Details of the physiology of the aerodynamic and heat and moisture transfer in the normal nasal cavity

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.

[Application of 3D printed nasal vestibular support in the treatment of anterior nostril stenosis]

Objective:To evaluate the efficacy of 3D printed nasal vestibular support on the recovery of nasal ventilation function and nostril shape after nostril stenosis treatment. Methods:Thirty-eight patients with unilateral traumatic nasal vestibular stenosis were selected and treated with 3D printed nasal vestibular support after operation. Subjective evaluation indicators, objective nostril local morphological and structural parameters, and nasal airflow dynamics parameters by numerical simulation were used. To evaluate the nostril morphological and nasal functional recovery after treatment. Results:The subjective nasal congestion and nostril symmetry satisfaction VAS scores of the patients after nasal vestibular support treatment were improved to varying degrees compared with those before surgery; The nostril morphological parameters showed that the Δlong-axis ratio and Δ short-axis ratio were significantly decreased after nasal vestibular support therapy （0.09±0.09 and 0.16±0.13） compared with those before surgery（0.21±0.20 and 0.28±0.21） respectively（P<0.01）. And the cross-sectional area of the nasal valve on the stenotic side nasal cavity increased from（0.40±0.27） cm² before operation to （0.71±0.26） cm² after treatment（P<0.01）; The nasal resistance on the stenosis side nasal cavity also decreased from （0.036±0.024） Pa·s/mL before operation to （0.022±0.008） Pa. s/mL after treatment（P<0.01）, and the total nasal resistance was decreased from （0.033±0.02） Pas/mL before operation to （0.021±0.007）Pa. s/mL after treatment（P<0.01） ; It also showed that NWE（nasal warming efficiency） and NHE（nasal humidification efficiency） on the stenotic side nasal cavity were significantly decreased after nasal vestibular support therapy（[95.92±2.8]% and [94.55±4.17]%） compared with those before surgery （[97.94±1.97 ]% and [96.19±2.94]%） respectively（P<0.01）. Conclusion:The 3D printed nasal vestibular support for postoperative support treatment on patients with anterior nostril stenosis can reflect the advantages of personalized treatment and allow patients to obtain satisfactory results, and the use of individually designed 3D printed nasal vestibular support can make the shape of anterior nostrils and nasal cavity normal ventilation function recover well, its clinical application prospect is worth looking forward to.

The role of normal nasal morphological variations from race and gender differences on respiratory physiology

This study identifies anatomical and airflow-induced relationships based on nasal morphological variations due to inter- and intra-racial differences and gender. Subject-specific nasal airway reconstruction was created from computed tomography images in 16 subjects: 4 subjects from each ethnic group (Black, East Asian, Caucasian, and Latino) comprising of 2 males and 2 females. Volume, surface area and nasal index were calculated, as well as airflow rate and nasal resistance after computational fluid dynamics simulations in the nasal airway. Results showed that nasal airspace surface area (p = 0.0499) and volume (p = 0.0281) were significantly greater in males than in females. Nasal volume was greatest in East Asians (Median = 20.38cm³, Interquartile Range [IQR] = 4.58 cm³), Latinos had the greatest surface area (Median = 219.70cm², IQR = 29.56cm²). On average, East Asian and Black females had larger nasal index than their male counterparts. Caucasians had the highest median nasal resistance (0.050 Pa.s/mL, IQR = 0.025 Pa.s/mL). Results indicate that there exist anatomical variabilities based on race and gender. However, these variabilities may not significantly influence nasal function.

In-silico investigation of airflow and micro-particle deposition in human nasal airway pre- and post-virtual transnasal sphenoidotomy surgery

Sphenoid sinus, located posterior to the nasal cavity, is difficult to reach for a surgery. Several operation procedures are available for sphenoidotomy, including endoscopic surgeries. Although the endoscopic sinus surgery is minimally invasive with low post-operative side effects, further optimization is required. Transnasal sphenoidotomy is a low invasive alternative to transethmoidal sphenoidotomy, but it still needs to be studied to understand its effects on the airflow pattern and the particle deposition. In this work, we simulated airflow and the micro-particle deposition in the nasal airway of a middle-aged man to investigate the change in particle deposition in the sphenoid sinus after virtual transnasal sphenoidotomy surgery. The results demonstrated that after transnasal sphenoidotomy, particle deposition in the targeted sphenoid sinus was an order of magnitude lower than that observed after virtual transethmoidal sphenoidotomy surgery. In addition, the diameter of the particles for the peak deposition fraction in the targeted sinus was shifted to smaller diameters after the transnasal sphenoidotomy surgery compared with that in the post-transethmoidal condition. These results suggest that the endoscopic transnasal sphenoidotomy can be a better procedure for sphenoid surgeries as it decreases the chance of bacterial contaminations and consequently lowers the surgical side effects and recovery time.

Analysis of nasal air conditioning in subjects with unilateral cleft lip nasal deformity

This study evaluated the impact of unilateral cleft lip nasal deformity (uCLND) on the ability of the nasal passages to warm and humidify inspired environmental air using computational fluid dynamics (CFD) modeling. Nasal air conditioning was simulated at resting inspiration in ten individuals with uCLND and seven individuals with normal anatomy. The overall heat and water transfer through nasal mucosa was significantly greater (p = 0.02 for both heat and moisture fluxes) on the non-cleft side than on the cleft side. Unilateral median and interquartile range (IQR) for heat flux (W/m²) was 190.3 (IQR 59.9) on the non-cleft side, 160.9 (IQR 105.0) on the cleft side, and 170.7 (IQR 87.8) for normal subjects. For moisture flux (mg/(s·m²), they were 357.4 (IQR 112.9), 298.7 (IQR 200.3) and 320.8 (IQR 173.0), respectively. Significant differences of SAHF50 between cleft side of uCLND and normal existed except for anterior region. Nevertheless, air conditioning ability in subjects with uCLND was generally comparable to that of normal subjects.

Numerical simulation of unsteady airflow in a nasal cavity for various sizes of maxillary sinus opening in a virtual endoscopic surgery

Functional endoscopic sinus surgery (FESS) is performed to treat sinusitis when treatment with medication fails. In the present study, three different virtual maxillary sinus endoscopic surgeries were performed on a realistic 3-D computational model of the nasal cavity of an adult male under the supervision of a specialist. They included only uncinectomy, uncinectomy + 8mm Middle Meatal Antrostomy (MMA) and uncinectomy + 18 mm MMA. Simulations were performed for two human activity respiratory rates, including rest and moderate activities, and effects of different surgeries and respiratory rates on maxillary sinus were investigated. It was found that after endoscopic sinus surgery, the volume of air entering the maxillary sinus increased significantly, and as the size of the MMA increased, or the breathing condition changed from rest to moderate activity, this volume of air increased. For the rest condition, on average for both nasal passages, for uncinectomy +8 mm MMA, around 15 % of the inhaled flow and 7 % of the exhaled flow enter the maxillary sinuses. For uncinectomy +18 mm MMA, these values are 24 % and 14 %, respectively. As human activity increases, a lower portion of inhaled and exhaled air enters the maxillary sinuses. For the moderate activity condition, on average for both nasal passages, for uncinectomy +8 mm MMA, around 11 % of the inhaled flow and 6 % of the exhaled flow rate enters the maxillary sinus. For uncinectomy +18 mm MMA, these values are 16 % and 8%, respectively. Comparing the steady and unsteady simulation results showed that the quasi-steady flow assumption could predict the flow in the maxillary sinus and the volume of air entering the sinuses, almost at any moment of respiration, with acceptable accuracy.

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.

Can computational fluid dynamic models help us in the treatment of chronic rhinosinusitis

PURPOSE OF REVIEW

The aim of this study was to review the recent literature (January 2017-July 2020) on computational fluid dynamics (CFD) studies relating to chronic rhinosinusitis (CRS), including airflow within the pre and postoperative sinonasal cavity, virtual surgery, topical drug and saline delivery (sprays, nebulizers and rinses) and olfaction.

RECENT FINDINGS

Novel CFD-specific parameters (heat flux and wall shear stress) are highly correlated with patient perception of nasal patency. Increased ostial size markedly improves sinus ventilation and drug delivery. New virtual surgery tools allow surgeons to optimize interventions. Sinus deposition of nasal sprays is more effective with smaller, low-inertia particles, outside of the range produced by many commercially available products. Saline irrigation effectiveness is improved using greater volume, with liquid entering sinuses via 'flooding' of ostia rather than direct jet entry.

SUMMARY

CFD has provided new insights into sinonasal airflow, air-conditioning function, the nasal cycle, novel measures of nasal patency and the impact of polyps and sinus surgery on olfaction. The deposition efficiency of topical medications on sinus mucosa can be markedly improved through parametric CFD experiments by optimising nasal spray particle size and velocity, nozzle angle and insertion location, while saline irrigation effectiveness can be optimized by modelling squeeze bottle volume and head position. More sophisticated CFD models (inhalation and exhalation, spray particle and saline irrigation) will increasingly provide translational benefits in the clinical management of CRS.