A new adaptive time step method for unsteady flow simulations in a human lung.

The innovation presented is a method for adaptive time-stepping that allows clustering of time steps in portions of the cycle for which flow variables are rapidly changing, based on the concept of using a uniform step in a relevant dependent variable rather than a uniform step in the independent variable time. A user-defined function was developed to adapt the magnitude of the time step (adaptive time step) to a defined rate of change in inlet velocity. Quantitative comparison indicates that the new adaptive time stepping method significantly improves accuracy for simulations using an equivalent number of time steps per cycle.

Double aortic arch diagnosed in a 44-year-old woman with recurring respiratory infections.

Complete vascular rings are originated because of the persistence of the fourth aortic arches, which surround the trachea and esophagus partially or completely, compressing them. The most common type of complete vascular ring is the double aortic arch. Symptoms usually appear in the first months of life, and are provoked by esophageal and tracheal compression.