Lung recruitment mechanics: coalescing tissue strains with organ expansion

Recruitment maneuvers are used to prevent atelectasis, or partial lung collapse, and to help prevent ventilator induced lung injury. Recruitment techniques remain a topic of debate due to the possibility for damage as they necessitate higher transpulmonary pressures, which are associated with inducing lung injury. We aim to evaluate and probe injury mechanisms and potential pressure inhomogeneities, expressed as heterogeneous lung recruitment and overdistension, by associating organ level compliances with continuous regional strains during the application of stepwise escalation contrasted with sustained inflation maneuvers.

An established breathing mimicry electromechanical system integrated with high spatio-temporal digital image correlation techniques coupled the global pressure-volume response of the lung with local deformations. Compliances, pressures, strains, heterogeneities and the expansion evolution pertaining to the inflation phase of two recruitment methods were quantified and contrasted.

Significant differences between the organ- and tissue-level responses of the sustained inflation versus escalation maneuver were found. The escalation maneuver exhibited greater starting compliance, whereas the sustained inflation showed increased inflation compliance. The localized strain distribution for the sustained inflation yielded increased 75th percentile strain, 90th percentile strain, and range at maximum inflation compared to the escalation maneuver.

Local and global findings indicate the escalation maneuver exhibits more homogeneous lung recruitment compared to sustained inflation. We also observe a correspondence between the significant organ-level compliance differences between the two maneuvers and the disparities observed in the evolutionary progression of localized strain distributions throughout inflation.