Vagal Reflex Is Not Responsible for Changes in Airway and Lung Tissue Mechanics Due to Vascular Engorgement in Young Piglets

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Abstract
Eleven open-chest piglets were studied to examine the effects of vascular engorgement on partitioned airway and lung tissue mechanics, and to investigate the role of vagal denervation on lung function during engorgement. Alveolar pressure was measured using alveolar capsules. Pulmonary elastance(EL) and resistance (RL), airway (Raw), and tissue(Vti) resistance were calculated during mechanical ventilation. Acute fluid administration with polygeline (10 mL/kg boluses up to a total of 30 mL/kg) resulted in an increase of RL with increases in both Raw and Vti. Vti rose 2-3-fold in comparison with Raw. To increase left atrial pressure, a balloon catheter was inserted into the left atrium of the heart and inflated with different volumes. The responses of EL, RL, Raw and Vti were comparable to those with acute fluid load. Alterations in pulmonary mechanics were closely correlated to mean pulmonary artery blood pressure. In another six animals the effect of vagotomy on vascular engorgement was studied. Vagotomy did not alter baseline airway or tissue mechanics. Furthermore, vagotomy did not influence the change of pulmonary mechanics to fluid load or increase of left atrial pressure. Our data indicate that in young piglets vascular engorgement causes alterations in airway and lung tissue mechanics that are not dependent on vagal influences.