Monitoring changes in the quantity and properties of human interstitial fluid and electromechanical design of a magnetic device to achieve this

Abstract

In a wearable device and method for monitoring changes in human interstitial fluid volume and properties associated with both normal and disease states using limb circumference and acceleration, raw data is transmitted from the wearable device to an external device for storage and evaluation. The data is compared to baseline information derived for the individual as well as a larger population of individuals and evaluated for health status and clinical implications. Relevant messages regarding the individual's status can be transmitted to interested parties, such as patients, caregivers, and medical professionals.

Description

[Background technology]

[0001] background Fluid balance is an important aspect of human physiology. The body naturally regulates fluid levels to maintain them under various conditions. Certain medical conditions, such as heart failure, kidney disease, etc., can exceed the body's regulatory mechanisms and result in excessive fluid retention or fluid load, which can manifest as, for example, peripheral edema or limb swelling. Summary of the Invention [Problem to be solved by the invention]

[0002] overview Fluid retention and edema, or limb swelling, can be associated with and signal an impending decompensation event in heart failure patients. Unfortunately, patients generally lack good tools to recognize the markers of a worsening condition, which often forces them to go to the hospital for treatment, which can be distressing, costly, and potentially life-threatening. [Means for solving the problem]

[0003] Measuring and managing fluid balance is related to many aspects of human health, including cardiac health, and many disease states and medication intervention trials could benefit from improved wearable devices that can detect early warning signs of new or worsening medical conditions in areas that may include, without limitation, nephrology, cardiology, sports medicine, prenatal care, migraines, drug testing, etc.

[0004] BRIEF DESCRIPTION OF THE DRAWINGS The detailed description will be set forth with reference to the accompanying figures which illustrate aspects of one or more embodiments described herein, in which the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears. Use of the same reference number in different figures indicates similar or identical items. [Brief explanation of the drawings]

[0005] [Figure 1] 1 shows an isometric view of an example device that can be configured to monitor changes in the quantity and properties of human interstitial fluid. [Figure 2] 2 shows an exploded view of an example of a measurement assembly, winder cassette, strap, and clasp of a device corresponding to the example shown in FIG. 1. [Figure 3] 10 shows an exploded view of the winder cassette, strap, and clasp that remain when the measurement assembly is removed in some embodiments. [Figure 4] FIG. 10 is a top view of the winder cassette relative to the strap and clasp. [Figure 5] 4A is a partial cross-sectional view AA of the assembled winder cassette; FIG. [Figure 6] FIG. 2 is a side view of a device that may correspond to the device shown in FIG. 1. [Figure 7] FIG. 7 is a detailed cross-sectional view taken along line BB through the measurement assembly, winder cassette, strap and clasp of the example device shown in FIG. 6. [Figure 8] FIG. 2 is an isometric view of a device that may correspond to the device shown in FIG. 1, with the housing of the measurement assembly removed. [Figure 9] 1 shows a plot of normal swelling (eg, limb swelling) over a 12-day period in a hypothetical heart failure patient. [Figure 10] 1 shows an 8-day plot of compensatory swelling events (eg, ankle swelling) associated with hypothetical fluid retention related to increased salt intake in patients with heart failure. [Figure 11] Plots of hypothetical episodes of decompensated fluid retention, such as those preceding hospitalization for heart failure, are shown. [Figure 12] 1 shows an example of a loop illustrating the effectiveness of integrating interstitial fluid volume monitoring via a device with determined outcomes. [Figure 13] 1 illustrates an example of integrating medication treatment logs with ankle circumference history. [Figure 14] 1 illustrates an example architecture for implementing monitoring of changes in the quantity and properties of human interstitial fluid in a patient. [Figure 15] 1 illustrates various components of a measurement assembly arranged in accordance with one or more embodiments described herein. [Figure 16] 13 illustrates an example of the database server shown in FIG. 12. [Figure 17] FIG. 10 is a flow diagram of an example process that may be performed at least in part by a measurement assembly for measuring limb circumference of a subject, generating a waveform of the measurements over time, and outputting an indication of the condition revealed by the waveform. [Figure 18] 1 shows an isometric view of another example device that can be configured to monitor changes in the quantity and properties of human interstitial fluid. [Figure 19] 19 shows an exploded view of an example measurement assembly, winder cassette, strap, and clasp of a device corresponding to the example shown in FIG. 18. [Figure 20] 10 shows an exploded view of the winder cassette, strap, and clasp that remain when the measurement assembly is removed in some embodiments. [Figure 21] This figure illustrates an example of a digital circuit that can be implemented to perform quadrature decoding, including rotation counting (digital passes through a 0 degree reference angle) detection, in software at a fraction of the power used by some microprocessor quadrature decoding circuits. [Figure 22] FIG. 10 is a top view of the winder cassette relative to the strap and clasp. [Figure 23] 22, a partial cross-sectional view AA of the winder cassette in an assembled state. [Figure 24] FIG. 19 is a side view of a device that may correspond to the device shown in FIG. 18. [Figure 25] A detailed cross-sectional view taken along line BB through the measurement assembly, winder cassette, strap, and clasp of the example device shown in Figure 24. [Figure 26]FIG. 19 is an isometric view of a device that may correspond to the device shown in FIG. 18, with the housing of the measurement assembly removed. DETAILED DESCRIPTION OF THE INVENTION

[0006] Detailed Description Interstitial fluid volume is an important medical concern in patients with conditions such as heart failure decompensation, renal failure, and similar physiological conditions. In one example of particular concern, increased interstitial fluid volume is associated with heart failure decompensation. Sometimes, specific measurements, perhaps performed during a physician's visit, can produce dramatically different and inconsistent results depending on the time of the visit and other factors. Perhaps in the absence of more sophisticated measurements, physicians often rely on rough approximations of the presence or absence of swelling, such as pressing a finger against the ankle, as being equivalent in validity. Furthermore, the lack of a practical and rigorous medical measurement limits the usefulness of this physiological parameter.

[0007] Previous approaches to monitoring limb circumference have focused on measuring circumference at known locations on the limb. The devices and techniques described herein do not rely on known locations on the limb, but rather measure at the smallest circumference as an indication of interstitial fluid volume, regardless of its location.

[0008] In some embodiments, the device includes a strap constructed to apply only light tension around the limb, which can be achieved by design including one or more of lightweight components, strap material properties, and strap width. These parameters, along with limb activity, can all be combined to allow the device to rest at the limb's minimum circumference, allowing the device to continuously sense the limb's minimum circumference without applying unnecessary pressure around the limb at the measurement point. For example, if the device is used to measure the volume of the wrist or ankle, the device will be anchored at or near the limb's minimum circumference so that measurements can be compared over time. The device may also be anchored in different, repeatable home positions depending on the details of its construction. Limb movement (e.g., standing or walking) facilitates mobility of the device on the limb.

[0009] The device can not only move along the limb axis, but also rotate around the limb axis. Limbs are generally not circular in cross section. As the device clockwise rotates around this perimeter, the area of ​​the winder cassette that contacts the limb is minimized, allowing the strap to fit more closely to the actual shape of the limb. Therefore, this device can enable consistent measurements regardless of the orientation of the clockwise rotation of the device around the limb axis.

[0010] The devices described herein can be configured to intermittently, periodically, and / or continuously measure limb circumference and acceleration, and to analyze the circumference measurements and the orientation of the device and / or subject, including comparing the current state or trend to the patient's baseline, normal, or desired state. The difference between the measured state and the desired state can be used as input to guide decisions regarding the subject's diet, activity, and, in some implementations, treatment, including medication, to encourage the subject toward the desired state and avoid potentially life-threatening events, such as hospitalization for shortness of breath in a heart failure patient, in addition to other events such as those described herein.

[0011] One embodiment of the device can include a low-tensioning element, for example, a lightweight strap (in one example, less than 1 / 2 ounce, including the device) configured to contain a load distributed over a wide area, allowing for uniform force distribution. Gravity acting on the mass of the device can also provide the force. Additional force can be provided by a mechanism that holds the device in place against the limb. For example, the tension on the subject's skin exerted by the device, particularly the tensioned strap, is less than or substantially equal to the interstitial fluid pressure at the site (there may be some slight compression of the skin), and can be distributed across the surface of the strap so that friction against the skin balances the force of gravity against the weight of the device. These together represent the binding force exerted over a designated area. One embodiment of the device can provide a wide surface, approximately 25 millimeters wide, around the limb to distribute a gravitational load of approximately 11 grams applied along the axis of the limb and a constant spring force of approximately 10 to 40 grams that causes the strap to fit snugly against the limb.

[0012] In at least one embodiment, the disclosed device measures circumference using a magnetic circuit and a strap that encircles the limb. The magnetic circuit includes or cooperates with a magnet and a magnetic sensor. As the limb changes size, the strap expands or contracts via the strap housing and tensioning mechanism, causing the magnet to rotate and enabling the magnetic sensor to detect the angle of rotation of the spool, which correlates with an increase or decrease in limb circumference.

[0013] For example, when a person is lying down, the interstitial fluid in the body is distributed fairly evenly along the length of the body. However, when standing or sitting in a relatively upright position, the interstitial fluid is redistributed by gravity to the extremities. This effect is more pronounced in the lower extremities.

[0014] In one embodiment, the device may be worn nearly continuously, and circumference and orientation data are collected at specified intervals and processed to determine each individual's daily swelling pattern and average daily swelling. The diurnal circumference change associated with interstitial fluid redistribution from lying down to standing is greater than the circumference change associated with fluid retention of interest, which is associated with health or disease conditions requiring attention. Thus, multiple measurements of circumference over a diurnal cycle can be used to detect longitudinal fluid retention.

[0015] Careful quantification and tracking over time has shown that even a mean change of just a few millimeters in interstitial fluid volume, a significant sign of disease progression, is directly related physiological information, but may be present as an unseen sign on a single examination or even on daily examinations, potentially providing a more accurate measurement than is possible with visual inspection alone. Because limb circumference can be a good surrogate for interstitial fluid volume, it can be beneficial to incorporate multiple measurements of minimum limb circumference, typical of the tapering areas of the limb at the ankle or wrist.

[0016] The device can also measure other physiological parameters, such as heart rate, peripheral capillary oxygen saturation (SpO2), respiratory rate, and non-invasive blood pressure (NIBP). By emitting light at various frequencies and evaluating the returned energy, several physiological phenomena can be assessed. For example, using green light to sense heart rate in conjunction with peripheral edema measurements can corroborate the detection of swelling events, improving certainty and more accurately assessing the progression of decompensation events. Similarly, using red and infrared light to assess blood oxygenation in conjunction with stress testing can provide valuable information regarding the current limitations of an oxygen delivery system, for example. This can further corroborate and calibrate peripheral edema measurements, appropriately scaling their response to changes in the patient's condition. Using optical measurements to assess a patient's non-invasive blood pressure is also contemplated.

[0017] Non-invasive blood pressure is used to define and adjust patient therapy, including the selection and administration of medication. Physiological parameters can be collected with separate devices, such as weight using a weighing scale or NIBP using a device that includes an inflatable blood pressure cuff, and used in analyzing the patient's condition.

[0018] Monitoring physiological parameters, particularly continuous monitoring, with remote devices such as those described herein may require that data collection by the device be timed to an established time standard, such as Coordinated Universal Time (UTC), external to the device, in which case the data can be stored and analyzed off-device. The device can calculate relative time, such as the time since initial startup, as the time a measurement is taken, which can then be resolved as actual time when utilized with an external device synchronized to a universal time standard to determine the measurement time with sufficient accuracy for planned use. This approach eliminates the need to perform at least some clock synchronization on the device at startup and during use, which may reduce operational complexity and power requirements compared to synchronizing a real-time clock on the device using other timekeeping methods. To integrate treatment plans with patient outcomes, medication treatment logs can be collected to correlate treatment plan modifications with patient outcomes.

[0019] In some embodiments, power requirements can be minimized by keeping the device (and specifically its processor) in sleep mode most of the time. Using timer and interrupt circuitry, the device can still respond to programmed and real-time events and be appropriately woken up when necessary. To this end, in at least one embodiment, an angle-sensing component is connected to a comparator to generate interrupts at 0 and 180 degrees of spool rotation. The interrupt rate associated with rapid extension or contraction of the strap can be used to wake up the processor. Significant power savings can be realized and battery life extended compared to internal or external quadrature detection, which is always powered on. Additionally, the interrupt circuitry can be used to trigger the processor to enter Bluetooth advertising mode or other communication protocols or other variable sections of software. In some embodiments of this device, the accelerometer can be used as an interrupt source to trigger additional actions by the processor, such as initiating communication protocols or other variable sections of software in response to detecting a change in position or orientation.

[0020] 1 shows an isometric view of an example device 100 that may be configured to monitor changes in the quantity and properties of human interstitial fluid. Device 100 may include a device assembly that includes, among other components, a measurement assembly 105, a winder cassette 110, a strap 115 configured to be placed around a subject's limb, and a clasp 120. In at least some embodiments, a subject may wear device 100 around the lower arm (i.e., below the elbow) or lower leg (i.e., below the knee), although the teachings herein may be applicable to other body parts, particularly body parts having axial portions, and thus should not be considered limited, except as to the type of data required and the locations where that data may be obtained.

[0021] The measurement assembly 105 can house an electronics subassembly for acquiring data and communicating the data or information based on the data. The electronics subassembly, in some embodiments, can include sensors and associated electronics that can perform analysis of the sensor data and output results of the analysis and / or recommendations or instructions based on those results. In some embodiments, as described more fully below, the electronics subassembly can include a sensor portion that includes one or more magnetic sensors positioned opposite one or more corresponding magnets on the winder cassette 110.

[0022] The winder cassette 110 generally cooperates with the strap 115 to allow a snug fit around the limb with loose tension, even when severe swelling is present. The device 100 typically does not fit tightly around the limb, even when severe swelling is present. Indeed, the strap 115 and winder cassette 110 are constructed to allow the strap 115 to expand and contract as the limb swells and contracts, allowing an essentially constant force to be applied to the limb. In some embodiments, the winder cassette 110 in combination with the strap 115 and clasp 120 can be a replaceable component that can be easily replaced by the user if it becomes soiled or broken.

[0023] FIG. 2 shows an exploded view of an example of the measurement assembly 105, winder cassette 110, strap 115, and clasp 120 of device 200 corresponding to the example shown in FIG. 1 . Housing 235 is configured to house one or more of: a battery drawer 205 supporting battery 210; an electronics subassembly 215 including a wireless module 220, an angle magnetic sensor 240, and one or more strap-sized magnetic sensors 245; an insulator 225; and a gasket 230. An identification label may be affixed to housing 235, although no limitation should be inferred. Etched labels, printed labels, and the like may also be used. In practice, the device may not have an identification label. Measurement assembly 105 may be substantially liquid-tight to prevent fluid ingress.

[0024] Battery 210 can be any type of so-called coin cell that meets the power and size requirements of device 200, particularly the requirements for powering the components of electronics subassembly 215 and other components, and the size requirements for fitting within battery drawer 205. In some examples, battery 210 may be captured between electronics subassembly 215 and the top of housing 235. In some embodiments, another portable power source may be used, such as a rechargeable battery, a fuel cell, a storage capacitor, energy harvested from the patient, energy harvested from the environment, etc.

[0025] Insulator 225 may be an electrical insulator and therefore may be positioned to insulate battery 210 from electronics subassembly 215, allowing battery 210 to be replaced without contacting any components or wiring on electronics subassembly 215 or on the electronics board substrate. In some embodiments, insulator 225 may be engraved or printed with configuration information, such as the version of device 200 or any of its components.

[0026] The electronics subassembly 215 may be a printed circuit board and may include electronic components that control and perform limb circumference sensing. In at least some embodiments, the limb circumference may be used by an on-board control system or transmitted to a remote computing device that runs algorithms on data from the sensed limb circumference and outputs messages and generates graphical results showing measurements over time that can be interpreted by a medical professional (for example) to provide insight into the current condition of the patient wearing the device 200. In some embodiments, the electronics may include one or more magnetic sensors, such as magnetic sensors 240, 245, one or more optical sensors, one or more processors, memory, and an accelerometer. The memory may store instructions that, when executed by the one or more processors, cause the one or more processors to perform various operations described herein. In at least some embodiments, the magnetic sensor may detect limb circumference. In at least some embodiments, the accelerometer may detect the patient's orientation and movement and output data that may be used by the on-board control system or transmitted to a remote computing device to determine the patient's level of activity. For example, the device may detect, accumulate, store, and / or transmit accelerometer measurements at a sufficiently high frequency depending on the information received from the accelerometer and correlate that information with the circumference readings to provide an adequate representation of the effects of gravity and activity on the limb during the time between circumference measurements.

[0027] The wireless module 220 can transmit digital or analog signals (e.g., containing patient movement information) to an external device, such as a nearby computer, smartphone, tablet, etc., that has the processing capability to receive the signals, analyze the data provided by the signals, output instructions or commands, and / or relay the signals to a remote computing device, such as a server, computer, or database (e.g., in a clinic or data center).

[0028] Gasket 230 is configured and positioned to seal housing 235 and prevent the ingress of dust or water that could damage sensitive internal components. For example, gasket 230 may be positioned between housing 235 and battery drawer 205. Gasket 230 may include, without limitation, any insulating material suitable for that purpose.

[0029] The measurement assembly 105 can be constructed so that the insulator 225 and electronics subassembly 215, including the wireless module 220, are inserted into the housing 235. The battery 210 can be attached to the battery drawer 205 with a gasket 230 positioned where the battery drawer 205 meets the housing 235 by a snap fit, allowing the battery drawer 205 to be easily removed for battery 210 replacement. In this example, the battery drawer 205 snaps into the housing 235, compressing the gasket 230, which seals the interior of the housing 235 from dust or water intrusion. The winder cassette 110 can then be mated to the measurement assembly 105 with a detent that holds the measurement assembly 105 and the winder cassette 110, including the strap 115, together.

[0030] The distal end of strap 115 is secured by threading it through the body of clasp 120 and adhering strap 115 to itself by heat bonding the end with an adhesive to the body of strap 115. However, it should be understood that many other attachment methods are within the scope of this disclosure, such as the material of strap 115 adhering to itself or to clasp 120, impinging, and similar means.

[0031] The clasp 120 can be joined to the electronics subassembly 215 by a latching mechanism that engages the shape of the battery drawer 205 on the electronics subassembly 215 to encircle the limb.

[0032] The winder cassette 110 can be constructed to accommodate straps of different lengths, allowing the device 200 to accommodate a wide range of applications, for example, from small wrists to significantly swollen legs. The sizing of the device can be defined by fixing the length of the straps 115. The winder cassette 110 can be assembled and labeled to identify strap sizes such as small, medium, large, and extra large. This sizing data can be collected, stored, and updated as needed when the "size" is readjusted or calibrated.

[0033] In some embodiments, the housing 235, battery drawer 205, and / or clasp 120 can be 3D printed by a mask-based stereolithography (MSLA) process from materials such as Siraya Tech Blu resin and Siraya Tech Blu Mecha-Nylon resin. The gasket 230 can include Poron (polyurethane foam). The strap 115 is generally flexible and inelastic and can be made of a biocompatible porous material for patient comfort. By way of example, the material can be an open-weave, 80 threads per inch, fused-edge polyester, .008" Teslin (PPG, Barberton, OH) or Tyvek (Wilmington, DL), or an open-weave nonwoven fabric such as embroidery stabilizing interlining.

[0034] FIG. 3 shows an exploded view of the winder cassette 110, strap 115, and clasp 120 that remain when the measurement assembly 105 is removed in some embodiments. The winder cassette 110 can include a winder cassette frame 330, a spring 315, and a spool 320. The winder cassette frame 330 can include a capture mechanism 340 that can include a strap-sized magnet 335. The capture mechanism 340 can further include a spring coupling formed by a pin 344 joined to the winder cassette frame 330. The spool 320 can be cylindrical and include an angle magnet 325. Once installed in the winder cassette frame 330, the strap 115 can be wound onto the spool 320, as described below. In some embodiments, the winder cassette 110, strap 115, and / or clasp 120 are replaceable individually or in combinations including any two or all three.

[0035] The winder cassette 110 can be constructed such that the spring 315 is attached to the capture mechanism 340 of the winder cassette frame 330 and to the inside of the spool 320. The spring 315 can provide a substantially constant spring force load (e.g., approximately 10-40 grams) sufficient to allow the strap 115 to fit snugly around the limb without unnecessary or uncomfortable pressure.

[0036] The strap 115 is attached to and wound around a spool 320. An angle magnet 325 can be pressed into an opening, gap, or recess in the spool 320 or otherwise fitted opposite an angle magnetic sensor 240 of the electronics subassembly 215 of the measurement assembly 105. A strap-sized magnet 335 can be pressed into an opening, gap, or recess in the winder cassette frame 330 or otherwise fitted opposite one or more of the strap-sized magnetic sensors 245 of the electronics subassembly 215 of the measurement assembly 105. The magnetic sensors 240 and 245 are configured and positioned to sense the magnetic fields of the magnets 325 and 335 through the housing 235.

[0037] The act of lengthening and shortening the length of strap 115 as the limb expands and contracts can be accomplished by a tensioning mechanism including a winder cassette frame 330 and a spring 315 within a spool 320, which can accommodate a portion of the length of strap 115 wound around spool 320. In some embodiments, spring 315 can be a constant tension spring. As the limb expands, strap 115 is unwound, increasing the length of strap 115 to accommodate the increasing circumference of the limb, while the constant force applied by spring 315 maintains constant tension in strap 115 around the limb. The tension in strap 115 can be matched to interstitial fluid pressure and skin elasticity so that the device stretches without causing significant indentation in the limb. In this regard, and in conjunction with other embodiments described herein, it is understood that constant force and tension need not be exact, but within reasonable tolerances that enable the device to perform its function of measuring limb circumference, particularly the difference in limb circumference relative to a baseline or other reference, in accordance with the principles outlined in this disclosure.

[0038] An angle magnet 325 fitted to the spool 320 can be sensed by the angle magnetic sensor 240 to rotate the spool 320 as the strap 115 is wound and unwound, and the angle of rotation of the spool 320 can be recognized by a signal output by the angle magnetic sensor 240 and received by the electronics assembly 215 electrically connected to the angle magnetic sensor 240.

[0039] The angle magnet sensor 240 can be comprised of multiple resistive elements arranged to output a set of variable signal strength voltages. In at least one embodiment, these correspond to the sine and cosine of the rotation angle of the angle magnet 325 embedded in the spool 320 relative to the angle magnetic sensor 240. This can be achieved, for example, with a full-bridge sensor using underlying spintronics technology (NVE Corporation, Eden Prairie, MN, currently produces suitable sensors). This produces a very low-power structure that is relatively insensitive to the distance between the angle magnet 325 and the angle magnet sensor 240 and to axial misalignment. Because the diameter of the spool 320 defines a known perimeter using the formula C = Pi x D, that diameter can be translated into a precise change in length measurement as the strap 115 stretches or shrinks. The diameter of the spool 320 can be determined / calibrated for each device during manufacturing.

[0040] In addition to measuring the angle of rotation of the magnet 325, the circuitry can maintain information about the rotation history. In this example, quadrature detection can be implemented in software or hardware to track the current rotation or number of rotations. In at least one embodiment, quadrature detection can be achieved by using a comparator circuit connected to a processor interrupt function. However, in other implementations, dedicated circuit counting and logic components, or functionality integrated into the processor itself, can perform this function. A count of rotations is maintained as the strap 115 wraps around the spool 320 more than 360 degrees. The count of rotations, combined with the current angle measurement, allows the software to calculate the total number of degrees of rotation. By combining the diameter of the spool 320 with the total number of degrees of rotation in conjunction with the length of the manufactured strap 115 without the spring 315, the length of the measurement assembly 105, and the clasp 120, a total circumference measurement can be determined.

[0041] There may be additional considerations for calculating the total length. As alluded to above, as the strap 115 is wound onto the spool 320, it changes the effective diameter of the wrap and the circumference of the spool 320 as the layers are stacked on top of each other. To account for this condition, it is possible to apply diameter variations consistent with the thickness of the strap 115 and the number of wraps of strap material around the spool 320, recognizing the rotational history and manufacturing design of the winder cassette 110.

[0042] The length of the strap 115 when the spring 315 is in a relaxed, unused state is controlled during the manufacture of the winder cassette 110. If the rotation angle of the magnet 325 matches a reference corresponding to the relaxed orientation after manufacture, the rotation history does not indicate additional wrapping, and there is no angle dithering due to wear, it can be assumed that the device is not being worn. In some embodiments, the spring 315 can retract the strap 115 to a home position, which can be read by software running to interpret a signal representing the detected spool 320 angle, and an indicator or message can be output. Detection of these states can also be used to indicate whether the device is being worn. Data from the device 100 in the “not worn” state can, in some embodiments, be ignored when assessing the wearer's condition. Furthermore, if this state persists, the patient can be contacted or examined regarding issues with wearing the device 100.

[0043] The device 100 can accommodate a range of limb sizes in at least two ways. For example, constructing the winder cassette 110 as in the example described above can provide significant strap 115 retraction. In this example, the winder cassette 110 can accommodate, for example, 100 millimeters of strap movement relative to circumference changes. Additionally or alternatively, additional range can be achieved by varying the total strap length to create winder cassettes 110 in various sizes, such as small, medium, large, and extra-large. One benefit of this sizing design is that the winder cassette 110 can accommodate a wide variation in patient limb size and even wider variation in ankle circumference due to the presence or absence of edema. This can reduce the difficulty of sizing and fitting the device to a particular patient and can accommodate the larger limb circumferences experienced by lymphedema patients. This reduces or eliminates the need to customize the strap 115 size for a particular individual, simplifying the sizing and fitting procedure.

[0044] This structure can provide at least two types of measurements: a relative measurement that quantifies only the change in circumference associated with the change in spool from the home position as a result of limb expansion and contraction; and an absolute measurement that can determine the total circumference of the limb by combining the relative measurement, the length of the electronics assembly 105, the clasp 120, and the length of the unused strap 115.

[0045] In the current example, a strap size magnet 335 in the winder cassette 110 can communicate with one or more strap size magnetic sensors 245 in the electronics subassembly 215. Several strap size magnetic sensors 245 can be positioned to recognize multiple strap sizes by the relative positions and orientations of the magnetic fields generated by the strap size magnets 335. In at least one embodiment, a single strap size magnet 335 can be used to recognize up to four strap sizes.

[0046] The strap-sized magnetic sensors 245 can recognize the presence and / or orientation of the strap-sized magnets 335 within the winder cassette 110. In some embodiments, two strap-sized magnetic sensors 245, such as Hall-effect sensors, can each output a signal in the presence of a north (north) pole magnetic field or a different signal in the presence of a south (south) pole magnetic field. By arranging the relative positions of the strap-sized magnetic sensors 245 and the orientation of the strap-sized magnets 335 within the winder cassette 110, five orientation states can be detected and communicated. For example, when no magnetic field is sensed, the winder cassette 110 is determined to be absent (e.g., decoded). That is, when the magnetic field axis is perpendicular to the circuit board supporting the strap-sized magnetic sensors 245, a north-north or south-south state can be sensed, and when the magnetic field axis is parallel to the axis along the strap-sized magnetic sensors 245, a north-south or south-north state can be sensed. By using the strap-sized magnet 335 plus the strap-sized magnetic sensor 245 to sense the presence or absence of the winder cassette 110, the combination may be able to recognize removal and replacement events. Additionally, sensing the orientation of the strap-sized magnet 335 facilitates recognition of winder cassette 110 sizes, such as small, medium, large, and extra large. Winder cassettes 110 with different lengths of strap 115 can be made with an orientation such that the magnetic field presented by the strap-sized magnet 335 to the strap-sized magnetic sensor 245, either in strength or field orientation, can be read by the circuitry to interpret and communicate the size of the winder cassette 110 attached to the measurement assembly 105.

[0047] In some embodiments, the winder cassette frame 330 and spool 320 are 3D printed by a mask-based stereolithography (MSLA) process from materials such as Siraya Tech Blu resin and Siraya Tech Blu Mecha-Nylon resin. The spring 315 can be 125 mm long x 10 mm wide x 0.001 in (0.025 mm) hard stainless steel shim stock (Precision Brands, Downers Grove, IL). The angle magnetic sensor 240 can be a giant magnetoresistive angle sensor, such as the AAT101-10E full-bridge angle sensor manufactured by NVE (Eden Prairie, MN). The strap-sized magnetic sensor 245 can be a dual-output unipolar Hall-effect switch, such as the AH1389 manufactured by Diodes Inc. (Plano, TX). The magnets 325 and 335 are neodymium, available from a variety of suppliers.

[0048] 4 is a top view of the winder cassette 110 relative to the strap 115 and clasp 120. From this view 400, the location of the partial cross section AA of the winder cassette 110 can be seen.

[0049] FIG. 5 is a partial cross-sectional view AA of the winder cassette 110 of FIG. 4 in an assembled state.

[0050] In some examples, the capture mechanism 340 may include a pin 344 secured within the winder cassette frame 330, such as within one or more tabs, grooves, or holes in an extension from one or both of the walls of the winder cassette frame that receive the corresponding end of the pin or the wall that mounts the hollow end of the pin. In some embodiments, one or both ends of the pin 344 may protrude from or be secured to one or more walls. In such embodiments, the spring 315 may be attached to the capture mechanism 340 mounted on the winder cassette frame 330 by, for example, inserting one end of the spring 315 into a gap in the pin 344 of the capture mechanism 340 and wrapping or bending the spring 315 around the pin.

[0051] The coil spring 315 can have, for example, a thin wire or a wide strip-like structure. To facilitate fastening the spring 315 to the capture mechanism 340 of the winder cassette frame 330, the end of the spring 315 inserted into the gap can be wound or bent and at least partially wrapped around the pin 344. The bent configuration 520 of the spring 315, consisting of two bent sections, can engage with the capture mechanism 340, as shown in FIG. 5. The tip of the spring 315 can be bonded to the spool 320 by adhesive 510. The spool 320 can then be attached to the strap 115 by adhesive 505. No limitations regarding a particular type of fastener or adhesive should be inferred. As a result, the force of the spring 315 is transferred from the capture mechanism 340 of the winder cassette frame 330 by the bent configuration 520 of the spring 315. The winder cassette frame 330 is attached to the spring 315 and glued 510 to the spool 320, which is then glued 505 to the strap 115, tensioning the assembly. Rotating the angle magnet 325 opposite the angle magnetic sensor 240 as the limb expands and contracts can be achieved by this tensioning mechanism.

[0052] 6 is a side view 600 of a device that may correspond to device 100. In practice, device 100 may drift to an operational and repeatable home position on the limb due to the effects of gravity and patient movement, influenced by friction between strap 115 and the limb.

[0053] 7 is a detailed cross-sectional view 700 of the example device shown in FIG. 6 taken along line BB through measurement assembly 105, winder cassette 110, strap 115, and clasp 120. It illustrates the use position with clasp 120 engaged with battery drawer 205 and the location of battery 210 within housing 235. A 3:1 scale is shown to give a sense of the size of devices that may correspond to device 100. However, the scale will vary depending on the size of the diagram presented on the page; i.e., enlargement or reduction will affect the scale, so 3:1 should not be considered limiting.

[0054] 7, the winder cassette 110 is in the use position. The winder cassette frame 330, spool 320, spring 315, angle magnet 325, and strap size magnet 335 cooperate to determine the rotation angle of the spool 320, determined as described elsewhere herein, the presence of the winder cassette 110, and the overall length of the circumference measurement about the wearer's limb.

[0055] FIG. 8 is an isometric view of a device that may correspond to the device shown in FIG. 1, with the measurement assembly housing removed. The illustration is oriented to show the electronics proximate the limb with the rear housing 235 removed. Components for sensing physiological parameters such as heart rate, SPO2, and NIBP may be present in the electronics subassembly 215. In this example, a light emitter 815, which may emit light at green, red, and infrared wavelengths, is shown and placed proximate the wearer's core. Light from this light emitter component travels into the wearer's skin. A portion of this light is reflected and sensed by detector components 805 and 810. The returned light is sensed and evaluated by software. Raw or evaluated measurements can then be transmitted to another computing device.

[0056] In some embodiments, device 100 can use orientation information detected by the accelerometer to detect when the patient is horizontal or at rest. Resting heart rate is sampled. Resting heart rate variability is known to change as the patient retains fluid. These heart rate readings can be used to increase the reliability of the interpretation of circumference measurements.

[0057] Limb circumference measurements and limb orientation data can be obtained continuously at evenly spaced intervals and processed to generate an individual daily swelling pattern for the subject wearing the device, characterized by a minimum limb circumference that occurs when the subject is lying down and a maximum circumference after the subject has been in an upright position, such as standing or sitting, for a period of time that is specific to that individual.

[0058] Trends in fluid gain or loss can be calculated for specified periods, such as days, weeks, or months. Fluid gain or loss and trends in fluid gain or loss can be compared to thresholds to identify conditions of interest. The system takes actions specific to the condition of interest, including sending messages and alerts to the user as well as support personnel, such as family caregivers, chronic care managers, and / or clinical personnel.

[0059] The rate at which fluid redistributes itself within the body when standing up vertically can indicate the viscosity of the interstitial fluid, and changes in viscosity are known to be associated with heart failure decompensation due to changes in protein levels in the interstitial fluid. This is typically assessed by a physician pressing firmly against the patient's ankle to see if the resulting "pitting" resolves quickly. If the pitting does not resolve quickly, the condition is described as pitting edema. This is an important medical sign and a useful part of the diagnostic methodology for characterizing a patient's condition.

[0060] The disclosed techniques can characterize the rate of change in interstitial fluid redistribution. By taking multiple measurements as a patient transitions from a supine to an upright position, typically in the morning, it is possible to track the time it takes for interstitial fluid redistribution to occur relative to the change in the direction of gravity. This measurement of the rate of change is directly related to the viscosity of the interstitial fluid. The ability to recognize interstitial fluid viscosity and its associated changes can provide further information to a medical professional or computational algorithm regarding changes in a patient's disease state, as the viscosity of the interstitial fluid can provide insight into the underlying cause of fluid load (e.g., changes in protein levels in the interstitial fluid).

[0061] FIG. 9 shows a plot 900 of normal swelling (e.g., limb swelling) over a 12-day period for a hypothetical heart failure patient. Reference numeral 905 relates to a plot of circumference readings captured by a device (e.g., device 100) versus time, showing a repetitive daily swelling pattern over the 12-day period. Reference numeral 910 relates to a rolling average of ankle circumference. In some embodiments, an exponential moving average can be used. Reference numeral 915 relates to a user's normal baseline circumference, derived from circumference readings measured during the user's normal or "dry" state in the example heart failure patient.

[0062] The swelling pattern can be represented by an "average" circumference that takes into account the minimum and maximum circumferences associated with the swelling pattern.

[0063] The baseline swelling pattern or baseline average swelling is identified as the daily swelling pattern or average daily swelling detected when the subject is in a normal state of health, typically referred to as a "dry" state in heart failure patients. The system can calculate or adjust the normal baseline over a period of use. The system maintains the normal baseline for comparison to calculate fluid gain or loss.

[0064] FIG. 10 shows an eight-day plot 1000 of compensatory swelling events (e.g., ankle swelling) associated with fluid retention related to increased salt intake in a hypothetical heart failure patient. Reference numeral 1005 relates to a plot of circumference readings captured by a device (e.g., device 100) versus time. Reference numeral 1010 relates to a rolling average of ankle circumference. A similar plot can be created when using an exponential moving average. Reference numeral 1015 relates to a circumference reading, e.g., the patient's normal baseline circumference, derived from circumference readings measured during the user's normal or "dry" state in the case of a heart failure patient. Reference numeral 1020 indicates deviations in the daily swelling pattern that may be associated with this patient's fluid retention, in this case indicating a high-salt diet intake on two consecutive days. Reference numeral 1025 refers to the corresponding change in average circumference that occurs during the swelling event. Reference numeral 1030 indicates that normal swelling returns in the days following the event as the patient's body compensates and expels excess fluid.

[0065] In Figure 10, there are very different waveform plots of individual measurements 1005. These patterns vary from person to person and from day to day, and this individual's pattern is much less regular than the previous example. However, the moving average trend line 1025 shows that a 4 millimeter increase in swelling occurred over two days, consistent with a high-salt diet. The swelling subsided over time as the body compensated for this infusion (1030).

[0066] FIG. 11 shows a plot 1100 of a hypothetical decompensated fluid retention episode, such as one preceding a hospitalization for heart failure. Reference numeral 1105 relates to a plot of circumference readings taken by a device (e.g., device 100) versus time over a four-week period. Reference numeral 1110 relates to a rolling average of ankle circumference. An exponential moving average can be used to create a similar plot. Reference numeral 1115 relates to a patient's normal baseline circumference, derived from circumference readings measured during the user's normal or "dry" state in the case of a heart failure patient. Reference numeral 1120 indicates a deviation in the daily swelling pattern that may be associated with fluid retention, in this case, a trend associated with decompensation related to a condition requiring clinical intervention. Reference numeral 1125 is the corresponding change in average circumference associated with increased fluid retention.

[0067] Plot 1100 in Figure 11 shows yet another pattern of measurements. While a daily average swelling signal change of a few millimeters is the signal of interest, the circumference measurement deviation can exceed 10 millimeters in a single day. The potential error of deviation from the arithmetically processed measurement is greater than the signal of a single measurement. This patient not only has a much wider range of daily measurements 1105, but also a much larger monthly deviation. There is a 17 millimeter swelling range over the entire month, essentially at the same location on the same ankle. Importantly, for the first two weeks, the average swelling remains within a ±1 millimeter range (1110). However, for the following two weeks, the average daily swelling increases to nearly 6 millimeters (1125) above the nominal baseline (1115). This represents a substantial and sustained trend in the circumference data, indicating an increase in the patient's fluid volume.

[0068] This ongoing trend, along with the individual patient's history, can be compared to patients who may have similar characteristics, such as, but not limited to, age, height, weight, left ventricular ejection fraction, co-morbidities, and / or similar measures. Additionally, other physiological measures, such as, but not limited to, heart rate, SpO2, NIBP, temperature, gait vibration impulse, pace, arrhythmia, tachycardia, bradycardia, atrial fibrillation, and / or heart rate variability, can also be considered in conjunction with these measurements. Processing this information using appropriate correlation algorithms may enable real-time, consistent, continuous, and / or instantaneous short-term assessment of the severity of trend events and predict the likelihood of impending decompensation events. In some embodiments, trained machine learning models or rule-application algorithms can be utilized and updated according to feedback (human or machine) from patient experience and / or patient populations to constantly improve the accuracy of these predictions; the more measurements, the more accurate the predictions, especially to minimize interpolation errors and determine an accurate model of daily limb swelling changes. Upon detection of a substantial swelling event exceeding a predetermined threshold stored on the device or remotely, the patient or their caregiver may be notified to take action, such as modifying the patient's overall activity, contacting the patient's healthcare provider, changing the amount of a therapeutic drug such as a diuretic, adding or reducing other medications, or implementing other methods that may alter the course of the disease. In some instances, responsive action is provided urgently, while in other instances, such as dietary changes, responsive action may be suggested or prescribed. Any changes in medication dosage will typically follow a pre-defined treatment plan by the patient's physician; for example, an additional dose of a diuretic may be prescribed if the patient has a substantial swelling event.

[0069] Given that the size of the arithmetically processed signal of interest is small compared to the range of circumference measurements over a day, it is desirable to minimize the sampling rate's distortion of the underlying continuously changing physiology. Linear interpolation that truncates the actual limb swelling excursion values ​​can significantly change the calculated signal of interest values. In the simplest example, a plot of circumference measurements at random times over the course of a week could yield substantially different results that may be substantially inconsistent with the same patient and condition sampled more densely. This is particularly true when assessing the rate of circumference change associated with changes in the patient's orientation to gravity.

[0070] In the non-limiting examples shown in Figures 9, 10, and 11, measurements are taken every 10 minutes, however, it is understood that different intervals are within the scope of the present disclosure.

[0071] These individual measurements can be mathematically aggregated over a period of time, such as a day, 48 hours, or any time suitable for monitoring and analysis. In this example, the aggregation uses a rolling average, although exponential moving averages are also contemplated. These series of aggregated measurements are then compared for evidence of deviation or divergence. For example, in the example of FIG. 9, there is a series of points representing individual circumference measurements. Note that there is a significant amount of variation in these measurements.

[0072] This individual's measurements varied by 10 millimeters from day to day and time to time for the same ankle location. However, the overall daily fluctuations in measurements are actually quite stable. As can be seen in the trend line 915 for average daily circumference, the range for this individual was approximately 1 millimeter.

[0073] While this specification describes methods for capturing multiple measurements of minimum limb circumferences, typical of limb narrowing points, such as the ankle or wrist, it should be noted that the teachings herein are applicable whether the minimum limb circumference is at a narrowing or tapering point, or at a location of a fixed circumference, such as a cylindrical body. Limb circumference also closely approximates interstitial fluid volume, which is an important medical concern in patients with conditions such as heart failure decompensation, renal dysfunction, and similar physiological conditions. Increased interstitial fluid volume is associated with heart failure decompensation. It should be clear from Figures 9, 10, and 11 that a single measurement, perhaps during a physician's visit, can yield dramatically different and inconsistent results at random times during the day. For this reason, physicians have been limited to rough indications of the presence or absence of swelling, such as by pressing a finger into the ankle. The lack of a practical and rigorous medical measurement has limited the usefulness of this physiological parameter. It is only by carefully quantifying and tracking over time that changes in fluid volume become apparent, providing pertinent physiological information. Average changes of a few millimeters can be important indicators of disease progression, but are not visible on a single or routine examination, and require more precise measurements than are possible by visual inspection alone.

[0074] It should be noted that a single measurement at a fixed time of day will certainly not provide accurate results: as can be seen in Figures 9, 10 and 11, extreme deviations in measurements do not necessarily occur at the same time each day.

[0075] 12 shows an example of a loop 1200 illustrating the effectiveness of integrating interstitial fluid volume monitoring via device 100 with decisions that can be automatically followed in accordance with the techniques and concepts described herein. That is, absolute measurements by device 100 and / or trends of those measurements over time (navigation) can be output as alerts (e.g., discrete data, waveforms, and / or simple notifications) for human or artificially intelligent clinical evaluation 1202, for example, based on machine learning principles (guidance). The results of clinical evaluation 1202 can be output as a treatment plan (which may include, among other things, advice or instructions to the patient, prescriptions for medication or therapy, etc.) and optionally entered into a treatment log 1204 (control). The loop 1200 concludes with an analysis of the patient's response to the treatment plan, completing the integration of navigation-guidance control of patient support made possible by the device 100 and its operation / functionality to monitor and / or measure swelling, and from there create not just simple data for evaluation, but real-time monitoring and action, eliminating the need for many consultations or interventions that until now have often been considered optimal, even necessary.

[0076] Plot 1300 in FIG. 13 illustrates an example of integrating medication treatment logs with ankle circumference history. The plot allows a healthcare professional to determine outcomes associated with a prescribed treatment plan. Circumference information can be used in combination with the prescribed treatment plan to determine whether medication achieved the desired outcome and adjust medication as needed to achieve the desired outcome. Average circumference 1305 is the patient's response to treatment plan 1315. A physician can evaluate the response to determine effectiveness and adjust treatment plan 1315 to achieve the desired outcome. Non-invasive blood pressure profile 1320 can be used to assess a patient's ability to tolerate medication treatment adjustments that can reduce fluid retention while remaining within an acceptable blood pressure range.

[0077] 14 illustrates an example architecture 1400 for implementing monitoring of changes in the quantity and characteristics of human interstitial fluid in a patient 1402. The illustrated architecture 1400 includes a device 1404, a healthcare entity 1406, personal contacts 1408, and a wireless access point 1410, although this is merely an example and other configurations including more or fewer components are also contemplated.

[0078] Healthcare entities 1406 may include, without limitation, medical facilities, caregivers, and / or other personnel associated with the care of a patient. Caregivers or other personnel may operate one or more computing devices as part of their care functions.

[0079] Personal contacts 1408 may include support personnel operating one or more computing devices connected to database server 1412 via a wireless or wired communication link (e.g., the Internet or other wireless and / or wired connection), using SMS messages, WIFI protocols, Bluetooth protocols, etc. Personal contacts 1408 may also include the patient's personal representative, family members, or other individuals who are set up to receive information obtained from device 100.

[0080] The control system may include a database server 1412 connected to a database 1414. The database 1414 may store pertinent data about the patient 1402 (such as patient history, patient records, etc.), trigger event levels, and addresses to which messages (e.g., notifications, alerts, etc.) should be sent.

[0081] Information from device 1404 can travel several alternative paths depending on implementation details. For example, information can be entered into a computing device (e.g., the patient's desktop computer, the patient's mobile phone, the patient's portable computer, etc.) connected to database server 1412 (or a web server) via the Internet, a cellular gateway, or other network. The computing device can forward the feedback information to database server 1412 directly or through access point 1410. Device 1404 can communicate device messages to the computing device, which then send them to database server 1412.

[0082] The device 1404 can continuously measure and store the position measurements at a predefined frequency either locally or remotely, for example, in a database 1414. The position, when combined with size information that establishes a relationship between the position of the spool 320 and a known circumference, can be interpreted as a relative circumference measurement when compared to any reference or absolute circumference measurement.

[0083] 15 illustrates various components of a measurement assembly 1505 arranged in accordance with one or more embodiments described herein. The measurement assembly 1505 may correspond, for example, to the measurement assembly 105 shown in FIG. 1. In the illustrated example, the measurement assembly 1505 may be configured to measure limb circumference using one or more sensors, such as magnetic sensors, by detecting stretching of a strap 115 attached to a winder cassette 110 coupled to the measurement assembly 1505.

[0084] As shown in FIG. 15 , the measurement assembly 1505 may include one or more of a communication interface 1502, a user interface 1504, one or more processors 1506, one or more magnetic sensors 1508, memory 1510, and device hardware 1512.

[0085] The communication interface 1502 may include wireless and / or wired communication components that enable the measurement assembly 1505 to transmit data to and receive data from other networked devices over a communication network such as that described with respect to FIG. 14 .

[0086] The user interface 1504 may enable a user to provide input to and receive output from the measurement assembly 1505, including, for example, providing one or more inputs to initiate device activation and / or configure metadata, tags, communication parameters, monitoring parameters, etc. The user interface 1504 may include a data output device (e.g., a visual display, an audio speaker) and one or more data input devices. The data input devices may include, but are not limited to, one or more combinations of a touchscreen, physical buttons, a camera, a fingerprint reader, a keypad, a keyboard, a mouse device, a microphone, a voice recognition package, and any other suitable device or other electronic / software selection method.

[0087] The processor 1506 and memory 1510 can implement an operating system. The operating system can include components that enable the measurement assembly 1505 not only to receive and transmit data via various interfaces (e.g., the user interface 1504, the communication interface 1502, and / or memory input / output devices), but also to process the data using the processor 1506 to generate output. The operating system can include a display component that presents the output (e.g., displaying the data on an electronic display, storing the data in memory, transmitting the data to another electronic device, etc.). In addition, the operating system can include other components that perform various additional functions generally associated with operating systems.

[0088] The magnetic sensor 1508 can be configured and positioned within the housing of a wearable device of the type described herein and can cooperate with an electromagnetic circuit to detect the amount of rotation of the magnet associated with winding and unwinding of the strap 115 to match the circumference of the limb.

[0089] The memory 1510 can be implemented using a computer-readable medium, such as a computer storage medium. Computer-readable media includes at least two types of computer-readable media: computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, random access memory (RAM), dynamic random access memory (DRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage devices, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device. A computer-readable storage medium is not composed of, nor is it exclusively formed by, a modulated data signal, such as a carrier wave. In contrast, communication media may embodi computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism.

[0090] The memory 1510 may contain data collected by the magnetic sensor 1508, entered by a user, or received from a remote source, along with an operating system, device software 1514, and one or more applications 1516. The applications 1516 may include any application software executable by the one or more processors 1506, including, for example, but not limited to, applications that facilitate the functionality of the wearable device 1505 to detect stretching of the strap 115 by detecting and processing the magnetic field of the magnet in the spool 320 and data derived therefrom; manipulating, formatting, adding, deleting, or modifying metadata; and image or data processing.

[0091] The device software 1516 may include software components that enable the measurement assembly 1505 to perform functions. For example, the device software 1516 may include a basic input / output system (BIOS), boot ROM, or boot loader that boots the measurement assembly 1505 and runs an operating system after the measurement assembly 1505 is powered on.

[0092] The device software 1516 may include software components that calculate relative times associated with data collection, which can be resolved to actual times in other computer systems synchronized to a universal time standard.

[0093] The device hardware 1512 may include additional hardware that facilitates the user interface 1504, data display, data communication, data storage, and / or performance of other device functions.

[0094] Figure 16 illustrates an example of the database server 1412 shown in Figure 14. The database server 1412 can include a communication interface 1602, one or more processors 1604, memory 1606, and hardware 1608. The communication interface 1602, like the communication interface 1502 of the measurement assembly 1505, can include wireless and / or wired communication components that enable the database server 1412 to send data to and receive data from the measurement assembly 1505 and other networked devices over a communication network such as described with respect to Figure 14.

[0095] The processor 1604 and memory 1606 may implement an operating system. The operating system may include components that enable the database server 1412 not only to receive and send data via various interfaces (e.g., communication interface 1602 and / or memory input / output devices) but also to process the data using the processor 1604 to generate output. The operating system may include display components that present output (e.g., displaying data on an electronic display, storing data in memory, transmitting data to another electronic device, etc.). In addition, the operating system may include other components that perform various additional functions generally associated with operating systems.

[0096] The memory 1606 can contain data collected by the magnetic sensor 1508, entered by a user, or received from a remote source, along with an operating system, device software, and one or more applications. The applications can include any application software executable by the one or more processors 1604, including, but not limited to, applications to train and / or execute rules or machine learning models and algorithms 1610 for processing data received from the measurement assembly 1505, including generating waveforms of circumference change, interpreting the data, applying activity information, the subject's medical history, drug treatment regimens, and other data, generating predicted outputs for analysis, and / or providing feedback to update or retrain the models.

[0097] Hardware 1608 may include additional hardware to facilitate data display, data communication, data storage, and / or other device functions.

[0098] FIG. 17 is a flow diagram of an example process 1700 that may be performed, at least in part, by the measurement assembly 105 for measuring a subject's limb circumference, generating a waveform of the measurements over time, and outputting an indication of the condition revealed by the waveform. Process 1700 is illustrated as a collection of logical flowchart blocks, which represent sequences of operations that may be implemented in hardware, software, or a combination thereof. In the context of software, the blocks represent computer-executable instructions that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions may include routines, programs, objects, components, data structures, etc. that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be considered limiting, and any number of the described blocks may be combined in any order and / or in parallel to implement the process. For purposes of discussion, the process will be described with reference to device 100 shown in FIG. 1.

[0099] At block 1702, device 100 can measure limb circumference as an indicator of interstitial fluid volume within the limb at a repeatable home position over a period of time. In some embodiments, device 100 can be applied to a limb of a human subject and moved to settle at a repeatable home position on the limb. In one or more embodiments, the repeatable home position can be the minimum limb circumference at which tension in the straps balances interstitial fluid pressure and allows the device to perform the measurements described above.

[0100] At block 1704, device 100 may generate a waveform indicative of current circumference data derived over time from the measured circumferences. In some embodiments, circumference measurements may be obtained periodically (e.g., once a day), intermittently (e.g., manually initiated), or continuously. In some embodiments, some or all of the data processing and waveform generation may be performed off-device, such as by a remote computing device.

[0101] In block 1706, the device 100 can compare the waveform to the waveform of the subject's baseline circumference data at a repeatable home position. The waveform differences can be interpreted by the device 105, transmitted off-device or to a remote location, such as a doctor's office, a mobile device, a portable computer, etc., or interpreted by a human.

[0102] At block 1708, device 100 may output the results of the comparison along with any indications revealed by the comparison. For example, if the current circumference measurement waveform indicates an increase over the subject's baseline waveform, an alert may be displayed on measurement assembly 105 and transmitted to a mobile device or a more remote endpoint. Additionally or alternatively, instructions may be output to, for example, advise the subject on changes to make in diet or exercise, review or make specific adjustments to treatment (including adjustments to medication dosage), etc.

[0103] 18-26 illustrate other exemplary devices. Device aspects similar to device 100 are designated with like reference numerals with a different initial letter indicating the figure in which the device is depicted (e.g., device 1800 depicted in FIG. 18 may correspond to device 100 depicted in FIG. 1).

[0104] 18 shows an isometric view of another example device 1800 that can be configured to monitor changes in the quantity and properties of human interstitial fluid. Device 1800 can include a device assembly that includes, among other components, a measurement assembly 1805, a winder cassette 1810, a strap 1815 configured to be placed around a subject's limb, and a clasp 1820. Like device 100, a subject can wear device 1800 around the lower arm (i.e., below the elbow) or lower leg (i.e., below the knee), although the teachings herein can be applied to other body parts, particularly body parts having axial portions, and thus should not be considered limited other than the type of data required and the location where the data may be obtained.

[0105] The measurement assembly 1805 can house an electronics subassembly for acquiring data and communicating the data or information based on the data. The electronics subassembly, in some embodiments, can include sensors and associated electronics that can perform analysis of the sensor data and output results of the analysis and / or recommendations or instructions based on those results, as described below. In some embodiments, as described more fully below, the electronics subassembly can include a sensor portion that includes one or more magnetic sensors positioned opposite one or more corresponding magnets on the winder cassette 1810.

[0106] The winder cassette 1810 generally cooperates with the strap 1815 to allow a snug fit to the limb with loose tension, even when severe swelling is present. Like device 100, device 1800 typically does not fit tightly to the limb, even when severe swelling is present. To this end, the strap 1815 and winder cassette 1810 are configured to allow the strap 1815 to expand and contract as the limb swells and contracts, allowing an essentially constant force to be applied to the limb. In some embodiments, the winder cassette 1810 in combination with the strap 1815 and clasp 1820 can be a replaceable component that can be easily replaced by the user if it becomes soiled or broken.

[0107] Figure 19 shows an exploded view of an example of a measurement assembly 1805, winder cassette 1810, strap 1815, and clasp 1820 of a device 1900 corresponding to the example shown in Figure 18. The housing 1935 and cover 1905 are configured to house the electronics subassembly 1915, which includes a battery 1910, a wireless module 1920, an angle magnetic sensor 1940, and one or more strap-sized magnetic sensors 1945, an insulator 1925, and a gasket 1930. The measurement assembly 1805 can be substantially liquid-tight to prevent the ingress of fluids.

[0108] Battery 1910 may be similar to battery 210. In some examples, battery 1910 may be captured between electronics subassembly 1915 and the top of housing 1935. In some embodiments, another portable power source may be used, such as a rechargeable battery, a fuel cell, a storage capacitor, energy harvested from the patient, energy harvested from the environment, etc.

[0109] Insulator 1925 may be an electrical insulator and therefore may be positioned to insulate battery 1910 from electronics subassembly 1915, allowing battery 1910 to be replaced without contacting any components or wiring on electronics subassembly 1915 or on the electronics board substrate. In some embodiments, insulator 1925 may be engraved or printed with configuration information such as the version of device 1900 or any of its components.

[0110] Similar to electronics subassembly 215, electronics subassembly 1915 can be a printed circuit board and can include electronic components that control and perform one or more of the limb circumference sensing. The limb circumference can be used by an onboard control system or transmitted to a remote computing device that runs algorithms on data from the sensed limb circumference and outputs messages and generates graphical results showing measurements over time that can be interpreted by a medical professional (for example) to provide insight into the current status of the patient wearing device 1900. In some embodiments, the electronics can include one or more magnetic sensors, such as magnetic sensors 1940, 1945, one or more optical sensors, one or more processors, memory, and an accelerometer. The memory can store instructions that, when executed by the one or more processors, cause the one or more processors to perform various operations described herein. In at least some embodiments, the magnetic sensor can detect limb circumference. In at least some embodiments, the accelerometer can detect the patient's orientation and movement and output data that can be used by the onboard control system or transmitted to a remote computing device to determine the patient's level of activity. For example, the device may detect, accumulate, store, and / or transmit accelerometer measurements at a sufficiently high frequency depending on the information received from the accelerometer and correlate that information with the circumference readings to provide an adequate representation of the effects of gravity and activity on the limb during the time between circumference measurements.

[0111] Like wireless module 220, wireless module 1920 can transmit digital or analog signals (e.g., containing patient movement information) to an external device, such as a nearby computer, smartphone, tablet, etc., that has the processing capability to receive the signals, analyze the data provided by the signals, output instructions or commands, and / or relay the signals to a remote computing device, such as a server, computer, or database (e.g., in a clinic or data center).

[0112] The gasket 1930 is configured and positioned to seal the housing 1935 and prevent the ingress of dust or water that could damage sensitive internal components. For example, the gasket 1930 can be positioned between the housing 1935 and the cover 1905. The gasket 1930 can include, without limitation, any insulating material suitable for that purpose. In at least one embodiment, the gasket 1930 can be solid rather than ring-shaped as disclosed in the example of gasket 230. In the illustrated gasket 1930, the gasket 1930 and the cover 1905 can have flat surfaces and ample tolerances to mate with openings in the housing 1935.

[0113] Like the measurement module 105, the measurement assembly 1805 can be constructed so that the insulator 1925 and electronics subassembly 1915, including the wireless module 1920, are inserted into a housing 1935. The cover 1905 can be joined with a gasket 1930 positioned where the cover 1905 meets the housing 1935 by a snap fit, allowing the cover 1905 to be easily removed for battery 1910 replacement. In this example, the cover 1905 snaps into the housing 1935, compressing the gasket 1930, which seals the interior of the housing 1935 from dust or water intrusion. The winder cassette 1810 can then be mated to the measurement assembly 1805 using a detent that holds the measurement assembly 1805 and the winder cassette 1810, including the strap 1815, together.

[0114] The distal end of the strap 1815 is secured by threading it through the body of the clasp 1820 and heat bonding the end to the body of the strap 1815 with an adhesive, thereby adhering the strap 1815 to itself. However, it should be understood that many other methods of attachment are within the scope of this disclosure, such as the material of the strap 1815 itself adhering to the clasp 1820, impingement, and similar means.

[0115] Similar to clasp 120, clasp 1820 can be joined to electronics subassembly 1915 by a latching mechanism that engages the shape of cover 1905 on electronics subassembly 1915 to enclose the limb.

[0116] As with the winder cassette 110, the winder cassette 1910 can be constructed to accommodate straps 1915 of different lengths, allowing the device 1900 to accommodate a wide range of applications, from small wrists to significantly swollen legs, for example.

[0117] In some embodiments, the housing 1935, cover 1905, and / or clasp 1820 can be 3D printed by a mask-based stereolithography (MSLA) process from materials such as Siraya Tech Blu resin and Siraya Tech Blu Mecha-Nylon resin. The gasket 1930 can include Poron (polyurethane foam). The strap 1815 can be made of a generally flexible, inelastic, biocompatible porous material for patient comfort. By way of example, the material can be an open-weave, 80 threads per inch, fused-edge polyester, .008" Teslin (PPG, Barberton, OH) or Tyvek (Wilmington, DL), or an open-weave nonwoven fabric such as embroidery stabilizing interlining.

[0118] 20 shows an exploded view of the winder cassette 1810, strap 1815, and clasp 1820 that remain when the measurement assembly 1805 is removed in some embodiments. The winder cassette 1810 can include a winder cassette frame 2030, a spring 2015, and a spool 2020. The winder cassette frame 2030 can include a capture mechanism 2040 for receiving a strap-sized magnet 2035. The winder cassette frame 2030 can be configured to receive a drive pin 2044. The drive pin 2044 can include a drive pin mechanism 2042 (e.g., a protrusion or a mechanism for receiving a protrusion) that is configured to mate with a corresponding mechanism on the winder cassette frame 2030 (e.g., a mechanism for receiving the protrusion of the drive pin mechanism 2042, or a protrusion that corresponds to the mechanism for receiving the drive pin mechanism 2042). The spool 2020 can be cylindrical and includes an angle magnet 2025. Once installed in the winder cassette frame 2030, the strap 1815 can be wound onto the spool 2020, as described below. In some embodiments, the winder cassette 1810, strap 1815, and / or clasp 1820 are replaceable individually or in combinations including any two or all three.

[0119] The spring 2015 may be a spiral metal foil having a hole 2050 in one portion that mates with a spring joint formed by a protrusion 2045 on the drive pin 2044, shown in FIG. 20, when the drive pin 2044 is inserted into the coil spring 2015. Another portion of the spring 2015 may have a hole 2055 that engages another spring joint formed by a protrusion 2060 on the spool 2020, shown in FIG. 20, for winding the spring 2015 and providing tension when the strap 1815 is stretched. The spring 2015 may provide a substantially constant spring force load (e.g., about 10-40 grams) sufficient to allow the strap 1815 to fit snugly around the limb without unnecessary or uncomfortable pressure.

[0120] The strap 1815 is attached to and wound around the spool 2020. The angle magnet 2025 can be pressed into an opening, gap, or recess in the spool 2020 or otherwise fitted opposite the angle magnetic sensor 1940 of the electronics subassembly 1915. The strap-sized magnet 2035 can be pressed into an opening, gap, or recess in the winder cassette frame 2030 or otherwise fitted opposite one or more of the strap-sized magnetic sensors 1945 of the electronics subassembly 1915 of the measurement assembly 1805. The magnetic sensors 1940 and 1945 are configured and positioned to sense the magnetic fields of the magnets 2025 and 2035 through the housing 1935.

[0121] The act of lengthening or shortening the length of the strap 1815 as the limb expands or contracts can be accomplished by a tensioning mechanism including a winder cassette frame 2030 and a spring 2015 within a spool 2020, which can accommodate a portion of the length of the strap 1815 wound around the spool 2020. In some embodiments, the spring 2015 can be a constant tension spring. As the limb expands, the strap 1815 is unwound, increasing the length of the strap 1815 to accommodate an increase in the circumference of the limb, while the constant force applied by the spring 2015 maintains a constant tension in the strap 1815 around the limb. The tension in the strap 1815 can be matched to interstitial fluid pressure and skin elasticity so that the device stretches without causing significant indentation in the limb. In this regard, and in conjunction with other embodiments described herein, it is understood that constant force and tension need not be exact, but within reasonable tolerances that enable the device to perform its function of measuring limb circumference, particularly the difference in limb circumference relative to a baseline or other reference, in accordance with the principles outlined in this disclosure.

[0122] An angle magnet 2025 fitted to the spool 2020 can be sensed by an angle magnetic sensor 1940 to rotate the spool 2020 as the strap 1815 is wound and unwound, and the angle or rotation of the spool 2020 can be recognized by a signal output by the angle magnetic sensor 1940 and received by an electronics assembly 1915 electrically connected to the angle magnetic sensor 1940.

[0123] The angle magnet sensor 1940 can be comprised of multiple resistive elements arranged to output a set of variable signal strength voltages. In at least one embodiment, these correspond to the sine and cosine of the angle of rotation of the magnet 2025's magnetic field relative to the magnetic sensor 1940. This can be achieved with a full-bridge sensor with underlying spintronics technology (NVE Corporation, Eden Prairie, MN currently produces suitable sensors). This produces a very low-power structure that is relatively insensitive to the distance between the magnet 2025 and the angle magnet sensor 1940 and to axial misalignment. Because the diameter of the spool 2020 defines a known perimeter using the formula C = Pi x D, that diameter can be translated into a precise change in length measurement as the strap 1815 stretches or shrinks. The diameter of the spool 2020 can be determined / calibrated for each device during manufacturing.

[0124] In addition to measuring the angle of rotation of the magnet 2025, the circuit maintains information about the rotation history. In this example, quadrature detection can be implemented in software or hardware to track the current rotation or number of rotations. In at least one embodiment, quadrature detection can be achieved by using a comparator circuit connected to a processor interrupt function. However, in other implementations, counter circuitry and logic components in a dedicated circuit, or functionality integrated into the processor itself, can perform this function. A count of rotations is kept as the strap 1815 wraps around the spool 2020 more than 360 degrees. The count of rotations, combined with the current angle measurement, allows the software to calculate the total number of degrees of rotation. The diameter of the spool 2020, combined with the length of the manufactured strap 1815 without the spring 1815, combined with the total number of degrees of rotation, determines the total circumference measurement.

[0125] As noted above in the description of Figure 3, there may be additional considerations for calculating the total length. As alluded to above, as the strap 1815 is wound onto the spool 2020, it changes the effective diameter of the wrap and the circumference of the spool 2020 as the layers are stacked on top of each other. To account for this condition, it is possible to apply diameter variations consistent with the thickness of the strap 1815 and the number of wraps of strap material around the spool 2020, recognizing the rotational history and manufacturing design of the winder cassette 1810.

[0126] The circumference of the limb is equal to the unwound length of the strap 1815 at the home or retracted position, plus the length of the measurement assembly 1805 body and clasp 1820, plus the "variable length" of the strap 1815 that wraps around and unwound from the spool 2020 as the limb expands and contracts at its minimum circumference or repeatable position. The variable length of the strap 1815 is equal to the proportional rotation corresponding to the current angle of rotation of the spool 2020 from the home position (defined as 0 degrees), plus the number of full rotations of the spool from the home position, taking into account the portion of the wrapped strap still on the spool, multiplied by the circumference of the spool (i.e., the diameter of the spool multiplied by pi). The current proportional rotation angle, measured as the number of rotations made from the home position, can be calculated from the arctangent of the sine / cosine provided by the magnetic sensor / magnet relationship and the quadrant in which it occurs. The home position is captured once the strap is placed at the home position. The number of full revolutions can be determined using quadrature detection (considering each 90 degree revolution measured from 0 degrees as one quadrant), in this example the number of times the spool has passed from quadrant 4 to quadrant 1 (see the quadrature plot below).

[0127] The length of the strap 1815 when the spring 2015 is in a relaxed, unused state is controlled during manufacture of the winder cassette 1810. If the rotation angle of the magnet 2025 matches a reference corresponding to the relaxed orientation after manufacture, the rotation history does not indicate additional wrapping, and there is no angle dithering due to wear, it can be assumed that the device 1900 is not being worn. In some embodiments, the spring 2015 can retract the strap 1815 to a home position, which can be read by software running to interpret a signal representing the detected spool 2020 angle, and an indicator or message can be output. Detection of these states can also be used to indicate whether the device is being worn. Data from the device 1900 in the “not worn” state can, in some embodiments, be ignored when assessing the wearer's condition. Furthermore, if this state persists, the patient can be contacted or examined regarding issues with wearing the device 1900.

[0128] Like device 100, device 1900 can accommodate a range of limb sizes in at least two ways: by substantially winding strap 1815 and / or by varying the total length of the strap to create different sized winder cassettes 1810.

[0129] This structure can provide at least two types of measurements: the first type is a relative measurement that quantifies only the change in circumference associated with the change in spool from the home position as a result of limb expansion and contraction, and the second type is an absolute measurement that can determine the total circumference of the limb by combining the relative measurement, the length of the electronics assembly 1805, the clasp 1820, and the length of the unused strap 1815.

[0130] In the current example, the strap size magnet 2025 of the winder cassette 1810 can communicate with one or more strap size magnetic sensors 1945 of the electronics subassembly 1915. Several strap size magnetic sensors 1945 can be positioned to recognize multiple strap sizes by the relative positions and orientations of the magnetic fields generated by the strap size magnets 2035. In at least one embodiment, a single strap size magnet 2035 can be used to recognize up to four strap sizes.

[0131] The strap-sized magnetic sensors 1945 can recognize the presence and / or orientation of the strap-sized magnets 2035 within the winder cassette 1810. In some embodiments, two strap-sized magnetic sensors 1945, such as Hall-effect sensors, can each output a signal in the presence of a north (north) pole magnetic field or a different signal in the presence of a south (south) pole magnetic field. By arranging the relative positions of the strap-sized magnetic sensors 1945 and the orientation of the strap-sized magnets 2035 within the winder cassette 1810, five orientation states can be detected and communicated. For example, when no magnetic field is sensed, the winder cassette 1810 is determined to be absent (e.g., decoded). That is, when the magnetic field axis is perpendicular to the circuit board supporting the strap-sized magnetic sensors 1945, a north-north or south-south state can be sensed, and when the magnetic field axis is parallel to the axis along the sensor 1945, a north-south or south-north state can be sensed. By using the strap-sized magnet 2035 plus the strap-sized magnetic sensor 1945 to sense the presence or absence of the winder cassette 1810, the coupling may be able to recognize removal and replacement events. Additionally, sensing the orientation of the strap-sized magnet 2035 facilitates recognition of winder cassette 1810 sizes, such as small, medium, large, and extra large. Winder cassettes 1810 with different lengths of strap 1815 can be made with orientations such that the magnetic field presented by the strap-sized magnet 2035 to the strap-sized magnetic sensor 1945, either in strength or field orientation, can be read by the circuitry to interpret and communicate the size of the winder cassette 1810 attached to the measurement assembly 1805.

[0132] In some embodiments, the winder cassette frame 2030 and spool 2020 are 3D printed by a mask-based stereolithography (MSLA) process from materials such as Siraya Tech Blu resin and Siraya Tech Blu Mecha-Nylon resin. The spring 2015 can be 125 millimeters long x 10 millimeters wide x 0.001 inches (0.025 millimeters) of hardened stainless steel shim stock (Precision Brands, Downers Grove, IL). The angle magnetic sensor 1940 can be a giant magnetoresistive angle sensor, such as the AAT101-10E full-bridge angle sensor manufactured by NVE (Eden Prairie, MN). The strap-sized magnetic sensor 1945 can be a dual-output unipolar Hall effect switch, such as the AH1389 manufactured by Diodes Inc. (Plano, TX). The magnets 2025 and 2035 are neodymium available from a variety of suppliers.

[0133] FIG. 21 illustrates an example of a digital circuit 2100 that may be implemented to perform quadrature decoding, including rotation counting (digital path through a 0-degree reference angle) detection, in software using a fraction of the power used by some microprocessor quadrature decoding circuits. Such a microprocessor quadrature detection circuit may send an interrupt to a microprocessor with quadrature detection functionality to count rotations, which requires the microprocessor to remain awake, which consumes power. Digital circuit 2100 combines interrupts with analog angle measurements in the context of reduced power consumption, utilizing the interrupts to track quadrants and thus accurately count rotations while accounting for dithering across the boundary between two adjacent quadrants. Note that digital circuit 2100 and / or the measurement techniques described therein may be implemented with other embodiments described herein.

[0134] The digital circuit 2100 can trigger an interrupt that can wake up a CPU or trigger additional software components to perform one or more of the operations described herein. In one example, an interrupt rate associated with rapid stretching of a strap can be used to wake up a processor. In some embodiments, the angle sensor 2105 can generate electrical values ​​corresponding to the sine 2110 and cosine 2115 of the angle of the magnetic field orientation of the angle magnet 2025 to which the sensor is exposed. The comparator 2120 simplifies the waveform from the angle sensor 2105 (corresponding to the angle magnet sensor 1940) and determines the 0-degree and 180-degree crossing signals 2125 of the waveform output (corresponding to the boundaries between quadrants Q4-Q1 and Q2-Q3, respectively). These crossing signals 2125 can be electrically connected to input pins of the CPU 2130 and can be used by the device 1900 as interrupts to the CPU 2130. These interrupts 2125 can be used to wake the CPU 2130 from a sleep state to an active state, and can also be used to trigger communication events such as a Bluetooth advertising state, or other software components.

[0135] In some embodiments, these crossing point signals 2125 can also be used in a low-power hybrid digital-analog approach to maintain an accurate count of rotations when "dithering" may be occurring, such as when crossing the 360 ​​to 0 degree boundary where the circuit detects or determines that a full rotation has occurred.

[0136] The diagram below illustrates how to keep a proper count of rotations.

[0137] [Table 1]

[0138] Considering a narrow range of -1 to +1 degrees from the reference 0 degrees, the area to the left of 0 degrees is called the West region, and the area to the right of 0 degrees is called the East region. In this example, the digital 0 degree interrupt sensing region can be called the revolution count region, and the analog sensing region can be called the angle region. In this range, very close to 0, sensing of either the analog (angle) or digital interrupt (revolution count) may not match. That is, when measuring the angle itself, the angle may be located at Q4 west of 0, while the digital interrupt that detects or determines the number of revolutions (i.e., the number of times it crosses the reference 0 degree intersection) may be slightly off, with the interrupt located at Q1 east of 0. If the revolution count region is considered correct, angle correction must be performed. For example, You can track the region via interrupts at both 1.0 and 180 degrees so that you know the current region where the rotation count is. 2. The angle domain can be defined as 0-->1 degrees = East, and 359-->0 = West. 3. If the area determination does not match within this ±1 degree range, 360 degrees can be added or subtracted from the angle measurement to match the rotation count area assumed to be correct. 4. If the rotation count area and the angle area match, the angle measurement value can be used as is.

[0139] As previously mentioned, the rotation count interrupt rate can be used to transition into advertising mode. More specifically, the low power detection of a rotation crossing, combined with the time the crossing occurs, can be used as a trigger to enter Bluetooth advertising mode, a similar communication protocol, or other variable section of software. In this way, the angle sensor interrupt can be used to both perform rotation counting and to quickly stretch or relax the strap, snapping it into advertising mode.

[0140] 22 is a top view 2200 of the winder cassette 1810 relative to the strap 1815 and clasp 1820. From this view, the location of partial cross section AA of the winder cassette 1810 can be seen.

[0141] FIG. 23 is a partial cross-sectional view AA of FIG. 22 of the winder cassette 1810 in an assembled state.

[0142] In some examples, the capture mechanism 2045 of the drive pin 2044 can fit within one or more tabs, grooves, or holes in one or more walls or in the winder cassette frame 2030. In some embodiments, one or both ends of the drive pin 2044 can protrude from or be fixed to one or more walls. In such embodiments, the spring 2015 can be attached to the capture mechanism 2045, which is mounted to the winder cassette frame 2030, for example, by inserting an end 2050 of the spring 2015 into a gap in the drive pin and wrapping or bending the spring 2015 around the drive pin 2044.

[0143] The coil spring 2015 can have, for example, a thin wire or a wide strip-like structure. To facilitate fastening the spring 2015 to the capture mechanism 2040 of the winder cassette frame 2030, the end of the spring 2015 inserted into the gap can be wrapped or bent so as to at least partially wrap around the drive pin 2044. A bent configuration 2320 of the spring 2015, consisting of two bent sections, can engage with the capture mechanism 2040, as shown in FIG. 23 . The tip of the spring 2015 can be bonded to the spool 2020 or the protrusion 2060 by adhesive 2310. The spool 2020 can then be attached to the strap 1815 by adhesive 2305. No limitation regarding a particular type of fastener or adhesive should be inferred. As a result, the force of the spring 2015 is transferred from the capture mechanism 2040 of the winder cassette frame 2030 by the bent configuration 2320 of the spring 2015. The winder cassette frame 2030 is attached to the spring 2015 and mated to the spool 2020 via the protrusions 2060, which are then glued 2305 to the strap 1815, tensioning the assembly. Rotation of the angle magnet 2025 to the opposite side of the angle magnetic sensor 1940 as the limb expands and contracts can be achieved by this tensioning mechanism.

[0144] 24 is a side view 2400 of a device that may correspond to device 1900. In practice, device 1900 may drift to an operational and repeatable home position on the limb due to the effects of gravity and patient movement affected by friction between strap 1815 and the limb.

[0145] FIG. 25 is a detailed cross-sectional view 2500 of the example device shown in FIG. 24 taken along line BB through the measurement assembly 1805, winder cassette 1810, strap 1815, and clasp 1820. This illustrates the use position with clasp 1820 engaged with cover 1905 and the location of battery 1910 within housing 1935. A 3:1 scale is shown to give a sense of the size of devices that may correspond to device 1900. However, the scale will vary depending on the size of the diagram presented on the page; i.e., enlargement or reduction will affect the scale, so 3:1 should not be considered limiting.

[0146] On the right side of Figure 25, the winder cassette 1810 is in a use position. The winder cassette frame 2030, spool 2020, spring 2015, angle magnet 2025, and drive pin 2044 cooperate to communicate the angle of rotation of the spool 2020, determined as described elsewhere herein, and the overall length of the circumference measurement about the wearer's limb.

[0147] FIG. 26 is an isometric view 2600 of a device that may correspond to the device 1800 shown in FIG. 18, with the measurement assembly housing removed. The orientation of the figure shows the electronics proximate the limb with the rear housing 1935 removed for illustrative purposes only. The electronics subassembly 1915 may include components for sensing physiological parameters such as heart rate, SPO2, and NIBP. In this example, a light emitter 2615, which may emit light at green, red, and infrared wavelengths, is shown and placed proximate the wearer's core. Light from this light emitter component travels into the wearer's skin. A portion of this light is reflected and sensed by detector components 2605 and 2610. The returned light is sensed and evaluated by software. The raw or evaluated measurements can then be transmitted to another computing device.

[0148] In some embodiments, the device 1900 can use orientation information detected by the accelerometer to detect when the patient is horizontal or at rest. Resting heart rate is sampled. Variability in resting heart rate is known to change as the patient retains fluid. These heart rate readings can be used to increase the reliability of the interpretation of circumference measurements.

[0149] Limb circumference measurements and limb orientation data can be obtained continuously at evenly spaced intervals and processed to generate an individual daily swelling pattern for the subject wearing the device, characterized by a minimum limb circumference that occurs when the subject is lying down and a maximum limb circumference after the subject has been in an upright position, such as standing or sitting, for a period of time that is specific to that individual.

[0150] Trends in fluid gain or loss can be calculated for specified periods, such as days, weeks, or months. Fluid gain or loss and trends in fluid gain or loss can be compared to thresholds to identify conditions of interest. The system takes actions specific to the condition of interest, including sending messages and alerts to the user as well as support personnel, such as family caregivers, chronic care managers, and / or clinical personnel.

[0151] The rate at which fluid redisperses itself within the body when standing up vertically can indicate the viscosity of the interstitial fluid, and changes in viscosity are known to be associated with heart failure decompensation due to changes in protein levels in the interstitial fluid. This is typically assessed by a physician pressing firmly against the patient's ankle to see if the resulting "pitting" resolves quickly. If the pitting does not resolve quickly, the condition is described as pitting edema. This is an important medical sign and a useful diagnostic tool in characterizing a patient's condition.

[0152] The disclosed techniques can characterize the rate of change in interstitial fluid redistribution. By taking multiple measurements as a patient transitions from a supine to an upright position, typically in the morning, it is possible to track the time it takes for interstitial fluid redistribution to occur relative to the change in the direction of gravity. This measurement of the rate of change is directly related to the viscosity of the interstitial fluid. The ability to recognize interstitial fluid viscosity and its associated changes can provide further information to a medical professional or computational algorithm regarding changes in a patient's disease state, as the viscosity of the interstitial fluid can provide insight into the underlying cause of fluid load (e.g., changes in protein levels in the interstitial fluid).

[0153] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of the claims that follow.

Claims

1. 1. A device for determining a level of interstitial swelling in a subject, comprising: A winder cassette, Frame, a capture mechanism supported by the frame, the capture mechanism including a drive pin, the drive pin having a first spring coupling portion; a spring coupled to the capture mechanism via the first spring coupling; and a spool supported by the frame and surrounding the spring, the spool supporting a first magnet and having a second spring coupling portion through which the spool is coupled to the spring; a winder cassette including:

1. A measurement assembly comprising: an electronics subassembly comprising: a measurement component including a first magnetic sensor positioned to be magnetically couplable to the first magnet; one or more processors; a memory; and executable instructions stored in the memory that, when executed by the one or more processors, cause the one or more processors to: determining a first measurement of a first magnetic coupling between the first magnet and the first magnetic sensor; determining a first angle of the spool around which the strap is wound based on the first measurement; determining a rotational speed of the spool; determining a length of strap unwound from the spool based on the first angle and number of rotations of the spool; determining a first perimeter representing interstitial fluid volume based on the length of the strap unwound from the spool; Executable instructions for performing operations including: a measurement assembly including the electronics subassembly, Devices that include:

2. at least one interrupt circuit including a magnetic sensor and configured to generate an interrupt to one of the one or more processors; 10. The device of claim 1, wherein in response to an interrupt rate exceeding a preset threshold, the one of the one or more processors enters a predefined state.

3. The device of claim 3 , wherein the predefined state is a power-on mode.

4. The device of claim 3 , wherein the predefined state is an advertisement mode.

5. a magnetic sensor configured to output at least two analog signals related to the angular position of the spool; at least one interrupt circuit including a magnetic sensor; and The device of claim 1 , wherein, in response to detecting an interrupt associated with a full rotation of the spool, the number of rotations is ascertained using the angle of the spool determined from the angular position.

6. further comprising a second magnet supported by the frame; the measuring component further includes a second magnetic sensor positioned to be magnetically coupleable to the second magnet, and the operation determining a polarity of a second magnetic coupling between the second magnet and the second magnetic sensor; determining a maximum stretch of the strap based on the polarity; The device of claim 1 further comprising:

7. 2. The device of claim 1, wherein the first spring coupling portion includes a protrusion configured to couple with a corresponding first opening of the spring, and the second spring coupling portion is a protrusion configured to couple with a corresponding second opening of the spring.

8. 1. A computer-implemented method for determining interstitial volume increase or decrease in a subject, comprising: via a frame, a capture mechanism supported by the frame, the capture mechanism including a magnet, a spring supported by the capture mechanism, and one or more magnetic sensors in a winder cassette including a spool supported by the frame and surrounding the spring, the spool supporting the magnet; and a measurement assembly, the measurement assembly including an electronics subassembly, the electronics subassembly including a measurement component including a magnetic sensor arranged to be magnetically coupleable to the magnet, one or more processors, a memory, and executable instructions stored in the memory; The executable instructions, when executed by the one or more processors, cause the one or more processors to: determining a measurement of magnetic coupling between the magnet and the magnetic sensor; determining a first diameter of the spool on which the strap is wound based on the measurements, the first diameter comprising the diameter of the spool itself plus a wound thickness of the strap wound on the spool; determining a first circumference of the wound spool based on the first diameter; determining a length of the strap wound on the spool based on the first circumference, the length being the total length of the strap minus the amount of the strap wound on the spool; determining a level of interstitial swelling based on said length; To perform an action including A method comprising:

9. determining a change in the circumference of the strap on the wound spool that exceeds a preset length threshold; triggering at least one of the one or more processors to enter a predefined state in response to determining the change in the perimeter exceeding the preset length threshold; The method of claim 8 further comprising:

10. The method of claim 9 , wherein the predefined state is a start-up mode.

11. determining an interrupt rate to one of the one or more processors; triggering the one of the one or more processors to enter a predefined state in response to the interrupt rate exceeding a preset threshold; The method of claim 8 further comprising:

12. The method of claim 11 , wherein the predefined state is a start-up mode.

13. determining a change in the circumference of the strap on the wound spool that exceeds a preset acceleration threshold; triggering the one of the one or more processors to enter a predefined state in response to determining the change in the perimeter exceeding the preset acceleration threshold; The method of claim 8 further comprising:

14. The method of claim 13 , wherein the predefined state is a start-up mode.

15. 10. The method of claim 8, further comprising integrating said determination of said level of interstitial swelling with automated real-time control of patient therapy.

16. 10. One or more non-transitory computer-readable media comprising executable instructions that, when executed by one or more processors, cause the one or more processors to perform operations to determine an increase or decrease in interstitial volume in a subject via a frame, a capture mechanism supported by the frame, the capture mechanism including a magnet, a spring supported by the capture mechanism, and one or more magnetic sensors in a winder cassette including a measurement assembly, the measurement assembly including: an electronics subassembly, the electronics subassembly including a measurement component including a magnetic sensor positioned to be magnetically coupleable to the magnet; the one or more processors; and a memory, the operations comprising: Determining a first measurement of a first magnetic coupling between the first magnet and the first magnetic sensor; determining a first angle of the spool around which the strap is wound based on the first measurement; determining a rotational speed of the spool; determining a length of strap unwound from the spool based on the first angle and number of rotations of the spool; determining a first perimeter representing the volume of interstitial fluid in the subject based on the length of the strap unwound from the spool; 1. One or more non-transitory computer-readable media including:

17. the electronics subassembly further includes at least one interrupt circuit, the interrupt circuit including a magnetic sensor, for generating an interrupt to one of the one or more processors, and the operation comprises: determining a rate of said interruption; triggering the one of the one or more processors to enter a predefined state in response to the interrupt rate exceeding a preset threshold; 20. The one or more non-transitory computer-readable media of claim 16, further comprising:

18. 20. The one or more non-transitory computer-readable media of claim 17, wherein the predefined state is a power-on mode.

19. 20. The one or more non-transitory computer-readable media of claim 17, wherein the predefined state is an advertise mode.

20. The operation is Integrating determination of the level of interstitial swelling with automated real-time control of patient therapy 20. The one or more non-transitory computer-readable media of claim 16, further comprising:

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