Dynamic sampling frequency adjustment for optical sensing

Abstract

According to some embodiments, a medical device includes an optical sensor arrangement configured to provide an optical signal associated with the patient, a processor, and a memory operably coupled to the processor and storing instructions. When executed by the processor, the instructions cause the medical device to perform operations including receiving the optical signal, identifying a target time interval in the optical signal, and modifying sampling parameters of the optical sensor arrangement such that the optical sensor arrangement provides the optical signal at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval, wherein the first sampling frequency and the second sampling frequency are different. The method may further include operating the optical sensor arrangement to provide the optical signal using the modified sampling parameters.

Description

Atty Ref. No. A0011262W001DYNAMIC SAMPLING FREQUENCY ADJUSTMENT FOR OPTICAL SENSING

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 733,327, filed December 12, 2024, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present technology relates to dynamic sampling frequency adjustment for optical sensing.BACKGROUND

[0003] Many medical devices (e.g., pulse oximeters) utilize photoplethysmography (PPG), an optical technique that can be used to detect volumetric changes in blood in peripheral circulation. For example, PPG can be used to detect blood volume changes in the microvascular bed of tissue. PPG can, for example, provide quantification of physiological metrics such as blood pressure, heart rate, and blood oxygenation levels.

[0004] In general, PPG involves operation of an optical emitter-detector pair, where the emitter is a light source that illuminates tissue of interest, and the detector operates in a reflectance mode or transmission mode to measure the amount of that light that is reflected or otherwise transmitted to the detector. Some PPG devices are external (e.g., wearable), while some PPG devices are implantable in a patient.

[0005] Implantable medical devices are often powered by a power supply (e.g., battery) having a finite energy supply that must be carefully budgeted for operation of the device. This problem is further exacerbated by the performance of optical sensing, which consumes a large amount of power compared to other operations, such as due to repeated and extended activation of optical emitters enabling optical sensing. Accordingly, power consumption often in particular limits the device lifetime and / or other operation of implanted optical sensing devices.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily toAtty Ref. No. A0011262W001 scale. Instead, emphasis is placed on illustrating clearly the principles of the present disclosure.10007] FIG. 1 is an illustrative conceptual diagram of an example optical device, in accordance with the present technology.10008] FIG. 2 is an illustrative schematic of example circuitry for processing signals from an optical sensor, in accordance with the present technology.

[0009] FIG. 3A is an illustrative schematic of an example embodiment of an implantable medical device, in accordance with the present technology.

[0010] FIG. 3B is an illustrative conceptual diagram of an example embodiment of an implantable medical device, in accordance with the present technology.

[0011] FIG. 4 is an illustrative schematic of a cardiac monitoring system including an implantable medical device placed in a patient, in accordance with the present technology.|0012] FIG. 5 is a conceptual perspective schematic diagram of an example embodiment of an implantable medical device, in accordance with various examples described in this disclosure.

[0013] FIG. 6 is an illustrative flowchart of an example method for operating a medical device with an optical sensor arrangement, in accordance with the present technology.

[0014] FIG. 7 is an illustrative schematic of an optical signal for a patient over multiple cycles, in accordance with the present technology.DETAILED DESCRIPTION

[0015] The present technology relates to methods and system for performing optical sensing. Some embodiments of the present technology, for example, are directed to dynamically adjusting the sampling frequency for optical sensing. Specific details of several embodiments of the technology are described below with reference to FIGS. 1-7.

[0016] Many implantable devices are limited in their operation (e.g., lifetime) due to power constraints, as they may be powered by a power supply of limited capacity (e.g., battery, or limited access to other external power source). Many sensing devices, for example, consume a large amount of power during the process of activating (e.g., turningAtty Ref. No. A0011262W001 on) one or more optical emitters to cause the emitter(s) to output light, and using one or more optical detectors in a reflectance mode and / or transmission mode to detect light to generate a meaningful optical signal (e.g., to provide information about the environment surrounding the sensing device). Such large power consumption can drain a power supply, thereby reducing the overall lifetime of the sensing device.

[0017] One strategy for extending device lifetime is reducing the amount of time that the optical sensing device actively performs optical sensing. For example, optical sensing may be performed only at limited times during the day (e.g., 1-5 minutes in total across a 24-hour period). Additionally or alternatively, each time optical sensing is performed, the optical emitter(s) may be activated at a low number of times per unit (e.g., at a reduced sampling frequency) to thereby conserve power. However, excessively reducing the amount of time for optical sensing and reducing the sampling frequency can result in loss of useful data, which in turn can limit the accuracy of optical measurements and any conclusions drawn from such optical measurements (e.g., physiological measurements for a patient).|0018] Described herein are methods and systems to reduce power consumption while maintaining accuracy and reliability of a cuffless blood pressure measurement, by dynamically adjusting the sampling rate of the emitter in a manner that balances power savings and optical data acquisition. As described in further detail herein, the sampling rate can, for example, be dynamically adjusted at least in part based on morphology of the optical signal (e.g., PPG waveform) and concurrent sensor data such as electrocardiogram (EGM) data, heart sound data, etc.

[0019] The techniques described herein may be used in various optical sensing devices configured to generate an optical signal using one or more optical emitters and one or more optical detectors. For example, FIG. 1 is an illustrative schematic of an example optical sensing device 100, which includes an optical sensor arrangement 110, electrical circuitry 120, and a power source 130.I. Optical sensing devices and systems

[0020] The optical sensor arrangement 110 may include a detector set of one or more detectors, and, in some embodiments, may further include an emitter set of one or more emitters. Embodiments of the optical sensor arrangement 110 may, for example, omit anAtty Ref. No. A0011262W001 emitter set and include the detector set for passive detection of light from ambient and / or external light sources. The emitter set and the detector set may, in some embodiments, be located under an optically transparent surface (e.g., sapphire, glass, ceramic) of the optical sensing device, so as to allow passage of light out of and into the optical sensing device 100. Each emitter may be configured, when activated, to emit light at a desired wavelength suitable for optical signal measurements, such as photoplethysmography (PPG). For example, an emitter in the optical sensor arrangement 110 may be configured to emit light at a red wavelength (e.g., 640 nanometers (nm)-660 nm, or about 660 nm), a green wavelength (e.g., 530 nm-550 nm, or about 550 nm), or an infrared wavelength (e.g., 880 nm-940 nm, or about 940 nm). In some embodiments, light emitted from an active emitter may be filtered with one or more suitable filters in the optical pathway between the emitter and a corresponding detector in an emitter-detector pair being used to generate an optical signal (e.g., a PPG signal). Such filter(s) may block wavelengths that are not of interest for illuminating tissue, and pass through wavelengths that are of interest for illuminating tissue. For example, the filter(s) may include one or more suitable low-pass filters, high-pass filters, bandpass filters, or bandstop filters. The filter(s) may be coupled to an output side of the emitter or otherwise located in the optical pathway between the emitter and the detector. The emitter set may include any suitable type of light source, including, for example, a lightemitting diode (LED). Furthermore, each detector in the detector set may be configured to detect light that is emitted from an emitter and reflected off tissue of interest, where an optical signal such as a PPG signal may be derived from measurements of the reflected light. For example, a detector in the optical sensor arrangement 110 may include a photodiode. Various example configurations of the optical sensor arrangement 110 are described in further detail below.|0021] The electrical circuitry 110 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for operating the optical sensor arrangement 110 (e.g., activating the emitter(s) in the emitter set) and / or generating a signal (e.g., a PPG signal). For example, the electrical circuitry 120 may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or other analog signal conditioning circuits.

[0022] The electrical circuitry 120 and / or other portions of the optical sensing device 100 may also include digital circuits, e.g., switches, logic gates, multiplexers, diodes,Atty Ref. No. A0011262W001 transistors, combinational or sequential logic circuits, state machines, digital filters, integrated circuits, one or more processors 124 (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices 126, or any other suitable components or combination thereof that provide the described functionality. For example, in some embodiments, the optical signal is analyzed (e.g., by the one or more processors 124) to obtain one or more various physiological metrics of the patient, such as blood volume, blood flow, blood pressure, heart rate, blood oxygenation, tissue perfusion, and / or the like. Rates of change and / or comparisons against threshold values for the one or more various physiological metrics of the patient can also be analyzed (e.g., by one or more processors).

[0023] In some embodiments, the electrical circuitry 120 includes and / or is coupled to additional circuitry that provides for analog-to-digital conversion of at least one signal (e.g., a voltage signal, a current signal). In some embodiments, the electrical circuitry 120 includes and / or is coupled to additional circuitry that provides for digital-to-analog conversion of at least one signal (e.g., a control signal, a current signal).

[0024] The power source 130 provides power to electrical circuitry 120, the optical sensor arrangement 110, as well as to any other components that require power. Power source 130 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries.

[0025] The electrical circuitry 120 may include optical circuitry 128 configured for processing one or more sensor outputs from the detector set. The optical circuitry 128 may comprise, for example, an integrator amplifier that transforms a signal from an optical detector to a voltage signal that can be delivered to one or more components in the electrical circuitry 120. The optical circuitry 128 can be electrically and / or operatively coupled to the optical sensor arrangement 110 and / or the power source 130.

[0026] FIG. 2 is an illustrative schematic of an example circuit 200 for processing signals from an optical sensor. FIG. 2 shows a representative example of an integrator amplifier circuit 200 configured to translate a current (IN) from a sensor (e.g., an optical detector) into a voltage waveform (VOUT) measurable by an analog-to-digital converter. More specifically, the circuit 200 includes an integrating capacitor (CINT) configured to integrate the detector current (IN) over a suitable integration time. In some embodiments, the integrating capacitor (CINT) is a non-polarized capacitor (e.g., a ceramic capacitor, a filmAtty Ref. No. A0011262W001 capacitor, a paper capacitor). In some embodiments, the integrating capacitor is a polarized capacitor (e.g., an electrolytic capacitor). Though only as a single integrating capacitor (CINT) in FIG. 2, one of skill in the art will be appreciated that two or more capacitors could be used, such as two or more capacitors in series, two or more capacitors in parallel, three or more capacitors in a series-parallel combination, three or more capacitors in a delta-wye combination, etc.|0027] In some embodiments of the present technology, a value associated with the detector current integrated over a period of time can be stored as a charge imbalance in the circuit 200 (e.g., as a voltage across the integrating capacitor (CINT)) and / or elsewhere (e.g. a component of the electrical circuitry 120). The capacitor may have a fixed or variable capacitance value, and the integration time may be fixed or adjustable. Thus, in some embodiments, the capacitance value and / or the integration time may be adjusted (e.g., via other components of electrical circuitry 120) to vary the gain and / or attenuation factor of the detector signal. Furthermore, the capacitance value and / or integration time may be measured (e.g., a timer can measure the integration time of the capacitor) and the measured value can be used to adjust one or more parameters of one or more components comprising the optical sensing device. For example, a magnitude of current delivered by the optical sensing device can be increased inversely with integration time of the capacitor. In some embodiments, a calibration current used to cancel a portion of an optical signal associated with ambient light is scaled to a ratio of time taken to saturate the capacitor (e.g., reach a maximal voltage across the capacitor) and the time taken to sense the ambient light.

[0028] In some embodiments, a switch (e.g., a reset switch) is in parallel with the integrating capacitor so as to facilitate discharging accumulated charges from the integrating capacitor (e.g., by shorting the capacitor). In some embodiments, one or more switches (e.g., float switches) are in series with the integrating capacitor so as to facilitate electrical isolation of the capacitor from other circuit elements. The integrating capacitor being electrically isolated from other circuit elements enables charge stored across the capacitor to be selectively engaged before, during, and / or after a sensing period. For example, during a first period of time, the integrating capacitor coupled in series to one or more switches is connected to the integrator amplifier and accumulates charge and during a second period of time, the one or more switches electrically disconnect the integrating capacitor from the integrator amplifier and stops accumulating charge. In some embodiments, during a thirdAtty Ref. No. A0011262W001 period of time, the capacitor can be reconnected to the integrator amplifier via the one or more switches and thereby cause charges stored through the capacitor to interact with the optical circuitry 200 (e.g., to condition a signal from the optical sensor).

[0029] Additionally or alternatively, the signal current of the detector may be sampled for more time (e.g., as controlled by other components of electrical circuitry 120), which may result in an increase of the gain and signal-to-noise ratio (SNR) of the optical signal, with the tradeoff of a lower available sampling rate. Further details regarding optical circuitry of the present technology are shown and described herein (e.g., in connection with FIGS. 6A-6B and 8A-8B).

[0030] In some embodiments, the techniques described herein for extending an ambient light cancellation range of optical sensing can be performed with respect to generating a PPG signal with an implantable device such as an implantable medical device. FIG. 3A is a conceptual diagram of an example of an implantable medical device (IMD) 300 (also referred to herein as a “cardiac monitoring device”) for detecting a bradycardia / asystole event, according to another embodiment of the present disclosure. Implantable medical device 300 is an example of optical sensing device 100. In the example shown in FIG. 3 A, implantable medical device 300 may be embodied as a monitoring device having housing 302, a first (e.g., proximal) electrode 304, and a second (e.g., distal) electrode 306. Housing 302 may further comprise a first major surface 308, a second major surface 310, a first (e.g., proximal) end 312, and a second (e.g., distal) end 314. Housing 302 encloses electronic circuitry 350 and power source 352 (shown in FIG. 3B) located inside the implantable medical device 300 and protects the circuitry contained therein from body fluids. Electrical feedthroughs provide electrical connection of electrodes 304 and 306.

[0031] In some embodiments such as that shown in FIG. 3A, implantable medical device 300 is defined by a length L, a width W and thickness or depth D. The implantable medical device 300 may be in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D. In some embodiments, the geometry of the implantable medical device 300 (for example, a width W greater than the depth D) may be selected to allow the implantable medical device 300 to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insert. For example, the device shown in FIG. 3 A may include radial asymmetries (notably, the rectangular shape) along the longitudinal axis thatAtty Ref. No. A0011262W001 maintains the device in the proper orientation following insertion. For example, in some embodiments the spacing between the proximal electrode 304 and distal electrode 306 may range from 30 millimeters (mm) to 55 mm, 35 mm to 55 mm, and from 40 mm to 55 mm and may be any range or individual spacing from 25 mm to 60 mm. In addition, implantable medical device 300 may have a length L that ranges from 30 mm to about 70 mm. In other embodiments, the length L may range from 40 mm to 60 mm, 45 mm to 60 mm and may be any length or range of lengths between about 30 mm and about 70 mm. In addition, the width W of major surface 308 may range from 3 mm to 10 mm and may be any single or range of widths between 3 mm and 10 mm. In some embodiments, the thickness of depth D of the implantable medical device 300 may range from 2 mm to 9 mm. For example, the depth D of the insertable cardiac monitor 300 may range from 2 mm to 5 mm and may be any single or range of depths from 2 mm to 9 mm. In addition, implantable medical device 300 according to an example embodiment of the present invention has a geometry and size designed for ease of implant and patient comfort. Embodiments of the implantable medical device 300 described in this disclosure may have a volume of three cubic centimeters (cm) or less, 1.5 cubic cm or less or any volume between three and 1.5 cubic centimeters.

[0032] In the example shown in FIG. 3A, once inserted within the patient, the first major surface 308 faces outward, toward the skin of the patient while the second major surface 310 is located opposite the first major surface 308. In addition, in the example shown in FIG. 3 A, proximal end 312 and distal end 314 are rounded to reduce discomfort and irritation to surrounding tissue once inserted under the skin of the patient. Implantable medical device 300, including instrument and method for inserting monitor 300 is described, for example, in U.S. Patent Publication No. 2014 / 0276928, incorporated herein by reference in its entirety.

[0033] In some embodiments a proximal electrode 304 and a distal electrode 306 are used to sense cardiac signals for determining a cardiac event (e.g., bradycardia or asystole event) such as EGM signals, intra-thoracically or extra-thoracically, which may be sub-muscularly or subcutaneously. EGM signals may be stored in a memory of the implantable medical device 300, and EGM data may be transmitted via integrated antenna 322 to another medical device, which may be another implantable device or an external device.Atty Ref. No. A0011262W001

[0034] In the example embodiment shown in FIG. 3A, proximal electrode 304 is in close proximity to the proximal end 312 and distal electrode 306 is in close proximity to distal end 314. In this embodiment, distal electrode 306 is not limited to a flattened, outward facing surface, but may extend from first major surface 308 around rounded edges 316 and onto the second major surface 310 so that the electrode 306 has a three-dimensional curved configuration. In the example embodiment shown in FIG. 3A, proximal electrode 304 is located on first major surface 308 and is substantially flat, outward facing. However, in other embodiments, proximal electrode 304 may utilize the three-dimensional curved configuration similar to that of distal electrode 306, providing a three-dimensional proximal electrode (not shown in this embodiment). Additionally or alternatively, in other embodiments, distal electrode 306 may utilize a substantially flat, outward facing electrode located on first major surface 308 similar to that shown with respect to proximal electrode 304. The various electrode configurations allow for configurations in which proximal electrode 304 and distal electrode 306 are located on both first major surface 308 and second major surface 310. In other configurations, such as that shown in FIG. 3 A, only one of proximal electrode 304 and distal electrode 306 is located on both major surfaces 308 and 310, and in still other configurations both proximal electrode 304 and distal electrode 306 are located on one of the first major surface 308 or the second major surface 310 (e.g., proximal electrode 304 located on first major surface 308 while distal electrode 306 is located on second major surface 310). In some embodiments, the implantable medical device 300 may include electrodes on both major surface 308 and 310 at or near the proximal and distal ends of the device, such that a total of at least four electrodes are included on implantable medical device 300. Electrodes 304 and 306 may be formed of a plurality of different types of biocompatible conductive material (e.g. stainless steel, titanium, platinum, iridium, or alloys thereof), and / or may utilize one or more coatings such as titanium nitride or fractal titanium nitride.

[0035] In the example shown in FIG. 3 A, proximal end 312 includes a header assembly 320 that includes one or more of proximal electrode 304, an integrated antenna 322, anti-migration projections 324, and / or suture hole 326. The integrated antenna 322 may be located on the same major surface (e.g., first major surface 308) as proximal electrode 304 and may also be included as part of header assembly 320. Integrated antenna 322 allows implantable medical device 300 to transmit and / or receive data. In some embodiments, integrated antenna 322 may be formed on the opposite major surface as proximal electrodeAtty Ref. No. A0011262W001304, or may be incorporated within the housing 322 of implantable medical device 300. In the example embodiment shown in FIG. 3 A, anti-migration projections 324 are located adjacent to integrated antenna 322 and protrude away from first major surface 308 to prevent longitudinal movement of the device, though may be arranged on any suitable surface of the implantable medical device 300. In the example embodiment shown in FIG. 3A, antimigration projections 324 include a plurality (e.g., nine) small bumps or protrusions extending away from first major surface 308; however, anti-migration projections 324 may additionally or alternatively be located on the opposite major surface as proximal electrode 304 and / or integrated antenna 322. As shown in FIG. 3A, the suture hole 326, which may be used to help secure the implantable medical device 300 in the patient to prevent movement following insertion of the implantable medical device 300, may be located adjacent to proximal electrode 304, though one or more suture holes 326 may additionally or alternatively be located in any other suitable location. In some embodiments, the header assembly 320 is a molded header assembly made from a polymeric or plastic material, which may be integrated or separable from the main portion of implantable medical device 300.10036] FIG. 5 is a conceptual perspective schematic diagram of an implantable medical device 500 (IMD 500), according to various examples described in this disclosure. IMD 500 may be a leadless, subcutaneously implantable monitoring device including a proximal electrode 502A located at proximal end 504, a distal electrode 502B located at distal end 506 (collectively “electrodes 502”), a housing 508, electrical circuitry, an optical sensor arrangement 510 (comprising, for example optical sensor(s)), an integrated antenna 512, and a power source. In particular, electrical circuitry is coupled to proximal electrode 502B and distal electrode 502A to sense cardiac signals and monitor events. Electrical circuitry may also be connected to transmit and receive communications via integrated antenna 512. The power source can provide power to electrical circuitry, as well as to any other components that require power. The power source may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. In some examples, electrical circuitry includes processing circuitry and a storage device, such as memory (e.g., as shown in FIG. 3B), the memory being operatively coupled to the processing circuitry and configured to store data and / or instructions.

[0037] In the example shown in FIG. 5, electrical circuitry may receive raw EGM or EMG (electromyography) signals monitored by the proximal electrode 502A and distalAtty Ref. No. A0011262W001 electrode 502B and raw optical signals monitored by the optical sensor arrangement 510. Electrical circuitry may include components / modules for converting the raw EGM signal to a processed EGM signal that can be analyzed to detect sense events and for converting the raw optical signals to calibrated processed optical signal(s) that can be analyzed to detect sense events. Although not shown, electrical circuitry may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for analyzing optical signal(s) to determine a health condition status of a patient. For example, the electrical circuitry may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or other analog signal conditioning circuits. The modules may also include digital circuits, e.g., digital filters, combinational or sequential logic circuits, state machines, integrated circuits, a processor (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices, or any other suitable components or combination thereof that provide the described functionality.

[0038] In one example, electrical circuitry includes a sensing unit for monitoring the EGM signal detected by the respective proximal 502A and distal electrodes 502B and light signals received by the optical sensor arrangement 510, respectively. In one example, electrical circuitry includes processing circuitry that is utilized to receive information regarding sensed events and implements one or more algorithms for determining a health condition status of a patient. In addition, the analog voltage signals received from the electrodes 502 may be passed to anal og-to-digi tai (A / D) converters included in the electrical circuitry and stored in a memory unit included as part of electrical circuitry for subsequent analysis with firmware executed by the processor included as part of electrical circuitry.

[0039] Some embodiments of the HMD 500 (e.g., examples shown in FIGS. 3 A, 3B, and 5) include a container 514 and an insulative cover 516. In some examples, the insulative cover 516 may include an optical window. In some examples, the optical window may be formed of the same material as insulative cover 516. In some examples, the optical window may be a portion of insulative cover 516. The proximal electrode 502A and the distal electrode 502B may be formed or placed on an outer surface of cover 516. The electrical circuitry may be formed or placed on an inner surface of cover 516, or within container 514. In some examples, the antenna 512 is formed or placed on the inner surface of cover 516. In other examples, antenna 512 is formed or placed on the outer surface of cover 516, andAtty Ref. No. A0011262W001 in other examples, antenna 512 may be formed or placed at least partially on the inner surface and partially on the outer surface of cover 516. In some examples, insulative cover 516 may be positioned over an open container 15 such that container 514 and cover 516 form housing 20 and enclose electrical circuitry (and in some cases antenna 512) and protect the circuitries from fluids such as body fluids. For example, the housing 508 may be a hermetically-sealed housing configured for subcutaneous implantation within a patient, wherein at least the power source, memory, and processing circuitry are within the hermetically-sealed case, and in some examples, the optical sensor arrangement 510 are within the hermetically-sealed case.

[0040] The electrical circuitry may be formed on the inner side of insulative cover 516, such as by using flip-chip or wire bond integrated circuit packaging technology. Insulative cover 516 may be flipped onto a container 514. When flipped and placed onto container 514, the components of IMD 500 formed on the inner side of insulative cover 516 may be positioned in a gap defined by container 514. The electrodes 502 and the antenna 512 (when placed or formed on the outer surface of cover 516) may be electrically connected to sensing circuitry and communication circuitry, respectively, e.g., through one or more vias formed through insulative cover 516. The insulative cover 516 may be formed of sapphire (i.e., corundum), glass, and / or any other suitable insulating material. The container 514 may be formed from any suitable material configured to house electrical circuitry, support and mate with cover 516 to isolate electrical circuitry from contact with tissue and / or fluids of a patient, and to be implantable within the patient. In some examples, container 514 may house power source (e.g., a battery). In some examples, container 514 may also be electrically conductive. For example, container 514 may be formed from titanium or any other suitable material (e.g., a biocompatible material). Electrodes 502 may be formed from any of stainless steel, titanium, platinum, iridium, or alloys thereof. In addition, electrodes 502 may be coated with a material such as titanium nitride or fractal titanium nitride, although other suitable materials and coatings for such electrodes may be used.

[0041] In some embodiments, the IMD 500 is defined by a length L, a width W and thickness or depth D and is in the form of an elongated rectangular prism wherein the length L is much larger than the width W, which in turn is larger than the depth D, as illustrated in FIG. 5. In one example, the geometry of the IMD 500 - in particular a width W greater thanAtty Ref. No. A0011262W001 the depth D - is selected to allow the IMD 500 to be inserted under the skin of the patient using a minimally invasive procedure and to remain in the desired orientation during insert. For example, the IMD 500 may include a radial asymmetry (notably, a rectangular shape) along the longitudinal axis that maintains the device in the proper orientation following insertion. For example, in one example the spacing between the proximal electrode 502A and the distal electrode 502B may range from 30 millimeters (mm) to 55 mm, 35 mm to 55 mm, and from 40 mm to 55 mm and may be any range or individual spacing from 25 mm to 60 mm. In another example the spacing between the proximal electrode 502A and the distal electrode 502B may range from 15 mm to 30 mm, 17 mm to 28 mm, and from 20 mm to 28 mm and may be any range or individual spacing from 12 mm to 30 mm. In addition, the IMD 500 may have a length L that ranges from 30 mm to about 70 mm. In other embodiments, the length L may range from 40 mm to 60 mm, 45 mm to 60 mm and may be any length or range of lengths between about 30 mm and about 70 mm. In some examples, the IMD 500 may have a length L that ranges from 15 mm to about 35 mm, or from 20 mm to 30 mm, 22 mm to 30 mm and may be any length or range of lengths between about 15 mm and about 35 mm. In addition, the width W of a major surface of the IMD 500, e.g., insulative cover 516 in the example shown in FIG. 5, may range from 3 mm to 10 mm and may be any single or range of widths between 3 mm and 10 mm, or may range from 1.5 mm to 5 mm and may be any single or range of width between 1.5 mm and 5 mm. The thickness of depth D of the IMD 500 may range from 2 mm to 9 mm, or from 1.5 mm to 4.5 mm. In other embodiments, the depth D of the IMD 500 may range from 2 mm to 5 mm and may be any single or range of depths from 2 mm to 9 mm, or may range from 1 mm to 2.5 mm and may be any single or range of depths from 1 mm to 4.5 mm. In addition, IMD 500 according to an example of the present invention has a geometry and size designed for ease of implant and patient comfort. Examples of the IMD 500 described in this disclosure may have a volume of 3 cubic centimeters (cm) or less, 1.5 cubic cm or less or any volume between 3 and 1.5 cubic centimeters, or may have a volume of 1.5 cubic centimeters (cm) or less, 0.75 cubic cm or less or any volume between 1.5 and 0.75 cubic centimeters.|0042] FIG. 3B is a functional schematic diagram of an implantable medical device, such as implantable medical device 300 as shown in FIG. 3 A in accordance with the present technology. Although the reference numbers refer to implantable medical device 300, it should be understood that other implantable medical devices (e.g., IMD 500) can include one or more components similar to that described below. Implantable medical device 300Atty Ref. No. A0011262W001 includes housing 302, proximal electrode 304 located at proximal end 312, distal electrode 306 located at distal end 314, integrated antenna 322, electrical circuitry 350 (which is an example of electrical circuitry 120), and power source 352 (which is an example of power source 130). In some embodiments, the implantable medical device 300 includes an optical sensor arrangement 360 (an example of optical sensor arrangement 110) comprising an emitter set of one or more optical light emitters and a detector set of one or more optical light detectors. The optical sensor arrangement 360 may, for example, be configured to provide a photoplethysmography (PPG) signal using the emitter and detector sets. The implantable medical device 300 may include a secondary sensor arrangement 370 including one or more sensors configured to provide additional sensing capabilities (e.g., other sensor data concurrently or asynchronously with optical sensor data from the optical sensor arrangement 360).

[0043] The optical sensor arrangement 360 can be configured to sense through one or more surfaces of the implantable medical device 300 (e.g., first major surface 308, second major surface 310, a surface of the header assembly 320). In some embodiments, one or more portions of the one or more surfaces comprise a material that is optically transparent to at least some wavelengths of light. For example, the one or more portions of the one or more surfaces through which the optical sensor arrangement 360 senses can be transparent to a red wavelength, transparent to a green wavelength, and / or transparent to an infrared wavelength. In some embodiments, the one or more portions of the one or more surfaces are optically transparent to visible light (e.g., electromagnetic radiation with a wavelength from approximately 380 nm to approximately 780 nm). The orientation of the optical sensor arrangement 360 with response to a patient is based on the implantation of the implantable medical device 300. For example, in some embodiments (e.g., embodiments wherein the optical sensor arrangement 360 senses through the first major surface 308), the optical sensor arrangement 360 is directed away from a center of the patient (e.g., oriented distally) when the implantable medical device 300 is implanted within the patient, and thus is exposed to a maximal amount of ambient light.

[0044] Fidelity of ambient light sensing can correlate to factors outside the optical sensor arrangement 360, such as physical activity of a patient and the environment surrounding the patient. Sensing from the optical sensor arrangement 360 can be affected when the patient moves vigorously and / or when then patient is in an environment of intenseAtty Ref. No. A0011262W001 and / or rapidly varying ambient light. In some embodiments, the optical sensor arrangement 360 is configured to sense in response to sensor data (e.g., motion data, optical data). For example, in some embodiments, the secondary sensor arrangement 370 may include a motion sensor (e.g., an accelerometer) that senses physical activity of the patient and while the patient is below a first motion threshold as sensed by the motion sensor (e.g., when the patient is resting, when the patient remains still), electrical circuitry 350 directs (e.g., via optical circuitry 358) the optical sensor arrangement 360 to sense. In some embodiments, the motion sensor senses the patient is above a second motion threshold (e.g., the patient is moving vigorously) and the electrical circuitry 350 directs the optical sensor arrangement 360 not to sense. In some embodiments, the optical sensor arrangement 360 senses for a first period of time to determine whether optical data is suitable for the optical sensor arrangement 360 to sense at a second period of time (e.g., immediately after, continuously until another condition is met) or whether the optical sensor arrangement 360 should sense at a third period of time (e.g., after a duration of time such as 1 minute).

[0045] As described above, the secondary sensor arrangement 370 may, in some embodiments, include a motion sensor such as an accelerometer. However, the secondary sensor arrangement 370 may additionally or alternatively include other suitable secondary sensors, including but not limited to an acoustic sensor (e.g., accelerometer, microphone), respiration sensor, and an impedance sensor (e.g., configured to measure thoracic impedance). The secondary sensor arrangement 370 may include an accelerometer that can provide various information including motion, posture, activity levels, respiration, and / or the like.

[0046] In some embodiments, some or all of the secondary sensor arrangement 370 may be on the implantable medical device 300, on an implantable device that is different from the implantable medical device 300, on an external device (e.g., smartwatch, smart ring, wearable fitness tracker, mobile device such as a mobile phone, other external computing device, etc.), or any combination thereof.

[0047] The electrical circuitry 350 may be coupled to the optical sensor arrangement 360 to sense optical signals (e.g., via the optical circuitry 358) corresponding to PPG and / or ambient light, and / or sense other secondary sensor signals from the secondary sensor arrangement 370. The electrical circuitry 350 may be coupled to the proximal electrode 304 and the distal electrode 306 to sense cardiac signals and monitor events (e.g., arrythmia,Atty Ref. No. A0011262W001 etc.). The electrical circuitry 350 is also connected to transmit and receive communications via integrated antenna 322. The power source 352 provides power to electrical circuitry 350, as well as to any other components that require power. Power source 352 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The implantable medical device 300 as shown in FIGS. 3A and 3B may be a monitoring-only device. However, in other examples, implantable medical device 300 may further provide therapy delivery capabilities.

[0048] The electrical circuitry 350 is configured to receive multiple signal types. For example, the electrical circuitry 350 can receive raw EGM signals monitored by proximal electrode 304 and distal electrode 306 and / or PPG signals monitored by the optical sensor arrangement 360. Electrical circuitry 350 may also include components / modules for converting a raw signal (e.g., EGM, PPG) to a processed signal that can be analyzed to detect sense events. Although not shown, electrical circuitry 350 may include any discrete and / or integrated electronic circuit components that implement analog and / or digital circuits capable of producing the functions described for analyzing EGM and / or PPG signals to detect / verify bradycardia and / or asystole events. For example, the electrical circuitry 350 may include analog circuits, e.g., pre-amplification circuits, filtering circuits, and / or other analog signal conditioning circuits. The modules may also include digital circuits, e.g., digital filters, combinational or sequential logic circuits, state machines, integrated circuits, one or more processors 354 (shared, dedicated, or group) that executes one or more software or firmware programs, memory devices 356, or any other suitable components or combination thereof that provide the described functionality.

[0049] In some embodiments, electrical circuitry 350 may include a sensing unit for monitoring signals detected (e.g., by the proximal electrode 304 and distal electrode 306, by the optical sensor arrangement 360), and at least one sensing channel that utilizes an algorithm for identifying events in the signal (e.g., the EGM signal, the PPG signal). For example, sensed events (e.g., R-waves) are utilized to detect one or more cardiac episodes. In some embodiments, electrical circuitry 350 includes a processor configured to receive information regarding the sensed events and implements one or more algorithms for determining whether a particular one or more events have occurred. In addition, the analog voltage signals received from electrodes 304 and 306 and / or the optical sensor arrangement 360 may be passed to analog-to-digital (A / D) converters (ADC) included in the electricalAtty Ref. No. A0011262W001 circuitry 350, and stored in a memory unit 356 included as part of electrical circuitry 350 for subsequent analysis with firmware executed by the processor(s) 354 included as part of electrical circuitry 350.10050] Electrical circuitry 350 may control implantable medical device 300 functions and process signals received from electrodes 304 and 306 (e.g., EGM signals) and / or the optical sensor arrangement 360 (e.g., optical signals) according to programmed signal analysis routines or algorithms. The implantable medical device 300 may include optical circuitry 358 to facilitate optical signal detection, processing, and / or control. The implantable medical device 300 may include other optional sensors (not shown) for monitoring physiological signals, such as an activity sensor, pressure sensor, oxygen sensor, accelerometer, and / or other sensor used to monitor a patient. These may also be provided to electrical circuitry 350 for processing.

[0051] Electrical circuitry 350 may similarly control monitoring time intervals and sampling rates according to a particular clinical application. In addition, electrical circuitry may include state machines or other sequential logic circuitry to control device functions and need not be implemented exclusively as a microprocessor. For example, electrical circuitry 350 may include timers utilized to detect asystole events as described in more detail below.

[0052] Electrical circuitry 350 communicates with integrated antenna 322 (shown in FIG. 3 A) or other communication to transmit electrical signal data, e.g. EGM signal data, stored in memory or received from electrical circuitry 350 in real time. Antenna 322 may be configured to transmit and receive communication signals via inductive coupling, electromagnetic coupling, tissue conductance, Near Field Communication (NFC), Radio Frequency Identification (RFID), BLUETOOTH®, WiFi, or other proprietary or nonproprietary wireless telemetry communication schemes.

[0053] The electrical circuitry 350 may include a communication module including the integrated antenna 322, so as to enable the implantable medical device 300 to communicate with one or more external devices located external to the device 300. For example, as shown in FIG. 4, a cardiac monitoring system 400 may include an implantable medical device 10 (e.g., of which implantable medical device 300 and implantable medical device 500 are examples), which may include a communication module for communicating with a programmer 410. The programmer 410 may include a user interface that presentsAtty Ref. No. A0011262W001 information to and receives input from a user. In some embodiments, the programmer 410 may include, for example, a suitable computing device such as a tablet, a smartphone, desktop computer, laptop computer, and / or the like. It should be noted that the user may also interact with programmer remotely via a networked computing device. As further shown in FIG. 4, in some embodiments, the implantable medical device 10 and / or the programmer 410 may be configured to transfer and / or receive information (e.g., cardiac data, such as EGM data and / or cardiac episode-related information derived from the EGM data) to and / or from a secondary memory storage device 420, such as over a wired or wireless network.

[0054] A user, such as a physician, technician, surgeon, electrophysiologist, other clinician, or patient, interacts with the programmer to communicate with implantable medical device 10. For example, the user may interact with the programmer to retrieve physiological or diagnostic information from the implantable medical device 10. A user may also interact with the programmer to program the implantable medical device 10, e.g., select values for operational parameters of the implantable medical device 10. For example, the user may use the programmer to retrieve information from the implantable medical device 10 regarding the rhythm of a patient heart, trends therein over time, or arrhythmic episodes. In some embodiments, alerts regarding device status (e.g., health state) and / or regarding type(s) of cardiac episode(s) detection may be provided to the patient or a clinician through the programmer 410, though they may be provided in any suitable manner (e.g., personal smartphone, other computing device, pushed through to an electronic medical record, etc.). The implantable medical device 10 and the programmer may communicate via wireless communication using any techniques known in the art.

[0055] In some embodiments, the implantable medical device 10 can be placed subcutaneously in a patient near or over the patient’s heart. For example, in some embodiments the implantable medical device 10 can be placed in a subcutaneous pocket located over an intercostal space (e.g., over the 4thintercostal space), and positioned at a desirable angle and / or displacement relative to the patient’s sternum (e.g., between about 0 and 45 degrees relative to the sternum, about 2 cm from the left edge of the sternum). Once inserted, the implantable medical device 300 may go through suitable setup and / or calibration processes.Atty Ref. No. A0011262W001

[0056] In some examples, the implantable medical device 10 is implanted outside of a thoracic cavity of a patient (e.g., subcutaneously in a pectoral location). The implantable medical device 10 may be positioned near the sternum near or just below the level of the heart of the patient, e.g., at least partially within the cardiac silhouette. In some embodiments, the implantable medical device 10 includes a plurality of electrodes and is configured to sense a cardiac electrogram (EGM) via the plurality of electrodes, as well as other physiological signals and / or parameters via the optical sensor arrangement 360. In some examples, the implantable medical device 10 takes the form of an insertable cardiac monitor (ICM) such as the LINQ™ or LINQ II™ ICM, or other ICM similar to, e.g., a version or modification of the LINQ™ or LINQ II™ ICM. Although described primarily in the context of examples in which implantable medical device 10 is an ICM, in various examples, the implantable medical device 10 may represent a cardiac monitor, a defibrillator, a cardiac resynchronization pacer / defibrillator, a pacemaker, an implantable pressure sensor, a neurostimulator, or any other implantable or external medical device.

[0057] Depiction of different features as modules is intended to highlight different functional aspects and does not necessarily imply that such modules must be realized by separate hardware or software components. Rather, functionality associated with one or more modules may be performed by separate hardware, firmware and / or software components, or integrated within common hardware, firmware and / or software components.

[0058] Furthermore, it should be understood that the systems and methods described herein in accordance with the present technology are not limited to the implantable medical devices 300, 500 described herein with respect to FIGS. 3A, 3B and 5. Rather, the systems and methods described herein in accordance with the present technology may additionally or alternatively be used in conjunction with other implantable medical device, in conjunction with other cardiac monitoring devices (e.g., other leadless cardiac monitoring devices, cardiac monitoring devices with leads, etc.), and / or in conjunction with other optical sensing devices (e.g., a wearable device measuring PPG).II. Dynamic sampling frequency adjustment

[0059] Methods and systems described herein can be used to perform optical sensing with dynamic adjustment of sampling frequency (e.g., rate at which one or more emitters in an optical sensing arrangement is activated for optical sensing purposes). The sampling frequency can, for example, be dynamically adjusted at least in part based on morphologyAtty Ref. No. A0011262W001 of the optical signal (e.g., PPG waveform) and concurrent sensor data such as electrocardiogram (EGM) data, heart sound data, etc. as further described herein.10060] For example, PPG signals are highly sparse on a frequency basis; that is, some portions of the PPG signal have relatively high bandwidth with high-frequency content, and these portions are embedded in longer portions of the PPG signal that have relatively low bandwidth with low-frequency content. Information of interest is typically derived from portions of the PPG signal with high relative bandwidth. In some embodiments in accordance with the present technology, the sampling frequency for an optical sensor arrangement can be dynamically adjusted throughout optical sensing as a function of (or in dependence upon) the local bandwidth of the signal, which represents the bandwidth of the PPG signal in a given time window. For example, in some embodiments, sampling frequency can be increased when the PPG signal is expected to include high-frequency content, and decreased when the PPG signal is not expected to include high-frequency content. As such, sampling frequency can be adaptive instead of uniform during optical sensing, thereby reducing overall power consumption via time-domain processing, without sacrificing accuracy of meaningful PPG measurements.10061] FIG. 6 is an illustrative flowchart of an example method 600 of operating an optical sensor arrangement in an optical sensing device with dynamic sampling frequency adjustment. Method 600 can, for example, be performed to operate any of the optical sensing devices described herein (e.g., optical sensing device 100 or optical sensing device 10, such as implantable medical device 300, implantable medical device 500, etc.), or other suitable optical sensing device. Method 600 includes receiving an optical signal from an optical sensor arrangement 610, identifying a target time interval with respect to a cardiac cycle of the patient 620, and modifying sampling parameters for the optical sensor arrangement 630. For example, the sampling parameters may be modified such that the optical sensor arrangement provides an optical signal (e.g., PPG signal) at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval. In some embodiments, the method 600 can further include receiving one or more secondary sensor signals 612 for the patient (e.g., where the secondary sensor signal(s) are concurrent with the optical signal), and the target time interval can be further identified based at least in part on at least one feature of the secondary sensor signal(s). The method 600 may further include operating the optical sensorAtty Ref. No. A0011262W001 arrangement to provide the optical signal in accordance with the modified sampling parameters 640.10062] Various processes of the method 600 may, for example, be performed by the medical device when one or more processors in the optical sensing device executes instructions stored by one or more memory devices in the optical sensing device.

[0063] Receiving an optical signal 610 functions to obtain an optical signal indicative of one or more physiological metrics for the patient in which the optical sensing device is placed (or worn, etc.). For example, in some embodiments the optical signal may be or include a PPG signal form which metrics such as blood pressure, blood oxygenation, heart rate, respiration, and / or the like may be derived. The optical signal may be provided by at least one emitter-detector pair in the optical sensing device, or may be provided by a separate emitter-detector pair such as one that is in proximity to the optical sensing device (e.g., as part of a wearable device, or second implantable device).10064] In some embodiments, the method 600 can further include receiving one or more secondary sensor signals for the patient 612. Such secondary sensor signal(s) can be obtained concurrently with the optical signal, for example, and can be correlated to the optical signal to help identify portion(s) of the optical signal that are expected to have high- frequency content. In some embodiments, the secondary sensor signals may be provided by a suitable sensor arrangement (including one or more secondary sensors) arranged inside and / or outside the patient, such as part of an implantable optical sensing device, an additional implantable sensing device separate from the optical sensing device, and / or an external sensing device wearable by the patient (e.g., adjacent to skin).

[0065] For example, in some embodiments, the secondary sensor signal(s) may include an electrogram (EGM) signal. For example, the optical sensing device may include one or more electrodes (e.g., electrode 304 or electrode 306, electrode 502A, electrode 502B, etc.) configured to provide an EGM signal indicative of cardiac electrical activity. Additionally or alternatively, the one or more electrodes may be part of a separate implantable device (e.g., implanted proximate the optical sensing device), or part of an external device that is wearable by the patient. As described further detail below, the EGM signal may be collected concurrently with the optical signal, and the EGM signal may be correlated with the optical signal so as to identify intervals with respect to the cardiac cycleAtty Ref. No. A0011262W001 of the patient that may have higher frequency content, and thus are candidates for target time intervals during which sampling frequency is increased.

[0066] Additionally or alternatively, in some embodiments, the secondary sensor signal(s) may include a heart sound signal. For example, the optical sensing device may include at least one accelerometer and / or microphone configured to provide a heart sound signal. The secondary sensor signals may additionally or alternatively include other suitable secondary sensor signals that are directly or indirectly obtained from secondary sensors, such as heart rate, heart rate variability, thoracic impedance, blood oxygen saturation (SpO2), tissue oxygen saturation (StO2), respiration, blood pressure, patient activity (e.g., sleep, movement), and / or patient posture. In some variations, at least some secondary sensor signals may be derived from the optical sensor arrangement in the optical sensing device, or from other suitable optical sensors.

[0067] Identifying a target time interval in the optical signal 620 functions to identify at least one duration of time where the optical signal includes high-frequency content, which may include more data of interest for analysis. Generally, the target time interval can be a period of time during which the optical signal has a higher signal bandwidth compared to the time outside the target time interval. In some embodiments, the target time interval can correspond to a portion of the optical signal including at least one change in slope of optical signal, where change in slope can be indicative of a portion of the optical signal having higher signal bandwidth than other portions of the optical signal that includes fewer or no changes in slope.10068] For example, FIG. 7 is a schematic illustration of a PPG signal over multiple (two) cardiac cycles. A single cardiac cycle is indicated in FIG. 7 as generally between the timepoints labeled “onset” and “end”, and thereafter repeated over time. Between “onset” and “end”, there are multiple slope changes, including at the systolic peak or first peak (Pl), second peak (P2), dicrotic notch (die), and diastolic peak or third peak (P3). In some embodiments, a target time interval (TTI) may be identified as including the dicrotic notch (die). The dicrotic notch may be characterized by notch morphology that is highly indicative of physiological characteristics (e.g., includes a significant amount of information) for the patient due to its role as a reference point in the timing of systolic and diastolic events. The dicrotic notch is a small deviation observed on the descending portion of the PPG waveforms, following the systolic peak, resulting from aortic valve closure. Furthermore,Atty Ref. No. A0011262W001 the dicrotic notch may typically include a falling slope with a higher frequency signature compared to other aspects of the PPG waveform. Due to the informative nature of the dicrotic notch in feature extraction for blood pressure estimation and the possibility of having high frequency content, it may be desirable to sample at a higher rate around the dicrotic notch to get a higher resolution PPG signal during more informative portions of the waveform, and then sample at a lower rate during other portions of the waveform (e.g., between heartbeats when the change in slope of the optical signal is small). The target time interval (TTI) may, for example, be defined as a time window around the dicrotic notch, such as between time (tl) and time (t2) (e.g., as identified as when the second peak (P2) and third peak (P3) occur, respectively) including the dicrotic notch. However, the TTI around the dicrotic notch may be defined in any suitable manner (e.g., based on percent change in slope around the dicrotic notch, based on n milliseconds before or after the dicrotic notch, etc.). The target time interval (TTI) may be anticipated to repeat in the next cardiac cycles thereafter, such as between time (t3) and time (t4), based on the expected repeated, periodic pattern of the PPG waveform. Detecting the temporal location of the dicrotic notch in a PPG waveform may depend on many factors including but not limited to heart rate, vascular compliance, blood pressure, peripheral vascular resistance, and the location of measurement; however, the dicrotic notch is frequently found approximately one-third of the way down the descending waveform following the systolic peak. Any suitable algorithm(s) may be used to detect the dicrotic notch and locate the target time interval (TTI) for higher sampling rate.10069] As another example, the target time interval may be defined based on one or more features of systolic phase in the optical signal. For example, the target time interval may include a period of time in the cardiac cycle including systolic phase features relating to a threshold pulse wave velocity (PWV) and / or pulse transit time (PTT), which may be indicative of portions of the cardiac cycle anticipated to have higher frequency content. For example, in some embodiments a target time interval may be defined as a time window around the systolic peak (Pl), the highest point in the pulse wave representing the maximum blood volume during cardiac contraction (systole) phase. The TTI around the systolic peak may be defined in any suitable manner (e.g., based on percent change in slope around the systolic peak, based on n milliseconds before or after the dicrotic notch, or n milliseconds before or after pulse wave onset / end, etc.). The target time interval (TTI) may be anticipated to repeat in the next cardiac cycles thereafter, based on the expected repeated, periodicAtty Ref. No. A0011262W001 pattern of the PPG waveform. Any suitable algorithm(s) may be used to detect the systolic peak and locate the target time interval (TTI) for higher sampling rate.10070] In embodiments in which secondary sensor signals are received, identifying the target time interval 620 can further include analyzing the one or more secondary sensor signals to identify a selected portion of the optical signal. For example, at least one secondary sensor signal may be correlated (e.g., time-synchronized with or without a known delay) with the optical signal, and a trigger feature of the secondary sensor signal may be identified as that correlated with a high-frequency portion of the optical signal. As such, the target time interval may be defined based at least in part on the trigger feature identified in the secondary sensor signal(s). The specific trigger feature may depend, for example, on the type of secondary sensor signal being analyzed.|0071] In some embodiments, as described above, the one or more secondary sensor signals may include an EGM and / or ECG signal for the patient, and the target time interval may be defined at least in part on one or more trigger features identified in the EGM signal. In these embodiments, the EGM signal may include, for example, at least one trigger feature correlated with a QRS complex of the cardiac cycle (e.g., onset of QRS complex, or any suitable feature thereof), dicrotic notch, one or more systolic phase features, one or more diastolic phase features, etc. It may, for example, be preferable to perform high-resolution optical sensor around the occurrence of the QRS complex or dicrotic notch. In an EGM or ECG signal, the systolic peak is typically associated with the R-wave, which indicates the electrical depolarization of the ventricles and the beginning of ventricular contraction, marking the start of the systolic phase. The R-wave marker will typically happen prior to the PPG systolic peak or dicrotic notch occurs, due to the time it takes for blood to travel to the PPG sensor location. Therefore, the R-wave or S-wave (the negative deflection in the QRS complex after the R-wave) can be used as an indicator to increase sampling rate of the optical sensor. The optical sensor may start increasing sampling rate immediately upon R- wave or S-wave detection, or may increase sample rate after a short delay. The delay may be fixed, programmable, or set specifically based on other patient-specific data. This method can, for example, be useful in making a more accurate measurement of Pulse Arrival Time (PAT) or Pulse Transit Time (PTT), the time difference between the ECG R-wave and the PPG systolic peak.Atty Ref. No. A0011262W001

[0072] Additionally or alternatively, in some embodiments, as described above, the one or more secondary sensor signals may include a heart sound signal for the patient, and the target time interval may be defined at least in part on one or more trigger features identified in the heart sound signal. In these embodiments, the heart sound signal may include, for example, at least one trigger feature including an SI heart sound (aligning to closure of mitral and tricuspid valves, at the beginning of systole, or ventricular contraction) and / or an S2 heart sound (aligning to closure of the aortic valve (A2 sound) or the pulmonary valve (P2 sound), at the end of a heartbeat). For example, a target time interval may be defined at least in part on the SI heart sound (e.g., onset of target time interval synchronized a known time interval relative to the SI heart sound), since systolic peak and high-frequency portion of the optical signal may be expected to occur after the SI heart sound or at approximately the same time as the second heart sound. The optical sensor may therefore start sampling at an increased rate immediately upon SI detection, or may increase sample rate after a short delay following SI detection. The delay may be fixed, programmable, or set specifically based on other patient-specific data. Likewise, increased optical sampling may be based to start or end based on the S2 heart sound or a time delay after the S2 heart sound.

[0073] Other secondary sensor signals may additionally or alternatively include other sensor data indicative of metrics such as heart rate, heart rate variability, thoracic impedance, blood oxygen saturation (SpO2), tissue oxygen saturation (StO2), respiration, blood pressure, patient activity, or patient posture. A target time interval may be defined based at least partially on such metrics, to enable adjustment of sampling frequency based on other concurrent sensor data and / or the patient’s individual daily trends (e.g., sleep, activity, posture, eating, respiration, etc.). For example, the target time interval may be defined as a time window during which the patient is not moving much, as it may be preferable to avoid performing optical sensing when the patient is engaging in physical activity (which may, for example, introduce undesired noise into the optical signal).

[0074] In some variations, identification of the target time interval may be based at least in part by any suitable algorithm, such as a thresholding algorithm using one or more predetermined threshold values (e.g., for bandwidth or number of slope changes in the optical signal over a period of time, etc.).Atty Ref. No. A0011262W001[00751 Modifying sampling parameters 630 functions to selectively and dynamically increase and / or decrease the sampling rate of the optical sensor arrangement in the optical sensing device relative to the target time interval. In some embodiments, the sampling parameters may be modified such that the optical sensor arrangement is configured to provide the optical signal at a first sampling frequency (or first average sampling frequency) during the target time interval, and at a second sampling frequency (or second average sampling frequency) during at least a portion of time outside the target time interval, where the first sampling frequency is different (e.g., higher) than the second sampling frequency. Modifying the sampling parameters may include determining suitable sampling parameters to be applied during the target time interval and outside the target time interval, and applying the sampling parameters for subsequent operation of the optical sensor arrangement.

[0076] In some embodiments, the sampling frequency for the time interval may be identified at least in part by a pre-trained machine learning algorithm. In some embodiments, the pre-trained machine learning algorithm may be trained to determine a suitable sampling frequency during a target time interval (and / or during some or all other time outside the target time interval) based on a typical or representative optical signal (e.g., PPG signal) morphology from training data obtained from a training population having demographics and / or health conditions matching that of the patient (e.g., age, sex, weight, BMI, height, type and / or stage of cardiac disease, etc.). For example, each representative optical signal from the training population may be converted to the frequency domain by taking a Fourier transform across a sliding time window across the representative optical signal. Analysis of the representative optical signals from the training population in the frequency domain may result in a determination of at which sampling frequency, on average across the sliding time windows, a sufficiently full optical signal can be obtained. Accordingly, a pre-trained machine learning algorithm may be trained on various training data for different patient population types to receive an input of an optical signal (and / or suitable patient characteristics such as demographics and / or health conditions), and provide an output of a suitable sampling frequency.

[0077] In some embodiments, the pre-trained machine learning algorithm may be trained to determine a suitable sampling frequency during a target time interval (and / or during some or all other time outside the target time interval) for the patient that is patient-Atty Ref. No. A0011262W001 specific or individualized to the specific patient. For example, such a machine learning algorithm may be trained in a process beginning with utilizing a uniform sampling rate meeting Nyquist criterion (that is, sampling frequency that is greater than twice the average optical signal bandwidth), then adjusted downwards across various sliding time windows, based on patient-specific patterns of what aspects of the optical signal most heavily influence blood pressure measurements and / or other physiological measurements derived from the optical signal.

[0078] In some variations, a pre-trained machine learning algorithm for identifying the target time interval may include a convolutional neural network, or a Generative Adversarial Network (GAN) trained to forecast PPG morphology, or other suitable machine learning algorithm.|0079] The specific sampling frequency for the target time interval may vary from patient to patient, as described above. However, generally, in some embodiments, the specific sampling frequency for obtaining the optical signal during the target time interval may be lower than the sampling frequency meeting the Nyquist criterion. For example, the sampling frequency during the target time interval may be no more than twice the average bandwidth of the optical signal outside the target time interval (e.g., between about 1.1 and about 1.9 times the average bandwidth of the optical signal outside the target time interval). Additionally or alternatively, in some embodiments, the ratio of the average sampling frequency during the target time interval to the average sampling frequency outside the target time interval may be between about 1.1 and about 1.9, between about 1.1 and about 1.5, between about 1.5 and about 1.9, or between about 1.3 and about 1.7). For example, in some embodiments, the sampling frequency of the optical signal during the target time interval may be less than about 128 Hz and the sampling frequency of the optical signal outside the target time interval may be about 64 Hz or 32 Hz or perhaps down to approximately 20 Hz.

[0080] In some embodiments, the sampling frequency during the target time interval may be substantially uniform (e.g., a single sampling frequency for the portion of the optical signal including the target time interval). However, in other embodiments the sampling frequency during the target time interval may vary; for example, the sampling frequency may ramp up gradually after the onset of the target time interval of the optical signal, and ramp down gradually prior to the endpoint of the target time interval of the optical signal.Atty Ref. No. A0011262W001[0081 J Similarly, in some embodiments, the sampling frequency outside of the target time interval may be substantially uniform (e.g., a single sampling frequency for portions of the optical signal not including the target time interval). However, in other embodiments the sampling frequency outside of the target time interval may vary; for example, the sampling frequency may ramp down gradually after the endpoint of the target time interval of the optical signal, and ramp up gradually prior to the onset of the target time interval of the optical signal.

[0082] Although the sampling frequency for during and outside the target timing interval are primarily described herein as determined with one or more pre-trained machine learning algorithms, in some embodiments, a sampling frequency for during the target time interval and / or outside the target time interval may be set or predetermined manually (and / or set by default) such as by a clinician or programmed default.

[0083] Once the modified sampling frequency for during the target time interval and / or a modified sampling frequency for outside the target time interval are determined, these sampling frequencies may be applied (e.g., in memory, set through processing circuitry, etc.) in preparation for obtaining the optical sensor in accordance with the modified sampling frequencies and / or other sampling parameters (e.g., timing of the target time interval).

[0084] After the modified sampling frequency or frequencies are applied, the method 600 may further include operating the optical sensor arrangement 640, in accordance with the modified sampling frequency or frequencies (and / or other sampling parameters). For example, the optical sensor arrangement of the optical sensing device may be operated at a first frequency (or first average frequency) during the target time interval, and operated at a second frequency (or second average frequency) that is different than the first frequency. In some embodiments, the first frequency is higher than the second frequency, as described herein.

[0085] Although the method 600 relates generally to the analysis of an optical signal and / or one or more secondary sensor signals to identify a target time interval during which sampling frequency may be adjusted, the present technology relates also to other techniques for dynamic adjustment of sampling frequency.Atty Ref. No. A0011262W001

[0086] For example, in some variations, sampling frequency may additionally or alternatively be dynamically adjusted based on an indication of patient condition (e.g., cardiac episode, worsening health state, etc.) derived from one or more secondary sensor signals. For example, a heart rate signal and / or a heart rate variability signal may indicate a likelihood that the patient is experiencing arrhythmia or some other anomalous state, and may trigger an increase in sampling frequency for the optical sensor arrangement to gather higher-resolution, more accurate optical sensor data for further monitoring and / or action. As another example, in some variations the secondary sensor signals may additionally or alternatively include a composite signal generated from multiple secondary sensor signals. For example, features from a secondary sensor signal, or from multiple secondary sensor signals (e.g., respiration, heart rate, heart rate variability, etc.), may be combined to generate a composite heart failure risk score, and / or other metric(s) indicative of a trend toward reduced ejection fraction. If the composite heart failure risk score and / or other metric meets a predetermined threshold, the sampling frequency of the optical sensing arrangement may be increased to gather higher-resolution, more accurate optical sensor data for further monitoring and / or action.

[0087] Additionally or alternatively, sampling frequency may be dynamically adjusted based on one or more secondary sensor signals that indicate the presence of a situation warranting higher optical signal resolution, such as to increase the robustness of the optical signal against noise. As an example, in response to detecting at least a threshold amount of motion from an activity sensor (e.g., accelerometer), the sampling frequency of the optical sensor arrangement may be increased in order to help increase the accuracy of the optical signal during a period of time in which noise caused by the patient motion may obfuscate the signal of interest.

[0088] Additionally or alternatively, sampling frequency may be reduced in instances where no analysis of the optical sensing is to be performed. For example, in embodiments in which the purpose of an optical sensing device is to perform blood pressure measurements using an optical signal, the sampling frequency of the optical sensor arrangement in the optical sensing device may be decreased (e.g., to zero or near zero) whenever the blood pressure measurements are not being performed (e.g., when ambient light is detected to be excessively high, when the patient is in excessive motion, etc.).ExamplesAtty Ref. No. A0011262W001

[0089] The subject technology is illustrated, for example, according to various aspects described herein, including with reference to FIGS. 1-7. Various examples of aspects of the subject technology are described as numbered clauses (1, 2, 3, etc.) for convenience. These are provided as examples and do not limit the subject technology.1. A system comprising: a medical device insertable in a patient and comprising an optical sensor arrangement configured to provide an optical signal associated with the patient; a processor; and a memory operably coupled to the processor and storing instructions that, when executed by the processor, cause the medical device to perform operations comprising: receiving the optical signal; identifying a target time interval in the optical signal with respect to a cardiac cycle of the patient; modifying sampling parameters of the optical sensor arrangement such that the optical sensor arrangement provides the optical signal at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval, wherein the first sampling frequency and the second sampling frequency are different; and operating the optical sensor arrangement to provide the optical signal in accordance with the modified sampling parameters.2. The system of clause 1, wherein the optical signal has a higher signal bandwidth during the target time interval than outside the target time interval, and wherein the first sampling frequency is higher than the second sampling frequency.3. The system of clause 1 or 2, wherein the target time interval is correlated with a portion of the optical signal comprising a change in slope of the optical signal.4. The system of any one of clauses 1-3, wherein the operations further comprise receiving one or more secondary sensor signals for the patient, and wherein identifying a target time interval comprises analyzing the one or more secondary sensor signals to identify a selected portion of the optical signal.5. The system of clause 4, wherein identifying a target time interval comprises identifying a trigger feature of the secondary sensor signal correlated with a high-Atty Ref. No. A0011262W001 frequency portion of the optical signal, and wherein the target time interval is defined based at least in part on the trigger feature.6. The system of clause 4, wherein the one or more secondary sensor signals comprises an electrogram (EGM) signal or electrocardiogram (ECG) signal for the patient.7. The system of clause 6, wherein the trigger feature is correlated with a QRS complex of the cardiac cycle.8. The system of clause 6, wherein the trigger feature is correlated with a portion of the optical signal comprising a dicrotic notch.9. The system of any one of clauses 4-8, wherein the one or more secondary sensor signals comprise at least one of heart sounds, heart rate, heart rate variability, thoracic impedance, blood oxygen saturation (SpCh), tissue oxygen saturation (StCE), respiration, blood pressure, patient activity, or patient posture.10. The system of any one of clauses 1-9, wherein the medical device includes the processor and is an insertable cardiac monitor, wherein the medical device further comprises a power source and one or more electrodes operably coupled to the processor.11. The system of clause 10, wherein the insertable cardiac monitor has a volume of about 1.5 cubic centimeters or less.12. A method for operating processing circuitry of a medical device, the method comprising: receiving, using processing circuitry included in a housing of the medical device an optical signal from an optical sensor arrangement of the medical device; identifying, using the processing circuitry, a target time interval in the optical signal with respect to a cardiac cycle of the patient; modifying, using the processing circuitry, sampling parameters of the optical sensor arrangement such that the optical sensor arrangement provides the optical signal at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval, wherein the first sampling frequency and the second sampling frequency are different; and operating the optical sensor arrangement to provide the optical signal in accordance with the modified sampling parameters.Atty Ref. No. A0011262W00113. The method of clause 12, wherein the optical signal has a higher signal bandwidth during the target time interval than outside the target time interval, and wherein the first sampling frequency is higher than the second sampling frequency.14. The method of clause 12 or 13, wherein the target time interval is correlated with a portion of the optical signal comprising a change in slope of the optical signal.15. The method of any one of clauses 12-14, further comprising receiving, using the processing circuitry, one or more secondary sensor signals for the patient, and wherein identifying a target time interval comprises analyzing the one or more sensor signals to identify a selected portion of the optical signal.16. The method of clause 15, wherein identifying a target time interval comprises identifying a trigger feature of the secondary sensor signal correlated with a high-frequency portion of the optical signal, and wherein the target time interval is defined based at least in part on the trigger feature.17. The method of clause 16, wherein the one or more secondary sensor signals comprises an electrogram (EGM) signal or electrocardiogram (ECG) signal for the patient.18. The method of clause 17, wherein the trigger feature is correlated with a QRS complex of the cardiac cycle, or a portion of the optical signal comprising a dicrotic notch, or both.19. The method of any one of clauses 15-18, wherein the one or more secondary sensor signals comprise at least one of heart sounds, heart rate, heart rate variability, thoracic impedance, blood oxygen saturation (SpCh), tissue oxygen saturation (StCE), respiration, blood pressure, patient activity, or patient posture.Atty Ref. No. A0011262W00120. An implantable medical device configured for placement in a patient, comprising: an optical sensor arrangement configured to provide a photoplethysmography (PPG) signal for the patient; a sensor configured to provide an electrogram (EGM) signal or electrocardiogram (ECG) signal for the patient; a processor; and a memory operably coupled to the processor and storing instructions that, when executed by the processor, cause the medical device to perform operations comprising: receiving the PPG signal and the EGM or ECG signal; identifying a target time interval with respect to a cardiac cycle of the patient, based on analysis of the optical signal, the EGM or ECG signal, or both; operating the optical sensor arrangement to provide the optical signal at a first sampling frequency during the target time interval; and operating the optical sensor arrangement to provide the optical signal at a second sampling frequency during at least a portion of time outside the target time interval, wherein the optical signal has a higher signal bandwidth during the target time interval than outside the target time interval, and wherein the first sampling frequency is higher than the second sampling frequency.Conclusion[0090J Although many of the embodiments are described above with respect to systems, devices, and methods for dynamically adjusting sampling frequency for optical sensing in an implantable medical device, the technology is applicable to other applications and / or other approaches, such as in other optical sensing devices. Moreover, other embodiments in addition to those described herein are within the scope of the technology. Additionally, several other embodiments of the technology can have different configurations, components, or procedures than those described herein. A person of ordinary skill in the art, therefore, will accordingly understand that the technology can have other embodiments with additional elements, or the technology can have other embodiments without several of the features shown and described above with reference to FIGS. 1-7.Atty Ref. No. A0011262W001

[0091] The descriptions of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise form disclosed above. Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, while steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments.

[0092] As used herein, the terms “generally,” “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent variations in measured or calculated values that would be recognized by those of ordinary skill in the art.

[0093] Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in reference to a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list. Additionally, the term "comprising" is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and / or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with certain embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.

Claims

Atty Ref. No. A0011262W001CLAIMSI / We claim:

1. A system comprising: a medical device insertable in a patient and comprising an optical sensor arrangement configured to provide an optical signal associated with the patient; a processor; and a memory operably coupled to the processor and storing instructions that, when executed by the processor, cause the medical device to perform operations comprising: receiving the optical signal; identifying a target time interval in the optical signal with respect to a cardiac cycle of the patient; modifying sampling parameters of the optical sensor arrangement such that the optical sensor arrangement provides the optical signal at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval, wherein the first sampling frequency and the second sampling frequency are different; and operating the optical sensor arrangement to provide the optical signal in accordance with the modified sampling parameters.

2. The system of claim 1, wherein the optical signal has a higher signal bandwidth during the target time interval than outside the target time interval, and wherein the first sampling frequency is higher than the second sampling frequency.

3. The system of claim 1 or 2, wherein the target time interval is correlated with a portion of the optical signal comprising a change in slope of the optical signal.

4. The system of any one of claims 1-3, wherein the operations further comprise receiving one or more secondary sensor signals for the patient, and wherein identifying a target time interval comprises analyzing the one or more secondary sensor signals to identify a selected portion of the optical signal.

5. The system of claim 4, wherein identifying a target time interval comprises identifying a trigger feature of the secondary sensor signal correlated with a high-Atty Ref. No. A0011262W001 frequency portion of the optical signal, and wherein the target time interval is defined based at least in part on the trigger feature.

6. The system of claim 4 or 5, wherein the one or more secondary sensor signals comprises an electrogram (EGM) signal or electrocardiogram (ECG) signal for the patient.

7. The system of claim 6, wherein the trigger feature is correlated with a QRS complex of the cardiac cycle, or a portion of the optical signal comprising a dicrotic notch, or both.

8. The system of any one of claims 1-7, wherein the medical device includes the processor and is an insertable cardiac monitor, wherein the medical device further comprises a power source and one or more electrodes operably coupled to the processor.

9. A method for operating processing circuitry of a medical device, the method comprising: receiving, using processing circuitry included in a housing of the medical device an optical signal from an optical sensor arrangement of the medical device; identifying, using the processing circuitry, a target time interval in the optical signal with respect to a cardiac cycle of the patient; modifying, using the processing circuitry, sampling parameters of the optical sensor arrangement such that the optical sensor arrangement provides the optical signal at a first sampling frequency during the target time interval, and at a second sampling frequency during at least a portion of time outside the target time interval, wherein the first sampling frequency and the second sampling frequency are different; and operating the optical sensor arrangement to provide the optical signal in accordance with the modified sampling parameters.

10. The method of claim 9, wherein the optical signal has a higher signal bandwidth during the target time interval than outside the target time interval, and wherein the first sampling frequency is higher than the second sampling frequency.

11. The method of claim 9 or 10, wherein the target time interval is correlated with a portion of the optical signal comprising a change in slope of the optical signal.

12. The method of any one of claims 9-11, further comprising receiving, using the processing circuitry, one or more secondary sensor signals for the patient, andAtty Ref. No. A0011262W001 wherein identifying a target time interval comprises analyzing the one or more sensor signals to identify a selected portion of the optical signal.

13. The method of claim 12, wherein identifying a target time interval comprises identifying a trigger feature of the secondary sensor signal correlated with a high- frequency portion of the optical signal, and wherein the target time interval is defined based at least in part on the trigger feature.

14. The method of claim 12 or 13, wherein the one or more secondary sensor signals comprises an electrogram (EGM) signal or electrocardiogram (ECG) signal for the patient.

15. The method of claim 14, wherein the trigger feature is correlated with a QRS complex of the cardiac cycle, or a portion of the optical signal comprising a dicrotic notch, or both.

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