[Positive alveolar pressure reduces bronchial systemic-to-pulmonary blood flow in man]

We studied in humans during total cardio-pulmonary by-pass the effects of positive alveolar pressure on systemic to pulmonary bronchial blood flow. Systemic to pulmonary bronchial blood flow is the entire bronchial blood flow to the lung and was measured as the volume of blood which accumulates in the left heart when there is no pulmonary flow. Systemic to pulmonary bronchial blood flow was vented by gravity via a cannula (18 French) introduced in the upper superior pulmonary vein and advanced into the lower most portion of the left heart. In Group A (10 patients) systemic to pulmonary bronchial blood flow was measured with alveolar pressure constant at 4.0 +/- 0.4 cm H2O for 53.5 +/- 6.2 min (range 25 to 95 min), and ranged between 0.32 and 2.76% of cardiac output (pump flow) remaining constant with time. In Group B (10 patients) systemic to pulmonary bronchial blood flow was measured for 2 periods of 20 min each with alveolar pressure equal 4.1 +/- 0.2 and 14.1 +/- 0.4 cm H2O respectively. The increase of alveolar pressure reduced systemic to pulmonary bronchial blood flow by almost 40%. The reduction of systemic to pulmonary bronchial blood flow we observed may be deleterious for the survival of the lung parenchyma particularly in some circumstances. This is the case of pulmonary embolism, when bronchial blood flow is the major source of blood to the lung parenchyma and serves to prevent pulmonary infarction, or the case of acute respiratory distress syndrome, when pulmonary flow is compromised and systemic to pulmonary bronchial blood flow increases.(ABSTRACT TRUNCATED AT 250 WORDS)