Cardiopulmonary effect of various inspiratory flow profiles during controlled mechanical ventilation in a porcine lung model.

We studied the influence of inspiratory flow (VI) patterns on gas exchange and hemodynamics after metacholine inhalation challenge (MIC) in seven swine mechanically ventilated with a constant, sinusoidal, accelerating, and decelerating flow pattern. Blood gas and expired CO2 tensions, pulmonary mechanics, and hemodynamics were measured during each pattern. Flow pattern sequence was randomized and MIC was repeated at 30 to 45-min intervals. MIC reliably reduced PaO2, and increased PaCO2 and peak tracheal pressure (PT). There was no significant difference in gas exchange or hemodynamics between various VI curves. Insufflation with an accelerated VI manifested a significantly higher PT than any other pattern. We conclude that no VI contour studied offers a unique advantage for gas exchange after MIC in swine. However, since accelerated gas flow generates significantly higher PT values, it is not recommended in the presence of significant airway resistance.