The role of ventilation frequency in airway reopening

摘要

Premature infants are often affected by respiratory insufficiency which is frequently caused by regional collapse of the airways. This leads to inhomogeneous lung ventilation. To treat respiratory insufficiency, atelectatic areas have to be recruited. Beside conventional mechanical ventilation, high frequency oscillatory ventilation (HFOV) is an efficient method for airway reopening. Using a transparent in vitro model of the human lung the influence of varying frequencies on the reopening behavior of atelectatic regions is investigated under the boundary conditions of HFOV. The reason for the use of an in vitro model is to analyze the underlying flow characteristics during ventilation by optical measurement techniques. The in vitro experiments have shown that higher ventilation frequencies enhance the reopening of collapsed lung regions and thus, lead to a more homogeneous distribution of air within the lung. This effect can be attributed (i) to larger flow velocities as the frequency increases whereas the tidal volume was kept constant and (ii) to higher values of the acceleration. Increased flow velocities lead to higher pressure losses in normally ventilated lung areas. Thus, the pressure in atelectatic regions can reach a level at which recruitment can be induced. This effect enables to ventilate the lung more homogeneously.