CN113551808A - Core body temperature monitoring experimental equipment - Google Patents
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Abstract
The application discloses core body temperature monitoring experimental facilities, it includes: a simulated body temperature generator and a core body temperature measuring device; wherein, simulation body temperature generator includes: the device comprises a barrel container, a first water pump, a second water pump and a constant-temperature water tank; the core body temperature measuring device includes: the temperature sensor comprises a containing element, a first thermistor, a second thermistor, a micro-heating piece, a control unit, a temperature detection unit and a shell. Because the constant temperature water tank is adopted, the simulated core body temperature is more stable, and in the core body temperature measuring device, because the micro-electrothermal sheet is arranged, the core body temperature measuring device has an environmental heat exchange compensation function, and even if the core body temperature measuring device is exposed in different cold and hot environments in a complex operation environment, the body temperature measuring result is not influenced by the change of an external temperature field and heat exchange, so that the body temperature data with high precision can be obtained in various states.
Description
Technical Field
The application relates to monitoring of human body parameters, in particular to core body temperature monitoring experimental equipment.
Background
The human body temperature is one of four vital signs of the human body, and the human body has different body parts, so that the temperature of the central part of the human body (core body temperature) is stable under the action of a physiological steady state regulating system, and the human body temperature becomes an important basis for judging whether the human body is healthy or not. Keeping constant body temperature is a necessary condition for ensuring normal metabolism and life activities. Effective monitoring of body temperature, particularly core body temperature, is an important issue. Under the scenes of auxiliary diagnosis of sleep disorder patients, female physiological cycle management, biological thermal strain monitoring and the like, the continuous monitoring of the core body temperature can obtain more accurate biological rhythm prediction and physiological condition evaluation.
Intensive study of core body temperature requires devices that mimic core body temperature. CN 101843476B proposes a calibration device for a non-invasive nuclear temperature measuring device, which utilizes a container filled with a liquid medium to simulate human tissue, and an electric heater is arranged in the container to regulate and control the core body temperature change. In the device, the temperature control system of the heater combined with the submersible pump has large fluctuation and cannot truly reflect the steady core body temperature of a human body, so that large errors can be introduced for subsequent detection and research of the core body temperature. In addition, because the water pump, the heating circuit and the like are all arranged in the container, the inlet and the outlet of more cables need to be reserved on the container, heat loss is easily caused, and the equipment maintenance is inconvenient. Furthermore, the device is difficult to simulate a variety of skin fold thicknesses, thereby ignoring the reality of the human epidermis.
The intensive study of the core body temperature also requires a core body temperature measuring device used in cooperation with a device for simulating the core body temperature.
The invention patent CN 110840416A discloses a non-invasive core body temperature detection probe comprising a plurality of heat transfer units, and the invention compensates and processes the measurement error caused by the non-uniform transverse heat flow of the human body through the combination of at least three heat transfer units in the core body temperature detection probe. The probe cannot consider measurement errors caused by factors such as individual difference and environmental temperature change, and has poor anti-interference capability.
The invention patent US5816706 discloses a temperature sensing unit based on two known heat conduction ratios to measure the core body temperature. The device has poor anti-interference capability, is often interfered by environmental factors such as temperature, wind speed and the like, and the original thermal stability of the heat transfer unit can be changed rapidly, so that the temperature measurement accuracy is low.
Disclosure of Invention
In view of the above problems, the present application is directed to provide a core body temperature monitoring experimental apparatus, wherein a simulated body temperature generator can truly simulate the core body temperature of a human body, provide a stable core body temperature, and a core body temperature measuring device has an environmental heat exchange compensation function.
The application discloses core body temperature monitoring experimental facilities, it includes: a simulated body temperature generator and a core body temperature measuring device;
wherein, simulation body temperature generator includes: the device comprises a barrel container, a first water pump, a second water pump and a constant-temperature water tank;
the barrel container is made of ABS plastic; the cylindrical container is filled with water medium; the port of the barrel container is sealed by heat insulation materials;
the constant-temperature water tank is arranged outside the barrel container, and a first pipeline and a second pipeline are formed between the constant-temperature water tank and the barrel container; the first pipeline and the second pipeline are respectively composed of heat insulation hoses; the first water pump is arranged in the first pipeline, and the second water pump is arranged in the second pipeline; the first pipeline is used for providing the water medium from the constant-temperature water tank to the barrel container, and the second pipeline is used for providing the water medium from the barrel container to the constant-temperature water tank;
a temperature measuring unit is arranged in the barrel container;
the barrel container comprises a plurality of temperature measuring positions, and each temperature measuring position corresponds to different wall thicknesses;
wherein, core body temperature measuring device includes: the temperature detection device comprises a containing element, a first thermistor, a second thermistor, a micro-heating sheet, a control unit, a temperature detection unit and a shell;
the containing element is made of anisotropic material, and a plurality of pipelines are formed from the first end to the second end of the containing element, and the first end and the second end of the plurality of pipelines are respectively closed; the first thermistor is arranged at the first end of the accommodating element and used for measuring the body surface temperature; the second thermistor is arranged at the second end of the accommodating element and used for measuring the ambient temperature; the micro-electrothermal sheet is arranged near the second thermistor and used for actively generating environmental temperature change;
the control unit controls the micro-electrothermal sheet to work; the first thermistor and the second thermistor are connected to the temperature detection unit, and the temperature detection unit is connected to the control unit;
the shell is made of heat insulating materials, is formed into a cylinder shape, has a first end which is opened and a second end which is closed, and is used for thermally isolating the interior of the core body temperature measuring device from the external environment; the accommodating element, the first thermistor, the second thermistor, the micro-heating sheet, the control unit and the temperature detection unit are enclosed inside the shell.
Preferably, in the core body temperature measuring device, the plurality of conduits of the receiving member have a straight shape or a curved shape.
Preferably, in the core body temperature measurement device, the first ends of the plurality of conduits are concentrated around the first thermistor; the second ends of the plurality of conduits are concentrated around the second thermistor.
Preferably, in the core body temperature measurement device, the plurality of conduits are equally spaced and parallel to each other.
Preferably, in the core body temperature measurement device, a biocompatible layer is provided at a first end of the containment element; the biocompatible layer closes the first end of the housing.
Preferably, in the core body temperature measuring device, a good heat conduction layer is connected between the second thermistor and the micro-electrothermal sheet.
Preferably, in the core body temperature measuring device, the receiving member is located at a central position of the housing, and a predetermined space is formed between an inner surface of the housing and an outer surface of the receiving member.
Preferably, the control unit and the temperature detection unit are arranged on the circuit board.
Preferably, in the core body temperature measuring device, the circuit board is located at the first end of the accommodated element, and covers the first thermistor.
Preferably, in the simulated body temperature generator, the first water pump and the second water pump are installed in a heat insulation box body.
The core body temperature monitoring experimental facility of this application, in simulation body temperature generator, owing to adopt the constant temperature basin, the core temperature of simulation is more stable for it is more feasible and accurate to verify in the experiment to estimate core body temperature from body surface temperature. The temperature measuring positions with different wall thicknesses are arranged on the container to simulate the change of the thermal resistance of the skin, so that the change condition of monitoring the core temperature at different positions can be simulated more accurately; in the core body temperature measuring device, because the micro-electrothermal sheet is arranged, the core body temperature measuring device has an environment heat exchange compensation function, even if the core body temperature measuring device is in a complex operation environment and is exposed in different cold and hot environments, the body temperature measuring result is not influenced by the change of an external temperature field and heat exchange, and therefore high-precision body temperature data can be obtained in various states.
Drawings
Fig. 1 is a schematic structural diagram of a core body temperature measuring device of the core body temperature monitoring experimental equipment of the present application;
FIG. 2 is a schematic connection diagram of a circuit portion of a core body temperature measuring device of the core body temperature monitoring experiment apparatus of the present application;
FIG. 3 is a schematic structural diagram of a core body temperature monitoring experiment apparatus according to the present application;
FIG. 4 is a schematic diagram of a lumped parameter thermal model;
FIG. 5 is a simplified variable parameter thermal model schematic;
FIG. 6 is a flow chart of the individualized correction factor P estimation;
FIG. 7 is a diagram of a temperature measurement accuracy test, Bland-Altman.
Detailed Description
The present application will be described in detail below with reference to the accompanying drawings.
The core body temperature monitoring experimental equipment of this application includes two parts: a body temperature simulation generator and a core body temperature measuring device; the core body temperature measuring device is arranged on the outer peripheral wall of the barrel container of the body temperature simulation generator so as to carry out experiments.
Body temperature simulation generator
A simulated body temperature generator for use in the present application, comprising: a barrel container 11, a first water pump 12a, a second water pump 12b and a constant temperature water tank 13.
The barrel container 11 is made of ABS plastic; the cylindrical container 11 is filled with water medium; the port of the drum container 11 is closed by a heat insulating material.
The constant-temperature water tank 13 is arranged outside the barrel container 11, and a first pipeline and a second pipeline are formed between the constant-temperature water tank 13 and the barrel container 11; the first pipeline and the second pipeline are respectively composed of heat insulation hoses 14; a first water pump 12a is installed in the first pipeline, and a second water pump 12b is installed in the second pipeline; the first line is used for supplying the water medium from the constant-temperature water tank 13 to the barrel container 11, and the second line is used for supplying the water medium from the barrel container to the constant-temperature water tank, so that water is circulated between the constant-temperature water tank and the barrel container.
A temperature measuring unit 15 is arranged in the cylindrical container 11. The temperature measuring unit 15 is a thermistor to measure the temperature of the aqueous medium in the drum container 11, which is the simulated core body temperature.
The inner wall or the outer wall of the barrel container 11 is provided with a radiation-proof layer to prevent heat loss caused by heat radiation, so that the simulated core body temperature is stable.
The first and second water pumps 12a and 12b are installed in the heat insulation box, thereby avoiding heat loss caused by the water pumps themselves as much as possible.
The drum container 11 comprises a plurality of temperature measuring locations 11a, 11b, each temperature measuring location corresponding to a different wall thickness. And the wall thickness corresponding to one temperature measuring position is 11 mm.
The barrel container 11 has a height of 250mm, an inner diameter of 80mm and a bottom thickness of 25 mm.
The constant-temperature water tank is used for controlling to generate constant heat, water in the constant-temperature water tank is conveyed into the barrel container through the first water pump, the water in the barrel container is conveyed into the constant-temperature water tank through the second water pump, heat balance is formed between the barrel container and the constant-temperature water tank, and therefore a uniform and stable body core heat source is generated in the body temperature generator. The wall of the barrel container is used for simulating the thermal resistance of skin (fat, muscle, epidermis and the like) with a certain thickness of a human body. The temperature measurement positions corresponding to different wall thicknesses represent the thermal resistance of the skin with different thicknesses.
The drum wall thickness is calculated as follows:
coefficient of thermal conductivity lambda of human skins0.47W/(m.k), coefficient of thermal conductivity of fat λfThe thickness of normal abdominal male skin fold (skin + subcutaneous fat) is 5-15 mm, and female skin fold is 12-20mm (0.21W/(m.k)). We take the average skin thickness δ to 10mm, where the skin thickness δs2mm, fat thickness deltafAnd (2) according to the heat conduction steady-state stage, the total thermal resistance is equal to the sum of the series thermal resistances, namely the formula 1:
calculating the average thermal conductivity of the wrinkles by substituting the data to obtain lambdaa0.236W/(m.k). The barrel wall of the body temperature simulation generator is made of ABS material with heat conductivity coefficient lambdaabs0.2512W/(m.k), the equivalent 10mm crimp thickness of ABS material thickness is based on the same principle of equal thermal resistance as described above
The thickness of the main body of the barrel wall of the body temperature simulation generator is 11 mm. The thickness of other thermometric locations may be 9mm, 10mm, 12mm, 13mm, etc.
In order to meet the experiment requirement, save materials and be convenient to carry, the overall size is determined to be 250mm of barrel height, 80mm of inner diameter and 25mm of ABS base thickness, and thermal insulation material is added for bedding in the experiment so as to reduce the temperature unevenness of the barrel wall caused by the loss of bottom heat. The top of the barrel container is a 10mm thick sealing ball valve, and a one-way heat insulation hose hole and an exhaust hole are reserved. The heat transfer medium in the barrel container is water, and the 12V 4W water pump is arranged in the heat insulation box body, so that the heat loss caused by the water pump is avoided. The water flow is stirred to make the temperature in the generator uniform. The temperature control precision of the constant temperature water tank is within the range of +/-0.05 ℃, and a constant temperature curve is drawn to test the temperature control capability.
Under the condition of stable core body temperature, different thermometric parts are easy to cause measurement errors due to the change of the thickness of skin folds. Therefore, different wall thicknesses are required on the body temperature generator to simulate changes in the body temperature site or differences in the thickness of the folds of the skin of a person. In addition, different wall thicknesses can also facilitate multi-point measurement of a plurality of temperature measuring devices, and parallel experiments can accelerate calibration of the thermometer.
Core body temperature measuring device
The core body temperature measuring device includes: the device comprises a containing element 7, a first thermistor 4, a second thermistor 3, a micro-heating plate 6, a control unit 81, a temperature detection unit 82 and a shell 1.
The accommodating element 7 is made of an anisotropic material, the heat conductivity coefficient is 0.05-0.3W/mK, and the polyether ether ketone (PEEK) material is preferred, so that the low heat conductivity is ensured, and the injection molding processing is easy. Materials such as Polyethylene (PE), polymethyl methacrylate (PMMA), Polycarbonate (PC), or Polysulfone (PSU) may also be selected. A plurality of pipelines are formed from the first end to the second end of the accommodating element 7, the first ends and the second ends of the pipelines are respectively closed, and air or foam (between 0.01 and 0.1W/mK) is accommodated in the pipelines. The pipeline can reduce radial heat conduction, reduces radial heat conduction error. The pipe allows the containing element to have remarkable anisotropy, is beneficial to providing a radial heat conduction level lower than axial heat conduction (2-20 times), and ensures the accuracy of measurement.
The first thermistor 4 is arranged at the first end of the accommodating element 7 and is used for measuring the body surface temperature; the second thermistor 3 is arranged at the second end of the accommodating element 7 for measuring the ambient temperature; the micro-heating sheet 6 is arranged near the second thermistor and is used for generating disturbance temperature and simulating the change of the ambient temperature in an active mode.
The control unit 81 controls the micro-electrothermal sheet 6 to work; the first thermistor 4 and the second thermistor 3 are connected to a temperature detection unit 82 through a switch circuit 84, and the temperature detection unit 82 is connected to the control unit 81; the control unit 81 may be connected with a bluetooth unit 83 to communicate with the outside. A battery 85 powers the entire circuit.
The control unit adopts STM32F103TBU6 of 36 pins, and the chip has few pins, small volume, low power consumption, low price, mature technology and stable performance. The temperature detection unit adopts MAX31865, and the chip has high integration level and high precision, the theoretical precision is 0.003, and the actual measurement precision is about 0.008. The switching circuit is an analog switch for switching the inputs of the two sensors. The Bluetooth module adopts a mature Bluetooth 4.0 module, and the power consumption is lower.
The shell 1 is made of heat insulating materials, is formed into a cylinder shape, has a first end which is opened and a second end which is closed, and is used for thermally isolating the interior of the core body temperature measuring device from the external environment so as to ensure that the disturbance of the passive environment temperature is as small as possible; the accommodating element 7, the first thermistor 4, the second thermistor 3, the micro-heating chip 6, the control unit 81, and the temperature detection unit 82 are enclosed in the housing 1, and are thermally insulated from the outside as much as possible.
The plurality of ducts of the containing element 7 are rectilinear or curvilinear in shape. The curved duct makes it possible to keep the height of the receiving element 7 as small as possible while ensuring the length of the duct.
The first ends of the plurality of tubes are concentrated around the first thermistor 4; the second ends of the plurality of tubes are concentrated around the second thermistor 3 so that the influence of the ambient temperature on the body surface temperature is as small as possible. The plurality of tubes are equally spaced and parallel to each other.
A biocompatible layer is provided at a first end of the containment element 7; the biocompatible layer closes the first end of the housing 1. The biocompatible layer in the present application may be coated with a biocompatible colloid. The biocompatible layer is disposed under the circuit structure and is for adhesively coupling the skin of the human body to the core body temperature measurement device. The biocompatible layer is tightly attached to the heat insulation shell, so that the requirement of long-term monitoring can be met while severe temperature disturbance of the environment is isolated.
A good heat conduction layer 5 is connected between the second thermistor 3 and the micro-heating plate 6, so that active environmental disturbance applied through the micro-heating plate 6 can be quickly reflected on the second thermistor 3.
The receiving member 7 is located at a central position of the housing 1, and a predetermined interval is formed between an inner surface of the housing 1 and an outer surface of the receiving member 7. The enclosure 1 may be evacuated of air to further avoid the influence of external temperature on the internal temperature of the enclosure.
The control unit 81, the temperature detection unit 82, the bluetooth unit 83, and the switch circuit 84 are provided on the circuit board 8.
The circuit board 8 is located at a first end of the receiving element 7 and overlies the first thermistor 4.
The first thermistor 4 is disposed in parallel with the second thermistor 3.
The measurements of the thermistors were calibrated using a Fluke thermometer reference device. The calibration test records are shown in table 1. The error value is about 0.003-0.01 ℃, and the precision is basically stabilized at 0.01 ℃ by using Kalman filtering. The temperature measured value is wirelessly transmitted to the upper computer through the Bluetooth.
TABLE 1 calibration experiment table for temperature sensing reading
Note that: the readings were 10 times at each bath temperature and the results were mean. + -. sd.
Establishing a two-channel heat flow model
The heat transfer coefficient of human tissue is assumed to be kg ≈ 45W/m2K, the axial heat transfer coefficient kv of the structured containment element 7 is approximately equal to 50W/m2K, the heat transfer coefficient ks of the good heat conduction layer 5 is approximately equal to 401W/m2K, the measuring device detects the near body skin temperature Ts and the far body environment temperature Te, wherein the main heat flow enters the heat flow insulator from the body tissue and flows to the temperature sensing element of the far body from the temperature sensing element of the near body, and then the human body core temperature Tcore can be calculated according to the formula 2.
Establishing a variable parameter thermal model
Briefly, the physiological temperature field is composed of an internal temperature Tc, an epidermal temperature Ts, an ambient temperature Te and the mutual relationship among the three.
The internal temperature field mainly comprises heat source substances in body surface tissues and substances with similar thermal properties (skin, fat and the like), on one hand, the internal temperature field comprises energy conversion efficiency (physiological state changes, such as eating, movement and the like) in the process of converting chemical energy of internal substances into heat energy, and according to the difference of physiological state levels, the energy provided by chemical reactions of different substances is uneven; on the other hand, when the physiological activities are in a normal state, the thermal properties of the deep tissues and the body surface tissues are highly consistent with the thermal properties of the heat insulating material, and the two parts jointly reflect the structure with the most sensitive internal temperature change, namely the composition of the internal temperature field. The epidermis temperature field is determined by the skin surface and the skin structure shape together, the thermal properties of different skin colors, hairs and parts show larger difference, the heat absorption efficiency and the heat conduction efficiency reflect the thermal properties shown by the skin, and the external shape measuring and calculating method of the skin can be specifically designed according to the placing part, the hair length and the placing surface area in combination with the internal temperature field, and the purpose is mainly to reduce the contact surface area as much as possible and reduce the heat dissipation efficiency so as to obtain more accurate temperature measurement values. The external temperature field is determined by the external environment, and the external environmental factors including the air temperature, the humidity and the external air velocity all affect the heat transfer rate in different degrees, thereby affecting the distribution of the external temperature field.
By combining the above analysis on the physiological temperature field, the factors influencing the temperature field change mainly include the change of the internal central thermal characteristic region, the non-uniform internal heat conduction rate, the non-uniform heat dissipation at different positions on the skin surface, the heat dissipation rate influenced by the external environment and the like; in addition, to some extent, physiological temperature field variations can be numerically reflected as variations in the internal temperature Tc, the skin temperature Ts, and the ambient temperature Te. In conclusion, different physiological thermal models can be obtained by processing the factors influencing the temperature field change in different ways.
Therefore, after analyzing the physiological temperature field, a physiological Lumped Parameter (Lumped Parameter) thermal model is the main model currently used to describe the thermal behavior in physiological states and to enable estimation of internal temperature. The model mainly comprises a body core heat generating source, internal heat conduction, surface heat absorption, external heat transfer and environmental temperature compensation, wherein a physiological temperature field is described in the model by utilizing a thermoelectric similarity principle, the whole temperature field is equivalent to internal heat capacity, heat generating rate, internal and external heat conduction rate which are expressed by thermal resistance, and the total parameter thermal model is shown as figure 4. In FIG. 4, Q is an internal heat source, Cc, Cs are internal and surface heat capacities, respectively, and Ri, Ro are internal and external heat resistances, respectively; in the physiological lumped-parameter thermal model, the thermal model parameters Cc, Cs, Ri, and Ro are treated in a constant manner, and the respective factors affecting the physiological temperature field variation cannot be sufficiently considered and appropriately treated.
In order to solve two problems of the lumped parameter model: 1) ri is different due to individual difference and physiological state of factors such as fat, muscle and the like on the body surface of a human body, and Ri needs to be calculated in an individualized mode; 2) the Ts variation is affected by the Tc and Te variations, and the dynamic switching of the temperature field needs to be considered. If Te is maintained constant, the change in Ts can directly reflect the dynamic change in Tc, and therefore, the effect of changes in ambient temperature needs to be removed from the change in Ts.
To achieve an accurate estimation of the physiological internal temperature, it is of utmost importance to establish a reasonable physiological thermal model. According to the Semenov combustion theory, the thermal model regards the internal temperature of the object as a uniform, periodic and stable structure, and is a scientific method which is applicable to analyzing and describing the internal heat distribution of the object.
Meanwhile, on the basis of the basic structure of the double thermistors shown in the figure 1, a micro-electrothermal sheet 6 is additionally arranged outside the accommodating element 8 and the second thermistor 3, the change of the environmental temperature is simulated through the micro-electrothermal sheet, the ratio of Rc to Re is obtained, the personalized correction is realized, and the quantization coefficient of the influence of the environmental temperature on the skin temperature is obtained.
Firstly, an environment heat source (micro-electric heating sheet) path is analyzed, the path has the main function of joule heat generated by equivalent ohmic internal resistance in the resistance wire, other heat generation and heat absorption in an environment thermal field can be ignored relative to the joule heat, and therefore a formula 3 heat generation rate calculation formula is adopted in the text. The heat transfer between the physiology and the external environment is mainly carried out in a heat exchange mode, and the heat transfer inside the physiology is mainly carried out in a heat conduction mode.
QH＝I2r (formula 3)
In the formula, QH is the heat production rate (unit: W) of an environment heat source (micro electric heating sheet), I is the working current (unit: A) of the micro electric heating sheet, and r is the equivalent ohmic internal resistance (unit: omega) of a resistance wire.
Secondly, factors such as the change of an internal central area, the uneven heat conduction rate of the internal, the uneven heat dissipation of different positions of the surface skin, the heat dissipation rate influenced by the external environment and the like are comprehensively considered, and the current thermal model is optimized. In the study, physiological internal temperature is regarded as equivalent and uniform, and the region has a certain degree of change, and the internal heat capacity is regarded as variable in order to reflect the influence of the change on the internal temperature in the experiment. Meanwhile, the difference between the internal heat conduction rate and the surface heat dissipation rate is large along with the position change, and although a certain difference exists, the internal heat conduction rate and the surface heat dissipation rate play a main role in heat transfer in the overall view, so that the internal heat conduction rate and the surface heat dissipation rate are respectively uniformly and equivalently processed when the internal heat conduction rate and the surface heat dissipation rate are modeled. In addition, in order to reflect the specific change of the external environment, the external heat transfer rate is considered to be uniform and variable, and meanwhile, the influence on the core temperature can be measured and calculated according to the heat flow of the electric heating piece. The problem of inconsistent heat capacity of the epidermis caused by different skin qualities is solved, the heat capacity of the epidermis is equivalently and uniformly treated, and modeling is facilitated.
On the basis of analyzing a physiological internal heat production mechanism, a heat transfer mechanism and a classic lumped parameter thermal model, the influence of the environmental temperature on the parameters of the thermal model is reflected by combining the research improvement content, so that the constructed physiological thermal model can be close to a real thermal model as far as possible. Meanwhile, in order to reduce the complexity of the model and increase the applicability, the invention establishes a simplified variable parameter thermal model fusing a variable internal heat capacity model and an external heat resistance model, as shown in FIG. 5.
In FIG. 5, Cc and Cs are the internal heat capacity and the surface heat capacity (unit: J/K) of the battery respectively, and represent the absorption and heat dissipation capacities of the substances; tc, Ts, Te are physiological internal, surface and ambient temperatures (unit:. degree. C.) respectively; ri represents the physiological internal heat conduction rate for the internal thermal resistance; ro is the external thermal resistance and represents the rate of heat exchange between the skin surface and the environment (unit: K/W); q is an internal heat source (physiological heat production rate); QH is an external heat source (rate of heat generation by micro-electrothermal sheet). Based on a simplified variable parameter thermal model, a first-order RC filter network is simulated by an energy conservation equation inside and outside a battery, a Fourier thermal law and a Newton heat dissipation law, and a system characteristic equation is as shown in a formula 4 and a formula 5:
to reflect the effect of Ta on Cc and Ro, the internal heat capacity and external heat resistance are modeled using equation 6:
and obtaining a core temperature estimation formula in a conclusion manner:
and the thermal model parameter measurement and calculation comprises equivalent ohmic internal resistance r, an individualized correction coefficient P, an environment temperature correction coefficient alpha, an environment temperature Te, an internal heat capacity Cc and an external heat resistance Ro relational equation. After a reasonable physiological thermal model is established, accurate identification of thermal model parameters and micro-electric heating sheet characteristic parameters is a key for realizing core temperature estimation, and on the basis, modeling is carried out on the parameters to analyze the mechanism of the parameter model.
Equivalent ohmic internal resistance modeling r
Errors in the design of thermal resistors mainly result from lead resistance, self-heating effects, non-linearity errors, and some minor errors on the circuit. In order to improve the estimation accuracy of the heat production rate of the environment heat source, the equivalent ohmic internal resistance of the micro-heating plate is further measured and modeled in consideration of the nonlinear influence of the environment temperature on the internal ohmic internal resistance, meanwhile, in order to avoid the nonlinear temperature measurement influence of the thermosensitive temperature measurement element, the experiment is limited to a narrower heating temperature, in order to simplify the calculation and enable the fitting result to be closer to the real internal resistance characteristic, the fitting relation is as follows:
r＝l×Te+m×Te 2+n×R+o×R2+z×Tex R + y + e (equation 7)
In the formula 7, l, m, n, o and z are coefficients to be fitted, y is a constant term, and epsilon is an error.
Designing an experiment, measuring and calculating at the temperature range of 25-30 ℃, and establishing a multiple regression model for fitting.
The regression fit equation is:
r＝-9.7441×Te-0.0377×Te 2+0.2399×R-0.0002×R2+0.0107×TeXR (equation 8)
The confidence intervals are [ -23804.2019862140,4316.03520634591], [ -92.1913388073052,16.7386726429827], [ -96.0680748222936, 575.938694895014], [ -0.575625139000544,0.0960727813991399], [ -4.68413278354100,26.0187150992556], [0,0] respectively.
TABLE 2 thermistor reading calibration experiment table
Measuring and calculating individual correction coefficient P and environment temperature correction coefficient alpha
The steady-state measurement result Ts of the skin temperature sensor is influenced by four factors, namely the core temperature Tc, the ambient temperature Te, the physical properties (thermal resistance Ro, density rho and specific heat capacity c) of the heat-insulating material and the equivalent thermal resistance Ri of the body surface tissue.
The transient heat conduction circuit model is formula 9:
the steady state thermal conduction circuit model is equation 10:
keeping the core temperature Tc constant, changing the ambient temperature Te to Te + Δ Te by heating the micro-electrothermal sheet, and recording the variation Δ Ts of Ts, so that the individualized correction coefficient is formula 11:
the ambient temperature correction coefficient is equation 12:
the individual correction coefficient P can be obtained through experimental calculation, and a numerical table or a relation function of Cs (heat capacity of the heat insulation material) at different temperatures can be obtained by looking up data.
The core temperature Tc was designed to be 35 ℃, the ambient temperature Te was heated by the micro-electrothermal sheet, and the variation Δ Ts of Ts was recorded, and the experimental record is shown in table 3.
TABLE 3 variation of skin temperature Ts with ambient temperature Te with core temperature Tc maintained at 35 deg.C
Modeling relation between environment temperature and internal heat capacity Cc and external heat resistance Ro
By analyzing the internal temperature balance, when the physiological internal temperature is in a thermal steady state, the change rate of the internal temperature is approximately zero, and the internal and external thermal resistances Ri and Ro at different environmental temperatures Te are firstly identified, and the process is as shown in fig. 6.
From the obtained Cs (thermal insulation material heat capacity) and the individualized correction coefficient P (i.e. the ratio of internal resistance to external resistance, R) at different ambient temperatures Te0). On the basis, thermoelectric parameters are identified by a least square method through a transient process of internal temperature change before thermal steady state and the combination of a formula 6. The values of internal and external thermal resistances at different ambient temperatures Te are recorded as shown in table 1 and non-linearly fitted to equation 13:
g. and s, u, j, q and h are coefficients to be fitted.
The fitting equation is:
TABLE 4 calculation of tissue heat capacity and external thermal resistance at different Te
Mechanism analysis of internal heat capacity Cc and external heat resistance Ro
According to the built variable internal heat capacity model, the characteristics that Cc changes with Te, internal temperature rise rate is inconsistent and the ratio of Tse to Tcs changes obviously under different Te can be shown, the reason is that when Te is low, the composition range of the region with similar internal central thermal characteristics is small, so that the internal structure heat capacity of the physiological epidermal tissue becomes small, and when Te rises, the composition range of the region with similar internal central thermal characteristics becomes large, and the characteristic of changing with Te reflects the influence of Te on Cc and cannot be simply reduced by a fixed value.
The heat exchange rate of the heat insulating material of the dual-temperature sensor is represented by external thermal resistance, wherein the heat conducting media (air molecules) around the surface have larger difference in density due to different Te, so that the temperature stratification is formed on the periphery of the surface to cause the external heat exchange rate to show the uneven characteristic, when the Te is lower, the heat dissipation rate of the heat conducting media around the surface is lower, and the heat dissipation rate tends to change in the opposite direction along with the increase of the Te. For convenience of calculation and showing the dynamic nonlinear relation of Cc and Ro changing with Te as much as possible, Cc and Ro are regarded as uniform and variable equivalently, and the heat transfer rate (equivalent ohmic internal resistance) of the micro-heating plate is fitted by formula 7.
Dynamic measurement algorithm for establishing extended Kalman filtering estimation model and determining core body temperature
An internal temperature estimation algorithm is established, based on the variable parameter thermal model established in the steps, the dynamic characteristic equation of the double temperature sensors and the complexity of the whole physiological temperature measurement system are combined, and the dynamic measurement algorithm of the core body temperature based on the Extended Kalman Filter (EKF) is adopted.
Modeling of state equations and observation equations
An EKF-based internal temperature estimation algorithm needs to accurately describe the characteristics of a variable parameter thermal model system of a physiological temperature measurement system by using a state space model. To characterize the dynamics of a variable parameter thermal model system, a state equation (equation 15) is established according to equation 4:
using the core temperature (Tc) as the system state variable and the micro-electric heating sheet current (I) as the system input
The observation vector of the dynamic system is the basis of the system self-adaptive filtering, the precision and the reliability of the system self-adaptive filtering are directly influenced, the combination formula (6) takes the skin temperature (Ts) and the environment temperature (Te) as the observation vector, and simultaneously, in order to represent the influence of Tc and Te on the change of Ts, the observation equation is expressed by a formula 16:
in the formulas 15 and 16, Tc (t), Ts (t) are Tc and Ts at time t, Tc (0) and Ts (0) are initial values (reference values) of Tc and Ts, I is the working current of the micro-electric heating sheet, and r is the equivalent ohmic internal resistance of the micro-electric heating sheet.
EKF discretization
In practical application, the established continuous dynamic system model is discretized in the past, and the discrete model has the specific advantages, so that the operation on a computer is facilitated, and the dynamic characteristics of the system can be more intuitively described by the discrete model. Based on the above analysis, firstly discretizing the state equation, simultaneously considering model errors, adding process noise, and substituting the variable internal heat capacity equivalent model established in the previous step into formula 15 to obtain a discretized state equation (formula 17):
secondly, discretizing a system observation equation, adding observation noise caused by observation errors, substituting the variable external thermal resistance equivalent model built above into a formula 16, and further obtaining a discretized observation equation (a formula 18):
in formulas 17 and 18, g, s and u are variable internal heat capacity fitting coefficients; l, m, n, o, z, y and epsilon are equivalent ohmic internal resistance fitting coefficients; j. q and h are variable external thermal resistance fitting coefficients; Δ t is the sampling time(s); w is ak、vkThe noise is mutually independent zero mean Gaussian white noise; k-1 and k are the k-1 and k calculation serial numbers; tc (k-1) and Ts (k-1) are the k-1 th calculated internal temperature and surface temperature, and Tc (k-1) and Ts (k) are the k-th calculated internal temperature and surface temperature.
EKF algorithm process
Specifically, xkFor the kth calculation of Tc (k), ukFor k time input ik，ykCalculating Ts (k) for the kth time
Defining:
setting a filtering initial value:
setting an initial value of variance:
and (3) state prediction:
error covariance prediction:
gain matrix:
and (3) updating the state:
error covariance update:
unit time delay: k is k +1
Temperature measurement precision test of temperature sensor
The core body temperature is designed to fluctuate from 26-46 ℃ by using a body temperature simulation generator, the estimated value of the core body temperature detection device to the core body temperature is recorded, and a Bland-Altman graph is drawn as shown in figure 7. The 95% consistency limit (95% limits of element, 95% LoA) is observed, and when the vast majority of differences are within this interval, the two methods can be considered to have better consistency. The average value of temperature measurement difference values of the core body temperature detection device in a temperature range of 26-46 ℃ is-0.14 ℃, the consistency limit is 0.41 ℃, and the core body temperature detection device has high temperature measurement precision.
Unless defined otherwise, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention relates. The materials, methods, and examples set forth in this application are illustrative only and not intended to be limiting.
Although the present invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the teachings of this application and yet remain within the scope of this application.
Claims (10)
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