System and method for non-invasive pulse pressure waveform measurement

Abstract

Systems and methods are provided for a non-invasive high-resolution pressure pulse waveform measurement system. The system can include a blood pressure cuff, an air pump for inflating the blood pressure cuff to a specific pressure level, a high-resolution pressure sensor configured to perform high-sensitivity signal acquisition at the specified pressure level, a high-range pressure sensor configured to measure an absolute reference of the signal and to calibrate the signal, pneumatic tubing connecting the air pump and the sensors with the cuff, and a fluidic dynamic filter configured as an input for the reference port of the high-resolution pressure sensor. The fluidic dynamic filter can be configured to transmit only the mean pressure by attenuating a selected frequency range of the signal.

Description

Technical Field

[0001] This disclosure generally relates to medical diagnostics, and in particular, some embodiments may relate to non-invasive cardiac waveform measurement. Background Technology

[0002] Heart disease is a leading cause of death for women and men in the United States and worldwide. Early and accurate diagnosis of heart disease can significantly improve patient health outcomes. However, many important cardiovascular health measurements currently involve invasive, expensive, and / or lengthy procedures. Consequently, critical conditions such as heart failure may be difficult to diagnose until late-stage disease progression occurs.

[0003] Several important measurements allow physicians to diagnose heart failure. For example, the pressure pulse waveform is a crucial measurement that allows medical professionals to quantitatively and qualitatively assess heart health. In a typical clinical setting, medical professionals use a handheld force sensor to measure the radial pulsation of the arteries. Measurements must be performed by a trained operator to ensure accuracy. Summary of the Invention

[0004] According to various embodiments of the disclosed technology, a non-invasive pressure pulse waveform measurement system is provided. The non-invasive pressure pulse waveform measurement system may include: a blood pressure cuff; an air pump for inflating the blood pressure cuff to a specific pressure level; high-resolution pressure sensors configured to perform high-sensitivity signal acquisition at a specified pressure level, wherein each high-resolution pressure sensor includes a measurement port and a reference port; a high-range pressure sensor configured to measure an absolute reference for the signal and calibrate the signal; a pneumatic tube connecting the air pump and the sensors to the cuff; and a hydrodynamic filter configured as an input to the reference port of each high-resolution pressure sensor.

[0005] In some embodiments, the hydrodynamic filter includes a resistance component and a capacitive component, wherein the hydrodynamic filter is configured to transmit only the average pressure by attenuating a selected frequency range of the signal. The resistance component of the hydrodynamic filter may be configured to apply resistance to the flow, thereby slowing it down. In some cases, the resistance component of the hydrodynamic filter comprises a rigid tube with an inner diameter in the range of 10-200 μm. The capacitive component is configured to reduce pressure changes by storing air volume. In some embodiments, the elasticity of the capacitive element is in the range of 0.2-2.0 MPa. The capacitive component may include a tube connecting the resistance component to a reference port.

[0006] Other features and aspects of the disclosed technology will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate features of embodiments according to the disclosed technology by way of example. This invention is not intended to limit the scope of any invention described herein, but is defined only by the appended claims. Attached Figure Description

[0007] The present disclosure is described in detail with reference to the following accompanying drawings, which illustrate one or more various embodiments. The drawings are provided for illustrative purposes only and depict only typical or exemplary embodiments.

[0008] Figure 1 This is a diagram illustrating an example of a blood pressure cuff system modified according to the systems and methods disclosed herein.

[0009] Figure 2A This is a diagram illustrating an example of a resistance assembly with a fixed hole according to the system and method disclosed herein.

[0010] Figure 2B This is a diagram illustrating an example of a resistance component with an inline filter according to the system and method disclosed herein.

[0011] Figure 2C This is a diagram illustrating an example of a resistance component with a reduced inner diameter according to the system and method disclosed herein.

[0012] Figure 2D This is a schematic diagram of a capacitive assembly including an elastic tube.

[0013] Figure 2E This is a schematic diagram of a capacitive assembly including a tube with a piston cylinder.

[0014] Figure 3 This is a flowchart illustrating an example of a pulse pressure waveform measurement method according to the system and method disclosed herein.

[0015] Figure 4A This is an example diagram of the left ventricular pressure-volume (“PV”) circuit in a young patient based on the systems and methods disclosed herein.

[0016] Figure 4B This is an example diagram of the left ventricular pressure-volume (“PV”) circuit in elderly patients, drawn according to the systems and methods disclosed herein.

[0017] Figure 5 This is a flowchart illustrating an example of a method for predicting left ventricular end-diastolic pressure (“LVEDP”) risk based on the systems and methods disclosed herein.

[0018] Figure 6 This is an example diagram of the envelope function reconstructed under a specified pressure level and three pressure holds, based on the system and method disclosed in this paper.

[0019] Figure 7 This is an example graph showing the envelope function of changes in systolic blood pressure (“SBP”) and diastolic blood pressure (“DBP”) after pulse amplitude fluctuations, based on the system and method disclosed in this paper.

[0020] The accompanying drawings are not exhaustive and do not limit this disclosure to the precise form disclosed. Detailed Implementation

[0021] Embodiments of the systems and methods disclosed herein can provide modified blood pressure (“BP”) cuffs that can be used to perform non-invasive yet accurate cardiac measurements. The systems and methods disclosed herein can be used to perform pressure pulse waveforms, left ventricular end-diastolic pressure (“LVEDP”) measurements, pressure-volume (“PV”) loop measurements, and other important cardiac measurements. The systems and methods in this document relate to modified BP cuff systems, methods for performing measurements, risk assessment measurements, and calibration methods.

[0022] Non-invasive pulse pressure waveform measurement

[0023] A modified blood pressure (BP) cuff can be used to measure pressure pulse waveforms. In some embodiments, the modified BP cuff system may include a dynamic pressure sensor in place of a static pressure sensor and / or a dynamic pressure sensor other than a static pressure sensor. A high-resolution pressure sensor may be included for high-sensitivity signal acquisition at a specified pressure level. The high-resolution pressure sensor may include a differential pressure sensor having a measurement port and a reference port, wherein the pressure sensor measures the difference between its measurement port and the reference port. A high-range absolute pressure sensor may be used to calibrate the signal. An air valve or filter may be included to maintain a specific pressure level at the reference port. Maintaining the pressure level allows the high-resolution pressure sensor to operate within its normal range. The pressure sensor may acquire the signal simultaneously during measurement.

[0024] High-range pressure sensors can measure relative to atmospheric pressure, while high-resolution pressure sensors can measure relative to a variable reference pressure. Pressure sensors can be connected in parallel to a BP cuff system. In some embodiments, the high-range and high-resolution pressure sensors may each have an operating range on the order of magnitude of the measurement and signal.

[0025] No control system is employed in the embodiments described herein. Such a control system could be used to dynamically control the air valve to open and close it at appropriate pressures to ensure accurate signal capture. In such a system, pressure fluctuations can cause sensor saturation, leading to serious malfunctions, signal drift, and loss of valuable information. For these reasons, air valve systems may have disadvantages not present in the embodiments described herein.

[0026] In some embodiments, a passive and self-adjusting non-invasive pulse pressure waveform measurement system may include a high-resolution pressure sensor in an expandable pressurized air chamber with resistive and capacitive components. Hydraulic filtering can be implemented through geometric conditions to passively generate a signal that only converts to the desired frequency. In some embodiments, the air valve may be replaced by a hydrodynamic filter. The hydrodynamic filter may include a fixed or adjustable orifice, an in-line filter, and / or a tube with an inner diameter (“ID”) significantly smaller than the inner diameter of the remaining tubes included in the modified BP cuff system.

[0027] A hydrodynamic filter can be implemented using a sequential combination of a resistance tube and a flexible tube. The resistance tube generates flow resistance, limiting the flow that can move through the element. The flexible tube stores the injected volume at a desired flexible rate. This hydraulic system produces the electrical equivalent of an RC low-pass filter. In this hydraulic system, the loop can be understood as the time required for the flexible element to be filled by the resistance element.

[0028] In some embodiments, the hydrodynamic filter includes a resistance component and a compliance component. The resistance component is configured to apply resistance to the flow, thereby slowing it down, while the compliance component includes a capacitive component configured to reduce pressure changes by storing air volume. In such embodiments, the compliance component may include a tube connecting the resistance component to a reference port. Alternatively, the resistance component of the hydrodynamic filter may include a rigid tube with an inner diameter in the range of 10-200 μm. In some cases, the elasticity of the capacitive component is in the range of 0.2-2.0 MPa. The hydrodynamic filter may form an input connection to a reference port to regulate the flow rate entering the reference port. This configuration can provide a stable pressure to the system, thereby generating a smooth signal.

[0029] Figure 1 An example of a system with a passive configuration for high-precision sensors is shown. For example... Figure 1 As shown, the system may include a BP cuff 100. The system may also include a pneumatic connection 106 for a high-resolution pressure sensor 114, a filter 112 including a resistance component 108 connected in series with the capacitive component 110, and a reference port 120. The system may also include an air pump 102 and a BP monitor 104. The air pump 102 can be used to inflate the cuff 100.

[0030] Figure 2A , Figure 2B and Figure 2C This is a schematic diagram of the resistance assembly 108, which includes a tube 130 with a fixed orifice 132, a tube with an in-line filter 134, and a tube with an ID 136 smaller than ID 138. Figure 2AAs shown, filter 134 may include aperture 132. For example... Figure 2B As shown, orifice 132 can be configured in pipe 130 connected to reference port 120. In another embodiment, the orifice can be adjustable. Figure 2B As shown, the tube 130 connected to the reference port 120 can be configured with an inline filter 134. For example... Figure 2C As shown, the conduit 130 connected to the reference port 120 may include a portion having a diameter or a smaller ID 136 that is smaller than the ID of the conduit 138.

[0031] In some embodiments, filter 134 may include a fixed or adjustable orifice 132. Orifice 132 controls the amount of air that can flow between the rest of the BP pressure cuff system and reference port 120. The airflow through orifice 132 is driven by differential pressure. Using an orifice instead of a valve to restrict flow between compartments results in smoothing pressure oscillations while maintaining an average signal, acting as a low-pass filter on the reference port side.

[0032] Figure 2D and 2E It includes elastic tubes ( Figure 2D ) and tubes with piston cylinders ( Figure 2E A schematic diagram of the capacitive component 110.

[0033] A crucial measurement is the difference between the signal measured at the measurement port and the signal measured at the reference port. Therefore, the output signal is equivalent to a high-pass filtered signal. Additionally, the self-adjusting reference port signal helps maintain a centered output signal. Unlike an air valve, the orifice allows the reference port to remain at the average pressure signal. Maintaining the average pressure signal is important for eliminating deviations in measurement pulsations and for keeping the signal centered using a high-resolution transducer.

[0034] In some embodiments, the hydrodynamic filter may include a resistance component comprising a tube with a small ID. In such embodiments, the resistance component may comprise a substantially rigid tube with an inner diameter in the range of 10-200 μm, and the ID of the tube in diameter may be significantly smaller than the ID of the tube connecting the rest of the BP pressure cuff system and the reference port. The tube with a small ID effectively functions as a filter, in which only the average pressure is transmitted, thereby creating a flow-dependent low-pass filter to the reference port. The specific cutoff frequency of the filter is designed using hydrodynamic principles and the characteristics of the signal and measurement system. The filtered signal will depend on a combination of the volumetric flow rate and the material properties on the reference port side.

[0035] In some embodiments, a commercial arm cuff BP system can be used to design the system. This system can be modified to include multiple pressure sensors with different operating ranges to measure and calibrate pressure waveforms with high accuracy. High-resolution pressure sensors can be used for precise signal measurement. Each high-resolution pressure sensor may include a measurement port and a reference port. High-range pressure sensors can be used for absolute reference and signal calibration.

[0036] In some embodiments, the system can be applied to any location in the body that has an artery close to its surface and can tolerate a temporary reduction or cessation of blood flow. Potential locations may include, but are not limited to, the humerus, radius, femur, and posterior tibia.

[0037] Pressure sensors can measure peripheral pressure pulses. Based on the fluid-solid interaction principle, the pressure during cuff inflation alters the pressure-flow behavior in the arteries. Combined waveform analysis can then be used for non-invasive assessment of cardiovascular health. Peripheral pulse waveforms can be measured, and then transformed to estimate the central waveform.

[0038] The pressure and flow rate in a closed system can be given by Bernoulli's equation (below). When the arm cuff is inflated, the externally applied force changes the radius of the artery, ultimately altering the pressure-flow ratio of the system. At the lower extreme, applying pressure below the minimum DBP to the artery will not cause a change in pressure-flow behavior or will cause only a minimal change. At the upper extreme, pressure above the maximum SBP in the artery causes arterial collapse and cessation of blood flow. Any pressure between these two extremes can produce a proportional change in the pressure-flow relationship, again given by Bernoulli's equation. Therefore, comparing waveforms measured at two different holding pressures allows for the derivation of the system's pressure-flow characteristics. Quantitative and qualitative comparisons of the waveforms can be performed. Plotting methods, such as waveform versus time or waveform versus waveform, can also be used.

[0039] Captured signals reflecting the pressure-flow relationship in elastic arteries can be used to derive additional waveforms that can further characterize the patient. Fluid dynamics principles enable the derivation of waveforms, including but not limited to flow rate, velocity, and radial displacement. Fluid dynamics principles involve parameters of a static system, such as pressure, velocity, force, and volume. Analyzing these systems with multiple measurement points allows for solving for the queried parameters. For example, velocity can be solved using DBP and super-SBP holding pressure waveforms. The super-SBP waveform completely obstructs flow, providing an absolute pressure reading. The DBP waveform represents a combination of pressure and flow rate. Therefore, the final flow rate can be measured during DBP holding pressure. Similar derivations can be applied to other holding pressure combinations. The significance of the results obtained may depend on the underlying physical properties of the captured waveforms.

[0040] Practical applications may require waveform synchronization. Solutions could include time synchronization using ECG or known timing events during the cardiac cycle, including maximum dP / dt, onset, and dicrotic notch. The cuff could have wired or wireless synchronization with other devices, such as Bluetooth or Wi-Fi with ECG.

[0041] Figure 3 An example of non-invasive pulse pressure waveform measurement is shown. The modified BP pressure cuff system described above can be used to record pressure pulsations in the brachial artery. To perform the measurement, the arm BP cuff can be inflated around the patient's arm. A pump system can be used to inflate the cuff. A first operation 302 can involve initiating the measurement process. At the first operation 302, the outputs of both the high-range pressure sensor and the high-resolution pressure sensor can be zero. The pressure sensors can be used to measure the patient's systolic BP (“SBP”) and diastolic BP (“DBP”). A second operation 304 can involve measuring BP using the high-range pressure sensor. At the time of the second operation 304, the output of the high-range sensor can be the patient's full BP range, and the output of the high-resolution pressure sensor can be zero.

[0042] As a third operation 306, a target and holding pressure and time can be set. For example, the cuff can be set to inflate to a pressure of 100 mmHg and held for 40 seconds. Other pressures and timings are also possible. During the third operation 306, the outputs of both the high-range pressure sensor and the high-resolution pressure sensor can be zero. The cuff inflation pressure reference and / or target can be obtained by performing a conventional blood pressure arm cuff measurement. For example, the holding pressure can be set at DBP, below DBP, at SBP, above SBP, and / or at MAP. Typical physiological ranges for these values ​​are as follows: DBP 40–120 mmHg; MAP 50–150 mmHg; and SBP 75–225 mmHg. Other pressures are also possible. For example, extremely ill subjects may have values ​​outside these ranges. For patient-specific values, a specified pressure level can be used to guide the selection of the holding pressure. To keep the high-resolution pressure sensor within its operating range, pressure can be applied to the reference port.

[0043] As a fourth operation 308, the cuff can be inflated and held at a given pressure. For example, the cuff can be inflated to the target pressure P, which can be one of the identified holding pressures. In the fourth operation 308, the high-range sensor output can be an absolute pressure value, and the high-resolution pressure output can be zero. As a fifth operation 310, the cuff can then be inflated to the target pressure. In the fifth operation 310, the high-range sensor can have a low-precision absolute pressure pulsation output. The high-resolution sensor can have a high-precision relative pressure pulsation output. As a sixth operation 312, the cuff can be deflated, thereby ending the measurement period. In the sixth operation 312, each of the high-resolution pressure sensor and the high-resolution pressure sensor can have zero output. For multiple holding pressures, operations three through six can be repeated. The output from operation five can be combined for calibration of the high-precision pulsation output.

[0044] In some embodiments, low and high holding pressures above the upper limit of pressure can be used to perform waveform capture comparisons. For example, for a low holding pressure, the pressure can be set to DBP or just below DBP. For a high holding pressure, the pressure can be set above SBP (“super-SBP”), thereby cutting off blood flow. For example, the pressure can be set to approximately SBP + 35 mmHg. At the lower limit, the waveform can represent a combination of static pressure and flow velocity. At the upper limit, the waveform only shows pressure characteristics. At the super-SBP holding pressure, the cessation of flow in the subclavian artery becomes the closest waveform used to represent the static pressure read from the orifice in the wall of the ascending aorta. This holding pressure allows for direct pressure waveform measurement in the central artery. The corresponding pressure waveforms between super-SBP and DBP can be plotted in a pressure-pressure (“PP”) loop for cardiac health and disease assessment. This allows for the creation of a pressure-velocity (“PV”) loop for use in health assessments.

[0045] Pressure-velocity loop example

[0046] As mentioned above, the flow rate at the brachial artery can be characterized by Bernoulli's equation for the average flow rate, given by the following formula:

[0047]

[0048] Where P B It is the pressure at the brachial artery, ρ is the fluid density, and u is the pressure at the brachial artery. b It is the flow velocity at the brachial artery, and P T It is the total pressure in the aortic arch.

[0049] Maintaining super SBP pressure (P) SS When the brachial artery is completely blocked, it leads to u b =0. Therefore, the pressure measured at the cuff is the pressure in the aortic arch. Therefore:

[0050] P Ss =P B =P T

[0051] Where P SS It maintains pressure beyond the SBP.

[0052] Pressure in the brachial artery was measured under pressure hold (PD) conditions. The pressure in the brachial artery conforms to Bernoulli's equation as follows:

[0053]

[0054] Where P D DBP maintains pressure.

[0055] The above equations are made equal by adjusting the total aortic arch pressure, and the velocity (u) is then solved. B ) give

[0056]

[0057]

[0058] The pressure exceeding SBP (P) SS ) and DBP speed (u D The graph plots the (“PV”) loop. Data can be plotted and analyzed at any intermediate step. For example, SBP pressure versus DBP pressure can be analyzed.

[0059] Figure 4 shows the elderly ( Figure 4A ) and young ( Figure 4B Examples of patient PV loop comparisons. Each PV loop has different characteristics and shape, and each includes a dashed line 402, which simulates the slope of the rising contraction portion. The slope can clearly distinguish patients by age, thus it is useful for diagnosis. Each also includes a solid line 404 as a scale line. Other parameters include loop area, curvature, indentation, peak offset, and other combinations of parameters.

[0060] Example of Risk Prediction for Left Ventricular End-Diastolic Pressure (“LVEDP”)

[0061] LVEDP is an important clinical measure for predicting, diagnosing, and / or assessing the risk of heart failure. Currently, the threshold for heart failure is a LVEDP measurement of approximately 18 mmHg. Because LVEDP is a valuable diagnostic measure, non-invasive methods for measuring LVEDP can allow clinicians to predict the risk of heart failure earlier and more accurately.

[0062] Non-invasive pulse waveform analysis and classification algorithms can be used to form LVEDP risk predictions.

[0063] Figure 5 An example of a non-invasive LVEDP risk prediction method 500 involving several operations is shown. A first operation 502 may involve performing patient measurements. A sub-operation 504 of the first operation 502 may involve measuring the patient's height. A sub-operation 506 of the first operation 502 may involve measuring the patient's weight. Other patient measurements may also be performed. A second operation 508 may involve obtaining the patient's medical history. A sub-operation 510 of the second operation 508 may involve recording the patient's surgery. Patient surgeries, such as cardiac surgery, may be recorded. Other medical information, such as treatment courses and other therapies, may also be recorded. A sub-operation 512 of the second operation 508 may involve recording the patient's condition. The patient's condition may include known instances of cardiovascular conditions, such as heart failure, myocardial infarction, and cardiomyopathy. Other cardiac conditions, comorbidities, and / or general health conditions may be recorded. Other patient information, such as genetic predisposition, family history, lifestyle factors, and other information, may also be recorded.

[0064] The third operation 516 may involve combining recorded patient measurements and medical history to form a comorbidity score.

[0065] The fourth procedure 518 may involve measuring the patient's blood pressure as SBP and DBP using a commercially available and / or standard arm cuff or some other measuring device.

[0066] The fifth operation 520 may involve measuring the patient's pulse waveform. The pulse waveform can be measured using a modified BP cuff according to the foregoing embodiments. For example, a modified blood pressure cuff can be used, which inflates to a specific pressure and maintains those pressures to capture the waveform at a set pressure. The maintenance pressure may include DBP, SBP, MAP, and / or sSBP. In some embodiments, sSBP, which completely blocks blood flow through the artery, can be used. The inflation pressure may be, for example, about 100 mmHg. The maintenance time may be, for example, about 40 seconds.

[0067] The sub-operation 522 of the fifth operation 520 may involve performing a pulse waveform measurement for a sufficiently long duration to account for pressure amplitude fluctuations throughout the respiratory cycle. The measured amplitude may be highest during the post-expiratory phase of the respiratory cycle.

[0068] The sixth operation 524 may include calibrating the measured pulse waveform using SBP and DBP measurements. The waveform may be calibrated using a pressure unit based on the BP measurement results. The calibration method may include the methods disclosed in the following sections of this disclosure.

[0069] The seventh step, 526, may include selecting multiple post-expiratory waveforms for feature extraction. Post-expiratory waveforms can be selected because these waveforms can track the highest LVEDP readings throughout the respiratory cycle. Features and / or parameters of interest extracted may include the expansion index (“AIX”), systolic pulse region, and / or systolic BP. Other desired and / or relevant features and / or parameters may also be extracted.

[0070] The eighth operation 528 may include measuring and / or extracting features and / or parameters of interest from the pulse waveform. A sub-operation 530 of the eighth operation 528 may involve extracting the SBP or constricted pulse region. A sub-operation 532 of the eighth operation 528 may involve extracting the AIX.

[0071] In some implementations, a classification algorithm can be used to assess risk. The algorithm's input can be pulse characteristics of the systolic pulse region, the dilation index, and patient characteristics such as weight and comorbidity scores. Using the input and the algorithm, probabilities of LVEDP with a value greater than or equal to a failure threshold can be generated. In one embodiment, the failure threshold can be set to approximately 18 mmHg. In another embodiment, the threshold can be set to approximately 15 mmHg or another clinically relevant value selected during algorithm training. This process can be repeated for the post-expiratory pulse over n respiratory cycles to generate n probability predictions. Multiple measurements can be performed. For example, in one embodiment, two or three measurements can be performed. An ensemble approach can be used to combine the probabilities of multiple individual pulses into a single risk prediction. The predictions can be processed together to generate a single LVEDP risk prediction. The ensemble approach can include more complex methods for averaging probabilities and / or may include aggregated probabilities.

[0072] Therefore, the ninth operation 534 may involve inputting selected features and / or parameters for each pulse to predict individual LVEDP risk. The selected features and / or parameters may include systolic pulse region, AIX, patient weight, and comorbidity score. Other parameters and / or combinations of parameters are also possible. Similarly, the tenth operation 536 may involve combining individual pulse risk predictions for patient LVEDP risk prediction.

[0073] Calibration Examples

[0074] BP cuff measurement can be used as a useful clinical measure because peripheral BP, as measured via cuff, tends to track central BP in healthy patients. Unfortunately, in patients experiencing cardiovascular problems, the relationship between peripheral and central BP may deteriorate. The severity of a patient's cardiovascular problem may affect the degree of deterioration in the peripheral-central BP relationship. However, because BP cuff measurement is quick, non-invasive, and inexpensive to perform, it remains an important diagnostic tool for patients experiencing cardiovascular problems. Although the peripheral-central BP relationship deteriorates in such patients, calibration methods can allow peripheral BP measurements, performed using, for example, an arm BP cuff, to be used as a proxy for central BP measurements, even in patients experiencing severe problems.

[0075] A modified BP cuff system (such as the system described in the foregoing embodiments) can be used to measure peripheral BP. Peripheral BP can be measured over several respiratory hold cycles due to pressure fluctuations caused by respiration. Non-invasive pulse signals measured using the modified BP cuff system can be calibrated to track the patient's central BP amplitude.

[0076] Envelope functions can be used to correct peripheral blood pressure (BP) measurements and calibrate the signal. An envelope function can represent the relationship between pulse amplitude and cuff pressure at the measurement site. The measurement site can be an artery. An envelope function can be constructed by measuring pulse amplitude corresponding to cuff pressure over multiple breath-hold measurements.

[0077] Calibration methods may include several procedures. The first procedure may involve measuring peripheral blood pressure in the form of systolic blood pressure (“SBP”), diastolic blood pressure (“DBP”), and mean arterial pressure (“MAP”) using a conventional and / or commercially available oscilloscope cuff. These measurements may be inaccurate. Specifically, due to amplitude fluctuations caused by respiration and / or due to other errors, these measurements may not be able to keep up with measurements taken in vivo.

[0078] The second operation may involve using a modified BP cuff. The modified BP cuff may be a modified BP system including a high-resolution pressure sensor and a high-range pressure sensor, as described in the foregoing embodiments. The second operation may involve inflating the modified BP cuff to a set pressure value. Pulses can be recorded at this pressure value. The BP cuff can be inflated within a range of the set pressure values. Pulses can be recorded for each pressure value. The second operation may involve performing the operation during multiple breath-holds to account for pressure fluctuations caused by breathing. For each breath-hold, the measured waveform can be analyzed to compare the signal pulse amplitude with the set pressure of the modified BP cuff. Measurements can be performed during multiple hold periods to reconstruct a proxy of the envelope function. For example, measurements can be performed during two, three, or more breath-holds.

[0079] The third step may involve using measurements taken during the second step to calculate parameters to correct for pressure fluctuations caused by changes in respiration, and ultimately calibrating peripheral measurements to central measurements. This can be achieved by using an envelope function to derive the parameters needed to correct peripheral measurements.

[0080] Figure 6 An example of reconstructing the envelope function using BP measurements and three pressure holds is shown. The three pressure holds are DBP, MAP, and superconstrictive BP (“sSBP”). For the DBP pressure hold, the modified BP cuff is inflated to minimum pressure, allowing blood to flow through the artery substantially unimpeded. For the MAP pressure hold, the modified BP cuff is inflated to MAP. For the sSBP hold, the modified pressure cuff is inflated to a pressure higher than SBP to effectively cut off any blood flow through the artery. Cuff pressure at… Figure 6 The dashed vertical lines represent the three hold values. The three hold values ​​are DBP hold 608, MAP hold 610, and sSBP hold 612.

[0081] Figure 6 Individually recorded pulsations measured at each holding pressure are also shown. Figure 6 Individual pulsations 602 maintained for DBP, 604 maintained for MAP, and 606 maintained for sSBP are shown. Figure 6 As shown in the example, multiple pulses can be recorded for each pressure. The pulse amplitude of each pulse 602, 604, and 606 can be measured using pressure sensors. Figure 6 In the example shown, the pulsation amplitude is reported in volts (V). These pulse amplitude measurements can also be converted to other pressure units.

[0082] As discussed above, respiration can cause significant fluctuations in central blood pressure (BP). Voltage-based signals from cuff pressure maintenance can reveal these respiratory fluctuations, as can be seen in the catheter-guided aortic signal. Therefore, BP values ​​reported by a modified BP cuff measurement can be assumed to be averages. The pulse signal can be calibrated to pressure units by adjusting the SBP and DBP values ​​on the respiratory pattern and properly scaling the measured pressure signal. For each individual pulse in a pulsatile segment, the difference in pulse amplitude from the average pulse amplitude of that segment can be used to correct for respiratory fluctuations in the SBP and / or DBP values.

[0083] For example, a model for correcting the DBP value from the periphery to the center using parameters derived from the envelope function is given by the following equation:

[0084]

[0085] Where A d / A mIt is the ratio between the pulse amplitude at DBP and MAP, and DBP cuff and MAP cuff are DBP and MAP reported by cuff BP readings respectively, and m1, m2 and b are coefficients optimized for correlation.

[0086] The SBP value can be corrected using the forward and reflected peaks that are measurable in the pulse waveform signal. For arm cuffs, the underlying holding pressure that reflects these characteristics is sSBP. The corrected SBP can be given by the following formula:

[0087] SBP corr =SBP cuff +m1*(P1-P2)+b

[0088] Among them, SBP corr It is the calibrated SBP value used to track the center BP. cuff These are SBP cuff readings, where P1 is the peak pressure of the first peak during systole, P2 is the peak pressure of the second peak during systole, and m1 and b are coefficients optimized for correlation.

[0089] The linear envelope function model can be used to calculate actual pressure, as shown in the following closed-form equation:

[0090]

[0091] Among them, P adj It is respiratory regulation pressure, P calib This is the BP report value, ΔPA is the pulse amplitude difference from the average value, and slope p It is for specific pressure (slope) DBP or slope SBP The slope of the envelope function of the pressure. The pressure can be SBP or DBP.

[0092] In the uncalibrated pulsatile segment, the above calculations are repeated for each pulsation within the segment, and signal scaling is applied. All pulsations can be calibrated using SBP and DBP values ​​reflecting the respiratory pattern. The presented model assumes a linear relationship between the measurement point and a fixed envelope function for a given object. By utilizing more holding pressure, a more detailed envelope function can be reconstructed, improving model accuracy. Calibration can be applied independently to SBP and / or DBP.

[0093] Figure 7 An example of an envelope function used to estimate the changes in SBP and DBP after pulse amplitude fluctuations is shown. Figure 6 As shown, the pressure cuff is maintained by the dashed vertical line. Figure 7The following values ​​are shown: DBP pressure cuff holding value 608, MAP pressure cuff holding value 610, and SBP pressure cuff holding value 700. Figure 7 Arrow 708 in the lower right corner shows the pulse amplitude deviation from the average pulse amplitude. Arrows 706 above and to the right of arrow 708 show an increase in SBP. Arrow 704 on the left side of the figure shows an increase in DBP. The envelope function 702 can then be used to estimate the changes in SBP and DBP following possible pulse amplitude fluctuations caused by respiration. Figure 7 An estimate of 710 is shown. Figure 7 This is merely an example. If the necessary information described is available, the above reference can be performed using different devices, threshold conditions, and quantities. Figure 7 The method described.

[0094] In some embodiments, calibration methods incorporating respiratory fluctuations can also be used as diagnostic tools in cardiology. For example, a paradoxical pulse condition is defined as a drop in SBP greater than about 10 mmHg during inspiration. This condition can be observed during cardiac tamponade or right ventricular dilation, such as in severe acute asthma or chronic obstructive pulmonary disease. Therefore, embodiments of the calibration method may involve setting a threshold of about 10 mmHg.

[0095] It should be understood that the various features, aspects, and functions described in one or more individual embodiments are not limited to their applicability to the particular embodiments in which they are described. Rather, they may be applied individually or in various combinations to one or more other embodiments, whether or not such embodiments are described, and whether or not such features are presented as part of the described embodiments. Therefore, the breadth and scope of this application should not be limited to any of the exemplary embodiments described above.

[0096] Unless otherwise expressly stated, the terms and phrases used in this document and their variations thereof should be interpreted as open-ended, not restrictive. As an example of the foregoing, the term “including” should be understood to mean “including, but not limited to”, etc. The term “example” is used to provide exemplary instances of the items under discussion, not an exhaustive or restrictive list thereof. The terms “a” or “an” should be understood to mean “at least one,” “one or more,” etc.; terms with similar meanings should not be construed as limiting the described items to a given time period or to items available at a given time. Rather, they should be understood to cover conventional, traditional, normal, or standard techniques that may be available or known at any time now or in the future. Where this document relates to techniques that are obvious or known to a person skilled in the art, such techniques include those that are obvious or known to a person skilled in the art at any time now or in the future.

[0097] In some cases, the presence of broadening terms and phrases such as “one or more,” “at least,” “but not limited to,” or other similar phrases should not be construed as implying an intention or need for a narrower scope where such broadening phrases might not exist. The use of the term “component” does not imply that aspects or functions described or claimed as part of a component are configured within a common encapsulation. In practice, any or all aspects of a component (whether control logic or other components) may be combined in a single encapsulation or maintained separately, and may be further distributed across multiple groups or encapsulations or across multiple locations.

[0098] Furthermore, the various embodiments described herein are based on exemplary block diagrams, flowcharts, and other illustrations. As will be apparent to those skilled in the art upon reading this document, the illustrated embodiments and various alternatives thereof can be implemented without being limited to the examples shown. For instance, the block diagrams and their accompanying descriptions should not be construed as imposing a particular architecture or configuration.

[0099] The terms “substantially,” “about,” and “approximately” used throughout this disclosure (including the claims) are used to describe and interpret small fluctuations, such as those caused by variations in the processing. For example, they may refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.

Claims

1. A non-invasive pressure pulse waveform measurement system, comprising: Blood pressure cuff; An air pump is used to inflate the blood pressure cuff to a specific pressure level; At least one high-resolution pressure sensor is configured to perform high-sensitivity signal acquisition at a specified pressure level, wherein each high-resolution pressure sensor includes a measurement port and a reference port; At least one high-range pressure sensor, the high-range pressure sensor being configured as an absolute reference for measuring the signal and calibrating the signal; A pneumatic tube connecting the air pump and the sensor to the cuff; and A hydrodynamic filter, configured at the input of the reference port of each high-resolution pressure sensor; The hydrodynamic filter is configured to transmit only the average pressure by attenuating a selected frequency range of the signal; The hydrodynamic filter described herein includes a drag component and a capacitive component; The drag component of the fluid dynamic filter is configured to apply resistance to the flow; The capacitive component is configured to reduce pressure changes by storing air volume.

2. The system of claim 1, wherein the capacitive component includes a tube connecting the resistive component to the reference port.

3. The system of claim 1, wherein the resistance component of the hydrodynamic filter comprises a rigid tube with an inner diameter in the range of 10-200 μm.

4. The system according to claim 1, wherein, The elasticity of the capacitive component is in the range of 0.2 MPa to 2.0 MPa.

5. The system according to claim 1, wherein, The blood pressure cuff is synchronized with an ECG device, smartphone, tablet, laptop, or desktop computer, thereby allowing wired or wireless data transmission.

6. The system of claim 5, wherein Bluetooth or Wi-Fi is used to transmit wireless data.

7. The system of claim 1, wherein the resistance component and the capacitive component are combined within a single component.

8. The system according to claim 1, wherein, The resistance assembly includes a resistance element, which includes an orifice or a physical filter.

9. The system according to claim 8, wherein, The orifice is fixed and / or adjustable.

10. The system of claim 1, wherein the capacitive component comprises a flexible tube, a tube with a small damper, or a tube with a piston cylinder.

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