CN114913752A

CN114913752A - Lumped parameter-based human respiratory system model

Info

Publication number: CN114913752A
Application number: CN202210588961.3A
Authority: CN
Inventors: 宗方; 郑然�; 马炬; 王莘文; 代婷钰; 陈哲; 何厚伯; 张文亮; 程桂禹; 黄昱; 王超
Original assignee: Third Military Medical University TMMU
Current assignee: Third Military Medical University TMMU
Priority date: 2022-05-26
Filing date: 2022-05-26
Publication date: 2022-08-16
Anticipated expiration: 2042-05-26
Also published as: CN114913752B

Abstract

The invention discloses a human respiratory system model based on lumped parameters, which belongs to the technical field of medical models. In the model, the carina compartment represents an anatomical region of the tracheal airway. The left and right anatomical dead space represent the bronchi and their branching bronchioles, which are part of the airways below the carina. The left and right alveolar chambers correspond to a collection of alveoli, with gas exchange occurring between the airway and the cardiovascular system. The left and right chest wall compartments represent the left and right sides of the chest wall, respectively. The new model also takes into account the pleural cavity induced by the circuit elements, while also including a pressure signal generator representing the driver of the respiratory muscle pressure source. The model employs a circuit-based lumped parameter mathematical model that allows patient-specific respiratory mechanics to be characterized with a relatively low computational burden.

Description

Lumped parameter-based human respiratory system model

Technical Field

The invention relates to the technical field of medical models, in particular to a human respiratory system model based on lumped parameters.

Background

The human respiratory system consists of the upper respiratory tract (the area above the cricoid), the lower respiratory tract, the lungs and respiratory muscles. The lower respiratory tract begins in the trachea, extends to the bronchi, bronchioles and alveoli. At the carina, the trachea is divided into two main bronchi, left and right. The bronchi branch into smaller bronchioles, which continue for up to 23 generations, forming a tracheobronchial tree terminating in alveoli. Alveolar ducts and alveolar sacs are the pulmonary operating unit that exchanges gas with pulmonary capillaries. The first few generations of airways where no gas exchange takes place constitute anatomical dead spaces, called conduction zones. In contrast, the process of ventilation promotes alveolar-capillary gas exchange, which is driven by intercostal muscle, internus muscle and chest wall recoil. These mechanisms work synergistically to actively drive fresh air into the lungs and passively remove gas from the lungs. Attached to the chest wall is a thin membrane (pleura) which folds back on itself to form two layers, called the viscera and parietal pleura. The pleural cavity is filled with fluid. The pressure in this space is called the intrapleural pressure, which is usually slightly below atmospheric pressure. Even without inspiratory muscle contraction, the mechanical interaction between the lung and chest wall pulls the two pleura apart, resulting in a slight decrease in intrapleural pressure (-3cm H2O to-5 cm H2O).

The diaphragm acts as a respiratory muscle and participates in the mechanical operation of the ventilator driver. The trachea branches into right and left bronchi, each further branching into smaller bronchioles of several generations. These bronchioles form the tracheobronchial tree, terminating in alveoli. The respiratory system supplies oxygen and removes waste carbon dioxide from the body by a combination of ventilation and gas exchange across the blood-gas barrier (pulmonary capillary-alveolar interface). The respiratory system is designed to simulate the ventilatory behavior (positive and negative) of the patient's respiratory system using an electrically simulated lumped parameter model. The breathing model employs realistic pressure source signals and chemical stimulus feedback mechanisms as drivers for spontaneous ventilation. The model can address a variety of patient conditions, including tension pneumothorax and airway obstruction.

The physiological model of the respiratory system is divided into a lung ventilation model and a respiratory mechanics model. The lung ventilation model models the mechanical processes and mechanisms of lung ventilation. The respiratory system is a mechanical system, and the acting force and the reacting force between the parts of the respiratory system follow Newton's third law. The respiratory system physiological model comprises a first-order linear model, a R.W.Jodat respiratory mechanics mechanical model and a R.M.Peters respiratory system mechanical model.

However, in practical applications, the above models require a large computational burden to characterize the patient-specific breathing mechanics.

Disclosure of Invention

The invention provides a human respiratory system model based on lumped parameters, which aims to solve the problem of large calculation burden in the prior art.

In order to solve the technical problems, the invention adopts the following technical scheme:

a human respiratory system model based on lumped parameters comprises a first loop, a second loop and a third loop;

a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third capacitor and a fourth capacitor are arranged on the first loop, the first resistor and a node of the first loop simulate the right atrium, the second resistor and a node of the first loop simulate the right ventricle, the third resistor and a node of the first loop simulate the left atrium, the fourth resistor and a node of the first loop simulate the left ventricle, a first line is connected between lines of the first capacitor and the third capacitor, the first line and the node of the first loop simulate respiratory muscles, and a pressure signal generator is arranged on the first line;

a first diode and a fifth resistor are arranged on the second loop, the second loop is connected into the first loop, wherein one end of the second loop, which is connected between the first capacitor and the second capacitor, simulates a right pleura, one end of the second loop, which is connected between the second capacitor and the second resistor, simulates a right alveolus, and one node between the first diode and the fifth resistor simulates a right alveolar branch;

the third loop is provided with a second diode and a sixth resistor, the third loop is connected into the first loop, one end of the third loop, which is connected between a third capacitor and a fourth capacitor, simulates a left pleura, one end of the third loop, which is connected between the fourth capacitor and a fourth resistor, simulates a left alveolus, and one node between the second diode and the sixth resistor simulates a left alveolar branch.

Further, a fourth circuit is connected between the first resistor and the third resistor, a contact node of the fourth circuit and the first circuit simulates a glomus of the trachea and the carina, a contact node of the fourth circuit and the fifth circuit simulates the oral cavity, a ninth resistor is arranged on the fourth circuit, a tenth resistor and a fifth capacitor are arranged on the fifth circuit, and one node between the tenth resistor and the fifth capacitor simulates the stomach.

Further, a second line is connected to the node simulating the right pleura, a seventh resistor and a third diode are arranged on the second line, and one node between the seventh resistor and the third diode simulates the right chest film.

Further, a third line is connected to a node simulating the left pleura, an eighth resistor and a fourth diode are arranged on the third line, and one node between the eighth resistor and the fourth diode simulates the left chest radiography.

Compared with the prior art, the invention has the beneficial effects that:

the breathing model provided by the invention provides a system-level calculation model, and can simulate normal lung physiology and respiratory distress in real time. The model employs a circuit-based lumped parameter mathematical model that allows patient-specific breathing mechanics to be characterized with a relatively low computational burden.

Drawings

Fig. 1 is a circuit diagram of a lumped parameter based model of the human respiratory system of the present invention.

Fig. 2 is a graph of total lung volume versus tidal volume for the present invention.

Figure 3 is a graph comparing the transpulmonary pressure of the present invention with the transpulmonary pressure of a bowden diagram.

Fig. 4 is a pressure-volume graph of the engine of the present invention.

Fig. 5 is a graph of the hattan pressure versus volume of the present invention.

Detailed Description

The following examples are given for the purpose of illustration of the present invention, and the present invention is not limited to the examples. Therefore, those skilled in the art can make insubstantial modifications and adaptations of the embodiments based on the above disclosure, and apply other embodiments within the scope of the invention.

An embodiment of the present invention provides a lumped parameter-based model of a human respiratory system, as shown in fig. 1, the model includes a first loop 1, a second loop 2, and a third loop 3.

A first resistor 4, a second resistor 5, a third resistor 6, a fourth resistor 7, a first capacitor 8, a second capacitor 9, a third capacitor 10 and a fourth capacitor 11 are arranged on the first circuit 1, the node of the first resistor 4 and the first circuit 1 simulates a right atrium, the node of the second resistor 5 and the first circuit 1 simulates a right ventricle, the node of the third resistor 6 and the first circuit 1 simulates a left atrium, the node of the fourth resistor 7 and the first circuit 1 simulates a left ventricle, a first line 12 is connected between lines of the first capacitor 8 and the third capacitor 9, the node of the first line 12 and the first circuit 1 simulates respiratory muscles, and a pressure signal generator 13 is arranged on the first line 12;

a first diode 14 and a fifth resistor 15 are arranged on the second loop 2, the second loop 2 is connected to the first loop 1, wherein one end of the second loop 2 connected between the first capacitor 8 and the second capacitor 9 simulates a right pleura, one end of the second loop 2 connected between the second capacitor 9 and the second resistor 8 simulates a right alveolus, and one node between the first diode 14 and the fifth resistor 15 simulates a right alveolar branch;

a second diode 16 and a sixth resistor 17 are arranged on the third loop 3, the third loop 3 is connected to the first loop 1, wherein one end of the third loop 3 connected between the third capacitor 10 and the fourth capacitor 11 simulates a left pleura, one end of the third loop 3 connected between the fourth capacitor 11 and the fourth resistor 7 simulates a left alveolus, and one node between the second diode 16 and the sixth resistor 17 simulates a left alveolar branch.

A fourth line 18 is connected between the first resistor 4 and the third resistor 6, the contact node of the fourth line 18 and the first circuit 1 simulates a trachea carina, the contact node of the fourth line 18 and the fifth line 19 simulates a mouth, a ninth resistor 20 is arranged on the fourth line 18, a tenth resistor 21 and a fifth capacitor 22 are arranged on the fifth line 19, and one node between the tenth resistor 21 and the fifth capacitor 22 simulates a stomach.

A second line 23 is connected to a node simulating the right pleura, a seventh resistor 24 and a third diode 25 are arranged on the second line 23, and a node between the seventh resistor 24 and the third diode 25 simulates the right chest piece.

A third line 26 is switched in at a node simulating the left pleura, an eighth resistor 27 and a fourth diode 28 are arranged on the third line 26, and a node between the eighth resistor 27 and the fourth diode 28 simulates the left pleura.

Based on the circuit structure of the above-mentioned model of the respiratory system of the human body, the following embodiments of the present invention will explain the working principle of the model in detail.

Many mathematical models of mechanical ventilation use lumped parameter models that represent the entire ventilation process, including a small number of unknowns. The simplest lumped parameter model of mechanical ventilation assumes that the conductive regions can be identified by connecting a set of alveoli to the atmosphere and applying aerodynamic resistance to the conduit. This type of model can be solved with lower computational cost, thereby reducing runtime. This is an important requirement for whole body models and simulations. A disadvantage of lumped parameter models may be that the required circuit parameters may yield a large number of parameters. It is important to identify key features and behaviors of any model to intelligently reduce the number of parameters required.

The most important parameters in the mechanical ventilation lumped parameter model correspond to the elastic behavior of the lung and the flow resistance of the airway. The thoracic cage and lung tissue exhibit an elastic behavior, which may be represented by one or more compliances. Compliance C is calculated by the ratio of the volume δ V to the change in pressure δ P as:

as a first order approximation, the volume of the functional unit may be approximated as:

V(P+δP)＝V(P)+CδP

in the respiratory system, the main source of flow resistance comes from the air flow flowing through the branches in the conduction zone. A mathematical model using a lumped parameter model selects the functional units for these regions and assigns a variable R for the aerodynamic drag. The pressure drop Δ P over the respiratory tree can thus be calculated as

ΔP＝RQ

Where Q is the volume flow. The above relationship assumes that the flow is laminar and that the gas is incompressible. For laminar, viscous, and incompressible flows, the Hagen-Poiseuille equation relates the pressure drop Δ P in a fluid flowing through a cylindrical pipe of length l and radius r to

Wherein m is dynamic viscosity. By defining the flow resistance R as

A relationship similar to ohm's law can be derived.

The respiratory model represents the two lungs and associated airways as five major functional units or compartments, designated as carina, left and right anatomical dead space, and left and right alveoli, respectively. In the model, the carina compartment represents an anatomical region of the tracheal airway. The left and right anatomical dead space represent the bronchi and their branching bronchioles, which are part of the airways below the carina. The left and right alveolar chambers correspond to a collection of alveoli, with gas exchange occurring between the airway and the cardiovascular system. The left and right chest wall compartments represent the left and right sides of the chest wall, respectively. The new model also takes into account the pleural cavity caused by a circuit element that allows flow into the pleural cavity if it involves a respiratory tract injury that leaks gas from the alveoli or chest wall. To account for flow through the esophagus (as may occur during mechanical ventilation (positive pressure ventilation)), the model provides a lower compartment representing the esophagus and stomach. The model also includes a pressure signal generator representative of a respiratory muscle pressure source driver. The model provides a lower compartment representing the esophagus and stomach. The model also includes a pressure signal generator representative of a respiratory muscle pressure source driver. The model provides a lower compartment representing the esophagus and stomach. The model also includes a pressure signal generator representative of a respiratory muscle pressure source driver.

The state of the respiratory system includes: pretreatment, processing and post-treatment. In the "preprocessing" step, the compliance is updated, such as chest wall compliance of the left and right thorax varies with volume, different conditions and procedures are set, and breathing parameters and breathing drivers can be modified based on injury and intervention. The process uses a circuit solver to calculate the new state of the system, and a generic loop method developed for the engine to solve for the pressure on each node or path in the equivalent loop, with the material volume and volume fraction (concentration) also calculated at this step. The post-processing is used to prepare the system for the passage of time, moving all the content calculated in the processing from the next time step calculation to the current time step calculation. In this way, all other systems can access the information upon completion of the pre-processing analysis of the next step. The evaluation is referred to as external to the system to allow information to be collected from multiple systems. The respiratory system includes a pulmonary function test assessment.

A breathing circuit: the respiratory system specifies a set of functional elements or compartments to simulate mechanical ventilation. The functional elements are represented by electrical analog circuits consisting of resistors, capacitors, switches, diodes and power supplies. The latter represents the driving pressure from the respiratory muscles. Resistors and capacitors represent resistance to flow through the airway and the elasticity of the airway, alveoli and chest wall.

Closed circuits for the master and slave compartments are shown in fig. 1, depicting a muscle pressure source as a respiratory system driver, with greater effort modeled as higher pressures. The lower level compartment has an "infinite" resistor and behaves as an open electrical switch unless altered by damage and tampering.

The breathing circuit employs circuit nodes and paths to represent physiological state variables belonging to functional units of the respiratory system. In this representation, the pressure across the cell is assigned to the node, while all other variables (flow, volume, hydraulic resistance and compliance) are assigned to the paths on the circuit. At any time, R on the path across the flow Q resistance can use the pressure difference to calculate Δ P across the path as Q between nodes ═ Δ P/R. Similarly, the distance between the nodes to which the volume change Δ V path of the respiratory element with compliance C is connected may be calculated as Δ V ═ C Δ P based on the pressure difference Δ P.

Standard lung volume and volume: a number of standard lung volumes and volumes were measured at different stages of the normal and deep respiratory cycles. Inspiratory Reserve (IRV), tidal volume (V T), Expiratory Reserve (ERV) and Residual Volume (RV) correspond to four standard lung volumes. Inspiratory Capacity (IC), Forced Residual Capacity (FRC), spirometric capacity (V C) and total spirometric capacity (TLC) are four standard spirometric capacities consisting of two or more standard spirometric capacities. These volumes and volumes may be a good diagnosis of lung function, and the breathing model will report their values as output.

ERV＝FRC-RV。

The relationship between total lung volume and tidal volume is shown in fig. 2.

Transpulmonary pressure: defined as the difference between alveolar pressure and intrapleural pressure. The respiratory system derives the transpulmonary pressure from the calculated values of alveolar pressure and intrapleural pressure. Alveolar pressure was obtained by averaging the left and right alveolar pressures.

Pressure-volume (PV) curve: one method of characterizing lung elastic behavior is to use a graph that correlates lung volume changes with pleural pressure changes. The pressure-volume curve of a healthy person shows hysteresis during inspiration and expiration. The pressure-volume of the data extracted in the breathing model is shown in fig. 3. For comparison, the figure also shows a graph of PV replicated from the literature. These figures show a plot of lung volume change versus pleural pressure for one respiratory cycle. The pleural pressure of this model is the average of the left and right pleural pressures. The lung volume change corresponds to a change in total lung volume throughout the respiratory cycle. The breathing model mimics the expected hysteresis of the PV curve, as shown in fig. 4 and 5.

And (3) interaction relation: the respiratory system interacts with other physiological systems directly or indirectly through processes involving gas transport and exchange, including natural gas transport, the environment, alveolar gas exchange, drug action, metabolism, anesthesia machines linkage.

Conditions are as follows: different conditions of the respiratory system can be simulated by setting different conditions: including chronic obstructive pulmonary disease, lobar pneumonia, pulmonary fibrosis, and impaired pulmonary alveoli interaction.

The actions are as follows: different actions can also be taken to simulate the cardiovascular: including cardiac airway obstruction, bronchoconstriction, tracheal intubation, acute asthma, and tension pneumothorax.

Intervention measures are as follows: dressing, needle decompression, mechanical ventilation and oxygen supplement.

In summary, the breathing model provides a system-level computational model that can simulate normal lung physiology and respiratory distress in real-time. The model employs a circuit-based lumped parameter mathematical model that allows patient-specific respiratory mechanics to be characterized with a relatively low computational burden. By coupling the respiratory system to the circulatory system through gas exchange and respiratory distress modifiers, the effect of respiration on hemodynamic variables can be reliably predicted.

The above description is intended to be illustrative and not restrictive. For example, the above-described examples (or one or more versions thereof) may be used in combination with each other. For example, other embodiments may be utilized by those of ordinary skill in the art upon reading the foregoing description. In addition, in the foregoing detailed description, various features may be grouped together to streamline the disclosure. This should not be interpreted as an intention that a disclosed feature not claimed is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the detailed description as examples or embodiments, with each claim standing on its own as a separate embodiment, and it is contemplated that these embodiments may be combined with each other in various combinations or permutations. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. A human respiratory system model based on lumped parameters is characterized by comprising a first loop, a second loop and a third loop;

a first diode and a fifth resistor are arranged on the second loop, the second loop is connected into the first loop, wherein one end of the second loop, which is connected between the first capacitor and the second capacitor, simulates a right pleura, one end of the second loop, which is connected between the second capacitor and the second resistor, simulates a right alveolus, and one node between the first diode and the fifth resistor simulates a right alveolus branch chain;

2. The lumped-parameter based model of human respiratory system as defined in claim 1, wherein a fourth line is connected between the first resistor and the third resistor, a contact node of the fourth line and the first circuit simulates a carina of trachea, a contact node of the fourth line and the fifth line simulates a mouth, a ninth resistor is disposed on the fourth line, a tenth resistor and a fifth capacitor are disposed on the fifth line, and a node between the tenth resistor and the fifth capacitor simulates a stomach.

3. Lumped-parameter based human respiratory system model as claimed in claim 1, wherein a second line is connected at a node simulating the right pleura, a seventh resistor and a third diode are arranged on the second line, and a node between the seventh resistor and the third diode simulates the right pleura.

4. Lumped-parameter based model of the human respiratory system according to claim 1, characterized in that a third line is connected to the node simulating the left pleura, an eighth resistor and a fourth diode are arranged on the third line, and a node between the eighth resistor and the fourth diode simulates the left pleura.