Regional distribution of transpulmonary pressure.

The pressure across the lung, so-called transpulmonary pressure (P), represents the main force acting toward to provide lung movement. During mechanical ventilation, P is provided by respiratory system pressurization, using specific ventilator setting settled by the operator, such as: tidal volume (V), positive end-expiratory pressure (PEEP), respiratory rate (RR), and inspiratory airway flow. Once P is developed throughout the lungs, its distribution is heterogeneous, being explained by the elastic properties of the lungs and pleural pressure gradient. There are different methods of P calculation, each one with importance and some limitations. Among the most known, it can be quoted: (I) direct measurement of P; (II) elastance derived method at end-inspiration of P; (III) transpulmonary driving pressure. Recent studies using pleural sensors in large animal models as also in human cadaver have added new and important information about P heterogeneous distribution across the lungs. Due to this heterogeneous distribution, lung damage could happen in specific areas of the lung. In addition, it is widely accepted that high P can cause lung damage, however the way it is delivered, whether it's compressible or tensile, may also further damage despite the values of P achieved. According to heterogeneous distribution of P across the lungs, the interstitium and lymphatic vessels may also interplay to disseminate lung inflammation toward peripheral organs through thoracic lymph tracts. Thus, it is conceivable that juxta-diaphragmatic area associated strong efforts leading to high values of P may be a source of dissemination of inflammatory cells, large molecules, and plasma contents able to perpetuate inflammation in distal organs.