CN117715582A - System and method for non-invasive pulse pressure waveform measurement - Google Patents

Abstract

Systems and methods for a non-invasive high resolution pressure pulse waveform measurement system are provided. The system may 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 calibrate the signal, a pneumatic tube connecting the air pump and sensor with the cuff, and a hydrodynamic filter configured as an input to a reference port of the high resolution pressure sensor. The hydrodynamic filter may be configured to transmit only the average pressure by attenuating a selected frequency range of the signal.

Description

System and method for non-invasive pulse pressure waveform measurement

Technical Field

The present disclosure relates generally to medical diagnostics, and in particular, some embodiments may relate to non-invasive cardiac waveform measurements.

Background

Heart disease is a leading cause of death in 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. Thus, it may be difficult to diagnose critical diseases, such as heart failure, until advanced disease progression occurs.

Several important measurements allow a physician to diagnose heart failure. For example, pressure pulse waveforms are important measurements that allow medical professionals to assess cardiac health quantitatively and qualitatively. In a typical clinical setting, a medical professional uses a hand-held force sensor to measure the radial pulsation of an artery. Measurements must be made by a trained operator to ensure accuracy.

Disclosure of Invention

In accordance with 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; a high resolution pressure sensor configured to perform high sensitivity signal acquisition at a specified pressure level, wherein each high resolution pressure sensor comprises a measurement port and a reference port; a high range pressure sensor configured to measure an absolute reference of the signal and calibrate the signal; a pneumatic tube connecting the air pump and the sensor with the cuff; and a hydrodynamic filter configured as an input to the reference port of each high resolution pressure sensor.

In some embodiments, the hydrodynamic filter includes a resistive 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 the flow. In some cases, the resistance assembly of the hydrodynamic filter includes a rigid tube having an inner diameter in the range of 10-200 μm. The capacitive assembly is configured to reduce pressure variations by storing an air volume. In some embodiments, the elasticity of the capacitive element is in the range of 0.2-2.0 MPa. The capacitive assembly may include a tube connecting the resistive assembly to the reference port.

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, by way of example, features in accordance with embodiments of the disclosed technology. This summary is not intended to limit the scope of any of the inventions described herein, which is limited only by the appended claims.

Drawings

The present disclosure in accordance with one or more various embodiments is described in detail with reference to the following figures. The drawings are provided for purposes of illustration only and depict only typical or example embodiments.

Fig. 1 is a diagram illustrating an example of a modified blood pressure cuff system in accordance with the systems and methods disclosed herein.

FIG. 2A is a diagram illustrating an example of a resistance assembly having a securing hole according to the systems and methods disclosed herein.

FIG. 2B is a diagram illustrating an example of a resistance assembly with an in-line filter according to the systems and methods disclosed herein.

FIG. 2C is a diagram illustrating an example of a resistance assembly having a reduced inner diameter according to the systems and methods disclosed herein.

Fig. 2D is a schematic diagram of a capacitive assembly including a flexible tube.

Fig. 2E is a schematic diagram of a capacitive assembly including a tube with a piston cylinder.

Fig. 3 is a flowchart illustrating an example of a pulse pressure waveform measurement method in accordance with the systems and methods disclosed herein.

Fig. 4A is an example diagram of a left ventricular pressure-volume ("PV") circuit of a young patient according to the systems and methods disclosed herein.

Fig. 4B is an exemplary diagram of an elderly patient left ventricular pressure-volume ("PV") circuit, drawn in accordance with the systems and methods disclosed herein.

Fig. 5 is a flowchart showing an example of a left ventricular end diastolic pressure ("LVEDP") risk prediction method in accordance with the systems and methods disclosed herein. .

FIG. 6 is an exemplary graph of envelope functions reconstructed at specified pressure levels and three pressure holds according to the systems and methods disclosed herein.

FIG. 7 is an exemplary graph of envelope functions for estimating systolic blood pressure ("SBP") and diastolic blood pressure ("DBP") changes after pulse amplitude fluctuations in accordance with the systems and methods disclosed herein. .

The drawings are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed.

Detailed Description

Embodiments of the systems and methods disclosed herein may provide a modified blood pressure ("BP") cuff that may be used to perform non-invasive but accurate cardiac measurements. The systems and methods disclosed herein may be used to perform pressure pulse waveforms, left ventricular end-diastole pressure ("LVEDP") measurements, pressure-volume ("PV") loop measurements, and other important cardiac measurements. The systems and methods herein relate to a modified BP cuff system, a method for performing measurements, a risk assessment measurement and a calibration method.

Non-invasive pulse pressure waveform measurement

A modified blood pressure "(BP") cuff may be used to measure the pressure pulse waveform. In some embodiments, the modified BP cuff system may include a dynamic pressure sensor in place of and/or in addition to the 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 a difference between its measurement port and reference port. High range absolute pressure sensors can be used to calibrate the signal. An air valve or filter may be included to maintain a particular pressure level at the reference port. Maintaining a pressure level may allow the high resolution pressure sensor to operate within its normal range. During the measurement, the pressure sensor may acquire signals simultaneously.

High range pressure sensors may measure against atmospheric pressure, while high resolution pressure sensors may measure against a variable reference pressure. The pressure sensor may be connected in parallel to the BP cuff system. In some embodiments, the high range and high resolution pressure sensors may have operating ranges on the order of the measurement and signal, respectively.

No control system is employed in the embodiments described herein. Such a control system may be used to dynamically control the air valve to open and close the valve under the appropriate pressure to ensure that the signal is captured correctly. In such systems, pressure fluctuations may cause the sensor to saturate, resulting in catastrophic failure, signal drift, and loss of valuable information. For these reasons, air valve systems may suffer from drawbacks not present in the embodiments described herein.

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

The hydrodynamic filter may be implemented using sequential combinations of resistance tubes and flexible tubes. The resistance tube creates a flow resistance that restricts the flow that can move through the element. The flexible tube stores the injection volume at a desired rate of flexibility. The hydraulic system produces an electrical equivalent of an RC low pass filter. In such a hydraulic system, the circuit may be understood as the time that the flexible element needs to be filled by the resistance element.

In some embodiments, the hydrodynamic filter includes a resistance assembly and a compliance assembly. The resistance assembly is configured to apply resistance to flow, thereby slowing flow, while the compliant assembly includes a capacitive assembly configured to reduce pressure variations by storing air volume. In such embodiments, the compliant assembly may include a tube that connects the resistance assembly to the reference port. Additionally, the resistance assembly of the hydrodynamic filter may comprise a rigid tube having 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 the reference port to regulate flow into the reference port. This configuration can provide a stable pressure to the system, thereby producing a smooth signal.

Fig. 1 shows an example of a system with passive configuration for high precision sensors. As shown in fig. 1, 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 assembly 108 in series with a capacitive assembly 110, and a reference port 120. The system may also include an air pump 102 and a BP monitor 104. An air pump 102 may be used to inflate the cuff 100.

Fig. 2A, 2B, and 2C are schematic diagrams of a resistance assembly 108, the resistance assembly 108 including a tube 130 having a fixed orifice 132, a tube having an in-line filter 134, and a tube having an ID 136 less than ID 138. As shown in fig. 2A, the filter 134 may include an aperture 132. As shown in fig. 2B, the orifice 132 may be configured in a tube 130 connected to the reference port 120. In further embodiments, the aperture may be adjustable. As shown in fig. 2B, the tube 130 connected to the reference port 120 may be configured with an in-line filter 134. As shown in fig. 2C, the tubing 130 connected to the reference port 120 may include a portion having a reduced diameter or small ID 136 relative to the ID of the tubing 138.

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

Fig. 2D and 2E are schematic diagrams of capacitive assembly 110 including an elastic tube (fig. 2D) and a tube with a piston cylinder (fig. 2E).

An important measurement may be the difference between the signal measured at the measurement port and the signal measured at the reference port. Thus, the output signal is equivalent to a high-pass filtered signal. In addition, the self-adjusting reference port signal may also maintain a centered output signal. In contrast to air valves, the use of an orifice allows the reference port to remain at the average pressure signal. Maintaining the average pressure signal is important to eliminate the bias in the measured pulsations and to maintain the center signal with a high resolution transducer.

In some embodiments, the hydrodynamic filter may include a resistance assembly including a tube having a small ID. In such embodiments, the resistance assembly may comprise a substantially rigid tube having an inner diameter in the range of 10-200 μm, and the ID of the tube may be significantly smaller in diameter than the ID of the tube connecting the rest of the BP pressure cuff system and the reference port. A tube with a small ID effectively acts as a filter where only the average pressure is transmitted, resulting in a low pass filter to the reference port that is flow dependent. The specific cut-off frequency of the filter is designed using the fluid dynamics principle and the characteristics of the signal and measurement system. The filtered signal will depend on the combination of the volumetric flow rate and the material properties of the reference port side.

In some embodiments, the system may be designed using a commercial arm cuff BP system. The system may 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 accurate signal measurements. Each high resolution pressure sensor may contain a measurement port and a reference port. High range pressure sensors can be used for absolute reference and signal calibration.

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

The pressure sensor may measure the peripheral pressure pulse. The pressure at which the cuff is inflated changes the pressure-flow behavior in the artery according to the fluid-solid interaction principle. The combined waveform analysis can then be used to non-invasively assess cardiovascular health. The peripheral pulse waveform may be measured and then transformed to estimate the center waveform.

The pressure and flow rate in the closed system can be given by the bernoulli equation (below). When the arm cuff is inflated, externally applied forces change the radius of the artery, ultimately changing the pressure to flow ratio of the system. At the lower extreme, application of pressure below the minimum DBP to the artery will not result in a change in pressure flow behavior or a minimal change in pressure flow behavior. At the upper limit, pressures above the maximum SBP in the artery cause arterial collapse and cessation of blood flow. Any pressure between these two extremes can produce a proportional change to the pressure-flow relationship, again given by the bernoulli equation. Thus, comparing waveforms measured at two different hold pressures allows the pressure-flow characteristics of the system to be derived. Quantitative and qualitative comparisons of waveforms may be performed. A mapping method such as waveform time or waveform-to-waveform may also be used.

The captured signal reflecting the pressure flow relationship in the elastic artery may be used to derive additional waveforms that may further characterize the patient. The fluid dynamics principle enables waveforms to be derived, including but not limited to flow, velocity and radial movement. The fluid dynamics principle relates to parameters of the static system such as pressure, velocity, force and volume. Analyzing these systems with multiple measurement points allows solving for parameters of the query. For example, the velocity may be solved by maintaining the pressure waveform using the DBP and super SBP. The super SBP waveform completely blocks flow, giving an absolute pressure reading. The DBP waveform represents a combination of pressure and flow. Thus, the final flow rate can be measured during the DBP hold pressure. Similar derivations may be applied to other holding pressure combinations. The importance of the results obtained may depend on the basic physical characteristics of the captured waveform.

Practical applications may require synchronization of waveforms. The solution may include time synchronization of different waveforms using ECG or using known timing events during the cardiac cycle, including maximum dP/dt, onset and dicrotic notch. The cuff may have wired or wireless synchronization with other devices, such as bluetooth or Wi-Fi with ECG.

Fig. 3 shows an example of non-invasive pulse pressure waveform measurement. The modified BP pressure cuff system as described above may be used to record pressure pulsations in the brachial artery. To perform the measurement, the arm BP cuff may be inflated around the arm of the patient. A pump system may be used to inflate the cuff. A first operation 302 may involve starting a measurement process. At a first operation 302, the output of both the high range pressure sensor and the high resolution pressure sensor may be zero. Pressure sensors may be used to measure the patient's systolic BP ("SBP") and diastolic BP ("DBP"). A second operation 304 may involve measuring BP with a high range pressure sensor. At the time of the second operation 304, the output of the high range sensor may be the full BP range of the patient and the output of the high resolution pressure sensor may be zero.

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

As a fourth operation 308, the cuff may be inflated and maintained at a given pressure. For example, the cuff may be inflated to a pressure of PHOT, which may be one of the identified holding pressures. At a fourth operation 308, the high range sensor output may be an absolute pressure value and the high resolution pressure output may be zero. As a fifth operation 310, the cuff may then be inflated to a target pressure. In a fifth operation 310, the high range sensor may have a low accuracy absolute pressure pulsation output. The high resolution sensor may have a high accuracy of the output of the relative pressure pulsation. As a sixth operation 312, the cuff may be deflated, ending the measurement period. At sixth operation 312, the high resolution pressure sensor and each of the high resolution pressure sensors may have zero output. For a plurality of holding pressures, operations three to six may be repeated. The outputs from operation five may be combined for calibrated high precision pulsating output.

In some embodiments, the comparison of waveform capture may be performed using a low hold pressure and a high hold pressure above an upper pressure limit. For example, for low hold pressures, the pressure may be set to DBP or just below DBP. For high maintenance pressures, the pressure may be set higher than the SBP ("super SBP") to shut off blood flow. For example, the pressure may be set to about SBP+35mmHg. At the lower limit, the waveform may represent a combination of static pressure and flow rate. At the upper limit, the waveform shows only the pressure characteristic. At the supersbp maintenance pressure, flow in the subclavian artery ceases to be the closest waveform representing the static pressure from Kong Douqu in the ascending aortic wall. This holding pressure allows for direct pressure waveform measurement in the central artery. The corresponding pressure waveforms between the supersbp and DBP may 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 assessment.

Pressure-velocity Loop embodiment

As described above, flow at the brachial artery can be characterized by the bernoulli equation for the average flow, given by:

wherein P is _B Is the pressure at the brachial artery, ρ is the fluid density, u _b Is the flow rate at the brachial artery, and P _T Is the total pressure in the aortic arch.

In the super SBP pressure maintenance (P _SS ) When the brachial artery is completely occluded, thereby causing u _b =0. Thus, the measured pressure at the cuff is the pressure in the aortic arch. Thus:

P _Ss ＝P _B ＝P _T

wherein P is _SS Is the super SBP holding pressure.

While DBP pressure is maintained (PD), the applanation condition measures the pressure in the brachial artery. The pressure in the brachial artery conforms to the bernoulli equation as shown below:

wherein P is _D Is the DBP hold pressure.

Equalizes the above equations by total aortic arch pressure and solves for velocity (u _B ) Give out

Super SBP pressure (P) _SS ) And DBP speed (u) _D ) The plot gives the ("PV") loop. The data may be plotted and analyzed at any intermediate step. For example, SBP pressure and DBP pressure may be analyzed.

Fig. 4 shows an example of PV loop comparison for elderly (fig. 4A) and young (fig. 4B) patients. Each PV loop has different characteristics and shapes, each including a dashed line 402 that simulates the slope of the rising pinch portion. The slope can clearly distinguish patients by age and therefore it is a useful diagnosis. Each further includes a solid line 404 as a proportional line. Other parameters include loop area, curvature, indentation, peak offset, and other combinations of parameters.

Left ventricular end-diastole pressure ("LVEDP") risk prediction embodiment

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 about 18mmHg. Because LVEDP is a valuable diagnostic measurement, a non-invasive method for measuring LVEDP may allow a clinician to predict the risk of heart failure earlier and accurately.

Non-invasive pulse waveform analysis and classification algorithms may be used to form the LVEDP risk prediction.

Fig. 5 illustrates an example of a non-invasive LVEDP risk prediction method 500 involving several operations. The first operation 502 may involve taking patient measurements. The sub-operation 504 of the first operation 502 may involve measuring the height of the patient. Sub-operation 506 of the first operation 502 may involve measuring a weight of the patient. Other patient measurements may also be made. A second operation 508 may involve taking a medical history of the patient. Sub-operation 510 of the second operation 508 may involve recording the patient procedure. Patient surgery, such as cardiac surgery, may be recorded. Other medical information, such as courses of treatment and other treatments, may also be recorded. Sub-operation 512 of the second operation 508 may involve recording the patient condition. Patient conditions may include known examples of cardiovascular conditions such as heart failure, myocardial infarction, and cardiomyopathy. Other cardiac conditions, co-morbid conditions, and/or general health conditions may be recorded. Other patient information may also be recorded, such as genetic predisposition, family history, lifestyle factors, and other information.

A third operation 516 may involve combining the recorded patient measurements and medical history to form a fraction of complications.

A fourth operation 518 may involve measuring the BP of the patient as SBP and DBP using a commercially available and/or conventional arm cuff or some other measurement device.

A fifth operation 520 may involve measuring a pulse waveform of the patient. Pulse waveforms may be measured using the modified BP cuff according to the previous embodiments. For example, a modified blood pressure cuff may be used that inflates to a specific pressure and maintains these pressures to capture the waveform at the set pressure. The holding pressure may include DBP, SBP, MAP and/or sbbp. In some embodiments, an sSBP that completely cuts off blood flow through an artery may be used. The inflation pressure may be, for example, about 100mmHg. The hold time may be, for example, about 40 seconds.

The sub-operation 522 of the fifth operation 520 may involve performing pulse waveform measurements for a duration long enough to account for pressure amplitude fluctuations throughout the respiratory cycle. The measured amplitude may be highest during the post-expiration phase of the respiratory cycle.

A sixth operation 524 may include calibrating the measured pulse waveform using the SBP and DBP measurements. The BP measurement can be used to calibrate the waveform with the pressure cell. The calibration method may include the methods disclosed in the following sections of the disclosure.

A seventh operation 526 may include selecting a plurality of post-exhalation waveforms for feature extraction. Post-exhalation waveforms may be selected because they can track the highest LVEDP reading throughout the respiratory cycle. The extracted features and/or parameters of interest may include an expansion index ("AIX"), a systolic pulse region, and/or a systolic BP. Other desired and/or relevant features and/or parameters may also be extracted.

An eighth operation 528 may include measuring and/or extracting features and/or parameters of interest in the pulse waveform. The sub-operation 530 of the eighth operation 528 may involve extracting the SBP or the contracted pulse region. The sub-operation 532 of the eighth operation 528 may involve extracting AIX.

In some embodiments, classification algorithms may be used to assess risk. The inputs to the algorithm may be the pulse characteristics of the contracted pulse region, the distension index, and the patient characteristics of the weight and complication score. Using inputs and algorithms, probabilities of LVEDP having a failure threshold value or greater can be generated. In an embodiment, the failure threshold may be set to about 18mmHg. In another embodiment, the threshold may be set to about 15mmHg or another value of clinical relevance selected when training the algorithm. This process may be repeated for post-expiration pulses over n respiratory cycles to generate n probability predictions. Multiple measurements may be made. For example, in an embodiment, two or three measurements may be made. The probabilities of multiple individual blogs may be combined into a single risk prediction using an integrated approach. The predictions may be processed together to generate a single LVEDP risk prediction. The integration methods may include more complex methods for average probabilities and/or may include aggregate probabilities.

Accordingly, a ninth operation 534 may involve inputting selected features and/or parameters of each pulse to predict an individual LVEDP risk. The selected features and/or parameters may include systolic pulse region, AIX, patient weight, and complications score. Other parameters and/or combinations of parameters are also possible. Likewise, a tenth operation 536 may involve combining individual pulse risk predictions for patient LVEDP risk prediction.

Calibration examples

BP cuff measurements can be used as a useful clinical measurement because peripheral BP as measured via the cuff tends to track the central BP of a healthy patient. Unfortunately, in patients experiencing cardiovascular problems, the relationship between peripheral BP and central BP may deteriorate. The severity of cardiovascular problems in a patient may affect the extent to which the peripheral-central BP relationship is degenerated. However, BP cuff measurements remain an important diagnostic tool for patients experiencing cardiovascular problems because they are fast, non-invasive and inexpensive to perform. Although the peripheral-central BP relationship is degraded in such patients, the calibration method may allow peripheral BP measurements performed with, for example, arm BP cuffs to be used as a proxy for central BP measurements, even in patients experiencing serious problems.

A modified BP cuff system (such as the system described in the previous embodiments) may be used to measure peripheral BP. Due to respiration-induced pressure fluctuations, the peripheral BP can be measured over several breath-hold periods. The non-invasive pulse signal measured using the modified BP cuff system may be calibrated to track the central BP amplitude of the patient.

The envelope function may be used to correct the peripheral BP measurement and calibrate the signal. The envelope function may comprise a relationship between the pulse amplitude at the measurement site and the cuff pressure. The measurement site may be an artery. The envelope function may be constructed by measuring the pulse amplitude corresponding to cuff pressure across multiple breath holds.

The calibration method may include several operations. The first operation may involve measuring peripheral BP in the form of systolic BP ("SBP"), diastolic BP ("DBP"), and mean arterial pressure ("MAP") using conventional and/or commercially available oscillometric cuffs. These measurements may be inaccurate. In particular, these measurements may not track measurements made in vivo due to amplitude fluctuations caused by respiration and/or due to other errors.

The second operation may involve the use of a modified BP cuff. The modified BP cuff may be a modified BP system comprising a high resolution pressure sensor and a high range pressure sensor, as described in the previous embodiments. The second operation may involve inflating the modified BP cuff to a set pressure value. The pulsation can be recorded at this pressure value. The BP cuff may be inflated within a range of set pressure values. Pulsation may be recorded for each pressure value. The second operation may involve operating during multiple breath holds to account for pressure fluctuations caused by the breath. For each breath hold, the measured waveform may be analyzed to compare the signal pulse amplitude to the set pressure of the modified BP cuff. Measurements may be made during multiple holds to reconstruct the proxy of the envelope function. For example, the measurement may be made in two, three or more breath holds.

The third operation may involve calculating parameters to correct pressure fluctuations due to respiratory variations using measurements made during the second operation, and finally calibrating the peripheral measurements as central measurements. This can be achieved by deriving the parameters required to correct the peripheral measurement using an envelope function.

Fig. 6 shows an example of an envelope function reconstructed with BP measurements and three pressure maintenance. The three pressure maintenance are DBP, MAP, and hypersystolic BP ("sSBP"). For DBP pressure maintenance, the modified BP cuff is inflated at a minimum pressure, allowing blood to flow through the artery substantially unimpeded. For MAP pressure maintenance, the modified BP cuff is inflated to MAP. For SBP maintenance, the modified pressure cuff is inflated to a pressure higher than the SBP to effectively shut off any blood flow through the artery. The cuff pressure is shown in fig. 6 as a dashed vertical line of three hold values. The three hold values include a DBP hold 608, a MAP hold 610, and a sSBP hold 612.

Figure 6 also shows the individual recorded pulsations measured at each holding pressure. FIG. 6 shows individual pulses 602 maintained for DBP, individual pulses 604 maintained for MAP, and individual pulses 606 maintained for sSBP. As shown in the example of fig. 6, multiple pulses may be recorded for each pressure hold. The pulse amplitude of each pulse 602, 604, 606 may be measured with a pressure sensor. In the example shown in fig. 6, the pulsation amplitude is reported in volts (V). These pulse amplitude measurements can also be converted into other pressure units.

As discussed above, respiration may cause significant fluctuations in the center BP. The voltage-based signal from cuff pressure maintenance may show respiratory fluctuations as in the catheter aortic signal. Thus, the BP value reported by the modified BP cuff measurement may be assumed to be an average value. The pulse signal may be calibrated to the pressure unit by adjusting the SBP and DBP values over the breathing pattern and correctly scaling the measured pressure signal. For each individual pulse in a pulse segment, the pulse amplitude difference from the average pulse amplitude for that segment can be used to correct the SBP and/or DBP values of the respiratory fluctuations.

For example, a model of correcting the DBP value from the periphery to the center DBP using parameters derived from the envelope function is given by:

wherein A is _d /A _m Is the ratio between the pulse amplitude at DBP and MAP, and DBP _cuff And MAP _cuff Is DBP and MAP reported by cuff BP readings, respectively, and m ₁ ，m ₂ And b is a coefficient optimized for correlation.

The SBP value may be corrected using the forward peak and the reflected peak that are measurable in the pulse waveform signal. For the arm cuff, the potential retention pressure showing these characteristics is sSBP. The corrected SBP may be given by:

SBP _corr ＝SBP _cuff +m ₁ *(P ₁ -P ₂ )+b

wherein, SBP _corr Is a corrected SBP value for tracking the center BP, SBP _cuff Is SBP cuff measurement reading, P ₁ Peak pressure, P, being the first peak in the systolic phase ₂ Is the peak pressure of the second peak in the systolic phase, and m ₁ And b is a coefficient optimized for correlation.

The linear envelope function model may be used to calculate the actual pressure as shown in the closed form equation:

wherein P is _adj Is respiratory regulation pressure, P _calib Is the BP report value, ΔPA is the pulse amplitude difference from the average, and slope _p Is specific to a specific pressure (slope) _DBP Or slope _SBP ) Is provided. The pressure may be SBP or DBP.

In an uncalibrated pulse segment, the above calculation is repeated for each pulse in the pulse segment and using a signal scaling method, all pulses can be calibrated with SBP and DBP values reflecting the breathing pattern. The presented model assumes a linear relationship between the measurement points and the fixed envelope function of the given object. With more hold pressure, a more detailed envelope function can be reconstructed and model accuracy can be improved. The calibration may be applied to the SBP and/or DBP independently.

FIG. 7 shows an example of an envelope function for estimating SBP and DBP changes after pulse amplitude fluctuations. As shown in fig. 6, the pressure cuff retention is indicated by the dashed vertical line. FIG. 7 shows DBP pressure cuff maintenance value 608, MAP pressure cuff maintenance value 610, and SBP pressure cuff maintenance value 700. The lower right arrow 708 of fig. 7 shows the pulse amplitude deviation from the average pulse amplitude. Arrow 706 above and to the right of arrow 708 shows the SBP increase. The arrow 704 on the left side of the figure shows the DBP increase. The envelope function 702 may then be used to estimate the SBP and DBP variations after pulse amplitude fluctuations that may be caused by respiration. Fig. 7 shows an estimate 710. Fig. 7 is merely exemplary. If the necessary information described is obtained, the method described above with reference to fig. 7 may be performed using different devices, threshold conditions, and numbers.

In some embodiments, the calibration method in combination with breathing fluctuations may also be used as a diagnostic tool in cardiology. For example, an abnormal pulse condition is defined as an SBP decrease of greater than about 10mmHg upon inspiration. This condition may be observed during cardiac tamponade or right ventricular dilation, for example in severe acute asthma or chronic obstructive pulmonary disease. Thus, an embodiment of the calibration method may involve setting a threshold of about 10mmHg.

It should be understood that the various features, aspects, and functions described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment in which they were described. Rather, they may be applied to one or more other embodiments, alone or in various combinations, whether or not such embodiments are described, and whether or not such features are presented as part of the described embodiments. Thus, the breadth and scope of the present application should not be limited by any of the above-described exemplary embodiments.

Unless explicitly stated otherwise, the terms and phrases used in this document and variations thereof should be construed to be open ended, and not limiting. As an example of the foregoing, the term "comprising" is to be understood to mean "including, but not limited to," etc. The term "example" is used to provide an illustrative instance of an item in question, rather than an exhaustive or limiting list thereof. The terms "a" or "an" are to be understood as meaning "at least one", "one or more", etc.; terms of similar meaning should not be construed to limit the described items to a given period of time or to items available at a given time. Rather, they should be understood to encompass conventional, traditional, normal, or standard techniques that may be available or known at any time now or in the future. Where the present document relates to techniques that are apparent or known to one of ordinary skill in the art, such techniques include techniques that are apparent or known to one of ordinary skill in the art now or at any time in the future.

In some cases, the presence of broadening words and phrases such as "one or more," "at least," "but not limited to" or other like phrases shall not be read to mean that the narrower case is intended or required in instances where such broadening phrases may not be present. The use of the term "component" does not imply that the aspects or functions described or claimed as part of the component are all configured in a common package. Indeed, any or all of the various aspects of the components (whether control logic or other components) may be combined in a single package or maintained separately, and may be further distributed in multiple groupings or packages or across multiple locations.

In addition, the various embodiments set forth herein are described in terms of exemplary block diagrams, flowcharts, and other illustrations. As will be apparent to one of ordinary skill in the art after reading this document, the illustrated embodiments and their various alternatives may be implemented without limitation to the illustrated examples. For example, block diagrams and their accompanying descriptions should not be construed as enforcing a particular architecture or configuration.

The terms "substantially," "about," and "approximately" are used throughout this disclosure (including the claims) to describe and explain small fluctuations such as those caused by variations in 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 (13)

1. A non-invasive pressure pulse waveform measurement system, comprising:

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 a specified pressure level, wherein each high resolution pressure sensor comprises a measurement port and a reference port;

a high range pressure sensor configured to measure an absolute reference of the signal and calibrate the signal;

a pneumatic tube connecting the air pump and the sensor with the cuff; and

a hydrodynamic filter configured as an input to the reference port of each high resolution pressure sensor;

wherein the hydrodynamic filter is configured to transmit only average pressure by attenuating a selected frequency range of the signal.

2. The system of claim 1, wherein the hydrodynamic filter comprises a resistive component and a capacitive component.

3. The system of claim 2, wherein the resistance component of the hydrodynamic filter is configured to apply resistance to flow.

4. The system of claim 2, wherein the capacitive assembly is configured to reduce pressure variations by storing air volumes.

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

6. The system of claim 2, wherein the resistance assembly of the hydrodynamic filter comprises a rigid tube having an inner diameter in the range of 10-200 μιη.

7. The system of claim 4, wherein the elasticity of the capacitive element is in the range of 0.2MPa to 2.0 MPa.

8. The system of claim 1, wherein the blood pressure cuff is synchronized with an ECG device, iPhone, tablet, computer or other device, allowing for the transmission of wired or wireless data.

9. The system of claim 8, wherein bluetooth or Wi-Fi is employed to transmit wireless data.

10. The system of claim 2, wherein the resistance component and the capacitive component are combined within a single component.

11. The system of claim 2, wherein the resistance assembly comprises a resistance element comprising an orifice or a physical filter.

12. The system of claim 11, wherein the aperture is fixed and/or adjustable.

13. The system of claim 2, wherein the capacitive assembly comprises a flexible elastic tube, a tube with a small damper, or a tube with a piston cylinder.