TIDAL VOLUME AND ALVEOLAR CLEARANCE OF INSOLUBLE PARTICLES

We studied the effect of 3 h of large tidal volume ventilation on alve olar clearance of 0.63-mu m fluorescent latex particles in rabbits dur ing pentobarbital anesthesia. After particle deposition, six animals w ere killed as controls, six were subjected to large tidal volume venti lation with a peak pressure of 27 cmH(2)O, and six were subjected to c onventional ventilation with a peak pressure of 11 cmH(2)O. Mean tidal volumes were 30.2 +/- 6.1 and 8.4 +/- 1.6 ml/kg in the large tidal vo lume and conventional groups, respectively. End-expiratory pressure wa s 2 cmH(2)O in all groups. Compliance decreased only after large tidal ventilation (P = 0.0036). Compared with controls the conventional ven tilation group showed no alveolar clearance, but more particles were c lustered within macrophages (P = 0.01). Compared with Other groups the large tidal volume group had fewer alveolar particles (P = 0.0005), m ost of which were single particles. Accordingly, large tidal volumes e nhance alveolar particle clearance, which is possibly related to diste nsion-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 embe dded in the surfactant film may be dragged by the fast-moving film tow ard the airways.