Tactile Blood Pressure Imager

Abstract

To provide a method directed to continuously, non-invasively and directly measuring the blood pressure, the method including providing a calibrated measurement device having a blood-flow control balloon and a sensor array.SOLUTION: The method further includes placing the sensor array in a non-invasive manner over the surface of a skin portion connected to an artery by adjoining soft tissues, and inflating the blood-flow control balloon with a controlled amount of pressure. In response to the inflation of the blood-flow control balloon, changes in the artery geometry and forces are detected, via the sensor array, during a heartbeat cycle. The changes correspond to spatio-temporal signals from the artery or in the adjoining soft tissues. The spatio-temporal signals are measured and processed, via a controller, to determine blood-pressure parameters.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] government support This invention was made with Government support under Grant No. 1 U01 EB018823001A1 awarded by the National Institutes of Health (NIH). The Government has certain rights in the invention.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 684,726, filed June 13, 2018, and U.S. Provisional Patent Application No. 62 / 652,180, filed April 3, 2018, each of which is incorporated by reference in its entirety.

[0003] The present invention relates generally to non-invasive estimation and continuous monitoring of arterial blood pressure, and more specifically to the use of skin surface displacement and force to directly measure and monitor arterial blood pressure. Summary of the Invention

[0004] According to one aspect of the disclosure, a method is directed to continuous, non-invasive, direct measurement of blood pressure and includes providing a calibrated measurement device having a flow-regulating balloon and a sensor array. The method further includes non-invasively placing the sensor array on a surface of a skin portion connected to an artery by being adjacent to soft tissue, and inflating the flow-regulating balloon with a regulated amount of pressure. In response to the inflation or deflation of the flow-regulating balloon, changes occur in the size and shape of the artery and the force it exerts on the surrounding tissue. Thus, changes occur in the contact between the skin and the sensor array during the cardiac cycle, as detected via the sensor array. The changes in the arterial shape and the arterial force correspond to spatiotemporal signals from the artery. The spatiotemporal signals are measured and processed via a processor to determine blood pressure parameters.

[0005] According to another aspect of the present disclosure, a calibrated measurement device is directed to continuous non-invasive direct measurement of blood pressure. The calibrated measurement device includes a strap and a flow-regulating balloon coupled to the strap, the flow-regulating balloon having an inflated state where a regulated amount of pressure causes spatiotemporal signals from the artery to be separated without compromising the venous and lymphatic circulation or flow of other arteries of the limb. The calibrated measurement device further includes a sensor array on a surface of the flow-regulating balloon for non-invasive direct measurement and monitoring of blood pressure. The sensor array detects changes in the shape and force of the artery when the flow-regulating balloon is in an inflated state during a cardiac cycle. The changes correspond to spatiotemporal signals from the artery.

[0006] Optionally, in the above aspects of the disclosure, the sensor array is implemented based on a painted surface, structured light, or gel film with optical markers attached to the outer surface of the blood flow regulation balloon. However, in another exemplary aspect of the disclosure, the sensor array is implemented based on a painted surface, and the optical markers or structured light pattern is on the inner or outer surface of the material of the blood flow regulation balloon. Furthermore, in another exemplary aspect of the disclosure, the sensor array is implemented based on optical markers or structured light patterns projected directly onto the skin surface.

[0007] According to another exemplary aspect of the present disclosure, a sensor array is implemented based on photometric stereo deformation sensing with the aid of a painted surface and a gel film with colored light. Optionally, another exemplary aspect is directed to a sensor array implemented based on individual force or displacement sensors. Specifically, the sensor array is implemented by assembling individual force or deformation sensors, such as resistive, piezoelectric, or capacitive elements.

[0008] Optionally, in one or more of the above aspects of the present disclosure, a gel membrane is attached to the outer surface of the blood flow regulating balloon. However, in another exemplary aspect of the present disclosure, the gel membrane is replaced with a painted surface or structured light pattern on the inner or outer surface of the material of the blood flow regulating balloon.

[0009] According to yet another alternative exemplary embodiment, a sensor is coupled to a mechanical mount and used to vary the attachment force (e.g., in a tabletop device). In this embodiment, instead of using a flow-regulating balloon, the attachment force is adjusted with the aid of a mechanical mount coupled with a force sensor and / or a displacement sensor.

[0010] To further adjust the contact condition, the flow-regulating balloon is fitted with (1) a pressure sensor that provides a direct measure of the spatial average value of the force on the contact area with the object (with or without the gel membrane), (2) an air pump that is used to actively change the contact condition (shape change and force change), and (3) a controller that provides some adjustment to the contact condition and its change over time, especially with feedback from the pressure sensor. Gels and other fluids other than air filling the flow-regulating balloon may be optionally considered based on the respective measurement task.

[0011] According to yet another aspect of the present disclosure, a method is directed to continuous, non-invasive, direct measurement of blood pressure in an artery. The method includes providing a calibrated measurement device having a strap for attachment on a limb, the strap carrying a blood flow regulation balloon, a strap adjustment balloon, and a strap force sensor on an inner surface thereof. The blood flow regulation balloon carries a sensor array on an inner surface thereof. The method further includes placing the strap on the limb such that the sensor array is in non-invasive contact with a skin surface over the artery, and inflating the blood flow regulation balloon with a regulated amount of pressure without impairing venous and lymphatic circulation or flow in other arteries of the limb. The method further includes detecting, via the sensor array in response to inflation of the blood flow regulation balloon, changes in shape and force of the artery during a cardiac cycle that correspond to spatiotemporal signals from the artery. The strap adjustment balloon is inflated with a regulated amount of pressure to apply a force between the strap and the skin surface. Based on detection by the sensor array and the strap force sensor, fine tuning pressure is applied by at least one of the blood flow regulation balloon or the strap adjustment balloon to enhance detection of spatiotemporal signals from the artery. The spatiotemporal signals are measured and processed, via a processor, to determine blood pressure parameters.

[0012] Other aspects of the present disclosure will become apparent to those skilled in the art upon consideration of the detailed description of the various embodiments, taken in conjunction with the drawings, a brief description of which is set forth below. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram showing changes in the curvature of a blood vessel wall. [Diagram 2] 1 is a cross-sectional view illustrating components of a calibration measurement device according to one embodiment of the present disclosure. [Figure 3A] FIG. 2 shows a first portion of data related to spatio-temporal signals and blood pressure markers, including raw spatial information, processed spatial information, and a height image. [Figure 3B]FIG. 3B shows a second portion of the data associated with the spatiotemporal signals and blood pressure markers of FIG. 3A, including plots of various signals. [Figure 3C] FIG. 3B shows a third portion of the data associated with the spatiotemporal signals and blood pressure markers of FIG. 3A, including a plot of group markers. [Figure 3D] FIG. 3B shows a fourth portion of the data associated with the spatiotemporal signals and blood pressure markers of FIG. 3A, including values ​​of various signals. [Figure 4A] 1 is a cross-sectional view illustrating components of a calibration measurement device including a camera according to another embodiment of the present disclosure. [Figure 4B] FIG. 4B illustrates the camera setup of the calibration measurement device of FIG. 4A with a light emitting diode (LED) adjuster. [Figure 4C] FIG. 4B is a perspective view of a tabletop version of the calibration measurement device of FIG. 4A. [Figure 4D] FIG. 4B is a perspective view of a wearable version of the calibration measurement device of FIG. 4A. [Figure 5A] 1 is a cross-sectional view illustrating components of a calibration measurement device including an optical marker according to another embodiment of the present disclosure. [Figure 5B] FIG. 5B is a perspective view of a tabletop version of the calibration measurement device of FIG. 5A. [Figure 5C] FIG. 5B is a perspective view of a wearable version of the calibration measurement device of FIG. 5A. [Figure 6A] 1 is a cross-sectional view illustrating components of a calibration measurement device including a piezoelectric sensor according to another embodiment of the present disclosure. [Figure 6B] FIG. 5B is a perspective view showing a piezoelectric sensor of the calibration measurement device of FIG. 5A attached to the underside of a balloon. [Figure 6C] FIG. 5B is a perspective view of the calibration measurement device of FIG. 5A attached to the wrist. [Figure 7A] FIG. 1 is a perspective view showing an animal experiment using a rabbit model. [Figure 7B] FIG. 1 is an enlarged perspective view of the experimental setup for the porcine model. [Figure 7C] FIG. 7C is a perspective view showing an overall view of the experimental setup of FIG. 7B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

[0015] The present disclosure is generally directed to novel approaches, methods, and associated device configurations for estimating and continuously monitoring intra-arterial blood pressure (BP) over time. Based on the disclosed methods, direct measurements are made for systolic blood pressure (SBP), mean arterial pressure (MAP), and diastolic blood pressure (DBP). A tactile blood pressure imager (TBPI), more commonly referred to as a blood pressure imager (BPI), is used to measure beat-to-beat variability of SBP, MAP, and DBP, including respiratory variations in blood pressure, over time. Based on this, TBPI can identify abnormal blood pressure patterns, such as white coat hypertension, masked hypertension, and reduced nocturnal BP dips during sleep and early morning BP rise, and other abnormal patterns. TBPI facilitates accurate evaluation of treatment efficacy and better individualization of therapy, and further identifies lifestyle motivations, such as to reduce smoking and stress, that are needed to lower a patient's blood pressure. TBPI continuously tracks heart rate (HR), and thus HR variability, as well as abnormal heart rhythms over time. BPI also continuously tracks respiratory rate (RR) and abnormal breathing patterns. TBPI additionally tracks beat-to-beat blood pressure and is a non-invasive alternative to invasive intra-arterial blood pressure monitoring.

[0016] Referring to Fig. 1, a schematic diagram shows how changes in blood pressure change the curvature of a blood vessel wall 100 and thus the skin surface 102. Blood pressure has a direct relationship with the size and shape of the artery (e.g., diameter 104), which determines the deformation of and spatial distribution of forces on the contact surface 106 of a force or deformation sensor array 108. The sensor array 108 contacts the skin surface 102, particularly at the location of a superficial artery 110, such as the radial artery at the wrist. The dynamics of blood pressure inside the artery 110 give rise to spatiotemporal dynamics in the contact surface profile. This basic principle is used to continuously estimate and track blood pressure.

[0017] When the sensor array 108 is mounted and pressed onto the skin surface 102 on the superficial blood vessel 110, the sensor array 108 captures the variations in the arterial cross section over space and time. Blood pressure has a direct relationship with the shape and size of the arterial cross section, which determines the interface profile (spatial distribution of deformations and forces) between the skin surface 102 and the sensor array 108. Thus, the dynamics of blood pressure inside the vessel gives rise to spatiotemporal dynamics in the interface profile that can be measured non-invasively.

[0018] 2, the TBPI is in the form of an exemplary calibration measurement device 200 including: (1) a strap force sensor (SFS) 202, which is a force sensing resistor (SFR); (2) a strap adjustment balloon 204 for adjusting the tightness of the strap 200; and (3) a flexible strap 201 including a flow regulation balloon 206, also called an attachment force adjustment balloon (MFAB), attached to a rigid support 207. A sensor array 208 is interposed between the flow regulation balloon 206 and a skin surface 210 to capture the spatiotemporal contact state. The flow regulation balloon 206 is actuated by an air pump 212, and an air pressure sensor 214 connected to the air pump 212 serves as a sensor for the flow regulation balloon 206.

[0019] Optionally, device 200 includes a controller 217 (including a processor and a memory device) configured to receive signals from strap force sensor 202 and / or sensor array 208. Controller 217 is further optionally configured to process the signals to determine blood pressure parameters, including estimating and monitoring blood pressure. Controller 217 may be integrated with device 200, e.g., attached to or located within strap 201, or may be a separate component from device 200, e.g., an external device (such as a computer) communicatively coupled to device 200.

[0020] According to another optional configuration, device 200 includes a display 219 for displaying various parameters associated with blood pressure monitoring. Display 219 is optionally attached to or integral with device 200.

[0021] According to another optional configuration, device 200 is communicatively coupled to an external device 221, such as a user's mobile phone. The user uses an application on mobile phone 221 to perform one or more tasks associated with device 200, including, for example, adjusting the inflation of strap adjustment balloon 204 and / or flow regulation balloon 206, receiving monitored arterial parameters, etc.

[0022] The blood flow regulation balloon 206 is initially set to a reference air pressure (e.g., 30-40 mmHg). The blood flow regulation balloon 206 and the sensor array 208 are then positioned over a peripheral artery 216 (e.g., the radial artery at the wrist) such that the sensor array 208 is approximately centered over the artery 216 so that the sensor array 208 captures pulsations (spatiotemporal contact state variations caused by blood pressure variations over the cardiac cycle) in a central region of the sensor array 208 while the blood flow regulation balloon 206 regulates blood flow in the artery 216 below.

[0023] The strap adjustment balloon 204 is then inflated to a level such that the reading from the strap force sensor 202 reaches a certain value. Based on the spatial information obtained from the sensor array 208, the dominant pulsation region is locked. The dominant pulsation region is the region whose temporal dynamics is above a certain threshold when the blood flow regulation balloon 206 and the strap force sensor 202 are adjusted to an optimal predetermined value. The strap adjustment balloon 204 and the strap force sensor 202 are primarily used to fine-tune the attachment of the calibration measurement device 200 to ensure optimal contact between the sensor array 208 and the skin surface 210 and to standardize the attachment of the calibration measurement device 200 between subjects. The signals obtained from the strap force sensor 202 and the strap adjustment balloon 204 are used to estimate and monitor blood pressure.

[0024] One beneficial unique aspect of the calibrating measuring device 200 is the effective separation of the main measurement and manipulation area on the targeted artery 216 from the remaining area under the strap 201. Achieving this separation eliminates the need to wrap a cuff around the entire circumference of the limb. The unique design of the calibrating measuring device 200 allows for its continuous use on the limb without compromising the venous and lymphatic circulation or the flow of other arteries in the limb. The sensor array 208 is positioned between the blood flow regulation balloon 206 and the skin surface 210 to capture the spatiotemporal contact conditions as the blood flow regulation balloon 206 inflates and deflates during the blood pressure estimation phase, and subsequently maintains the nominal pressure during the blood pressure monitoring phase.

[0025] With reference to Figures 3A-3D, the data shows the estimated spatiotemporal signals and blood pressure markers. After the TBPI attachment is standardized, the TBPI (such as the calibrating measurement device 200) is calibrated by estimating the user's DBP, MAP, and SBP. This is accomplished using the TBPI itself. The calibration process involves a stepwise increase and decrease in the pressure of the MFAB, which is called a pressure sweep. In the rising sweep, the air pressure of the MFAB is increased stepwise from a low value (~30mmHg) at a standard rate for conventional blood pressure measurement (2-4mmHg / sec). The rising sweep continues until the air pump is saturated (~270mmHg) or the amplitude of the pulsation of the measurement signal decays below a certain threshold, provided that the air pump is saturated (~270mmHg) or the amplitude of the pulsation of the measurement signal reaches some nominal value (such as 180mmHg). Then, in the falling sweep, the air pressure is decreased back to the low pressure (~30mmHg). This allows for calibration and estimation of blood pressure twice per complete sweep.

[0026] To reduce the calibration time, either the rising half-sweep or the falling half-sweep can be made faster and the calibration is done on the slower half. In estimating blood pressure from the sweep, the mean pressure (averaged over the cardiac cycle) of the MFAB, called "MFAB pressure", is considered as the primary measurement for blood pressure estimation. Different features of the spatiotemporal signal from the underlying sensor array are considered as markers for SBP or MAP or DBP estimation. The MFAB pressure at which the marker reaches a certain threshold is mapped to SBP or MAP or DBP. The markers used in the blood pressure estimation method are classified into two groups. Markers in group 1 are the spatial coincidence / mismatch of pulsation over the cardiac cycle within the contact area between the skin and the sensor array. Markers in group 2 are the amplitude of pulsation averaged over space. Markers from both group 1 and group 2 are estimated simultaneously over any half-sweep. Blood pressure estimates based on multiple markers are combined to improve the accuracy and robustness of the final blood pressure estimate.

[0027] Referring to the group 1 markers, the spatial information from the locked pulsating region is divided into proximal and distal regions in relation to the direction of blood flow in the heart or vessel (such as the Y-axis in FIG. 1). After segmentation, the average height of the pulsation is calculated for the proximal and distal parts individually. These two time signals effectively represent the proximal and distal pressure waves. After high-pass filtering and normalization of these heights over the past cardiac cycle, the similarities and differences between these proximal and distal regions are considered as blood pressure markers. The estimation of these blood pressure markers is a useful and unique application of TBPI. The group 1 markers essentially rely on the spatial information of the pressure wave. To quantitatively measure the similarities between the proximal and distal pressure waves, the dot products of the proximal and distal pressure waves are calculated over the period of the recent cardiac cycle and estimated in real time. The markers are called selected dot products (SDPs). While SDP is a quantitative measure of similarity, selected cross product (SCP) is one measure of dissimilarity represented graphically as the area under a Lissajous plot of normalized proximal versus distal pressure waves.

[0028] Another approach to quantitatively measure the difference is to calculate the selected instantaneous difference (SID) signal between the normalized proximal and distal pressure waves, and then consider the height of the SID over one cardiac cycle as the blood pressure marker. The SID is also passed through different bandpass filters to capture harmonics due to turbulence in the blood flow in the artery when the blood flow in the artery starts to collapse. These signals are called SF1, SF2, etc., and the corresponding blood pressure markers are calculated similarly to the SID (see Figure 2).

[0029] Referring to the group 2 markers, the first marker in this group is called the image average height (IAH) and provides deformation or force information obtained from the sensor array averaged over space, which is passed through a high-pass filter and an amplitude estimator. The amplitude estimation is performed over the period of the recent cardiac cycle. The group 2 markers do not fundamentally rely on the spatial information of the pressure wave. However, since these markers are derived from the dominant pulsatile region, they use the spatial information obtained from the sensor array. The MFAB pressure at which the group 2 marker reaches a maximum value is mapped to the MAP. The air pressure range in which the marker remains above a certain threshold(s) indicates the intra-arterial pulse pressure (PP), which is the difference between the SBP and the DBP. Thus, focusing on the falling half-sweep, the MFAB pressure at which the marker crosses a certain "first falling" threshold is mapped to the SBP. After reaching a maximum value, the marker crosses another "second falling" threshold again, and the corresponding MFAB pressure is mapped to the DBP.

[0030] Group 2 markers are also derived directly from the high-pass filtered and amplitude estimator passed MFAB pressure signal. Over the half sweep, the average or low-pass filtered MFAB pressure where any of these markers reach a maximum value is mapped to MAP. The range of average MFAB pressure where the marker remains above a certain threshold(s) indicates intra-arterial PP. Thus, looking at the falling half sweep, the average MFAB pressure where the marker crosses a certain first falling threshold is mapped to SBP. After reaching a maximum value, the marker crosses the same or a different second falling threshold again, and the corresponding average MFAB pressure is mapped to DBP. Group 2 markers are derived from the high-pass filtered MFAB pressure and are similar to standard oscillometric markers, except that in TBPI, the MFAB pressure signal is obtained from a separate skin sub-area connected to the artery by soft tissue, rather than a skin area covering the entire circumference of the limb as in the case of conventional blood pressure cuffs.

[0031] The blood pressure is tracked continuously using the TBPI. After the calibration of the TBPI is completed, the pressure of the MFAB is increased back to a level such that the pulsation of the captured signal reaches a certain amplitude or signal-to-noise ratio (SNR). Under this condition, the IAH is calibrated over two points, with the maximum value mapped to the SBP and the minimum value mapped to the DBP as obtained from the calibration method. This two-point calibration is sufficient to identify small variations in blood pressure on the operating point. If the operating point shifts above a threshold, which may be caused by a large change in blood pressure or based on artifacts that largely invalidate the linear calibration, a recalibration is performed. Instead of the IAH, the pressure signal from the MFAB is also calibrated and used for continuous monitoring. However, the IAH shows a lower sensitivity to artifacts related to movement and material relaxation.

[0032] 4A and 4B, TBPI is in the form of another exemplary calibration measurement device 300 in which a sensor array 308 is implemented based on deformation sensing with the aid of photometric stereo effect captured by a camera 303. The device 300 includes a flexible strap 301 supported on a transparent rigid support (such as glass) 307, a strap force sensor 302, a strap adjustment balloon 304, and a blood flow adjustment balloon 306. In this embodiment, the sensor surface 309 contacts the skin surface 310, which is coated with a pigment such as bronze powder, which creates a specular reflective layer 311. A transparent soft silicone elastomer (such as gel) is used as a substrate for the reflective layer 311. The gel is supported by the glass support 307 such that the reflective surface of the gel remains in intimate contact with the skin surface 310. The camera 303 is mounted vertically on a frame 315 above the glass support 307.

[0033] As shown in FIG. 1, the curvature of the blood vessel 110 along the ZX plane is P in and ambient pressure P outThe curvature varies with the difference between the ZX plane and the Y axis. Therefore, the primary measurement in this embodiment is the ZX plane curvature of the contact surface 309 and its variation along the Y axis, i.e. the longitudinal axis of the blood vessel. Thus, two arrays of highly directional (beam angle of ∼15°) red and green LEDs 317, 319 are placed along the Y axis. The entire camera assembly 321 is optically isolated from the ambient light. The LEDs 317, 319 are placed at low grazing angles to avoid the camera 303 capturing direct reflections of the LEDs 317, 319 from the optical interface.

[0034] Referring to FIG. 4C, the tabletop version 321 of the calibration measurement device 300 includes a 5 or 6 degree of freedom positioner and an adjustable back support 323 with a ball and socket joint 325. The back support can support a phantom artery or an animal body part or a human wrist. In all cases, the system has at least one mounting force or pressure (MPF) sensor. In tabletop experiments, MPF sensing is performed using a 6 degree of freedom force sensor or a force sensing resistor (FSR). The tabletop version 321 further includes a type of TBPI such as a wearable part 327 described below.

[0035] 4D, the wearable 329 of the calibration measurement device 300 includes a machine vision camera 331, leads 333 from the force sensing resistor FSR, and a glass support 335 encased in a transparent strap 336. Inside the transparent strap 336 is a red LED array 337 and an air pump actuated balloon 339 connected to the primary MPF sensor. The wearable 329 further includes independently adjustable red and green LED regulators 341, 343, and a USB 3.0 camera 345 for capturing video images.

[0036] 5A, TBPI is another exemplary form of calibration measurement device 400 in which a sensor array 408 is implemented based on structured light using projected light patterns (such as stripes) or optical markers (such as dots or holes) on the inner or outer surface of 408 in contact with the skin surface 410 (or, for example, directly on the skin surface 210). The movement of these patterns or markers is captured by a camera 403, which may also be placed in different positions and orientations than shown in FIG. 5A. In this embodiment, similar to, but not necessarily identical to, the above embodiment, the sensor array 408 is implemented based on triangulation of optical patterns or markers on the sensing surface 409 (which is the outer surface of the sensor array 408) or on the inner surface of the sensor array 408 (or, for example, directly on the skin surface 210). Based on data from a camera appropriately positioned to capture an image of the pattern or marker on the surface in contact with the skin surface 410 or on the direct skin surface 210, the deformation along the Z axis is captured from the movement of the markers in the XY plane. Thus, changes in curvature in the ZX plane are sensed through the movement of the marker in the X axis as seen by the camera 403. The calibration measurement device 400 optionally includes one or more components of any of the other exemplary calibration measurement devices described in this disclosure. With further reference to Figures 5B and 5C, the tabletop version 421 and the wearable version 429 include a projector 440 and a machine vision camera 441.

[0037] With reference to FIG. 6A, the TBPI is in the form of another exemplary calibration measurement device 500 in which a sensor array 508 is implemented based on individual force or displacement sensors 550. Specifically, the sensor array 508 is implemented by assembling individual force or deformation sensors 550, such as resistive, piezoelectric, or capacitive elements 550. The calibration measurement device 500 is similar, but not necessarily identical, to one or more of the other exemplary calibration measurement devices described. For example, the calibration measurement device 500 includes a flexible strap 501 supported on a rigid support 507, a strap force sensor 502, a strap adjustment balloon 504, and a blood flow regulation balloon 506. With further reference to FIG. 6B, the sensor 550 is attached to the underside of the blood flow regulation balloon 506. With further reference to FIG. 6C, the calibration measurement device 500 is attached to the wrist 551.

[0038] Optionally, the individual sensors can be fabricated with a thin film of piezoelectric polymer such as polyvinylidene fluoride (PVDF) coated on both sides with silver ink acting as electrodes. The electrodes are further covered with an insulating material to avoid electrical conduction between the skin and the sensor. The thickness of the sensing element is kept thin enough to achieve good mechanical coupling with the skin. In the simplest configuration, only two sensing elements are used, one for the detection of proximal pulsation and the other for distal pulsation. The number of elements can be increased to extract more complex markers if required. The signal from the sensor is passed through a signal conditioner and sent to the TBPI processor. These two proximal and distal signals from the piezoelectric film sensor can be processed equivalently to the above IAH for BP estimation.

[0039] 7A-7C, an experimental setup 600 shows animal testing of a rabbit model (FIG. 7A) and a pig model (FIGS. 7B and 7C). The setup 600 includes an anesthesia device 660, a back support 662, an arterial access catheter 664, and a drug and saline drip 666. The setup 600 further includes an optical fiber 668 connected to the tip of a fiber optic pressure sensor (e.g., from FISO), a height adjustment control 670 of a 6-DOF positioner, a type of TBPI 672, a position lock 674, and a 6-DOF force sensor 676 (e.g., from ATI). The setup 600 also includes an anesthetized pig 678, an anesthetized rabbit 680, a TPS 682 from ICU Medical, and a 6-DOF (Zrot) 684 added to the animal testing positioner.

[0040] According to an alternative exemplary embodiment, the sensor array directly measures the movement of the arterial wall. For example, in this embodiment, the ultrasound sensing elements of the sensor array directly measure the curvature of the targeted blood vessel, rather than its indentation against the skin surface. This embodiment optionally includes one or more components of any of the disclosed calibration measurement devices, with the modification of having at least one ultrasound sensing element on the sensor array.

[0041] According to another alternative exemplary embodiment, a sensor is coupled to a mechanical mount and used to vary the attachment force (e.g., in a tabletop device). In this embodiment, instead of using a flow-regulating balloon, the attachment force is adjusted with the aid of a mechanical mount coupled with a force sensor and / or a displacement sensor.

[0042] Thus, according to disclosed embodiments, the spatial mechanical state of the skin in BPI is measured by a sensor array, such as those described above. The sensor array may include, for example, optical sensors (such as photometric stereo or structured light) as described above. In other examples, ultrasound imaging and / or tactile sensor arrays are used instead of or in addition to optical sensors. The sensor array is positioned above an artery, the radial artery being one example of an artery.

[0043] The change in skin pressure is applied using an external device coupled to a force sensor. The external device includes a blood flow regulation balloon, while the sensor array described above is an example of a portion of the force sensor. Spatiotemporal variations in contact force and / or shape are recorded as the skin pressure changes. Characteristic spatiotemporal signals corresponding to systolic and diastolic pressures are determined. Examples of characteristic spatiotemporal signals include the contrast between upstream and downstream as described above or maximum pulsation. The determined values ​​of the characteristic spatiotemporal signals are used to calibrate the measurement device, and the calibration is used to continuously estimate the blood pressure by analyzing the successive spatiotemporal signals. For improved continuous monitoring, optical sensors for oscillometry provide beneficial results.

[0044] According to one exemplary advantage of the present disclosure, the disclosed apparatus and method for monitoring intra-arterial blood pressure occludes the target artery while simultaneously occluding lymphatics, veins, and other arteries, thus eliminating the need for invasive limb-encircling blood pressure cuffs and high pressures required to cut off blood circulation in a limb (such as an arm). For example, during the calibration phase of the disclosed BPI, the radial artery may be occluded by a flow-regulating balloon, while blood circulation through the ulnar artery, veins, and lymphatics remains intact.

[0045] In accordance with another exemplary advantage of the present disclosure, the disclosed apparatus and method for monitoring intra-arterial blood pressure provides a continuous instantaneous blood pressure versus time trace based on direct observation of blood pressure relative to skin topography, without reliance on indirect empirical correlations or models derived from proprietary, proprietary algorithms that are not amenable to independent verification or scientific criticism.

[0046] According to yet another exemplary advantage of the present disclosure, the disclosed devices and methods for monitoring intra-arterial blood pressure facilitate direct derivation of SBP, MAP, and / or DBP from continuous beat-to-beat blood pressure versus time tracings. A further advantage is that the disclosed devices and methods measure blood pressure over multiple cardiac and respiratory cycles to provide a more accurate measure of blood pressure and useful information regarding beat-to-beat blood pressure variability. Yet another advantage is that the disclosed devices and methods provide additional data of clinical interest such as heart rate, cardiac rhythm, respiratory rate, respiratory pattern, and apnea.

[0047] According to a further advantage of the present disclosure, the device for monitoring intra-arterial blood pressure is a wearable device integrated with an existing mobile phone, and data is transferred instantly between the device and the mobile phone via a low bandwidth cellular connection for online / remote management of hypertension.

[0048] According to a further advantage of the present disclosure, the disclosed device and method for monitoring intra-arterial blood pressure provides continuous ambulatory blood pressure monitoring that identifies abnormal blood pressure patterns including white coat hypertension, masked hypertension, reduced nocturnal blood pressure drop or increased blood pressure during sleep and early morning blood pressure rise, which further provides accurate assessment of treatment effectiveness and improved individualization of therapy, identifies lifestyle incentives (such as reducing smoking and stress) needed to lower the patient's blood pressure, and provides graphical feedback to review with the patient to assist in patient compliance with treatment.

[0049] According to other advantages of the present disclosure, the disclosed devices and methods provide reliable 24-hour beat-to-beat monitoring of blood pressure for use in acute hospital settings as an alternative to invasive (using intra-arterial catheters) monitoring. Additionally, other advantages include affordability since the BPI is optionally constructed from off-the-shelf components, and no need for an additional power source since the BPI is optionally battery powered.

[0050] The disclosed devices and methods are also useful for other purposes, including, for example, blood sampling or catheter insertion. For example, devices for such exemplary purposes include flexible straps, strap force sensors, strap adjustment balloons, and / or blood flow regulation balloons. Optionally, optical sensors or other skin surface sensing elements as described above are used to enhance and improve the performance of the calibrated measurement device. Optionally, further, a particular combination of flexible straps, sensing means (optical, ultrasonic, capacitance-based tactile array, etc.), calibration method, and blood pressure monitoring is optimally implemented depending on the arterial location (radial, brachial, etc.), purpose (health monitoring, screening, emergency care, etc.), and setting (hospital, home, wearable, etc.).

[0051] Although the present invention has been described with reference to one or more specific embodiments, those skilled in the art will recognize that many modifications may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the present invention. It is also contemplated that further embodiments according to aspects of the present invention may combine any number of features from any of the embodiments described herein.

Claims

1. 1. A method for directly measuring blood pressure based on skin displacement, comprising: Providing a calibration measurement device having a sensor array with a sensor surface; placing the sensor surface in direct contact with a skin surface adjacent a superficial artery; applying a controlled amount of pressure to press the sensor surface against a skin surface with a respective force; generating skin deformations at the skin surface based on changes in size and shape of the superficial artery in response to each of the forces; generating a sensor deformation at the sensor surface in response to a skin deformation at the skin surface; detecting a deformation signal of the sensor surface during a cardiac cycle via the sensor array in response to the sensor deformation, wherein the deformation signal captures a spatiotemporal contact state of a superficial artery; measuring and processing said deformation signal via a controller to determine a blood pressure parameter; A method comprising:

2. The method of claim 1 , wherein the superficial artery is the radial artery.

3. The method of claim 1 , wherein the sensor array includes one or more of a tactile sensor, an ultrasonic imaging sensor, a resistive sensor, a piezoelectric sensor, and a capacitive sensor.

4. The method of claim 1 , wherein the regulated amount of pressure is applied by a flow regulating balloon, the flow regulating balloon being mechanically coupled to the sensor array.

5. The method of claim 4 , wherein the regulated amount of pressure is achieved by inflating or deflating the flow regulating balloon.

6. The method of claim 1 , wherein the adjusted amount of pressure is an oscillometric blood pressure parameter.

7. The method of claim 1 , wherein the controller is configured to estimate blood pressure from a pressure sweep that includes stepwise increases and decreases in pressure of the adjusted amount.

8. 8. The method of claim 7, wherein the pressure sweep includes a rising sweep in which air pressure is increased from a low value at a standard rate for blood pressure measurement, the rising sweep continuing until the amplitude of pulsations in the deformation signal decays below a certain threshold, provided that (a) a saturation pressure is reached or (b) the air pressure reaches a nominal value.

9. The method of claim 8 , wherein the pressure sweep includes a falling sweep in which the air pressure decreases back to a lower value.

10. The method of claim 7 , wherein the pressure sweep comprises a mean pressure averaged over a cardiac cycle, the mean pressure being the primary measurement for estimating blood pressure.

11. The method of claim 1 , further comprising displaying at least one of the one or more blood pressure parameters on a display, the display being communicatively coupled to the controller.

12. The method of claim 1 , further comprising adjusting the amount of pressure via an external device, the external device being communicatively coupled to the calibration measurement device.

13. 1. A system for directly measuring blood pressure based on skin displacement, comprising: a balloon having an inflation state in which a controlled amount of pressure causes spatiotemporal signals from a superficial artery to be isolated without compromising the venous and lymphatic circulation or the flow of other arteries in the limb including said superficial artery; a sensor array positioned between the balloon and a skin surface for non-invasively monitoring blood pressure, the sensor array having a sensor surface in direct contact with the skin surface near a superficial artery, the sensor surface being pressed against the skin surface in an inflated state of the balloon to produce skin deformations on the skin surface based on changes in size and shape of the superficial artery; a controller having a processor and a memory device, the controller configured to receive a deformation signal from the sensor array, the deformation signal being generated by detecting a sensor deformation of the sensor surface in response to the skin deformation, the deformation signal being detected during at least one cardiac cycle, the deformation signal capturing a spatiotemporal contact state of a superficial artery, and a controller that measures and processes the deformation signal to determine a blood pressure parameter.

14. The system of claim 13 , wherein the sensor array includes one or more of a tactile sensor, an ultrasonic imaging sensor, a resistive sensor, a piezoelectric sensor, and a capacitive sensor.

15. The system of claim 13 , wherein the adjusted amount of pressure is an oscillometric blood pressure parameter.

16. The system of claim 13 , wherein the controller is further configured to estimate blood pressure from a pressure sweep comprising stepwise increases and decreases in the adjusted amount of pressure.

17. 17. The system of claim 16, wherein the pressure sweep includes a rising sweep in which air pressure is increased from a low value at a standard rate for blood pressure measurement, the rising sweep continuing until (a) a saturation pressure is reached or (b) the amplitude of pulsations in the deformation signal decays below a certain threshold, provided that the air pressure reaches a nominal value.

18. The system of claim 13 , further comprising a display communicatively coupled to the controller, the display displaying a blood pressure parameter.

19. 14. The system of claim 13, further comprising an external device communicatively coupled to the balloon, the external device adjusting the amount the balloon is inflated or deflated.

20. 20. The system of claim 19, wherein the external device is a user's mobile phone.

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