Obligate nasal breathing

Obligate nasal breathing describes a physiological necessity to breathe through the nose (or other forms of external nasal passages, depending on the species) as opposed to breathing through the mouth. The term may be misleading, as it implies that the organism has no choice but to breathe through its nose; however, it is also used to describe cases where effective breathing through the mouth is possible but not preferred. Alternatively, the term has been defined by some as the ability to breathe through the nose while swallowing. While this ability is a common trait of obligate nasal breathers, the definition does not require that nasal breathing is necessary for the animal. Even in obligate nasal breathers such as horses, rabbits, and rodents, there is a potential patent path for air to travel from the mouth to the lungs which can be used for endotracheal intubation. It has been suggested that obligate nasal breathing is an adaptation especially useful in prey species, as it allows an animal to feed while preserving their ability to detect predators by scent. Horses are considered obligate nasal breathers. The respiratory system of the horse prevents horses from breathing orally. The epiglottis rests above the soft palate while the animal is not swallowing, forming an airtight seal. Oral breathing can only occur with significant anatomical abnormalities or pathological conditions. For example, denervation of the pharyngeal branch of the vagus nerve results in the dorsal displacement of the soft palate (DDSP), and it has been suggested that this leads to a clinical syndrome which may include oral breathing. However, significant respiratory dysfunction including airway obstruction is observed with DDSP, and the animal cannot function normally in this state. Rabbits, cats, and rodents are also obligate nasal breathers. Like horses, the normal anatomical position of the epiglottis causes it to be engaged over the caudal rim of the soft palate, sealing the oral pharynx from the lower airways.