The effect of pulmonary arterial flow and positive end-expiratory pressure on retrograde bronchial mucosal blood flow

Bronchial viability within the first few days after lung transplantation depends on collateral blood flow from the pulmonary to the bronchial circulation. In the present study the relationship between pulmonary arterial flow and retrograde bronchial blood flow, and the effect of positive end-expiratory pressure on bronchial blood flow were evaluated by laser Doppler velocimetry in an isolated in situ lung perfusion model. Nine adult mongrel dogs were exsanguinated by way of a left atrial cannula. Blood was pumped by a roller pump into the main pulmonary artery. Lungs were perfused at random flow (in 0.5 L/min increments) at rates of 1 to 3 L/min. Steady-state laser Doppler velocimetric measurements at each level of flow were made at the tracheal carina and both bronchial carinae. Pump flow was then set at baseline cardiac output and positive end-expiratory pressure was applied. Steady-state laser Doppler velocimetric measurements were obtained at each level of positive end-expiratory pressure (5 cm H₂O and 10 cm H₂O). Bronchial blood flow correlated well with pulmonary arterial flow (for the tracheal carina; rs = 0.912 and p < 0.0005; for the right bronchial carina, rs = 0.799, p < 0.0005; for the left bronchial carina, rs = 0.917, p < 0.0005; where rs is the common correlation coefficient). The bronchial blood flow at the left bronchial carina and the right bronchial carina were significantly higher than at the tracheal carina (p < 0.005 and p < 0.05, respectively). At baseline cardiac output, bronchial blood flow in the situ model was approximately 50% lower than observed in the intact animals. Positive end-expiratory pressure increased the bronchial blood flow at the tracheal carina and both bronchial carinae (p < 0.05)..