Introduction
Enclosed is your report with the simulation results of the airflow inside the nasal cavity using Computational Fluid Mechanics (CFD) and Virtual Surgery (VS) techniques.
CFD is a field of Physics (Fluid Mechanics) that uses computers to solve problems involving fluid flows. The huge computational power of computers is used by Flowgy to calculate the millions of operations required to solve the interaction of air flow with the complex and unique geometry of the nasal cavity.
CFD and VS techniques are, unlike techniques such as rhinomanometry or acoustic rhinometry, non-invasive and allow you to modify the geometry of the patient’s nostrils as many times as you wish, and then analyze and compare the functional results, thus allowing you to optimize and at the same time predict surgical results.
The starting point for CFD and VS analysis is a CT scan or similar of the patient. From this CT scan, an optimized 3D model of the nasal cavity is obtained for the simulation of the airflow inside the nasal cavity and the virtual surgery.
After solving the air flow, Flowgy extracts the fields of the fluid variables (pressure, temperature, velocity, humidity, etc.) resulting from the simulation, and presents them in the form of tables, graphs, images, etc. in a way that makes their reading and interpretation an easy task.
How can this report help you?
The results of these simulations will provide you with valuable objective and quantitative information about the real behavior of the air in the nasal cavity, which will help you in your daily clinical practice to accurately detect the different alterations in the upper airway tract of your patients, serving as a support for diagnosis and decision making.
OBSERVATIONS – FUNCTIONAL CFD STUDY
The flow in inspiration has been solved using computational fluid mechanics techniques (CFD) on the geometry of the nasal cavity of the patient. The geometry was obtained from a CT scan provided by the patient directly.
The CFD solution obtained indicates a severe obstruction of the nasal cavity (right nostril).
The inspiration flow presents a very high flow asymmetry, with a very high volumetric flow in the left nostril
relative to the right nostril.
Resistance is normal, although a very high resistance is seen in the right nostril compared to a very low
resistance in the left nostril.
OBSERVATIONS – VIRTUAL SURGERY CFD STUDY
The ENT specialist has performed 4 virtual surgeries. The results of the CFD analysis of all surgeries have allowed the specialist to determine the optimal surgery for his patient. The selected surgery is the one that provides the least invasive and the best results to improve the patient s obstruction.
Virtual Surgery
Through virtual surgery we can simulate a surgical intervention, removing tissue, adding air or simply deforming the anatomical structure with total freedom, either on the CT scan itself or on a three-dimensional model of the patient’s head (generated from the CT scan).
Once the virtual surgery has been performed, we solve the CFD flow in the postoperative nasal cavity and compare the functional respiratory results of the new anatomical structure with the CFD data of the functional study. This comparison should indicate whether or not the surgery will result in a functional improvement in the patient’s respiratory capacity.
Images corresponding to the virtual surgery performed. The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
CFD Results
For the CFD simulation, a three-dimensional digital model of the patient’s nasal cavity will be created from the CT data provided.
On the generated three-dimensional model a stationary laminar inspiratory flow is simulated to solve the RANS equations, which will provide us with the CFD analysis values: Flow, Pressure, Nasal Resistance, Temperature, Velocity, etc.
All the resulting data are post-processed for visual representation. Likewise, in order to guarantee its easy interpretation, the engineering terminology is adapted to a medical language.
DATA FROM CFD SOLUTION AND VIRTUAL SURGERY
Computational Fluid Dynamics Results
Streamlines
Streamlines show the flow of air entering the nasal cavity and its behavior within the nasal and paranasal cavities.
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Pressure Field
Pressure is defined as the force per unit area acting in the normal direction to that area.
The figure shows the solid surface bounding the nasal cavity through which air flows, and this surface has been colored with the values of the pressure at each point on the surface. The color scheme shows a range of colors from blue (low pressure) to red (high pressure).
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Velocity Field
Velocity is defined as a vector measurement of the rate and direction of motion. Put simply, velocity is the speed at which something moves in one direction. Flowgy displays the results of velocity in units of m/s (meters per second).
The color scheme shows a range of colors from blue (low velocity) to red (high velocity).
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Temperature Field
Temperature is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy, present in all matter.
Flowgy displays temperature results in degrees Celsius. The color scheme shows a range of colors from
blue (low temperature) to red (high temperature).
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Humidity
Humidity is the concentration of water vapour present in the air. It depends on the temperature and pressure of the system of the nasal cavity.
The color scheme shows a range of colors from blue (low humidity) to red (high humidity).
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Wall Shear Stress (WSS)
Wall shear stress is the shear stress in the layer of fluid next to the wall. The wall shear stress expresses the force per unit area exerted by the wall on the fluid in a direction on the local tangent plane. The color scheme shows a range of colors from blue (low WSS) to red (high WSS).
The left column shows the nasal cavity before virtual surgery and the right column post virtual surgery.
Convergence Residuals and Non-Dimensional Estimators
The residual is one of the most fundamental measures of an iterative solution’s convergence, as it directly quantifies the error in the solution of the system of equations. In a CFD analysis, the residual measures the local imbalance of a conserved variable in each control volume. The lower the residual value is, the more numerically accurate the solution.
Graphical representation of dimensional estimators. Φ: parameter measuring flow symmetry. R: parameter measuring the resistance.
