Neil Bailie

Noise exposure in orthopaedic practice: potential health risk

Noise exposure is one of the major causes of permanent hearing loss in society. Exposure of health service staff to intense levels of noise in the workplace is a potential risk for the development of temporary and permanent hearing loss. In this prospective study, 18 members of the orthopaedic staff underwent hearing assessment by pure tone audiometry and speech discrimination prior to noise exposure at the workplace and immediately following cessation of work. The number of hours of exposure and noise levels in the workplace was also analysed. Only minimal temporary sensorineural threshold shifts were detected post-noise exposure. There was no change in speech discrimination scores and no individuals complained of tinnitus. The number of hours of exposure ranged from 1.5 to 8.5 hours (mean 5.2 hours). Recorded sound levels for instruments ranged from 119.6 dB at source to 73.1 decibels at 3 metres. Although high sound levels are recorded in the orthopaedic operating theatre, the intermittent nature exposure to the intense noise may protect staff against hearing loss, speech discrimination difficulties and tinnitus.

A model of airflow in the nasal cavities: Implications for nasal air conditioning and epistaxis.

Background A friction force is generated when moving air contacts the nasal walls, referred to as wall shear stress. This interaction facilitates heat and mass transfer between the mucosa and air, i.e., air-conditioning. The objective of this research was to study the distribution of wall shear stress within the nasal cavity to identify areas that contribute significantly to air-conditioning within the nasal cavity. Methods Three-dimensional computational models of the nasal airways of five healthy subjects (three male and two female subjects) were constructed from nasal CT scans. Numerical simulations of nasal airflow were conducted using the commercial computational fluid dynamics code Fluent 6 (Ansys, Inc., Canonsburg, PA). Wall shear stress was derived from the numerical simulation. Air-conditioning was simulated to confirm the relationship with wall shear stress. Results Nasal airflow simulations predicted high wall shear stress along the anterior aspect of the inferior turbinate, the anteroinferior aspect of the middle turbinate, and within Littles area. Conclusion The airflow simulations indicate that the inferior and middle turbinates and Littles area on the anterior nasal septum contribute significantly to nasal air-conditioning. The concentration of wall shear stress within Littles area indicates a desiccating and potentially traumatic effect of inhaled air that may explain the predilection for spontaneous epistaxis at this site.

Morphological consequences of lateral outfracture of the inferior turbinate

OBJECTIVE We report three cases of lateral outfracture of the inferior turbinate, which demonstrate a range of changes in the size, position and shape of the inferior turbinate. METHOD During a study of the validity of computer modelling of nasal airflow, computed tomography scans of the noses of patients who had undergone lateral outfracture of the inferior turbinate were collected. The pre-operative scan was compared with the post-operative scan six weeks later. RESULTS In one patient, there was only a small lateral displacement of the inferior turbinate. In the other two cases, appreciable reduction in the volume of one inferior turbinate was noted, in addition to minor changes in the shape. CONCLUSION Lateral outfracture of the inferior turbinate produces varied and inconsistent changes in morphology which may affect the shape, size and position of the turbinate.

Visualization of nasal airflow patterns in a patient affected with atrophic rhinitis using particle image velocimetry

The relationship between airflow patterns in the nasal cavity and nasal function is poorly understood. This paper reports an experimental study of the interplay between symptoms and airflow patterns in a patient affected with atrophic rhinitis. This pathology is characterized by mucosal dryness, fetor, progressive atrophy of anatomical structures, a spacious nasal cavity, and a paradoxical sensation of nasal congestion. A physical replica of the patients nasal geometry was made and particle image velocimetry (PIV) was used to visualize and measure the flow field. The nasal replica was based on computed tomography (CT) scans of the patient and was built in three steps: three-dimensional reconstruction of the CT scans; rapid prototyping of a cast; and sacrificial use of the cast to form a model of the nasal passage in clear silicone. Flow patterns were measured by running a water-glycerol mixture through the replica and evaluating the displacement of particles dispersed in the liquid using PIV. The water-glycerol flow rate used corresponded to an air flow rate representative of a human breathing at rest. The trajectory of the flow observed in the left passage of the nose (more affected by atrophic rhinitis) differed markedly from what is considered normal, and was consistent with patterns of epithelial damage observed in cases of the condition. The data are also useful for validation of computational fluid dynamics predictions.

Computational fluid dynamics in the investigation and treatment of nasal obstruction

It is estimated that approximately one-third of adults report long-term dissatisfaction with their ability to breathe through their nose. Despite this, there is currently no generally accepted method to objectively characterise airfl ow within an individual nose. In addition, controversy exists about the behaviour of respired air currents within the nasal cavity. Ear, nose and throat (ENT) surgeons must rely solely on subjective judgement, when deciding whether a patient suffering nasal obstruction would benefi t from surgery. Unfortunately, the results of such surgical intervention are not always favourable. The aim of this research was to develop accurate numerical models of nasal airfl ow, using computational fl uid dynamics (CFD); to improve understanding of nasal airfl ow and to conceive a clinical tool to aid in decision-making process regarding nasal surgery. Computational grids were derived from computerised tomography (CT) scans of six adult nasal airways using MIMICS™ and ICEMCFD Tetra™. Numerical airfl ow predictions were made using the FLUENT 6™ commercial CFD code (Fluent Inc., Lebanon, USA). The numerical predictions were validated by comparison to experimental results obtained from an exact solid model of one of the computational grids. This work represents the largest series of nasal geometries studied to date. Numerical predictions showed good agreement with experimentally measured data. Nasal airfl ow characteristics in healthy nasal airways were found to be consistent. However, potentially important inter-individual variations in fl ow characteristics were predicted, particularly in relation to anatomically abnormal nasal passages. Analysis of skin friction (wall shear stress) on the walls of the nasal cavity has demonstrated an area of high friction in the anterior nasal septum at the site of predilection for epistaxis (a nose bleed), suggesting a link between the two. Numerical modelling of nasal airfl ow shows good potential as a clinical tool to characterise nasal airfl ow objectively. Alteration of the computational grid to mimic surgical intervention (Virtual Nasal Surgery) may allow the surgical outcome to be predicted preoperatively.

Numerical modeling of nasal airflow

Problem: The objective of the research was to develop accurate numerical models of nasal airflow using computational fluid dynamics (CFD), a computer-based flow modeling technology widely used in engineering, to improve understanding of nasal airflow with a view to developing a method to assist in planning of nasal surgery. Methods: Computer-aided design (CAD) models of the nasal cavity were generated from nasal CT scans of healthy volunteers using specialized computer software (Mimics, Materialise, Belgium). These anatomically accurate CAD models were used as the basis for 3-dimensional computer grids (meshes) of the nasal cavity. Numerical simulations of nasal airflow were performed on the meshed models using commercial CFD software (Fluent 6, Fluent Inc, Lebanon, NH). Numerical flow predictions were validated using experimental data obtained from an exact solid model of one of the healthy nasal passages. Results: Numerical simulations of nasal airflow showed good agreement with experimental results and with the results of previous experimental studies published in the literature. Potentially important inter-individual variations have been noted, which may account for the outcome variability of some forms of surgical intervention (eg, inferior turbinate surgery). Analysis of wall shear stress (friction) within the nasal cavity has revealed high levels in Little’s area, suggesting a possible connection to the predilection of anterior epistaxis for this site. Conclusion: Numerical simulation of nasal airflow using computational fluid dynamics techniques offers a novel, noninvasive method of assessing of nasal airflow and related phenomena. Alteration of the computer model can be performed to simulate pre-operatively the results of nasal surgery (Virtual Surgery), which may be of considerable clinical benefit. Significance: Numerical modeling of nasal airflow provides objective, patient-specific information regarding nasal airflow characteristics that is not currently available by other methods. It also potentially offers a unique method of preoperatively planning surgery for nasal obstruction. Support: United Hospital’s Trust Research Fellowship.