Cardiac output estimation method based on catheter pump

Abstract

The invention provides a cardiac output estimation method based on a catheter pump, and the method comprises the following steps: collecting the pressure of the outlet end of the catheter pump, and obtaining the current heart rate; the rotating speed and current of the conduit pump are collected, the pressure difference is obtained according to the relation between the pressure difference between the outlet end and the inlet end of the conduit pump and the current of the conduit pump, and the pressure of the inlet end is calculated; the opening time and the closing time of the aortic valve are obtained through the pressure of the outlet end and the pressure of the inlet end; 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 property of the catheter pump, the volume V1 of blood sprayed through the aortic valve and the volume V2 of blood sprayed through the catheter pump in one cycle are calculated; through the rotating speed of the catheter pump and the conduction property of the catheter pump, the volume V3 of blood jetted through work of a catheter pump motor in one period is obtained; and calculating the total volume V of the sprayed blood in one cycle and the current cardiac output.

Description

Technical Field

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

[0002] At present, in the process of treating heart failure with transcatheter ventricular pump assist devices, due to mechanical size, there is no way to add sensors to directly detect the value of cardiac output, but cardiac output is an important medical indicator for monitoring patients, and the device needs to provide relevant information. The existing technology generally uses indirect methods or empirical data to obtain cardiac output values.

[0003] The existing technology has the following shortcomings: 1. The existing technology uses data measured in an external test environment to estimate blood flow. Due to the gap between the external test environment and the human body environment, and also the gap between each individual, the estimated value is biased; 2. There are many factors that determine cardiac output, including various individual data and motor speed. The angle of cardiac output determined by flow and speed is single and lacks accuracy.

[0004] Therefore, it is necessary to design a catheter-pump-based cardiac output estimation method to solve the above problems. Summary of the invention

[0005] The technical problem solved by the embodiment of the present invention is mainly to consider the cardiac output of the aortic valve itself, the flow through the catheter pump and the work done by the catheter pump, and calculate the cardiac output from multiple angles to make the calculation result of the cardiac output more accurate.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method for estimating cardiac output based on a catheter pump. The method for estimating cardiac output based on a catheter pump comprises the following steps:

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

[0008] 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;

[0009] The opening and closing time of the aortic valve are obtained through the pressure at the outlet and the pressure at the inlet;

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

[0011] 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;

[0012] 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;

[0013] The total volume V of blood ejected in one cycle is calculated by the blood volumes V1, V2 and V3. The current cardiac output is calculated based on the total blood volume V and the current heart rate.

[0014] Preferably, collecting the pressure at the outlet of the catheter pump to obtain the current heart rate includes the following steps:

[0015] 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 ];

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

[0017] 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 ];

[0018] 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.

[0019] Preferably, collecting the rotation speed and current of the catheter pump, obtaining the pressure difference 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; and determining the pressure at the inlet end based on the pressure difference, comprises the following steps:

[0020] 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;

[0021] 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;

[0022] 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.

[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 the current range adjustment parameters, and b and β are the pressure difference range adjustment parameters.

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

[0027] 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 ];

[0028] 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.

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

[0030]

[0031] 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;

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

[0033]

[0034] Wherein, V1 is the volume of blood ejected through the aortic valve itself in one cycle; I t1 is the instantaneous flow of blood through 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.

[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, P LV (t) is the inlet pressure at time t; P AO (t) is the outlet pressure at time t;

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

[0039]

[0040] 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;

[0041]

[0042] Wherein, T represents a cycle; HR is the current heart rate.

[0043] Preferably, 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, comprising the following steps:

[0044] 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;

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

[0046] V3=I(ω)*T

[0047] 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;

[0048]

[0049] Wherein, T represents a cycle; HR is the current heart rate.

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

[0051] I(ω)=γ1*ω 2 +γ2*ω+γ3

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

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

[0054] V=V1+V2+V3

[0055] 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;

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

[0057] CO=V*HR

[0058] Among them, CO represents cardiac output; V is the total volume of blood ejected in 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, the present invention is based on the cardiac output estimation method of the catheter pump. Since there is always a pressure difference between the aorta and the ventricle, some blood must flow through the catheter pump due to the effect of pressure. Considering the blood flow passing through the catheter pump itself, compared with the cardiac output that only considers the heart itself and the rotation work of the catheter pump, the calculation result is more accurate; the cardiac output is calculated by the pressure at both ends of the outlet and the inlet. Compared with estimating the cardiac output only by the change in the outlet pressure, the cardiac output obtained by the pressure difference at both ends of the aortic valve is more in line with the pumping law of the heart itself; the current cardiac output is obtained by calculating the blood volume ejected in a single cycle and accumulating the blood volume of all cycles within one minute according to the current heart rate. Compared with the calculation result obtained by directly estimating the cardiac output, the cardiac output is more accurate.

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

[0062] For another example, the catheter pump speed and flow collected under experimental conditions are fitted with a second-order function to obtain the relationship between the flow and speed of the catheter pump; the actual catheter pump speed and catheter pump motor pumping flow are used to calculate the blood volume ejected by the catheter pump motor in one cycle, and the calculation result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is a flow chart of a method for estimating cardiac output based on a catheter pump in an embodiment of the present invention;

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

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

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

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

[0068] Figure 6 is a pressure difference and current relationship diagram of adjusting the adjustment parameter b by fitting the pressure difference and current relationship in the embodiment of the present invention;

[0069] Figure 7 is a pressure difference and current relationship diagram of the pressure difference and current relationship adjustment parameter β fitted in the embodiment of the present invention;

[0070] Figure 8 It is a graph showing the changing trend of aortic pressure and left ventricular pressure when the heart beats. DETAILED DESCRIPTION

[0071] In order to make the purpose, features and beneficial effects of the present invention more obvious and understandable, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It is understood that the specific embodiments described below are only used to explain the present invention, rather than to limit the present invention. In addition, the same or similar reference numerals may be used in the figures to refer to the same or similar elements in different embodiments, and the description of the same or similar elements in different embodiments and the description of the prior art elements, features, effects, etc. may be omitted.

[0072] Cardiac output generally refers to the amount of blood output per minute of heart beats, with the unit of L / min. One cycle refers to the time it takes for the heart to beat once, and the heart rate refers to the number of heart beats per minute. The length of one cycle depends on the heart rate. For example, if the heart rate is 80, then one cycle is 0.75 seconds. If the heart rate is 60, then one cycle is 1 second. The amount of blood output in one cycle is generally called the stroke volume.

[0073] Reference Figure 1-Figure 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 set in the left ventricle, and the outlet end is set in the ascending aorta. When the catheter pump is working, the blood in the left ventricle is pumped to the ascending aorta through the catheter pump and transported to the whole body through 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 cardiac output estimation method based on the catheter pump comprises the following steps:

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

[0077] 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 ];

[0078] 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 ];

[0079] The value of N is based on the sampling frequency of the data (pressure at the outlet 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 higher the value of N; if the sampling frequency is determined, the larger the value of N, the finer the frequency interval after conversion, and the slower the update speed of the calculation result of the current heart rate; when the sampling rate is selected to be 25Hz and N is 600, the calculation result of the current heart rate is updated every 24s, which meets the actual application requirements, and N is an even number to facilitate Fourier transform.

[0080] Since the collected pressure data has a fluctuating nature as it accumulates over time, discrete Fourier transform is used to transform the signal in the time domain (ie, time domain) into a signal in the frequency domain (ie, frequency domain), thereby obtaining the heart's beating frequency.

[0081] 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 ];

[0082] 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.

[0083] The threshold is set to determine whether a set of data fluctuates at a certain frequency. For example, if the threshold is set to 70%, if the energy proportion of a certain frequency exceeds this preset value, it is considered that the data fluctuates at this frequency. In actual applications, the collected data may contain some high-frequency clutter. Generally, setting the threshold at 60%-70% can meet actual application needs.

[0084] S2: collecting the rotation speed and current of the catheter pump, obtaining the pressure difference 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; determining the pressure at the inlet end based on the pressure difference; specifically including:

[0085] 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;

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

[0087]

[0088] 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.

[0089] The use of hyperbolic function fitting can better meet the relationship between pressure difference and current, and the hyperbolic function fitting at the corners is more natural.

[0090] 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;

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

[0092] Adjust parameter a, a is -800, see Figure 4 , corresponding to the x-axis coordinate, we can see that the function is shifted 800 to the right;

[0093] Then adjust the parameter α, α is 0.01, see Figure 5 , corresponding to the x-axis coordinate, you can see that the coordinate range has expanded 100 times;

[0094] Then adjust the parameter b, b is 100, see Figure 6 , corresponding to the y-axis coordinate, we can see that the function is shifted upward by 100;

[0095] Then adjust the parameter β, β is 30, see Figure 7 , corresponding to the y-axis coordinate, you can see that the coordinate range has expanded 30 times.

[0096] 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.

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

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

[0099] 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.

[0100] In practical applications, data is discrete, and the density of 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 differential. In applications, the time interval Δt cannot really approach 0, but a period of time, such as Δt = 0.01s, can be used to approximate the change of a certain time value, which is generally called increment; the smaller Δt is, the smaller the error compared with the differential, and vice versa; therefore, the incremental data can be used to approximate the differential, and the opening time Ts is determined to be the moment when the left ventricular increment value is just less than 0, and the closing time Te is the moment when the left ventricular increment value is less than 0 and just greater than 0.

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

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

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

[0104]

[0105] 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;

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

[0107]

[0108] Wherein, V1 is the volume of blood ejected through the aortic valve itself in one cycle; I t1 is the instantaneous flow of blood through 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.

[0109] The cardiac output ejected by the heart's aortic valve is calculated by the pressure difference between the outlet and inlet ends. Compared with estimating the cardiac output using only the outlet pressure change, the obtained cardiac output is more consistent with the heart's own pumping law.

[0110] S5: According to the pressure difference between the outlet and 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; since there is always a pressure difference between the aorta and the ventricle, some blood must flow through the catheter pump due to the pressure. Considering the blood flow through the catheter pump itself, the calculation result is more accurate than only considering the cardiac output of the heart itself and the work done by the catheter pump.

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

[0112]

[0113] 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;

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

[0115]

[0116] 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;

[0117]

[0118] Wherein, T represents a cycle; HR is the current heart rate.

[0119] The cardiac output of the blood flowing through the catheter pump is calculated by the pressure difference between the outlet and inlet ends. Compared with estimating the cardiac output only by the change in outlet pressure, the obtained cardiac output is more consistent with the pumping law of the heart itself.

[0120] S6: Obtaining the blood volume V3 ejected by the catheter pump motor in one cycle through the catheter pump rotation speed and the conduction properties of the catheter pump itself; specifically including:

[0121] 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 speed and flow of the catheter pump are fitted using a second-order equation. The relationship function between the flow and speed of the catheter pump is expressed as follows:

[0122] I(ω)=γ1*ω 2 +γ2*ω+γ3

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

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

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

[0126] V3=I(ω)*T

[0127] 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;

[0128]

[0129] Wherein, T represents a cycle; HR is the current heart rate.

[0130] S7: The total volume V of blood 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.

[0131] The total volume of blood ejected in one cycle, V, 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 ejected through the catheter pump in one cycle; V3 is the volume of blood ejected through the catheter pump motor in one cycle;

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

[0135] CO=V*HR

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

[0137] In summary, the present invention is based on the cardiac output estimation method of the catheter pump, which takes into account the blood flow through the catheter pump itself. Since there is always a pressure difference between the aorta and the ventricle, some blood must flow through the catheter pump due to the effect 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; the cardiac output of the heart itself and the blood flowing through the catheter pump is calculated by the pressure at both ends of the outlet and the inlet. Compared with estimating the cardiac output only by the change in the outlet pressure, the cardiac output obtained by the pressure difference at both ends of the aortic valve is more in line with the pumping law of the heart itself; the current cardiac output is obtained by calculating the blood volume ejected in a single cycle and accumulating the blood volume of all cycles within one minute according to the current heart rate. Compared with the calculation result obtained by directly estimating the cardiac output, it is more accurate.

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

[0139] Furthermore, the present invention uses a second-order function to fit the catheter pump speed and flow collected under experimental conditions to obtain the relationship between the flow and speed of the catheter pump; the actual catheter pump speed and catheter pump motor pumping flow are used to calculate the blood volume ejected by the catheter pump motor in one cycle, and the calculation result is more accurate.

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

[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 inlet ends, 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 volume V of blood ejected in one cycle is calculated by the blood volumes V1, V2 and V3. The current cardiac output is calculated based on the total blood volume V and the current 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 flow of blood through 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)=γ1*ω 2 +γ2*ω+Y3 Where I(ω) is the flow rate of the catheter pump; ω is the speed of the catheter pump; γ1, γ2 and γ3 are all fitting coefficients.

10. The cardiac output estimation method according to claim 1, characterized in that: 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.

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