One of these studies also included efforts to recruit collapsed lung units and to keep these units open [ 18].
Lung atelectasis may also promote the development of VILI by lung overdistension and by cyclic opening and closing of lung units at the boundary between the normally inflated and collapsed lung units.
The differences between these two phenomena merit some further explanation: when previously collapsed lung units reopen, the same amount of gas distributes to a higher number of lung units (a larger lung open to aeration), giving as net effect a decrease in pressure.
These results suggest a continuous alveolar recruitment of previously collapsed lung units during insufflation in ZEEP and a distension or over-distension of previously open lung units at higher level of pressure in PEEP.
Lung recruitment, defined as an opening of previously collapsed lung units, is thus not necessary per se for prone position to improve lung mechanical properties and increase lung gas content.
Altogether, these results make very unlikely that the opening of previously collapsed lung units, corresponding to lung CT scan analysis of non-aerated lung tissue (≥−100 H.U). which becomes aerated (<−100 H.U ., substantially accounted for the observed increase in FRC.
This refers to the dynamic process of opening previously collapsed lung units by increasing transpulmonary pressure.
The latter might be especially important when collapsed lung units are re-expanded.
