Inspiratory aerodynamic valving occurs in the ostrich, Struthio camelus lung: A computational fluid dynamics study under resting unsteady state inhalation

In the avian lung, inhaled air is shunted past the openings of the medioventral secondary bronchi (MVSB) by a mechanism termed ‘inspiratory aerodynamic valving’ (IAV). Sizes and orientations of the trachea (Tr), syrinx (Sx), extrapulmonary primary bronchus (EPPB), intrapulmonary primary bronchus (IPPB), MVSB, mediodorsal secondary bronchi (MDSB), lateroventral secondary bronchi (LVSB) and the ostium (Ot) were determined in the ostrich, Struthio camelus. Air flow was simulated through computationally generated models and its dynamics analysed. The ‘truncated normal model’ (TNM) consisted of the Tr, Sx, EPPB, IPPB, MVSB and the Ot. For the ‘inclusive normal model’ (INM), the MDSB and the LDSB were added. Variations of these models included the ‘truncated MVSB1 rotated model’ (TMVSB1RM), the ‘truncated constriction fitted model’ (TCFM) and the ‘inclusive MVSB1 rotated model’ (IMVSB1RM). In the TNM, the TMVSB1RM and the TCFM, the air flow exited through the MVSB while for the INM and the IMVSB1RM, very little of it did: IAV did not occur in the partial models. In the IMVSB1RM, rotating the MVSB1 clockwise did not affect IAV. The incomplete models may be faulty because the velocity/pressure profiles in different parts of the interconnected airways form an integrated functional continuum in which different parts of the system considerably impact on each other.