These animals can have a variety of problems contributing to their breathing problems such as narrow nostrils, excessive soft tissue in the mouth and throat like the soft palate and relatively large tongues and they also tend to have very narrow tracheas (windpipes) compared to normal animals of a similar size. (vetsagainstbrachycephalism.com)
Babies with Down syndrome are often born with larger tongues which means they have them sticking out. (babygaga.com)
Key anatomical characteristics, such as larger tongues that fall back in the mouth during deep sleep, can obstruct the airway during sleep; and sensitivity to air blowing onto their faces through a mask makes it difficult for some patients to tolerate a continuous positive airway pressure (CPAP) machine, the traditional therapy for OSA. (sciencedaily.com)