Further structural and hardware details of implantable device configurations are disclosed in Applicant’s granted U.S. Patent No. 11,452,497, which is incorporated herein by reference in its entirety.

[0024] An energy-efficient blood pressure management system 28 is configured to predict the timing of minimum and maximum diameter and / or pressure of the artery 32 using energy-efficient pulsing methods described above. The ultrasound processor 40 is configured to receive an ECG of a7 Attorney Docket No. 17961-007WOU1patient, and the timing of the minimum and maximum diameter and / or pressure is anticipated by synchronizing ultrasound pulsing for blood pressure measurement with the patient’s ECG. A first measurement window is set around the minimum and a second measurement window is set around the maximum, and pulses from the ultrasound transducer 30 are only delivered during those measurement windows. By avoiding measurements outside the measurement windows, system resources (energy, processor usage, and memory) are reserved, and consequently the ultrasound transducer, the ultrasound processor, and the ultrasound controller can be made smaller and last longer. Decreasing power consumption extends battery life. In addition, ultrasound transducers have a finite service life associated with pulsing, so fewer pulses yields greater longevity.

[0025] During the measurement windows, pulsing is taken in a relatively rapid way, such as, but not limited to, less than 0.2 seconds. In some embodiments, the windows are each about 0.1 second and pulsing is done between 20 and 1,000 times per second, but more preferably between 20 and 50 times per second. As an exemplary upper bound, the maximum number of samples would be: 2 windows * 0.1 sec / window * 1,000 pulses / sec = 200 samples. By contrast, a conventional system implementing continuous sampling for a one-second cardiac cycle at 1,000 samples per second would require 1,000 samples. This is a 5: 1 reduction in pulsing, with no reduction in fidelity for capturing the pressure maximum and minimum values (since the sampling rates at the points of interest are identical for both methods).II. Limited Sampling and Waveform Fitting

[0026] FIG. 4 is an example ultrasound M-mode image 48 showing the change in arterial diameter over several heartbeats. The shading of the original M-mode image has been inverted for clarity, so that dark areas in the original image are now light, and light areas in the original image are now dark. As can be seen in FIG. 4, the change in arterial diameter over each heartbeat is a periodic function. The ultrasound M-mode image 48 comprises two sawtooth-shaped lines 50, 52, which are associated with the near and far edges of the inner lumen of the artery. The vertical distance space 54 between the two sawtooth-shaped lines 50, 52 is associated with reflections from the near and far edges of the inner lumen of the artery. The distance between the two sawtooth-shaped lines 50, 52 is the difference in time for the two reflections to reach the ultrasound sense transducer and is directly proportional to arterial diameter, with the constant of proportionality being the speed of sound in blood.

[0027] The periodicity of the arterial diameter signal in FIG. 4 is clear when expressed over several heartbeats. Because the signal is periodic, in accordance with the present disclosure, it need 8 Attorney Docket No. 17961-007WOU1not be measured over every heartbeat. In FIG. 4, the space 54 clearly has a saw-tooth-like shape. FIG. 5 presents a more detailed representation of pressure response in a vessel. While FIG. 4 shows the diameter of a vessel, FIG. 5 shows a graph 56 of a waveform 58 based on the pressure in a vessel, which has a close relationship to the diameter. In both examples, mathematical functions as may be determined by persons of ordinary skill based on the teachings of the present disclosure can express the shape of each wave shape.

[0028] In some embodiments, limited sampling is conducted to deliver a number of pulses that is greater than or equal to the number of parameters that describe a wave shape. For example, if a wave shape is described by three parameters and a heartbeat duration is one second, the minimum sampling rate is three per second. In other embodiments, a greater number of pulses may be used to improve accuracy, such as, but not limited to, up to 20 pulses or up to 50 pulses during a cardiac cycle. Even so, these methods require fewer pulses than would be done in conventional systems that employ continuous high-rate sampling.

[0029] In one less complex embodiment, a single wave shape function may apply to all patients, with unique fited parameters for each. Alternatively, different patient physiologies may lead to slightly different general wave shapes. In embodiments where different wave shape functions are applied to different patients, a device may have access to a stored library of functions, from which one is selected. A selection process is then used to determine which of the wave shape functions is most appropriate for a given device in each patient. There are multiple ways to determine which wave shape function is most appropriate. For example, more frequent pulsing may be conducted using the ultrasound transducer itself, to establish a high resolution empirical waveform. As other examples, the appropriate function may be derived from another diagnostic technique (e.g., ultrasound imaging, ECG, or blood pressure measurements, such as by an arterial line). Curve fitting or pattern matching with a quantitative score (such as correlation coefficient) is used to select the most appropriate general shape from the set. Selection of this type is part of device programming, and it may be performed once at the time of implant, or it may be refreshed over intervals. Triggering a refresh may happen at a pre-set time interval, or by some internal or external assessment of device performance / accuracy, or it may be initiated by a clinician. Even though curve selection may involve more frequent pulsing, the total energy consumption from these infrequent episodes is relatively low over the device lifetime in embodiments where the curve selection process is not done as frequently as the pressure measurement itself.9 Atorney Docket No. 17961-007WOU1

[0030] Curve fitting enables at least two general algorithms for measuring vessel diameter and pressure without conducting continuous application of rapid ultrasound pulses, which are shown in FIG. 6A and FIG. 6B. Other algorithm variations are possible based on the teachings of the present disclosure. Such control algorithms also may be implemented using devices 28A or 28B as described above, or other suitable implantable ultrasound sensor devices.a. Multiple Sample Rates

[0031] FIG. 6A is a flow diagram showing an example method 60 of calculating blood pressure using limited ultrasound sampling and waveform fitting. At step 62A, limited ultrasound sampling is conducted. As described above, in some embodiments, limited ultrasound sampling comprises delivering a number of pulses that is greater than or equal to the number of parameters that describe a wave shape. In some embodiments, limited ultrasound sampling comprises administering 3 to 20 pulses per cardiac cycle, where the resulting measurements can later be fit to a parameterized function that describes the waveform of vessel diameter. At step 64, data from the limited ultrasound sampling is used to estimate a function representing vessel diameter over a cardiac cycle. At step 66A, the function may be stored to a stored library of functions for future use in step 66B, when the function may be retrieved from the stored library of functions. At step 68, time windows for maximum and minimum vessel diameters over a heartbeat are determined for rapid sampling to take place. Exemplary time windows are described above, such as time windows that are less than 0.2 seconds. In other words, once the fitted parameters are established, they are used in the mathematical function itself to predict the time-points associated with maximum and minimum values of the function over an interval. Windows are then set to correspond to the maximum and minimum values. The curve fit predicts given windows forwards in time. In some embodiments, this is accomplished by taking measurements early in a half-cycle (before the minimum or maximum is reached). In other embodiments, the maximum and the minimum for a function are established and then the periodic nature of a heartbeat is used to predict the occurrence of the maximum and minimum one or more heartbeats later, which would be less time-intensive than taking measurements early in a half-cycle. At step 70A, sampling is conducted during windows in a manner similar to what was described in Section I with respect to ECG synchronization. In some embodiments, pulses are administered between 20 and 1,000 times per second or between 20 and 50 times per second in time windows that are less than 0.2 seconds, such as about 0.1 second.10 Attorney Docket No. 17961-007WOU1

[0032] At step 70B, it is determined whether the time windows captured the maximum and minimum vessel diameters. This can be done, for example, by checking if a window captured a peak where the slope of the function changes from positive to negative (indicating the maximum) or from negative to positive (indicating the minimum). If the time windows captured the maximum and minimum, then at step 72, the maximum and minimum vessel diameters are determined during the windows. If, on the other hand, the time windows did not capture at least one of the maximum and minimum, then at step 70C, the windows are adjusted and the stored function is updated to re-predict where the maximum and / or minimum will be. Steps 66B, 68, 70A, and 70B may then be repeated until the windows capture both the maximum and the minimum diameters. At step 74, systolic and diastolic pressure are calculated using the diameters.

[0033] Tn some embodiments, instead of using data from limited ultrasound sampling to estimate the function representing vessel diameter over a cardiac cycle, at step 62B, conventional ultrasound sampling may be done to generate the function, which may then be stored to the stored library of functions at step 66A for future use. In some embodiments, the algorithm of method 60 is implemented using devices 28A or 28B as described above, or other suitable implantable ultrasound sensor devices, and step 62B is done prior to implant. In yet other embodiments, the stored library of functions contains generic functions representing vessel diameter over a cardiac cycle that could be retrieved for use at step 66B, as described above.b. Curve Fitting with Low-Rate Sampling

[0034] FIG. 6B is a flow diagram showing another example method 76 of calculating blood pressure using limited ultrasound sampling and waveform fitting. The method 76 may require fewer processing steps than the method 60. As with the method 60, the method 76 begins at step 78A with conducting limited ultrasound sampling. At step 80, data from the limited ultrasound sampling is used to estimate a function representing vessel diameter over a cardiac cycle. At step 82A, the function may be stored to a stored library of functions for future use in step 82B, when the function may be retrieved from the stored library of functions. Once the wave shape parameters are fit, at step 84, the maximum and minimum of the given wave shape are computed directly from the resulting function, using standard methods for determining maximum and minimum values of a mathematical function over an interval. At step 86, these maximum and minimum values are used to directly calculate systolic and diastolic pressure using any method for converting arterial diameter to pressure.11 Attorney Docket No. 17961-007WOU1

[0035] In some embodiments, instead of using data from limited ultrasound sampling to estimate the function representing vessel diameter over a cardiac cycle, at step 78B, conventional ultrasound sampling may be done to generate the function, which may then be stored to the stored library of functions at step 82A for future use. In some embodiments, the algorithm of method 76 is implemented using devices 28A or 28B as described above, or other suitable implantable ultrasound sensor devices, and step 78B is done prior to implant. In yet other embodiments, the stored library of functions contains generic functions representing vessel diameter over a cardiac cycle that could be retrieved for use at step 82B, as described above.c. Additional Alternative Embodiments

[0036] Tn one further alternative embodiment, a blood pressure measurement system according to the present disclosure comprises an implantable device and a non-transient data store, which may be a part of the implantable device or disposed remotely from the implantable device and communicates wirelessly therewith. The implantable device may comprise an implantable housing, at least one processor within the implantable housing, and an ultrasound pulser within the implantable housing and in communication with the processor. The non-transient data store is configured to communicate with the at least one processor and contains an instruction set comprising machine-executable instructions that, when executed by the processor cause the ultrasound pulser to conduct ultrasound sampling at a lower or limited energy efficient pulsing rate except when specific measurement time windows are identified and then optionally increase the pulsing rate during the specific measurement time windows in order to determine one or more characteristic feature of the vessel during a cardiac cycle representing maximum and minimum diameters of the target vessel using either the lower or limited energy efficient pulsing rate or an increased measurement pulsing rate in order to determine maximum and minimum diameters for the target vessel, and then to calculate blood pressure using the determined maximum and minimum diameters.

[0037] In some embodiments, the lower or limited energy-efficient pulsing rate may be at a rate of 50 or fewer pulses per cardiac cycle, and may in some embodiments comprise pulsing between 3 and 20 pulses per cardiac cycle. In other embodiments, the pulsing rate during identified measurement time windows may be at a rate of between 20 and 1,000 times per second, and in some embodiments, the pulsing rate during an identified measurement time window may be between 20 and 50 times per second, whereas in further alternative embodiments it may be at a pulse rate exceeding 50 times per second.12 Attorney Docket No. 17961-007WOU1

[0038] In one further variation of such an alternative embodiment, the at least one processor comprises an ultrasound processor which is further configured to receive an electrocardiogram (ECG) of a patient. In this alternative, the ultrasound pulser is configured to conduct ultrasound pulsing for blood pressure measurement synchronized to the ECG and the instruction set further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound processor to determine a first triggering feature of the ECG at a first time, determine a first measurement window based on the first triggering feature at the first time, and cause the ultrasound pulser to conduct said ultrasound sampling for blood pressure measurement during the first measurement window.

[0039] In another variation of such an alternative embodiment, the instruction set further comprises machine-executable instructions that, when executed by the processor cause the ultrasound pulser to conduct ultrasound sampling of a target vessel by pulsing between 1 and 50 times per cardiac cycle for at least one cardiac cycle and to estimate a function representing vessel diameter over a cardiac cycle based on data from the said ultrasound sampling. A maximum diameter of the function and a minimum diameter of the function are then determined and blood pressure is calculated for the patient using the determined maximum diameter and the minimum diameters.

[0040] In yet another variation of such an alternative embodiment, the stored machineexecutable instructions cause the at least one ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement by pulsing between 1 and 50 times per cardiac cycle for at least one cardiac cycle, estimate a function representing vessel diameter over cardiac cycle based on data from said ultrasound sampling, determine maximum and minimum diameters for the target vessel, and calculate blood pressure using the determined maximum and minimum diameters.

[0041] The foregoing has been a detailed description of illustrative embodiments of the disclosure. It is noted that in the present specification and claims appended hereto, conjunctive language such as is used in the phrases “at least one of X, Y and Z” and “one or more of X, Y, and Z,” unless specifically stated or indicated otherwise, shall be taken to mean that each item in the conjunctive list can be present in any number exclusive of every other item in the list or in any number in combination with any or all other item(s) in the conjunctive list, each of which may also be present in any number. Applying this general rule, the conjunctive phrases in the foregoing examples in which the conjunctive list consists of X, Y, and Z shall each encompass: one or more of X; one or more of13 Atorney Docket No. 17961-007WOU1Y ; one or more of Z; one or more of X and one or more of Y ; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y and one or more of Z.

[0042] Various modifications and additions can be made without departing from the spirit and scope of this disclosure. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present disclosure. Additionally, although particular methods herein may be illustrated and / or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this disclosure.

[0043] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present disclosure.14 Attorney Docket No. 17961-007WOU1

Claims

What is claimed is:

1. A blood pressure measurement system, comprising:an implantable device comprising an implantable housing, at least one processor within the implantable housing, and an ultrasound pulser within the implantable housing and in communication with the processor; anda non-transient data store in communication with the at least one processor, the non-transient data store containing an instruction set comprising machine-executable instructions that, when executed by the processor (i) cause the ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement only during defined time windows correlated to one or more characteristic features of the vessel during a cardiac cycle representing maximum and minimum diameters of the target vessel, (ii) determine maximum and minimum diameters for the target vessel, and (iii) calculate blood pressure using the determined maximum and minimum diameters.

2. The blood pressure measurement system of claim 1, wherein the ultrasound pulser comprises an ultrasound controller and at least one ultrasound transducer.

3. The blood pressure measurement system of claim 1 or claim 2, wherein the non-transient data store is disposed within the implantable housing.

4. The blood pressure measurement system of any of claims 1-3, wherein:the at least one processor comprises an ultrasound processor;the ultrasound processor is further configured to receive an electrocardiogram (ECG) of a patient; andthe ultrasound pulser is configured to conduct ultrasound pulsing for blood pressure measurement synchronized to the ECG; andthe instruction set further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound processor to determine a first triggering feature of the ECG at a first time, determine a first measurement window based on the first triggering feature at the first time, and cause the ultrasound pulser to conduct said ultrasound sampling for blood pressure measurement during the first measurement window.

5. The blood pressure measurement system of claim 4, wherein the first triggering feature of the ECG is selected from a group consisting of an R-wave, a T-wave, a P-wave, a Q-wave, and an S-wave.15 Attorney Docket No. 17961-007WOU16. The blood pressure measurement system of claim 4 or claim 5, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor, delay after the first time for a delay period associated with a pulse transit-time for the patient before conducting ultrasound measurements of vessel diameter during the first measurement window.

7. The blood pressure measurement system of any of claims 4-6, wherein the first measurement window is less than 0.2 seconds, and the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound pulser to pulse between 20 and 1,000 times per second during the first measurement window.

8. The blood pressure measurement system of any of claims 4-7, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound pulser to pulse between 20 and 50 times per second during the first measurement window.

9. The blood pressure measurement system of any of claims 4-8, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor:determine a second triggering feature of the ECG at a second time;determine a second measurement window based on the second triggering feature at the second time; andconduct ultrasound sampling for blood pressure measurement during the second measurement window.

10. The blood pressure measurement system of claim 9, wherein the second triggering feature of the ECG is selected from the group consisting of an R-wave, a T-wave, a P-wave, a Q-wave, and an S-wave.

11. The blood pressure measurement system of claim 9 or claim 10, wherein:the first triggering feature is an R-wave and the second triggering feature is a T-wave; and the instruction set contained in the non-transient data store further comprises machineexecutable instructions that, when executed by the ultrasound processor, measure16 Atorney Docket No. 17961-007WOU1maximum vessel diameter in the first measurement window and measure minimum vessel diameter in the second measurement window.

12. The blood pressure measurement system of any of claims 9-11, wherein the second measurement window is less than 0.2 seconds, and the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound pulser to pulse between 20 and 1,000 times per second during the second measurement window.

13. The blood pressure measurement system of claims 9-12, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the ultrasound processor, cause the ultrasound pulser to pulse between 20 and 50 times per second during the second measurement window.

14. The blood pressure measurement system of any of claims 4-13, wherein the implantable device further comprises a battery that supplies power to the ultrasound processor and the ultrasound pulser.

15. The blood pressure measurement system of any of claims 4-14, wherein the implantable device further comprises:at least one ECG electrode;an ECG amplifier in communication with the ECG electrode; andan ECG processor in communication with the ECG amplifier, the ultrasound processor, and the ultrasound pulser;wherein the non-transient data store is in communication with the ECG processor, and wherein the instruction set contained in the non-transient data store further comprises machineexecutable instructions that, when executed by the ECG processor:cause the ECG electrode to detect a plurality of ECG signals for the patient; cause the ECG amplifier to amplify the plurality of ECG signals;cause the ECG processor to generate the ECG of the patient based on the plurality of ECG signals and deliver the ECG of the patient to the ultrasound processor.

16. The blood pressure measurement system of any of claims 1-3, wherein the instruction set further comprises machine-executable instructions that, when executed by the processor:17 Atorney Docket No. 17961-007WOU1cause the ultrasound pulser to conduct ultrasound sampling on a patient by pulsing between 1 and 50 times per cardiac cycle for at least one cardiac cycle;estimate a function representing vessel diameter over a cardiac cycle based on data from the said ultrasound sampling;determine a maximum diameter of the function and a minimum diameter of the function; and calculate blood pressure of the patient using the determined maximum diameter and the minimum diameters.

17. The blood pressure measurement system of claim 16, wherein the ultrasound sampling comprises 3 to 20 pulses per cardiac cycle.

18. The blood pressure measurement system of claim 16 or claim 17, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the processor:predict a first time window associated with the maximum diameter and a second time window associated with the minimum diameter based on the function; andconduct ultrasound sampling during the first time window and the second time window; wherein determining the maximum diameter of the function and the minimum diameter of the function comprises determining the maximum diameter during the first time window and the minimum diameter during the second time window.

19. The blood pressure measurement system of any of claims 16-18, wherein the non-transient data store comprises a stored library of functions, and the instruction set further comprises machineexecutable instructions that, when executed by the processor, store the function to the stored library of functions.

20. The blood pressure measurement system of claim 18, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the processor:determine whether the first time window captured the maximum diameter and the second time window captured the minimum diameter, and,if yes, compute the maximum diameter of the function and the minimum diameter of the function, and,if no, adjust the first time window and the second time window and update the function in the stored library of functions.18 Atorney Docket No. 17961-007WOU121. The blood pressure measurement system of any of claims 17-20, wherein the first time window and the second time window are each less than 0.2 seconds, and the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the processor, cause the ultrasound pulser to pulse between 20 and 1,000 times per second during the first time window and the second time window.

22. The blood pressure measurement system of any of claims 17-21, wherein the instruction set contained in the non-transient data store further comprises machine-executable instructions that, when executed by the processor, cause the ultrasound pulser to pulse between 20 and 50 times per second during the first time window and the second time window.

23. The blood pressure measurement system of any of claims 16-22, wherein the implantable device further comprises a battery that supplies power to the processor and the ultrasound pulser.

24. A method for calculating blood pressure, comprising:conducting an electrocardiogram (ECG) for a patient;determining a first triggering feature of the ECG at a first time;determining a first measurement window based on the first triggering feature at the first time; conducting ultrasound measurements of vessel diameter during the first measurement window;andcalculating blood pressure of the patient using the ultrasound measurements of vessel diameter.

25. The method for calculating blood pressure of claim 24, wherein the first triggering feature of the ECG is selected from a group consisting of an R-wave, a T-wave, a P-wave, a Q-wave, and an S- wave.

26. The method for calculating blood pressure of claim 24 or claim 25, further comprising delaying after the first time for a delay period associated with a pulse transit-time for the patient before conducting the ultrasound measurements of vessel diameter during the first measurement window.

27. The method for calculating blood pressure of any of claims 24-26, wherein the first measurement window is less than 0.2 seconds, and wherein conducting ultrasound measurements of vessel diameter during the first measurement window comprises administering pulses between 20 and 1,000 times per second.19 Atorney Docket No. 17961-007WOU128. The method for calculating blood pressure of any of claims 24-27, wherein conducting ultrasound measurements of vessel diameter during the first measurement window comprises administering pulses between 20 and 50 times per second.

29. The method for calculating blood pressure of any of claims 24-28, further comprising:determining a second triggering feature of the ECG at a second time;determining a second measurement window based on the second triggering feature at the second time; andconducting ultrasound measurements of vessel diameter during the second measurement window.

30. The method for calculating blood pressure of claim 29, wherein the second triggering feature of the ECG is selected from a group consisting of an R-wave, a T-wave, a P-wave, a Q-wave, and an S-wave.

31. The method for calculating blood pressure of claim 29 or claim 30, further comprising delaying after the second time for a delay period associated with a pulse transit-time for the patient before conducting the ultrasound measurements of vessel diameter during the second measurement window.

32. The method for calculating blood pressure of any of claims 29-31, wherein the second measurement window is less than 0.2 seconds, and wherein conducting ultrasound measurements of vessel diameter during the second measurement window comprises administering pulses between 20 and 1,000 times per second.

33. The method for calculating blood pressure of any of claims 29-32, wherein conducting ultrasound measurements of vessel diameter during the second measurement window comprises administering pulses between 20 and 50 times per second.

34. The method for calculating blood pressure of any of claims 29-33, wherein the first triggering feature is an R-wave and the second triggering feature is a T-wave.

35. A method for calculating blood pressure, comprising:conducting limited ultrasound sampling on a patient by administering between 1 and 50 pulses per cardiac cycle for at least one cardiac cycle;20 Atorney Docket No. 17961-007WOU1estimating a function based on data from the limited ultrasound sampling, wherein the function represents vessel diameter over a cardiac cycle;computing a maximum diameter of the function and a minimum diameter of the function; and calculating blood pressure of the patient using the maximum diameter and the minimum diameter.

36. The method for calculating blood pressure of claim 35, wherein computing the maximum diameter of the function and the minimum diameter of the function further comprises:predicting a first time window associated with the maximum diameter of the function and a second time window associated with the minimum diameter of the function; conducting ultrasound sampling during the first time window and the second time window; and wherein computing the maximum diameter of the function and the minimum diameter of the function comprises determining the maximum diameter during the first time window and determining the minimum diameter during the second time window.

37. The method for calculating blood pressure of claim 35 or claim 36, further comprising:storing the function to a stored library of functions;determining whether the first time window captured the maximum diameter and the second time window captured the minimum diameter, and,if yes, computing the maximum diameter of the function and the minimum diameter of the function, and,if no, adjusting the first time window and the second time window, updating the function in the stored library of functions, and repeating the steps of conducting ultrasound sampling during the first time window and the second time window and determining whether the first time window captured the maximum diameter and the second time window captured the minimum diameter.

38. The method for calculating blood pressure of any of claims 35-37, wherein conducting limited ultrasound sampling on a patient comprises administering between 3 and 20 pulses per cardiac cycle.

39. The method for calculating blood pressure of any of claims 36-38, wherein the first time window and the second time window are each less than 0.2 seconds, and wherein conducting ultrasound sampling during the first time window and the second time window comprises administering pulses between 20 and 1,000 times per second.21 Attorney Docket No. 17961-007WOU140. The method for calculating blood pressure of any of claims 36-39, wherein conducting ultrasound sampling during the first time window and the second time window comprises administering pulses between 20 and 50 times per second.

41. A method for calculating blood pressure, comprising:conducting ultrasound sampling on a patient to determine a function, wherein the function represents vessel diameter over a cardiac cycle;storing the function to a stored library of functions;retrieving the function from the stored library of functions;predicting a first time window associated with a maximum diameter of the function and a second time window associated with a minimum diameter of the function;conducting ultrasound sampling during the first time window and the second time window; determining the maximum diameter during the first time window and determining the minimum diameter during the second time window; andcalculating blood pressure of the patient using the maximum diameter and the minimum diameter.

42. A blood pressure measurement system, comprising:an implantable device comprising an implantable housing, at least one processor within the implantable housing, and at least one ultrasound pulser within the implantable housing and in communication with the processor; anda non-transient data store in communication with the at least one processor, the non-transient data store containing an instruction set comprising machine-executable instructions that, when executed by the processor (i) cause the at least one ultrasound pulser to conduct ultrasound sampling of a target vessel for blood pressure measurement by pulsing between 1 and 50 times per cardiac cycle for at least one cardiac cycle, (ii) estimate a function representing vessel diameter over cardiac cycle based on data from said ultrasound sampling; (iii) determine maximum and minimum diameters for the target vessel, and (iv) calculate blood pressure using the determined maximum and minimum diameters.

43. The blood pressure measurement system of claim 42, wherein the ultrasound sampling comprises pulsing between 3 and 20 pulses per cardiac cycle.22 Atorney Docket No. 17961-007WOU1

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