Computational Fluid Dynamic Modeling Reveals Nonlinear Airway Stress during Trachea Development.

Normative trachea dimensions and aerodynamic information during development was collected to establish clinical benchmarks and showed that airway development seems to outpace respiratory demands. Infants and toddlers' trachea exhibit higher aerodynamic stress that significantly decreases by teenage years. This implies large airway pathology in younger children may have a more substantial clinical impact.

The cotton test redistributes nasal airflow in patients with empty nose syndrome.

BACKGROUND: Empty nose syndrome (ENS) remains a controversial disease primarily associated with inferior turbinate tissue loss. Cotton placement into the inferior meatus often alleviates ENS symptoms within minutes, but the physiologic explanation for this phenomenon is unknown. Computational fluid dynamics (CFD) was employed to evaluate the mechanisms of altered nasal airflow conferred by cotton testing. METHODS: Six ENS patients (12 sides) with pre-existing sinus computed tomography (CT) imaging were enrolled after marked symptomatic improvement (decrease in score on the Empty Nose Syndrome 6-Item Questionnaire [ENS6Q] of >7 points) with office-based cotton testing. The fashioned cotton plug was labeled in situ with iohexol contrast spray, and sinus CT was immediately obtained to detect cotton contouring in the inferior meatus. CT imaging from pre- and post-cotton placement was analyzed using comparative CFD techniques. RESULTS: After cotton placement, significant symptomatic improvement and reduced ENS6Q scores (16.8 ± 4.1 to 3.1 ± 2.4; p < 0.001) were recorded. Using CFD, cotton placement produced an expected 21% increase in upper airway resistance (p < 0.05). However, a significant shift in the nasal airflow distribution was also detected, with a transition of airflow vectors away from a middle meatus jetstream (-41%; p < 0.002). CONCLUSION: Objective CFD assessment confirmed that the cotton test not only increases nasal resistance, but also restores airflow distribution to the inferior meatus in symptomatic ENS patients. These results highlight the potential efficacy of cotton test in ENS patients and further bolster the utility of this tool in identifying appropriate candidates for the inferior meatus augmentation procedure.

Computational fluid dynamic analysis of aggressive turbinate reductions: is it a culprit of empty nose syndrome?

BACKGROUND: Empty nose syndrome (ENS) remains highly controversial, with aggressive inferior turbinate reduction (ITR) or mucociliary dysfunction frequently implicated. However, the appropriate degree of ITR is highly debatable. METHODS: We applied individual computed tomography (CT)-based computational fluid dynamics (CFD) to 5 patients receiving relatively aggressive ITR but with no ENS symptoms, and compared them to 27 symptomatic ENS patients who all had histories of aggressive ITRs, and 42 healthy controls. Patients' surgical outcomes were confirmed with 22-item Sino-Nasal Outcome Test (SNOT-22) (ITR: 6.40 ± 4.56; ENS: 58.2 ± 15.9; healthy: 13.2 ± 14.9), Nasal Obstruction Symptom Evaluation (NOSE) scores (ITR: 4.00 ± 2.24; ENS: 69.4 ± 17.1; healthy: 11.9 ± 12.9), and Empty Nose Syndrome 6-Item Questionnaire (ENS6Q) (≥11 for ENS). RESULTS: Both aggressive ITR without ENS symptoms and symptomatic ENS patients had significantly lower nasal resistance (ITR: 0.059 ± 0.020 Pa·s/mL; ENS: 0.052 ± 0.015 Pa·s/mL; healthy: 0.070 ± 0.021 Pa·s/mL) and higher cross-sectional areas surrounding the inferior turbinate (ITR: 0.94 ± 0.21 cm2 ; ENS: 1.19 ± 1.05 cm2 ; healthy: 0.42 ± 0.22 cm2 ) than healthy controls. The lack of significant differences among patient groups indicated similar degrees of surgeries between ITR with and without ENS symptom cohorts. However, symptomatic ENS patients have paradoxical significantly less airflow in the inferior meatus (ITR: 47.7% ± 23.6%; ENS: 25.8% ± 17.6%; healthy: 36.5 ± 15.9%; both p < 0.01), but higher airflow around the middle meatus (ITR: 49.7% ± 22.6%; ENS: 66.5% ± 18.3%; healthy: 49.9% ± 15.1%, p < 0.0001) than aggressive ITR without symptoms and controls. Aggressive ITR patients have increased inferior meatus airflow as expected (p < 0.05). This imbalanced airflow produced less inferior wall-shear-stress distribution among symptomatic ENS patients only (ITR: 42.45% ± 11.4%; ENS: 32.2% ± 12.6%; healthy: 49.7% ± 9.9%). ENS patients (n = 12) also had impaired nasal trigeminal function, as measured by menthol lateralization detection thresholds (ITR: 15.2 ± 1.2; ENS: 10.3 ± 3.9; healthy: 13.8 ± 3.09, both p < 0.0001). Surprisingly, aggressive ITR patients without ENS symptoms have better menthol lateralization detection thresholds (LDTs) than healthy controls. CONCLUSION: Although turbinate tissue loss is linked with ENS, the degree of ITR that might distinguish postoperative patient satisfaction in their nasal breathing vs development of ENS symptoms is unclear. Our results suggest that a combination of distorted nasal aerodynamics and loss of mucosal sensory function may potentially lead to ENS symptomology.

Investigation of the abnormal nasal aerodynamics and trigeminal functions among empty nose syndrome patients.

BACKGROUND: Abnormal nasal aerodynamics or trigeminal functions have been frequently implicated in the symptomology of empty nose syndrome (ENS), yet with limited evidence. METHODS: Individual computed tomography (CT)-based computational fluid dynamics (CFD) was applied to 27 ENS patients to simulate their nasal aerodynamics and compared with 42 healthy controls. Patients' symptoms were confirmed with Empty Nose Syndrome 6-item Questionnaire (ENS6Q), 22-item Sino-Nasal Outcome Test (SNOT-22), and Nasal Obstruction Symptom Evaluation (NOSE) scores. Nasal trigeminal sensitivity was measured with menthol lateralization detection thresholds (LDTs). RESULTS: ENS patients had significantly lower (∼25.7%) nasal resistance and higher (∼2.8 times) cross-sectional areas compared to healthy controls (both p < 0.001). Despite inferior turbinate reductions, CFD analysis demonstrated that ENS patients had increased airflow concentrated in the middle meatus region (66.5% ± 18.3%) compared to healthy controls (49.9% ± 15.1%, p < 0.0001). Significantly less airflow (25.8% ± 17.6%) and lower peak wall shear stress (WSS) (0.58 ± 0.24 Pa) were found in the inferior meatus (vs healthy: 36.5% ± 15.9%; 1.18 ± 0.81 Pa, both p < 0.05), with the latter significantly correlated with the symptom scores of ENS6Q (r = -0.398, p = 0.003). Item-wise, complaints of "suffocation" and "nose feels too open" were also found to be significantly correlated with peak WSS around the inferior turbinate (r = -0.295, p = 0.031; and r = -0.388, p = 0.004, respectively). These correlations were all negative, indicating that less air-mucosal stimulations resulted in worse symptom scores. ENS patients (n = 12) also had impaired menthol LDT when compared to healthy controls (p < 0.0001). CONCLUSION: This is the first CFD examination of nasal aerodynamics in a large cohort of ENS patients. The results indicated that a combination of loss of neural sensitivity and poorer inferior air-mucosal stimulation may potentially lead to ENS symptomology.