A novel method of tracheal anastomosis healing using a single submucosal injection of basic fibroblast growth factor: initial report.

OBJECTIVES: For the technical management of tracheal anastomosis, developing new and simple methods is required to relieve anastomotic tension. This study aimed to investigate whether basic fibroblast growth factor (bFGF) only once injected immediately before anastomosis promotes cartilage regeneration at the tracheal anastomosis and whether the regenerated cartilage has the effect of reinforcing the anastomosis in a rabbit model. METHODS: New Zealand white rabbits were anaesthetized, and the cervical trachea was exposed through a cervical midline incision, followed by resection of the 10th tracheal cartilage. The rabbits were categorized into 2 groups: the bFGF group (n = 6) and the control group (n = 6). In the former group, bFGF (25 µg) was administered into the submucosal layer of the cartilage using a 27-G needle immediately before tracheal anastomosis. The animals were sacrificed 4 weeks later. Histological, mechanical and biochemical evaluations were performed on this anastomosed trachea. RESULTS: At 4 weeks of age, the anastomoses were spindle-shaped and displayed maximum diameter at the injection site compared with those in the control group. Histological evaluation showed that cartilage tissue had regenerated between the 9th and 11th tracheal cartilage rings. Tensile test showed that the anastomoses displayed a significantly high strain/stress ratio (P = 0.035). The collagen type II and glycosaminoglycan levels were significantly increased, and the collagen type I level was significantly decreased (P = 0.019, P = 0.013 and P = 0.045, respectively). CONCLUSIONS: A new wound-healing concept of airway anastomosis could be provided by the results that single injection of bFGF regenerated tracheal cartilage in rabbits and strengthened the anastomosis by bridging the regenerated and well-matured cartilage. Further investigation of this method will lead to potential clinical applications for reinforcement of tracheal anastomoses.

Construction of a computational mechanical model of bronchi for practical simulation of the optimal positive intrathoracic pressure conditions during general thoracic surgery.

BACKGROUND: Thoracic CO2 insufflation with positive intrathoracic pressure is usually effective during thoracoscopic surgery, however, lung collapse is sometimes insufficient. We hypothesized that inappropriate bronchial collapse might cause this unsuccessful lung collapse. OBJECTIVE: The objective of this study was to construct a computational mechanical model of bronchi for practical simulation to discover the optimal conditions of positive intrathoracic pressure during thoracoscopic surgery. METHODS: Micro-focus high-resolution X-ray computed tomography measurements of lungs from just-slaughtered swine were extracted, and the three-dimensional geometries of the bronchi under pressurized and depressurized conditions were measured accurately. The mechanical properties of the bronchus were also measured. Computational fluid dynamics (CFD) and computational structural mechanics (CSM) analyses were conducted. RESULTS: The CSM results indicated that the present structural model could simulate bronchial occlusion. The CFD results showed that airflows from pressed lung alveoli might cause low-internal-pressure regions when suddenly or heterogeneously pushed airflow was injected from a small branching bronchus to a large bronchus. A preliminary computational mechanical model of bronchi was constructed. CONCLUSIONS: We demonstrated the performance of the mechanical model of bronchi in rough simulations of bronchial occlusions. However, this model should be verified further using human data to facilitate its introduction to clinical use.

A preoperative predictive study of advantages of airway changes after maxillomandibular advancement surgery using computational fluid dynamics analysis.

The purpose of this study was to develop a simulation approach for predicting maxillomandibular advancement-induced airway changes using computational fluid dynamics. Eight patients with jaw deformities who underwent maxillomandibular advancement and genioglossus advancement surgery were included in this study. Computed tomography scans and rhinomanometric readings were performed both preoperatively and postoperatively. Computational fluid dynamics models were created, and airflow simulations were performed using computational fluid dynamics software; the preferable number of computational mesh points was at least 10 million cells. The results for the right and left nares, including simulation and postoperative measurements, were qualitatively consistent, and surgery reduced airflow pressure loss. Geometry prediction simulation results were qualitatively consistent with the postoperative stereolithography data and postoperative simulation results. Simulations were performed with either the right or left naris blocked, and the predicted values were similar to those found clinically. In addition, geometry prediction simulation results were qualitatively consistent with the postoperative stereolithography data and postoperative simulation results. These findings suggest that geometry prediction simulation facilitates the preoperative prediction of the postoperative structural outcome.

The effect of nasal and oral breathing on airway collapsibility in patients with obstructive sleep apnea: Computational fluid dynamics analyses.

OBJECTIVE: The purpose of this study was to investigate the effect of breathing route on the collapsibility of the pharyngeal airway in patients with obstructive sleep apnea by using computational fluid dynamics technology. METHODS: This study examined Japanese men with obstructive sleep apnea. Computed tomography scans of the nose and pharynx were taken during nasal breathing with closed mouth, nasal breathing with open mouth, and oral breathing while they were awake. Three-dimensional reconstructed stereolithography models and digital unstructured grid models were created and airflow simulations were performed using computational fluid dynamics software. RESULTS: Airflow velocity was significantly higher during oral breathing than during nasal breathing with open or closed mouth. No significant difference in maximum velocity was noted between nasal breathing with closed and open mouth. However, airflow during nasal breathing with open mouth was slow but rapidly sped up at the lower level of the velopharynx, and then spread and became a disturbed, unsteady stream. In contrast, airflow during nasal breathing with closed mouth gradually sped up at the oropharyngeal level without spreading or disturbance. Negative static pressure during oral breathing was significantly decreased; however, there were no significant differences between nasal breathing with closed or open mouth. CONCLUSIONS: Computational fluid dynamics results during nasal and oral breathing revealed that oral breathing is the primary condition leading to pharyngeal airway collapse based on the concept of the Starling Resistor model. Airflow throughout the entirety of the breathing route was smoother during nasal breathing with closed mouth than that with open mouth.

Computational fluid dynamics analysis for the preoperative prediction of airway changes after maxillomandibular advancement surgery.

Maxillomandibular advancement surgery is useful for treatment of sleep apnea. However, preoperative analysis and evaluation to facilitate decision-making regarding the direction and distance of maxillomandibular movement has primarily consisted of morphological analysis; physiological function is not evaluated. To improve preoperative prediction, this study used fluid simulation to investigate the characteristics and effects of airway changes associated with maxillomandibular movement. A one-dimensional model with general applicability was thus developed. Actual measurements of flow in patients were used in this fluid simulation, thus achieving an analysis closer to clinical conditions. The simulation results were qualitatively consistent with the actual measurements, which confirmed the usefulness of the simulation. In addition, the results of the one-dimensional model were within the error ranges of the actual measurements. The present results establish a foundation for using accumulating preoperative measurement data for more-precise prediction of postoperative outcomes.

Effect of Nasal Obstruction on Continuous Positive Airway Pressure Treatment: Computational Fluid Dynamics Analyses.

OBJECTIVE: Nasal obstruction is a common problem in continuous positive airway pressure (CPAP) therapy for obstructive sleep apnea and limits treatment compliance. The purpose of this study is to model the effects of nasal obstruction on airflow parameters under CPAP using computational fluid dynamics (CFD), and to clarify quantitatively the relation between airflow velocity and pressure loss coefficient in subjects with and without nasal obstruction. METHODS: We conducted an observational cross-sectional study of 16 Japanese adult subjects, of whom 9 had nasal obstruction and 7 did not (control group). Three-dimensional reconstructed models of the nasal cavity and nasopharynx with a CPAP mask fitted to the nostrils were created from each subject's CT scans. The digital models were meshed with tetrahedral cells and stereolithography formats were created. CPAP airflow simulations were conducted using CFD software. Airflow streamlines and velocity contours in the nasal cavities and nasopharynx were compared between groups. Simulation models were confirmed to agree with actual measurements of nasal flow rate and with pressure and flow rate in the CPAP machine. RESULTS: Under 10 cmH2O CPAP, average maximum airflow velocity during inspiration was 17.6 ± 5.6 m/s in the nasal obstruction group but only 11.8 ± 1.4 m/s in the control group. The average pressure drop in the nasopharynx relative to inlet static pressure was 2.44 ± 1.41 cmH2O in the nasal obstruction group but only 1.17 ± 0.29 cmH2O in the control group. The nasal obstruction and control groups were clearly separated by a velocity threshold of 13.5 m/s, and pressure loss coefficient threshold of approximately 10.0. In contrast, there was no significant difference in expiratory pressure in the nasopharynx between the groups. CONCLUSION: This is the first CFD analysis of the effect of nasal obstruction on CPAP treatment. A strong correlation between the inspiratory pressure loss coefficient and maximum airflow velocity was found.