The finite element (FEM) analysis of continuous positive airway pressure (CPAP)
masks was proved feasible in previous work, where a comparison was made with
laboratory results obtained by making use of a rigid dummy head. The long-term
purpose of that work was an accurate numerical analysis of the mechanical effects,
possibly dangerous from the medical viewpoint, of CPAP masks applied to human
faces, such as recently employed for the care of COVID-19 patients, or other
purposes. The present work explores the importance of introducing, into the FEM
models, the head soft tissues. The numerical description of the soft tissues produces a
significant increase both in the complexity of the modeling phase and of
the computational cost of the analyses. The focus of the present work is
mainly in trying to understand if this increase is justified by a significant
change of the calculated mechanical quantities of interest, with respect to the
relatively simpler case of modeling the head as a rigid surface. It was found that,
at least under short-term loading, the global behavior of the mask is very
marginally affected by the presence of the soft tissues which, instead, does
somewhat influence the local contact pressures between the mask and the head
face, but not in a decisive way. In particular, even in the presence of the
soft skin-like layer the distribution of the contact pressures remains uneven,
with many zones of detachment. This seems to suggest that in this type of
analyses it may be acceptable to model the head face as a rigid surface, thus
containing significantly both the modeling phase and the computational
costs.
