Mayo Clinic SURF: What fluid mechanic models make sense of improved sinus irrigation with air bubble introduction?
Research Overview: Summer undergraduate research experience at Mayo Clinic in Rochester, Minnesota working in the Wilking and Chang Microfluidics Laboratory. My research focused on the investigating how introducing aeration into sinus irrigation protocol affects efficacy of biofilm clearance and solution delivery to the paranasal sinuses of chronic sinusitis (CS) patients. I developed an experimental setup using 3D printing by modeling a sinus cavity from CT scans. I utilized ANSYS for CFD analysis of air pockets flowing through the inferior and middle turbinates to calculate the increased shearing of biofilms in those regions.
My Role: Research Fellow
Research
- Volume Rendering from Computed Topography (CT) Scans
- Digital Modeling and CT Segmentation
- SLA Printing
- Rapid Prototyping
- Fluid Mechanic Analysis of Aerated Sinus Irrigation
Technology
- Experimental Setup
- 3D Slicer
- Blender
- Solidworks
- Analysis
- ANSYS
- Phantom High Speed Camera
Deliverables
- Poster Presentation at Fellow Research Symposium
- Final Project Report
- Developed Anatomically Accurate Physical Sinus Model and Novel Experimental Setup
Key Outcomes:
Presented research poster at the Summer Undergraduate Research Symposium at Mayo Clinic
Developed a fluid dynamics model that approximates the increased shearing behavior of aerated sinus irrigation in the middle and inferior turbinates relative to conventional flow.
Research Process:
Background:
Sinusitis affects 30 million people every year. It occurs when the tissue lining the sinuses becomes inflamed, and as a result, obstruct the mucus transport and airflow through the nasal passageway. The inflammation leads to the narrowing or full obstruction of the ostium which functions to relieve the sinuses of mucus, conventionally through the upper or middle turbinates and into the nasopharynx. Oftentimes, the buildup of mucus in the frontal and maxillary sinuses leads to sinus infections, headaches, and nasal congestion. Common treatments for the symptoms of sinusitis include sinus irrigation and nasal decongestants. Sinus irrigation, also known as sinus rinsing, flushes the sinuses of mucus buildup and debris. It concurrently acts to thin the secreted mucus and moisturize the ciliated epithelial membrane to improve mucociliary clearance.
Four Sets of Paranasal Sinuses:
Methods Pt. 1:
Sinus Modeling from CT Scans:
The 3 dimensional model for the fluid flow analysis was rendered from a computed tomography (CT) scene of the head. DICOM files were uploaded to 3D Slicer, an open source software. The software provides rendering, visualization, and segmentation capabilities that allow for the conversion to an STL file, a 3D printable file extension. By leveraging contrast thresholding, the Grow From Seeds effect, and other manual effects in the segment editor I was able to isolate the sinus cavity from the rest of the head CT. In order to modify the sinus segment into a cavity with solid walls that allow for a realistic model of the sinus cavity to process fluid through, the Hollow effect within Segment Editor was leveraged. This effect converts the visible segment into a cavity with a uniform wall encompassing it, with a thickness determined by the user. The thickness specified in the sinus segment was 2.5mm which optimizes transparency and print structural integrity. Lastly, due to digital quality of the CT scans DICOM files, the model had some missing interpolations between slices that had to be fixed using Blender software prior to printing.
3D Slicer Sinus Segmentation Process:
Final Sinus Model:
Methods Pt. 2:
Rapid Prototyping:
A Bambu Lab X1 Carbon (FDM) printer was employed for rapid prototyping and to validate the effectiveness of the Blender interpolation edits. Subsequently, a Formlabs (SLA) printer was used for the final prints and the experimental setup. To visualize internal fluid flow, sagittal slices of the digital model were created using Blender, extending along the nasal septum and midway through each maxillary sinus, creating 4 separate parts.
Sinus Models: Printed (left), Whole Digital (middle), Sliced Digital (right)
Prototypes:
Methods Pt. 3:
Sinus Irrigation Fluid Flow Visualization:
To achieve an unobstructed view of the sinus irrigation flow, one of the sagittal septum slices was mounted onto a glass panel. I designed a custom test stand using CAD to hold the sinus irrigation squeeze bottle at an optimized 35-degree angle from vertical. A Phantom high-speed camera was used to record the progression of the two irrigation solution flows, as shown below. The red circle on the aerated flow progression emphasizes a consistently observed behavior: air bubbles flowing individually through the middle and inferior nasal turbinates. Both solution delivery to the maxillary sinus and shearing behavior in the turbinate region were measured.
Sagittal Septum Slice:
Experimental Setup:
Irrigation Flow Progression Comparison: Conventional Irrigation (Top), Aerated Irrigation (Bottom)
Results:
Discussion:
Using the internal visualization of sinus irrigation fluid flow to compare conventional and aerated flows, a fluid mechanics model was developed to explain the observed improvements in biofilm clearance. This model applied conventional pipe flow dynamics and single-wall shearing approximations. According to the model, aerated flow generated approximately 2.5 times the shear rate of conventional flow. However, improvements in solution delivery were inconclusive and require further testing.
