Forces involved in lobar atelectasis in intact dogs

Area of Science:

• Respiratory Physiology
• Thoracic Biomechanics

Background:

• Lung lobe atelectasis (lung collapse) in isolation differs in shape from collapse within an intact chest cavity.
• The chest wall exerts deforming forces on a collapsing lung lobe.

Purpose of the Study:

• To measure lung and lobar volumes and pressures during atelectasis in anesthetized dogs.
• To quantify the pressure difference caused by chest wall deformation on a collapsing lung lobe.
• To investigate the effect of pleural fluid on these deforming forces.

Main Methods:

• Anesthetized dogs were positioned in the left lateral position.
• Lung and lobar volumes were measured using a nitrogen washout technique with 88% O2-12% N2.
• Transpulmonary and "translobar" pressures were measured during induced atelectasis.
• Pleural saline infusion was used to assess the role of pleural fluid.

Main Results:

• Translobar pressures were more negative than transpulmonary pressures at equivalent relative lung volumes during isolated lobar collapse, averaging 3 cmH2O at 50% Functional Residual Capacity (FRC).
• This pressure difference represents the net deforming force applied to the lobe.
• Infusion of a small volume of saline into the pleural space significantly reduced this pressure difference, suggesting localized deforming forces.

Conclusions:

• The chest wall applies significant deforming forces to collapsing lung lobes, altering their pressure dynamics.
• These forces are likely generated in localized areas of the chest wall, such as sharply angled regions.
• Pleural fluid can mitigate the effects of these deforming forces on lung collapse mechanics.