EFFECTS OF LEFT ATRIAL AND AIRWAY PRESSURES ON AIRWAY BLOOD-FLOW

The blood flow contributions of the pulmonary and systemic circulation s to airway blood flow from the trachea down to the 5th generation air ways when either 15 cmH2O positive end expiratory pressure (PEEP) or 2 0 mmHg left atrial pressure was applied were assessed in anesthetized dogs by injections 15-mum radiolabeled microspheres into the right and left heart, respectively. After the microsphere injections, the anima ls were killed, and the tracheal cartilage, tracheal muscle-mucosa, ma in bronchi and the 2nd generation bronchi down to the 5th generation a irways were excised and collected for radioactive counting. The result s of this study showed that under normal conditions, tracheal blood fl ow was primarily systemic (> 95% of total tracheal blood flow) averagi ng 15-26 ml.min-1.(100 g)-1, while both the pulmonary [10 ml.min-1.(10 0 g)-1] and systemic circulations [15 ml.min-1.(100 g)-1] contributed substantially to main bronchi blood flow. The systemic blood flow cont ribution to the lower airway generations (2nd to the 5th generation ai rways) stayed relatively constant, averaging 13-31 ml.min-1.(100 g)-1 while the pulmonary blood flow contribution increased significantly in these airway segments to a maximum of over 100 ml.min-1.(100 g)-1 at the 5th generation. At 15 cmH2O PEEP, the systemic contribution to all of the airway segments (except the 5th generation, P<0.09) and the pu lmonary component to the main bronchi, significantly decreased (P<0.05 ). In contrast, elevated left atrial pressure had little effect on the pulmonary and systemic contributions to airway blood flow. The result s of this study suggest that elevated PEEP has a greater effect than e levated left atrial pressure on the systemic blood flow contribution t o the airways, while the pulmonary blood flow contribution to the airw ays is affected very little by either of these perturbations.