Objective: To assess the effects of positive end-expiratory pressure on regional ventilation distribution in normal lung and after histamine-induced bronchoconstriction.
Design: Experimental study.
Setting: International research laboratory.
Subjects: Six healthy New Zealand rabbits weighing 2.5 ± 0.1 kg.
Interventions: Rabbits were anesthetized, tracheostomized, paralyzed, and mechanically ventilated. Synchrotron radiation computed tomography images of tissue density and specific ventilation were acquired using K-edge subtraction imaging with inhaled stable xenon gas in middle and caudal thoracic levels on 0 and 5 cm H2O positive end-expiratory pressure at baseline and twice after histamine inhalation.
Measurements and Main Results: At baseline, a positive end-expiratory pressure of 5 cm H2O significantly increased lung volume. Histamine inhalation caused patchy areas of decreased specific ventilation, including some areas with no ventilation. After histamine, positive end-expiratory pressure significantly increased the area of well-ventilated lung regions and decreased the heterogeneity of specific ventilation. This improvement went together with a significant but limited increase in the area of hyperinflated lung zones.
Conclusions: The findings of this study suggest that in mechanically ventilated rabbit with severely heterogeneous bronchoconstriction, a positive end-expiratory pressure of 5 cm H2O significantly improves regional ventilation homogeneity through dilation of flow-limited airways and recruitment of closed airways.