What is normal nasal airflow? A computational study of 22 healthy adults

Anatomy and Physiology of the Nasal Valves

The nasal valves are not simple, 2-dimensional cross-sections but rather a complex, 3-dimensional, collapsible, and heterogeneous structure. Historically, the internal nasal valve (INV) is defined by the septum medially, the caudal margin of the upper lateral cartilage laterally, and the inferior turbinate inferiorly. Typically located 1.3 cm deep into the nasal cavity, the INV angle delineated by the upper lateral cartilage and septum typically measures 10° to 15° in the Caucasian population. As computational methods reveal new insights into nasal valve function, a new conceptual framework is needed to guide rhinoplasty surgical decision-making.

Which Nasal Airway Dimensions Correlate with Nasal Airflow and with Nasal Breathing Sensation?

Background: Rhinoplasty modifies the nasal pyramid, thereby also modifying the nasal airway. Objectives: To correlate the sensation of nasal breathing, as measured by patient-reported outcome measures, and nasal airflow, as assessed by peak nasal inspiratory flow (PNIF), with nasal airway dimensions, as measured on computed tomography (CT) images. Methods: Fifty Caucasian patients were studied through visual analogue scale (VAS), nasal obstruction symptom evaluation (NOSE) and PNIF. Measurements of the nasal airway were made on CT images: minimal distance between septum and inferior and middle turbinates, nasal valve angle, and nasal valve area. Results: There was a significant association between PNIF and nasal valve area, between VAS and the narrower nasal valve angle and between NOSE and minimal distance between septum and middle turbinate of the narrower side. Conclusions: This study suggests that the dimensions of the nasal valve and of the middle nasal airway have a substantial impact on nasal breathing capacity. It also highlights the importance of unilateral nasal airway obstruction to nasal breathing.

Impact of Intra-Phenotypic Nasal Vestibular Variation on Local Airflow Dynamics

OBJECTIVES

Many individuals with healthy normal nasal anatomy and function exhibit a prominent notch indentation at the junction of the ala and sidewall, specifically around the anterior-superior region of the unilateral nasal vestibule up to the internal nasal valve. This study evaluates the influence of various sizes of notched indentations at the anterior nasal airway on local airflow pattern.

METHODS

A retrospective study involving 25 healthy individuals, each exhibiting at least one unilateral notched indentation (40 total airways). Each individual's notched indentation was quantified after subject-specific three-dimensional nasal airway reconstruction from radiographic images. Computational fluid dynamics modeling was used to simulate nasal inspiratory airflow in each nasal airway at 15 L/min. Localized airflow distributions passing through the inferior, middle, and superior regions were calculated at 15 cross sections.

RESULTS

Notched indentation size ranged 1.75-86.84 mm2 (average = 22.37 mm2). At the anterior airway, notched size significantly correlated with inferior airflow volume (R = 0.32, p = 0.04) but not in the middle (R = 0.21, p = 0.20) or superior (R = 0.06, p = 0.70) regions, whereas middle and superior regional resistance values were significantly correlated with notched size (middle: R = 0.54, p < 0.001; superior: R = 0.41, p = 0.009). Medially, resistance at the middle region significantly correlated with notched size (R = 0.56, p < 0.001). At the posterior airway, airflow distributions through the inferior, middle, and superior regions demonstrated weak correlation with notched size (inferior: R = 0.24, p = 0.14, middle: R = 0.24, p = 0.13; superior:R = 0.03, p = 0.83), whereas resistance was significantly correlated in the middle and inferior regions (middle: R = 0.56, p < 0.001;inferior: R = 0.43, p = 0.006).

CONCLUSIONS

Anterior nasal airway notched indentation size had significantly stronger influence on localized airflow volume through the anterior-inferior airway than other regions of the nasal passage.

LEVEL OF EVIDENCE

N/A Laryngoscope, 2024.

Oxymetazoline as a predictor of turbinate reduction surgery outcomes: Objective support from a prospective, single-blinded, computational fluid dynamics study

BACKGROUND

A patient's subjective response to topical nasal decongestant is often used to screen for turbinate reduction surgery suitability. However, this anecdotal strategy has not been objectively and quantitatively evaluated.

METHODS

Prospective, longitudinal, and single-blinded cohort study employing computational fluid dynamic modeling based on computed tomography scans at baseline, 30 min postoxymetazoline, and 2 months postsurgery on 11 patients with chronic turbinate hypertrophy.

RESULTS

Nasal obstruction symptom evaluation (NOSE) and visual analogue scale (VAS) obstruction scores significantly improved from baseline to postoxymetazoline and again to postsurgery (NOSE: 71.82 ± 14.19 to 42.27 ± 25.26 to 22.27 ± 21.04; VAS: 6.09 ± 2.41 to 4.14 ± 2.20 to 2.08 ± 1.56; each interaction p < 0.05), with significant correlation between the latter two states (r∼0.37-0.69, p < 0.05). Oxymetazoline had a broader anatomical impact throughout inferior and middle turbinates than surgery (many p < 0.05); however, the improvement in regional airflow is similar (most p > 0.05) and predominantly surrounding the inferior turbinate. Strong postoxymetazoline to postsurgery correlations were observed in decreased nasal resistance (r = 0.79, p < 0.05), increased regional airflow rates (r = -0.47 to -0.55, p < 0.05) and regional air/mucosa shear force and heat flux (r = 0.43 to 0.58, p < 0.05); however, only increasing peak heat flux significantly correlated to symptom score improvement (NOSE: r = 0.48, p < 0.05).

CONCLUSION

We present the first objective evidence that the "topical decongestant test" can help predict turbinate reduction surgery outcomes. The predictive effect is driven by similar improvementin regional airflow that leading to improved air/mucosa stimulations (peak heat flux) rather than through reduced nasal resistance.

The effect of including dynamic imaging derived airway wall motion in CFD simulations of respiratory airflow in patients with OSA

Obstructive sleep apnea (OSA) is an airway disease caused by periodic collapse of the airway during sleep. Imaging-based subject-specific computational fluid dynamics (CFD) simulations allow non-invasive assessment of clinically relevant metrics such as total pressure loss (TPL) in patients with OSA. However, most of such studies use static airway geometries, which neglect physiological airway motion. This study aims to quantify how much the airway moves during the respiratory cycle, and to determine how much this motion affects CFD pressure loss predictions. Motion of the airway wall was quantified using cine MRI data captured over a single respiratory cycle in three subjects with OSA. Synchronously-measured respiratory airflow was used as the flow boundary condition for all simulations. Simulations were performed for full respiratory cycles with 5 different wall boundary conditions: (1) a moving airway wall, and static airway walls at (2) peak inhalation, (3) end inhalation, (4) peak exhalation, and (5) end exhalation. Geometric analysis exposed significant local airway cross-sectional area (CSA) variability, with local CSA varying as much as 300%. The comparative CFD simulations revealed the discrepancies between dynamic and static wall simulations are subject-specific, with TPL differing by up to 400% between static and dynamic simulations. There is no consistent pattern to which static wall CFD simulations overestimate or underestimate the airway TPL. This variability underscores the complexity of accurately modeling airway physiology and the importance of considering dynamic anatomical factors to predict realistic respiratory airflow dynamics in patients with OSA.

Whole-Genome Deep Sequencing of the Healthy Adult Nasal Microbiome

This study aimed to determine shifts in microbial populations regarding richness and diversity from the daily use of a popular over-the-counter nasal spray. In addition, the finding of nasal commensal bacterial species that overlap with the oral microbiome may prove to be potential probiotics for the "gateway microbiomes". Nasal swab samples were obtained before and after using the most popular over-the-counter (OTC) nasal spray in 10 participants aged 18-48. All participants were healthy volunteers with no significant medical histories. The participants were randomly assigned a number by randomizing software and consisted of five men and five women. The sampling consisted of placing a nasal swab atraumatically into the nasal cavity. The samples were preserved and sent to Northwestern University Sequencing Center for whole-genome deep sequencing. After 21 days of OTC nasal spray use twice daily, the participants returned for further nasal microbiome sampling. The microbial analysis included all bacteria, archaea, viruses, molds, and yeasts via deep sequencing for species analysis. The Northwestern University Sequencing Center utilized artificial intelligence analysis to determine shifts in species and strains following nasal spray use that resulted in changes in diversity and richness.

Assessing nasal airway resistance and symmetry: An approach to global perspective through computational fluid dynamics

This study aimed to explore the variability in nasal airflow patterns among different sexes and populations using computational fluid dynamics (CFD). We focused on evaluating the universality and applicability of dimensionless parameters R (bilateral nasal resistance) and ϕ (nasal flow asymmetry), initially established in a Caucasian Spanish cohort, across a broader spectrum of human populations to assess normal breathing function in healthy airways. In this retrospective study, CT scans from Cambodia (20 males, 20 females), Russia (20 males, 18 females), and Spain (19 males, 19 females) were analyzed. A standardized CFD workflow was implemented to calculate R-ϕ parameters from these scans. Statistical analyses were conducted to assess and compare these parameters across different sexes and populations, emphasizing their distribution and variances. Our results indicated no significant sex-based differences in the R parameter across the populations. However, moderate sexual dimorphism in the ϕ parameter was observed in the Cambodian group. Notably, no geographical differences were found in either R or ϕ parameters, suggesting consistent nasal airflow characteristics across the diverse human groups studied. The study also emphasized the importance of using dimensionless variables to effectively analyze the relationships between form and function in nasal airflow. The observed consistency of R-ϕ parameters across various populations highlights their potential as reliable indicators in both medical practice and further CFD research, particularly in diverse human populations. Our findings suggest the potential applicability of dimensionless CFD parameters in analyzing nasal airflow, highlighting their utility across diverse demographic and geographic contexts. This research advances our understanding of nasal airflow dynamics and underscores the need for additional studies to validate these parameters in broader population cohorts. The approach of employing dimensionless parameters paves the way for future research that eliminates confounding size effects, enabling more accurate comparisons across different populations and sexes. The implications of this study are significant for the advancement of personalized medicine and the development of diagnostic tools that accommodate individual variations in nasal airflow.

Algorithm for Nasal Breathing Impairment Evaluation

Assessing patients with complaints of nasal obstruction has traditionally been done by evaluation of the nasal airway looking for fixed or dynamic obstructive locations that could impair nasal airflow. Not infrequently, however, symptoms of nasal obstruction do not match the clinical examination of the nasal airway. Addressing this subset of patients may be a challenge to the surgeon. Evaluation of patients with symptoms of nasal obstruction should include a combination of a patient-reported assessment of nasal breathing and at least one objective method for measuring nasal airflow or nasal airway resistance or dimensions. This will allow distinction between patients with symptoms of nasal obstruction and low airflow or high nasal airway resistance and patients with similar symptoms but whose objective evaluation demonstrates normal nasal airflow or normal airway dimensions or resistance. Patients with low nasal airflow or high nasal airway resistance will require treatment to increase nasal airflow as a necessary step to improve symptoms, whereas patients with normal nasal airflow or nasal airway resistance will require a multidimensional assessment looking for less obvious causes of impaired nasal breathing sensation.

Beyond skeletal studies: A computational analysis of nasal airway function in climate adaptation

OBJECTIVES

Ecogeographic variation in human nasal anatomy has historically been analyzed on skeletal morphology and interpreted in the context of climatic adaptations to respiratory air-conditioning. Only a few studies have analyzed nasal soft tissue morphology, actively involved in air-conditioning physiology.

MATERIALS AND METHODS

We used in vivo computer tomographic scans of (N = 146) adult individuals from Cambodia, Chile, Russia, and Spain. We conducted (N = 438) airflow simulations during inspiration using computational fluid dynamics to analyze the air-conditioning capacities of the nasal soft tissue in the inflow, functional, and outflow tract, under three different environmental conditions: cold-dry; hot-dry; and hot-humid. We performed statistical comparisons between populations and sexes.

RESULTS

Subjects from hot-humid regions showed significantly lower air-conditioning capacities than subjects from colder regions in all the three conditions, specifically within the isthmus region in the inflow tract, and the anterior part of the internal functional tract. Posterior to the functional tract, no differences were detected. No differences between sexes were found in any of the tracts and under any of the conditions.

DISCUSSION

Our statistical analyses support models of climatic adaptations of anterior nasal soft tissue morphology that fit with, and complement, previous research on dry skulls. However, our results challenge a morpho-functional model that attributes air-conditioning capacities exclusively to the functional tract located within the nasal cavity. Instead, our findings support studies that have suggested that both, the external nose and the intra-facial soft tissue airways contribute to efficiently warming and humidifying air during inspiration. This supports functional interpretations in modern midfacial variation and evolution.

Computational Fluid Dynamics and Its Potential Applications for the ENT Clinician

This article is an examination of computational fluid dynamics in the field of otolaryngology, specifically rhinology. The historical development and subsequent application of computational fluid dynamics continues to enhance our understanding of various sinonasal conditions and surgical planning in the field today. This article aims to provide a description of computational fluid dynamics, the methods for its application, and the clinical relevance of its results. Consideration of recent research and data in computational fluid dynamics demonstrates its use in nonhistological disease pathology exploration, accompanied by a large potential for surgical guidance applications. Additionally, this article defines in lay terms the variables analyzed in the computational fluid dynamic process, including velocity, wall shear stress, area, resistance, and heat flux.

Overview of Nasal Airway and Nasal Breathing Evaluation

Several methods are available for evaluating nasal breathing and nasal airflow, as this evaluation may be made from several different perspectives.Physiologic methods for nasal airway evaluation directly measure nasal airflow or nasal airway resistance, while anatomical methods measure nasal airway dimensions. Subjective methods evaluate nasal breathing through several validated patient-reported scales assessing nasal breathing. Computational fluid dynamics evaluates nasal airflow through the analysis of several physics' variables of the nasal airway.Being familiar to these methods is of utmost importance for the nasal surgeon to be able to understand data provided by the different methods and to be able to choose the combination of evaluation methods that will provide the information most relevant to each clinical situation.

Reducing variability in nasal surgery outcomes through computational fluid dynamics and advanced 3D virtual surgery techniques

Objectives

This study aims to delineate the specific impact of using computational fluid dynamics (CFD) and 3D virtual surgery techniques in otolaryngology surgery, focusing on their roles in enhancing the precision of nasal surgery and optimizing future patient outcomes. The central objective was to assess whether these advanced technologies could reduce variability in surgical approaches and decision-making among specialists, thereby improving the consistency and efficacy of patient care in cases of nasal obstruction.

Methods and results

Our methodology involved a detailed analysis of pre- and post-operative scenarios using CFD feedback. Six otolaryngologists participated, employing virtual surgery techniques on two patients with diagnosed nasal obstruction. The CFD analysis focused on quantifying key airflow parameters: right nasal flow rate (QR), left nasal flow rate (QL), flow symmetry (Ф), and bilateral nasal resistance (R). These parameters were meticulously compared before and after the application of CFD feedback to evaluate changes in surgical planning and outcomes. Quantitative analysis revealed a notable decrease in the standard deviation of the measured parameters among the specialists post-CFD feedback, indicating reduced variability in surgical approaches. Specifically, for Patient #1 the standard deviation for QR values dropped from 0.694 L/min to 0.602 L/min, and for QL values from 0.676 L/min to 0.584 L/min, and for Patient #2, the standard deviation for QR values decreased from 2.204 L/min to 0.958 L/min, and for QL values from 2.295 L/min to 1.014 L/min. Moreover, the variability range, represented by the differences between the maximum and minimum values for Ф and R, diminished significantly. Post-operative average values for all parameters showed a convergence towards ideal basal levels, suggesting a more uniform and effective surgical strategy across different surgeons.

Conclusions

Both integration of CFD and 3D virtual surgery techniques in otolaryngology can substantially reduce variability in surgical planning and decision-making, ultimately leading to improved patient outcomes. These advanced tools have the potential to standardize the diagnosis and treatment of nasal pathologies, contributing to more effective and consistent care. Future research in this area should focus on larger patient cohorts and further exploration of the potential benefits and applications of CFD and virtual surgery in otolaryngology.

How Does Oxymetazoline Change Nasal Aerodynamics and Symptomatology in Patients with Turbinate Hypertrophy?

OBJECTIVES

Oxymetazoline relieves nasal obstructive symptoms via vasoconstriction, however, the changes in nasal structures and aerodynamics that impact symptoms the most remain unclear.

METHODS

This prospective, longitudinal, and single blinded cohort study applied Computational Fluid Dynamic (CFD) modeling based on CT scans at baseline and post-oxymetazoline on 13 consecutive patients with chronic nasal obstruction secondary to inferior turbinate hypertrophy from a tertiary medical center. To account for placebo effect, a sham saline spray was administered with subject blindfolded prior to oxymetazoline, with 30 min rest in between. Nasal Obstruction Symptom Evaluation (NOSE) and unilateral Visual Analogue Scale (VAS) scores of nasal obstructions were collected at baseline, after sham, and 30 min after oxymetazoline.

RESULTS

Both VAS and NOSE scores significantly improved from baseline to post-oxymetazoline (NOSE: 62.3 ± 12.4 to 31.5 ± 22.5, p < 0.01; VAS: 5.27 ± 2.63 to 3.85 ± 2.59, p < 0.05), but not significantly from baseline to post-sham. The anatomical effects of oxymetazoline were observed broadly throughout the entire length of the inferior and middle turbinates (p < 0.05). Among many variables that changed significantly post-oxymetazoline, only decreased nasal resistance (spearman r = 0.4, p < 0.05), increased regional flow rates (r = -0.3 to -0.5, p < 0.05) and mucosal cooling heat flux (r = -0.42, p < 0.01) in the inferior but not middle turbinate regions, and nasal valve Wall Shear Stress (WSS r = -0.43, p < 0.05) strongly correlated with symptom improvement.

CONCLUSION

Oxymetazoline broadly affects the inferior and middle turbinates, however, symptomatic improvement appears to be driven more by global nasal resistance and regional increases in airflow rate, mucosal cooling, and WSS, especially near the head of the inferior turbinate.

LEVEL OF EVIDENCE

3: Well-designed, prospective, single blinded cohort trial. Laryngoscope, 134:1100-1106, 2024.

Computational Rhinology: Unraveling Discrepancies between In Silico and In Vivo Nasal Airflow Assessments for Enhanced Clinical Decision Support

Computational rhinology is a specialized branch of biomechanics leveraging engineering techniques for mathematical modelling and simulation to complement the medical field of rhinology. Computational rhinology has already contributed significantly to advancing our understanding of the nasal function, including airflow patterns, mucosal cooling, particle deposition, and drug delivery, and is foreseen as a crucial element in, e.g., the development of virtual surgery as a clinical, patient-specific decision support tool. The current paper delves into the field of computational rhinology from a nasal airflow perspective, highlighting the use of computational fluid dynamics to enhance diagnostics and treatment of breathing disorders. This paper consists of three distinct parts-an introduction to and review of the field of computational rhinology, a review of the published literature on in vitro and in silico studies of nasal airflow, and the presentation and analysis of previously unpublished high-fidelity CFD simulation data of in silico rhinomanometry. While the two first parts of this paper summarize the current status and challenges in the application of computational tools in rhinology, the last part addresses the gross disagreement commonly observed when comparing in silico and in vivo rhinomanometry results. It is concluded that this discrepancy cannot readily be explained by CFD model deficiencies caused by poor choice of turbulence model, insufficient spatial or temporal resolution, or neglecting transient effects. Hence, alternative explanations such as nasal cavity compliance or drag effects due to nasal hair should be investigated.

On the comparison between pre- and post-surgery nasal anatomies via computational fluid dynamics

Nasal breathing difficulties (NBD) are widespread and difficult to diagnose; the failure rate of their surgical corrections is high. Computational fluid dynamics (CFD) enables diagnosis of NBD and surgery planning, by comparing a pre-operative (pre-op) situation with the outcome of virtual surgery (post-op). An equivalent comparison is involved when considering distinct anatomies in the search for the functionally normal nose. Currently, this comparison is carried out in more than one way, under the implicit assumption that results are unchanged, which reflects our limited understanding of the driver of the respiratory function. The study describes how to set up a meaningful comparison. A pre-op anatomy, derived via segmentation from a CT scan, is compared with a post-op anatomy obtained via virtual surgery. State-of-the-art numerical simulations for a steady inspiration carry out the comparison under three types of global constraints, derived from the field of turbulent flow control: a constant pressure drop (CPG) between external ambient and throat, a constant flow rate (CFR) through the airways and a constant power input (CPI) from the lungs can be enforced. A significant difference in the quantities of interest is observed depending on the type of comparison. Global quantities (flow rate, pressure drop and nasal resistance) as well as local ones are affected. The type of flow forcing affects the outcome of the comparison between pre-op and post-op anatomies. Among the three available options, we argue that CPG is the least adequate. Arguments favouring either CFR or CPI are presented.

Comparison of microparticle transport and deposition in nasal cavity of three different age groups

Objective: The nasal cavity effectively captures the particles present in inhaled air, thereby preventing harmful and toxic pollutants from reaching the lungs. This filtering ability of the nasal cavity can be effectively utilized for targeted nasal drug delivery applications. This study aims to understand the particle deposition patterns in three age groups: neonate, infant, and adult.Materials and methods: The CT scans are built using MIMICS 21.0, followed by CATIA V6 to generate a patient-specific airway model. Fluid flow is simulated using ANSYS FLUENT 2021 R2. Spherical monodisperse microparticles ranging from 2 to 60 µm and a density of 1100 kg/m3 are simulated at steady-state and sedentary inspiration conditions.Results: The highest nasal valve depositions for the neonate are 25% for 20 µm, for infants, 10% for 50 µm, 15% for adults, and 15% for 15 µm. At mid nasal region, deposition of 15% for 20 µm is observed for infant and 8% for neonate and adult nasal cavities at a particle size of 10 and 20 µm, respectively. The highest particle deposition at the olfactory region is about 2.7% for the adult nasal cavity for 20 µm, and it is <1% for neonate and infant nasal cavities.Discussion and conclusions: The study of preferred nasal depositions during natural sedentary breathing conditions is utilized to determine the size that allows medication particles to be targeted to specific nose regions.

Modelling the effects of post-FESS middle turbinate synechiae on sinonasal physiology: A computational fluid dynamics study

OBJECTIVE(S)

Chronic rhinosinusitis (CRS) is common and often requires surgical intervention. Surgical failure may lead to persistent symptoms and recalcitrant disease, often secondary to synechiae between the middle turbinate (MT) and lateral nasal wall. Synechiae prevention techniques have been extensively investigated, however evidence for the effect of synechiae on sinonasal physiology is lacking. We aimed to model the effects of MT synechiae on a post-functional endoscopic sinus surgery (FESS) sinonasal cavity using computational fluid dynamics (CFD).

METHODS

DICOM data from a CT-sinus of a healthy 25-year-old female was segmented to create a three-dimensional model. Virtual surgery was performed to simulate a "full-house" FESS procedure. Multiple models were created, each with a single unilateral virtual MT synechia of varying extent. CFD analysis was performed on each model and compared with a post-FESS control model without synechiae. Airflow velocity, humidity and mucosal surface and air temperature values were calculated.

RESULTS

All synechiae models demonstrated aberrant downstream sinonasal airflow. There was reduced ventilation of the ipsilateral frontal, ethmoid and sphenoid sinuses, with a concentrated central "jet" in the middle meatus region. Effects were proportionate to the size of synechiae. The impact on bulk inspired airflow was negligible.

CONCLUSION

Post-FESS synechiae between the MT and lateral nasal wall significantly disrupt local downstream sinus ventilation and nasal airflow. These findings may explain the persistent symptoms seen in post-FESS CRS patients with MT synechiae, reinforcing the importance of prevention and adhesiolysis. Larger cohort studies with multiple models of actual post-FESS patients with synechiae are required to validate these findings.

3D Printing as a Planning Tool to Optimize Sinonasal Irrigation

BACKGROUND

Topical sinus irrigation plays a critical role in the management of sinonasal diseases. Yet, the penetration of irrigant to targeted sinuses may be highly variable and difficult to predict. Here, we investigate the use of 3D printing as a planning tool to optimize outcomes.

METHODS

Eight post-operative models were 3D printed with a FormLabs Form3 printer based on individual CT scans. Irrigations were performed and video recorded with a squeeze bottle attached via silicon water-tight seal, in 4 head positions: 45° to-the-side, 90° to-the-side, 45° forward and 45° to-the-side, and 90° forward, with irrigation fluid entering the upper (conventional) or lower (backfill) nostrils.

RESULTS

Significant individual variations were observed in sinus penetration as a function of head position. In general, the maxillary sinus was the easiest to irrigate in most head positions (P < .05), followed by frontal and ethmoid, with sphenoid being the most difficult. Both the 90°-to-the-side and the 90°-forward positions were significantly more effective than the others (P < .05), with 90°-forward better for frontal sinuses and 90°-to-the-side superior for all other sinuses. The backfill was significantly superior to conventional technique in head positions involving a side tilt (P < .05).

CONCLUSION

Variations in technique and position significantly impacted irrigation outcome. Backfill irrigation that pushes fluid against gravity to pool around the ostium, seems to provide overall better outcomes. This study demonstrates the advantage of 3D printing as a rapid planning tool to guide irrigation strategies.

Value of Opening the Middle Meatus in Patients With Nasal Airway Obstruction

OBJECTIVES

While surgeries to correct the anatomical malformations that cause nasal airway obstruction (NAO) are generally successful, the outcomes of such procedures are often unsatisfactory. The aim of the present study was to assess the value of opening the middle meatus in patients with NAO.

METHODS

Thirty-four patients with nasal obstruction due to nasal septal deviation were included in this study. After randomization, the middle meatus was either opened or not opened during septoplasty. The patients were evaluated through pre- and postoperative rhinomanometry and acoustic rhinometry. The Visual Analog Scale (VAS) scores of subjective symptoms along with responses to the 20-item Sinonasal Outcome Test (SNOT-20) were obtained before surgery and three months after surgery.

RESULTS

The VAS scores and SNOT-20 responses improved significantly in both groups after surgery. The effective treatment rate based on the nasal congestion score (NCS) was 64.7% in the single group (septoplasty alone) and 100% in the combined group (septoplasty in conjunction with opening the middle meatus), and the difference was statistically significant (P = .018). In both groups, surgery significantly improved nasal flow, resistance, minimal cross-sectional area, cross-sectional area 6 cm (CA6) from the anterior nostril and nasal volume. Nasal volume and CA6 after surgery were statistically different between the 2 groups (P = .004 and .019, respectively).

CONCLUSIONS

Opening the middle meatus may further improve the subjective perception of patency on the basis of septoplasty.

Effect of ambient temperature and respiration rate on nasal dominance: preliminary findings from a nostril-specific wearable

The nasal dominance (ND) determination is crucial for nasal synchronized ventilator, optimum nasal drug delivery, identifying brain hemispheric dominance, nasal airway obstruction surgery, mindfulness breathing, and for possible markers of a conscious state. Given these wider applications of ND, it is interesting to understand the patterns of ND with varying temperature and respiration rates. In this paper, we propose a method which measures peak-to-peak temperature oscillations (difference between end-expiratory and end-inspiratory temperature) for the left and right nostrils during nasal breathing. These nostril-specific temperature oscillations are further used to calculate the nasal dominance index (NDI), nasal laterality ratio (NLR), inter-nostril correlation, and mean of peak-to-peak temperature oscillation for inspiratory and expiratory phase at (1) different ambient temperatures of 18 °C, 28 °C, and 38 °C and (2) at three different respiration rate of 6 bpm, 12 bpm, and 18 bpm. The peak-to-peak temperature (Tpp) oscillation range (averaged across participants;n= 8) for the left and right nostril were 3.80 ± 0.57 °C and 2.34 ± 0.61 °C, 2.03 ± 0.20 °C and 1.40 ± 0.26 °C, and 0.20 ± 0.02 °C and 0.29 ± 0.03 °C at the ambient temperature of 18 °C, 28 °C, and 38 °C respectively (averaged across participants and respiration rates). The NDI and NLR averaged across participants and three different respiration rates were 35.67 ± 5.53 and 2.03 ± 1.12; 8.36 ± 10.61 and 2.49 ± 3.69; and -25.04 ± 14.50 and 0.82 ± 0.54 at the ambient temperature of 18 °C, 28 °C, and 38 °C respectively. The Shapiro-Wilk test, and non-parametric Friedman test showed a significant effect of ambient temperature conditions on both NDI and NLR. No significant effect of respiration rate condition was observed on both NDI and NLR. The findings of the proposed study indicate the importance of ambient temperature while determining ND during the diagnosis of breathing disorders such as septum deviation, nasal polyps, nosebleeds, rhinitis, and nasal fractions, and in the intensive care unit for nasal synchronized ventilator.

Effect of Age and Head Position on Total and Regional Aerosol Deposition in Three-Dimensional Models of Human Intranasal Airways Using a Mucosal Atomization Device

Background: This study examined the effect of age and head position on total and regional deposition of aerosol delivered by a mucosal atomization device (MAD™) in three-dimensional (3D) models of the intranasal airways of an 18-, 5-, and 2-year-old human. Models consisted of four pieces: anterior nose and nasal cavity that was divided horizontally into upper, middle, and lower thirds. Methods: Models were tested six times at supine, supine with head backward at 45° (supine45), and sitting with head backward at 45° (sitting45). The MAD delivered saline/fluorescein aerosol into model nostrils, during static airflow. Model pieces were tested for fluorescence using a fluorometer, and deposition calculated as percent fluorescence per piece relative to its reference. Total deposition (four pieces combined) and regional deposition (four pieces separately) were calculated. Results: Age and head position had little effect on total deposition. In contrast, deposition in the upper and middle third supine45 and in the lower third sitting45 was significantly different in the 2-year-old model, compared with the two older models. In addition, some head positions significantly increased deposition in the upper, middle, and lower thirds within each model, compared with other positions. Upper deposition was significantly greater at supine45, compared with sitting45 (18-year-old) and supine45, compared with supine and sitting45 (5-year-old). Middle deposition was significantly greater at supine and supine45, compared with sitting45 (2-year-old). Lower deposition was significantly greater at sitting45, compared with supine45 (18-year-old); supine and sitting45, compared with supine45 (5-year-old); and sitting45, compared with supine45 and supine (2-year-old). Conclusions: Age and head position significantly affected regional deposition of aerosol delivered by the MAD in these 3D models. Such models might be used to study other methods for targeting intranasal regions with aerosolized medications in children and adults.

Changes in nasolabial angle may alter nasal valve morphology and airflow: a computational fluid dynamics study

Aim: Nasal valve (NV) dysfunctions are a significant cause of nasal obstruction. Changes in the nasolabial angle (NLA) may also cause changes in NV morphology. The effect of changes in the 3D structure of the nasal valve region (NVR) on nasal airflow has yet to be studied sufficiently. The accuracy of computational fluid dynamics (CFD) simulation results of nasal airflow has been confirmed by in vitro tests. Therefore, this study aimed to evaluate the effect of changes in NV structure and volume on nasal airflow based on the CFD method. Material and Method: We used CT images to create a 3D structural model of the NVR. First, CT images were transferred to MIMICS® software, and the nasal air passage was modeled. A solid reference model of the NVR was then created using SolidWorks software. Five different solid 3D nasal valve models were created with nasolabial angles of 85˚ in Model 1, 90˚ in Model 2, 95˚ in Model 3, 100˚ in Model 4, and 105˚ in Model 5. To simulate breathing during rest and exercise using the CFD method, the unilateral nasal airflow rates were set at 150 ml/s and 500 ml/s, respectively. The CFD method was then used to calculate each model’s airflow properties. Finally, the volumes of the models, pressure at the NV outlet, and airflow velocity were evaluated and calculated to investigate each model’s NV airflow characteristics. Results: Our study found a significant correlation between the nasolabial angle (NLA) and NVR volume (r=-0.998, p=0.000), flow rate and velocity (r=0.984, p=0.000), velocity and maximum pressure (r=0.920, p=0.000), velocity and minimum pressure (r=-0.969, p=0.000), flow rate and maximum pressure (r=0.974, p=0.000), and flow rate and minimum pressure (r=-0.950, p=0.000). There was no correlation between NLA increase and nasal airflow velocity. We determined that the highest pressure and lowest airflow velocity values were in the upper angle region and that the lowest pressure and highest airflow velocity values were at the bottom of the NVR in all models. Conclusion: Using the CFD method, we found a decrease in NVR volume and an increase in airflow velocity with an increase in NLA. In addition, we found that the pressure values in the NVR did not change significantly with the increase in NLA.

Subjective symptoms as predictors for eosinophilic chronic rhinosinusitis with nasal polyps in the Chinese population

PURPOSE

To evaluate the putative association between subjective symptoms and eosinophilic inflammation in patients with chronic rhinosinusitis with nasal polyps (CRSwNP).

METHODS

A total of 102 patients with CRSwNP who underwent endoscopic sinus surgery were prospectively enrolled. The Sinonasal Outcomes Test-22 scores (SNOT-22), EuroQol 5-dimensional Questionnaire scores (ED-5D), and Lund-Mackay scores by computed tomography (CT) were obtained. Patients were grouped as eosinophilic CRSwNP (eCRSwNP) and non-eosinophilic CRSwNP (neCRSwNP). ECRSwNP was defined if tissue eosinophils of nasal polyps were greater than or equal to 8/HPF according to positive major basic protein (MBP) staining, and neCRSwNP otherwise.

RESULTS

Thirty neCRSwNP and 72 eCRSwNP patients were included. ECRSwNP patients had higher incidences of asthma (p = 0.001), allergic rhinitis (p = 0.001), and ethmoid-to-maxillary opacification ratio on CT scans (p < 0.001), whereas the proportion of purulent discharge (p < 0.001) and maxillary sinus score (p = 0.002) was higher in the neCRSwNP patients. There were no significant differences between patients on the mains of the EQ-5D health utility values and total SNOT-22 score. However, eCRSwNP patients had higher SNOT-22 scores of sneezing (p = 0.006), runny nose (p < 0.001), and ear/facial domain (p = 0.012), and lower scores of thick nasal discharge (p = 0.015) and blockage (p = 0.042). Sneezing, thick nasal discharge, and blockage/congestion of nose were recognized as independent factors of CRSwNP.

CONCLUSION

Sneezing was an independent predictor of eCRSwNP, and thick nasal discharge and blockage/congestion of nose were independent predictors of neCRSwNP.

Gender Differences in Nasal Anatomy and Function Among Caucasians

Background: Anatomical variations influence nasal physiology, yet sex differences in physiology remains unclear. Objective: To investigate sex differences among Caucasians using computational fluid dynamics. Methods: Adult subjects were selected with normal nasal cone beam computed tomography (CBCT) images and Nasal Obstruction Symptom Evaluation scores ≤30. The CBCT images were used to create subject-specific airway models. Nasal surface area (SA) and volume were computed, and airflow and heat transfer were simulated. Results: The CBCT scans were taken from 23 females and 12 males. The SA and volume (males: mean = 25.0 cm3; females: mean = 19.5 cm3; p < 0.001; Cohen's d = 1.51) were significantly larger for males, but SA-to-volume ratio did not differ significantly. Although unilateral nasal resistance did not vary greatly, females had higher bilateral resistance (males: mean = 0.04 Pa.s/mL; females: mean = 0.05 Pa.s/mL; p = 0.044; Cohen's d = 0.37). Females had higher heat flux (males: mean = 158.5 W/m2; females: mean = 191.8 W/m2; p = 0.012; Cohen's d = 0.79), but males had larger SA where mucosal heat flux exceeds 50 W/m2. Conclusions: These findings suggest differences in normal nasal anatomy and physiology between Caucasian males and females, which may be useful when assessing sex-specific functional outcomes after nasal surgery.

Computational Fluid Dynamics Could Enable Individualized Surgical Treatment of Nasal Obstruction (A Preliminary Study)

Passage of nasal airflow during breathing is crucial in achieving accurate diagnosis and optimal therapy for patients with nasal disorders. Computational fluid dynamics (CFD) is the dominant method for simulating and studying airflow. The present study aimed to create a CFD nasal airflow model to determine the major routes of airflow through the nasal cavity and thus help with individualization of surgical treatment of nasal disorders. The three-dimensional nasal cavity model was based on computed tomography scans of the nasal cavity of an adult patient without nasal breathing problems. The model showed the main routes of airflow in the inferior meatus and inferior part of the common meatus, but also surprisingly in the middle meatus and in the middle part of the common nasal meatus. It indicates that the lower meatus and the lower part of the common meatus should not be the only consideration in case of surgery for nasal obstruction in our patient. CFD surgical planning could enable individualized precise surgical treatment of nasal disorders. It could be beneficial mainly in challenging cases such as patients with persistent nasal obstruction after surgery, patients with empty nose syndrome, and patients with a significant discrepancy between the clinical findings and subjective complaints.

Correlating Nasal Patency with Obstructive Sleep Apnea in Obese Versus Non-Obese Patients: An Acoustic Rhinometry Study

The aim of this study was to correlate nasal patency with Obstructive Sleep Apnea (OSA) in obese versus non-obese patients using Acoustic Rhinometry (AR). Eccovision® Acoustic Rhinometer equipment was used to compare nasal cross-sectional areas (CSA1,2 & 3 corresponding to nasal valve region, anterior portion of middle & inferior turbinate and posterior portion of middle & inferior turbinate respectively) and volume in age and gender matched sample divided into three groups: Group 1: Non-obese patients without OSA (25 patients, 13 males and 12 females); Group 2: Non-obese patients with OSA (25 patients, 14 males and 11 females); Group 3: Obese patients with OSA (25 patients, 13 males and 12 females). The mean nasal cross-sectional areas and volume were lower in Group 2 compared to Group 1 but statistically non-significant (P value > 0.05 for all). The mean nasal cross-sectional areas and volume were significantly lower in Group 3 as compared to Groups 1 and 2 (P value < 0.05 for all). BMI showed a statistically significant positive (direct) correlation with AHI in Groups 2 and 3 (P value < 0.05 for both). The nasal cross-sectional areas and volume showed a statistically significant negative (inverse) correlation with AHI in Groups 2 and 3 (P value < 0.05 for both). OSA diagnosed cases with high BMI may not present with an obvious nasal obstruction; the nasal patency may still be compromised due to reduced nasal lumen secondary to obesity. AR, being cost-effective and non-invasive modality; is advocated to evaluate pre-treatment nasal patency, as well as follow up evaluation to ascertain improvement after the intervention.

Analyses on the influence of normal nasal morphological variations on odorant transport to the olfactory cleft

OBJECTIVE

Olfaction requires a combination of sensorineural components and conductive components, but conductive mechanisms have not typically received much attention. This study investigates the role of normal nasal vestibule morphological variations in ten healthy subjects on odorant flux in the olfactory cleft.

MATERIALS AND METHODS

Computed tomography images were used to create subject-specific nasal models. Each subject's unilateral nasal cavity was classified according to its nasal vestibule shape as Standard or Notched. Inspiratory airflow simulations were performed at 15 L/min, simulating resting inspiration using computational fluid dynamics modeling. Odorant transport simulations for three odorants (limonene, 2,4-dinitrotoluene, and acetaldehyde) were then performed at concentrations of 200 ppm for limonene and acetaldehyde, and 0.2 ppm for dinitrotoluene. Olfactory cleft odorant flux was computed for each simulation.

RESULTS AND DISCUSSION AND CONCLUSION

Simulated results showed airflow in the olfactory cleft was greater in the Standard phenotype compared to the Notched phenotype. For Standard, median airflow was greatest in the anterior region (0.5006 L/min) and lowest in the posterior region (0.1009 L/min). Median airflow in Notched was greatest in the medial region (0.3267 L/min) and lowest in the posterior region (0.0756 L/min). Median olfactory odorant flux for acetaldehyde and limonene was greater in Standard (Acetaldehyde: Standard = 140.45 pg/cm2-s; Notched = 122.20 pg/cm2-s. Limonene: Standard = 0.67 pg/cm2-s; Notched = 0.65 pg/cm2-s). Median dinitrotoluene flux was greater in Notched (Standard = 2.86 × 10-4pg/cm2-s; Notched = 4.29 × 10-4 pg/cm2-s). The impact of nasal vestibule morphological variations on odorant flux at the olfactory cleft may have implications on individual differences in olfaction, which should be investigated further.

Numerical Analysis of Nasal Flow Characteristics with Microparticles

This study was to investigate the airflow characteristics in nasal cavity under different conditions and analyze the effects of different respiratory intensity, particle diameter, and particle density on the deposition of particles carried by airflow in the nasal cavity, respectively. The three-dimensional geometric model of the nasal cavity was established based on typical medical images. The SST k-ω turbulence model in the computational fluid dynamics (CFD) was used to simulate the airflow in the nasal cavity, and the deposition of particles in the airflow was analyzed with the Lagrange discrete phase model. The results showed that the air in the nasal cavity flows in the left and right nasal passages through the perforation in front of the nasal septum and forms a vortex structure at the perforation site, and the particle deposition efficiencies (DE) under perforation nasal cavity are higher than that under normal nasal cavity. Different parameters had different effects on the particle DE. The results showed that the DE of particles with smaller size (≤2.5 μm) is lower; the higher the respiration intensity, the greater the influence on the DE of the larger particle size; and the larger particle density (>1550 kg·m⁻³) has little effect on the DE of larger particle size (DP = 10 μm). The results agree well with the corresponding research data.

On the Design and Testing of an Origami Inspired Nasal Cover: Mitigating Aerosol Risks During Endoscopic Sinus Procedures

Aerosols generated during endoscopic sinus procedures present a concern to the health and safety of healthcare personnel especially with the presence of COVID-19. The purpose of this study is to describe the design and testing of a nasal cover to restrict aerosolized pathogens. The nasal cover was designed to sit overtop the nose with conformal slits for insertion of endoscopic instrumentation. Polydimethylsiloxane (PDMS) was chosen as the nasal mask material and its composition, thickness, and slit geometry were selected using a Taguchi experimental design and survey with clinical collaborators at Penn State Milton S. Hershey Medical Center. The nasal cover was designed using principles of origami engineering to be manufactured flat then folded into its operating state. Form and functionality were evaluated by surgeons, fellows, and residents in the aforementioned survey. Aerosol containment was evaluated by measuring smoke, representative of surgical aerosols, with an optical particle counter. A 25:1 composition PDMS with 3mm thickness and vertical slit geometry was chosen for the nasal cover design. Survey results demonstrated that the origami cover sat well on the nose and did not significantly impact the surgical conditions with single instrumentation. On average, this nasal cover was found to restrict more than 93% of 0.3µm aerosols, and more than 99% of all aerosols larger than 0.5µm in size. Use of a patient worn nasal cover has the potential to drastically reduce the risk to hospital personnel during endonasal surgeries by reducing aerosol generation and potential pathogen spread.

Comparison of rhinomanometric and computational fluid dynamic assessment of nasal resistance with respect to measurement accuracy

PURPOSE

Computational fluid dynamics (CFD)-based calculation of intranasal airflow became an important method in rhinologic research. Current evidence shows weak to moderate correlation as well as a systematic underprediction of nasal resistance by numerical simulations. In this study, we investigate whether these differences can be explained by measurement uncertainties caused by rhinomanometric devices and procedures. Furthermore, preliminary findings regarding the impact of tissue movements are reported.

METHODS

A retrospective sample of 17 patients, who reported impaired nasal breathing and for which rhinomanometric (RMM) measurements using two different devices as well as computed tomography scans were available, was investigated in this study. Three patients also exhibited a marked collapse of the nasal valve. Agreement between both rhinomanometric measurements as well as between rhinomanometry and CFD-based calculations was assessed using linear correlation and Bland-Altman analyses. These analyses were performed for the volume flow rates measured at trans-nasal pressure differences of 75 and 150 Pa during inspiration and expiration.

RESULTS

The correlation between volume flow rates measured using both RMM devices was good (R² > 0.72 for all breathing states), and no relevant differences in measured flow rates was observed (21.6 ml/s and 14.8 ml/s for 75 and 150 Pa, respectively). In contrast, correlation between RMM and CFD was poor (R² < 0.5) and CFD systematically overpredicted RMM-based flow rate measurements (231.8 ml/s and 328.3 ml/s). No differences between patients with and without nasal valve collapse nor between inspiration and expiration were observed.

CONCLUSION

Biases introduced during RMM measurements, by either the chosen device, the operator or other aspects as for example the nasal cycle, are not strong enough to explain the gross differences commonly reported between RMM- and CFD-based measurement of nasal resistance. Additionally, tissue movement during breathing is most likely also no sufficient explanation for these differences.

[Correlation between nasal mucosal temperature change and nasal airflow perception]

The mechanism of nasal airflow perception remains little known. It is currently believed that the main mechanism for perceiving nasal patency is to activate transient receptor potential melastatin subtype 8. Computer fluent dynamics show that increased airflow and heat flux are associated with higher subjective scores. Similarly, physical measurements of the nasal cavity using a temperature probe show a correlation between the lower nasal mucosa temperature and better results. Trigeminal function detection also indirectly confirms this. This literature review aimed to explore the role of nasal mucosal temperature change in the subjective perception of nasal patency and the secondary aim was to appraise the relevant evidence about the mechanism.

CFD SIMULATIONS AND ANALYSES OF ASYMPTOMATIC AND SYMPTOMATIC NASAL AIRWAY OBSTRUCTIONS

The numerical simulations of the flow in nasal airways were performed for two different clinical cases. The results comprised the distributions of scalars at five different sections and included contours of pressure, velocity magnitude, turbulent kinetic energy and vorticity magnitude. Simulations showed the air branching occurring at the inferior meatus is unaffected by the variations in the volumetric flow rate or the changes in the flow regime through the olfactory cleft. However, the contractions and the following rapid change in the cross-section of the nasopharynx preclude the upward penetration of the vacuum field set by the lungs during the inhalation process. As a result, considerably low velocities and significant cross-sectional nonuniformities are observed, which lead to the appearances of the secondary flow structures and strong unsteadiness. Increased interactions between the airflow and the walls of the nasal cavity resulted in an increase in the vorticity on the right middle meatus and upper inferior meatus. The vorticity was also very high in the nostrils, where the flow was not fully developed.

Evidence of Nasal Cooling and Sensory Impairments Driving Patient Symptoms With Septal Deviation

OBJECTIVES/HYPOTHESIS

About 260,000 septoplasties are performed annually in the US to address nasal septal deviation (NSD). Yet, we do not consistently understand what aspects of NSD result in symptoms.

STUDY DESIGN

Blinded cohort study.

METHODS

Two fellowship-trained surgeons blindly reviewed computerized tomography (CTs) of 10 confirmed NSD patients mixed with 36 healthy controls. All patients were correctly identified, however, 24/36 controls were falsely identified by both surgeons as patients (33.3% specificity), which were grouped as asymptomatic NSD (aNSD), while the remaining controls as non-NSD (healthy). Acoustic rhinometry, rhinomanometry, individual CT-based computational fluid dynamics and nasal sensory testing were applied to address the puzzling questions of why these aNSD had no symptoms and, more fundamentally, what caused symptoms in sNSD patients.

RESULTS

aNSD reported no nasal symptoms - Nasal Obstruction Symptom Evaluation score (sNSD: 60.50 ± 13.00; aNSD: 5.20 ± 5.41; non-NSD: 6.66 ± 7.17, P < .05); 22-item Sino-Nasal Outcome Test score (sNSD: 32.60 ± 14.13; aNSD: 10.04 ± 10.10; non-NSD: 9.08 ± 12.42, P < .001). No significant differences in measured nasal resistance, minimum cross-sectional area (MCA), degree of septal deviation, and nasal airflow distributions were found between sNSD and aNSD groups. Only three variables differentiate sNSD versus aNSD: anterior averaged heat flux on deviated side, inferior turbinate peak heat flux on non-deviated side, and nasal cool sensitivity measured by menthol lateralization threshold, with no significant differences among these variables found between the two healthy groups (aNSD vs. non-NSD). These variables by themselves or combined can differentiate sNSD from controls with higher specificity than the physicians (ROC area under the curve = 0.84 with 70% sensitivity and 91.6% specificity).

CONCLUSIONS

This study sheds light on the potential mechanisms of NSD symptomatology: distorted nasal cooling due to NSD exacerbated by poorer nasal mucosal sensitivity. It further supports our previous hypothesis that nasal obstruction complaints do not result directly from obstruction, rather from the capacity of our nose to subjectively sense airflow cooling.

LEVEL OF EVIDENCE

3 Laryngoscope, 132:509-517, 2022.

Nasal airflow comparison in neonates, infant and adult nasal cavities using computational fluid dynamics

BACKGROUND AND OBJECTIVE

Neonates are preferential nasal breathers up to 3 months of age. The nasal anatomy in neonates and infants is at developing stages whereas the adult nasal cavities are fully grown which implies that the study of airflow dynamics in the neonates and infants are significant. In the present study, the nasal airways of the neonate, infant and adult are anatomically compared and their airflow patterns are investigated.

METHODS

Computational Fluid Dynamics (CFD) approach is used to simulate the airflow in a neonate, an infant and an adult in sedentary breathing conditions. The healthy CT scans are segmented using MIMICS 21.0 (Materialise, Ann arbor, MI). The patient-specific 3D airway models are analyzed for low Reynolds number flow using ANSYS FLUENT 2020 R2. The applicability of the Grid Convergence Index (GCI) for polyhedral mesh adopted in this work is also verified.

RESULTS

This study shows that the inferior meatus of neonates accounted for only 15% of the total airflow. This was in contrast to the infants and adults who experienced 49 and 31% of airflow at the inferior meatus region. Superior meatus experienced 25% of total flow which is more than normal for the neonate. The highest velocity of 1.8, 2.6 and 3.7 m/s was observed at the nasal valve region for neonates, infants and adults, respectively. The anterior portion of the nasal cavity experienced maximum wall shear stress with average values of 0.48, 0.25 and 0.58 Pa for the neonates, infants and adults.

CONCLUSIONS

The neonates have an underdeveloped nasal cavity which significantly affects their airway distribution. The absence of inferior meatus in the neonates has limited the flow through the inferior regions and resulted in uneven flow distribution.

A Useful Tool for Various Problems in Nasal Tip: The Cephalic Transdomal Suture

ABSTRACT

Surgical manipulation of the nasal tip is a critical point in functional and aesthetic rhinoplasty procedure. Cephalic strip excision from the lower lateral cartilages, elongation or shortening the caudal septum, structural grafting for supporting the medial and lateral crura are major structural moves in building a durable cartilaginous framework. However, it is suture techniques that make up the final touch in fine tuning of the shape, projection, definition, and angulation (rotation) of the nasal tip over this framework.Problems with fine-tuning of the nasal tip include inadequate or excessive definition, or projection resulting with bulbous or boxy appearance can be overcome reversibly with correctly placed sutures. One of the most decisive sutures in this context is transdomal sutures. Incorrect placement of which can result with too narrow or too wide nostril apices, as well as a cephalic malposition deformity of the lower lateral cartilages, botching an otherwise perfectly executed rhinoplasty procedure.In this article, cephalad placement of the transdomal sutures, and its relevance is disclosed in 223 consecutive cases of primary rhinoplasty.

3D printed transwell-integrated nose-on-chip model to evaluate effects of air flow-induced mechanical stresses on mucous secretion

While there are many chip models that simulate the air-tissue interface of the respiratory system, only a few represent the upper respiratory system. These chips are restricted to unidirectional flow patterns that are not comparable to the highly dynamic and variable flow patterns found in the native nasal cavity. Here we describe the development of a tunable nose-on-chip device that mimics the air-mucosa interface and is coupled to an air delivery system that simulates natural breathing patterns through the generation of bi-directional air flow. Additionally, we employ computational modeling to demonstrate how the device design can be tuned to replicate desired mechanical characteristics within specific regions of the human nasal cavity. We also demonstrate how to culture human nasal epithelial cell line RPMI 2650 within the lab-on-chip (LOC) device. Lastly, Alcian Blue histological staining was performed to label mucin proteins, which play important roles in mucous secretion. Our results revealed that dynamic flow conditions can increase mucous secretion for RPMI 2650 cells, when compared to no flow, or stationary, conditions.

Inspiration After Posterior Pharyngeal Flap Palatoplasty: A Preliminary Study Using Computational Fluid Dynamic Analysis

Posterior pharyngeal flap palatoplasty (PPF) is one of the most commonly used surgical procedures to correct speech, especially for patients suffering from velopharyngeal insufficiency (VPI). During PPF, surgeons use the catheter to control the lateral velopharyngeal port on each side. Airway obstruction and sleep apnea are common after PPF. To understand the air dynamics of the upper airway after PPF, we used computational fluid dynamics (CFD) to demonstrate the airflow. In our previous study, we have revealed the expiration process of the upper airway after PPF and shown the features of how PPF successfully restores the oral pressure for speech. In this study, we focus on examining the inspiration process. Normal airway structures were included. For the normal velopharyngeal structure, one cylinder was applied to each model. For recapitulating the velopharyngeal structure after PPF, two cylinders were used in each model. The ports for borderline/inadequate closure, which can help the oral cavity get the required pressure, were chosen for this study. A real-time CFD simulation was used to capture the airflow through the ports. We found that the airflow dynamics of the upper airway's inspiration were dependent on the velopharyngeal structure. Although the airflow patterns were similar, the velocities between one-port and two-port structures were different, which explained why patients after PPF breathed harder than before and suggested that the one-port structure might be a better choice for secondary VPI reconstruction based on the CFD analyses.

Use of computational fluid dynamics (CFD) to model observed nasal nitric oxide levels in human subjects

BACKGROUND

Upper airway nitric oxide (NO) is physiologically important in airway regulation and defense, and nasal NO (nNO) levels typically exceed those in exhaled breath (fractional exhaled NO [FeNO]). Elevated concentrations of NO sampled from the nose, in turn, reflect even higher concentrations in the paranasal sinuses, suggesting a "reservoir" role for the latter. However, the dynamics of NO flux within the sinonasal compartment are poorly understood.

METHODS

Data from 10 human subjects who had previously undergone both real-time nNO sampling and computed tomography (CT) scanning of the sinuses were analyzed using computational fluid dynamics (CFD) methods. Modeled and observed nNO values during the initial 2-s transient ("spike") during nasal exhalation were then compared.

RESULTS

Examining the initial 2-s transient spike for each subject (as well as the pooled group), there was a statistically significant correlation between modeled and observed nNO levels, with r values ranging from 0.43 to 0.89 (p values ranging from <0.05 to <0.0001). Model performance varied between subjects, with weaker correlations evident in those with high background (FeNO) levels. In addition, the CFD simulation suggests that ethmoid sinuses (>60%) and diffusion process (>54%) contributed most to total nasal NO emissions.

CONCLUSION

Analysis of this dataset confirms that CFD is a valuable modeling tool for nNO dynamics, and highlights the importance of the ethmoid sinuses, as well as the role of diffusion as an initiating step in sinonasal NO flux. Future model iterations may apply more generally if baseline FeNO is taken into account.

Ontogenetic variation in human nasal morphology

Internal nasal cavity morphology has long been thought to reflect respiratory pressures related to heating and humidifying inspired air. Yet, despite the widely recognized importance of ontogeny in understanding climatic and thermoregulatory adaptations, most research on nasal variation in modern and fossil humans focuses on static adult morphology. This study utilizes cross-sectional CT data of three morphologically distinct samples (African, European, Arctic) spanning from infancy to adulthood (total n = 321). Eighteen landmarks capturing external and internal regions of the face and nose were subjected to generalized Procrustes and form-space principal component analyses (separately conducted on global and individual samples) to ascertain when adult-specific nasal morphology emerges during ontogeny. Across the global sample, PC1 (67.18% of the variation) tracks age-related size changes regardless of ancestry, while PC2 (6.86%) differentiates between the ancestral groups irrespective of age. Growth curves tracking morphological changes by age-in-years indicate comparable growth trajectories across all three samples, with the majority of nasal size and shape established early in ontogeny (<5 years of age). Sex-based trends are also evident, with females exhibiting a more truncated growth period than males, particularly for nasal height dimensions. Differences are also evident between the anterior and posterior nose, with the height and breadth dimensions of the anterior nasal aperture and nasal cavity showing differential ontogenetic patterns compared to the choanae. Cumulatively, these results suggest that multiple selective pressures influence human nasal morphology through ontogenetic processes, including metabolic demands for sufficient oxygen intake and climatic demands for adequate intranasal air conditioning.

Human upper-airway respiratory airflow: In vivo comparison of computational fluid dynamics simulations and hyperpolarized 129Xe phase contrast MRI velocimetry

Computational fluid dynamics (CFD) simulations of respiratory airflow have the potential to change the clinical assessment of regional airway function in health and disease, in pulmonary medicine and otolaryngology. For example, in diseases where multiple sites of airway obstruction occur, such as obstructive sleep apnea (OSA), CFD simulations can identify which sites of obstruction contribute most to airway resistance and may therefore be candidate sites for airway surgery. The main barrier to clinical uptake of respiratory CFD to date has been the difficulty in validating CFD results against a clinical gold standard. Invasive instrumentation of the upper airway to measure respiratory airflow velocity or pressure can disrupt the airflow and alter the subject's natural breathing patterns. Therefore, in this study, we instead propose phase contrast (PC) velocimetry magnetic resonance imaging (MRI) of inhaled hyperpolarized 129Xe gas as a non-invasive reference to which airflow velocities calculated via CFD can be compared. To that end, we performed subject-specific CFD simulations in airway models derived from 1H MRI, and using respiratory flowrate measurements acquired synchronously with MRI. Airflow velocity vectors calculated by CFD simulations were then qualitatively and quantitatively compared to velocity maps derived from PC velocimetry MRI of inhaled hyperpolarized 129Xe gas. The results show both techniques produce similar spatial distributions of high velocity regions in the anterior-posterior and foot-head directions, indicating good qualitative agreement. Statistically significant correlations and low Bland-Altman bias between the local velocity values produced by the two techniques indicates quantitative agreement. This preliminary in vivo comparison of respiratory airway CFD and PC MRI of hyperpolarized 129Xe gas demonstrates the feasibility of PC MRI as a technique to validate respiratory CFD and forms the basis for further comprehensive validation studies. This study is therefore a first step in the pathway towards clinical adoption of respiratory CFD.

Computational modeling of nasal nitric oxide flux from the paranasal sinuses: Validation against human experiment

BACKGROUND

Nitric oxide (NO) is important in respiratory physiology and airway defense. Although the paranasal sinuses are the major source of nasal NO, transport dynamics between the sinuses and nasal cavities are poorly understood.

METHODS

Exhaled nasal NO tracings were measured in two non-asthmatic subjects (one with allergic rhinitis, one without) using NO analyzer connected via face mask. We subsequently performed computational fluid dynamics NO emission simulations based on individual CT scans and compared to the experimental data.

RESULTS

Simulated exhaled NO tracings match well with experimental data (r > 0.84, p < 0.01) for both subjects, with measured peaks reaching 319.6 ppb in one subject (allergic-rhinitis), and 196.9 ppb in the other. The CFD simulation accurately captured the peak differences, even though the initial sinus NO concentration for both cases was set to the same 9000 ppb based on literature value. Further, the CFD simulation suggests that ethmoid sinuses contributed the most (>67%, other sinuses combined <33%) to total nasal NO emission in both cases and that diffusion contributes more than convective transport. By turning off diffusion (setting NO diffusivity to ~0), the NO emission peaks for both cases were reduced by >70%.

CONCLUSION

Historically, nasal NO emissions were thought to be contributed mostly by the maxillary sinuses (the largest sinuses) and active air movement (convection). Here, we showed that the ethmoid sinuses and diffusive transport dominate the process. These findings may have a substantial impact on our view of nasal NO emission mechanisms and sinus physiopathology in general.

The effect of decongestion on nasal airway patency and airflow

Nasal decongestant reduces blood flow to the nasal turbinates, reducing tissue volume and increasing nasal airway patency. This study maps the changes in nasal anatomy and measures how these changes affect nasal resistance, flow partitioning between superior and inferior cavity, flow patterns and wall shear stress. High-resolution MRI was applied to capture nasal anatomy in 10 healthy subjects before and after application of a topical decongestant. Computational fluid dynamics simulated nasal airflow at steady inspiratory flow rates of 15 L.min[Formula: see text] and 30 L.min[Formula: see text]. The results show decongestion mainly increases the cross-sectional area in the turbinate region and SAVR is reduced (median approximately 40[Formula: see text] reduction) in middle and lower parts of the cavity. Decongestion reduces nasal resistance by 50[Formula: see text] on average, while in the posterior cavity, nasal resistance decreases by a median factor of approximately 3 after decongestion. We also find decongestant regularises nasal airflow and alters the partitioning of flow, significantly decreasing flow through the superior portions of the nasal cavity. By comparing nasal anatomies and airflow in their normal state with that when pharmacologically decongested, this study provides data for a broad range of anatomy and airflow conditions, which may help characterize the extent of nasal variability.

Objective measurement and patient-reported evaluation of the nasal airway: Is correlation dependent on symptoms or on nasal airflow?

BACKGROUND

Evidence has shown that the sensation of nasal breathing is related to variations in nasal mucosa temperature produced by airflow. An appropriate nasal airflow is necessary for changing mucosal temperature. Therefore, the correlation between objective measurements of nasal airflow and patient-reported evaluation of nasal breathing should be dependent on the level of nasal airflow.

OBJECTIVES

To find if the correlation between patient-reported assessment of nasal breathing and objective measurement of nasal airflow is dependent on the severity of symptoms of nasal obstruction or on the level of nasal airflow.

METHODS

The airway of 79 patients was evaluated using NOSE score and peak nasal inspiratory flow (PNIF). Three subgroups were created based on NOSE and three subgroups were created based on PNIF level to find if correlation was dependent on nasal symptoms or airflow.

RESULTS

The mean value of PNIF for the 79 patients was 92.6 L/min (SD 28.1 L/min). The mean NOSE score was 48.4 (SD 24.4). The correlation between PNIF and NOSE was statistically significant (P = .03), but with a weak association between the two variables (r = -.248). Evaluation of correlation based on symptoms demonstrated a weak or very weak association in each subgroup (r = -.250, r = -.007, r = -.104). Evaluation of correlation based on nasal airflow demonstrated a very weak association for the subgroups with middle-level and high PNIF values (r = -.190, r = -.014), but a moderate association for the subgroup with low PNIF values (r = -.404).

CONCLUSIONS

This study demonstrated a weak correlation between NOSE scores and PNIF values in patients non-selected according to symptoms of nasal obstruction or to airflow. It demonstrated that patients with symptoms of nasal obstruction have different levels of nasal airflow and that low nasal airflow prevents the sensation of good nasal breathing. Therefore, patients with symptoms of nasal obstruction may require improving nasal airflow to improve nasal breathing sensation.

An Overview of Computational Fluid Dynamics Preoperative Analysis of the Nasal Airway

Evaluation of the nasal airway is crucial for every patient with symptoms of nasal obstruction as well as for every patient with other nasal symptoms. This assessment of the nasal airway comprises clinical examination together with imaging studies, with the correlation between findings of this evaluation and symptoms reported by the patient being based on the experience of the surgeon. Measuring nasal airway resistance or nasal airflow can provide additional data regarding the nasal airway, but the benefit of these objective measurements is limited due to their lack of correlation with patient-reported evaluation of nasal breathing. Computational fluid dynamics (CFD) has emerged as a valuable tool to assess the nasal airway, as it provides objective measurements that correlate with patient-reported evaluation of nasal breathing. CFD is able to evaluate nasal airflow and measure variables such as heat transfer or nasal wall shear stress, which seem to reflect the activity of the nasal trigeminal sensitive endings that provide sensation of nasal breathing. Furthermore, CFD has the unique capacity of making airway analysis of virtual surgery, predicting airflow changes after trial virtual modifications of the nasal airway. Thereby, CFD can assist the surgeon in deciding surgery and selecting the surgical techniques that better address the features of each specific nose. CFD has thus become a trend in nasal airflow assessment, providing reliable results that have been validated for analyzing airflow in the human nasal cavity. All these features make CFD analysis a mainstay in the armamentarium of the nasal surgeon. CFD analysis may become the gold standard for preoperative assessment of the nasal airway.

Regional deposition of the allergens and micro-aerosols in the healthy human nasal airways

The nasal cavity is the inlet to the human respiratory system and is responsible for the olfactory sensation, filtering pollutant particulate matter, and humidifying the air. Many research studies have been performed to numerically predict allergens, contaminants, and/or drug particle deposition in the human nasal cavity; however, the majority of these investigations studied only one or a small number of nasal passages. In the present study, a series of Computed Tomography (CT) scan images of the nasal cavities from ten healthy subjects were collected and used to reconstruct accurate 3D models. All models were divided into twelve anatomical regions in order to study the transport and deposition features of different regions of the nasal cavity with specific functions. The flow field and micro-particle transport equations were solved, and the total and regional particle deposition fractions were evaluated for the rest and low activity breathing conditions. The results show that there are large variations among different subjects. The standard deviation of the total deposition fraction in the nasal cavities was the highest for 5 × 10 4 <impaction parameter (IP)< 1.125 × 10 5 with a maximum of 20%. The achieved results highlighted the nasal cavity sections that are more involved in the particle deposition. Particles with IP = 30,000 deposit more in the middle turbinate and nasopharynx areas, while for particles with IP = 300,000, deposition is mainly in the anterior parts (kiesselbach and vestibule regions). For small IP values, the amounts of deposition fractions in different regions of the nasal cavity are more uniform.

Role of nasal vestibule morphological variations on olfactory airflow dynamics

BACKGROUND

The conductive mechanisms of olfaction are typically given little priority in the evaluation of olfactory function. The objective of this study is to investigate the role of nasal vestibule morphological variations on airflow volume at the olfactory recess in healthy subjects.

METHODS

Anatomically realistic three-dimensional nasal airway models were constructed from computed tomography scans in five subjects. Each individual's unilateral nasal cavity (10 total) was classified according to the shape of their nasal vestibule: Standard, Notched, or Elongated. Nasal airflow simulations were performed using computational fluid dynamics modeling at two inspiratory flow rates (15 L/min and 30 L/min) to reflect resting and moderate breathing rates. Olfactory airflow volume and cross-sectional flow resistance were computed.

FINDINGS

Average olfactory airflow volumes (and percent airflow in olfactory) were: 0.25 L/min to 0.64 L/min (3.0%-7.7%; 15 L/min simulations) and 0.53 L/min to 1.30 L/min (3.2%-7.8%; 30 L/min simulations) for Standard; 0.13 L/min - 0.47 L/min (2.0%-6.8%; 15 L/min simulations) and 0.06 L/min - 0.82 L/min (1.7%-6.1%; 30 L/min simulations) for Notched; and 0.07 L/min - 0.39 L/min (1.2%-5.4%; 15 L/min simulations) and 0.30 L/min - 0.99 L/min (2.1%-6.7%; 30 L/min simulations) for Elongated. On average, relative difference in olfactory resistance between left and right sides was 141.5% for patients with different unilateral phenotypes and 82.2% for patients with identical unilateral phenotype.

INTERPRETATION

Olfactory cleft airflow volume was highest in the Standard nasal vestibule phenotype, followed by Notched phenotype for 15 L/min simulations and Elongated phenotype for 30 L/min simulations. Further, intra-patient variation in olfactory cleft airflow resistance differs greatly for patients with different unilateral phenotypes compared to patients with identical unilateral phenotype.