Tidal volume and alveolar clearance of insoluble particles

We studied the effect of 3 h of large tidal volume ventilation on alveolar clearance of 0.63-micron fluorescent latex particles in rabbits during pentobarbital anesthesia. After particle deposition, six animals were killed as controls, six were subjected to large tidal volume ventilation with a peak pressure of 27 cmH2O, and six were subjected to conventional ventilation with a peak pressure of 11 cmH2O. Mean tidal volumes were 30.2 +/- 6.1 and 8.4 +/- 1.6 ml/kg in the large tidal volume and conventional groups, respectively. End-expiratory pressure was 2 cmH2O in all groups. Compliance decreased only after large tidal ventilation (P = 0.0036). Compared with controls the conventional ventilation group showed no alveolar clearance, but more particles were clustered within macrophages (P = 0.01). Compared with other groups the large tidal volume group had fewer alveolar particles (P = 0.0005), most of which were single particles. Accordingly, large tidal volumes enhance alveolar particle clearance, which is possibly related to distension-related evacuation of surfactant to proximal airways. Clearance may be due to accelerated motion of the particle-loaded macrophage in response to the fast film motion. Alternatively, single particles embedded in the surfactant film may be dragged by the fast-moving film toward the airways.