Computational fluid dynamics benchmark dataset of airflow in tracheas.

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 employed in 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 vivo validation 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 time scales. 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 effects of curvature and constriction on airflow and energy loss in pathological tracheas.

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 the 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.

Power loss mechanisms in pathological tracheas.

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.

Tissue-Engineered Tracheal Replacement in a Child: A 4-Year Follow-Up Study.

In 2010, a tissue-engineered trachea was transplanted into a 10-year-old child using a decellularized deceased donor trachea repopulated with the recipient's respiratory epithelium and mesenchymal stromal cells. We report the child's clinical progress, tracheal epithelialization and costs over the 4 years. A chronology of events was derived from clinical notes and costs determined using reference costs per procedure. Serial tracheoscopy images, lung function tests and anti-HLA blood samples were compared. Epithelial morphology and T cell, Ki67 and cleaved caspase 3 activity were examined. Computational fluid dynamic simulations determined flow, velocity and airway pressure drops. After the first year following transplantation, the number of interventions fell and the child is currently clinically well and continues in education. Endoscopy demonstrated a complete mucosal lining at 15 months, despite retention of a stent. Histocytology indicates a differentiated respiratory layer and no abnormal immune activity. Computational fluid dynamic analysis demonstrated increased velocity and pressure drops around a distal tracheal narrowing. Cross-sectional area analysis showed restriction of growth within an area of in-stent stenosis. This report demonstrates the long-term viability of a decellularized tissue-engineered trachea within a child. Further research is needed to develop bioengineered pediatric tracheal replacements with lower morbidity, better biomechanics and lower costs.

Dynamics of airflow in a short inhalation.

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.

Long-term quality-of-life outcomes in children undergoing adenotonsillectomy for obstructive sleep apnoea: a longitudinal study.

OBJECTIVES: To assess a cohort of patients who underwent adenotonsillectomy for obstructive sleep apnoea, 4 years after surgery for evidence of continued and long-term improvement in quality of life. We also sought to compare our results to Child Health Questionnaire scores obtained from our previous study. We also compared our data with a healthy UK children population from normative data available. DESIGN: Longitudinal study. SETTINGS: University Hospital Tertiary Referral Centre. PARTICIPANTS: A 4-year follow-up study of 37 children who underwent adenotonsillectomy for obstructive sleep apnoea confirmed on polysomnography. There were 19 boys and 18 girls from our initial cohort. The primary caregiver completed the validated Child Health Questionnaire Parental Form version-28, 4 years after initial surgery. Our control group consist of 221 healthy children aged 6-18 that were included as 'normal' controls in a study looking at children with juvenile arthritis. The children were defined as healthy by a physician and/or after declaration by the parent. MAIN OUTCOME MEASURE: Child Health Questionnaire Parental Form version-28 scores. RESULTS: A total of 33 patients (89%) from our initial cohort were contacted. The mean age was 10.6 (median, 11; range, 5-16). When compared with results obtained 3 months postoperatively, the mean scores were higher in five domains and were statistically significant in three subscales (Role Limitations P < 0.00001; Bodily Pain P < 0.002; and Global Health P < 0.02). There was a significant deterioration in Behaviour subscale (P < 0.0007) in spite of surgery. Compared with controls, 4-year follow-up scores were higher in five domains with the Global Health domain (P < 0.0004) being statistically significant. When the 4-year follow-up scores were compared with preoperative values, these were higher in all 13 domains with statistically significant improvements in nine domains, indicating that improvements had persisted 4 years after surgery. At 4 years, however, the means scores in many domains remain lower when compared with controls. CONCLUSION: Quality-of-life data are an important measure when deciding on a specific clinical intervention. In the short term, quality-of-life measures have been shown to improve after adenotonsillectomy for obstructive sleep apnoea. Our study demonstrates that the benefits of surgery are still persistent and the children continue to improve in the long term.

Improving tracheostomy care: a prospective study of the multidisciplinary approach.

OBJECTIVES: Suboptimal standards in tracheostomy care have been highlighted as a growing concern in view of the increasing demands for intensive care services. Our objective is to assess the impact of our model for tracheostomy care on patients with short-term tracheostomies (<4 months in situ) following their discharge from the intensive care unit. The model has three components: The St Mary's tracheostomy care bundle checklist, a dedicated tracheostomy multidisciplinary team and an educational programme. DESIGN: A 38-month prospective cohort study. SETTING: A London Teaching Hospital. PARTICIPANTS: A total of 102 patients with tracheostomy within the 19-month pre-intervention cohort and 95 patients in the 19-month post-intervention cohort. MAIN OUTCOME MEASURES: The number of clinical incidents, mean time taken for decannulation, mean total tracheostomy time and total number of days spent in the intensive care unit were assessed before and after the intervention. RESULTS: Time to decannulation following intensive care unit discharge decreased from 21 to 11 days, as did the mean total tracheostomy time, from 34 to 25 days (both statistically significant with a P < 0.0001 Mann-Whitney U-test). The number of critical incidents, which included all patients prior to exclusion, substantially declined following the introduction of intervention from 58 to 7 in the second year after intervention. CONCLUSIONS: A multidisciplinary care model significantly expedited the decannulation process and reduced the overall time that a tracheostomy was in situ. The intervention was associated with a reduction in clinical incidents and shorter intensive care unit admissions, which can be associated with significant monetary savings.