Ventilation-perfusion distribution related to different inspiratory flow patterns in experimental lung injury

In acute lung injury (ALI), controlled mechanical ventilation with decelerating inspiratory flow (V-dec) has been suggested to improve oxygenation when compared with constant flow, (V-con) by improving the distribution of ventilation and perfusion (V-A/Q). We performed the present study to test this hypothesis in an animal model of ALI. Furthermore, the effects of combined decelerating and constant flow (V-deco) were evaluated. Thus, 18 pigs with experimental ALI were randomized to receive mechanical ventilation with either V-con, V-dec or a fixed combination of both flow wave forms (V-deco) at the same tidal volume and positive end-expiratory pressure level for 6 h. Hemodynamics, gas exchange, and VA/Q distribution were determined. The results revealed an improvement of oxygenation resulting from a decrease of pulmonary shunt within each group (P < 0.05). However, blood flow to lung areas with a normal VA/Q distribution increased only during ventilation with V-con (P < 0.05). Accordingly, Pao(2) was higher with V-con than with V-dec and V-deco (P < 0.05). We conclude that contrary to the hypothesis, V-con provides a more favorable V-A/Q distribution, and hence better oxygenation, when compared with V-dec and V-deco in this model of ALI.