- Definition
- Pathophysiology
- Systems Affected
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- In animals, dyspnea is used to describe clinical signs associated with difficult, labored breathing or respiratory distress, which can be present throughout the respiratory cycle or be primarily associated with either inhalation (i.e. inspiratory dyspnea) or exhalation (i.e. expiratory dyspnea)
- The lay term for expiratory dyspnea in horses (i.e. heaves) describes the prolonged abdominal push at the end of expiration
- As a primary clinical sign, usually associated with obstruction of the lower (intrathoracic) airways by mucus, edema, or bronchospasm; the abdominal muscles are recruited to move air out of the lungs through partially obstructed airways and a forced abdominal exhalation is noticeable
- Can also accompany inspiratory dyspnea in any animal with severe impairment of gas exchange
Depends on the underlying cause, but equine asthma usually occurs in mature to old animals.
- Expiratory dyspnea is a sign, but associated signs can indicate the source of dyspnea
- An accompanying cough indicates inflammation of the tracheobronchial tree
- Inflammation of the lower airway can result in bilateral mucopurulent nasal discharge
- Unilateral or bilateral nasal discharge, either purulent or hemorrhagic, can be a sign of a nasal or pharyngeal mass causing severe airway obstruction
- Accompanying inspiratory dyspnea and loud respiratory noises are indicative of a fixed airway obstruction (e.g. mass encroaching into the upper airways)
Exposure to environmental risk factors (e.g. indoor housing, poor ventilation, dust, humidity, ammonia, use of hay or straw containing microorganisms such as microscopic molds and bacteria).
- Forced and prolonged abdominal component to expiration, particularly obvious at end exhalation. If severe, the horse may rock forward during the abdominal effort
- Bulging and mobilization of the anus, synchronous to breathing (abdominal effort raises intra-abdominal pressure)
- Hypertrophy of the external abdominal muscle can be seen (“heaves line”)
- Flared nostrils and increased excursions of the thorax during breathing are common since dyspnea is often mixed (expiratory and inspiratory)
- Fixed airway obstruction—nasal discharge, sometimes foul breath, and both inspiratory and expiratory dyspnea
- Bronchitis/bronchiolitis—cough, wheezing audible on lung auscultation, increased breath sounds or crackles on both inhalation and exhalation,
- Anxiety and anorexia can occur
- Cyanotic mucosa in severe cases
- Fever is unusual without a viral or bacterial cause
- Extrathoracic causes are usually accompanied by inspiratory dyspnea—congestion of the nasal mucosa (e.g. Horner syndrome, inflammatory disease), deviation of the nasal septum, space-occupying lesion affecting the nasal cavity (e.g. foreign body, intraluminal mass, ethmoid hematoma, extraluminal mass or swelling), congenital pharyngeal cysts, space-occupying masses encroaching on the pharynx (e.g. enlarged lymph nodes), guttural pouch enlargement (usually by tympanites), deformity of the larynx (e.g. edema, epiglottiditis, chondritis), and tracheal obstruction caused by trauma, masses, or a foreign body (see chapter Inspiratory dyspnea)
- Lower respiratory tract—equine asthma (heaves, pasture asthma), pulmonary edema, infiltrative disease of the alveolar interstitium (interstitial pneumonia)
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS