Changes

==Diagnosis==

==Diagnosis==

A presumptive diagnosis may be made on the basis of the history and clinical examination.

A presumptive diagnosis may be made on the basis of the history and clinical examination. Bronchoalveolar lavage may also prove useful.

===Clinical Signs===

===Clinical Signs===

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}. Fever does not normally develop unless there are secondary bacterial complications.

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^{1, 6, 8}. Fever does not normally develop unless there are secondary bacterial complications.

On physical examination, thoracic auscultation typically reveals a prolonged expiratory phase of respiration and adventitious respiratory noises. Wheezes are most pronounced during expiration, and crackles are associated with the excessive mucus production^merck. However, the airways are so obstructed in some severely affected animals that there is insufficient air movement to generate audible breath sounds, and the lungs are very quiet on auscultation¹. In mildly affected horses, a rebreathing bag can be used to aid auscultation, but this should never be performed in dyspnoeic animals^{1, allen}. There may be an increased sensitivity of the cough reflex on tracheal compression.

On physical examination, thoracic auscultation typically reveals a prolonged expiratory phase of respiration and adventitious respiratory noises. Wheezes are most pronounced during expiration, and crackles are associated with the excessive mucus production⁸. However, the airways are so obstructed in some severely affected animals that there is insufficient air movement to generate audible breath sounds, and the lungs are very quiet on auscultation¹. In mildly affected horses a rebreathing bag can be used to aid auscultation, but this should never be performed in dyspnoeic animals^{1, 6}. There may be an increased sensitivity of the cough reflex on tracheal compression.

===Diagnostic Imaging===

===Diagnostic Imaging===

Endoscopy reveals excessive mucopurulent secretions in the trachea. Thoracic radiographs may be useful in cases that are not typical in their presentation or response to treatment, as they may help rule out other differentials such as including interstitial pneumonia, pulmonary fibrosis, or bacterial pneumonia^{1, allen}.

Endoscopy reveals excessive mucopurulent secretions in the trachea. Thoracic radiographs may be useful in cases that are not typical in their presentation or response to treatment, as they may help rule out other differentials such as including interstitial pneumonia, pulmonary fibrosis, or bacterial pneumonia^{1, 6, 8}.

 

===Laboratory Tests===

===Laboratory Tests===

Routine haematology and biochemistry are usually within normal limits, and there is little evidence to support the use of serum and intradermal allergy testing in the diagnosis of RAO^allen.

Routine haematology and biochemistry are usually within normal limits, and there is little evidence to support the use of serum and intradermal allergy testing in the diagnosis of RAO⁶.

Fluids obtained from bronchoalveolar lavage or tracheal wash may be useful in the diagnosis of RAO. The presence of greater than 20% neutrophils in BALF confirms the presence of lower airway inflammation, thus and differentiates horses with RAO from those with eosinophilic pneumonitis, fungal pneumonia, or lungworm infestation. Normal horses have fewer than 10% neutrophils in BALF. Cytology of bronchoalveolar lavage fluid may also reveal Curschmann’s spirals , which represent inspissated mucus/cellular casts from obstructed small airways¹. BAL should not be performed in markedly dyspnoeic horses, and instead should be postponed until the dyspnoea is controlled. Aspiration of tracheal mucus or a tracheal lavage can also be used to evaluate lung inflammation but it is less reliable than BALF.

Fluids obtained from bronchoalveolar lavage or tracheal wash may be useful in the diagnosis of RAO. The presence of greater than 20% neutrophils in BALF confirms the presence of lower airway inflammation, thus and differentiates horses with RAO from those with eosinophilic pneumonitis, fungal pneumonia, or lungworm infestation. Normal horses have fewer than 10% neutrophils in BALF. Cytology of bronchoalveolar lavage fluid may also reveal Curschmann’s spirals , which represent inspissated mucus and cellular casts from obstructed small airways¹. BAL should not be performed in markedly dyspnoeic horses, and instead should be postponed until the dyspnoea is controlled. Aspiration of tracheal mucus or a tracheal lavage can also be used to evaluate lung inflammation but is less reliable than BALF.

===Other Tests===

===Other Tests===

Reduction of respiratory distress after the administration of a bronchodilator confirms the presence of bronchospasm^{1, allen}. To test this, intravenous atropine can be administered at 0.02mg/kg. Horses with RAO (or SPAOD) should respond within 15 minutes¹. The dose of atropine should not be repeated as there is a risk of intestinal stasis.

Reduction of respiratory distress after the administration of a bronchodilator confirms the presence of bronchospasm^{1, 6}. To test this, intravenous atropine can be administered at 0.02mg/kg. Horses with RAO (or SPAOD) should respond within 15 minutes¹. The dose of atropine should not be repeated as there is a risk of intestinal stasis.

 

===Pathology===

===Pathology===

[[Image:COPD scanning micrograph.jpg|right|thumb|200px|Scanning electron micrograph of lung in RAO. Image sourced from Bristol Biomed Image Archive with permission]]

[[Image:COPD scanning micrograph.jpg|right|thumb|100px|<small><center>COPD scanning electron micrograph (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]

The post-mortem findings in RAO are variable. Lungs can appear grossly normal, or may hyperinflated a result of gas trapping<SUP>book</sup>. They may also deflate slowly. Exudate is commonly found in the airways, and the weight of the right ventricle in comparison to the left ventricle may be increased.  

The post-mortem findings in RAO are variable. Lungs can appear grossly normal, or may hyperinflated as a result of gas trapping<SUP>9</sup>. They may also deflate slowly. Exudate is commonly found in the airways, and the weight of the right ventricle in comparison to the left ventricle may be increased.  

The histopathology associated with recurrent airway obstruction is primarily bronchiolitis, although changes of larger airway are also seen^Kaup. Neutrophils accumulate in the lumen of bronchioles, which are plugged by mucus. Other inflammatory cells are also seen in the connective tissue surrounding the bronchioles. These include lymphocytes, monocytes and eosinophils. The bronchiolar epithelium undergoes mucus metaplasia, and the airway smooth muscle is seen to be thickened. Alveoli are filled with mucus overspilling from the airways.

The histopathology associated with recurrent airway obstruction is primarily bronchiolitis, although changes of larger airway are also seen¹⁰. Neutrophils accumulate in the lumen of bronchioles, which are plugged by mucus. Other inflammatory cells are also seen in the connective tissue surrounding the bronchioles. These include lymphocytes, monocytes and eosinophils. The bronchiolar epithelium undergoes mucus metaplasia, and the airway smooth muscle is seen to be thickened. Alveoli are filled with mucus overspilling from the airways.

==Treatment==

==Treatment==