Effects of positive end expiratory pressure on shunt flow in atelectasis

We studied the effects of positive end expiratory pressure (PEEP) on vascular pressure flow relationships in atelectatic lobes in closed-chest pigs and compared our results to measurements we previously obtained in sublobar atelectasis. Regional hemodynamic responses to lung inflation were significantly different between lobes and sublobar regions. PEEP caused marked increase in the fraction of cardiac output perfusing the atelectatic lobe from 16.5 ± 2.0% (SE) to 32.5 ± 2.0% at similar pulmonary vascular transmural pressures. In contrast, similar levels of PEEP failed to redistribute blood flow to the atelectatic sublobar regions. We propose that distortion of the sublobar region with inflation of the surrounding lung may be responsible for the failure of redistribution of pulmonary blood flow with application of PEEP.