Reduced Surfactant Contributes to Increased Lung Stiffness Induced by Rapid Inspiratory Flow.

Introduction: The mechanism of fast inspiratory flow rate (V') induced lung injury is unclear. As fast V' increases hysteresis, a measure of surface tension at the air-liquid interface, surfactant release or function may be important. This experimental study examines the contribution of impaired surfactant release or function to dynamic-VILI.

Methods: Isolated perfused lungs from male Sprague Dawley rats were randomly allocated to four groups: a long or short inspiratory time (Ti = 0.5 s; slow V' or Ti = 0.1 s; fast V') at PEEP of 2 or 10 cmHO. Tidal volume was constant (7 ml/kg), with f = 60 breath/min. Forced impedance mechanics (tissue elastance (Htis), tissue resistance (Gtis) and airway resistance (Raw) were measured at 30, 60 and 90 min following which the lung was lavaged for surfactant phospholipids (PL) and disaturated PL (DSP).

Results: Fast V' resulted in a stiffer lung. Concurrently, PL and DSP were decreased in both tubular myelin rich and poor fractions. Phospholipid decreases were similar with PEEP. In a subsequent cohort, laser confocal microscopy-based assessment demonstrated increased cellular injury with increased V' at both 30 and 90 min ventilation.

Conclusion: Rapid V' may contribute to ventilator induced lung injury (VILI) through reduced surfactant release and/or more rapid reuptake despite unchanged tidal stretch.