Diseases and abnormalities of the upper airways are one of the main reasons for poor
performance in the athletic horse. Understanding the upper airways and possible diseases are
crucial in making the correct diagnosis. Horses are obligate nasal breathers, meaning that air
needed for gas exchange can only pass through the upper airways. This happens both at rest and
during exercise. Due to airway dynamics, the upper airway provides a high airflow resistance.
During inspiration there is negative airway pressure that increases during exercise. Inspiration is
performed as an active abduction, while expiration is a passive process, except during exercise.
Minor changes can lead to decreased oxygen uptake and thereby greatly influence the
performance of the horse.