LUNG MUCOCILIARY TRANSPORT DURING HIGH-FREQUENCY VENTILATION

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Abstract
Effects of high-frequency, low-tidal-volume ventilation (HFV) and conventional intermittent positive-pressure ventilation (IPPV) on lung mucociliary transport were compared in 5 anesthetized, intubated mongrel dogs with a radioactive label. An aerosol of [99mTc]sulfur colloid was delivered to the dogs'' airways and the subsequent clearance of isotope was followed over 4 h of HFV or IPPV. After 4 h of IPPV, .apprx. 8-10% of the initial activity had cleared from the lung. Practically all the isotope remained in the lung after 4 h of HFV. Large amounts of mucus were visible in the trachea immediately after each of the 4-h HFV studies; this was so in only 1 of the IPPV studies. In 5 of 6 studies, a bolus of radioactive label placed on the posterior trachea after 4 h of HFV dispersed and moved rapidly toward distal airways under the influence of HFV. Despite these findings of disturbed mucociliary transport during HFV, measurements of tracheal velocity, by a radioactive bolus technique during conventional ventilation, were the same after 4 h of HFV as after 4 h of IPPV (18.4 .+-. 2.6 and 15.0 .+-. 1.6 mm/min, respectively). In the anesthetized dog HFV may alter mucociliary transport. This is unlikely to be the result of major structural damage to the mucosal surface, because tracheal mucous velocity measured after 4 h of HFV was not different from that after IPPV. It may be partly explained by the retrograde flow of mucus that was observed during HFV in 5 of 6 studies.