Patent Description:
The present disclosure generally relates to the field of miniaturized implantable vital signs monitoring devices and methods. In particular, the present disclosure is directed to subcutaneously injectable blood pressure monitoring systems suitable, inter alia, for long-term monitoring of cardiovascular signals.

Hypertension is a significant precursor to cardiovascular disease and death. It is estimated that there are <NUM> billion people worldwide with hypertension, over <NUM> million in the United States alone, and less than one-third are under control. Hypertension is costly and deadly. There are an estimated <NUM> million deaths each year due to hypertension, and it costs the United States an estimated $<NUM> billion annually due to lost productivity and healthcare costs. Due to its deadliness and costs, it has been a target of government, academic, for-profit, and non-profit organizations. A recent task force has been formed to help reduce the incidence and prevalence of hypertension.

While there are many effective therapies and management protocols to prevent the progression of cardiovascular disease, patients and clinicians are challenged to achieve optimal management for a variety of reasons. First, hypertension is largely asymptomatic. Patients are often unaware they have hypertension which creates skepticism and doubt whether they need to take their prescribed medications or follow diet and exercise recommendations. Secondly, doctors only have sporadic, point-in-time data with varying accuracy of the measurement taken when it is taken outside the clinic. When measurements are taken in a clinic setting, patients may experience either White Coat Syndrome, or Masked Hypertension. This lack of consistent and accurate blood pressure data and trends decreases confidence in the right medical management decisions. Clinicians do not have enough data to make an accurate therapeutic change that could benefit the patient.

Current practices to improve blood control status and management include home blood pressure monitoring and ambulatory blood pressure monitoring. Many patients use, and clinicians prescribe, home blood pressure monitors to augment in-clinic measurements. These traditional home blood pressure monitors are point-in-time and require the patient to take action regularly, and to have cognitive physical ability to accurately place the blood pressure cuff and collect multiple measurements that can be averaged to filter out inaccuracies or outliers. Another challenge with traditional home blood pressure monitoring is that it does not allow a patient to take their blood pressure at night for obvious reasons. It is also not possible to capture blood pressure readings during different activities compared to resting. Clinical research has demonstrated the clinical relevance and importance of day vs. night blood pressure and the relationship to when medications are administered.

In <CIT> a hemodynamic monitoring device is disclosed including an implantable ultrasonic vascular sensor for implantation at a fixed location within a vessel, comprising at least one ultrasound transducer, a transducer drive circuit, and means for wirelessly transmitting ultrasound data from the at least one ultrasound transducer,.

Another prescribed technology is Ambulatory Blood Pressure Monitoring (ABPM). Recent FDA approvals and CMS coverage decisions for ABPM are promising and the technology addresses some of the challenges of traditional home blood pressure monitoring systems. But the technology continues to be a barrier to patient and physician adoption. ABPM technology available today uses traditional sphygmomanometer methods to capture blood pressure measurements every <NUM> minutes for a period of <NUM>-<NUM> or even <NUM> hours. While the patient can be "ambulatory", the patient wears a cuff that inflates as often as every <NUM> minutes continuously for up to <NUM> hours causing pain and bruises. It keeps the patient awake at night, and it is an inconvenient system to wear during activities or even during a working day. It is intrusive into the patient's life and indiscreet.

Accordingly, there remains a clinical need for effective and minimally invasive and minimally intrusive methods to monitor and track blood pressure continuously over time.

The present invention is defined by the appended claims only, in particular by the scope of appended independent claim. References to "embodiments" throughout the description which are not under the scope of the appended claims merely represents possible exemplary executions and are therefore not part of the present invention.

In one implementation, the present disclosure is directed to a hemodynamic sensor system. The system includes a sensor implant, comprising a housing configured and dimensioned to be delivered subcutaneously through a hollow introducer sheath into tissue adjacent a target blood vessel in a patient, and at least one tissue fixation feature on an outer surface of the housing, the sensor implant further comprising within the housing: at least one sensor modules configured to detect changes in one or more physiological parameters indicative of patient hemodynamic condition, wherein at least one the sensor module comprises an ultrasound transducer; and a communication module communicating with the at least one sensor module to transmit one or more signals comprising signals representative of the detected changes to an external receiver.

In another implementation, the present disclosure is directed to a hemodynamic sensor system that includes a sensor implant configured to be implanted in patient tissue adjacent a target blood vessel, wherein the sensor implant comprises: a housing having a housing axis; at least one tissue fixation feature on an outer surface of the housing; at least two ultrasound transducers disposed in the housing along the housing axis with a known distance along the axis between the ultrasound transducers, each the ultrasound transducer positioned to detect a change in diameter of the target blood vessel in response to a cardiac pulse and produce signals representative of detected changes in diameter; at least one accelerometer disposed in the housing configured to detect movement or changes in position of the patient and produce signals representative of the movement or changes in position; a control module disposed in the housing configured to detect timing of and process the signals from the ultrasound transducers and the at least one accelerometer to produce a data stream from which pulse wave velocity for the target blood vessel, and patient blood pressure can be calculated; a communication module disposed in the housing configured to transmit the data stream to an external receiver; and a power source disposed in the housing operatively connected to power the sensor implant.

In yet another implementation, the present disclosure is directed to a hemodynamic monitoring method. The method includes subcutaneously placing a sensor implant in a patient in tissue adjacent a target blood vessel; generating a data stream with the sensor implant from which pulse wave velocity of the target blood vessel and patient blood pressure can be calculated; and transmitting the data stream to a computing device configured to calculate pulse wave velocity and blood pressure based on the data stream.

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:.

Embodiments of the present disclosure provide unobtrusive, minimally invasive, active implantable sensor devices, sensor systems and methods that meet current clinical needs. Disclosed devices, systems and methods use one or more micro-electrical mechanical system (MEMS) sensors for the accurate and continuous measurement of physiological hemodynamic signals such as diastolic and systolic blood pressure. In certain variations, embodiments disclosed herein may include any, or all, of the following additional clinical signals of overall patient status: heart rate, activity level (patient movement or position), temperature, heart rate variability, and stenosis. Disclosed embodiments can provide a long-term sensor system will provide accurate (equivalent to current standard of care) blood pressure over an extended duration (for instance, months or years), enabling the clinician to provide appropriate treatment recommendations.

The use of microelectromechanical systems (MEMS) manufacturing techniques in disclosed embodiments provides a unique micro-sized design, construction, and fixation that allows the implanted sensor system to be fixated just outside the target blood vessel wall, or in some alternatives in the vessel wall, using methods familiar to clinicians trained in accessing a blood vessel (such as ultrasound-guided imaging, and standard needle and syringe access to artery) and minimally invasive outpatient procedures. MEMS construction, unique materials and resultant miniaturized design also promotes efficient use of power compared to more conventional ultrasound transducers. Typical sizes of disclosed sensor implants are millimeter size scale; for example, in some embodiments sensor implant size will have dimensions ranging from about <NUM> to about <NUM> in any of length, width and height directions, and more typically may be in the range <NUM>-<NUM> width x <NUM>-<NUM> length x <NUM>-<NUM> height Novel injection tools enable the sensor implant to be inserted in an outpatient or clinic setting within minutes. A benefit of a clinic setting is that the patient acceptance increases, and more physicians will be skilled/trained in the minimally invasive procedure.

Persons skilled in the art will appreciate various features and advantages of devices, systems and methods of the present disclosure, including, but not limited to active implant (battery or inductively powered) to help reduce patient compliance challenges; fixation mechanism that allows the sensor system to be injected, but fixated outside the artery (in some embodiments, e.g. extravascular) to help reduce thrombus that can lead to signal drift and decreased sensitivity, minimize dislodgement, and clot adverse events compared to an intravascular sensor; MEMS-based-sensor module that incorporates one or more of sensors (strain/piezoelectric resistive transducer, piezoelectric/capacitive ultrasound); biocompatible nano-coatings to minimize encapsulation/biofouling; and ability to continuously capture and store cardiovascular signals for an extended duration.

As illustrated in <FIG>, components of a basic system <NUM> according to the present disclosure may comprise injectable sensor implant <NUM>, injection device <NUM>, local control module <NUM>, network-based analytics and data management modules <NUM> and clinician module <NUM> comprising user interfaces/applications for data access, analysis and alerts. Local control module <NUM> may take a variety of forms. In some embodiments, module <NUM> may comprise simply a communications module, facilitating communication between sensor implant <NUM> and network-based modules <NUM> and/or clinician module <NUM>. In other embodiments, in addition to a communications sub-module, local module may include processing and/or data storage sub-modules configured to store patient data from sensor implant <NUM> and/or determine patient parameters, such as blood pressure and fluid status, as described herein below. Module <NUM> also may function as an edge device for communication with network-based analytics, storage and data management modules. Module <NUM> thus may comprise one or more processors, memories and associated computing components commensurate with the functionality of module <NUM> in a specific configuration as may be devised by persons skilled in the art based on the teachings of the present disclosure. In some embodiments, local control module <NUM> may comprise a personal mobile device, such as a cell phone or tablet, running an downloadable app.

Clinician module <NUM> may comprise wirelessly connected devices such as computers, cell phones or tablets. Clinician module <NUM> also may be configured as a patient interface. In some embodiments, particularly where configured as a patient interface, module <NUM> may comprise an app running on the same device as running an app for local module <NUM>. In some embodiments, the functionality of both modules <NUM> and <NUM> may be incorporated into a single app executed on a mobile device.

Wireless communication links 112a and 112b are provided between sensor <NUM>, local module <NUM> and network-based analytics or data management modules <NUM>. Communication link 112b also may comprise a wired communication link. Communication links <NUM> between local module <NUM> and user interfaces <NUM> may be wired or wireless. Additionally, clinician module <NUM> may communicate directly with network-based analytics module <NUM>. Communication links 112a, 112b and <NUM> may comprise any of a number of known communication protocols. For example communication link 112a may comprise a personal area network (PAN) using communications based on technologies such as IrDA, Wireless USB, Bluetooth or ZigBee. Communication links 112b, <NUM> may comprise longer range, larger bandwidth communications such as LAN, WLAN or IAN. In a further alternative embodiment, one or more sensor implants <NUM> may communicate wirelessly with other sensor types of sensor modules via a body area network (BAN).

As shown in <FIG>, sensor implants <NUM> according to the present disclosure may generally comprise a layered MEMS structure with typically three functional layers made up of functional modules and sub-modules: power supply and communication layer <NUM> comprising elements such as a primary cell batteries conventionally used to power micro-sized medical implants or, in some embodiments, a solid state lithium ion rechargeable battery and RF antenna for charging and communication, ASIC and memory layer <NUM> comprising amplifiers, filters, processing and memory storage, and sensor layer <NUM> comprising one or more sensor modules, which may comprise piezoelectric micromachined ultrasonic transducers (pMUT) or capacitive micromachined ultrasonic transducers (cMUT). In some embodiments, capacitive pressure sensing may be employed. Other sensing modules may be configured as patient status sensors with additional sensing capabilities as described herein below. Functional layers <NUM>, <NUM> and <NUM>, together comprise a sensor package contained within a biocompatible housing <NUM>. In some embodiments, power supply and communication layer <NUM> may be configured for inductive coupling for charging and/or communications.

The layered MEMS structures described herein provide actively powered, integrated sensor implants well-suited to long-term sub-cutaneous and extravascular monitoring of blood pressure and other cardiovascular vital signs using ultrasound (US). The disclosed structures thus address challenges of previous approaches to collect reliable continuous blood pressure over time. <FIG> illustrate a number of alternative configurations for sensor implant <NUM> that achieve these advantages.

Sensor implant 102a, shown in <FIG>, includes power module <NUM> and communications module <NUM> in functional layer <NUM>. In some embodiments where inductive power coupling is used as the power source, the power module <NUM> and communications module <NUM> may be integrated as a single communications/power source module. Control and signal processing module <NUM> resides in functional layer <NUM>. In this embodiment, MUT sensor array <NUM>, along with status sensor module <NUM> and optional acoustic lens <NUM> comprise sensor layer <NUM>. This layered MEMS structure is contained within biocompatible housing <NUM>. In some embodiments, housing <NUM> may comprise rigid materials such as titanium, stainless steel or nitinol. Biocompatible plastics or silicone also may be used as a housing material. Ifthe material for housing <NUM> is not freely transmissive of US signals, one or more appropriate US transmissive window(s) <NUM> may be provided aligned with US sensor array <NUM>, such that housing <NUM> may comprise non-US transmissive portions <NUM> and transmissive portions <NUM>. Materials for US transmissive window(s) <NUM> include biocompatible materials such as polydimethylsiloxane (PDMS), silicone, glass, ceramic or parylene coatings.

Outer surfaces of housing <NUM> may be provided with a coating of materials to promote tissue adhesion, such as collagen, fibrin, chitosan, hyaluronic acid, and alginate, and/or may have textured, roughened or featured surfaces for this purpose. Other surfaces, such as US transmissive windows <NUM>, may have coatings to prevent tissue adhesion. Examples of adhesion preventative coatings include polymer brushes and self-assembled monolayers. As shown in <FIG>, fixation features <NUM> may comprise three-dimensional surface irregularities designed to create friction and prevent device migration over time. These irregularities may be rigid structures or compliant structures, such as fabric mesh or loops. In other embodiments, retractable tines with memory and flexibility (nitinol) are optimally placed to promote stable implant position over time. Fixation tines are collapsible and are collapsed inside of an insertion tool and engage when released from the insertion tool. Alternatively, one or more wings, or flaps, are optimally placed to promote stable implant position over time, and may be configured to collapse when inside the insertion tool and engage when released from the insertion tool. In some embodiments, fixation features <NUM> also may be configured as antennas as a part of communications module <NUM>. Sensor implants <NUM> also may include an attachment and release feature <NUM> on an outer surface of housing <NUM>. Attachment and release feature <NUM> may comprise a loop or recess that is releasably engageable by a delivery and retrieval mechanism as described in more detail below.

As indicated in <FIG>, extravascular sensor implants according to the present disclosure are preferably positioned at a known distance from the outer wall of the blood vessel (BV) to be interrogated. Optimum placement distance from the blood vessel may be set by persons of ordinary skill based on the teachings of the present disclosure taking into account parameters such as a sensor array configuration, tuning of the US signal using system electronics and selection of an acoustic lens. An advantage of injection devices <NUM> hereinafter described is that they allow for precise placement at a preferred sensing distance using visualization such as external ultrasound visualization. In some embodiments, sensing distance from the blood vessel outer wall will be in the range of about <NUM> to about <NUM>. In other embodiments, a narrower distance range of about <NUM> to about <NUM> may be preferable and, in some cases, a placement of <NUM> to <NUM> may be ideal.

While sensor implant 102a includes only a single sensor array <NUM>, often it will be preferable to include at least two, spaced-apart sensor arrays <NUM> in order to facilitate pulse wave velocity (PWV) measurements as in sensor implant 102b, shown in <FIG>. Sensor implant 102b is configured substantially the same as sensor implant I02a, with the exception of the accommodation of two sensor arrays <NUM> and corresponding two US transmissive windows <NUM>. Alternatively, rather than discrete windows, the two ends of the sensor implant may be transparent and comprised of material that supports ultrasound and communication. Examples of such materials include polydimethylsiloxane (PDMS), silicone, glass and ceramic. In a further alternative, the entire housing <NUM> may comprise a US transparent material that also permits transmission of communications signals from the antenna structure of communication module <NUM>.

<FIG> illustrates a further alternative embodiment, including multiple (NI through Nn) sensor arrays <NUM>, wherein sensor implant 102c is entirely a flexible construction including housing <NUM> being made of flexible material that also permits US signal transmission and communication signal transmission from communication module <NUM>. An example of such a housing material includes certain polymers and ceramic. Flexible functional layers <NUM>, <NUM> and <NUM> may be fabricated using carbon nanotubes or ultrathin silicon integrated circuit technologies. <FIG> also illustrates a further alternative fixation feature <NUM>, in the form of micro hooks. Such hooks may be comprised of resilient materials such as nitinol wire or biocompatible fabrics formed as hooks of hook and loop fasteners material.

Embodiments of sensor implants disclosed herein are physically arranged in a manner to promote accurate readings regardless of migration or changes in orientation after implantation. This will include a combination of unique sensor fabrication that physically orients transducers in a fashion that will maintain focus on vessel of interest regardless of modest migration or movement of sensor away from vessel of interest. Aspects of this physical arrangement include the elongated configuration of housing <NUM> with plural spaced-apart sensor arrays <NUM> positioned on one side of the sensor implant, with appropriately positioned fixation features <NUM>. These aspects of the disclosed sensors present a unique advantage over prior systems by making PWV calculations and blood pressure calculations based on the PWV calculations possible using only a single, unitary sensor implant to provide not only all necessary timing and dimensional data at two spaced-apart locations, but also, in some embodiments, additional patient position and movement data to allow more accurate assessment of patient hemodynamic state, and blood pressure in particular.

<FIG> presents a representative block diagram of major functional blocks within embodiments of implant sensors <NUM> as disclosed herein. As shown therein, power module <NUM> provides a power source in the form of a power supply comprising battery <NUM> and power management sub-module <NUM>. Note that the battery can be generalized to any suitable implantable primary cell or rechargeable power source as may be devised by persons of ordinary skill. Power management sub-module <NUM> is configured for battery optimization to power US wireless communication, etc., with no required patient interaction to power the device, which is a substantial improvement over prior devices. Long-term monitoring can be achieved through the application of algorithms that reduce power consumption during idle times and optimize overall battery consumption, including detecting power requirements and automatedly switching appropriate modules or sub-modules to "power off' mode when power is not required in those modules or sub-modules.

Communications module <NUM> comprises a transceiver sub-module configured for the selected communications mode and corresponding antenna, which is preferably positioned opposite the sensor modules at or through housing <NUM>. In some embodiments, the antenna may comprise fixation features <NUM> (e.g., <FIG>). Control and signal processing module <NUM> may comprise memory <NUM>, digital control <NUM>, transmit and receive electronics sub-module <NUM>, data converter <NUM> and processing sub-module <NUM> including at least one microprocessor. These components may be configured by persons skilled in the art based on the teachings contained herein. As will be appreciated, sensor integration with ASIC provides efficiency gains in power and size by integrating the MEMS sensor into the ASIC design. While in some embodiments pulse wave velocity and patient blood pressure may be calculated within sensor implant <NUM>, it may be preferable to configure processing module <NUM> with instructions to produce a data stream from which pulse wave velocity for the blood vessel and patient blood pressure (optionally also heart rate) can be calculated.

Status sensor module <NUM> may comprise one or a collection of several different sensor types, including but not limited to inertial measurement unit (IMU), accelerometer, temperature sensor, electrodes for ECG or impedance, and oxygen saturation. Status sensor module <NUM> thus provides for monitoring of a number of different physiologic parameters, such as temperature, body position, activity, ECG and fluid retention, to compliment blood pressure measurements to assist in assessment of patient's overall condition. In most embodiments, at least a status sensor module with an accelerometer will be included to allow the data stream produced by control and processing module <NUM> to include information needed to adjust the blood pressure calculation to compensate for patient position and/or movement.

<FIG> illustrates sensor array state configurations. When multiple sensor arrays are employed, for example as in sensor implant I02c, shown in <FIG>, with each additional sensor array, its operation state during use (Tx or Rx) is flexible. As an example, a configuration where Sensor NI and Sensor N2 are present is shown in <FIG>, wherein each sensor array has options of receive, transmit and active switching between receive and transmit. Sensor state is programmable via electronics sub-module <NUM>.

A two-dimensional representation of a cMUT or pMUT array is shown in <FIG>. In this example, sensor module <NUM> comprises substrate <NUM> with an array of sensor elements <NUM>. Ideally, the array parameters, Ds (sensor element diameter), Hs (array height) and Ls (array length), are optimized for performance within a specific sensor implant and system. For example, Ds is preferably selected based at least in part on a desired frequency of operation, thus defining a minimum vessel diameter change that can be detected by the sensor implant. Hs and Ls define number of sensor elements and are selected at least in part to optimize signal-to-noise ratio (SNR) as the pulse echo amplitude is defined by these parameters. Sensor array size can also be selected in combination with the number of plural sensor modules (as in, for example, sensor implant 102c (<FIG>) in order to facilitate position identification and compensation as discussed below. In some embodiments a preferred material for sensor array <NUM>/<NUM> is aluminium nitride (AlN), which provides US power-efficient and biocompatible sensor array substrate compatible with human implantation. Previous lead-based ultrasound transducers require 1OOx more energy to power sensor and are also not biocompatible for implantable use in living beings. Further details of MUT sensor constructs suitable for use in sensor implants according to the present disclosure can be found, for example, in <CIT>, entitled "Piezoelectric transducers and methods of making and using the same," and <CIT>, entitled "Miniature ultrasonic imaging system".

A variety of alternative embodiments of sensor package form-factor and delivery systems will now be described in more detail with reference to <FIG> through lOB. In one alternative embodiment, shown in <FIG>, sensor implant 102d comprises housing <NUM> containing a sensor package as described in various embodiments above. Sensor implant 102d includes tissue-engaging tines as fixation features <NUM> for securing the implant in proximity to blood vessel (BV) within which measurements are to be made. Tissue-engaging tines as fixation features <NUM> may be configured to engage and anchor in tissues such as muscle tissue, skin tissue, outer layers of the blood vessel itself or other suitable tissues in sufficient proximity to the vessel in which measurements are to be made. The tines may have barbs or other retention features (not shown) to increase the anchoring function.

In another alternative embodiment, shown in <FIG>, injectable sensor 102e may utilize a passive anchor system as fixation feature <NUM>. In this example, resilient cuff as fixation feature <NUM> engages around the blood vessel (BV) and thus positions sensor housing <NUM> in close proximity to the blood vessel (BV) or in contact therewith. A method and deployment device for a resilient cuff-type fixation feature is shown in <FIG> and described in more detail below.

In yet another alternative embodiment, shown in <FIG>, sensor implant 102f comprises housing <NUM> with fixation feature <NUM> comprised of anchor element <NUM> disposed on the end of flexible member <NUM> extending from the sensor housing. In this arrangement, housing <NUM> of sensor implant 102f may be disposed on the inside of the blood vessel (BV) with flexible member <NUM> extending through the blood vessel wall, capped with anchor element <NUM>. This arrangement may also allow the use of alternative sensor types requiring contact with the fluid to be measured, such as MEMS capacitive sensors. Sensor implant 102f may be placed with instrumentation and procedures as used for vascular electrode placement or for certain vascular closure devices having anchor member placed within the vascular lumen.

<FIG> shows deployment may be accomplished with alternative injection device 104a, including an outer sheath <NUM> with a sharpened, needle-like distal end terminating in a shovel-like protective extension <NUM>. Injection device 104a otherwise may in general be configured similar to a larger-sized syringe device, wherein only the distal end portion is shown in <FIG>. Outer sheath <NUM> is inserted through tissue such that protective shovel portion <NUM> is disposed at the intended deployment site. Tether <NUM> serves as both a pusher and retrieval member for deployment of sensor 102d including anchoring tines as shown in <FIG>. When the distal end of injection device 104a is properly positioned, tether <NUM> is used to move sensor 102d to an exposed position over shovel-like extension <NUM>. This allows the tines forming fixation feature <NUM> of sensor 102d to engage overlying tissue while protecting the blood vessel disposed below shovel-like projection <NUM>. Tether <NUM> may then be disengaged and with the tines of sensor 102d engaged on overlying tissue, injection device 104a may be withdrawn. Alternatively, if positioning is not as desired, tether <NUM> may be used to draw sensor 102d back within sheath <NUM> for repositioning. Tether <NUM> may engage with attachment and release feature <NUM> as previously described. Outer sheath <NUM>, shown in <FIG> with a slight distal bend, may alternatively be straight.

<FIG>, <FIG> and <FIG> illustrate an embodiment of injection device <NUM>, configured for delivering an injectable sensor such as sensor 102e (<FIG>) utilizing a resilient cuff as a passive fixation feature <NUM>. Injection device <NUM> is configured generally as a syringe-type device with an outer introducer <NUM> surrounding an inner sheath <NUM> having a resiliently curved distal tip. Device injector <NUM> (e.g. a pusher) is concentrically disposed in the center lumen of inner sheath <NUM> and comprises a release and retrieval mechanism with a hook at the distal end <NUM> that opens and closes to release or grab sensor 102e as needed. In one embodiment the release mechanism may comprise pull wire <NUM> (<FIG>).

After the distal end of introducer <NUM> is positioned subcutaneously in the area of deployment, inner sheath <NUM> is extended and its resilient curvature causes it to wrap around the BV at the site of interest as shown in <FIG>. Device injector <NUM> is used to position or maintain sensor 102e at the distal end of inner sheath <NUM> as it surrounds the blood vessel. Once positioned as shown in <FIG>, inner sheath <NUM> may be withdrawn to expose sensor 102e as in <FIG>. Resilient anchor cuff <NUM> then surrounds the blood vessel (BV) while still secured to device injector <NUM> by retrieval mechanism hook <NUM>. Optionally, position may be confirmed by visualization such as by ultrasound or fluoroscopy. With sensor 102e and cuff <NUM> positioned around the blood vessel at the site of interest, hook <NUM> may be disengaged by pulling release wire <NUM>. In some embodiments, atraumatic passive ball <NUM> may be disposed on the end of cuff <NUM> opposite sensor housing <NUM>. Anchor cuff <NUM> may be made of resilient, shape-memory materials such as nitinol.

<FIG>, lOA and lOB illustrate a further alternative injection device <NUM> suitable for placement of a number of different sensor implants <NUM> at monitoring locations in tissue adjacent to targeted blood vessels according to the present disclosure. As shown therein, injection device <NUM> comprises outer introducer <NUM> with a sharpened, needle or syringe-like distal end, an inner atraumatic curved sheath <NUM> and device injector <NUM> sliding within inner sheath <NUM>. Injection device <NUM> is also generally configured as a syringe-type device. In order to deploy sensor implant <NUM> with injection device <NUM>, introducer <NUM> is positioned subcutaneously at the desired location, preferably under visualization, such as with ultrasound. When appropriate positioning is confirmed, inner sheath <NUM> is advanced out of the distal end of introducer <NUM>. Atraumatic distal end of inner sheath <NUM> facilitates positioning in close proximity to a blood vessel of interest while minimizing possibility of trauma to the blood vessel during the sensor injection procedure. Distal end of inner sheath <NUM> may have a pre-set curve as shown in FIGS. 1OA and lOB such that after exiting outer introducer the inner sheath automatically assumes the pre-set curvature thereby facilitating placement with reduced risk of trauma to the adjacent blood vessel. After inner sheath <NUM> is properly positioned, sensor <NUM> is advanced out of the distal end by device injector <NUM>. The distal end of device injector <NUM> may be provided with a retrieval mechanism such as a hook as described herein. After position of sensor <NUM> and engagement of the fixation feature is confirmed, inner sheath <NUM> may be withdrawn and then the sensor disengaged from device injector <NUM>. Injection device <NUM> as a whole is then withdrawn.

<FIG> illustrates the use of MEMS ultrasound in sensor implant <NUM> to determine blood pressure and other vitals based on pulse transit time and pulse wave velocity measurements <NUM>, which are amplified, filtered and processed <NUM> to provide a data stream from which blood pressure over time <NUM> may be calculated according to known correlations between blood pressure and pulse wave velocity. Ultrasound is the transmission of sound waves through a medium. When the ultrasound sound waves reach a surface or differing medium, the wave reflects and travels back in the originating direction. The time it takes for the ultrasound wave to travel can be used to calculate the distance from the reflecting surface. This ultrasound concept may be used in embodiments of the present disclosure to calculate the diameter of the vessel wall and can be used to estimate volumetric changes in the vessel as a pulse wave travels through the vessel. Based on the wave transmission and properties, the ability to differentiate the variability in reflecting mediums, such as hard plaque or wall stiffness, is also possible.

One example of known algorithms for blood pressure calculation on this basis is described by<NPL>.

In in vitro experiments, Ma, et al. have validated correlation of pulse wave velocity (PWV) to blood pressure through the integral of the inner artery radius to the outer artery radius after artery deformation (before and after the pulse travels through the artery). Embodiments disclosed herein employ and improve upon the concepts suggested by Ma et al. in an implanted MEMS sensor that is injected near the target vessel.

Using at least two sensor arrays, for example as in sensor implant 102b, shown in <FIG>, vessel dimensions as well as PWV can be determined as illustrated in <FIG>. With appropriate signal processing and focusing of the US beams, four separate US pulses can be defined, representing the outer surface of the near (proximal) wall, the inner surface of the near (proximal) wall, the inner surface of the far (distal) wall, and the outer surface of the far (distal) wall. This allows determination of not only the diameter of the inner vessel, but also the thickness of the arterial wall. Heart rate is also directly determinable from this signal over time.

Using these US measurements, plus the known distance between sensor <NUM> and sensor <NUM>, the PWV can be calculated as PWV = (d)/ T. It is to be noted that the pulse echo shown can be the statistical sum of pulse echo received from several sensors and reflects all pre-processing completed in hardware.

<FIG> depicts an embodiment of a process flow for determination of patient blood pressure and general hemodynamic state. Placement of sensor implants <NUM> according to the present disclosure as described above may be performed as an in- or outpatient procedure, employing clinically accepted practices for subcutaneous insertion. Typical placement sites include the upper arm targeting the brachial artery for monitoring, or the thoracic region targeting the subclavian artery in the delta pectoral groove for monitoring. At time of placement (step <NUM>), patient diastolic blood pressure is measured and input to the system, for example via interface <NUM> (step <NUM>). Other patient data may be input at this time to improve accuracy of hemodynamic state assessment. Such other information may include patient age, sex, weight, height and any known comorbidities. After sensor implant placement is verified, the system is initialized (step <NUM>). At this stage, monitoring begins with US sensor modules <NUM> and status sensor module <NUM> (step <NUM>). At a minimum, body position or changes in body position are detected (step <NUM>) with an accelerometer included in status sensor module <NUM> to permit adjustment of the calculated blood pressure to take into account variations based on body position and movement. Sensor module operation may be programmed on an intermittent basis at specific periods or may be continuous or near-continuous.

US pulse echo signals, as shown in <FIG>, are received (step <NUM>) initially by electronics sub-module <NUM> for processing in control and signal processing module <NUM>. In some embodiments, processing at this point may be minimal, such as filtering and signal amplification, with the signal data thereafter transmitted via communications module for further signal processing in external module <NUM> or in other networked processing environments such as network-based systems <NUM> or a computing system associated with user interface <NUM>. Alternatively, in more preferred embodiments, further signal as described in the following steps <NUM>-<NUM> is executed within control and signal processing module <NUM> of sensor implant <NUM> according to instructions stored in memory sub-module <NUM>. Regardless of locus of execution, envelope detection (step <NUM>), region-of-interest (ROI) detection (step <NUM>), and peak detection (step <NUM>) are executed in accordance with known signal-processing algorithms for processing of US signals. A variety of such algorithms are well-known in the art and may be selected by persons of ordinary skill based in the teaching contained herein. With signal data appropriately processed for interpretation by the designated computing device (internal, external or networked), vessel diameter as a function of time is determined based on analysis of the US signals (step <NUM>). Measured and recorded data stored in memory module <NUM> may include, for example, vessel inner and outer diameters at each US sensor array, L'. 1T between the different US sensor array readings, heart rate/interval, temperature and patient or sensor implant orientation.

Pulse wave velocity (PWV) is determined and recorded at step <NUM> based on parameters determined in prior steps. Based on determined PWV and at least the previously measured and entered Diastole BP (step <NUM>), blood pressure is calculated (step <NUM>), according to correlations known in the art, for example, using algorithms described by Ma et al. as explained above. Additional inputs to blood pressure calculation (step <NUM>), which may increase accuracy of the calculated blood pressure, may include other measured parameters (step <NUM>) such as patient activity or orientation (as determined by accelerometer or IMU in status sensor module <NUM>) and body temperature (as determined by temperature sensor in module <NUM>). Other parameters as described hereinabove also may be factored in by persons of ordinary skill based on the teachings of the present disclosure. Patient blood pressure and other hemodynamic parameters as measured and determined, along with measured parameters (step <NUM>) are delivered to the clinician/patient interface, such as interface <NUM> (step <NUM>). In one embodiment, calculation of blood pressure is executed in network-based systems through appropriate network connections with local control module <NUM>.

<FIG> illustrates a further alternative embodiment of a system 1OOa according to the present disclosure. In this example, sensor implant <NUM> includes at least two ultrasound sensor modules comprised of micromachined ultrasonic transducer arrays, a status sensor module comprised of at least an accelerometer, and a control module including at least one microprocessor and at least one memory containing instructions and configured to allow the sensor implant to perform at least sensing and processing steps <NUM> through <NUM>. In this specific example, communication module <NUM> uses Bluetooth communication to transmit a processed data stream containing blood vessel dimension, timing and accelerometer information as needed to permit calculation of pulse wave velocity and patient blood pressure. In this example, a personal mobile device is configured as one or both of local module <NUM> and patient interface <NUM> using a mobile device app and transmits the processed data stream to a networked computer for calculation of pulse wave velocity and patient blood pressure according to stored algorithms discussed herein. Patient blood pressure information is conveyed back to the patient via the mobile device <NUM>/<NUM>. Optionally, a separate clinician interface may receive the patient data directly from networked computing device <NUM> via the network or through the patient mobile device <NUM>/<NUM>.

Parameters utilized in processing may include those parameters that are determined during initial implantation of implant sensor <NUM> and as may be updated as needed with periodic calibration. In some embodiments periodic calibration may include analysis to determine placement relative to initial placement location. Given the unique implant structure employing, in some embodiments (e.g. sensor implants 102b and 102c), multiple sensor MUT modules positioned at known fixed distances with respect to one another, analysis of returned US signals allows for continually accurate PWV calculation by using changes in the US-viewed orientation relative to the observed vascular structure to determine a skew factor for correcting PWV calculations. For example, using anatomical markers as detected by sensor modules <NUM> and interpreted by control and signal processing module <NUM>, the system may determine that the longitudinal axis of the sensor implant, originally preferably implanted in alignment with direction of blood flow or at a known orientation with respect thereto, has become skewed relative to flow direction by a determined skew angle. The system may then recalculate the distance between N and N+ <NUM> sensor modules <NUM> as (cos[skew angle]) / [fixed sensor module spacing] = [skew adjusted sensor spacing].

As will be appreciated by persons skilled in the art, devices, systems and methods disclosed herein, given the large and varied amount of physiological and specifically hemodynamic data generated, allow for accurate detection and classification of arrythmias, such as bradycardia, ventricular tachy-cardia, atrial fibrillation, atrial tachycardia, and sinus pause using data generated in accordance with the teaching of the present disclosure in known diagnostic algorithms. Further, one or more of the following vital signals: systolic BP, diastolic BP, mean arterial BP, Pulse Wave Velocity (PWV), blood flow, arterial stiffness, elasticity modulus, ECG waveform, heart rate, heart rhythm, atrial fibrillation, bradycardia, tachycardia, sinus pause, activity, body position, blood pressure variability, heart rate variability, endothelial function, coronary artery disease, blood oxygen saturation (<NUM> sat), composite score or indication of cardiovascular health and risk may be calculated, stored and uploaded to network-based systems for accurate patient assessments over extended times without requiring in-patient or clinic visits for data collection. In a further aspect of the present disclosure, patient-centered engagement apps employing user interfaces on mobile devices or home computing devices to encourage adherence and patient behaviors may be driven based on collected data and analysis thereof.

In some embodiments, various aspects of the present disclosure, including, for example, local module <NUM>, network-based modules <NUM>, clinician user interface/application <NUM>, and control and signal processing module <NUM> among others, may be executed as one or more computing devices <NUM> as illustrated in <FIG>. In this example, computing device <NUM> includes one or more processors <NUM>, memory <NUM>, storage device <NUM>, high-speed interface <NUM> connecting to memory <NUM> and high-speed expansion ports <NUM>, and a low speed interface <NUM> connecting to low speed bus <NUM> and storage device <NUM>. Each of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, are interconnected using various busses or other suitable connections as indicated in <FIG> by arrows connecting components. Processor <NUM> can process instructions for execution within the computing device <NUM>, including instructions stored in the memory <NUM> or on the storage device <NUM> to display graphical information via GUI <NUM> with display <NUM>, or on an external user interface device, coupled to high speed interface <NUM>. In other implementations, multiple processors and/or multiple busses may be used, as appropriate, along with multiple memories and types of memory.

Memory <NUM> stores information within the computing device <NUM>. Memory within implant <NUM> may store, for example data from ultrasound readings representing vessel dimensions and sensor timing and patient movement based on accelerometer data. Such data also may comprise a data stream communicated from the sensor implant computing device and may be stored in a network-based memory along with pulse wave velocity and blood pressure calculations executed in a network-based computing device.

Storage device <NUM> is capable of providing mass storage for the computing device <NUM>, and may contain information such as the database of tile display information described hereinabove. In one implementation, storage device <NUM> is a computer-readable medium. In various different implementations, storage device <NUM> may be a floppy disk device, a hard disk device, an optical disk device, or a tape device, a flash memory or other similar solid state memory device, or an array of devices, including devices in a storage area network or other configurations.

High speed controller <NUM> manages bandwidth-intensive operations for the computing device <NUM>, while low speed controller <NUM> manages lower bandwidth-intensive operations. In one implementation, high-speed controller <NUM> is coupled to memory <NUM>, display <NUM> (e.g., through a graphics processor or accelerator), and to high-speed expansion ports <NUM>, which may accept various expansion cards (not shown). The low-speed expansion port, which may include various communication ports (e.g., USB, Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or more input/output devices as part of GUI <NUM> or as a further external user interface, such as a keyboard, a pointing device, a scanner, or a networking device such as a switch or router, e.g., through a network adapter.

These computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/ machine language.

To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device (e.g., an LED, OLED or LCD display) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer.

The components of the system can be interconnected by any form or medium of wired or wireless digital data communication (e.g., a communication network).

Other features and advantages include that the implanted sensor system is actively powered with a rechargeable battery that is integrated into the implanted sensor system, which has the benefit of minimizing patient burden while allowing long-term (for months to years) of functional use. The implanted sensor system will automatically connect to the external charging and communication module when the patient is within range of the charging and communication module. When connected the external charging and communication system will charge the battery in the implanted sensor system. A benefit of the active implanted sensor system with automatic charging is that the patient does not need to take action to recharge the battery. The implanted sensor system has a longevity of months to years.

Implanted/injectable sensor systems as disclosed herein may also store sensor signal data (for instance, up to a week) in the memory chip that is designed into the ASIC and memory module of the implanted sensor system. This can further reduce the burden to the patient to be in range of the external charging and communication system and reduces the risk of lost data.

Disclosed delivery embodiments also provide an ability to retract and reposition the implanted/injectable sensor prior to final fixation to find optimal sensor placement. This is due to the functions of the injection tool in combination with the fixation design of the implanted sensor system. One benefit of this feature is to enable sensor repositioning for optimal sensor accuracy.

Implanted/injectable sensor systems as disclosed may employ an RF communication module to enable transfer of implanted sensor signal data to the external charging and communication system. The RF communication module optionally may be designed to support charging of the implanted sensor system.

Implanted/injectable sensors as disclosed are hermetically sealed to protect the sensor components for chronic implantation. The sensor package may be coated with a biocompatible material that prevents tissue growth and blood clotting.

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 of Y; 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.

Claim 1:
A hemodynamic sensor system, comprising:
a sensor implant (<NUM>, 102b, 102c, 102d, 102e, 102f), comprising a housing (<NUM>) configured along a housing axis to be positioned subcutaneously in tissue adjacent a target blood vessel in a patient, and at least one tissue fixation feature (<NUM>) on an outer surface of the housing, the sensor implant further comprising within the housing at least two ultrasound transducers (<NUM>) positioned along said housing axis with a known distance between the ultrasound sensor transducers, said ultrasound transducers configured to produce signals indicative of a change in diameter of the target blood vessel at spaced apart locations in response to pulsations of the cardiac cycle; and
at least one processor (<NUM>, <NUM>) and at least one memory (<NUM>, <NUM>) in operative communication with the at least one processor, the memory containing an instruction set comprising machine-executable instructions that, when executed by the at least one processor determine a pulse wave velocity for the target blood vessel based in part on said signals indicative of changes in diameter at the spaced apart locations.