Distribution of pulmonary blood flow in the perfluorocarbon-filled lung

Abstract

Objective: Partial liquid ventilation (PLV) improves gas exchange in animal studies of lung injury. Perfluorocarbons (PFCs) are heavy liquids and are therefore preferentially delivered to the most dependent areas of lung. We hypothesised that improved oxygenation during PLV might be the consequence of a redistribution of pulmonary blood flow away from poorly ventilated, dependent alveoli, leading to improved ventilation/perfusion (V/Q) matching. This study investigated whether partially filling the lung with PFC would result in a redistribution of pulmonary blood flow. Design: Prospective experimental study. Setting: Hospital research institute laboratory. Participants: Six anaesthetised pigs without lung injury. Interventions: Animals were anaesthetised and ventilated (gas tidal volume 12 ml/kg, PEEP 5, FIO2 1.0, rate 16). Whilst the pigs were maintained in the supine position, regional pulmonary blood flow was measured during conventional gas ventilation and repeated during PLV. Flow to regions of lung was determined by injection of radioactive microspheres (Co57, Sn113, Sc46). Measurements were performed with ventilation held at end-expiratory pressure and, in two PLV animals only, repeated with ventilation held at peak inspiratory pressure. Results: During conventional gas ventilation, blood flow followed a linear distribution with the highest flow to the most dependent lung. In the lung partially filled with PFC a diversion of blood flow away from the most dependent lung was seen (p = 0.007), resulting in a more uniform distribution of flow down the lung (p = 0.006). Linear regression analysis (r2 = 0.75) also confirmed a difference in distribution pattern. On applying an inspiratory hold to the liquid-containing lung, blood flow was redistributed back towards the dependent lung. Conclusions: Partially filling the lung with PFC results in a redistribution of pulmonary blood flow away from the dependent region of the lung. During PLV a different blood flow distribution may be seen between inspiration and expiration. The clinical significance of these findings has yet to be determined.