Partitioning of alterations in pulmonary mechanics due to vascular engorgement in piglets

The aim of our study was to determine the effects of pulmonary vascular engorgement on airways and pulmonary tissues in juvenile animals before and after methacholine (Mch)-induced changes in lung function. Five anesthetized, paralyzed, and thoracotomized piglets were studied before and during pulmonary vascular engorgement, induced by inflating a left atrial balloon catheter and by calculating respiratory mechanics from measurements of airway opening (Pao) and alveolar pressures (PA), respiratory flow (V'), and volume (V) recorded during mechanical ventilation, using the multilinear regression technique. A maximal increase of 15 mmHg in pulmonary artery pressure (Ppa) resulted in a mean increase in total lung elastance (EL) of 28.6% and in total lung resistance (RL) of 14.9%. Mch increased EL by 21.7% and RL by 29.0%. Inflation of the left atrial balloon with an associated increase in Ppa by 15 mmHg in the presence of Mch resulted in an increase in EL by a further 12.4% (to 135.4% of baseline) and in RL by a further 9.0% (to 139.5% of baseline). The change in RL was associated with a qualitatively similar change in both tissue resistance (Vti) and airway resistance (Raw) before and after Mch-induced changes in lung function. We conclude that increasing pulmonary vascular pressures, by increasing left partial pressure, alters lung function in juvenile animals by altering the mechanical properties of both airways and lung tissues. The methods used in the present study allow a direct assessment of the site of action of vascular engorgement in the lungs and provide a useful model for studying this phenomenon further.