Adaptive servo gain control for multi-wavelength volume clamping

Abstract

A blood specialty sensing system includes a light emitter, a light sensor, and a pressurizable cuff. The system surrounds a sensing region of a patient appendage with a pressurizable cuff, emits light of a plurality of discrete wavelengths into the sensing region, and senses an amplitude of each wavelength received through the patient appendage. Sensed plethysmogram values reflecting the arterial volume are generated based on these sensed amplitudes, and the compression of the cuff is adjusted via a closed loop control algorithm to partially clamp the arterial volume within the sensing region based on the sensed plethysmogram values and the set point plethysmogram values. Differential absorption of the sensing wavelength is used to produce an analytical component of arterial blood within the sensing region, and arterial blood pressure is sensed based on the compression of the cuff required to partially grip the arterial volume.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 63 / 479,721, filed by Guelen et al. on January 12, 2023, entitled “ADAPTIVE SERVO GAIN CONTROL FOR MULTIWAVELENGTH VOLUME CLAMP,” the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0003] The present disclosure relates generally to blood property sensing, and more particularly to gain control for volume clamping in a multifunctional multi-wavelength arterial blood pressure and blood composition sensor.

[0004] Some non-invasive arterial blood pressure sensors generate pressure readings by clamping (i.e., holding constant) the arterial volume within a sensing area, such as a portion of a finger enclosed by a pressurizable cuff. Such systems directly assess arterial volume, for example, optically, increasing or decreasing the contraction applied by the pressurizable cuff via closed-loop control to compensate for fluctuations in arterial volume caused by the pulsation of blood. The resulting clamped pressure serves as a proxy or estimate of the arterial blood pressure waveform (AP), allowing blood pressure to be monitored non-invasively over long periods of time without interruption. In some examples, the arterial volume waveform can also be directly analyzed to estimate mean arterial blood pressure, diastolic pressure, or systolic pressure.

[0005] Some non-invasive blood composition sensors estimate properties such as blood oxygen saturation and hemoglobin composition based on the differential absorption of a spectrum of wavelengths of light by blood during arterial pulsation. Summary of the Invention

[0006] The present disclosure discloses a method for operating a blood property sensing system. The sensing system includes a light emitter, a light sensor, and a pressurizable cuff. The system operates by surrounding a sensing region of a patient's appendage with the pressurizable cuff, emitting light at multiple discrete wavelengths from the light emitter into the sensing region of the patient's appendage, and sensing the amplitude of light received by the light sensor from the light emitter through the patient's appendage for each discrete wavelength. A sensed plethysmogram value reflecting arterial volume within the sensing region is generated based on the sensed light amplitude. In response to a closed-loop error value reflecting the difference between the sensed plethysmogram value and a setpoint plethysmogram value, the pressurization of the pressurizable cuff is adjusted via a closed-loop control algorithm to partially clamp the arterial volume within the sensing region. A compositional analysis of the arterial blood within the sensing region is then generated based on differential absorption of the multiple discrete wavelengths of light sensed by the light sensor during arterial pulsations within the sensing region. A sensed arterial blood pressure is generated based on the pressurization of the pressurizable cuff required to partially clamp the arterial volume.

[0007] The present disclosure also presents a non-invasive sensor system comprising a pressurizable cuff, a light emitter, a light sensor, a composition analysis module, and a controller. The pressurizable cuff is pressurized via a metered fluid supply and is sized to surround a patient's appendage and define a sensing area. The light emitter is anchored to the pressurizable cuff and is configured to emit light at a plurality of discrete wavelengths through the sensing area of the patient's appendage. The light sensor is also anchored to the pressurizable cuff, positioned to receive the light emitted by the light emitter, and configured to generate a sensed plethysmogram signal based on the received light. The composition analysis module is configured to assess blood composition within the sensing area based on differential absorption of discrete wavelengths emitted by the light emitter detected by the light sensor during arterial pulsation within the sensing area. The controller is configured to calculate an error value as a difference between the sensed plethysmogram signal and a set-point plethysmogram value, and to operate a closed-loop control mode in which a metered fluid supply is driven to partially clamp the artery within the sensing region based on the error value and a gain level, thereby adjusting a clamping pressure equivalent to the sensed arterial blood pressure.

[0008] The present disclosure is provided by way of example only and not limitation. Other aspects of the present disclosure will be understood in view of the entire disclosure (including text, claims and drawings). BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a simplified perspective diagram of a non-invasive sensor system mounted on a human hand.

[0010] Figure 2 It is in operation Figure 1 Schematic diagram of the non-invasive sensor system.

[0011] Figure 3 is Figure 1 and Figure 2 Parallel graphs of cuff pressure and overall light level as a function of time in an illustrative example of an operating cycle of a non-invasive sensor system.

[0012] Figure 4 It shows Figure 1 and Figure 2 A flow chart of a method of operating a non-invasive sensor system.

[0013] Figure 5 It is shown for Figure 1 and Figure 2 Functional block diagram of the control process of the non-intrusive sensor system.

[0014] Although the above-mentioned drawings illustrate one or more examples of the present disclosure, other examples are also contemplated, as described in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that those skilled in the art can devise numerous other modifications and examples that fall within the scope and spirit of the principles of the present invention. The drawings may not be drawn to scale, and applications and examples of the present invention may include features and components not specifically shown in the drawings. DETAILED DESCRIPTION

[0015] The present disclosure describes a method for volume clamping control in a multifunctional sensor system. The system uses the received light amplitude as a sensed plethysmogram value (hereinafter referred to as a "pleth signal") representing the arterial volume within the sensing area, physically clamps the arterial volume via closed-loop control based on the plethysmogram reading, and reports the resulting clamping pressure as an arterial blood pressure waveform. Through further analysis, systolic (SYS), diastolic (DIA) and mean arterial pressure (MAP) can be derived from the waveform. Light used to generate the plethysmogram signal is emitted across multiple wavelengths, allowing blood composition (e.g., blood oxygen saturation, total hemoglobin, methemoglobin percentage, carboxyhemoglobin percentage) to be analyzed by comparing light absorption at multiple wavelengths during arterial pulsation. This method allows a single non-invasive multifunctional sensor to produce readings of both arterial blood pressure and arterial blood composition.

[0016] The volume clamping mentioned above for arterial blood pressure sensing appears to be inconsistent with the requirement to allow the artery to pulsate (i.e., not clamp) in order to assess blood composition based on differential wavelength absorption. The present disclosure provides methods and systems for closed-loop clamping using adaptive gain control that is tailored to provide sufficient clamping to accurately sense arterial blood pressure while still allowing sufficient arterial pulsation to enable blood composition assessment. This balance between clamping gain being "too high" (preventing composition analysis) and "too low" (compromising arterial blood pressure sensing accuracy) is described in detail below. The present method adjusts the gain of the closed-loop volume clamping control to avoid completely clamping the artery while still clamping sufficiently to produce an arterial blood pressure reading with negligible loss of accuracy.

[0017] Figure 1 A simplified perspective view of sensor system 12 attached to hand 14 is provided. Figure 2 is a schematic diagram of the sensor system 12 in operation. Figure 1 and Figure 2 Mainly described together. Figure 1 As shown, the sensor system 12 is a non-invasive hemodynamic sensor capable of generating arterial blood pressure measurements by volume clamping. The sensor system 12 may include a housing 16, a connector 18, a cuff 20, and a pressurizable bladder 22. In the illustrated embodiment, the cuff 20 is a ring or similar structure that surrounds or supports a finger 24 of the hand 14, and the housing 16 is a wrist-worn device coupled to the cuff 20 via the connector 18. However, in the most general case, the sensor system 12 may be substantially different from Figure 1 Layout shown. The sensor system 12 can include multiple separate connectors 18, for example, between elements attached to the finger 24 (e.g., the cuff 20), and / or the housing 16 can be relocated to another location (e.g., integrated with the cuff 20 or separately provided at a peripheral location). In the illustrated example, the cuff 20 surrounds a sensing area of the finger 24 of the hand 14. At least one artery 26 passes through the sensing area. The cuff 20 also anchors a pressurizable bladder 22, which can be, for example, an inflatable annular bladder fed by an air line contained within the connector 18 or from another source. However, in the most general case, the pressurizable bladder 22 can be any type of mechanism suitable for applying pressure to the finger 24 based on control as described below. The sensor system 12 and the hand 14 together constitute a combined physical system 10 (sometimes referred to as a plant or plant system) that responds to both changes in the patient and changes in the control of the sensor system 12.

[0018] like Figure 2 As shown, the cuff 20 includes a light emitter 28 and a light sensor 30. The light emitter 28 transmits light through the sensing area (in the Figure 224 (represented by a path line through finger 24) emits light at multiple discrete wavelengths for receipt by light sensor 30. In the example described in detail below, the wavelengths of light emitted by light emitter 28 may all fall within the visible to infrared spectrum. Light sensor 30 detects both the total received light amplitude and the specific received light amplitude at each discrete wavelength emitted by light emitter 28. In some examples, light emitter 28 and light sensor 30 may be located on opposite sides of cuff 20 such that light travels directly from light emitter 28 through the sensing area of finger 24 to light sensor 30. More generally, however, scattering of light from light emitter 28 within the tissue of finger 24 allows light emitter 28 and light sensor 30 to be effective even when not located on opposite sides of cuff 20 (e.g., when positioned proximate to each other).

[0019] The total amplitude of light transmitted from emitter 28 and received at light sensor 30 is hereinafter referred to as the plethysmogram signal and is used as a proxy for the inverse arterial volume within the sensing region, where a decrease in received light corresponds to an increase in arterial volume. The two arteries and connected capillaries of the finger pulsate during normal blood flow, expanding (with systolic pressure) and relaxing (with diastolic pressure) in volume during each heartbeat cycle. Larger arterial volumes increase the absorption of emitted light, reducing the fraction of emitted light received at light sensor 30.

[0020] As generally described herein, the sensor system 12 clamps the arterial volume within the sensing region via the pneumatically pressurizable bladder 22 by actuation of the valve 32, thereby regulating the air pressure provided to the top of the bladder 22 via the connector 18. Although generally referred to herein as a valve, the valve 32 can most generally be any type of flow metering element, such as a servo valve or a piezoelectric pump. The sensor system 12 can clamp the arterial volume by any method that applies a known pressure to the sensing region of the finger 24.

[0021] The sensor system 12 includes a controller 34 having hardware with logic capabilities that is configured to adjust the setting of the valve 32 in a control loop in response to the volume wave signal. The controller 34 can be, for example, a control module instantiated in dedicated hardware, or a software module running on hardware within the sensor system 12 or external to the sensor system 12 (e.g., running on a communication connected device). The increased flow into the pressurizable bladder 22 through the valve 32 causes the pressurizable bladder 22 to expand, which physically compresses the finger 24 and thereby compresses the arterial volume in the sensing area. The difference between the volume wave value and the corresponding target set point (hereinafter identified as the "volume wave error") is used as an input for the controller 34 to control the valve 32. In the detailed description provided below, the control scheme and method (see Figure 3 and Figure 4 ) is described as involving proportional-integral-derivative (PID) control based on volume wave errors. However, in the most general case, other forms of closed-loop control may be substituted for PID control. The controller 34 drives the pressurizable bladder 22 through actuation of the valve 32 to mechanically resist changes in arterial volume within the sensing area, thereby reducing the amplitude of arterial volume fluctuations and keeping the arterial volume relatively constant. The valve pressure generated by this clamping process is used as a measure of arterial blood pressure. In some examples, both the valve 32 and the controller 34 may be located within the housing 16. More generally, however, the valve 32 may be located in any suitable location to meter the pressurization of the pressurizable bladder 22, and the controller 34 may be located within the housing 16, within or closer to the cuff 22, or at any other location capable of supporting processing to control the actuation of the valve 32. In some examples, some of the functions of the controller 34 may be offloaded to a peripheral device ( Figure 1 not shown).

[0022] Light emitter 28 emits a discrete or fixed known spectrum of light across a range of wavelengths (e.g., a range of visible to infrared wavelengths or a range consisting primarily of visible to infrared wavelengths) within which absorption differences across the material composition of interest can be detected. In one illustrative example, light emitter 28 may emit a wavelength range solely within the infrared band (700 nm to 1000 nm). In alternative examples, a wider range of light (e.g., 500 nm to 1100 nm) including visible and / or microwave band light may be used. In the most general case, light emitter 28 generates light of known amplitude within a wavelength range that is sufficiently wide to distinguish absorption spectra associated with at least two parameters, including, but not limited to, blood oxygen saturation, total hemoglobin, methemoglobin percentage, or carboxyhemoglobin percentage.

[0023] The composition analysis module 36 assesses blood composition based on the differential absorption of light of various discrete wavelengths emitted by the light emitter 28 during arterial pulsation, as detected by the light sensor 30. As an example, different materials, such as oxygenated hemoglobin (O2Hb; saturated blood), deoxygenated hemoglobin (HHb; desaturated blood), and water, all have detectably different absorption spectra.

[0024] In one embodiment, the component analysis module 36 determines arterial oxygen saturation, which can be calculated using pulse oximetry. To perform pulse oximetry, two or more discrete wavelengths of light can be utilized. In some embodiments, a light emitter 28 is used to perform pulse oximetry. Additionally or alternatively, in some embodiments, the light emitter 28 includes a single emission source (e.g., a diode) that can provide two or more discrete wavelengths of light (or bands of light wavelengths). In some embodiments, the light emitter 28 includes at least two emission sources (e.g., at least two diodes) such that two or more discrete wavelengths of light (or bands of light wavelengths) can be emitted simultaneously. Typically, when utilizing at least two emission sources, the light emission sources can be provided close to each other (e.g., within 0.5 mm) to produce similar light paths, but any configuration can be utilized. As previously described, light emitter 28 may emit wavelengths only within the infrared band (700 nm to 1000 nm), or may use visible and / or microwave band light (eg, 500 nm to 1100 nm) to perform pulse oximetry.

[0025] Pulse oximetry relies on the fact that the fraction of the light signal absorbed is constant regardless of the moment in the cardiac cycle (e.g., light absorbed by tissue, venous blood, and non-pulsating arterial blood), and the fraction of the light signal absorbed will vary depending on the pulsation of arterial blood associated with the cardiac cycle. This constant light signal is referred to as the DC signal, and the variable light signal is referred to as the AC signal. Using the DC and AC signals of two wavelengths of light (λ1 and λ2), the ratio (R) can be calculated as follows:

[0026]

[0027] The ratio R can be plotted against an experimentally determined oxygen saturation value (eg, SpO2) to generate a calibration curve. This calibration curve can be used to analyze arterial oxygen saturation determined using a PPG mounted on a body appendage.

[0028] Because arterial pulsation is used to distinguish pulsating arterial blood from other biological materials (e.g., to distinguish AC signals from DC signals), compositional analysis is only possible during arterial pulsation. The method described below adjusts the proportional gain of the PID control at the controller 34 to sufficiently clamp the arterial volume, thereby generating an accurate and reliable measurement of arterial blood pressure based on the pressure of the pressurizable bladder 22 to maintain the arterial volume relatively constant while allowing sufficient arterial pulsation for the compositional analysis module 36 to distinguish arterial blood from other materials. In the illustrative example, the gain generated and adjusted in this manner controls the actuation of the pressurizable bladder 22 by varying the gas flow through the valve 32, thereby adjusting the resulting mechanical clamping force of the pressurizable bladder 22 on the finger 24.

[0029] Figure 3 3 is a parallel plot of cuff pressure 300 and plethysmographic signal 302 as a function of time in an illustrative example of an operating cycle of sensing system 10 . Figure 3 The operation of the sensing system 10 is shown through the end of the first closed-loop cycle 304a, transitioning to the open-loop cycle 306 at time t0, and then transitioning to the updated closed-loop cycle 304b at time t1. Figure 1 and Figure 2 Said and referred to below Figure 4 and Figure 5 As further described, the sensor system 12 operates in closed-loop mode to achieve volume clamping of the sensing region, thereby sensing arterial blood pressure based on the resulting pressurization of the pressurizable bladder 22. Periods 304a and 304b are time windows during which the cuff pressure is managed by the closed-loop control so that the arterial volume remains relatively constant. However, during the open-loop period 306, the controller 34 evaluates the volume wave value while maintaining the pressure of the pressurizable bladder 22 constant, thereby allowing the arterial volume to expand as it pulsates. The open-loop period 306 is used to recalibrate the baseline arterial volume in the form of a volume wave set point used for closed-loop control throughout subsequent closed-loop periods 304b. This open-loop calibration period is used both for initial setup (i.e., determining the initial set point for a new patient or cuff setup) and periodically during patient monitoring to adjust for changes in the patient's condition. This set point ideally corresponds to the resting and unstressed arterial volume (i.e., not distended by arterial pulsations) within the sensing area for the current conditions of the finger 24, including the patient's hand orientation / posture and blood perfusion. Closed-loop volume clamping can be interrupted for open-loop calibration, which is scheduled to adjust for small changes in patient orientation or condition, and triggered (unscheduled) to respond to irregularities that indicate the current pleth set point requires recalibration.

[0030] Figure 3 Also refer to the following Figure 4 and Figure 5Several volume wave signal amplitudes are mentioned to provide labels. Specifically, Figure 3 The first closed-loop amplitude A is shown respectively CL1 and the second closed-loop amplitude A CL2 and respectively show the first open loop amplitude A OL1 and the second open-loop amplitude A OL2 The first open loop amplitude A OL1 and the first closed-loop amplitude A CL1 Indicates the maximum fluctuation amplitude relative to the baseline volume wave signal level. Second open loop amplitude A OL2 and the second closed-loop amplitude A CL2 represents the maximum peak-to-trough volume wave signal amplitude. As described below, the first amplitude value or the second amplitude value is used to constrain the closed-loop control gain to allow both arterial blood pressure measurement and blood composition sensing based on volume clamping.

[0031] Figure 4 is a flow chart illustrating a ratio-based gain control method 400. The ratio-based gain control method 400 is a generalized example of a portion of a method of operation of the sensor system 10.

[0032] The ratio-based gain control method 400 begins by attaching the pressurizable bladder 22 around the finger 24. (Step 402). Once the pressurizable bladder 22 is in place and the hand 14 is substantially stationary, the controller 34 engages the open loop calibration mode (see Figure 3 During the open loop calibration mode, the controller 34 stores or records the open loop amplitude A while maintaining the cuff pressure constant. OL , for example, the first open-loop amplitude A as described above OL1 Or the second open loop amplitude A OL2 or both. (Step 406). The controller then adjusts or limits the volume wave set point based on the volume wave value in the open loop calibration mode (Step 408) and enters the closed loop control mode (see Figure 2 and Figure 3 The controller stores or records the closed loop amplitude A during the closed loop control mode. CL , for example, the first closed-loop amplitude A as described above CL1 Or the second closed-loop amplitude A CL2or both. (Step 412). In some embodiments, both sets of open-loop and closed-loop amplitudes can be recorded and used as surrogate or comparison inputs. As described above, controller 34 can periodically cycle between open-loop and closed-loop control to update and calibrate the volume wave setpoint, or in response to an indication that recalibration is needed. Such indications can include, for example, increased oscillation instability or increased volume wave error within a set time window.

[0033] Controller 34 is based on A CL and A OL To calculate the amplitude ratio R A (Step 414). This ratio is used to determine whether the gain of the closed loop control mode (410) should be adjusted to allow accurate sensing of both blood composition and arterial blood pressure. Specifically, the controller 34 evaluates the calculated R A Whether the ratio falls within the allowable range (band). (Step 416). Figure 5 This interval is discussed in more detail. A sufficiently high level of gain that causes overshoot in PID control is unsuitable for both arterial blood pressure and blood composition sensing, but an appropriate level of gain for arterial blood pressure sensing may result in clamping of the artery that is too aggressive to allow sufficient pulsation for accurate blood composition sensing. Conversely, if the gain is at too low a level, the clamping will not be sufficient to ensure reliable and accurate arterial blood pressure sensing, but will allow sufficient blood composition sensing. Therefore, the gain between these two extremes (e.g., the total gain, or any combination of P gain, I gain, or D gain in the example of PID control) should be maintained at a level that enables successful utilization of a single multifunction sensor to detect both arterial blood pressure and blood composition. To ensure success, the controller 34 responds to the ratio R falling below the acceptance interval by increasing the gain (step 418) of the closed-loop control mode (step 410). A , and responds to the ratio R being above the acceptance interval by reducing the gain (step 420) of the closed loop control mode (step 410) A The gain within the acceptance interval does not need to be adjusted (step 422).

[0034] Figure 5 is a functional block diagram illustrating a control process 500 for sensor system 10 that expands upon ratio-based gain control method 400 in a more specific form. Essentially as described above with respect to closed-loop control, controller 34 receives a volume wave signal (step 502) and a volume wave setpoint (step 504). The difference between these values is adjusted based on various factors to generate an adaptive gain modification in the form of a multiplicative adjustment AG, described in greater detail below (step 506). Specifically, controller 34 records the open-loop amplitude A over time. OL (Step 508) and closed loop amplitude ACL (Step 510), which are used to generate the amplitude ratio R A (Step 512).

[0035] The controller 34 uses the open loop amplitude A OL and amplitude ratio R A For reference Figure 4 More specifically, the adaptive gain can be described as:

[0036] [Equation 2] AG = GainMod / PropPletGainDivid

[0037] Where AG is the adaptive gain; PropPletGainDivid=C*(A CL +M), where M and C can be constants; and GainMod is an adjustment factor initially set to 1.0. In some examples, the value of M can be selected to allow R min Depending on the vasoconstrictive state of hand 24, and may depend on both patient details (e.g., age and / or skin temperature) and the amplification of the sensor and transmitter hardware, which may change over time and / or based on circumstances, controller 34 may respond to amplitude ratio R as more generally described above with respect to method 400. A Falling from the minimum ratio R min Span to the maximum ratio R max The adaptive gain AG is adjusted when the value is outside the acceptance interval, where:

[0038] [Equation 3] R A =(A OL +M) / AvgA CL

[0039] And AvgA CL is the average of the closed-loop amplitude over at least two heartbeats. To reduce the influence of the breathing signal, for example, AvgA CL It can be the average closed-loop amplitude value over eight or more patient heartbeats. A The value of GainMod is adjusted incrementally, and the gain is adaptively adjusted toward satisfying R min <R A <R max The value of the drive. Amplitude ratio R A The target interval can be, for example, min =5 to R max = 20. In more constrained cases, this interval can be min =12 to R max =14. If the amplitude ratio RA Descend to R in a specific evaluation loop min Below, increase GainMod, for example, so that:

[0040] [Equation 4] GainMod*=A*(R min / R A )

[0041] Where A is an adjustment factor greater than 1, such as 1.05. Similarly, if the amplitude is greater than R A Rising to R in a particular assessment cycle max Above, reduce GainMod, for example, so that:

[0042] [Equation 5] GainMod*=B*(Rmax / RA)

[0043] Where B is an adjustment factor less than 1, for example 0.95. The adjustment factors A and B are chosen to be minimal to avoid overshooting the desired value, i.e. to prevent any correction from increasing the magnitude by more than R A Reduce to the new R A <R min Or the amplitude R A Increase to the new R A >R max In other illustrative examples, A and B may be set to other values, such as 1.1 and 0.9, respectively.

[0044] In some examples, the adaptive gain AG can also be adjusted based on the detection of excessive oscillations in the volume wave signal. (Step 514). Specifically, if the oscillation level is unacceptable (e.g., indicated by a count of PID overshoot oscillations exceeding a threshold value (e.g., 4)), the controller 34 can adjust the R min Incrementally decrease to a decreasing R min The minimum lower limit of R min This lower limit value can be, for example, greater than R min In some examples, R can be reduced based on the state of vasoconstriction within the sensing region. min to R max The adaptive gain AG can be limited by a damping factor, which limits the amplitude of the gain change between two adjacent processing iterations.

[0045] Controller 34 sets adaptive gain AG based on the aforementioned factors. To avoid rapid fluctuations in gain, controller 34 can be limited to adjusting GainMod only after at least a threshold number of heartbeats (e.g., 8) have passed since the previous adjustment. This timing requirement can be waived immediately after the open-loop calibration cycle. The adaptive gain generated by controller 34 in step 506 drives valve actuation (step 516). In some examples, further control parameter processing for other purposes can be included between steps 506 and 516.

[0046] The methods and apparatus described herein allow a single multifunctional sensor to sense both arterial blood pressure and blood composition using a multi-wavelength optical emitter and sensor. This is achieved through gain control that targets a gain range that produces a gain high enough to partially clamp the arterial volume and thereby generate accurate and reliable arterial blood pressure readings, but low enough to maintain sufficient arterial pulsatility to distinguish blood composition from non-blood-related differential light absorption.

[0047] Example

[0048] What follows is a non-exclusive description of possible examples for implementing the various concepts of this disclosure.

[0049] A method of operating a non-invasive blood characteristic sensing system, the non-invasive blood characteristic sensing system comprising a light emitter, a light sensor, and a pressurizable cuff, the method comprising: surrounding a sensing area of a patient's appendage with the pressurizable cuff; emitting light of a plurality of discrete wavelengths from the light emitter into the sensing area of the patient's appendage; sensing, for each of the discrete wavelengths of light, an amplitude of light received by the light sensor from the light emitter through the patient's appendage; generating a sensed plethysmogram value reflecting an arterial volume within the sensing area based on the sensed light amplitude; and generating a pressure-sensitive plethysmogram value in response to a difference between the sensed plethysmogram value and a setpoint plethysmogram value. and , adjusting the pressurization of the pressurizable cuff in a closed-loop control mode via a closed-loop control algorithm to partially clamp the arterial volume within the sensing region based on a closed-loop error value of the difference between the plurality of discrete wavelengths of light sensed by the light sensor during arterial pulsations within the sensing region; generating a composition analysis of the arterial blood within the sensing region based on the differential absorption of the plurality of discrete wavelengths of light sensed by the light sensor during arterial pulsations within the sensing region; and generating a sensed arterial blood pressure based on the pressurization of the pressurizable cuff required to partially clamp the arterial volume, wherein partially clamping the arterial volume within the sensing region includes suppressing but not eliminating arterial pulsations, such that generation of the composition analysis can be performed simultaneously with partially clamping the arterial volume.

[0050] Additionally and / or alternatively, the method of the preceding paragraph may optionally include any one or more of the following features, configurations, and / or additional components:

[0051] The method as described above also includes: maintaining constant pressurization of the pressurizable cuff during a cyclic open-loop calibration mode; sensing an open-loop error value reflecting the difference between the sensed plethysmogram value and the set-point plethysmogram value during the open-loop calibration mode; and calibrating the set-point plethysmogram value based on the open-loop error value.

[0052] The method as described above also includes: calculating a ratio of the maximum open-loop error value amplitude during the cyclic open-loop calibration mode to the maximum closed-loop error amplitude during the closed-loop control mode; and adjusting the gain of the closed-loop control algorithm to drive the calculated ratio toward a value within a preset range.

[0053] The method as described above, wherein the preset range is 5 to 20.

[0054] The method as described above further includes narrowing the preset range based on the vasoconstriction state within the sensing area.

[0055] As described above, the method of adjusting the gain of the closed-loop control algorithm includes: increasing the gain in proportion to the extent to which the calculated ratio is lower than the lower limit of the preset range, and decreasing the gain in proportion to the extent to which the calculated ratio exceeds the upper limit of the preset range.

[0056] The method as above, wherein the adjustment of the incremental change in gain is limited according to the attenuation value.

[0057] The method as described above, wherein each of the open-loop error magnitude and the closed-loop error magnitude is evaluated within a time window that includes multiple heartbeats of the patient.

[0058] The method as described above, wherein the time window is selected to include at least two heartbeats of the patient.

[0059] The method as described above, further comprising detecting plethysmographic signal oscillations caused by overcorrection, and reducing the gain of the closed-loop control algorithm in response to the detected signal oscillations.

[0060] The method as above, wherein said generating of said component analysis occurs during both said repetitive open-loop calibration mode and said closed-loop control mode.

[0061] A method as described above, wherein the set-point plethysmogram value corresponds to a resting and unstressed arterial volume.

[0062] The method as described above, wherein the component analysis includes identifying at least one blood component characteristic selected from the group consisting of blood oxygen saturation, total hemoglobin, methemoglobin percentage, and carboxyhemoglobin percentage.

[0063] A non-invasive sensor system comprising: a pressurizable cuff pressurized via a metered fluid supply and sized to surround a patient appendage and define a sensing region; a light emitter anchored to the pressurizable cuff and configured to emit light at a plurality of discrete wavelengths through the sensing region of the patient appendage; a light sensor anchored to the pressurizable cuff, positioned to receive the light emitted by the light emitter, and configured to generate a sensed plethysmogram signal therefrom; and a component analysis module configured to generate a component analysis signal based on differences in the plurality of discrete wavelengths detected by the light sensor during arterial pulsations within the sensing region. and a controller configured to: calculate an error value as a difference between the sensed plethysmogram signal and a set-point plethysmogram value; operate a closed-loop control mode in which the metered fluid supply is driven to partially clamp the artery within the sensing region based on the error value and the gain level; and output a sensed arterial blood pressure based on a clamping pressure generated by the closed-loop control, wherein partially clamping the arterial volume within the sensing region includes suppressing but not eliminating arterial pulsations, such that generation of the composition analysis can be performed concurrently with partially clamping the arterial volume.

[0064] Additionally and / or alternatively, the non-invasive sensor system of the preceding paragraph may optionally include any one or more of the following features, configurations, and / or additional components:

[0065] The non-invasive sensor system as described above, wherein the controller is further configured to maintain the pressure of the pressurizable cuff constant during a cyclic open-loop configuration mode, and to recalibrate the set-point plethysmogram value based on a sensed difference between the set-point plethysmogram value and the sensed plethysmogram signal sensed during the open-loop configuration mode.

[0066] A non-intrusive sensor system as described above, wherein the controller is further configured to: record the maximum amplitude of the error value during the closed-loop control mode as the closed-loop amplitude; record the maximum amplitude of the error value during the open-loop configuration mode as the open-loop amplitude; calculate the ratio of the open-loop amplitude to the closed-loop amplitude; increase the gain level of the closed-loop control mode in response to the ratio falling below a lower limit value; and decrease the gain level of the closed-loop control mode in response to the ratio rising above an upper limit value.

[0067] A non-invasive sensor system as described above, wherein the upper limit value corresponds to a maximum gain level that allows the arterial pulsation within the sensing region to be sufficient to enable assessment of blood components.

[0068] A non-invasive sensor system as described above, wherein the upper limit value is approximately 20.

[0069] The non-invasive sensor system as described above, wherein the lower limit value is approximately 5.

[0070] The non-invasive sensor system as described above, wherein the controller is configured to set the upper limit value based on the patient's vasoconstriction state.

[0071] The non-invasive sensor system as described above, wherein the lower limit value corresponds to a minimum gain level, and the minimum gain level is sufficient to suppress arterial pulsation in the sensing area to minimize an error in the sensed arterial blood pressure.

[0072] The non-invasive sensor system as described above further comprises a metering element configured to provide the metered fluid supply to the pressurizable cuff, the metering element being controlled by the controller in the closed-loop control mode and the open-loop calibration mode.

[0073] The non-invasive sensor system as described above, wherein the metering element is a servo valve or a piezoelectric pump.

[0074] Although the present invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the basic scope of the present invention. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method of operating a non-invasive blood property sensing system, the non-invasive blood property sensing system comprising a light emitter, a light sensor, and a pressurizable cuff, the method comprising: surrounding a sensing area of the patient's appendage with the compressible cuff; emitting light of a plurality of discrete wavelengths from the light emitter into the sensing region of the patient appendage; sensing, for each of the discrete wavelengths of light, an amplitude of light received by the light sensor from the light emitter through the patient appendage; generating a sensed plethysmogram value reflecting an arterial volume within the sensing region based on the sensed light amplitude; adjusting, via a closed-loop control algorithm, pressurization of the pressurizable cuff in a closed-loop control mode to partially clamp arterial volume within the sensing region in response to a closed-loop error value reflecting a difference between the sensed plethysmogram value and a set-point plethysmogram value; generating a compositional analysis of arterial blood within the sensing region based on differential absorption of the plurality of discrete wavelengths of light sensed by the light sensor during arterial pulsation within the sensing region; and generating a sensed arterial blood pressure based on pressurization of the pressurizable cuff required to partially clamp the arterial volume, Partially clamping the arterial volume within the sensing region includes suppressing but not eliminating arterial pulsations, such that generating the component analysis can be performed concurrently with partially clamping the arterial volume.

2. The method according to claim 1, further comprising: maintaining constant pressurization of the pressurizable cuff during a cyclic open-loop calibration mode; sensing an open-loop error value reflecting a difference between the sensed plethysmogram value and the set-point plethysmogram value during the open-loop calibration mode; as well as The setpoint plethysmogram value is calibrated based on the open-loop error value.

3. The method according to claim 2, further comprising: calculating a ratio of a maximum open-loop error magnitude during the cyclic open-loop calibration mode to a maximum closed-loop error magnitude during the closed-loop control mode; as well as The gain of the closed-loop control algorithm is adjusted to drive the calculated ratio toward a value within a preset range. The method according to claim 3 , wherein the preset range is 5 to 20. The method according to claim 3 , further comprising narrowing the preset range based on a vasoconstriction state within the sensing area.

6. The method of claim 3, wherein said adjusting the gain of said closed-loop control algorithm comprises: The gain is increased in proportion to the extent to which the calculated ratio is below a lower limit of the preset range, and the gain is decreased in proportion to the extent to which the calculated ratio exceeds an upper limit of the preset range. The method of claim 6 , wherein adjusting the incremental change in gain is limited according to an attenuation value.

8. The method of claim 6, wherein each of the open-loop error magnitude and the closed-loop error magnitude is evaluated over a time window that includes multiple heartbeats of the patient.

9. The method of claim 8, wherein the time window is selected to include at least two heartbeats of the patient.

10. The method of claim 6, further comprising detecting plethysmographic signal oscillations caused by overcorrection, and reducing the gain of the closed-loop control algorithm in response to the detected signal oscillations.

11. The method of claim 2, wherein the generating of the composition analysis occurs during both the repetitive open-loop calibration mode and the closed-loop control mode.

12. The method of claim 2 or 11, wherein the set-point plethysmographic value corresponds to a resting and unstressed arterial volume.

13. The method of any one of claims 1 and 10-11, wherein the component analysis comprises identifying at least one blood component characteristic selected from the group consisting of blood oxygen saturation, total hemoglobin, methemoglobin percentage, and carboxyhemoglobin percentage.

14. The method of claim 13, wherein the component analysis includes identifying blood oxygen saturation via pulse oximetry.

15. The method of claim 14, wherein the step of generating a compositional analysis of arterial blood comprises comparing absorption of the plurality of discrete wavelengths of light that is constant during arterial pulsation with absorption of the plurality of discrete wavelengths of light that varies due to arterial pulsation.

16. A non-invasive sensor system comprising: a pressurizable cuff pressurized via a metered fluid supply and sized to encircle the patient's appendage and define a sensing area; a light emitter anchored to the pressurizable cuff and configured to emit light at a plurality of discrete wavelengths across the sensing region of the patient appendage; a light sensor anchored to the compressible cuff, positioned to receive light emitted by the light emitter, and configured to generate a sensed plethysmogram signal therefrom; a composition analysis module configured to assess blood composition within the sensing region based on differential absorption of the plurality of discrete wavelengths detected by the light sensor during arterial pulsation within the sensing region; as well as A controller configured to: calculating an error value as a difference between the sensed plethysmogram signal and a setpoint plethysmogram value; operating a closed-loop control mode in which the metered fluid supply is driven to partially clamp the artery within the sensing region based on the error value and the gain level; as well as outputting a sensed arterial blood pressure based on the clamping pressure generated by the closed-loop control, Partially clamping the artery within the sensing region includes suppressing but not eliminating arterial pulsations, such that generating the compositional analysis can be performed concurrently with partially clamping the arterial volume.

17. The non-invasive sensor system of claim 16 , wherein the controller is further configured to maintain the pressure of the pressurizable cuff at a constant value during a cyclic open-loop configuration mode, and to recalibrate the set-point plethysmogram value based on a sensed difference between the set-point plethysmogram value and the sensed plethysmogram signal sensed during the open-loop configuration mode.

18. The non-invasive sensor system of claim 17, wherein the controller is further configured to: recording a maximum magnitude of the error value during the closed-loop control mode as a closed-loop magnitude; recording a maximum magnitude of the error value during the open-loop configuration mode as an open-loop magnitude; calculating a ratio of the open-loop amplitude to the closed-loop amplitude; increasing the gain level of the closed-loop control mode in response to the ratio falling below a lower limit; and The gain level of the closed-loop control mode is reduced in response to the ratio rising above an upper limit value.

19. The non-invasive sensor system of claim 18, wherein the upper limit value corresponds to a maximum gain level that allows arterial pulsation within the sensing region to be sufficient to enable blood composition to be assessed via the composition analysis module.

20. The non-invasive sensor system of claim 19, wherein the upper limit value is approximately 20.

21. The non-invasive sensor system of claim 20, wherein the lower limit value is approximately 5.

22. The non-invasive sensor system of claim 19, wherein the controller is configured to set the upper limit value based on a vasoconstrictive state of the patient.

23. The non-invasive sensor system of claim 19, wherein the lower limit value corresponds to a minimum gain level sufficient to suppress arterial pulsations within the sensing region to minimize errors in the sensed arterial blood pressure.

24. The non-invasive sensor system of claim 19, wherein the assessment of the blood composition comprises identifying at least one blood composition characteristic selected from the group consisting of blood oxygen saturation, total hemoglobin, methemoglobin percentage, and carboxyhemoglobin percentage.

25. The method of claim 24, wherein the assessment of blood composition comprises identifying blood oxygen saturation via pulse oximetry.

26. The non-invasive sensor system of claim 16, further comprising a metering element configured to provide the metered fluid supply to the pressurizable cuff, the metering element being controlled by the controller in both the closed-loop control mode and the open-loop configuration mode.

27. The non-invasive sensor system of claim 26, wherein the metering element is a servo valve or a piezoelectric pump.

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