Soft Palate Stability: Does it Need more Stiffness?

Obstructive disorders of the upper respiratory tract (URT) have been recognised as important causes of poor performance in the equine athlete for many years. Collapse of structures within the upper airways results in a reduction in the diameter of airway and causes increased resistance to airflow, an increase in the work of breathing and a reduction in ventilation, thereby reducing the oxygen supply to the exercising muscles. It is now acknowledged that resting endoscopic findings alone are not necessarily representative of the situation occurring during strenuous exercise and that exercising endoscopy is necessary in order to make a definitive diagnosis in many cases (Kannegieter et al., 1995; Tan et al., 2005; Lane et al., 2006b). This is perhaps not surprising when we consider the changes that occur within the respiratory system between rest and fast exercise. Breathing and stride frequency are matched at canter and gallop. The breathing frequency increases from 8 -12 breaths per minute at rest to approximately 120 breaths per minute during strenuous exercise. Tidal volume also increases (approximately threefold) resulting in the minute ventilation increasing from 50l/min at rest to over 2000 l/min when galloping (Lekeux and Art, 1994). In order to drive ventilation, the pressures within the airway increase dramatically during exercise (Ducharme et al., 1994). Any weakness (either pathological or physiological) of the upper airway musculature may result in an inability to resist the increased negative airway pressures associated with exercise and hence will result in dynamic airway collapse. […]