Common carotid artery system hemodynamic parameter detection method based on blood pressure-pipe diameter prior relation

Abstract

The invention discloses a method for detecting hemodynamic parameters of a common carotid artery system based on a blood pressure-tube diameter prior relationship. The method comprises the following steps: firstly, acquiring an inner diameter waveform and a blood pressure waveform of a human common carotid artery, and establishing a mathematical model for describing a quantitative relation between blood pressure and an artery inner radius based on a vascular mechanics principle as priori knowledge; measuring a carotid artery blood pressure waveform by using a pressure sensor, and obtaining an intravascular radius waveform corresponding to the blood pressure waveform based on a prior relationship; the carotid artery blood flow waveform is calculated by combining and utilizing a continuous ultrasonic Doppler probe to measure the average blood flow velocity waveform of the common carotid artery; finally, a distribution-lumped parameter coupling model for describing hemodynamic parameters of the common carotid artery local and post-load system is established, the model is composed of a nonlinear pulsating blood flow model and a five-element lumped parameter model for describing the common carotid artery post-load system, and a control equation of the distribution-lumped parameter coupling model is solved. And obtaining a wall shear stress waveform and element parameter values of the five-element lumped parameter model.

Description

Technical Field

[0001] The present invention belongs to the field of medical information detection technology and health engineering, and relates to a non-invasive detection method for the hemodynamic parameters of the human common carotid artery system. A method is established based on the prior relationship between the blood pressure and the diameter of the common carotid artery, and uses a pressure sensor to measure the blood pressure waveform of the common carotid artery and ultrasonic Doppler technology to measure the average blood flow velocity waveform of the common carotid artery to determine the overall hemodynamic parameters of the local common carotid artery and its afterload system. Background Art

[0002] Cardiovascular diseases such as ischemic heart disease and stroke consistently rank at the top of the list of disease mortality rates. The cost of treating cardiovascular and cerebrovascular diseases has also been increasing rapidly, placing a heavy burden on society and countless families. With the increasing public awareness of health, the early diagnosis and prevention of cardiovascular and cerebrovascular diseases are receiving increasing attention. Abnormal changes in hemodynamic indicators are a sign of cardiovascular and cerebrovascular disease. The World Health Organization has recognized that pathological changes in hemodynamic parameters (such as arterial compliance and peripheral resistance) are high-risk factors for stroke, and such changes often precede changes in imaging parameters obtained by techniques such as computed tomography (CT) and magnetic resonance imaging (MRI). Studies have also shown that changes in certain hemodynamic parameters (such as blood pressure and wall shear stress) can induce the secretion of reactive oxygen species and inflammatory factors, further damaging endothelial cells and causing endothelial dysfunction, such as cardiovascular and cerebrovascular diseases such as atherosclerosis and thrombosis.

[0003] The common carotid artery is one of the most important blood vessels connecting the heart and brain, gathering hemodynamic information from the upstream heart and downstream cerebral vascular bed. Abnormalities in its hemodynamic parameters are closely linked to cardiovascular and cerebrovascular diseases such as atherosclerosis, stroke, and coronary heart disease. It serves as a crucial "window" for the prevention, early diagnosis, clinical treatment, and rehabilitation evaluation of cardiovascular and cerebrovascular diseases. Therefore, the detection and analysis of hemodynamic parameters of the common carotid artery system is of great clinical significance for the early diagnosis and treatment evaluation of cardiovascular and cerebrovascular diseases.

[0004] At present, the detection of hemodynamic parameters in clinical practice mostly adopts non-invasive detection technologies such as color Doppler ultrasound, CT, and MRI, and has gradually replaced invasive detection methods such as pulmonary artery catheter (PAC) and arterial puncture, becoming the "gold standard" for the detection of hemodynamic parameters. These detection technologies are now very mature, with high resolution and accuracy, and have been widely used in clinical and scientific research. It dynamically captures the geometric structure and changes of the arterial wall through anatomical imaging and image recognition technology, and uses Doppler ultrasound to obtain blood flow velocity waveforms. Based on the hemodynamic model, relevant hemodynamic parameters such as arterial compliance (C), peripheral resistance (R), flow (L), wall shear stress (τ w ), blood flow (q(t)), etc. However, most detection instruments with anatomical imaging capabilities are expensive, bulky, complex to operate, and highly dependent on technology. Therefore, they are currently only used for intermittent testing in large hospitals or research institutions, and it is difficult to achieve real-time, continuous measurement in vivo.

[0005] In contrast, by measuring the blood pressure, caliber, and blood flow waveform of the common carotid artery and establishing a hemodynamic model of the common carotid artery system, the local blood flow wall shear stress waveform of the common carotid artery and the model parameter values such as compliance, inertia, and peripheral resistance of the downstream cerebral vascular bed can be calculated and analyzed, thereby achieving real-time and continuous measurement of the hemodynamic parameters of the common carotid artery and afterload (downstream cerebral vascular bed) system. This type of method is suitable for the development of portable, wearable, and miniaturized common carotid artery system hemodynamic parameter detection equipment, which has the advantages of being non-invasive, economical, and easy to operate. However, the measurement of the common carotid artery caliber and blood flow waveform often requires the combined use of pulsed (diameter measurement) and continuous (flow velocity measurement) Doppler ultrasound detection technology, which undoubtedly increases the cost of the detection equipment.

[0006] Based on the above reasons, the present invention proposes a method for detecting hemodynamic parameters of the common carotid artery system based on the blood pressure-diameter prior relationship. The method first uses a large-scale color Doppler ultrasound instrument and a pressure sensor used clinically to synchronously obtain the diameter waveform and blood pressure waveform of the human common carotid artery under different physiological states, and establishes a mathematical model describing the quantitative relationship between the blood pressure and diameter of the human common carotid artery based on the principle of vascular mechanics, and uses this model as the prior knowledge of the present invention; secondly, the common carotid artery blood pressure waveform is measured using a pressure sensor, and then the diameter waveform corresponding to the blood pressure waveform is obtained based on the prior knowledge of blood pressure-diameter; further combined with the common carotid artery average blood flow velocity waveform measured by a continuous ultrasonic Doppler probe, a distributed-lumped parameter coupling model of the common carotid artery-afterload system is established, and the blood flow waveform is obtained from the common carotid artery average blood flow velocity waveform and the common carotid artery inner diameter waveform. The common carotid artery wall shear stress waveform and the common carotid artery circumferential strain waveform are further calculated, and the blood pressure waveform and flow waveform are Fourier decomposed. The amplitude-frequency and phase-frequency curves of the input electrical impedance of the cerebral vascular bed downstream of the common carotid artery are obtained using a five-element lumped parameter model. The input impedance curve is fitted using the least squares method to obtain the five-element lumped parameters describing the common carotid artery and the afterload system. It has very important clinical reference value for the early diagnosis of cerebrovascular diseases and rehabilitation evaluation of cerebrovascular diseases. Summary of the Invention

[0007] like Figure 1 As shown in the flowchart, the present invention first uses a large color Doppler ultrasound instrument and a pressure sensor used clinically to synchronously obtain the inner diameter waveform and blood pressure waveform of the human common carotid artery under different physiological conditions, and establishes a method to describe the blood pressure p and the inner radius r of the artery based on the principle of vascular mechanics. i The mathematical model of the quantitative relationship between the two is used as the prior knowledge of the present invention; secondly, the pressure sensor is used to measure the blood pressure waveform p(t) of the common carotid artery, and then the blood vessel radius waveform r corresponding to the blood pressure waveform is obtained based on the prior knowledge of blood pressure-inner diameter. i (t); further, the average blood flow velocity waveform u of the common carotid artery was measured by continuous ultrasound Doppler probe. m (t) Calculate the common carotid artery blood flow waveform q(t); Finally, establish a distributed-lumped parameter coupling model (such as Figure 2 The model consists of a nonlinear pulsating blood flow model based on the Ling-Atabek hypothesis in a uniform elastic circular tube and a five-element lumped parameter model describing the common carotid artery and afterload (downstream cerebral vascular bed) system. The governing equations of the above-mentioned distributed-lumped parameter coupling model are solved to obtain the wall shear stress waveform τ w And the component parameter values of the five-component (C1, R1, C2, R2, L) lumped parameter model.

[0008] The present invention provides the following common carotid artery local hemodynamic parameters:

[0009] 1. Maximum, minimum, and average internal radius r of the common carotid artery during one cardiac cycle i_max ,r i_min ,r i_mean

[0010] The diameter of the common carotid artery mainly depends on the mechanical properties of the vessel wall and blood pressure.

[0011] 2. Maximum, minimum, and average blood flow q of the common carotid artery during one cardiac cycle max ,q min and q mean

[0012] It represents the blood volume flow rate flowing through a certain section of the common carotid artery per unit time.

[0013] 3. Maximum, minimum, and average wall shear stress τ of the common carotid artery during one cardiac cycle w_max , τ w_min and τ w_mean

[0014] It represents the viscous friction force between the blood flow in the common carotid artery and the vascular endothelium.

[0015] 4. Maximum and average circumferential strain ε of the common carotid artery during one cardiac cycle max and ε mean

[0016] It represents the circumferential deformation of the common carotid artery wall during the cardiac cycle and is a relatively objective indicator for evaluating circumferential vascular motion. Furthermore, the present invention provides the following overall hemodynamic parameters for the common carotid artery and afterload system (i.e., the downstream cerebral vascular bed):

[0017] 5. Compliance of the common carotid artery segment C1

[0018] It reflects the ability of the common carotid artery segment to increase the volume of the vascular wall without rupture under unit pressure, and can evaluate the overall elastic performance of the common carotid artery segment.

[0019] 6. Resistance of the common carotid artery segment R1

[0020] An indicator that reflects the smooth flow of blood in the common carotid artery segment.

[0021] 7. Total compliance of the downstream cerebral vascular bed C2

[0022] Reflects the overall compliance of the downstream cerebral vascular bed.

[0023] 8. Total inertia of the downstream cerebral vascular bed L

[0024] A quantity that reflects the ease with which blood flow in blood vessels changes. The greater the flow inertia, the more difficult it is to change blood flow.

[0025] 9. Total flow resistance R2 of the downstream cerebral vascular bed

[0026] An indicator that reflects the smooth flow of blood in the peripheral vascular bed of the downstream cerebral blood vessels. Thrombosis, infarction, stenosis, and increased blood viscosity in the cerebral blood vessels will increase R2.

[0027] The technical solutions of the present invention are as follows:

[0028] Step 1: Synchronously obtain the inner radius waveform r of the human common carotid artery under different physiological conditions using a clinically used color Doppler ultrasound instrument and a pressure sensor. i (t) and blood pressure waveform p(t), based on the principle of vascular mechanics, a method describing blood pressure p and tube radius r is established. i The mathematical model of the quantitative relationship between them is used as prior knowledge; the specific method is as follows:

[0029] For a tube with a thickness of h and an inner radius of r i For an isotropic, incompressible, homogeneous common carotid artery wall, under the plane strain assumption, Hooke's law in polar coordinate form is:

[0030]

[0031] Where ε is the circumferential strain, σ θ and σ r They represent circumferential stress and radial stress respectively, E is the elastic modulus, and μ is Poisson's ratio.

[0032] Assuming that the wall of the common carotid artery is thin, σ r =0, according to Laplace's law we have Substituting into equation (1) we can get:

[0033]

[0034] For the circumferential strain ε, we have

[0035]

[0036] Among them, r d Take the end-diastolic internal diameter value.

[0037] Due to the influence of multiple factors such as collagen fibers and smooth muscles, blood vessels exhibit viscoelastic behavior. Therefore, the viscoelastic term is added to the right side of equation (2): Where φ0 is the viscosity coefficient, is the strain rate. The following p and r can be obtained by synthesis: i Relational equation:

[0038]

[0039] In the formula, A, B, and C are all constants.

[0040] Based on the existing blood vessel radius waveform r i (t) and blood pressure waveform p(t), the values of the three constants A, B, and C can be obtained by least squares fitting to minimize the residual sum of squares (RSS1), and the expression is as follows:

[0041]

[0042] Where m is the total number of sampling points, is the fitting value of the inner radius of the common carotid artery calculated by equation (4), r i (p) is the measured value of the inner radius of the common carotid artery. After obtaining the values of parameters A, B, and C in equation (4), the mathematical model describing the blood pressure-radius relationship in equation (4) can be used as prior knowledge.

[0043] Step 2: Based on the blood pressure waveform p(t) of the common carotid artery measured by the pressure sensor, the blood pressure-radius relationship mathematical model of equation (4) is used to calculate the common carotid artery inner radius waveform r i (t), the average blood flow velocity waveform u of the common carotid artery measured by continuous ultrasound Doppler technology m (t), calculate the common carotid artery blood flow waveform

[0044] Step 3: Establish a distributed-lumped parameter coupled model describing the hemodynamic parameters of the local common carotid artery and the overall afterload system. This model consists of a nonlinear pulsatile blood flow model in a uniform elastic circular tube based on the "Ling-Atabek hypothesis" and a five-element lumped parameter model describing the common carotid artery and afterload (downstream cerebral vascular bed) system.

[0045] Furthermore, the nonlinear pulsating blood flow model is used to calculate the wall shear stress τ w The specific steps are as follows:

[0046] like Figure 2 As shown in the figure, the wall of the common carotid artery is assumed to be an elastic straight circular tube, and the pulsating fluid in the common carotid artery is considered to be an incompressible Newtonian fluid. The governing equations for the pulsating fluid in the elastic straight circular tube are simplified as follows:

[0047]

[0048] Where t is time, u represents axial velocity, v represents radial velocity, η and ρ represent blood viscosity and density, respectively, and x and r represent axial and radial coordinates, respectively.

[0049] The boundary conditions are as follows:

[0050]

[0051] The relative radius y = r / r i Substituting into equation (6), the expression of the axial flow velocity u in the elastic straight circular tube is as follows:

[0052]

[0053] Integrating both sides of equation (6) along the cross section of the common carotid artery, taking into account the continuity equation and boundary conditions (7) to (9), the governing equation for the flow rate q(t) is obtained as:

[0054]

[0055] Where,

[0056]

[0057] Here, u m is the average value of the axial flow velocity u along the cross section of the artery.

[0058] According to the Ling-Atabek hypothesis, the gradient of the axial velocity u satisfies the following equation:

[0059]

[0060] Where f(x,t) is a function of x and t. Substituting equation (13) into equation (7), the expression of radial velocity v is as follows:

[0061]

[0062] Boundary conditions (8) and (9) become:

[0063]

[0064] In formula (14), The expression is as follows:

[0065]

[0066] Therefore, the radial flow velocity v is expressed as follows according to equations (14)-(17):

[0067]

[0068] Once p(t),q(t) and The axial velocity u can be calculated by equations (10) to (12)(15)(16). The radial shear stress is negligible, and the wall shear stress τw The expression is as follows:

[0069]

[0070] Furthermore, the specific calculation method of the parameters of the five-element lumped parameter model describing the common carotid artery and afterload (downstream cerebral vascular bed) system is as follows:

[0071] Perform Fourier decomposition on the blood pressure waveform p(t) measured by the pressure sensor and the blood flow waveform q(t) calculated by equation (12) to obtain the angular frequency ω n =2πnf0 corresponding to the blood pressure and flow harmonic components P n (ω n ) and Q n (ω n ), n is the number of harmonics, f0 is the fundamental frequency, so the input impedance Z in (ω n )=P n (ω n ) / Q n (ω n ), whose amplitude |Z in (ω n )| and phase ∠Z in (ω n ) is expressed as:

[0072] |Z in (ω n )|=|P n (ω n )| / |Q n (ω n )| (20)

[0073] ∠Z in (ω n )=∠P n (ω n )-∠Q n (ω n ) (twenty one)

[0074] The amplitude-frequency and phase-frequency curves of the input impedance of the cerebral vascular bed downstream of the common carotid artery are obtained. The equivalent input impedance curve obtained according to the five-element lumped parameter model is:

[0075]

[0076] Where j is the imaginary unit;

[0077] Equivalent input impedance The component parameters of expression (22) are obtained based on the least squares fitting method according to the actual input impedance curve of the common carotid artery, so that the sum of square residuals (RSS2) is minimized. Its expression is as follows:

[0078]

[0079] Where N is the total number of harmonics, is the magnitude of the equivalent input impedance, is the phase of the equivalent input impedance.

[0080] Beneficial effects of this invention:

[0081] The present invention is a method for determining the hemodynamic parameters of the local common carotid artery and its afterload system as a whole, based on the prior relationship between common carotid artery blood pressure and diameter, using a pressure sensor to measure the common carotid artery blood pressure waveform and ultrasonic Doppler technology to measure the common carotid artery mean blood flow velocity waveform. This method can monitor the hemodynamic indicators of the human common carotid artery online and in real time, including: arterial diameter, blood pressure, blood flow, wall shear stress, compliance, inertia, and peripheral resistance of the cerebral vascular bed. These hemodynamic parameters have certain clinical reference value for the early diagnosis and prevention of cardiovascular and cerebrovascular diseases. In addition, the hemodynamic detection method proposed in the present invention also provides key technical support for the development of wearable, portable, and miniaturized detection equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 This is the analysis flow chart in the patent of this invention;

[0083] Figure 2 This is a schematic diagram of the hemodynamic distribution-lumped parameter coupling model of the common carotid artery and afterload system;

[0084] Figure 3 It is a dynamic parameter diagram of the human common carotid artery under different physiological conditions based on the synchronous acquisition of a large clinical color Doppler ultrasound instrument and a non-invasive blood pressure probe. Among them, the discrete points in (a) are five groups of arterial inner radius r i (t) is the measured waveform. The discrete points in (b) are the measured data of the blood pressure waveform p(t) recorded synchronously. The discrete points in (c) are the corresponding blood pressure p and radius r. i Relationship curve. The inner radius waveform r is obtained by fitting the average value of the five blood pressure waveforms p (solid line in (b)). i (t) Fitting diagram (solid line in (a)), and corresponding blood pressure p and radius r i Relationship graph (solid line in (c));

[0085] Figure 4(a) is the average flow velocity waveform u measured by the continuous ultrasound Doppler probe m (t) graph;

[0086] Figure 4(b) is a diagram of the calculated flow waveform q(t);

[0087] Figure 4(c) is the wall shear stress waveform τ w (t) graph;

[0088] Figure 5 Graphs showing the input impedance of the common carotid artery and afterload (downstream vascular bed) system and its equivalent circuit fitting curves, where (a) is the amplitude-frequency graph and (b) is the phase-frequency graph. DETAILED DESCRIPTION

[0089] Refer to the attached Figure 1 , for the method of detecting hemodynamic parameters of the common carotid artery system based on the prior relationship between blood pressure and diameter, the specific implementation method is described:

[0090] Refer to the attached Figure 2 The patent of this invention establishes a distributed-lumped parameter coupling model to describe the hemodynamic parameters of the local and afterload systems of the common carotid artery. The model consists of a nonlinear pulsating blood flow model based on the "Ling-Atabek hypothesis" in a uniform elastic circular tube and a five-element lumped parameter model describing the common carotid artery and afterload (downstream cerebral vascular bed) system.

[0091] Refer to the attached Figure 3 , the large color Doppler ultrasound instrument and pressure sensor used in clinical practice were used to synchronously obtain the inner radius waveform and blood pressure waveform of the human common carotid artery in multiple cycles under different physiological conditions. The original inner radius waveform is shown in the attached figure. Figure 3 The discrete points in (a) of the blood pressure waveform refer to the attached Figure 3 The discrete points in (b), the corresponding blood pressure p and radius r i See attached for the relationship curve diagram Figure 3 Based on the principle of vascular mechanics, the blood pressure p and the diameter r are established. i The mathematical model of the quantitative relationship between blood pressure (p) and tube diameter (r) is used as a priori knowledge (Equations (1) to (5)). i ) waveform pairs to obtain the equation parameters A, B, and C values as shown in Table 1. The average value of the parameters of the five cycles is used as the prior knowledge, that is, A = 4.28 × 10 5 dyne / cm 2 , B=1.23×10 5 dyne / cm, C=1.95×10 4 dyne / cm 2 According to prior knowledge, the average blood pressure waveforms p of five groups (see Appendix Figure 3 The solid line in (b) is the fitted radius waveform r i , the inner radius waveform fitting value refers to the attached Figure 3 The solid line in (a) corresponds to the blood pressure p and radius r i Please refer to the attached diagram for the relationship curve fitting. Figure 3 The solid line in (c) .

[0092] Referring to FIG4(a), the present invention uses a continuous ultrasonic Doppler probe and applies a coupling agent to the transducer and the subject's neck to measure the average blood flow velocity waveform of the common carotid artery; referring to FIG4(b), the average blood flow velocity waveform can be calculated by equation (11) to obtain the common carotid artery blood flow waveform; referring to FIG4(c), the common carotid artery blood pressure waveform p(t) and the common carotid artery inner radius waveform r obtained by prior knowledge are combined to obtain the average blood flow velocity waveform. i (t)(Equation (4)) and the average blood flow velocity waveform u m (t), wall shear stress τ is calculated by nonlinear pulsating blood flow model w Waveform (Equations (5) to (19)).

[0093] Through the above implementation process, the local hemodynamic parameters of the common carotid artery can be obtained as shown in Table 2. Among them: r i_max 、r i_min 、r i_mean Represents the inner radius waveform r i The maximum, minimum and average values of (t); q max ,q min ,q mean Respectively represent the maximum, minimum and average values of the blood flow waveform q(t); τ w_max , τ w_min , τ w_mean are the wall shear stress τ w The maximum, minimum and average values of the waveform; the circumferential strain waveform ε can be calculated by equation (3), ε max , ε mean Respectively represent the maximum value and average value of the circumferential strain waveform.

[0094] Refer to the attached Figure 5 In the present invention, the non-invasive assessment of the hemodynamic parameters of the cerebral vascular bed downstream of the common carotid artery is carried out. First, the blood pressure and flow signals of the common carotid artery are Fourier transformed. According to the definition of the input impedance of the common carotid artery (Equations (20) and (21)), the amplitude-frequency characteristic curve of the five-element lumped parameter model is obtained through Equation (22). The amplitude-frequency characteristic curve is fitted with the actual input impedance model of the common carotid artery in vivo by the least squares method to minimize the residual sum of squares RSS2 (Equation (23)). The amplitude-frequency curve is shown in FIG. Figure 5 As shown in (a) in the figure; the phase-frequency curve is Figure 5 Through this implementation process, the overall hemodynamic parameters of the common carotid artery and afterload system can be obtained as shown in Table 3.

[0095] Table 1. Parameter values in equation (4) for fitting five groups of common carotid artery blood pressure-inner diameter waveforms in the present invention

[0096]

[0097] Table 2. Local hemodynamic parameters of the common carotid artery obtained by the present invention

[0098]

[0099] Table 3. Overall hemodynamic parameters of the common carotid artery and afterload system obtained by the present invention

[0100]

Claims

1. A method for detecting hemodynamic parameters of the common carotid artery system based on a priori relationship between blood pressure and vessel diameter, characterized in that: The specific method is: Step 1: Using a large color Doppler ultrasound instrument and pressure sensor used clinically, the inner diameter waveform and blood pressure waveform of the human common carotid artery under different physiological conditions are synchronously acquired. Based on the principles of vascular mechanics, a mathematical model describing the quantitative relationship between blood pressure and inner arterial radius is established as prior knowledge. Step 2: Using a pressure sensor to measure the blood pressure waveform of the common carotid artery, and then based on the prior knowledge of blood pressure-inner diameter, obtaining the corresponding blood vessel inner radius waveform; further, combining the common carotid artery mean blood flow velocity waveform measured by a continuous ultrasonic Doppler probe to calculate the common carotid artery blood flow waveform; Step 3. Establish a distributed-lumped parameter coupling model to describe the hemodynamic parameters of the local common carotid artery and the overall afterload system. The model consists of a nonlinear pulsating blood flow model based on the "Ling-Atabek hypothesis" in a uniform elastic circular tube and a five-element lumped parameter model describing the common carotid artery and the afterload system. Solve the governing equations of the distributed-lumped parameter coupling model to obtain the wall shear stress waveform and the element parameter values of the five-element lumped parameter model; the five elements include the compliance C1 of the common carotid artery segment, the resistance R1 of the common carotid artery segment, the total compliance C2 of the downstream cerebral vascular bed, the total inertia L of the downstream cerebral vascular bed, and the total flow resistance R2 of the downstream cerebral vascular bed.

2. The method for detecting hemodynamic parameters of the common carotid artery system based on a priori relationship between blood pressure and diameter according to claim 1, characterized in that: Step 1 is as follows: The color Doppler ultrasound instrument and pressure sensor used in clinical practice are used to synchronously obtain the inner radius waveform r of the human common carotid artery under different physiological conditions. i (t) and blood pressure waveform p(t), based on the principle of vascular mechanics, a method describing blood pressure p and tube radius r is established. i The mathematical model of the quantitative relationship between them is used as prior knowledge; the specific method is as follows: For a tube with a thickness of h and an inner radius of r i For an isotropic, incompressible, homogeneous common carotid artery wall, under the plane strain assumption, Hooke's law in polar coordinate form is: Where ε is the circumferential strain, σ θ and σ r represent circumferential stress and radial stress respectively, E is the elastic modulus, and μ is Poisson’s ratio; Assuming that the wall of the common carotid artery is thin, σ r =0, according to Laplace's law we have Substituting into equation (1) we can get: For the circumferential strain ε, we have Among them, r d Take the end-diastolic internal diameter value; Blood vessels exhibit viscoelastic behavior, so a viscoelastic term is added to the right side of equation (2): Where φ0 is the viscosity coefficient, is the strain rate; the following p and r can be obtained by synthesis i Relational equation: In the formula, A, B, and C are all constants. Based on the existing blood vessel radius waveform r i (t) and blood pressure waveform p(t), the values of the three constants A, B, and C can be obtained by least squares fitting to minimize the square residual and RSS1. The expressions are as follows: Where m is the total number of sampling points, is the fitting value of the inner radius of the common carotid artery calculated by equation (4), r i (p) is the measured value of the inner radius of the common carotid artery; after obtaining the values of parameters A, B, and C in equation (4), the mathematical model describing the blood pressure-radius relationship in equation (4) can be used as prior knowledge.

3. The method for detecting hemodynamic parameters of the common carotid artery system based on a priori relationship between blood pressure and vessel diameter according to claim 1, characterized in that: Step 2 is as follows: Based on the blood pressure waveform p(t) of the common carotid artery measured by the pressure sensor, the blood pressure-radius relationship mathematical model of equation (4) is used to calculate the common carotid artery inner radius waveform r i (t), the average blood flow velocity waveform u of the common carotid artery measured by continuous ultrasound Doppler technology m (t), calculate the common carotid artery blood flow waveform q(t) = u m πr i 2 .

4. The method for detecting hemodynamic parameters of the common carotid artery system based on a priori relationship between blood pressure and vessel diameter according to claim 1, characterized in that: In step 3, the nonlinear pulsating blood flow model is used to calculate the wall shear stress τ w The specific steps are as follows: The wall of the common carotid artery is set as an elastic straight circular tube, and the pulsating fluid in the common carotid artery is regarded as an incompressible Newtonian fluid. The governing equation of the pulsating fluid in the elastic straight circular tube is simplified as follows: Where t is time, u represents axial velocity, v represents radial velocity, η and ρ are blood viscosity and density, respectively, and x and r represent axial and radial coordinates, respectively; The boundary conditions are as follows: The relative radius y = r / r i Substituting into equation (6), the expression of the axial flow velocity u in the elastic straight circular tube is as follows: Integrating both sides of equation (6) along the cross section of the common carotid artery, taking into account the continuity equation and boundary conditions (7) to (9), the governing equation for the flow rate q(t) is obtained as: Where, Here, u m is the average value of the axial flow velocity u along the cross section of the artery; According to the Ling-Atabek hypothesis, the gradient of the axial flow velocity u satisfies the following equation: Where f(x,t) is a function of x and t. Substituting equation (13) into equation (7), the expression of radial velocity v is as follows: Boundary conditions (8) and (9) become: In formula (14), The expression is as follows: Therefore, the radial flow velocity v is expressed as follows according to equations (14)-(17): Once p(t),q(t) and The axial velocity u can be calculated by equations (10) to (12) (15) (16); the radial shear stress is negligible, and the wall shear stress τ w The expression is as follows:

5. The method for detecting hemodynamic parameters of the common carotid artery system based on a priori relationship between blood pressure and vessel diameter according to claim 1, characterized in that: The specific calculation method for the parameters of the five-element lumped parameter model describing the common carotid artery and afterload system in step 3 is as follows: Perform Fourier decomposition on the blood pressure waveform p(t) measured by the pressure sensor and the blood flow waveform q(t) calculated by equation (12) to obtain the angular frequency ω n =2πnf0 corresponding to the blood pressure and flow harmonic components P n (ω n ) and Q n (ω n ), n is the number of harmonics, f0 is the fundamental frequency, so the input impedance Z in (ω n )=P n (ω n ) / Q n (ω n ), whose amplitude |Z in (ω n )| and phase ∠Z in (ω n ) is expressed as: |Z in (oh n )|=|P n (oh n )| / |Q n (oh n )| (20) ∠Z in (oh n )=∠P n (oh n )-∠Q n (oh n ) (21) The amplitude-frequency and phase-frequency curves of the input impedance of the cerebral vascular bed downstream of the common carotid artery were obtained; the equivalent input impedance curve obtained according to the five-element lumped parameter model is: Where j is the imaginary unit; Equivalent input impedance The component parameters of expression (22) are obtained based on the least squares fitting method according to the actual input impedance curve of the common carotid artery, so that the square residual and RSS2 are minimized. Its expression is as follows: Where N is the total number of harmonics, is the magnitude of the equivalent input impedance, is the phase of the equivalent input impedance.

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