225 results found
Kimura S, Miura S, Sera T, et al., 2020, Voxel-based simulation of flow and temperature in the human nasal cavity, COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING, Vol: 24, Pages: 459-466, ISSN: 1025-5842
Schroter RC, 2020, Social distancing for covid-19: is 2 metres far enough?, BMJ-BRITISH MEDICAL JOURNAL, Vol: 369, ISSN: 1756-1833
Xiao Q, Cetto R, Doorly D, et al., 2019, Assessing changes in airflow and energy loss in a progressive tracheal compression before and after surgical correction, Annals of Biomedical Engineering, Vol: 48, Pages: 822-833, ISSN: 0090-6964
The energy needed to drive airflow through the trachea normally constitutes a minor component of the work ofbreathing. However, with progressive tracheal compression, patient subjective symptoms can include severe breathingdifficulties. Many patients suffer multiple respiratory co-morbidities and so it is important to assess compression effectswhen evaluating the need for surgery. This work describes the use of computational prediction to determine airflowresistance in compressed tracheal geometries reconstructed from a series of CT scans. Using energy flux analysis, theregions that contribute the most to airway resistance during inhalation are identified. The principal such region is where flowemerging from the zone of maximum constriction undergoes breakup and turbulent mixing. Secondary regions are alsofound below the tongue base and around the glottis, with overall airway resistance scaling nearly quadratically with flowrate. Since the anatomical extent of the imaged airway varied between scans - as commonly occurs with clinical data andwhen assessing reported differences between research studies - the effect of sub-glottic inflow truncation is considered.Analysis shows truncation alters the location of jet breakup and weakly influences the pattern of pressure recovery. Testsalso show that placing a simple artificial glottis in the inflow to a truncated model can replicate patterns of energy loss inmore extensive models, suggesting a means to assess sensitivity to domain truncation in tracheal airflow simulations.
Doorly D, Kimura S, Sakamoto T, et al., 2019, Voxel-based modeling of airflow in the human nasal cavity, Computer Methods in Biomechanics and Biomedical Engineering, ISSN: 1025-5842
Kimura S, Sakamoto T, Sera T, et al., 2019, Voxel-based modeling of airflow in the human nasal cavity, Computer Methods in Biomechanics and Biomedical Engineering, Vol: 22, Pages: 331-339, ISSN: 1025-5842
This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity.
arora H, nila A, Vitharana K, et al., 2017, Microstructural consequences of blast lung injury characterised with digital volume correlation, Frontiers in Materials, Vol: 4, ISSN: 2296-8016
This study focuses on microstructural changes that occur within the mammalian lung when subject to blast and how these changes influence strain distributions within the tissue. Shock tube experiments were performed to generate the blast injured specimens (cadaveric Sprague-Dawley rats). Blast overpressures of 100 and 180 kPa were studied. Synchrotron tomography imaging was used to capture volumetric image data of lungs. Specimens were ventilated using a custom-built system to study multiple inflation pressures during each tomography scan. These data enabled the first digital volume correlation (DVC) measurements in lung tissue to be performed. Quantitative analysis was performed to describe the damaged architecture of the lung. No clear changes in the microstructure of the tissue morphology were observed due to controlled low- to moderate-level blast exposure. However, significant focal sites of injury were observed using DVC, which allowed the detection of bias and concentration in the patterns of strain level. Morphological analysis corroborated the findings, illustrating that the focal damage caused by a blast can give rise to diffuse influence across the tissue. It is important to characterize the non-instantly fatal doses of blast, given the transient nature of blast lung in the clinical setting. This research has highlighted the need for better understanding of focal injury and its zone of influence (alveolar interdependency and neighboring tissue burden as a result of focal injury). DVC techniques show great promise as a tool to advance this endeavor, providing a new perspective on lung mechanics after blast.
Bates AJ, Cetto R, Doorly DJ, et al., 2016, The effects of curvature and constriction on airflow and energy loss in pathological tracheas, Respiratory Physiology & Neurobiology, Vol: 234, Pages: 69-78, ISSN: 1569-9048
This paper considers factors that play a significant role in determining inspiratory pressure and energy losses in the human trachea. Previous characterisations of pathological geometry changes have focussed on relating airway constriction and subsequent pressure loss, however many pathologies that affect the trachea cause deviation, increased curvature, constriction or a combination of these. This study investigates the effects of these measures on tracheal flow mechanics, using compressive goitre (a thyroid gland enlargement) as an example. Computational fluid dynamics simulations were performed in airways affected by goitres (with differing geometric consequences) and a normal geometry for comparison. Realistic airways, derived from medical images, were used because idealised geometries often oversimplify the complex anatomy of the larynx and its effects on the flow. Two mechanisms, distinct from stenosis, were found to strongly affect airflow energy dissipation in the pathological tracheas. The jet emanating from the glottis displayed different impingement and breakdown patterns in pathological geometries and increased loss was associated with curvature.
Doorly DJ, Bates A, Comerford A, et al., 2016, Computational fluid dynamics benchmark dataset of airflow in tracheas, Data in Brief, Vol: 10, Pages: 101-107, ISSN: 2352-3409
Computational Fluid Dynamics (CFD) is fast becoming a useful tool to aid clinicians in pre-surgical planning through the ability to provide information that could otherwise be extremely difficult if not impossible to obtain. However, in order to provide clinically relevant metrics, the accuracy of the computational method must be sufficiently high. There are many alternative methods employedin the process of performing CFD simulations within the airways, including different segmentation and meshing strategies, as well as alternative approaches to solving the Navier-Stokes equations.However, as in vivovalidation of the simulated flow patterns within the airways is not possible, little exists in the way of validation of the various simulation techniques. The data presented here consists of very highly resolved flow data. The degree of resolution is compared to the highest necessary resolutions of the Kolmogorov length and timescales. Therefore this data is ideally suited to act as a benchmark case to which cheaper computational methods may be compared.A dataset and solution setup for one such more efficient method, large eddy simulation (LES), is also presented.
The effort required to inhale a breath of air is a critically important measure in assessing airway function. Although the contribution of the trachea to the total flow resistance of the airways is generally modest, pathological alterations in tracheal geometry can have a significant negative effect. This study investigates the mechanisms of flow energy loss in a healthy trachea and in four geometries affected by retrosternal goitre which can cause significant distortions of tracheal geometry including constriction and deviation with abnormal curvature. By separating out the component of energy loss related to the wall shear (frictional loss), striking differences are found between the patterns of energy dissipation in the normal and pathological tracheas. Furthermore the ratio of frictional to total loss is dramatically reduced in the pathological geometries.
During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective transport of an inhaled gas were investigated in a subject geometry extending from the nose to the bronchi. The progress of flow transition and the advance of an inhaled non-absorbed gas were determined using highly resolved simulations of a sniff 0.5 s long, 1 l s⁻¹ peak flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved through three phases: (i) an initial transient of about 50 ms, roughly the filling time for a nasal volume, (ii) quasi-equilibrium over the majority of the inhalation, and (iii) a terminating phase. Flow transition commenced in the supraglottic region within 20 ms, resulting in large-amplitude fluctuations persisting throughout the inhalation; in the nose, fluctuations that arose nearer peak flow were of much reduced intensity and diminished in the flow decay phase. Measures of gas concentration showed non-uniform build-up and wash-out of the inhaled gas in the nose. At the carina, the form of the temporal concentration profile reflected both shear dispersion and airway filling defects owing to recirculation regions.
Sera T, Yokota H, Tanaka G, et al., 2013, Murine pulmonary acinar mechanics during quasi-static inflation using synchrotron refraction-enhanced computed tomography, JOURNAL OF APPLIED PHYSIOLOGY, Vol: 115, Pages: 219-228, ISSN: 8750-7587
Schroter RC, Kamm RD, Kessler JO, 2012, Life's flows - reflections on T. J. Pedley's career in biological fluid mechanics, JOURNAL OF FLUID MECHANICS, Vol: 705, Pages: 2-6, ISSN: 0022-1120
Objective: We present a study investigating the effect of a decongestant on the nasal mucosa, showing results in terms of the change in erectile tissue volume (ETV) in normal subjects using high resolution 3T-MRI scanning. Method: Seven volunteers with no nasal complaints (SNOT-22) or obvious rhinoscopic abnormalities were studied. Each subject underwent 2 MRI scans producing a series of 120 contiguous 1.2 mm sections pre- and postdecongestion. Patients were decongested with xylometazoline-HCL, remaining immobilized following the first scan. The scans were segmented using ITK-Snap and analyzed using MATLAB. Results: Subject age ranged from 21-38 years (mean = 28). The SNOT-22 scores ranged from 1-10 (mean = 4.8). Decongestion had the greatest effect in 3 sites: the inferior turbinates, middle turbinates, and septum. The greatest change in ETV was observed in the inferior turbinates (P <.005), reducing by up to 1/3 at the posterior aspect of the inferior turbinate following decongestion. Changes were also seen in ETV of the middle turbinate and septal mucosa to a lesser extent. Conclusion: The effect of decongestion on ETV has been investigated here in far greater detail than previously studied, and at higher spatial resolution. 3T-MRI was found to be an excellent modality for mapping changes in nasal mucosa. Our results demonstrate the significant effect of decongestion on ETV of the inferior turbinates.
Rennie CE, Hood CM, Blenke EJSM, et al., 2011, Physical and computational modelling of ventilation of the maxillary sinus, Otolaryngology-Head and Neck Surgery, Vol: 145, ISSN: 0194-5998
BackgroundThis study quantifies the time-varying flow rate during inspiration at rest and in sniffing, both predecongestion and postdecongestion. It aims to provide a better understanding of nasal airflow mechanics, for application to the physiological modeling of nasal respiration and to therapeutic drug delivery.MethodsThe temporal profiles of nasal inspiration were measured at high fidelity in 14 healthy individuals using simultaneous bilateral hot-wire anemometry. Peak nasal inspiratory flow (PNIF) rate, acoustic rhinometry (AR), and the sinonasal outcome test (SNOT) provided complementary clinical measurements. The impact of decongestion was also investigated.ResultsIn the initial phase of inspiration, a rapid rise in flow rate was observed. Flow first exceeded 150 mL/second in either passage within a median time of approximately 120 ms for inspiration at rest and approximately 60 ms in sniffing (∼20 ms in the fastest sniffs). The mean sustained flow rate attained and the overall period of each measured inspiratory profile were analyzed. AR showed a significant change in nasal volume with decongestion, although these change were not manifest in the temporal profiles of inspiratory flow (barring a weak effect associated with the most vigorous sniffs).ConclusionNovel methods were applied to investigate the temporal profiles of nasal inspiration. Characteristic features of the profile were identified and found to be significantly different between inspiration at rest and sniffing. Decongestion was found to have little effect on the temporal profiles for the flow regimes studied.
Denison D, Porter A, Mills M, et al., 2011, Forensic implications of respiratory derived blood spatter distributions, FORENSIC SCIENCE INTERNATIONAL, Vol: 204, Pages: 144-155, ISSN: 0379-0738
Taylor DJ, Doorly DJ, Schroter RC, 2010, Inflow boundary profile prescription for numerical simulation of nasal airflow, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 7, Pages: 515-527, ISSN: 1742-5689
Hood CM, Schroter RC, Doorly DJ, et al., 2010, Modeling of Human Maxillary Sinus Nitric Oxide Transport, 6th World Congress of Biomechanics (WCB 2010), Publisher: SPRINGER, Pages: 706-+, ISSN: 1680-0737
Hood CM, Schroter RC, Doorly DJ, et al., 2009, Computational modeling of flow and gas exchange in models of the human maxillary sinus, JOURNAL OF APPLIED PHYSIOLOGY, Vol: 107, Pages: 1195-1203, ISSN: 8750-7587
Taylor DJ, Doorly DJ, Schroter RC, 2009, AIRFLOW IN THE HUMAN NASAL CAVITY: AN INTER-SUBJECT COMPARISON, ASME Summer Bioengineering Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 1071-1072
Williams RJ, Nankervis KJ, Colborne GR, et al., 2009, Heart rate, net transport cost and stride characteristics of horses exercising at walk and trot on positive and negative gradients, Comp. Exercise Physiol.
Elad D, Schroter RC, 2008, Special Issue: Respiratory Biomechanics Foreword, RESPIRATORY PHYSIOLOGY & NEUROBIOLOGY, Vol: 163, Pages: 1-2, ISSN: 1569-9048
Doorly DJ, Taylor DJ, Schroter RC, 2008, Mechanics of Airflow in the Human Nasal Airways, Respiratory Physiology & Neurobiology, Vol: 163, Pages: 100-110
The mechanics of airflow in the human nasal airways is reviewed, drawing on the findings of experimental and computational model studies. Modelling inevitably requires simplifications and assumptions, particularly given the complexity of the nasal airways. The processes entailed in modelling the nasal airways (from defining the model, to its production and, finally, validating the results) is critically examined, both for physical models and for computational simulations. Uncertainty still surrounds the appropriateness of the various assumptions made in modelling, particularly with regard to the nature of flow. New results are presented in which high-speed particle image velocimetry (PIV) and direct numerical simulation are applied to investigate the development of flow instability in the nasal cavity. These illustrate some of the improved capabilities afforded by technological developments for future model studies. The need for further improvements in characterising airway geometry and flow together with promising new methods are briefly discussed.
Current approaches to model nasal airflow are reviewed in this study, and new findings presented. These new results make use of improvements to computational and experimental techniques and resources, which now allow key dynamical features to be investigated, and offer rational procedures to relate variations in anatomical form. Specifically, both replica and simplified airways of a single subject were investigated and compared with the replica airways of two other individuals with overtly differing geometries. Procedures to characterize and compare complex nasal airway geometry are first outlined. It is then shown that coupled computational and experimental studies, capable of obtaining highly resolved data, reveal internal flow structures in both intrinsically steady and unsteady situations. The results presented demonstrate that the intimate relation between nasal form and flow can be explored in greater detail than hitherto possible. By outlining means to compare complex airway geometries and demonstrating the effects of rational geometric simplification on the flow structure, this work offers a fresh approach to studies of how natural conduits guide and control flow. The concepts and tools address issues that are thus generic to flow studies in other physiological systems.
Leeming A, Schroter R, 2008, A model morphology of the pulmonary acinus, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 222, Pages: 429-437, ISSN: 0954-4119
Doorly DJ, Taylor DJ, Franke P, 2008, Experimental investigation of nasal airflow, Journal of Engineering in Medicine, Vol: 222
The airway geometry of the nasal cavity is manifestly complex, and the manner in which it controls the airflow to accomplish its various physiological functions is not fully understood. Since the complex morphology and inaccessibility of the nasal passageways precludes detailed in-vivo measurements, either computational simulation or in-vitro experiments are needed to determine how anatomical form and function are related. The fabrication of a replica model of the nasal cavity, of a high optical clarity and derived from invivo scan data is described here, together with characteristics of the flow field investigated using particle image velocimetry (PIV) and flow visualization. Flow visualization is shown to be a capable and convenient technique for identifying key phenomena. Specifically the emergence of the jet from the internal nasal valve into the main cavity, how it impacts on the middle turbinate, and the large enhancement of dispersion that accompanies the initial appearance of flow instability are revealed as particularly significant features. The findings from the visualization experiments are complemented by PIV imaging, which provides quantitative detail on the variations in velocity in different regions of the nasal cavity. These results demonstrate the effectiveness of the cavity geometry in partitioning the flow into high shear zones, which facilitate rapid heat transfer and humidification from the nasal mucosa, and slower zones affording greater residence times to facilitate olfactory sensing. The experimental results not only provide a basis for comparison with other computational modelling but also demonstrate an alternative and flexible means to investigate complex flows, relevant to studies in different parts of the respiratory or cardiovascular systems.
Deaton CM, Brown-Feltner H, Henley WE, et al., 2006, The effect of inspired gas density on pulmonary artery transmural pressure and exercise induced pulmonary haemorrhage., Equine Vet J Suppl, Vol: 36, Pages: 490-494
REASONS FOR PERFORMING STUDY: Pulmonary capillary stress failure, largely as a result of high pulmonary vascular pressures, has been implicated in the aetiology of EIPH. However, the role of the respiratory system in determining the magnitude of EIPH has received little attention. HYPOTHESIS: Horses breathing a gas of greater density than air will exhibit greater transmural pulmonary arterial pressures (TPAP) and more severe EIPH, and horses breathing a gas of lower density than air will exhibit lower TPAP and less severe EIPH, both compared with horses breathing air. METHODS: Following a warm-up, 8 Thoroughbred horses were exercised for 1 min at 10, 11 and 12 m/sec (5 degrees incline) breathing air or 21% oxygen/79% helium or 21% oxygen/79% argon in a randomised order. Heart rate, respiratory rate, pulmonary arterial pressure and oesophageal pressure were measured during exercise. Bronchoalveolar lavage fluid (BALF) was collected from the dorsocaudal regions of the left and right lungs 40 min post exercise and red blood cell (RBC) counts were performed. RESULTS: The exercise tests induced mild EIPH. Maximum changes in oesophageal pressure were lower on helium-oxygen compared to argon-oxygen (P<0.001). TPAP and median RBC counts did not differ between gas mixtures. BALF RBC counts from the left lung correlated with counts from the right lung (P<0.0001). However BALF RBC counts from the left lung were higher than those from the right lung (P = 0.004). CONCLUSION: As alterations in pulmonary arterial and oesophageal pressure caused by changes in inspired gas density were of similar magnitude, TPAP remained unchanged and there was no significant effect on EIPH severity. POTENTIAL RELEVANCE: Manipulations that decrease swings in intrapleural pressure may only decrease the degree of EIPH in horses severely affected by the condition.
Schott HC, Marlin DJ, Geor RJ, et al., 2006, Changes in selected physiological and laboratory measurements in elite horses competing in a 160 km endurance ride., Equine Vet J Suppl, Vol: 36, Pages: 37-42
REASON FOR PERFORMING STUDY: Limited information exists about the physiological changes and clinical problems that occur in elite horses competing in high-speed 160 km endurance races. OBJECTIVES: To provide initial data describing changes in physiological and laboratory measurements in horses competing in a high-speed, 160 km endurance race under temperate conditions and to compare data between horses that successfully completed the race and those that failed to finish. METHODS: Body mass (BM) was measured, blood samples were collected, and veterinary examinations performed on horses before, during, and at the finish of a CEI*** 160 km endurance race. RESULTS: Of 36 horses participating in the study, 22 (61%) completed the race. Twelve horses were eliminated for lameness and 2 for persistent heart rate elevation. Mean speed of finishers was 15.2 km/h. Mean +/- s.d. BM loss of finishers at the end of the race (5.7 +/- 2.6%) was not different (P = 0.58) from BM loss of nonfinishers at elimination (6.7 +/- 34%). Similarly, there were no significant differences in heart rate or veterinary assessment of hydration at the race end for finishers as compared to the elimination point for nonfinishers. PCV increased while sodium, chloride and potassium concentrations decreased with exercise but differences between finishers and nonfinishers were not detected. In contrast, both total and ionised calcium concentrations decreased in successful horses but remained unchanged in nonfinishers. CONCLUSIONS: Elite endurance horses are more likely to be eliminated from competition for lameness than metabolic problems; however, it remains unclear whether these conditions are entirely distinct. The magnitude of the decrease in sodium concentration in both finishers and nonfinishers was greater than in previous reports of 160 km rides. POTENTIAL RELEVANCE: These data should be of use for both organisers and participants in elite 160 km endurance races. The tendency toward hyponatraemia as
Denny E, Schroter RC, 2006, A model of non-uniform lung parenchyma distortion, JOURNAL OF BIOMECHANICS, Vol: 39, Pages: 652-663, ISSN: 0021-9290
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