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 H(2)O 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 H(2)O 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 H(2)O significantly improves regional ventilation homogeneity through dilation of flow-limited airways and recruitment of closed airways.
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 H(2)O 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 H(2)O 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 H(2)O significantly improves regional ventilation homogeneity through dilation of flow-limited airways and recruitment of closed airways.
Authors: Tyler J Wellman; Tilo Winkler; Eduardo L V Costa; Guido Musch; R Scott Harris; Jose G Venegas; Marcos F Vidal Melo Journal: J Appl Physiol (1985) Date: 2012-06-07
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