An ultrasound imaging method for in vivo tracheal bulk and Young's moduli of elasticity

Effect of continuous positive airway pressure treatment on permeability, inflammation and mucus production of human epithelial cells

Continuous positive airway pressure (CPAP) therapy is the gold standard treatment for obstructive sleep apnoea, which affects millions of people worldwide. However, this therapy normally results in symptoms such as dryness, sneezing, rhinorrhoea, post-nasal drip, nasal congestion and epistaxis in the upper airways. Using bronchial epithelial (Calu-3) and nasal epithelial (RPMI 2650) cells in an in vitro respiratory model, this study, for the first time, investigates the effect of CPAP positive pressure on the human respiratory epithelial mechanisms that regulate upper airways lubrication characteristics. To understand how the epithelium and mucus are affected by this therapy, several parameters were determined before and after positive pressure application. This work demonstrates that the positive pressure not only compresses the cells, but also reduces their permeability and mucus secretion rate, thus drying the airway surface liquid layer and altering the mucus/water ratio. It is also observed that the respiratory epithelia is equally inflamed without or with external humidification during CPAP application. These findings clearly identify the causes of the side-effects reported by patients under CPAP therapy.

Calculation of human femoral vein wall parameters in vivo from clinical data for specific patient

A common problem in the elaboration of biomechanical models is determining the properties and characteristics (measures) of the physical behavior of in vivo tissues in the human body. Correct estimates must be made of the tissue's physical properties and its surroundings. We suggest a method to compute the constitutive modeling of venous tissue, for every specific patient, from clinically registered ultrasounds images. The vein is modeled as a hyperelastic, incompressible, thin-walled cylinder and the membrane stresses are computed using strain energy. The approach is based on a strain-energy function suggested by Holzapfel capturing the characteristic nonlinear anisotropic responses of femoral veins with its collagen fibers.

Brief mechanical ventilation impacts airway cartilage properties in neonatal lambs

Ultrasound imaging allows in vivo assessment of tracheal kinetics and cartilage structure. To date, the impact of mechanical ventilation (MV) on extracellular matrix (ECM) in airway cartilage is unclear, but an indication of its functional and structural change may support the development of protective therapies. The objective of this study was to characterize changes in mechanical properties of the neonatal airway during MV with alterations in cartilage ECM. Trachea segments were isolated in a neonatal lamb model; ultrasound dimensions and pressure-volume relationships were measured on sham (no MV; n = 6) and MV (n = 7) airways for 4 hr. Tracheal cross-sections were harvested at 4 hr, tissues were fixed and stained, and Fourier transform infrared imaging spectroscopy (FT-IRIS) was performed. Over 4 hr of MV, bulk modulus (28%) and elastic modulus (282%) increased. The MV tracheae showed higher collagen, proteoglycan content, and collagen integrity (new tissue formation); whereas no changes were seen in the controls. These data are clinically relevant in that airway properties can be correlated with MV and changes in cartilage ECM. MV increases the in vivo dimensions of the trachea and is associated with evidence of airway tissue remodeling. Injury to the neonatal airway from MV may have relevance for the development of tracheomalacia. We demonstrated active airway tissue remodeling during MV using an FT-IRIS technique which identifies changes in ECM.

Young's modulus measurement on pig trachea and bronchial airways

Young's Modulus was measured on the trachea and first three generations of pig airways by compression. A simple and low-cost system for measuring the elastic properties of small bio-materials is presented. The force-displacement measurements have been undertaken on dissected cartilage and trachea mucosa from pig trachea and bronchial segments. Young's Modulus of trachea wall, 1.78 ± 0.51 MPa, is found to be dominated by the trachea cartilage of value 1.74 ± 0.85 MPa while the modulus for trachea mucosa was 0.15 ± 0.03 MPa. The Young's Modulus of the airway wall from the first three generations of bronchi decreases from 1.35 ± 0.17 to 0.35 ± 0.10 MPa which is also found to be dominated by the airway cartilage. Airway mucosa is found to have similar Young's modulus of 0.036 ± 0.005 MPa for the first three generations of bronchial airways.

Biomechanical properties of adult-excised porcine trachea for tracheal xenotransplantation

BACKGROUND

To investigate and evaluate the biomechanical properties of adult-excised porcine trachea, thereby providing experimental methods and evidence for biomedical engineering of artificial trachea.

METHODS

The TY8000 servo-handle tension test machine was used to measure biomechanical indices, such as bending stiffness, radial pedestal, and stress-straining. The residual stress and bursting strength of adult-excised porcine trachea was evaluated.

RESULTS

Residual stress was retained in the adult-excised porcine trachea. The force of radial pedestal was detected as 10 N, when the diameter of a 50-mm trachea was compressed to 50%. The bursting strength decreased from 180 mmHg of pharyngeal portion to 110 mmHg in tracheal carina. When the trachea flexed forward or either right or left by 50 degrees , tension reached 0.296 to 0.131 N and 0.254 to 0.150 N, respectively. The curve of stress-straining measured, according to computer data and results, suggested that tension was maintained at a low level at 50% strain.

CONCLUSIONS

Residual stress was retained in the excised porcine trachea, and the porcine trachea membrane disrupted when pressure in the inner wall increased. The porcine trachea exhibits good radial pedestal force, bending, and elongation properties.

Heat shock protein 70 secretion by neonatal tracheal tissue during mechanical ventilation: association with indices of tissue function and modeling

Mechanical ventilation (MV) of the neonatal airway alters mechanical properties and activates tissue-modeling pathways. Heat shock protein (HSP70) is a marker of tissue injury and modulates inflammation, which may influence subsequent pulmonary tissue modeling by matrix metalloproteinases (MMPs). HSP70 secretion is up-regulated in MV airway tissues and associated with changes in airway elasticity and secretion of MMPs. Proximal tracheal segments were isolated in 13 newborn lambs and were either MV for 4 h or SHAM. At baseline and hourly, tracheal segments were flushed and tracheal elasticity was determined. Tracheal wash fluid was assayed for HSP70 by ELISA and for MMPs by substrate zymography. HSP70 secretion increased from baseline to a peak at 1 h in both groups (p < 0.01), greater in the MV group (p < 0.05), and returned to baseline values by 2 h. This response was in contrast to the progressive decrease in tracheal elasticity (p < 0.05). The HSP70 elevation pattern was noted in MMP-2, but beyond 1 h, MMP-2 returned to baseline values in MV group but remained elevated in SHAM (p < 0.05). HSP70 secretion is associated with the degree of biophysical tracheal injury as well as the time course of MMP-2 secretion by tracheal tissues.

Airway mechanics and methods used to visualize smooth muscle dynamics in vitro

Contraction of airway smooth muscle (ASM) is regulated by the physiological, structural and mechanical environment in the lung. We review two in vitro techniques, lung slices and airway segment preparations, that enable in situ ASM contraction and airway narrowing to be visualized. Lung slices and airway segment approaches bridge a gap between cell culture and isolated ASM, and whole animal studies. Imaging techniques enable key upstream events involved in airway narrowing, such as ASM cell signalling and structural and mechanical events impinging on ASM, to be investigated.