Pathophysiology of airway obstruction in horses: a review.

This research article explores the common issue of airway obstruction in horses, discussing the various causes and effects of such obstructions in both the upper and lower airways. The study particularly focuses on problems arising from exercise, and suggests a link between obstruction and intrapulmonary hemorrhage during racing.

Causes of Airway Obstruction

• The study first discusses the obstruction of upper airways, which often occurs due to paresis, a condition of muscular weakness, of abductor muscles in the nares (nostrils) and larynx (voice box). This condition can lead to the inspiratory collapse of soft tissues.
• The research denotes that this type of obstruction is worsened by factors that increase upper airway resistance, and by high inspiratory flow rates, which often occur during strenuous activities, such as exercising or racing.
• The obstruction of intrapulmonary (within the lungs) airways is another area of focus in the article, caused by the accumulation of secretions, the release of chemical mediators in response to various stimuli, and parasympathetic (part of the nervous system that serves to slow the heart rate, increase intestinal and glandular activity, and relax the sphincter muscles) stimulation of airways.

Effects of Airway Obstruction

• Obstructions within the large airways increase the work of breathing. This means they require the horse to use more energy and effort to intake and exhale air, which can negatively affect the horse’s overall wellness and performance.
• On the other hand, small airway obstructions do not necessarily result in a measurable increase in resistance. However, they do cause an uneven distribution of ventilation, leading to low levels of oxygen in blood (hypoxemia) – an issue that becomes particularly problematic during exercise.
• The study suggests a potential link between poor collateral ventilation, which aggravates gas exchange problems in horses with airway obstruction, and intrapulmonary hemorrhage (bleeding within the lungs) during racing. This implies that airway obstructions might result in serious health risks for horses, particularly those used in racing.