Changes

===Clinical Signs===

===Clinical Signs===

Horses present with flared nostrils, tachypnea, cough, and a heave line. The typical breathing pattern is characterized by a prolonged, labored expiratory phase of respiration. Cough may be productive and often occurs during feeding or exercise. The abdominal muscles respond by assisting with expiration, and hypertrophy of these muscles produces the classic heave line. Characteristic auscultatory findings include a prolonged expiratory phase of respiration, wheezes, tracheal rattle, and over-expanded lung fields. Wheezes are generated by airflow through narrowed airways, and are most pronounced during expiration. Crackles may be present and are associated with excessive mucus production. Mild to moderately affected horses may present with minimal clinical signs at rest, but coughing and exercise intolerance are noted during performance. Horses with RAO are not typically febrile unless secondary bacterial pneumonia has developed.  

Mildly affected horses generally present with a history of occasional coughing and exercise intolerance. Signs become more obvious as the disease progresses. Tachypnoea is often seen, and there may be a mucopurulent nasal discharge. Severely affected animals show signs of respiratory distress at rest. These can include flared nostrils, wheezing, paroxysmal bouts of coughing and a laboured abdominal component to expiration. Chronically, marked dyspnoea increases energy expenditure and the animal may lose condition, as well as developing a "heave line" due to hypertrophy of the external abdominal oblique muscle^{allen, merck, ivis}.

A horse with severe RAO or SPAOD is easily recognized by its signs of respiratory distress. The nostrils are flared, respiratory rate is increased, the horse uses its abdomen to assist expiration, and it often appears anxious. Abdominal effort can be so marked that the horse many rock to and fro during breathing. If respiratory distress is very severe, the horse may be unable to eat adequately and therefore loses weight. The horse may have a nasal discharge. Clinical signs in the less severely affected animal include coughing associated with activity or during feeding and cleaning out, reduced exercise tolerance and delayed recovery from exercise.

merck Characteristic auscultatory findings include a prolonged expiratory phase of respiration, wheezes, tracheal rattle, and over-expanded lung fields. Wheezes are generated by airflow through narrowed airways, and are most pronounced during expiration. Crackles may be present and are associated with excessive mucus production. Mild to moderately affected horses may present with minimal clinical signs at rest, but coughing and exercise intolerance are noted during performance. Horses with RAO are not typically febrile unless secondary bacterial pneumonia has developed.  

On physical examination, clinical sings are restricted to the respiratory system. The nostrils may be flared and there may be a milky mucus discharge from the nose. Compression of the cranial trachea may reveal an increased sensitivity of the cough reflex. Depending on the severity of airway obstruction, the horse may use its abdominal muscle for exhalation to an exaggerated degree and, if the animal has had respiratory distress for some time, a heave line may be obvious. The heave line is due to hypertrophy of the external abdominal oblique muscle.

Abnormal lung sounds are heard to varying degrees depending on the severity of airway obstruction. In some severely affected animals, the lungs can be quite silent despite very strong inspiratory and expiratory efforts. This is because the airways are so obstructed that there is insufficient air movement to generate audible breath sounds. Usually however, breath sounds are increased at all levels of the airways but particularly over the peripheral lung fields. Wheezing is heard quite commonly but it is wise to listen for several breaths at many points over the lung because wheezing can be intermittent. Wheezes referred from deeper in the lung may be heard over the trachea and sometimes simply by listening at the nostrils. In horses that are less severely affected, ventilation may have to be increased by use of a rebreathing bag or exercise in order to hear abnormal lung sounds. Percussion will reveal increased size of the lung field in severely affected animals.

Abnormal lung sounds are heard to varying degrees depending on the severity of airway obstruction. In some severely affected animals, the lungs can be quite silent despite very strong inspiratory and expiratory efforts. This is because the airways are so obstructed that there is insufficient air movement to generate audible breath sounds. Usually however, breath sounds are increased at all levels of the airways but particularly over the peripheral lung fields. Wheezing is heard quite commonly but it is wise to listen for several breaths at many points over the lung because wheezing can be intermittent. Wheezes referred from deeper in the lung may be heard over the trachea and sometimes simply by listening at the nostrils. In horses that are less severely affected, ventilation may have to be increased by use of a rebreathing bag or exercise in order to hear abnormal lung sounds. Percussion will reveal increased size of the lung field in severely affected animals.