Adaptive servo gain control for multiwavelength volume clamping.

Abstract

The blood property sensing system includes a light emitter, a light sensor, and a pressurizable cuff. The system surrounds a sensing area of ​​the patient's appendage with the pressurizable cuff, emits light of multiple discrete wavelengths into the sensing area, and senses the amplitude for each wavelength received through the patient's appendage. Sensed plethysmogram values ​​reflecting arterial volume are generated based on these sensed amplitudes, and cuff pressurization is adjusted to partially clamp the arterial volume within the sensing area via a closed-loop control algorithm based on the sensed plethysmogram values ​​and a setpoint plethysmogram value. The differential absorption of the sensed wavelengths is used to generate an analytical composition of arterial blood within the sensing area, and arterial blood pressure is sensed based on the cuff pressurization required to partially clamp the arterial volume.

Description

[Technical Field]

[0001] The present disclosure relates generally to blood property sensing, and more particularly to gain control of volume clamping in a multifunction multi-wavelength arterial blood pressure and blood composition sensor. [Background technology]

[0002] Some noninvasive arterial blood pressure sensors generate pressure readings by clamping (i.e., holding constant) arterial volume within a sensing area, such as a portion of a finger surrounded by a pressurizable cuff. Such systems directly assess arterial volume, e.g., optically, and increase or decrease the constriction provided by the pressurizable cuff via closed-loop control to compensate for variations in arterial volume caused by blood pulsation. The resulting clamped pressure is used as a surrogate or estimate of the arterial blood pressure waveform (AP), allowing blood pressure to be monitored noninvasively over long periods of time without interruption. In some instances, the arterial volume waveform can also be directly analyzed to estimate mean arterial blood pressure, diastolic blood pressure, or systolic blood pressure.

[0003] 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 [Means for solving the problem]

[0004] The present disclosure presents a method of operating a blood characteristic sensing system. The sensing system includes a light emitter, a light sensor, and a pressurizable cuff. The system operates by surrounding a sensing area of ​​a patient's appendage with the pressurizable cuff, emitting light of multiple discrete wavelengths from the light emitter into the sensing area of ​​the patient's appendage, and sensing the amplitude of light received from the light emitter through the patient's appendage by the light sensor for each of the discrete wavelengths. A sensed plethysmogram value reflecting arterial volume within the sensing area is generated based on the sensed light amplitude, and pressurization of the pressurizable cuff is adjusted via a closed-loop control algorithm to partially clamp the arterial volume within the sensing area in response to a closed-loop error value reflecting the difference between the sensed plethysmogram value and a setpoint plethysmogram value. A compositional analysis of arterial blood within the sensing area is then generated based on differential absorption of the multiple discrete wavelengths of light as sensed by the light sensor during arterial pulsation within the sensed area. A sensed arterial blood pressure is generated based on the pressurization of the pressurizable cuff required to partially clamp the arterial volume.

[0005] The present disclosure also provides a noninvasive sensor system including a pressurizable cuff, a light emitter, an optical 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 region. The light emitter is secured to the pressurizable cuff and configured to emit light at a plurality of discrete wavelengths through the sensing region of the patient's appendage. The optical sensor is also secured to the pressurizable cuff and positioned to receive 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 region based on differential absorption of the discrete wavelengths emitted by the light emitter as detected by the optical sensor during arterial pulsation within the sensing region. The controller is configured to calculate an error value as the difference between the sensed volume pulse signal and a set point plethysmogram value and to operate in a closed loop control mode, wherein 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 the clamping pressure corresponding to the sensed arterial blood pressure.

[0006] The Summary of the Invention is presented by way of example only, and not by way of limitation. Other aspects of the disclosure will be understood with reference to the entire disclosure, including the entire text, claims, and accompanying drawings. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a simplified perspective view of a non-invasive sensor system that fits in a human hand. [Figure 2] FIG. 2 is a schematic diagram of the non-invasive sensor system of FIG. 1 in operation. [Figure 3] 3 is a parallel graph of cuff pressure and overall light level as a function of time during an illustrative example of an operating period of the noninvasive sensor system of FIGS. 1 and 2; [Figure 4] 3 is a flowchart illustrating a method of operation of the non-invasive sensor system of FIGS. 1 and 2. [Figure 5] FIG. 3 is a functional block diagram illustrating a control process for the non-invasive sensor system of FIGS. 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] The above figures set forth one or more examples of the present disclosure; other examples are contemplated, as noted in the description. In all cases, the present disclosure presents the invention by way of illustration and not limitation. It should be understood that numerous other modifications and examples may be devised by those skilled in the art which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings.

[0009] This disclosure describes one approach to volume clamping control in a multifunction sensor system. The system uses received light amplitude as a sensed plethysmogram value (hereinafter, "plethysmogram signal") representing arterial volume within the sensed region, physically clamps the arterial volume via closed-loop control based on the plethysmogram reading, and reports the resulting clamped pressure as an arterial blood pressure waveform. Further analysis of this waveform can derive systolic (SYS) blood pressure, diastolic (DIA) blood pressure, and mean arterial pressure (MAP). The light used to generate the plethysmogram signal is emitted across multiple wavelengths, thereby enabling analysis of blood composition (e.g., blood oxygen saturation, total hemoglobin, percentage methemoglobin, and percentage carboxyhemoglobin) by comparing light absorption at multiple wavelengths during arterial pulsation. This approach allows a single noninvasive multifunction sensor to provide measurements for both arterial blood pressure and arterial blood composition.

[0010] The volume clamping described above for arterial blood pressure sensing superficially contradicts the requirement that arterial pulsation be tolerated (i.e., not clamped) to assess blood composition based on differential wavelength absorption. The present disclosure provides a method and system for closed-loop clamping that uses adaptive gain control tailored to provide sufficient clamping to accurately sense arterial blood pressure while allowing enough arterial pulsation to enable blood composition assessment. This balancing of clamping gain between "too high" (preventing composition analysis) and "too low" (compromising arterial blood pressure sensing accuracy) is described in more detail below. The present approach adjusts the gain for the closed-loop volume clamp control to avoid completely clamping the artery while providing enough clamping to produce an arterial blood pressure reading with negligible loss of accuracy.

[0011] FIG. 1 presents a simplified perspective view of sensor system 12 attached to hand 14. FIG. 2 is a schematic diagram of sensor system 12 in operation. FIGS. 1 and 2 are primarily described together. As shown in FIG. 1, sensor system 12 is a noninvasive hemodynamic sensor capable of generating arterial blood pressure measurements through a volume clamp. Sensor system 12 can include a housing 16, a connector 18, a cuff 20, and a pressurizable bladder 22. In the illustrated embodiment, cuff 20 is a ring or similar structure that encircles or brackets a finger 24 of hand 14, and housing 16 is a wrist-worn device coupled to cuff 20 via connector 18. However, in the most general case, sensor system 12 can differ substantially from the layout illustrated in FIG. 1. The sensor system 12 may, for example, include multiple separate connectors 18 between elements attached to the finger 24 (e.g., the cuff 20) and / or the housing 16 may be relocated elsewhere (e.g., integrated with the cuff 20 or separately disposed in a peripheral location). In the illustrated example, the cuff 20 surrounds the sensing area of ​​the finger 24 of the hand 14. At least one artery 26 passes through the sensing area. The cuff 20 also secures a pressurizable bladder 22, which may be, for example, an inflatable annular air bladder supplied by an air line contained within the connector 18 or from a separate source. However, in the most general case, the pressurizable bladder 22 may be any type of mechanism suitable for applying pressure to the finger 24 under control as described below. Together, the sensor system 12 and the hand 14 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.

[0012] As shown in FIG. 2 , the cuff 20 includes a light emitter 28 and a light sensor 30. The light emitter 28 emits light at multiple discrete wavelengths through a sensing region (represented in FIG. 2 by path lines through the finger 24) for reception by the light sensor 30. In examples described in detail below, the wavelengths of light emitted by the light emitter 28 may all fall within a spectrum ranging from visible to infrared. The light sensor 30 detects both the overall received light amplitude and the specific received light amplitude at each of the discrete wavelengths emitted by the light emitter 28. In some examples, the light emitter 28 and the light sensor 30 are located on opposite sides of the cuff 20, allowing light to travel directly through the sensing region of the finger 24 from the light emitter 28 to the light sensor 30. However, more commonly, scattering of light from the light emitter 28 within the tissue of the finger 24 allows the light emitter 28 and the light sensor 30 to be effective even when not disposed on opposite sides of the cuff 20, for example, when positioned adjacent to one another.

[0013] The overall light amplitude received at photosensor 30 from transmission by light emitter 28 is hereafter referred to as the plethysmogram signal and is used as a proxy for the inverse arterial volume within the sensing area, with a decrease in received light corresponding to an increase in arterial volume. The two arteries and connected capillaries in the finger pulsate during normal blood flow, expanding (at systolic pressure) and relaxing (at diastolic pressure) in volume during each cardiac cycle. The larger the arterial volume, the greater the absorption of emitted light, reducing the proportion of emitted light received at photosensor 30.

[0014] As primarily described herein, sensor system 12 clamps the arterial volume within the sensing region by a pneumatically pressurizable bladder 22 through actuation of a valve 32, thereby regulating the air pressure supplied onto air bladder 22 through connector 18. While generally referred to herein as a valve, valve 32 can be any type of fluid airflow metering element, most commonly a servo valve or a piezoelectric pump. Sensor system 12 can clamp the arterial volume by any approach that applies a known pressure to the sensing region of finger 24.

[0015] The sensor system 12 includes a controller 34 having logic-enabled hardware configured to adjust the setting of the valve 32 in a control loop responsive to the plethysmogram signal. The controller 34 may be, for example, a control module instantiated in dedicated hardware, or hardware within the sensor system 12, or a software module executing outside the sensor system 12, e.g., on a communicatively connected device. Increased flow through the valve 32 into the pressurizable bladder 22 results in the pressurizable bladder 22 expanding, physically constricting the finger 24 and thereby increasing the arterial volume of the sensing area. The difference between the plethysmogram value and the corresponding target set point (hereinafter designated "plethysmogram error") is used as an input for control of the valve 32 by the controller 34. In the detailed description presented hereafter, this control scheme and method (see FIGS. 3 and 4) is described as involving proportional-integral-derivative (PID) control based on the plethysmogram error. However, in the most general case, other forms of closed-loop control may be used in place of PID control. The controller 34 drives the pressurizable bladder 22 through actuation of the valve 32, mechanically counteracting changes in arterial volume within the sensing region, reducing the magnitude of arterial volume fluctuations and keeping the arterial volume relatively constant. The valve pressure generated by this clamping process serves as a measure of arterial blood pressure. In some examples, the valve 32 and the controller 34 may both be located within the housing 16. However, more generally, the valve 32 may be positioned in any suitable location for metering pressurization of the pressurizable bladder 22, and the controller 34 may be located within the housing 16, within or near the cuff 20, or any other location capable of supporting processing for controlling the actuation of the valve 32. In some examples, some functions of the controller 34 may be offloaded to a peripheral device (not shown in FIG. 1 ).

[0016] Light emitter 28 emits a discrete or fixed, known spectrum of light across a range of wavelengths (e.g., primarily visible to infrared wavelengths or a range including such) that detectably vary in absorption across the material composition of interest. In one illustrative example, light emitter 28 can emit a range of wavelengths exclusively within the infrared band (700 nm to 1000 nm). In alternative examples, a broader range of light can be used (e.g., 500 nm to 1100 nm), including light in the visible and / or microwave bands. In the most general case, light emitter 28 generates light of known amplitude over a range of wavelengths wide enough to distinguish absorption spectra associated with at least two parameters, including, but not limited to, blood oxygen saturation, total hemoglobin, percentage methemoglobin, or percentage carboxyhemoglobin.

[0017] Composition analysis module 36 assesses blood composition based on the differential absorption of various discrete wavelengths of light emitted by light emitter 28 during arterial pulsation, as detected by optical sensor 30. Different substances, such as oxyhemoglobin (OHb, oxygen-saturated blood), deoxyhemoglobin (HHb, oxygen-unsaturated blood), and water, by way of example, all have detectably different absorption spectra.

[0018] In one implementation, the composition analysis module 36 determines arterial blood oxygen saturation, which can be calculated using pulse oximetry. Two or more discrete wavelengths of light can be utilized to perform pulse oximetry. In some implementations, a light emitter 28 is utilized to perform pulse oximetry. Additionally or alternatively, in some implementations, the light emitter 28 includes a single light source (e.g., a diode) capable of providing two or more discrete wavelengths of light (or bands of wavelengths of light). In some implementations, the light emitter 28 includes at least two light sources (e.g., at least two diodes) so that two or more discrete wavelengths of light (or bands of wavelengths of light) can be emitted simultaneously. Generally, when at least two light sources are utilized, the light sources can be positioned close to each other (e.g., within 0.5 mm) to form similar light paths, although any configuration can be utilized. As previously mentioned, the light emitter 28 may emit light in a wavelength range exclusively within the infrared band (700 nm to 1000 nm), or light in the visible and / or microwave bands may be used to perform pulse oximetry (e.g., 500 nm to 1100 nm).

[0019] Pulse oximetry relies on the fact that a portion of the absorbed optical signal (e.g., light absorbed by tissue, venous blood, and non-pulsatile arterial blood) is constant regardless of the moment of the cardiac cycle, and a portion of the absorbed optical signal varies depending on the arterial blood pulsation as related to the cardiac cycle. This constant optical signal is referred to as the DC signal, and the variable optical signal is referred to as the AC signal. Using DC and AC signals of light at two wavelengths (λ1 and λ2), the ratio (R) can be calculated using the equation

[0020]

number

[0021] It can be calculated by: The ratio R can be plotted against experimentally determined oxygen saturation values ​​(e.g., SpO2) to obtain a calibration curve that can be used in the analysis of arterial oxygen saturation as determined using a body-appended PPG.

[0022] Because arterial pulsation is used to distinguish pulsating arterial blood from other biological materials (e.g., distinguishing between AC and DC signals), compositional analysis is therefore only possible during arterial pulsation. The approach defined hereinafter adjusts the proportional gain of the PID control in controller 34 to clamp the arterial volume sufficiently to keep it relatively constant to generate an accurate and reliable measurement of arterial blood pressure based on the pressure in pressurizable bladder 22, while allowing sufficient arterial pulsation for compositional analysis module 36 to distinguish between arterial blood and other materials. In one illustrative example, the adjusted gain thus generated controls actuation of pressurizable bladder 22 by varying the airflow through valve 32, thereby adjusting the resulting mechanical clamping force of pressurizable bladder 22 against finger 24.

[0023] FIG. 3 is a parallel graph of cuff pressure 300 and plethysmogram signal 302 as a function of time during an illustrative example of an operating period of sensing system 10. FIG. 3 illustrates the operation of sensing system 10 through the end of a first closed-loop period 304a, transitioning to an open-loop period 306 at time t0 and then to an updated closed-loop period 304b at time t1. As explained above with reference to FIGS. 1 and 2 above, and further below with reference to FIGS. 4 and 5, 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 pressurizable bladder 22. Periods 304a and 304b are time windows during which cuff pressure is controlled by this closed-loop control so that arterial volume remains relatively constant. However, during open-loop period 306, controller 34 evaluates plethysmogram values ​​and allows arterial volume expansion as it pulsates, while holding the pressure in pressurizable bladder 22 constant. The open-loop period 306 is used to recalibrate the baseline arterial volume in the form of a plethysmogram set point used in closed-loop control throughout the subsequent closed-loop period 304b. This open-loop calibration period is used periodically during patient monitoring to confirm the initial setup, i.e., the initial setting for a new patient or cuff setup, and, in conjunction with that, adjust for changes in the patient's condition. This set point ideally corresponds to the resting, unstressed arterial volume (i.e., not dilated by arterial pulsation) within the sensing region for the current state of the finger 24, including the patient's hand position / posture and blood perfusion. The closed-loop volume clamp can be interrupted for open-loop calibration either on a scheduled basis to adjust for small changes in the patient's position or condition, or on a triggered (non-scheduled) basis in response to irregularities indicating the current plethysmogram set point requires recalibration.

[0024] FIG. 3 also provides labels for several plethysmogram signal amplitudes that are referenced below with reference to FIGS. 4 and 5. In particular, FIG. 3 provides labels for the first and second closed-loop amplitudes A CL1and A CL2 and the first and second open-loop amplitudes A OL1 and A OL2 The first open loop amplitude A OL1 and the closed-loop amplitude A CL1 represents the maximum fluctuation amplitude about the baseline plethysmogram signal level. OL2 and the closed-loop amplitude A CL2 where ρ represents the maximum peak-to-trough plethysmogram signal amplitude. As described below, the first or second amplitude value is used to constrain the closed-loop control gain to enable both volume-clamp-based arterial blood pressure measurement and blood composition sensing.

[0025] 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 partial operational method for the sensor system 12.

[0026] The ratio-based gain control method 400 begins with the placement of the pressurizable bladder 22 around the finger 24 (step 402). After the pressurizable bladder 22 is in place and the hand 14 is generally stationary, the controller 34 enters an open-loop calibration mode (see open-loop period 306 in FIG. 3 ) and records plethysmogram values ​​while holding the cuff pressure constant (step 404). While in the open-loop calibration mode, the controller 34 adjusts the open-loop amplitude A OL , for example, the first open-loop amplitude A OL1 or the second open-loop amplitude A OL2 or both (step 406). The controller then adjusts or defines the plethysmogram set point based on the plethysmogram values ​​in the open-loop calibration mode (step 408) and enters a closed-loop control mode (see closed-loop periods 304a and 304b in Figures 2 and 3) (step 410), operating in this closed loop to maintain the volume clamp until the next open-loop calibration period. While in the closed-loop control mode, the controller adjusts or defines the closed-loop amplitude A CL, for example, the first closed-loop amplitude A CL1 or the second closed-loop amplitude A CL2 or both are stored or recorded (step 412). In some implementations, both sets of open-loop and closed-loop amplitudes are recorded and may be used as alternative or comparison inputs. As noted above, the controller 34 may periodically cycle between open-loop and closed-loop control to update and calibrate the plethysmogram setpoints or respond to indications that recalibration is required. Such indications may include, for example, increased vibration instability or increased plethysmogram error over a set time window.

[0027] The controller 34 is CL and A OL Based on the amplitude ratio R A (step 414). This ratio is used to determine whether the gain for the closed-loop control mode (410) should be adjusted to allow both blood composition and arterial blood pressure to be accurately sensed. In particular, the controller 34 calculates R AThe calculated ratio of R to ρ is evaluated (step 416) to see if it falls within an acceptable band. This band is described in more detail below with respect to FIG. 5. A sufficiently high level of gain that causes overshoot in the PID control would be inappropriate for sensing both arterial blood pressure and blood composition, while an appropriate level of gain for arterial blood pressure sensing may result in too aggressive clamping of the artery to allow sufficient pulsation for accurate blood composition sensing. Conversely, if the gain is too low, the clamping is insufficient to ensure reliable and accurate arterial blood pressure sensing, but allows sufficient blood composition sensing. Therefore, gain between these two extremes (e.g., overall gain, or any combination of P-, I-, or D-gains in the example of PID control) should be maintained at a level such that a single multifunction sensor can successfully detect both arterial blood pressure and blood composition. To ensure success, the controller 34 increases the gain (step 418) for the closed-loop control mode (step 410) to increase the ratio R to ρ below the acceptable band. A , and reducing the gain (step 420) for the closed-loop control mode (step 410) to reduce the ratio R A The gain in the observed band does not require adjustment (step 422).

[0028] 5 is a functional block diagram illustrating a control process 500 for sensor system 12, which is a more specific extension of ratio-based gain control method 400. Essentially as described with respect to closed-loop control above, controller 34 receives a plethysmogram signal (step 502) and a plethysmogram setpoint (step 504). The difference between these values ​​is adjusted based on various factors to generate an adaptive gain correction (step 506) in the form of a multiplicative adjustment A G , which is described in more detail below. In particular, controller 34 adjusts the open-loop amplitude A OL (Step 508) and the closed-loop amplitude A CL (step 510) are recorded over time, and these are the amplitude ratio R A(Step 512).

[0029] The controller 34 controls the open loop amplitude A OL and amplitude ratio R A is used to broadly adjust the adaptation gain as described with reference to Figure 4. More specifically, the adaptation gain can be described by the following equation: [Formula 2] AG=GainMod / PropPletGainDivid where AG is the adaptive gain and PropPletGainDivid=C*(A CL +M), where M and C can be constants; GainMod is an adjustment factor that is initialized to 1.0. In some examples, the value of M is min may be selected to allow the amplitude ratio R to be made dependent on the state of vasoconstriction of the hand 14, and may depend on both patient details (e.g., age and / or skin temperature) and the amplification of the sensor and light emitter hardware, which may change over time and / or based on circumstances. As discussed more generally above with respect to method 400, the controller 34 may adjust the amplitude ratio R A is the minimum ratio R min to the maximum ratio R max adjusts the adaptive gain A G in response to the signal being outside an allowable band spanning [Formula 3] R A =(A OL +M) / AvgA CL and AvgA CL is the average closed-loop amplitude over at least two heartbeats. To reduce the signal effect of respiration, for example, AvgA CL may be the average closed-loop amplitude value over eight or more patient heartbeats. The gain is determined by the amplitude ratio R A R by incrementally adjusting GainMod depending on the value of min <R A <R max The amplitude ratio R A The target bandwidth of, for example, R min =5 to Rmax = 20. In more restrictive cases, the bandwidth can be R min =12 to R max = 14. In a particular evaluation cycle, the amplitude ratio R A R min If it is lower, the GainMod is increased, for example: [Formula 4] GainMod*=A*(R min / R A ) where A is an adjustment factor greater than 1, e.g., 1.05. Similarly, the amplitude ratio R A R max If it is higher, the GainMod is reduced, for example: [Formula 5] GainMod*=B*(R max / R A ) where B is an adjustment factor less than 1, for example 0.95. The adjustment factors A and B are selected to be minimum values ​​to avoid overshooting the desired value, i.e., the correction is made to the amplitude ratio R A New R A <R min or amplitude R A New R A >R max In other illustrative examples, A and B may be set to other values, for example, 1.1 and 0.9, respectively.

[0030] The adaptive gain A G may also be adjusted in some examples based on detection of excessive oscillations in the plethysmogram signal (step 514). In particular, the controller 34 may adjust R if the level of oscillation is unacceptable, for example, as indicated by a count of PID overshoot oscillations exceeding a threshold value (e.g., 4). min , the reduced R min can be gradually reduced to the smallest lower limit of R. min This lower limit of, for example, R min can be reduced by up to 30% from the initial value of Rmin From R max The range of may be reduced based on the state of vasoconstriction within the sensing region. The adaptive gain A G may be limited by a fade factor that limits the amount the gain may change from one process iteration to the next.

[0031] The controller 34 sets the adaptive gain A G based on the aforementioned coefficients. To avoid rapid fluctuations in gain, the controller 34 may be limited to adjusting GainMod only after at least a threshold number of heartbeats (e.g., 8) have elapsed since the previous adjustment. This timing requirement may be waived immediately after an open-loop calibration period. The adaptive gain generated by the controller 34 in step 506 drives valve actuation (step 516). In some examples, further control parameter processing may be included between steps 506 and 516 for other purposes.

[0032] The methods and apparatus described herein enable a single multifunction sensor to sense both arterial blood pressure and blood composition using a multi-wavelength light emitter and sensor. This approach is enabled by gain control that partially clamps the arterial volume, thereby targeting a gain band that produces gain high enough to produce accurate and reliable arterial blood pressure readings, yet low enough to preserve sufficient arterial pulsation to distinguish blood composition from non-blood-related differential light absorption.

[0033] (Example) The following is a non-exclusive description of possible examples for implementing various concepts of the present disclosure.

[0034] A method of operating a non-invasive blood characteristic sensing system including 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 an amplitude of light received by the light sensor from the light emitter through the patient's appendage for each of the discrete wavelengths of light; generating a sensed plethysmogram value reflecting an arterial volume within the sensing area based on the sensed light amplitude; and controlling a closed-loop control in response to a closed-loop error value reflecting a difference between the sensed plethysmogram value and a setpoint plethysmogram value. 1. A method comprising: adjusting pressurization of a pressurizable cuff in a closed-loop control mode via an algorithm to partially clamp an arterial volume within a sensing region; generating a compositional analysis of arterial blood within the sensing region based on differential absorption of light at a plurality of discrete wavelengths as sensed by an optical sensor during arterial pulsation within the sensed 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 attenuates but does not eliminate the arterial pulsation, whereby generating the compositional analysis can be performed simultaneously with partially clamping the arterial volume.

[0035] The method of the previous paragraph may optionally, additionally and / or alternatively include any one or more of the following features, configurations, and / or additional components.

[0036] The above method, further comprising maintaining constant pressurization of the pressurizable cuff in a repeated open-loop calibration mode, sensing an open-loop error value reflecting a difference between a sensed plethysmogram value in the open-loop calibration mode and a set point plethysmogram value, and calibrating the set point plethysmogram value based on the open-loop error value.

[0037] The above method further comprising: calculating a ratio of a maximum open-loop error amplitude in the repeated open-loop calibration mode to a maximum closed-loop error amplitude in the closed-loop control mode; and adjusting a gain of the closed-loop control algorithm to drive the calculated ratio toward a value within a preset range.

[0038] The above method, with preset ranges from 5 to 20.

[0039] The method as above, further comprising narrowing the preset range based on a state of vasoconstriction within the sensing region.

[0040] The above method, wherein adjusting the gain of the closed-loop control algorithm includes increasing the gain in proportion to the extent to which the calculated ratio falls below a lower limit of a preset range, and decreasing the gain in proportion to the extent to which the calculated ratio exceeds an upper limit of the preset range.

[0041] The above method, wherein the adjustment of the incremental change to the gain is limited according to the fade value.

[0042] The above method, wherein the open-loop error amplitude and the closed-loop error amplitude are each evaluated over a time window that includes multiple heartbeats of the patient.

[0043] The method above, wherein the time window is selected to include at least two heartbeats of the patient.

[0044] The above method, further comprising detecting plethysmogram signal oscillations caused by overcorrection, and reducing a gain of the closed-loop control algorithm in response to the detected signal oscillations.

[0045] The above method, wherein the compositional analysis is generated in both a repeated open-loop calibration mode and a closed-loop control mode.

[0046] The set point plethysmogram value corresponds to the unstressed arterial volume at rest, as described above.

[0047] The method as described above, wherein the compositional analysis comprises identification of at least one blood composition characteristic selected from the group consisting of blood oxygen saturation, total hemoglobin, percentage methemoglobin, and percentage carboxyhemoglobin.

[0048] A non-invasive sensor system comprising: a pressurizable cuff pressurized via a metered fluid supply and sized to surround a patient's appendage and define a sensing region; a light emitter secured to the pressurizable cuff and configured to emit light through the sensing region of the patient's appendage at a plurality of discrete wavelengths; a light sensor secured to the pressurizable cuff and positioned to receive light emitted by the light emitter and configured to generate a sensed plethysmogram signal therefrom; and a composition analysis module configured to assess blood composition within the sensing region based on differential absorption of the plurality of discrete wavelengths as detected by the light sensor during arterial pulsation within the sensing region. and a controller configured to: calculate an error value as the difference between a sensed plethysmogram signal and a setpoint plethysmogram value; operate a closed-loop control mode in which a metered fluid supply is driven to partially clamp an artery within the sensing area based on the error value and a gain level; and output a sensed arterial blood pressure based on a clamping pressure resulting from the closed-loop control, wherein partially clamping the arterial volume within the sensing area attenuates but does not eliminate arterial pulsations, whereby generation of a compositional analysis can be performed simultaneously with partially clamping the arterial volume.

[0049] The non-invasive sensor system of the previous paragraph may optionally, additionally and / or alternatively include any one or more of the following features, configurations, and / or additional components.

[0050] The non-invasive sensor system as described above, wherein the controller is additionally configured to hold the pressure in the pressurizable cuff constant in the repeated 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 as sensed in the open-loop configuration mode.

[0051] the controller is additionally configured to: record a maximum amplitude of the error value in the closed-loop control mode as a closed-loop amplitude; record a maximum amplitude of the error value in the open-loop control mode as an open-loop amplitude; calculate a ratio of the open-loop amplitude to the closed-loop amplitude; increase a gain level of the closed-loop control mode in response to the ratio being below a lower limit; and decrease a gain level of the closed-loop control mode in response to the ratio being above an upper limit.

[0052] The upper limit corresponds to the maximum gain level that allows some arterial pulsation within the sensing region to sufficiently allow assessment of blood composition, for the non-invasive sensor system described above.

[0053] The upper limit is about 20, for the non-invasive sensor system mentioned above.

[0054] The lower limit is about 5 for the non-invasive sensor system described above.

[0055] The non-invasive sensor system as described above, wherein the controller is configured to set the upper limit value based on a state of patient vasoconstriction.

[0056] The non-invasive sensor system as described above, wherein the lower limit corresponds to a minimum gain level suitable for suppressing arterial pulsations within the sensing region so as to sufficiently minimize errors in the sensed arterial blood pressure.

[0057] The non-invasive sensor system as described above, further comprising a metering element configured to provide a metered fluid delivery to the pressurizable cuff, the metering element being controlled by the controller in a closed-loop control mode and an open-loop calibration mode.

[0058] The non-invasive sensor system as above, wherein the metering element is a servo valve or a piezoelectric pump.

[0059] While the present invention has been described in terms of exemplary embodiments, those skilled in the art will recognize that various modifications can be made and equivalents can be substituted for these elements without departing from the scope of the invention. Additionally, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is not intended that the invention be limited to the particular embodiments disclosed, but the invention will include all embodiments falling within the scope of the appended claims. [Explanation of symbols]

[0060] 12 Sensor System 14 moves 16 Housing 18 Connectors 20 Cuff 22 Pressurizable Bladder 24 fingers 28 Luminous Object 30 Light Sensor 32 valves 34 Controller 36 Composition Analysis Module 300 Cuff Pressure 302 Plethysmogram signal 304a First Closed Loop Period 304b Closed Loop Period 306 Open Loop Period 400 Ratio-Based Gain Control Method 410 Closed Loop Control Mode

Claims

1. 1. A method of operating a non-invasive blood property sensing system including a light emitter, a light sensor, and a pressurizable cuff, comprising: encircling a sensing area of ​​the 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 an amplitude of light received by the light sensor from the light emitter through the patient's appendage for each of the discrete wavelengths of light; generating a sensed plethysmogram value reflective of arterial volume within the sensing area based on the sensed light amplitude; adjusting inflation of the pressurizable cuff in a closed-loop control mode to partially clamp an arterial volume within the sensed region via a closed-loop control algorithm in response to a closed-loop error value reflecting a difference between the sensed plethysmogram value and a setpoint plethysmogram value; generating a compositional analysis of arterial blood within the sensing area based on differential absorption of light at the plurality of discrete wavelengths as sensed by the optical sensor during arterial pulsation within the sensing area; generating a sensed arterial blood pressure based on the pressurization of the pressurizable cuff required to partially clamp the arterial volume; Including, The method, wherein the step of partially clamping the arterial volume within the sensing region attenuates but does not eliminate arterial pulsations, whereby the generation of the compositional analysis can be performed simultaneously with the step of partially clamping the arterial volume.

2. maintaining a constant pressurization of said pressurizable cuff in a repeated open-loop calibration mode; sensing an open-loop error value reflecting a difference between the sensed plethysmogram value and the setpoint plethysmogram value in the open-loop calibration mode; calibrating the set point plethysmogram value based on the open loop error value; The method of claim 1 further comprising:

3. calculating a ratio of a maximum open-loop error amplitude in the repeated open-loop calibration mode to a maximum closed-loop error amplitude in the closed-loop control mode; adjusting a gain of the closed-loop control algorithm to urge the calculated ratio toward a value within a preset range; The method of claim 2 further comprising:

4. The method of claim 3 , wherein the preset range is from 5 to 20.

5. The method of claim 3 , further comprising narrowing the preset range based on a state of vasoconstriction within the sensing area.

6. 4. The method of claim 3, wherein adjusting the gain of the closed-loop control algorithm comprises increasing the gain in proportion to the extent to which the calculated ratio falls below a lower limit of the preset range, and decreasing the gain in proportion to the extent to which the calculated ratio exceeds an upper limit of the preset range.

7. The method of claim 6 , wherein the incremental change adjustment to the gain is limited according to a fade value.

8. 7. The method of claim 6, wherein the open-loop error amplitude and the closed-loop error amplitude are each evaluated over a time window comprising 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. 7. The method of claim 6, further comprising detecting plethysmogram 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 compositional analysis occurs in both the repeated open-loop calibration mode and the closed-loop control mode.

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

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

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

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

16. 1. A non-invasive sensor system, comprising: a pressurizable cuff that is pressurized via a metered fluid supply and that is sized to surround the patient's appendage and define a sensing area; a light emitter secured to the pressurizable cuff and configured to emit light through the sensing area of ​​the patient's appendage at a plurality of discrete wavelengths; an optical sensor secured to the pressurizable cuff and 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 area based on differential absorption of the plurality of discrete wavelengths as detected by the optical sensor during arterial pulsation within the sensing area; and a controller, calculating an error value as the difference between the sensed plethysmogram signal and a set point plethysmogram value; operating a closed loop control mode in which the metered fluid delivery is driven to partially clamp an artery within the sensing region based on the error value and a gain level; outputting a sensed arterial blood pressure based on a clamping pressure resulting from said closed-loop control; A controller configured to Equipped with A non-invasive sensor system in which partially clamping the artery within the sensing region attenuates but does not eliminate arterial pulsations, whereby generation of a compositional analysis can be performed simultaneously with partially clamping the arterial volume.

17. 17. The noninvasive sensor system of claim 16, wherein the controller is additionally configured to hold the pressure of the pressurizable cuff at a constant value in repeated open-loop configuration modes and recalibrate the setpoint plethysmogram value based on a sensed difference between the setpoint plethysmogram value and the sensed plethysmogram signal as sensed in the open-loop configuration mode.

18. The controller recording the maximum amplitude of the error value in the closed-loop control mode as a closed-loop amplitude; recording the maximum amplitude of the error value in the open loop configuration mode as an open loop amplitude; calculating a ratio between the open loop amplitude and the closed loop amplitude; increasing the gain level of the closed loop control mode in response to the ratio being below a lower limit; reducing the gain level of the closed loop control mode in response to the ratio being higher than an upper limit value; 20. The noninvasive sensor system of claim 17, additionally configured to:

19. 20. The noninvasive sensor system of claim 18, wherein the upper limit value corresponds to a maximum gain level that allows some arterial pulsation within the sensing region sufficient to allow assessment of blood composition via the composition analysis module.

20. 20. The noninvasive sensor system of claim 19, wherein the upper limit is about 20.

21. 21. The noninvasive sensor system of claim 20, wherein the lower limit is about 5.

22. 20. The noninvasive sensor system of claim 19, wherein the controller is configured to set the upper limit based on a patient vasoconstriction state.

23. 20. The noninvasive sensor system of claim 19, wherein the lower limit corresponds to a minimum gain level suitable for suppressing arterial pulsations within the sensing region so as to sufficiently minimize errors in the sensed arterial blood pressure.

24. 20. The noninvasive sensor system of claim 19, wherein said assessment of blood composition includes identification of at least one blood composition characteristic selected from the group consisting of blood oxygen saturation, total hemoglobin, percentage methemoglobin, and percentage carboxyhemoglobin.

25. 25. The noninvasive sensor system of claim 24, wherein the assessment of blood composition includes identifying blood oxygen saturation via pulse oximetry.

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

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

Images