A method for estimating cardiac output based on a catheter pump

Abstract

The present invention provides a method for estimating cardiac output based on a catheter pump, comprising the following steps: collecting the pressure at the outlet end of the catheter pump to obtain the current heart rate; collecting the rotational speed and current of the catheter pump, obtaining the pressure difference according to the relationship between the pressure difference between the outlet end and the inlet end of the catheter pump and the current of the catheter pump, and calculating the pressure at the inlet end; obtaining the opening time and closing time of the aortic valve through the pressures at the outlet end and the inlet end; calculating the blood volume V1 ejected through the aortic valve itself and the blood volume V2 through the catheter pump in one cycle according to the opening time and closing time of the aortic valve, the pressure difference between the outlet end and the inlet end, the current heart rate, the biological characteristics of the aortic valve, and the impedance properties of the catheter pump itself; obtaining the blood volume V3 ejected through the operation of the catheter pump motor in one cycle through the rotational speed of the catheter pump and the conduction properties of the catheter pump itself; calculating the total blood volume V ejected in one cycle and the current cardiac output.

Description

Technical Field

[0001] The present invention relates to the technical field of medical devices, and particularly relates to a method for estimating cardiac output based on a catheter pump. Background Art

[0002] Currently, during the treatment of heart failure diseases with transcatheter ventricular assist devices, due to mechanical size reasons, it is impossible to add sensors to directly detect the value of cardiac output. However, as an important medical indicator for monitoring patients, the device needs to provide relevant information. Existing technologies generally use indirect methods or empirical data to obtain the cardiac output value.

[0003] The existing technologies have the following disadvantages: 1. The existing technologies use the data measured in an external test environment to estimate blood flow. Since there are differences between the external test environment and the human body environment, and there are also differences between individuals, the estimated values have deviations; 2. There are many factors that determine cardiac output, including various individual data and motor speed. Determining the cardiac output angle through flow and speed is single and the accuracy is insufficient.

[0004] Therefore, it is necessary to design a method for estimating cardiac output based on a catheter pump to solve the above problems. Summary of the Invention

[0005] The technical problem solved by the embodiments of the present invention mainly lies in considering the cardiac output from three aspects: the aortic valve itself, the flow through the catheter pump, and the work done by the rotation of the catheter pump, and calculating the cardiac output from multiple angles to make the calculation result of the cardiac output more accurate.

[0006] To solve the above technical problem, the embodiments of the present invention provide a method for estimating cardiac output based on a catheter pump. The method for estimating cardiac output based on a catheter pump includes the following steps:

[0007] Collect the pressure at the outlet end of the catheter pump and obtain the current heart rate;

[0008] Collect the rotation speed and current of the catheter pump, obtain the pressure difference according to the relationship between the pressure difference between the outlet end and the inlet end of the catheter pump and the current of the catheter pump; based on the pressure difference, determine the pressure at the inlet end;

[0009] Obtain the opening time and closing time of the aortic valve through the pressure at the outlet end and the pressure at the inlet end;

[0010] According to the opening time and closing time of the aortic valve, the pressure difference between the outlet end and the inlet end, and the biological characteristics of the aortic valve, obtain the blood volume V1 ejected through the aortic valve itself in one cycle;

[0011] Obtain the blood volume V2 passing through the catheter pump in one cycle according to the pressure difference between the outlet end and the inlet end, the current heart rate, and the impedance property of the catheter pump itself;

[0012] Obtain the blood volume V3 ejected by the operation of the catheter pump motor in one cycle through the rotational speed of the catheter pump and the conduction property of the catheter pump itself;

[0013] Calculate the total blood volume V ejected in one cycle through the blood volumes V1, V2, and V3, and calculate the current cardiac output based on the total blood volume V and the current heart rate.

[0014] Preferably, collect the pressure at the outlet end of the catheter pump and obtain the current heart rate, including the following steps:

[0015] Collect the pressure at the outlet end of the catheter pump at a fixed time interval Δt, and the collected outlet end pressure data is [P AO1 , P AO2 … P AOn ;

[0016] Obtain N outlet end pressure data of a set quantity, where N is an even number n = N, perform a discrete Fourier transform on the collected N outlet end pressure data, and obtain the converted frequencies [f1, f2… f n / 2 and the corresponding amplitudes [A1, A2… A n / 2 ;

[0017] According to the characteristic that energy is proportional to the square of the amplitude, calculate the respective energy ratios [E1, E2… E n / 2 corresponding to the frequencies [f1, f2… f n / 2 ;

[0018] Select the frequency with the highest energy ratio. If it is determined that the energy ratio of this frequency exceeds the set threshold, then use this frequency as the heart frequency, that is, the current heart rate HR. Otherwise, re-collect the pressure at the outlet end of the catheter pump until the energy ratio of the frequency with the highest energy ratio exceeds the set threshold.

[0019] Preferably, collect the rotational speed and current of the catheter pump, and obtain the pressure difference according to the relationship between the current of the catheter pump and the pressure difference between the outlet end and the inlet end of the catheter pump; based on the pressure difference, determine the pressure at the inlet end, including the following steps:

[0020] According to the catheter pump rotational speed, current, and pressure difference data between the outlet end and the inlet end of the catheter pump collected under experimental conditions, fit the pressure difference between the outlet end and the inlet end of the catheter pump at a set rotational speed with the current to obtain the relationship function between the pressure difference and the current;

[0021] Adjust the adjustment parameters according to the relationship function between the pressure difference and the current at different rotational speeds to obtain the corresponding relationship between the pressure difference and the current at different gear rotational speeds;

[0022] Collect the rotational speed and current of the catheter pump, calculate the pressure difference according to the corresponding relationship between the pressure difference and the current; calculate the inlet pressure according to the pressure difference and the pressure at the outlet end.

[0023] Preferably, the corresponding relationship between the pressure difference and the current is expressed as follows:

[0024]

[0025] Wherein, x represents the current; y represents the pressure difference, a and α are current range adjustment parameters, and b and β are pressure difference range adjustment parameters.

[0026] Preferably, the opening time and closing time of the aortic valve are obtained through the pressure difference, the pressure at the outlet end, and the pressure at the inlet end, including the following steps:

[0027] Obtain the outlet pressure data [P AO1 , P AO2 … P AOn collected at a fixed time interval Δt, calculate the inlet pressure data [P LV1 , P LV2 … P LVn , and respectively obtain the increments [ΔP AO1 , ΔP AO2 … ΔP AOn-1 and [ΔP LV1 , ΔP LV2 … ΔP LVn-1 ;

[0028] Determine the opening time Ts and closing time Te of the aortic valve through the numerical characteristics of the increments, that is, the positive and negative values of the increments and the magnitudes of the increments.

[0029] Preferably, the instantaneous blood flow rate through the aortic valve is calculated by the following formula:

[0030]

[0031] Wherein, I t1 is the instantaneous blood flow rate through the aortic valve at time t; R V is the biological characteristic value of the aortic valve, P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t;

[0032] The volume of blood ejected through the aortic valve itself in one cycle V1 is calculated by the following formula:

[0033]

[0034] Among them, V1 is the volume of blood ejected through the aortic valve itself in one cycle; I t1 is the instantaneous flow rate of blood through the aortic valve at time t; T s is the opening time of the aortic valve, and T e is the closing time of the aortic valve, and Δt is the sampling time interval of the outlet pressure.

[0035] Preferably, the instantaneous flow rate of blood through the catheter pump is calculated by the following formula:

[0036]

[0037] Among them, I t2 is the instantaneous flow rate of blood through the catheter pump at time t; R P is the impedance property of the catheter pump itself, and P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t;

[0038] The volume of blood V2 passing through the catheter pump in one cycle is calculated by the following formula:

[0039]

[0040] Among them, V2 is the volume of blood passing through the catheter pump in one cycle; I t2 is the instantaneous flow rate of blood through the catheter pump at time t; T represents one cycle; Δt is the sampling time interval of the outlet pressure;

[0041]

[0042] Among them, T represents one cycle; HR is the current heart rate.

[0043] Preferably, the volume of blood V3 ejected by the operation of the catheter pump motor in one cycle is obtained through the rotational speed of the catheter pump and the conduction property of the catheter pump itself, including the following steps:

[0044] According to the rotational speed and flow rate data of the catheter pump collected under experimental conditions, the flow rate and rotational speed are fitted to obtain the relationship function I(ω) between the flow rate and rotational speed of the catheter pump;

[0045] The volume of blood V3 ejected by the operation of the catheter pump motor in one cycle is calculated by the following formula:

[0046] V3 = I(ω) * T

[0047] Among them, V3 is the volume of blood ejected by the catheter pump motor during one cycle; I(ω) is the flow rate of the catheter pump; T represents one cycle;

[0048]

[0049] Among them, T represents one cycle; HR is the current heart rate.

[0050] Preferably, a second-order equation is used to fit the rotational speed and flow rate of the catheter pump. The relationship function between the flow rate and rotational speed of the catheter pump is expressed as follows:

[0051] I(ω) = γ1 * ω 2 + γ2 * ω + γ3

[0052] Among them, I(ω) is the flow rate of the catheter pump; ω is the rotational speed of the catheter pump; γ1, γ2, and Υ3 are all fitting coefficients.

[0053] Preferably, the total volume of blood V ejected within one cycle is calculated by the following formula:

[0054] V = V1 + V2 + V3

[0055] Among them, V is the total volume of blood ejected within one cycle; V1 is the volume of blood ejected through the aortic valve itself during one cycle; V2 is the volume of blood passing through the catheter pump during one cycle; V3 is the volume of blood ejected by the catheter pump motor during one cycle;

[0056] The current cardiac output is calculated by the following formula:

[0057] CO = V * HR

[0058] Among them, CO represents cardiac output; V is the total volume of blood ejected within one cycle; HR is the heart rate.

[0059] Compared with the prior art, the technical solution of the embodiment of the present invention has beneficial effects.

[0060] For example, in the cardiac output estimation method based on the catheter pump of the present invention, since there is always a pressure difference between the aorta and the ventricle, there must be a part of the blood flowing through the catheter pump due to the action of the pressure. Considering the blood flow through the catheter pump itself, compared with the cardiac output that only considers the heart itself and the rotational work of the catheter pump, the calculation result is more accurate; calculating the cardiac output through the pressures at both the outlet end and the inlet end, compared with estimating the cardiac output only by the pressure change at the outlet end, the cardiac output obtained through the pressure difference across the aortic valve is more in line with the blood pumping law of the heart itself; by calculating the volume of blood ejected in a single cycle and accumulating the blood volumes of all cycles within one minute according to the current heart rate to obtain the current cardiac output, the calculation result is more accurate than directly estimating the cardiac output.

[0061] For another example, the pressure difference between the outlet end and the inlet end and the current collected under experimental conditions are fitted with a hyperbolic function to obtain the relationship between the pressure difference and the current. The inlet end pressure is calculated through the actual outlet end pressure and the catheter pump current, and the calculation result is more accurate.

[0062] For another example, the rotational speed and flow rate of the catheter pump collected under experimental conditions are fitted with a second-order function to obtain the relationship between the flow rate and the rotational speed of the catheter pump; the blood volume ejected by the catheter pump motor during one cycle is calculated through the actual rotational speed of the catheter pump and the pumping flow rate of the catheter pump motor, and the calculation result is more accurate. Description of the Drawings

[0063] Figure 1 is a flowchart of the cardiac output estimation method based on a catheter pump in an embodiment of the present invention;

[0064] Figure 2 is a schematic diagram of the relationship between the pressure difference and the current between the outlet end and the inlet end of the catheter pump at a set rotational speed under experimental conditions;

[0065] Figure 3 is a graph of the fitted relationship between the pressure difference and the current in an embodiment of the present invention;

[0066] Figure 4 is a graph of the relationship between the pressure difference and the current obtained by adjusting the adjustment parameter a for the fitted relationship between the pressure difference and the current in an embodiment of the present invention;

[0067] Figure 5 is a graph of the relationship between the pressure difference and the current obtained by adjusting the adjustment parameter α for the fitted relationship between the pressure difference and the current in an embodiment of the present invention;

[0068] Figure 6 is a graph of the relationship between the pressure difference and the current obtained by adjusting the adjustment parameter b for the fitted relationship between the pressure difference and the current in an embodiment of the present invention;

[0069] Figure 7 is a graph of the relationship between the pressure difference and the current obtained by adjusting the adjustment parameter β for the fitted relationship between the pressure difference and the current in an embodiment of the present invention;

[0070] Figure 8 is a graph of the changing trends of the aortic pressure and the left ventricular pressure during cardiac pulsation. Detailed Embodiments

[0071] To make the objectives, features, and beneficial effects of the present invention more obvious and understandable, the following provides a detailed description of the specific embodiments of the present invention with reference to the accompanying drawings. It can be understood that the following described specific embodiments are only for explaining the present invention and are not intended to limit the present invention. Also, in the figures, the same or similar reference numerals may be used to refer to the same or similar elements in different embodiments, and the descriptions of the same or similar elements in different embodiments as well as the descriptions of the elements, features, effects, etc. of the prior art may be omitted.

[0072] Cardiac output generally refers to the volume of blood pumped by the heart per minute, with the unit of L / min; a cycle refers to the time for one heartbeat, and the heart rate refers to the number of heartbeats per minute. How long a cycle is depends on the heart rate. For example, if the heart rate is 80, then a cycle is 0.75 seconds. If the heart rate is 60, then a cycle is 1 second. The volume of blood output in one cycle is generally referred to as the stroke volume.

[0073] Refer to Figures 1 - 8 , an embodiment of the present invention provides a method for estimating cardiac output based on a catheter pump.

[0074] Taking the left ventricular catheter pump as an example, the inlet end of the catheter pump is arranged in the left ventricle, and the outlet end is arranged at the ascending aorta. When the catheter pump works, the blood in the left ventricle is pumped through the catheter pump to the ascending aorta and then transported throughout the body via the aorta; the pressure at the outlet end of the catheter pump is the pressure of the aorta, and the pressure at the inlet end of the catheter pump is the pressure of the left ventricle.

[0075] Specifically, the method for estimating cardiac output based on a catheter pump includes the following steps:

[0076] S1: Collect the pressure at the outlet end of the catheter pump and obtain the current heart rate; specifically including:

[0077] Collect the pressure at the outlet end of the catheter pump at a fixed time interval Δt, and the collected outlet end pressure data is [P AO1 ,P AO2 …P AOn ;

[0078] Obtain N outlet end pressure data of a set quantity, where N is an even number and n = N. Perform a discrete Fourier transform on the collected N outlet end pressure data to obtain the converted frequencies [f1, f2…f n / 2 and the corresponding amplitudes [A1, A2…A n / 2 ;

[0079] The value of N is based on the sampling frequency of the data (the pressure at the outlet end of the catheter pump) and the update speed of the calculation result of the current heart rate; when the update speed of the calculation result of the current heart rate is constant, the higher the sampling frequency, the corresponding increase in the value of N; if the sampling frequency is determined, when the value of N is larger, the converted frequency interval will be more detailed, and the update speed of the calculation result of the current heart rate will be slower; when the sampling rate is selected as 25Hz and N is taken as 600, the calculation result of the current heart rate is updated every 24s, which meets the actual application requirements, and taking N as an even number is convenient for performing Fourier transform.

[0080] Due to the fluctuating nature of the collected pressure data with the accumulation of time, the discrete Fourier transform is used to transform the signal in the time domain (i.e., the time domain) into a signal in the frequency domain (i.e., the frequency domain), thereby obtaining the beating frequency of the heart.

[0081] According to the characteristic that the energy is proportional to the square of the amplitude, calculate the respective energy ratios [E1, E2... E n / 2 corresponding to the frequencies [f1, f2... f n / 2 ;

[0082] Select the frequency with the highest energy ratio. If it is determined that the energy ratio of this frequency exceeds the set threshold, then take this frequency as the heart frequency, that is, the current heart rate HR; otherwise, re-collect the pressure at the outlet end of the catheter pump until the energy ratio of the frequency with the highest energy ratio exceeds the set threshold.

[0083] The setting of the threshold is to determine whether a set of data fluctuates at a certain frequency. For example, the threshold is set to 70%. If the energy ratio of a certain frequency exceeds this set threshold, it is considered that this set of data fluctuates at this frequency; in actual applications, there may be some high-frequency clutter in the collected data, and generally setting the threshold between 60% - 70% can meet the actual application requirements.

[0084] S2: Collect the rotation speed and current of the catheter pump, and obtain the pressure difference according to the relationship between the pressure difference between the outlet end and the inlet end of the catheter pump and the current of the catheter pump; based on the pressure difference, determine the pressure at the inlet end; specifically including:

[0085] According to the data of the rotation speed, current of the catheter pump and the pressure difference between the outlet end and the inlet end of the catheter pump collected under experimental conditions, fit the pressure difference between the outlet end and the inlet end of the catheter pump and the current at the set rotation speed to obtain the relationship function between the pressure difference and the current;

[0086] See Figure 2, the horizontal axis represents current in mA, and the vertical axis represents pressure difference in mmHg. The relationship between current and pressure difference at different rotational speeds is represented by curves of different colors. At the same rotational speed, the corresponding relationship between current and pressure difference generally conforms to the inverse hyperbolic tangent function (arctanh). The corresponding relationship between pressure difference and current is expressed as follows:

[0087]

[0088] Where x represents current; y represents pressure difference, a and α are current range adjustment parameters, and b and β are pressure difference range adjustment parameters.

[0089] Using hyperbolic function fitting can better satisfy the relationship between pressure difference and current, and the fitting at the turning point is more natural with hyperbolic functions.

[0090] According to the relationship function between pressure difference and current at different rotational speeds, adjust the adjustment parameters to obtain the corresponding relationship between pressure difference and current at different gear rotational speeds;

[0091] When the adjustment parameters are a = 0, b = 0, α = 1, and β = 1, the corresponding relationship between pressure difference and current is as Figure 3 shown;

[0092] Adjust the parameter a, a takes -800, see Figure 4 , corresponding to the x-axis coordinate, it can be seen that the function shifts 800 to the right;

[0093] Then adjust the parameter α, α takes 0.01, see Figure 5 , corresponding to the x-axis coordinate, it can be seen that the coordinate range expands 100 times;

[0094] Then adjust the parameter b, b takes 100, see Figure 6 , corresponding to the y-axis coordinate, it can be seen that the function shifts 100 upward;

[0095] Then adjust the parameter β, β takes 30, see Figure 7 , corresponding to the y-axis coordinate, it can be seen that the coordinate range expands 30 times.

[0096] Collect the rotational speed and current of the catheter pump, calculate the pressure difference according to the corresponding relationship between pressure difference and current; calculate the inlet pressure according to the pressure difference and the pressure at the outlet end.

[0097] S3: Obtain the opening time and closing time of the aortic valve through the pressure at the outlet end and the pressure at the inlet end; specifically including:

[0098] Obtain the outlet pressure data [P AO1 ,P AO2 …P AOn collected at a fixed time interval Δt, and calculate the inlet pressure data [PLV1 , P LV2 …P LVn , respectively obtain the increments [ΔP AO1 , ΔP AO2 …ΔP AOn-1 and [ΔP LV1 , ΔP LV2 …ΔP LVn-1 ;

[0099] Determine the opening time Ts and closing time Te of the aortic valve based on the numerical characteristics of the increments, i.e., the positive and negative values of the increments and the magnitude of the increments.

[0100] In practical applications, the data is discrete, and the density of the data is directly related to the time interval Δt; the derivative is the rate of change near a certain point when the time interval Δt approaches 0, which is generally called the differential. In applications, the time interval Δt cannot truly approach 0, but a period of time, such as Δt = 0.01 s, can be used to approximately represent the change of a certain time value, which is generally called the increment; the smaller Δt is, the smaller the error compared with the differential, and vice versa; therefore, the data of the increment can be used to approximately represent the differential, and it is determined that the opening time Ts is the moment when the increment value of the left ventricle is just less than 0, and the closing time Te is the moment when the increment value of the left ventricle is just greater than 0 after being less than 0.

[0101] See Figure 8 , the horizontal axis represents time with the unit of s, the vertical axis represents pressure with the unit of mmHg, where the red line represents the aortic pressure (AoP), and the blue line represents the left ventricular pressure (LvP); in the first cycle in the figure, the opening time Ts is at 0.08 s, and the closing time Te is at 0.24 s.

[0102] S4: According to the opening time and closing time of the aortic valve, the pressure difference between the outlet end and the inlet end, and the biological characteristics of the aortic valve, obtain the blood volume V1 ejected through the aortic valve itself in one cycle;

[0103] The instantaneous flow rate of the blood through the aortic valve is calculated by the following formula:

[0104]

[0105] where, I t1 is the instantaneous flow rate of the blood through the aortic valve at time t; R V is the biological characteristic value of the aortic valve, P LV (t) is the inlet end pressure at time t; P AO (t) is the outlet end pressure at time t;

[0106] The blood volume V1 ejected through the aortic valve itself in one cycle is calculated by the following formula:

[0107]

[0108] Among them, V1 is the volume of blood ejected through the aortic valve itself in one cycle; I t1 is the instantaneous flow rate of blood in the aortic valve at time t; T s is the opening time of the aortic valve, T e is the closing time of the aortic valve, and Δt is the sampling time interval of the outlet pressure.

[0109] Calculating the cardiac output of the aortic valve ejection of the heart itself through the pressure difference between the outlet and the inlet ends, compared with estimating the cardiac output only by the change of the outlet pressure, the obtained cardiac output is more in line with the blood pumping law of the heart itself.

[0110] S5: Obtain the volume of blood V2 passing through the catheter pump in one cycle according to the pressure difference between the outlet and the inlet ends, the current heart rate, and the impedance property of the catheter pump itself; since there is always a pressure difference between the aorta and the ventricle, there must be a part of the blood flowing through the catheter pump due to the action of the pressure. Considering the blood flow rate passing through the catheter pump itself, compared with only considering the cardiac output of the heart itself and the rotational work of the catheter pump, the calculation result is more accurate;

[0111] The instantaneous flow rate of the blood passing through the catheter pump is calculated by the following formula:

[0112]

[0113] Among them, I t2 is the instantaneous flow rate of the blood passing through the catheter pump at time t; R P is the impedance property of the catheter pump itself, P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t;

[0114] The volume of blood V2 passing through the catheter pump in one cycle is calculated by the following formula:

[0115]

[0116] Among them, V2 is the volume of blood passing through the catheter pump in one cycle; I t2 is the instantaneous flow rate of the blood in the catheter pump at time t; T represents one cycle; Δt is the sampling time interval of the outlet pressure;

[0117]

[0118] Among them, T represents one cycle; HR is the current heart rate.

[0119] Calculating the cardiac output flowing through the catheter pump based on the pressure difference between the outlet end and the inlet end. Compared with estimating the cardiac output only by the pressure change at the outlet end, the obtained cardiac output is more in line with the blood pumping law of the heart itself.

[0120] S6: Obtain the blood volume V3 ejected by the catheter pump motor during one cycle through the rotation speed of the catheter pump and the conduction property of the catheter pump itself. Specifically, it includes:

[0121] According to the rotation speed and flow rate data of the catheter pump collected under experimental conditions, fit the flow rate and rotation speed to obtain the relationship function I(ω) between the flow rate and rotation speed of the catheter pump. A second-order equation is used to fit the rotation speed and flow rate of the catheter pump. The relationship function between the flow rate and rotation speed of the catheter pump is expressed as follows:

[0122] I(ω) = γ1 * ω 2 +γ2 * ω + γ3

[0123] where, I(ω) is the flow rate of the catheter pump; ω is the rotation speed of the catheter pump; γ1, γ2, and γ3 are all fitting coefficients.

[0124] Theoretically, the flow rate is proportional to the rotation speed. However, considering the certain viscosity of the blood, using a second-order function to fit the relationship between the flow rate and rotation speed is more in line with practical applications.

[0125] The blood volume V3 ejected by the catheter pump motor during one cycle is calculated by the following formula:

[0126] V3 = I(ω) * T

[0127] where, V3 is the blood volume ejected by the catheter pump motor during one cycle; I(ω) is the flow rate of the catheter pump; T represents one cycle;

[0128]

[0129] where, T represents one cycle; HR is the current heart rate.

[0130] S7: Calculate the total blood volume V ejected during one cycle through the blood volumes V1, V2, and V3. Based on the total blood volume V and the current heart rate, calculate the current cardiac output.

[0131] The total blood volume V ejected during one cycle is calculated by the following formula:

[0132] V = V1 + V2 + V3

[0133] Wherein, V is the total volume of blood ejected in one cycle; V1 is the volume of blood ejected through the aortic valve itself in one cycle; V2 is the volume of blood passing through the catheter pump in one cycle; V3 is the volume of blood ejected through the operation of the catheter pump motor in one cycle;

[0134] The current cardiac output is calculated by the following formula:

[0135] CO = V * HR

[0136] Wherein, CO represents the cardiac output; V is the total volume of blood ejected in one cycle; HR is the heart rate.

[0137] In summary, the cardiac output estimation method of the present invention based on a catheter pump considers the blood flow through the catheter pump itself. Since there is always a pressure difference between the aorta and the ventricle, a certain amount of blood must flow through the catheter pump due to the action of pressure. Compared with the cardiac output that only considers the heart itself and the work done by the rotation of the catheter pump, the calculation result is more accurate; by calculating the cardiac output of the heart itself and the blood passing through the catheter pump through the pressures at the outlet end and the inlet end, compared with estimating the cardiac output only by the pressure change at the outlet end, the cardiac output obtained through the pressure difference across the aortic valve conforms more to the blood pumping law of the heart itself; by calculating the volume of blood ejected in a single cycle and accumulating the blood volumes of all cycles within one minute according to the current heart rate to obtain the current cardiac output, the calculation result is more accurate than directly estimating the cardiac output.

[0138] Furthermore, the present invention fits the pressure difference and current collected under experimental conditions using a hyperbolic function to obtain the relationship between the pressure difference and the current, and calculates the inlet end pressure through the actual outlet end pressure and the catheter pump current, and the calculation result is more accurate.

[0139] Furthermore, the present invention fits the rotational speed and flow rate of the catheter pump collected under experimental conditions using a second-order function to obtain the relationship between the flow rate and the rotational speed of the catheter pump; calculates the volume of blood ejected through the operation of the catheter pump motor in one cycle through the actual rotational speed of the catheter pump and the pumping flow rate of the catheter pump motor, and the calculation result is more accurate.

[0140] Although the specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even when describing a single embodiment with respect to specific features. The feature examples provided in the present disclosure are intended for illustration rather than limitation, unless otherwise stated. In specific implementations, according to actual needs and where technically feasible, the technical features of one or more dependent claims can be combined with the technical features of the independent claim, and can be combined in any appropriate manner rather than only through the specific combinations listed in the claims from the technical features of the corresponding independent claim.

[0141] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for estimating cardiac output based on a catheter pump, characterized in that: The steps include: Collect the pressure at the outlet of the catheter pump to obtain the current heart rate; The rotation speed and current of the catheter pump are collected, and the pressure difference is obtained according to the relationship between the pressure difference between the outlet and inlet ends of the catheter pump and the current of the catheter pump; based on the pressure difference, the pressure at the inlet end is determined; The opening and closing time of the aortic valve are obtained through the pressure at the outlet and the pressure at the inlet; According to the opening and closing time of the aortic valve, the pressure difference between the outlet and the inlet, and the biological characteristics of the aortic valve, the blood volume V1 ejected through the aortic valve itself in one cycle is obtained; According to the pressure difference between the outlet and the inlet, the current heart rate and the impedance property of the catheter pump itself, the blood volume V2 passing through the catheter pump in one cycle is obtained; The blood volume V3 ejected by the catheter pump motor in one cycle is obtained through the catheter pump rotation speed and the conduction properties of the catheter pump itself; The total blood volume V ejected in one cycle is calculated by using the blood volumes V1, V2 and V3, and the current cardiac output is calculated based on the total blood volume V and the current heart rate; The total volume of blood ejected in one cycle, V, is calculated by the following formula: V=V1+V2+V3 Wherein, V is the total volume of blood ejected in one cycle; V1 is the volume of blood ejected through the aortic valve itself in one cycle; V2 is the volume of blood ejected through the catheter pump in one cycle; V3 is the volume of blood ejected through the catheter pump motor in one cycle; The current cardiac output is calculated using the following formula: CO=V*HR Among them, CO represents cardiac output; V is the total volume of blood ejected in one cycle; HR is the heart rate.

2. The cardiac output estimation method according to claim 1, characterized in that: Collecting the pressure at the outlet of the catheter pump to obtain the current heart rate includes the following steps: The pressure at the outlet of the catheter pump is collected at a fixed time interval Δt. The collected outlet pressure data is [P AO1 ,P AO2 …P AOn ]; Obtain a set number of N outlet pressure data, where N is an even number, n = N, perform discrete Fourier transform on the collected N outlet pressure data, and obtain the converted frequency [f1, f2…f n / 2 ] and the corresponding amplitude [A1, A2…A n / 2 ]; According to the characteristic that energy is proportional to the square of amplitude, the frequency corresponding to [f1,f2…f n / 2 ]’s respective energy proportions [E1,E2…E n / 2 ]; The frequency with the highest energy proportion is selected, and if it is determined that the energy proportion of the frequency exceeds the set threshold, the frequency is used as the heart frequency, that is, the current heart rate HR. Otherwise, the pressure at the outlet of the catheter pump is re-collected until the energy proportion of the frequency with the highest energy proportion exceeds the set threshold.

3. The cardiac output estimation method according to claim 1, characterized in that: The speed and current of the catheter pump are collected, and the pressure difference is obtained according to the relationship between the current of the catheter pump and the pressure difference between the outlet and inlet ends of the catheter pump; based on the pressure difference, the pressure at the inlet end is determined, including the following steps: According to the data of the speed and current of the catheter pump and the pressure difference between the outlet and inlet of the catheter pump collected under the experimental conditions, the pressure difference and current between the outlet and inlet of the catheter pump at the set speed are fitted to obtain the relationship function between the pressure difference and the current; According to the relationship function between the pressure difference and the current at different speeds, the adjustment parameters are adjusted to obtain the corresponding relationship between the pressure difference and the current at different gear speeds; The rotation speed and current of the catheter pump are collected, and the pressure difference is calculated based on the corresponding relationship between the pressure difference and the current; the pressure at the inlet end is calculated based on the pressure difference and the pressure at the outlet end.

4. The cardiac output estimation method according to claim 3, characterized in that: The corresponding relationship between pressure difference and current is expressed as follows: Wherein, x represents the current; y represents the pressure difference, a and α are the current range adjustment parameters, and b and β are the pressure difference range adjustment parameters.

5. The cardiac output estimation method according to claim 1, characterized in that: The opening time and closing time of the aortic valve are obtained by the pressure difference, the pressure at the outlet, and the pressure at the inlet, including the following steps: Get the outlet pressure data collected at a fixed time interval Δt [P AO1 ,P AO2 …P AOn ], calculate the inlet pressure data [P LV1 ,P LV2 …P LVn ], respectively calculate the increment [ΔP AO1 ,ΔP AO2 …ΔP AOn-1 ] and [ΔP LV1 ,ΔP LV2 …ΔP LVn-1 ]; The opening time Ts and closing time Te of the aortic valve are determined by the numerical characteristics of the increment, namely the positive and negative value of the increment and the size of the increment.

6. The cardiac output estimation method according to claim 1, characterized in that: The instantaneous flow of blood through the aortic valve is calculated by the following formula: Among them, I t1 is the instantaneous flow of blood through the aortic valve at time t; R V is the biological characteristic value of the aortic valve, P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t; The blood volume V1 ejected through the aortic valve itself in one cycle is calculated by the following formula: Wherein, V1 is the volume of blood ejected through the aortic valve itself in one cycle; I t1 is the instantaneous blood flow of the aortic valve at time t; T s is the opening time of the aortic valve, T e is the closing time of the aortic valve, and Δt is the time interval for sampling the outlet pressure.

7. The cardiac output estimation method according to claim 1, characterized in that: The instantaneous flow rate of blood through the catheter pump is calculated by the following formula: Among them, I t2 is the instantaneous flow rate of blood through the catheter pump at time t; R P is the impedance property of the catheter pump itself, P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t; The blood volume V2 pumped through the catheter in one cycle is calculated by the following formula: Wherein, V2 is the blood volume pumped through the catheter in one cycle; I t2 is the instantaneous flow rate of blood in the catheter pump at time t; T represents a cycle; Δt is the time interval for sampling the outlet pressure; Wherein, T represents a cycle; HR is the current heart rate.

8. The cardiac output estimation method according to claim 1, characterized in that: The blood volume V3 ejected by the catheter pump motor in one cycle is obtained by the catheter pump speed and the conductive properties of the catheter pump itself, including the following steps: According to the speed and flow data of the catheter pump collected under experimental conditions, the flow and speed are fitted to obtain the relationship function I(ω) between the flow and speed of the catheter pump; The blood volume V3 ejected by the catheter pump motor in one cycle is calculated by the following formula: V3=I(ω)*T Wherein, V3 is the blood volume ejected by the catheter pump motor in one cycle; I(ω) is the flow rate of the catheter pump; T represents one cycle; Wherein, T represents a cycle; HR is the current heart rate.

9. The cardiac output estimation method according to claim 8, characterized in that: The second-order equation is used to fit the speed and flow of the catheter pump. The relationship function between the flow and speed of the catheter pump is expressed as follows: I(ω)=Y1*ω 2 +Y2*ω+Y3 Wherein, I(ω) is the flow rate of the catheter pump; ω is the rotation speed of the catheter pump; Υ1, Υ2 and Υ3 are all fitting coefficients.

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