Use of computational fluid dynamics to study the influence of the uncinate process on nasal airflow

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.

Effect of Partial Uncinectomy After Balloon Sinuplasty on Maxillary Sinus Irrigant Penetration: A Cadaveric Study

Objective

The uncinate process may play a role in the amount of irrigation penetrance. In this cadaver study, we aimed to investigate if the addition of partial uncinectomy provides better maxillary sinus irrigation penetrance than balloon sinuplasty (BSP) alone.

Study Design

Cadaveric study.

Setting

Simulation laboratory at the Mayo Clinic in Florida.

Methods

Five fresh-frozen human cadaveric heads (10 sides) were used to assess maxillary sinus irrigation penetration after 3 interventions performed sequentially: irrigation penetrance with no intervention, irrigation after BSP, and irrigation after BSP and partial removal of the uncinate. Penetrance was recorded with intrasinus endoscopy and scored by 4 blinded observers using a scale from 0 (no irrigation) to 5 (fully irrigated). The diameter of the maxillary ostium was measured before and after BSP. Internal consistency was evaluated with Cronbach’s alpha.

Results

Mean ostium size increased from 4.1 to 6.8 mm after BSP (P = .013). Cronbach’s alpha was 0.93. The median scores of irrigation penetration after no intervention, BSP, and BSP and partial uncinectomy were 2.5, 3, and 4, respectively. We found a significantly higher penetrance following partial uncinectomy plus BSP versus BSP alone (P = .008). Both interventions had a statistically significant difference in irrigation penetrance as compared with no intervention (P = .0001).

Conclusion

Maxillary sinus irrigation penetration increased from baseline after BSP. The addition of a partial uncinectomy to the balloon dilation of the maxillary sinus was associated with a statistically significant increase in irrigation penetrance scores as compared with BSP alone.

Computational investigation of dust mite allergens in a realistic human nasal cavity

Aim: Inhaled allergens from house dust mite (HDM) are a major source of allergic disease such as allergic rhinitis and asthma. It has been a challenge to properly evaluate health risks caused by HDM related allergens including mite bodies, eggs and fecal pellets. This paper presents a numerical study on particle deposition of dust mite allergens in a human nasal cavity. Materials and methods: A realistic nasal cavity model was reconstructed from CT scans and a Computational Fluid Dynamics analysis of steady airflow was simulated. The discrete phase model was used to trace particle trajectories of three dust mite related particles. Results: The flow and particle model were validated by comparing with nasal resistance measurement and previous literature respectively. Aerodynamic characteristics and deposition of dust mite allergens in the nasal cavity were analyzed under different breathing conditions including rest and exercising conditions. Conclusions: The numerical results revealed the roles of different nasal cavity regions in filtering various types of dust mite allergens with consideration of breathing conditions.

Transseptal Subperichondrial Endoscopic Hypophysectomy With Preservation of Vital Nasal Structures

INTRODUCTION

Pituitary surgery involving different techniques is often applied to the excision of benign adenomas. Operative interventions involved various approaches and techniques. Endoscopic transsphenoidal approach is the less traumatic route to the sella turcica, avoiding brain retraction, and also permitting good visualization, with lower rates of morbidity and mortality. Although mortality of pituitary surgery decreased by advances in surgical techniques morbidities such as synechiae formation, anosmia, bleeding, nasal septal perforations, drying, and incrustation due to traumatization of the nasal structures such as septum, nasal mucosa, and middle concha are the current problems in pituitary surgery. Here, the authors described an endoscopic transseptal subpericondrial hypophysectomy with minimal damage to normal anatomy and physiology and discussed advantages of this technique.

METHODS

The authors performed endoscopic transseptal subpericondrial hypophysectomy to 2 patients and evaluated intraoperative and postoperative results.

RESULTS

No complication was noted during surgery or postoperative period with endoscopic transseptal subpericondrial hypophysectomy technique.

CONCLUSIONS

Endoscopic transseptal subpericondrial hypophysectomy is a safe technique and, requires only a short surgery time and does not require the removal of any physiological tissue or cause any bleeding.

Numerical study on the effect of uncinectomy on airflow modification and ventilation characteristics of the maxillary sinus

In this study, we examined the effect of uncinectomy on the alteration in local airflows and on the resulting effect on gas exchange in the maxillary sinus, by using computational fluid dynamics in two nasal cavity models: one with a preserved uncinate process, and the other with the uncinate process removed virtually. Uncinectomy distinctively changed the local flow topology by triggering the formation of counter-rotating vortices in the ostiomeatal complex, except for the instants with relatively low airflow rate when the respiration phase changed, ultimately leading to a change in the velocity field inside the ostium and maxillary sinus. Despite a significant increase in the maximum air velocity through the maxillary ostium, ventilation was found to increase only slightly when the uncinate process was removed. Furthermore, the degree of maxillary sinus ventilation by inhaled air was comparable to that by exhaled air. This was true to both models and was independent of the presence of the uncinate process.

Uncinatotomy: performing endoscopic sinus surgery without an uncinectomy

BACKGROUND

The results of endoscopic sinus surgery performed for chronic rhinosinusitis are controversial. For a better surgical outcome, different surgical techniques involving an uncinectomy as the primary step of the operation have been proposed. The surgery should resolve the pathophysiologic problems caused by the disease and preserve the normal anatomy and physiology. We developed a technique to remove the pathology localized to isolated maxillary and anterior ethmoid cells, without excising the uncinate process. The infundibular area was exposed with medialization of the uncinate with a bipedicle flap prepared 1.5 cm from the insertion of the uncinate to the nasal wall, and then the sinus pathology was removed. At the end of the surgery, the uncinate was returned to its original position.

METHODS

We performed this new technique to 3 patients and evaluated postoperative results.

RESULTS

Primary disease was eradicated, and no complication was noted.

CONCLUSIONS

With this technique, it is possible to perform all steps of sinus surgery without excising any anatomic structure.

Numerical simulation of airflow and micro-particle deposition in human nasal airway pre- and post-virtual sphenoidotomy surgery

In the present study, the effects of endoscopic sphenoidotomy surgery on the flow patterns and deposition of micro-particles in the human nasal airway and sphenoid sinus were investigated. A realistic model of a human nasal passage including nasal cavity and paranasal sinuses was constructed using a series of CT scan images of a healthy subject. Then, a virtual sphenoidotomy by endoscopic sinus surgery was performed in the left nasal passage and sphenoid sinus. Transient airflow patterns pre- and post-surgery during a full breathing cycle (inhalation and exhalation) were simulated numerically under cyclic flow condition. The Lagrangian approach was used for evaluating the transport and deposition of inhaled micro-particles. An unsteady particle tracking was performed for the inhalation phase of the breathing cycle for the case that particles were continuously entering into the nasal airway. The total deposition pattern and sphenoid deposition fraction of micro-particles were evaluated and compared for pre- and post-surgery cases. The presented results show that sphenoidotomy increased the airflow into the sphenoid sinus, which led to increased deposition of micro-particles in this region. Particles up to 25 μm were able to penetrate into the sphenoid in the post-operation case, and the highest deposition in the sphenoid for the resting breathing rate occurred for 10 μm particles at about 1.5%.

[The paranasal sinuses as the nitric oxide depot]

This paper was designed to report the currently available data on physiology of the nasal cavity and paranasal sinuses together with the results of national and international investigations on the computer modeling of the air flow in these structures. Also discussed are the gas composition in the paranasal sinuses and the potential factors responsible for the changes in the concentration of nitric oxide with the chemical formula of NO in the nasal cavity and paranasal sinuses.

Numerical investigation of the flow field in realistic nasal septal perforation geometry

The computational fluid dynamics (CFD) are used to evaluate the physiological function of the nose. We evaluated the aerodynamics of the nasal cavity in a patient with septal perforation (SP), pre- and postvirtual repair. Three-dimensional nasal models were reconstructed, and then a wide range of the pressure drops and flow rates were analyzed. The airflow velocity is higher in the central region and is lower around the boundary of the SP. The air velocity in the SP increases as the pressure drop increases. Furthermore, at the anterior part of the SP, the shear stress is higher in the upper part. In addition, the repair of SP does not affect the total nasal airflow rate and the velocity contour patterns. The potential usage of the CFD technique as a predictive technique to explore the details and a preoperative assessment tool to help in clinical decision making in nasal surgery is emphasized.

Assessment of airflow ventilation in human nasal cavity and maxillary sinus before and after targeted sinonasal surgery: a numerical case study

In this study, we evaluated the effects of targeted sinonasal surgery on nasal and maxillary sinus airflow patterns. A patient, who underwent right balloon sinuplasty and left uncinectomy for recurrent maxillary sinus barometric pressure, and concomitant septoplasty and bilateral inferior turbinate reduction for deviated nasal septum and inferior turbinate hypertrophy, was selected. Two 3D models representing both pre- and post-operative sinonasal morphology were constructed. The models were then used to evaluate nasal and maxillary sinus airflow patterns during respiration at ventilation rates of 7.5 L/min, 15 L/min and 30 L/min using computational fluid dynamics. The results showed that septoplasty and inferior turbinate reduction increased the nasal volume by 13.6%. The airflow patterns in the nasal cavity showed reasonably decreased resistance and slightly more even flow partitioning after the operation. Maxillary sinus ventilation significantly increased during inspiration in the left sinus after uncinectomy, and during expiration in right sinus after balloon sinuplasty. This study demonstrates computational fluid dynamics simulation is a tool in the investigation of outcomes after targeted, minimally invasive sinonasal surgery.

Patient specific CFD models of nasal airflow: overview of methods and challenges

Respiratory physiology and pathology are strongly dependent on the airflow inside the nasal cavity. However, the nasal anatomy, which is characterized by complex airway channels and significant individual differences, is difficult to analyze. Thus, commonly adopted diagnostic tools have yielded limited success. Nevertheless, with the rapid advances in computer resources, there have been more elaborate attempts to correlate airflow characteristics in human nasal airways with the symptoms and functions of the nose by computational fluid dynamics study. Furthermore, the computed nasal geometry can be virtually modified to reflect predicted results of the proposed surgical technique. In this article, several computational fluid mechanics (CFD) issues on patient-specific three dimensional (3D) modeling of nasal cavity and clinical applications were reviewed in relation to the cases of deviated nasal septum (decision for surgery), turbinectomy, and maxillary sinus ventilation (simulated- and post-surgery). Clinical relevance of fluid mechanical parameters, such as nasal resistance, flow allocation, wall shear stress, heat/humidity/NO gas distributions, to the symptoms and surgical outcome were discussed. Absolute values of such parameters reported by many research groups were different each other due to individual difference of nasal anatomy, the methodology for 3D modeling and numerical grid, laminar/turbulent flow model in CFD code. But, the correlation of these parameters to symptoms and surgery outcome seems to be obvious in each research group with subject-specific models and its variations (virtual- and post-surgery models). For the more reliable, patient-specific, and objective tools for diagnosis and outcomes of nasal surgery by using CFD, the future challenges will be the standardizations on the methodology for creating 3D airway models and the CFD procedures.