Thomas Hildebrandt

Visual Exploration of Nasal Airflow

Rhinologists are often faced with the challenge of assessing nasal breathing from a functional point of view to derive effective therapeutic interventions. While the complex nasal anatomy can be revealed by visual inspection and medical imaging, only vague information is available regarding the nasal airflow itself: Rhinomanometry delivers rather unspecific integral information on the pressure gradient as well as on total flow and nasal flow resistance. In this article we demonstrate how the understanding of physiological nasal breathing can be improved by simulating and visually analyzing nasal airflow, based on an anatomically correct model of the upper human respiratory tract. In particular we demonstrate how various information visualization (InfoVis) techniques, such as a highly scalable implementation of parallel coordinates, time series visualizations, as well as unstructured grid multi-volume rendering, all integrated within a multiple linked views framework, can be utilized to gain a deeper understanding of nasal breathing. Evaluation is accomplished by visual exploration of spatio-temporal airflow characteristics that include not only information on flow features but also on accompanying quantities such as temperature and humidity. To our knowledge, this is the first in-depth visual exploration of the physiological function of the nose over several simulated breathing cycles under consideration of a complete model of the nasal airways, realistic boundary conditions, and all physically relevant time-varying quantities.

The concept of rhinorespiratory homeostasis--a new approach to nasal breathing.

The suggested concept of rhinorespiratory homeostasis is a new theoretical model for the discussion of physiologic and physical principles of nasal breathing. This model is based on a comprehensive view of nasal functions that takes comparative animal physiology into account. Consequently, it has a universal cross-species character and emphasizes the central role of nasal secretion. In contrast to the established view, the focus is transferred from the inspired air to the nasal wall. This concept considers the parietal effect of airflow represented by wall shear stress with special regard to the epithelial lining fluid. It delivers one possible mechanism of an inherent triggering of the nasal cycle. Furthermore, the issue of biological fluid-structure interaction is introduced. This article presents a rethinking of nasal breathing that was inspired by clinical experience and results of flow field investigations through computational fluid dynamics.

Evaluation of the intranasal flow field through computational fluid dynamics.

A reliable and comprehensive assessment of nasal breathing is problematic and still a common issue in rhinosurgery. Impairments of nasal breathing need an objective approach. In this regard, currently rhinomanometry is the only standard diagnostic tool available but has various limitations. However, in the last decade, computational fluid dynamics (CFD) has become a promising method in facing the challenge of qualifying nasal breathing. This article presents use of CFD with a symptom-free subject and a symptomatic patient. Thereby, certain flow field features and changes before and after surgery were investigated. Moreover, the study outlines suggestions for concrete rhinologic CFD applications.

An interactive three-dimensional nose model for rhinosurgery.

The motivation behind the development of a new interactive three-dimensional (3D) model of the cartilaginous and bony framework of the nose originated from the significant demand for sophisticated patient communication and for accurate documentation of the surgical steps in rhinoplasty. Basically, the model consists of three features--the viewer function, the freehand function, and default applications--enabling the surgeon to replicate fundamental compilations of findings and to graphically document operative measures easily. The user is able to save all graphics in two-dimensional format and allocate them to patient files. Because the application was designed to be sufficiently universal without being too complex, the 3D model provides a well-balanced mix between freehand and default functions, representing the consistent development of currently available tools.

Numerical Analysis of Nasal Breathing - A Pilot Study

Abstract Currently, there is no fully sufficient way to differentiate between symptomatic and normal nasal breathing. Using the noses total resistance is disputed as a valid means to objectify nasal airflow, and the need for a more comprehensive diagnostic method is increasing. This works aim was to test a novel approach considering intranasal wall shear stress (WSS) as well as static pressure maps obtained by computational fluid dynamics (CFD). X‐ray computed tomography (CT) scan data of six symptom‐free subjects and seven symptomatic patients were used. Patient‐specific geometries of the nasal cavity were segmented from these datasets. Inspiratory and expiratory steady airflow simulations were performed using CFD. Calculated static pressures and WSSs were mapped onto a common template of the nasal septum, allowing for comparison of these parameters between the two patient groups. Significant differences in WSS distributions during the inspiratory phase could be identified between the two groups, whereas no differences were found for the expiratory phase. It is assumed that one essential feature of normal nasal breathing probably consists of distinctively different intranasal flow fields for inspiration and expiration. This is in accordance with previous investigations. The proposed method seems to be a promising tool for developing a new kind of patient‐specific assessment of nasal breathing. However, more studies and a greater case number of data with an expanded focus would be ideal.

Assessment of nasal resistance using computational fluid dynamics

Abstract Anterior rhinomanometry is the current gold standard for the objective assessment of nasal breathing by determining the nasal resistance. However, computational fluid dynamics would allow spatially and temporally well- resolved investigation of additional flow parameters. In this study, measured values of nasal resistance are compared with measured values. An unclear discrepancy between the two methods was found, suggesting further investigation.