Correlation of Nasal Mucosal Temperature and Nasal Patency-A Computational Fluid Dynamics Study.

OBJECTIVES: Recent evidence suggests that detection of nasal mucosal temperature, rather than direct airflow detection, is the primary determinant of subjective nasal patency. This study examines the role of nasal mucosal temperature in the perception of nasal patency using in vivo and computational fluid dynamics (CFD) measurements. METHODS: Healthy adult participants completed Nasal Obstruction Symptom Evaluation (NOSE) and Visual Analogue Scale (VAS) questionnaires. A temperature probe measured nasal mucosal temperature at the vestibule, inferior turbinate, middle turbinate, and nasopharynx bilaterally. Participants underwent a CT scan, used to create a 3D nasal anatomy model to perform CFD analysis of nasal mucosal and inspired air temperature and heat flux along with mucosal surface area where heat flux >50 W/m2 (SAHF50). RESULTS: Eleven participants with a median age of 27 (IQR 24; 48) were recruited. Probe-measured temperature values correlated strongly with CFD-derived values (r = 0.87, p < 0.05). Correlations were seen anteriorly in the vestibule and inferior turbinate regions between nasal mucosal temperature and unilateral VAS (r = 0.42-0.46; p < 0.05), between SAHF50 and unilateral VAS (r = -0.31 to -0.36; p < 0.05) and between nasal mucosal temperature and SAHF50 (r = -0.37 to -0.41; p < 0.05). Subjects with high patency (VAS ≤10) had increased heat flux anteriorly compared with lower patency subjects (VAS >10; p < 0.05). CONCLUSION: Lower nasal mucosal temperature and higher heat flux within the anterior nasal cavity correlates with a perception of improved unilateral nasal patency in healthy individuals. LEVEL OF EVIDENCE: 4 Laryngoscope, 133:1328-1335, 2023.

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.

The Impact of Adhesions on Nasal Airflow: A Quantitative Analysis Using Computational Fluid Dynamics.

BACKGROUND: Nasal adhesions (NAs) are a known complication of nasal airway surgery. Even minor NAs can lead to significant postoperative nasal airway obstruction (NAO). Division of such NAs often provides much greater relief than anticipated. OBJECTIVE: We examine the impact of NAs at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD) and multiple test subjects. METHODS: CT scans of healthy adult subjects were used to construct three-dimensional nasal airway computational models. A single virtual 2.5 mm diameter NA was placed at one of five sites commonly seen following NAO surgery within each nasal cavity bilaterally, resulting in 10 NA models and 1 NA-free control for each subject. CFD analysis was performed on each NA model and compared with the subject's NA-free control model. RESULTS: 4 subjects were recruited to create 44 computational models. The NAs caused the airflow streamlines to separate, leading to a statistically significant increase in mucosal temperature immediately downstream to the NAs (wake region). Changes in the mucosal temperature in the wake region of the NAs were most prominent in anteriorly located NAs with a mean increase of 1.62 °C for the anterior inferior turbinate NAs (P < .001) and 0.63 °C for the internal valve NAs (P < .001). CONCLUSION: NAs result in marked disruption to airflow patterns and reduced mucosal cooling on critical surfaces, particularly in the wake region. Reduced wake region mucosal cooling may be a contributing factor to the exaggerated perception of nasal obstruction experienced by patients with NAs.

Computational investigation of nasal surface coverage from squeeze bottle and Neti Pot saline irrigation flow.

BACKGROUND AND OBJECTIVE: Nasal saline irrigation is a common therapy for inflammatory nasal and paranasal disease or for managing post nasal and sinus surgery recovery. Two common irrigation devices include the netipot and squeeze bottles, where anecdotally, these devices alleviate congestion, facial pain, and pressure. However, a quantitative evaluation of these devices' performance and the fluid dynamics responsible for the irrigation distribution through the nose is lacking. This study tracked the liquid surface coverage and wall shear stresses during nasal saline irrigation produced from a Neti Pot and squeeze bottle. METHODS: This study used transient computational fluid dynamics (CFD) simulations to investigate the saline irrigation flow field in a subject-specific sinonasal model. The computational nasal cavity model was constructed from a high-resolution computed tomography scan (CT). The irrigation procedure applied a head position tilted at 90° forward using an 80 ml squeeze bottle and 120 ml Neti Pot. RESULTS: The results from a single sinonasal model demonstrated that the Neti Pot irrigation was more effective in delivering saline solution to the nasal cavity on the contralateral side of irrigation due to typically larger volumes but at the expense of reduced flow and shearing rates, as the flow entered under gravitational forces. The squeeze bottle irrigation provided greater surface coverage on the side of irrigation. CONCLUSIONS: The results from the single patient model, demonstrated the Neti Pot increased surface coverage in the paranasal sinuses. Reducing the jet diameter may aid the direct targeting of a specific region at the side of irrigation by preventing the impingement of the jet to the nasal passage surface and redirection of the flow. Evaluating this performance across a wider cohort of patients can strengthen the findings.

Flow Patterns and Particle Residence Times in the Oral Cavity during Inhaled Drug Delivery.

Pulmonary drug delivery aims to deliver particles deep into the lungs, bypassing the mouth−throat airway geometry. However, micron particles under high flow rates are susceptible to inertial impaction on anatomical sites that serve as a defense system to filter and prevent foreign particles from entering the lungs. The aim of this study was to understand particle aerodynamics and its possible deposition in the mouth−throat airway that inhibits pulmonary drug delivery. In this study, we present an analysis of the aerodynamics of inhaled particles inside a patient-specific mouth−throat model generated from MRI scans. Computational Fluid Dynamics with a Discrete Phase Model for tracking particles was used to characterize the airflow patterns for a constant inhalation flow rate of 30 L/min. Monodisperse particles with diameters of 7 µm to 26 µm were introduced to the domain within a 3 cm-diameter sphere in front of the oral cavity. The main outcomes of this study showed that the time taken for particle deposition to occur was 0.5 s; a narrow stream of particles (medially and superiorly) were transported by the flow field; larger particles > 20 µm deposited onto the oropharnyx, while smaller particles < 12 µm were more disperse throughout the oral cavity and navigated the curved geometry and laryngeal jet to escape through the tracheal outlet. It was concluded that at a flow rate of 30 L/min the particle diameters depositing on the larynx and trachea in this specific patient model are likely to be in the range of 7 µm to 16 µm. Particles larger than 16 µm primarily deposited on the oropharynx.

Nasal Irrigation Delivery in Three Post-FESS Models From a Squeeze-bottle Using CFD.

PURPOSE: Nasal saline irrigation is highly recommended in patients following functional endoscopic sinus surgery (FESS) to aid the postoperative recovery. Post-FESS patients have significantly altered anatomy leading to markedly different flow dynamics from those found in pre-op or non-diseased airways, resulting in unknown flow dynamics. METHODS: This work investigated how the liquid stream disperses through altered nasal cavities following surgery using Computational Fluid Dynamics (CFD). A realistic squeeze profile was determined from physical experiments with a 27-year-old male using a squeeze bottle with load sensors. The administration technique involved a head tilt of 45-degrees forward to represent a head position over a sink. After the irrigation event that lasted 4.5 s, the simulation continued for an additional 1.5 s, with the head orientation returning to an upright position. RESULTS: The results demonstrated that a large maxillary sinus ostium on the right side allows saline penetration into this sinus. The increased volume of saline entering the maxillary sinus limits the saline volume available to the rest of the sinonasal cavity and reduces the surface coverage of the other paranasal sinuses. The average wall shear stress was higher on the right side than on the other side for two patients. The results also revealed that head position alters the sinuses' saline residual, especially the frontal sinuses. CONCLUSION: While greater access to sinuses is achieved through FESS surgery, patients without a nasal septum limits posterior sinus penetration due to the liquid crossing over to the contralateral cavity and exiting the nasal cavity early.

Wet surface wall model for latent heat exchange during evaporation.

Air conditioning is a dual heat and mass transfer process, and the human nasal cavity achieves this through the mucosal wall surface, which is supplied with an energy source through the sub-epithelial network of capillaries. Computational studies of air conditioning in the nasal cavity have included temperature and humidity, but most studies solved these flow parameters separately, and in some cases, a constant mucosal surface temperature was used. Recent developments demonstrated that both heat and mass transfer need to be modeled. This work expands on existing modeling efforts in accounting for the nasal cavity's dual heat and mass transfer process by introducing a new subwall model, given in the Supplementary Materials. The model was applied to a pipe geometry, and a human nasal cavity was recreated from CT-scans, and six inhalation conditions were studied. The results showed that when the energy transfer from the latent heat of evaporation is included, there is a cooling effect on the mucosal surface temperature.

N95 respirator mask breathing leads to excessive carbon dioxide inhalation and reduced heat transfer in a human nasal cavity.

Face masks and respirators are used to filter inhaled air, which may contain airborne droplets and high particulate matter (PM) concentrations. The respirators act as a barrier to the inhaled and exhaled air, which may change the nasal airflow characteristics and air-conditioning function of the nose. This study aims to investigate the nasal airflow dynamics during respiration with and without an N95 respirator driven by airflow through the nasal cavity to assess the effect of the respirator on breathing conditions during respiration. To achieve the objective of this study, transient computational fluid dynamics simulations have been utilized. The nasal geometry was reconstructed from high-resolution Computed Tomography scans of a healthy 25-year-old female subject. The species transport method was used to analyze the airflow, temperature, carbon dioxide (CO2), moisture content (H2O), and temperature distribution within the nasal cavity with and without an N95 respirator during eight consecutive respiration cycles with a tidal volume of 500 ml. The results demonstrated that a respirator caused excessive CO2 inhalation by approximately 7 × greater per breath compared with normal breathing. Furthermore, heat and mass transfer in the nasal cavity was reduced, which influences the perception of nasal patency. It is suggested that wearers of high-efficiency masks that have minimal porosity and low air exchange for CO2 regulation should consider the amount of time they wear the mask.

The impact of nasal adhesions on airflow and mucosal cooling - A computational fluid dynamics analysis.

Nasal adhesions are a known postoperative complication following surgical procedures for nasal airway obstruction (NAO); and are a common cause of surgical failure, with patients often reporting significant NAO, despite relatively minor adhesion size. Division of such nasal adhesions often provides much greater relief than anticipated, based on the minimal reduction in cross-sectional area associated with the adhesion. The available literature regarding nasal adhesions provides little evidence examining their quantitative and qualitative effects on nasal airflow using objective measures. This study examined the impact of nasal adhesions at various anatomical sites on nasal airflow and mucosal cooling using computational fluid dynamics (CFD). A high-resolution CT scan of the paranasal sinuses of a 25-year-old, healthy female patient was segmented to create a three-dimensional nasal airway model. Virtual nasal adhesions of 2.5 mm diameter were added to various locations within the nasal cavity, representing common sites seen following NAO surgery. A series of models with single adhesions were created. CFD analysis was performed on each model and compared with a baseline no-adhesion model, comparing airflow and heat and mass transfer. The nasal adhesions resulted in no significant change in bulk airflow patterns through the nasal cavity. However, significant changes were observed in local airflow and mucosal cooling around and immediately downstream to the nasal adhesions. These were most evident with anterior nasal adhesions at the internal valve and anterior inferior turbinate. Postoperative nasal adhesions create local airflow disruption, resulting in reduced local mucosal cooling on critical surfaces, explaining the exaggerated perception of nasal obstruction. In particular, anteriorly located adhesions created greater disruption to local airflow and mucosal cooling, explaining their associated greater subjective sensation of obstruction.

Effects of head tilt on squeeze-bottle nasal irrigation - A computational fluid dynamics study.

Nasal irrigation is a widely recognized treatment for several sinonasal diseases. However, there is a lack of clear evidence-based guidelines for optimal irrigation delivery to improve lavage and topical drug delivery. This study uses computational fluid dynamics (CFD) to assess the effects of different head tilt positions on sinonasal coverage, residence time and shear stresses in squeeze-bottle nasal irrigation. A sinonasal cavity computational model was constructed from a high-resolution CT scan of a healthy, 25-year-old Asian female. The Volume of Fluid method was used to track the interface between the two immiscible fluids (air and water). The direction of gravity was varied to simulate different head tilt-positions (0° Straight, 45° Forward, 45° Left, 45° Right and 45° Backward) during nasal irrigation with 150 mL liquid via a squeeze bottle through the left nostril for 2 s with a 0.1 s acceleration/deceleration time. The results showed that the 45° backward head tilt position was the most effective in delivering irrigation to the ethmoid, frontal and sphenoid sinuses. Altering head tilt had minimal impact on irrigation delivery to the maxillary sinuses. Maximum wall shear stresses seen in localized areas of the sinus mucosa varied significantly with different head tilt angles. However, the difference in mean wall shear stress on the sinus surfaces was marginal with changing head tilt position. The findings suggest that an optimized head tilt position can be identified to improve liquid irrigation to targeted sinuses, as per treatment requirements (lavage and topical drug delivery).

Neti pot irrigation volume filling simulation using anatomically accurate in-vivo nasal airway geometry.

Nasal saline irrigation is frequently utilised in rhinosinusitis management, and after nasal and sinus surgery. Nasal saline irrigation improves mucociliary transport and assists inflammatory mediator and post-surgical debris removal. The aim of this study was to assess the influence different head positions, irrigation inflow nostril, and the nasal cycle have on Neti pot nasal saline volume filling within the nasal passages and maxillary sinuses. Computational fluid dynamics modelling using anatomically correct nasal geometry found only minor difference in nasal cavity volume filling with inflow from either side of the nose however both head position and inflow direction were both found to have a major influence on maxillary sinus volume filling. Computational modelling flow velocity results at the nasopharynx were validated using particle image velocimetry. It was also found that directing irrigation inflow into the patent side of the nose while in the head-back position achieved the highest volume filling of both maxillary sinuses.

Nasal saline irrigation - A review of current anatomical, clinical and computational modelling approaches.

Nasal saline irrigation is frequently utilised in allergic rhinitis and rhinosinusitis management, and after nasal and sinus surgery. Anatomical modelling, clinical and computational studies guide treatment optimisation. This review offers a comprehensive summary of the modelling methodologies used in previous nasal irrigation studies by undertaking a systematic analysis of anatomical, clinical and computational investigations that assessed nasal saline irrigation using Medline, EMBASE, and Cochrane Review databases. Both procedural and assessment methods were reviewed. It was found that all twenty-four publications reviewed did not discuss the influence of the nasal cycle on internasal geometry and nasal resistance. Cadaver studies misrepresent in vivo nasal geometry. Irrigation pressure and shear forces, which could influence mucociliary transport and postoperative cleaning, were not evaluated. Previous studies focus on irrigation coverage and have not considered the nasal cycle which influences unilateral nasal resistance and thus pressure/ flow relationships and may also increase nasal air-locking. New computational fluid dynamic models could better inform nasal irrigation clinical practice.

Thermodynamic analysis and optimization of a high temperature triple absorption heat transformer.

First law of thermodynamics has been used to analyze and optimize inclusively the performance of a triple absorption heat transformer operating with LiBr/H2O as the working pair. A thermodynamic model was developed in EES (engineering equation solver) to estimate the performance of the system in terms of the most essential parameters. The assumed parameters are the temperature of the main components, weak and strong solutions, economizers' efficiencies, and bypass ratios. The whole cycle is optimized by EES software from the viewpoint of maximizing the COP via applying the direct search method. The optimization results showed that the COP of 0.2491 is reachable by the proposed cycle.