Computer simulation of human respiratory droplets

Abstract

To provide a computer-aided technique, a computer system, and a preliminary computer program product for simulating human respiratory events.SOLUTION: A process 70 for conducting a multi-component fluid-flow simulation for a respiratory event originating at an entrance to the oropharynx is provided, the process comprising conducting (72) a geometrical analysis of a typical upper respiratory tract. A simulation engine produces (76) a respiratory event by combining exhalation rate profiles, particle distribution sizes, and concentration data. A boundary condition for the simulation of cough is established (74) assuming that the cough occurs deep inside the throat in or beyond the region of the oropharynx.SELECTED DRAWING: Figure 5

Description

[Background technology]

[0001] Human respiratory droplets are released when people breathe, talk, sing, cough, sneeze, etc. The ability to predict how these particles will disperse within the environment is useful for creating social distancing guidelines, making design changes to improve air quality, reducing the risk of infection, and generating effective personal protective equipment. Summary of the Invention

[0002] According to one aspect, a computer-implemented method performed by one or more computer systems includes accessing a model including a portion of a person's airway that models the person's airway as a volumetric region; initiating a respiratory event into the volumetric region, the respiratory event occurring in the accessed model at a depth within the modeled airway; simulating movement of elements of the respiratory event within the volumetric region, the elements representing particles of the respiratory event at an inlet boundary condition that represents an area of the model at a threshold depth within the airway; and obtaining from the simulation representations of trajectories of the particles of the respiratory event.

[0003] Embodiments of the computer-implemented method may include any one or more of the following features or other features disclosed herein.

[0004] The representation of the airway includes a model of the pharynx. The representation of the airway includes a model of an oropharyngeal region of the pharynx. The initiation occurs in a region representing the oropharyngeal region of the pharynx, and the simulation further includes simulating fluid flow of a respiratory event from the oropharyngeal region of the pharynx through the oral cavity and out of the person's mouth. The initiation occurs in a region representing the pharyngeal region of the pharynx, and the simulation further includes simulating fluid flow of a respiratory event from the pharyngeal region of the pharynx, through the oropharyngeal region, the oral cavity and out of the person's mouth. The simulated respiratory event is a cough.

[0005] According to an additional aspect, a computer system includes one or more processor devices, a memory coupled to the one or more processor devices, and storage storing executable computer instructions for performing a fluid simulation of a human respiratory event, the instructions being for configuring the one or more processors to: access a model including a portion of the airway that models the person's airway as a volumetric region; initiate a respiratory event into the volumetric region, the respiratory event occurring in the accessed model at a depth within the modeled airway; simulate movement of elements of the respiratory event within the volumetric region, the elements representing particles of the respiratory event at an inlet boundary condition that represents an area of the model that is at a threshold depth within the airway; and obtain from the simulation a representation of the trajectories of the particles of the respiratory event.

[0006] Embodiments of the computer system may include any one or more of the following features or other features disclosed herein.

[0007] The representation of the airway includes a model of the pharynx. The representation of the airway includes a model of an oropharyngeal region of the pharynx. Initiation occurs in a region representing the oropharyngeal region of the pharynx, and the instructions for simulating further include instructions for simulating fluid flow of a respiratory event from the oropharyngeal region of the pharynx through the oral cavity and out of the person's mouth. The system is further configured to initiate in a region representing the pharyngeal-laryngeal region of the pharynx, and the simulation is further configured to simulate fluid flow of a respiratory event from the pharyngeal region of the pharynx, through the oropharyngeal region, the oral cavity and out of the person's mouth. The respiratory event is a cough.

[0008] According to a further aspect, a computer program product tangibly stored on a computer-readable non-transitory storage device storing executable computer instructions for simulating a human respiratory event, the instructions causing a computing system to: access a model including a portion of the airway that models the person's airway as a volumetric region; initiate a respiratory event into the volumetric region, the respiratory event occurring in the accessed model at a depth within the modeled airway; simulate movement of elements of the respiratory event within the volumetric region, the elements representing particles of the respiratory event at an inlet boundary condition that represents an area of the model that is at a threshold depth within the airway; and obtain from the simulation a representation of the trajectories of the particles of the respiratory event.

[0009] Embodiments of the computer program product may include any one or more of the following features or other features disclosed herein.

[0010] The representation of the airway includes a model of the pharynx. The representation of the airway includes a model of an oropharyngeal region of the pharynx. The instructions to actuate occur in a region representing the oropharyngeal region of the pharynx, the instructions further including instructions for simulating fluid flow of a respiratory event from the oropharyngeal region of the pharynx through the oral cavity and out of the person's mouth. The instructions further include instructions to actuate in a region representing the pharyngeal-laryngeal region of the pharynx, and the instructions to simulate further including instructions for simulating fluid flow of a respiratory event from the pharyngeal region of the pharynx, through the oropharyngeal region, the oral cavity and out of the person's mouth. The simulated respiratory event is a cough.

[0011] One or more of the above aspects can provide one or more of the following advantages.

[0012] Simulations using the above method provide realistic respiratory droplet clouds. These clouds are much more dispersed than those from other methods and represent experimentally imaged respiratory clouds. Other methods tend to underpredict droplet dispersion. By having an inlet boundary condition inside the throat, it is not necessary to set a cone angle based on experimental results or introduce artificial turbulence to achieve a realistic cough. In fact, these characteristics are measures that can verify the accurate simulation of respiratory events.

[0013] The above technique is also applicable to lattice Boltzmann methods, including finite volume methods, finite element methods, and other computational fluid dynamics methods.

[0014] Other features and advantages of the invention will become apparent from the following description and claims. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 illustrates a system for simulation of respiratory events. [Figure 2] 1 is an image showing the state of a person's upper respiratory tract. [Figure 3] FIG. 1 illustrates conventional modeling of respiratory events. [Figure 4] FIG. 1 illustrates an alternative technique for modeling respiratory events. [Figure 5] 5 is a flow diagram of a process for modeling the respiratory events of FIG. 4. [Figure 6] FIG. 1 illustrates simulated coughing behavior. [Figure 7] FIG. 1 illustrates simulated coughing behavior. [Figure 8] 1 is a graph showing cough flow versus time. [Figure 9] FIG. 1 illustrates velocity components of two LBM models (prior art). [Figure 10] FIG. 1 illustrates velocity components of two LBM models (prior art). [Figure 11] 2 is a flowchart of the procedure followed by the simulation system of FIG. 1. [Figure 12] FIG. 1 is a perspective view of a microblock (prior art). [Figure 13A] FIG. 2 is a diagram of a grating structure used by the system of FIG. 1 (prior art). [Figure 13B] FIG. 2 is a diagram of a grating structure used by the system of FIG. 1 (prior art). [Figure 14] FIG. 1 illustrates variable decomposition technique (prior art). [Figure 15] FIG. 1 illustrates variable decomposition technique (prior art). [Figure 16] FIG. 1 shows the area affected by surface facets (prior art). [Figure 17A-B] FIG. 1 illustrates a cough simulated by placing boundary conditions outside the mouth and inside the mouth (prior art). [Figure 18] FIG. 1 illustrates a cough simulated by placement of boundary conditions at the oropharynx exit. [Figure 19A-B] FIG. 19 shows details of the cough cloud for the placement of boundary conditions at the oropharynx exit of FIG. 18. DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring to Figure 1, a system 10 for simulating respiratory events is shown. Simulations can be performed for a variety of purposes, such as creating social distancing guides, making design changes to improve air quality, reducing the risk of infection, and for generating effective personal protective equipment. The focus of the discussion herein is on simulating coughs as respiratory events. The cough simulation is initiated at a location within a person's airway.

[0017] Generally, system 10 in this embodiment is based on a client-server or cloud-based architecture and includes a server system 12 implemented as a massively parallel computing system 12 (standalone or cloud-based) and a client system 14. Server system 12 includes memory 18, a bus system 11, an interface 20 (e.g., a user interface / network interface / display or monitor interface, etc.), and a processing device 24.

[0018] In the example of a cough simulation, memory 18 includes a breathing engine 32 that operates on a digital representation 40' of a person's airway 40 (FIG. 2), which digitally represents various spaces and objects in the person's airway 40 (FIG. 2). The digital representation 40' of a user's airway 40 (FIG. 2) also includes the person's throat. The digital representation 40' of a user's airway 40 (FIG. 2) includes the person's throat, including the nasopharynx, oropharynx, and laryngopharynx portions of the throat (FIG. 2, see description below). System 10 requires that the digital representation 40' of a person's airway 40 (FIG. 2) include the mouth and throat portions of the person's airway. Within the throat portion of the person's airway 40 (FIG. 2) are boundary conditions for initiating a respiratory event, such as a cough.

[0019] One approach to providing a digital representation 40' of a person's airway is to obtain the digital representation 40' from a model generated by a third party.

[0020] The memory 18 may also store other parameters such as fluid characteristics 33a, for example, characteristics of oral fluids (e.g., saliva) that coat various objects in the mouth. The memory 18 also stores parameters such as mucus membranes that secrete mucus.

[0021] The system 10 has access to a data repository 38 that stores 2D and / or 3D meshes, coordinate systems, and libraries that can be used for respiratory event simulation using any known computational technique, such as computational fluid dynamics or the so-called lattice Boltzmann method.

[0022] The respiratory engine 32 initiates a cough, i.e., a respiratory event, in the throat, e.g., the pharyngeal portion of the airway. In one embodiment, the pharyngeal portion is limited to the mesopharyngeal and laryngopharyngeal portions of the pharynx. In other embodiments, the nasopharyngeal portion of the pharynx can be used to simulate a sneeze and / or cough.

[0023] Referring momentarily to FIG. 2, a diagram of a person's upper airway 40 is shown. The diagram was adapted from an image available at https: / / en.wikipedia.org / wiki / Respiratory_tract. The diagram of the person's airway 40 represents a living person. The representation 40 is converted into a digital representation 40' of the person's airway, which is used to perform the simulation. Major objects within the person's airway 40 are labeled with names. Among these major objects, some are labeled with names and reference letters and include the mouth 42a and lips 42b. Other major objects, also labeled with names and reference letters, include the throat, e.g., the pharynx 52, including the nasopharynx 52a, the oropharynx 52b, and the laryngopharynx 52c. Other portions of the upper airway 40 include the hard palate, the soft palate, the teeth (not labeled), the fluid membrane, the oral cavity, including at least the oral cavity proper, and the vestibular portion of the oral cavity (not labeled).

[0024] Referring now to FIG. 3 , as is conventionally understood, a simulation event is modeled as occurring at the exit of a person's mouth 42 a, e.g., lips 42 b. That is, a so-called inlet boundary condition 45 occurs at the mouth exit, e.g., lips 42 b. Therefore, to achieve a realistic cough simulation, users of the system 10 must set cone angles 44 (α), 46 (β1), and 48 (β2) based on experimental results and introduce artificial turbulence. Typically, a cough setup has an ovoid or spherical inlet boundary condition 45. The inlet is located directly in front of or inside the mouth opening, as shown. The user specifies angles α, β1, and β2 so that the inlet boundary condition achieves the desired conical shape. This can be done by varying the inlet velocity condition or through control of the radius and solid angle of the spherical inlet shape. For a higher-fidelity simulation, artificial turbulence must be introduced to generate the cough structure. However, this is often ignored. (See the article entitled "Flow Dynamics and Characterization of a Cough" by Jitendra K. Gupta et al., published in Indoor Air, 19, 517-525 (2009), which is incorporated herein by reference.)

[0025] 4, as used herein, a simulation event, e.g., a cough, is modeled as occurring within a person's throat or pharynx 52. More specifically, the simulation engine 34 initiates the modeled cough from at least a portion of the person's throat around the exit of the oropharynx 52b, e.g., the rear corners of the oral cavity, to ensure proper flow development. In some embodiments, cough initiation occurs at the entrance to the oropharynx 52b or the entrance to the laryngopharynx 52c of the pharynx 52. In terms of computer-generated simulation, the initiation point of the cough is a so-called "boundary condition 60."

[0026] By moving the inlet boundary condition 55 from the mouth to an inlet boundary condition 60 inside the throat 52, it is no longer necessary to specify a specific cone angle or solid angle at the inlet. The inlet becomes a mass flow inlet boundary condition. Also, it is no longer necessary to introduce artificial turbulence because the simulated flow through the throat and mouth geometry generates these structures. Therefore, the angles α, β1, and β2 specified in the above paper now become simulation results and can be used to verify cough results.

[0027] The deep cough boundary conditions 60 within the airway allow turbulent structures in the fluid flow to develop naturally during the simulation, resulting in cough structures with more realistic intensities and length scales than would be possible if they were artificially generated.

[0028] The development of these cough structures can be captured using high-fidelity flow simulations, such as PowerFLOW, available from Dassault Systems SIMUOLIA Corp. Correct modeling of these cough structures improves the accuracy of respiratory droplet dispersion into the environment.

[0029] 5, a process 70 for performing a multi-component fluid flow simulation for a respiratory event occurring at least at the entrance to the oropharynx 52b is shown. The process 70 uses a simulation of a human upper airway as an example. The process 70 includes performing a geometric analysis 72 of the general upper airway using an x-ray or other type of image to identify various objects that are modeled in the upper airway under study.

[0030] The simulation engine generates respiratory events by combining exhalation velocity profiles, particle distribution size, and concentration data. (76) One example is to obtain these data from the literature. These data are used to approximate exhalation events.

[0031] The decisions regarding where to place the boundary conditions for particle and airflow introduction, when guided by prior literature, result in a histogram of particle size distribution, but do not specify the timing at which these different sized particles are released. Furthermore, the initial velocity of the particles is not specified. The concentration data available from the literature are also average data, which do not include information about the time variation of respiratory droplets during an event.

[0032] The method described here establishes boundary conditions for cough simulation as occurring deep within the throat, in the oropharynx region or beyond. (74) The need for an entrance so deep within the airway allows for the turbulent flow structures of the flow through the remainder of the upper airway to develop naturally according to the model of the airway. This results in cough structures with more realistic intensities and length scales than would be possible if they were artificially generated.

[0033] Upon generating a respiratory event, the process performs a complete simulation of the generated event by propagating the event through a model of the upper airway of person 40 .

[0034] 6 shows velocity slices 80 of a cough occurring in the oropharynx, generated by process 76. This shows an example of how the resulting flow interacts with the characteristics of the mouth to develop a cough jet output from mouth 42a.

[0035] Figure 7 shows a volumetric visualization of droplet concentration 82, which shows how the cough jet disperses particles.

[0036] These images are compared to results shown in Gupta, J., Lin, C.-H. and Chen, Q. 2009 "Flow dynamics and characterization of a cough" Indoor Air, 19, 517-525.

[0037] A thermal study was also included, where breaths were introduced at temperatures above ambient or close to the subject's internal temperature. The particle size distribution used in the model is a normal distribution centered at 0.3 μm and fitted to the diameter data of Zayas et al. (2012). This distribution was chosen because it captures smaller particles than other previous experiments due to improvements in measurement techniques.

[0038] As shown in Figure 8, the cough can be two coughs with flow rate fluctuations over time taken from Gupta, Lin, and Chen (2009).

[0039] Simulation examples are described in the following discussion. Figures 9, 10, and 12-16 are labeled as "Prior Art" because these figures can be found in other applications / patents of the assignee. However, the above discussion is not found in those applications. The following discussion is one way of simulating a cough event. Other simulation techniques may be used.

[0040] Referring to Figure 9, the first model (2D-1) 100 is a two-dimensional model containing 21 velocities. Of the 21 velocities, one (105) represents a particle that is not moving, three sets of four velocities represent particles moving at normalized velocity (r) (110-113), twice the normalized velocity (2r) (120-123), or three times the normalized velocity (3r) (130-133) in either the positive or negative direction along either the x or y axis of the grid, and two sets of four velocities represent particles moving at normalized velocity (r) (140-143), twice the normalized velocity (2r) (150-153) relative to both the x and y grid axes.

[0041] 10, the second model (3D-1) 200 is a three-dimensional model that includes 39 velocities, where each velocity is represented by one of the arrowheads in FIG. 8. Of the 39 velocities, one represents a particle that is not moving, three sets of six velocities represent particles moving at a normalized velocity (r), twice the normalized velocity (2r), or three times the normalized velocity (3r) in either the positive or negative direction along the x, y, or z axis of the grid, eight represent particles moving at a normalized velocity (r) with respect to all three of the x, y, and z grid axes, and twelve represent particles moving at twice the normalized velocity (2r) with respect to two of the x, y, and z grid axes.

[0042] More complex models may also be used, such as a 3D-2 model containing 101 velocities, or a 2D-2 model containing 37 velocities. The velocities are more clearly represented by their components along each axis, as recorded in Tables 1 and 2, respectively.

[0043] For the 3D model 3D-2, there are 101 velocities; one represents particles that are not moving (group 1); three sets of six velocities represent particles moving at normalized velocity (r), twice the normalized velocity (2r), or three times the normalized velocity (3r) in either the positive or negative direction along the x, y, or z axis of the lattice (groups 2, 4, and 7); and three sets of eight velocities represent particles moving at normalized velocity (r), twice the normalized velocity (2r), or three times the normalized velocity (3r) for all three of the x, y, and z lattice axes. 12 represent particles moving at twice the normalized velocity (2r) along two of the x, y, and z lattice axes (Group 6); 24 represent particles moving at normalized velocity (r) and twice the normalized velocity (2r) along two of the x, y, and z lattice axes and not moving along the remaining axes (Group 5); and 24 represent particles moving at normalized velocity (r) along two of the x, y, and z lattice axes and three times the normalized velocity (3r) along the remaining axes (Group 9).

[0044] For the 2D model 2D-2, there are 37 velocities: one representing non-moving particles (group 1); three sets of four velocities representing particles moving at normalized velocity (r), twice the normalized velocity (2r), or three times the normalized velocity (3r) in either the positive or negative direction along either the x or y axis of the lattice (groups 2, 4, and 7); two sets of four velocities representing particles moving at normalized velocity (r) or twice the normalized velocity (2r) relative to both the x and y lattice axes; eight velocities representing particles moving at normalized velocity (r) relative to one of the x and y lattice axes and twice the normalized velocity (2r) relative to the other axis; and eight velocities representing particles moving at normalized velocity (r) relative to one of the x and y lattice axes and three times the normalized velocity (3r) relative to the other axis.

[0045] The LBM model described above provides a specific class of efficient and robust discrete velocity kinetic models for the numerical simulation of flows in both two and three dimensions. This type of model contains a specific set of discrete velocities and weights associated with these velocities. The velocities correspond to Cartesian grid points in velocity space, which facilitates accurate and efficient implementation of discrete velocity models, particularly the type known as lattice Boltzmann models. Such models can be used to simulate flows with high fidelity.

[0046] Referring to FIG. 11 , a physical process simulation system operates according to procedure 300 to simulate a physical process, such as fluid flow resulting from a cough. Prior to simulation, a simulation space is modeled as a collection of voxels using the cough setup of FIG. 4 (step 302). Typically, the simulation space is generated using a computer-aided design (CAD) program. For example, the CAD program can be used to depict the upper airway of a person positioned in a room. The data generated by the CAD program is then processed to add a grid structure with appropriate resolution and to account for objects and surfaces within the airway simulation space.

[0047] The grid resolution can be selected based on the Reynolds number, which is related to the velocity of the flow (v), the characteristic length of an object in the flow (L), and the characteristic velocity of the flow (u). Re=uL / ν Equation (I-3)

[0048] The characteristic length of the object in the airway represents the object seen in the airway. The resolution of the simulation event can be increased or an area of increased resolution can be used around the region of interest. The voxel dimensions decrease as the grid resolution increases.

[0049] The state space is f i (x,t), where f i represents the number of elements or particles per unit volume in state i (i.e., the density of particles in state i) at the lattice site described by the three-dimensional vector x at time t. For a known time increment, the number of particles is simply f i The combination of all states of the lattice site is denoted as f(x).

[0050] The number of states is determined by the number of possible velocity vectors within each energy level. A velocity vector consists of integer linear velocities in a space with three dimensions x, y, and z. The number of states is increased for multi-species simulations.

[0051] Each state i represents a different velocity vector at a particular energy level (i.e., energy level 0, 1, or 2). The velocity c of each state i is expressed in terms of its "velocity" in each of the three dimensions as follows: c i =(c i,x ,c i,y ,c i,z ) Formula (I-4)

[0052] The energy level 0 state represents a stationary particle that is not moving in any dimension, i.e., c stopped =(0,0,0). Energy level 1 states represent particles with velocities of ±1 in one of the three dimensions and 0 in the other two. Energy level 2 states represent particles with velocities of ±1 in all three dimensions, or ±2 in one of the three dimensions and 0 in the other two.

[0053] Generating all possible permutations of the three energy levels results in a total of 39 possible states (1 energy 0 state, 6 energy 1 states, 8 energy 3 states, 6 energy 4 states, 12 energy 8 states, and 6 energy 9 states).

[0054] Each voxel (i.e., each lattice site) is represented by a state vector f(x). The state vector completely defines the status of the voxel and contains 39 entries. The 39 entries correspond to one energy 0 state, six energy 1 states, eight energy 3 states, six energy 4 states, twelve energy 8 states, and six energy 9 states. Using this set of velocities, the system can generate Maxwell-Boltzmann statistics for the achieved equilibrium state vector.

[0055] Referring now to Figure 12, a microblock is shown. For efficiency of processing, voxels are grouped into 2x2x2 volumes called microblocks. The microblocks are organized to allow parallel processing of the voxels and minimize the overhead associated with the data structure. A shorthand notation for the voxels in a microblock is N i (n), where n represents the relative position of the lattice site within the microblock, n∈{0, 1, 2, ..., 7}.

[0056] 13A and 13B, a surface S (FIG. 13A) is defined in the simulation space (FIG. 13B) by a facet F α It is represented as a set of S = {Fα} Equation (I-5) where α is an index that lists a particular facet. Facets are not constrained by voxel boundaries and are typically on the order of the size of the voxels adjacent to them, or slightly smaller, allowing a facet to affect a relatively small number of voxels. Properties are assigned to facets for the purposes of implementing surface dynamics. In particular, each facet F α is the unit normal (n α ) and surface area (A α ) and the central location (x α ) and the facet distribution function (f i (α)).

[0057] 14, different levels of resolution can be used in different regions of the simulation space to improve processing efficiency. Typically, the region 650 around the object 655 is of the most interest and is therefore simulated at the highest resolution. Because the effect of viscosity decreases with distance from the object, decreasing levels of decomposition (i.e., expanded voxel volumes) are used to simulate regions 660, 665 spaced at increasing distances from the object 655.

[0058] Similarly, as shown in Figure 15, a lower level of decomposition can be used to simulate regions 770 around less important features of an object 775, while the highest level of resolution is used to simulate regions 780 around the most important features (e.g., the front and back surfaces) of the object 775. An off-center region 785 is simulated using the lowest level of resolution and the largest voxels.

[0059] Identifying voxels affected by facets Referring again to Figure 11, once the simulation space is modeled (step 302), voxels that are influenced by one or more facets are identified (step 304). A voxel may be influenced by a facet in several ways. First, voxels that intersect with one or more facets are influenced in that the voxel has a reduced volume relative to non-intersecting voxels. This occurs because the facet, and the material underlying the surface represented by the facet, occupies a fraction of the voxel. A fractional factor P f (x) indicates the portion of the voxel that is not affected by the facet (i.e., the portion that can be occupied by the fluid or other material whose flow is being simulated). For non-intersecting voxels, P f (x) is equal to 1.

[0060] Voxels that intersect with one or more facets by transferring particles to the facet or receiving particles from the facet are also identified as voxels influenced by the facet. All voxels that intersect with a facet contain at least one state that receives particles from the facet and at least one state that transfers particles to the facet. In most cases, additional voxels will also contain such states.

[0061] Referring to Figure 16, a non-zero velocity vector c i For each state i with facet F αis a particle with a velocity vector c i and the unit normal of the facet n α The magnitude of the vector dot product (|c i n i |) and the parallelepiped G iα Volume V iα The surface area of the facet, A, is equal to α A parallelepiped G with a base defined by iα Received from or transferred to the area defined by V iα =|c i n α |A α Formula (I-6)

[0062] Facet F α is the velocity vector of the state when it moves towards the facet (|c i n i |<0), volume V iα When a particle is received from the facet and the velocity vector of the state is pointing away from the facet (|c i n i |>0), transporting the particle into the region. As discussed below, this representation is iα must be modified when it occupies a portion of , which is a condition that can arise in the vicinity of non-convex features such as interior angles.

[0063] Facet F α Parallelepiped G iα can overlap some or all of multiple voxels. The number of voxels or portions thereof depends on the size of the facet relative to the size of the voxel, the energy of the state, and the orientation of the facet relative to the lattice structure. The number of affected voxels increases with the size of the facet. Therefore, as mentioned above, the size of the facet is typically chosen to be on the order of or smaller than the size of the voxels located near the facet.

[0064] parallelepiped G iαThe part of the voxel N(x) where V overlaps is iα (x). Using this term, we can calculate the relationship between voxel N(x) and facet F α The flux Γ of particles in state i moving between iα (x) is the density of particles of state i in a voxel (N i (x)) and the volume of the area overlapping with the voxel (V iα It is equal to multiplying (x) by (x). Gamma iα (x)=N i (x)V iα (x) Formula (I-7)

[0065] parallelepiped G iα When intersects with one or more facets, the following conditions are true: V iα =ΣV α (x)+ΣV iα (β) Formula (I-8) where the first summation is G iα The second term considers all voxels that overlap with G iα Consider all facets that intersect with the parallelepiped G iα When does not intersect with another facet, this expression reduces to: V iα =ΣV iα (x) Formula (I-9)

[0066] Running the simulation Once voxels affected by one or more facets are identified (step 304), a timer is started to begin the simulation (step 306). During each time increment of the simulation, particle movement between voxels is simulated by an advection stage that takes into account particle interactions with surface facets (steps 308-316). Next, an impact stage (step 318) simulates particle interactions within each voxel. A timer is then incremented (step 320). If the incremented timer does not indicate that the simulation is complete (step 322), the advection and impact stages (steps 308-320) are repeated. If the incremented timer indicates that the simulation is complete (step 322), the results of the simulation are stored and / or displayed (step 324).

[0067] Figures 17A and 17B show simulated cough jets with boundary condition configurations outside the mouth (Figure 17A) and inside the mouth (Figure 17B). In Figure 17A, the cough jet is not deflected downward enough and does not disperse correctly in agreement with experimental observations. In Figure 17B, the cough jet is an improvement over Figure 17A, but still does not deflect downward enough and does not disperse correctly according to experimental observations.

[0068] Figure 18 shows the simulated cough jet with the boundary condition placement at the oropharynx exit. In Figure 18, the cough jet is now deflected downward, matching the experimental observations, where the angle for the cough cloud is correct, as also shown in Figure 19B. The flow angle, velocity, and momentum of both the case phase and the particle phase exiting the mouth are available for post-processing.

[0069] FIG. 19A shows side and front views of the cough jet for the placement of boundary conditions at the mouth exit of FIG. 17A.

[0070] FIG. 19B shows side and front views of the cough jet with respect to the placement of boundary conditions in the oropharyngeal region of the pharynx as in FIG. 17B (similar to FIG. 7, but with angles shown).

[0071] Embodiments of the subject matter and functional operations described herein can be implemented in digital electronic circuitry, tangibly embodied computer software or firmware, computer hardware (including the structures disclosed herein and structural equivalents thereof), or a combination of one or more of them. Embodiments of the subject matter described herein can be implemented as one or more computer programs (i.e., one or more modules of computer program instructions encoded on a tangible non-primary program carrier for execution by or control of the operation of a data processing apparatus). A computer storage medium can be a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them.

[0072] A computer program, which may also be referred to or described as a program, software, software application, module, software module, script, or code, can be written in any type of programming language, including compiled or interpreted, or declarative or procedural, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can correspond to a file in a file system, but this is not required. A program can be stored as part of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document, a single file dedicated to the program in question, or multiple organized files (e.g., files storing one or more modules, subprograms, or portions of code)). A computer program can be deployed so that the program is executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a data communications network.

[0073] A computer suitable for running a computer program can be based on a general-purpose microprocessor, a special-purpose microprocessor, or both, or any other type of central processing unit. Generally, the central processing unit receives instructions and data from a read-only memory, a random-access memory, or both. The essential elements of a computer are a central processing unit for performing or executing instructions, and one or more memory devices for storing instructions and data. Generally, a computer also includes, or is operatively coupled to, one or more mass storage devices for storing data (including, for example, magnetic disks, magneto-optical disks, or optical disks), so as to receive data from, transfer data to, or both. However, a computer need not have such devices.

[0074] Computer-readable media suitable for storing computer program instructions and data include, by way of example, all forms of non-volatile memory and memory devices on a medium, including semiconductor memory devices (e.g., EPROM, EEPROM, and flash memory devices), magnetic disks (e.g., internal hard disks or removable disks), magneto-optical disks, and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, dedicated logic circuitry. [Explanation of symbols]

[0075] 10 Systems 11 Bus System 12 Server Systems 18 Memory 20 Interface 24 Processing Device 32 Breathing Engine 33a Fluid properties 34 Simulation Engine 38 Data Repositories 40 Airway 40' Digital Representation 42a mouth 42b lips 52 Pharynx 52a Nasopharynx 52b Oropharynx 52c Larynx

Claims

1. 1. A method executed by one or more computer systems for simulating a respiratory event, the method comprising: digitally processing, by one or more computer systems, one or more images of the person's airway to identify one or more objects in the person's airway being modeled; generating, by the one or more computer systems, a model including a portion of the person's airway based on the one or more objects identified in the one or more digitally processed images, the airway being represented as a volumetric region including a plurality of voxels, the model having a higher resolution level for one or more regions of interest in the model than for one or more regions of the model outside the one or more regions of interest; initiating a respiratory event into the volumetric region by simulating a cough in the volumetric region with the one or more computer systems, the simulated cough occurring in the generated model at a depth within the modeled airway; simulating, with the one or more computer systems, movement of elements of the respiratory event within the volumetric volume, the elements representing particles of the respiratory event at an inlet boundary condition occurring at one or more voxels representing an oropharyngeal or laryngopharyngeal region of the person's airway; obtaining, by the one or more computer systems, a visual representation of particle trajectories of the respiratory event from the simulation; and displaying, by the one or more computer systems, the visual representation on a display device, including the simulated movement of particles of the respiratory event within the volumetric region by displaying in a user interface one or more regions of the visual representation corresponding to the one or more regions of interest in the model having a higher resolution level than one or more regions of the visual representation corresponding to the one or more regions of the model outside the one or more regions of interest; A method comprising:

2. The method of claim 1 , wherein the visual representation of the airway includes a model of the pharynx.

3. The method of claim 2 , wherein the visual representation of the airway includes a model of the oropharyngeal region of the pharynx.

4. The starting point occurs in a region representing the mid-pharyngeal region of the pharynx, and the simulation is The method of claim 1 , further comprising simulating fluid flow of the respiratory event from the oropharyngeal region of the pharynx through an oral cavity and out of a person's mouth.

5. The starting point occurs in a region representing the pharynx and the simulation is The method of claim 1 , further comprising simulating fluid flow of the respiratory event from the pharyngeal and laryngopharyngeal region of the pharynx, through the oropharynx region, through the oral cavity, and out the person's mouth.

6. 1. A computer system comprising: one or more processor devices; a memory coupled to the one or more processor devices; 1. A storage medium storing executable computer instructions for simulating human respiratory events, the instructions comprising: digitally processing one or more images of the person's airway to identify one or more objects in the person's airway to be modeled; generating a model including a portion of the person's airway based on the one or more objects identified in the one or more digitally processed images, the model modeling the airway as a volumetric region including a plurality of voxels, the model having a higher resolution level for one or more regions of interest in the model than for one or more regions of the model outside the one or more regions of interest; initiating a respiratory event into the volumetric region by simulating a cough in the volumetric region with the one or more computer systems, the simulated cough occurring in the generated model at a depth within the modeled airway; simulating movement of elements of the respiratory event within the volumetric volume, the elements representing particles of the respiratory event at an inlet boundary condition occurring at one or more voxels representing an oropharyngeal or laryngopharyngeal region of the person's airway; obtaining a visual representation of particle trajectories of the respiratory event from the simulation; displaying the visual representation on a display device, the visual representation including the simulated movement of particles of the respiratory event within the volumetric region, by displaying in a user interface one or more regions of the visual representation corresponding to the one or more regions of interest in the model having a higher resolution level than one or more regions of the visual representation corresponding to the one or more regions of the model outside the one or more regions of interest; 2. A computer system for configuring the one or more processors to perform:

7. The system of claim 6 , wherein the visual representation of the airway includes a model of the pharynx.

8. The system of claim 7 , wherein the visual representation of the airway includes a model of the oropharyngeal region of the pharynx.

9. The system comprises: and further configured to initiate a respiratory event in a region representing an oropharyngeal region of the pharynx, the system comprising:

7. The system of claim 6, further configured to simulate fluid flow of the respiratory event from the oropharyngeal region of the pharynx through the oral cavity and out of the person's mouth.

10. The system comprises: and further configured to initiate in a region representative of the pharynx-laryngopharyngeal region of the pharynx, the system comprising:

7. The system of claim 6, further configured to simulate fluid flow of the respiratory event from the laryngopharyngeal region of the pharynx, through the oropharynx region, through the oral cavity and out the person's mouth.

11. A computer program tangibly stored on a computer-readable non-transitory storage device storing executable computer instructions for simulating human respiratory events, the instructions comprising: digitally processing one or more images of the person's airway to identify one or more objects in the person's airway to be modeled; generating a model including a portion of the person's airway based on the one or more objects identified in the one or more digitally processed images, the airway being represented as a volumetric region including a plurality of voxels, the model having a higher resolution level for one or more regions of interest in the model than for one or more regions of the model outside the one or more regions of interest; initiating a respiratory event into the volumetric region by simulating a cough in the volumetric region with the one or more computer systems, the simulated cough occurring in the generated model at a depth within the modeled airway; simulating movement of elements of the respiratory event within the volumetric volume, the elements representing particles of the respiratory event at an inlet boundary condition occurring at one or more voxels representing an oropharyngeal or laryngopharyngeal region of the person's airway; obtaining a visual representation of particle trajectories of the respiratory event from the simulation; displaying the visual representation on a display device, the visual representation including the simulated movement of particles of the respiratory event within the volumetric region, by displaying in a user interface one or more regions of the visual representation corresponding to the one or more regions of interest in the model having a higher resolution level than one or more regions of the visual representation corresponding to the one or more regions of the model outside the one or more regions of interest; A computer program that performs the following:

12. The computer program of claim 11 , wherein the visual representation of the airway includes a model of the pharynx.

13. The computer program of claim 12 , wherein the visual representation of the airway includes a model of the oropharyngeal region of the pharynx.

14. The actuating command occurs in a region representing the oropharyngeal region of the pharynx, said command comprising:

12. The computer program of claim 11, further comprising instructions for simulating fluid flow of the respiratory event from the oropharyngeal region of the pharynx through the oral cavity and out of the person's mouth.

15. The instruction: and further including instructions to start in a region representing the pharynx-laryngopharyngeal region of the pharynx, the instructions to simulate comprising:

12. The computer program of claim 11, further comprising instructions for simulating fluid flow of the respiratory event from the laryngopharyngeal region of the pharynx, through the oropharynx region, through the oral cavity and out the person's mouth.

16. The method of claim 1 , wherein the simulated cough is based on a combination of exhalation velocity profile, particle distribution size and concentration data.

17. 2. The method of claim 1, wherein the model including one or more smaller voxels in the one or more regions of interest and one or more larger voxels in the one or more regions outside the one or more regions of interest improves processing efficiency of triggering the respiratory event by the one or more computers and simulating the movement of the element by the one or more computers compared to a model including uniformly sized voxels.

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