Why is this patient dyspneic (Proceedings)

Dyspnea is the sensation of having difficult or laborious breathing. It is a subjective phenomenon that needs to be inferred by the clinician in companion animals. Dyspnea, tachypnea (rapid breathing), and hyperpnea (increased ventilation) are not synonymous but are frequently grouped together in veterinary patients. Dyspnea occurs when the demand for ventilation is out of proportion to the animal's ability to respond to this demand. Thus, breathing becomes difficult, uncomfortable, or labored. Dyspnea may result from alterations in any portion of the respiratory system or be due to abnormal mechanics of the lung and chest wall.

Look: When does the Dyspnea occur?

Inspiration x Expiration x Both

The timing and pattern of respiration helps to determine the structure most likely responsible for the dyspnea. Dyspnea may occur during inspiration, expiration or both (mixed). Clinically, pure inspiratory dyspnea implies a lesion in the respiratory tract outside the thorax, whereas expiratory and mixed dyspneas occur in patients with thoracic or metabolic disease.

Look: What is the pattern of respiration?

Obstructive x Restrictive

Mixed or expiratory dyspnea should be further classified as obstructive or restrictive. Obstructive diseases are associated with increased airway resistance in the tracheobronchial tree. Obstructive diseases may also occur in the upper respiratory tract, but those patients have inspiratory dyspnea. Patients with obstructive disease have decreased expiratory flows and hyperinflated lungs (e.g.; cats with asthma). Restrictive diseases are those in which expansion of the lungs is restricted (e.g.; pulmonary fibrosis, pleural effusion). Lungs of patients with restrictive disease operate at smaller volumes and the patient has a rapid shallow breath. In patients with a non-pulmonary cause of restrictive, residual volume is normal or increased.

Listen: Can you hear Respiratory Sounds?

Normal sounds? Abnormal sounds

The physical examination assists in identifying the cause for the dyspnea. In patients with restrictive pulmonary disease, absence of respiratory sounds indicates a pleural cavity disease, whereas presence of pulmonary sounds occurs in patients with parenchymal pulmonary disease, metabolic diseases or abdominal distention

Inspiratory dyspnea

Inspiratory dyspnea occurs with extrathoracic lesions in the respiratory tract (table 1). Patients with isolated pure nasal problems are able to breathe normally when the mouth is open. Presence of abnormal respiratory sounds may help to localize the problem. Stridor is a loud musical inspiratory sound of constant pitch associated with laryngeal (and occasionally tracheal) alterations. Rhoncus is a rattling in the throat associated with pharyngeal or proximal tracheal diseases. Cough may occur in patients with inspiratory dyspnea. Cough receptors are located in the larynx, pharynx, and large airways. Diseases in any of those locations may be associated with cough. In patients with extrathoracic disease, cough is usually paroxystic and loud. Direct visual inspection or bronchoscopy is necessary determine the cause.  

Table 1. Causes of Inspiratory Dyspnea

Nostrils Stenotic nares Larynx/pharynx Elongated soft palate   Caudal palate   Laryngeal paralysis   Laryngeal edema   Everted laryngeal sacules   Laryngeal laceration/trauma   Laryngeal neoplasia   Hyoidal fracture   Retropharyngeal polyps Nasal cavity Foreign bodies Nasal mass Rhinitis Cervical trachea Tracheal collapse   Tracheitis   Parasites   Extraluminal compression   Foreign body

Obstructive expiratory dyspnea

Obstructive expiratory dyspnea occurs in patients with intrathoracic airway diseases (table 2). Patients may have wheezes and cough. Wheezes are continuous musical sounds generated by air forced to pass through a narrow region abruptly into a wider region in the larger airways. Good quality chest radiographs and tracheal wash are necessary to rule in or rule out specific diagnosis. 

         Table 2. Causes of Obstructive Expiratory Dyspnea

  Thoracic trachea Tracheal collapse     Tracheobronchitis     Extraluminal compression     Foreign body     Neoplasia   Bronchial tree Bronchitis Asthma   Extraluminal compression Neoplasia     Lymph nodes     Enlarged left atrium

Silent restrictive expiratory dyspnea

Silent restrictive expiratory dyspnea occurs in patients with pleural cavity disease (table 3). Pulmonary sounds are absent or may be heard at specific locations (e.g. dorsal lung fields in patients with pleural effusion). Cough is usually absent. Chest radiographs and thoracocentesis are necessary to rule in or rule out the differentials.

 Table 3. Causes of Silent Restrictive Expiratory Dyspnea

  Pleural cavity Pneumothorax   Pleural effusion   Diaphragmatic hernia   Chest tumors

Noisy restrictive expiratory dyspnea

Noisy restrictive expiratory dyspnea occurs in patients with parenchymal pulmonary diseases (table 4). Pulmonary sounds are audible and abnormal sounds like crackles might be heard. Crackles are short, explosive, non-musical sounds that are a non-specific sign of small airway disease. Cough may occur if small airways are also involved and is usually not loud. Chest radiographs and tracheal wash or bronchoalveolar lavage are necessary to rule in or rule out the differentials.

Table 4. Causes of Noisy Restrictive Dyspnea

Pulmonary parenchyma Edema     Pneumonia     Fibrosis     Neoplasia     Hemorrhage/contusion     Embolism   Metabolic Anemia     Anxiety/fear     Metabolic acidosis   Abdominal distension Ascites     Pregnancy     Organomegaly Gastric dilatation-volvulus     Neoplasia

Careful interpretation of the information obtained in the history and physical examination determining the timing and pattern of the dyspnea allow the veterinary practitioner to anatomically locate the origin of the dyspnea in most cases. Direct inspection visually or endoscopically, radiographs, and cytology are necessary to determine the cause of the dyspnea.

References

Bauer, T. Clinical approach to cardiopulmonary disorders. In: Kirk, RW, Bonagura, JD. Current Veterinary Therapy X. 10.ed. Philadelphia, WB Saunders, pp. 188-194, 1989.

de Morais HSA and Faria MLE. Dyspnea: Stop, look and listen. In: Proceedings XXVII World Congress of the World Small Animal Veterinary Association. Granada, Spain. October 2002

de Morais HSA and Schwartz DS. Pathophysiology of heart failure. In: Ettinger SJ and Feldman EC (eds). Textbook of Veterinary Internal Medicine. 6th ed., Philadelphia, W.B. Saunders, 2005, pp: 914-940.

Mawby DL. Dyspnea and Tachypnea. In: Ettinger SJ and Feldman EC (eds). Textbook of Veterinary Internal Medicine. 6th ed., Philadelphia, W.B. Saunders, 2005, pp: 192-195.

Sisson, D. D. and Ettinger, S. J. The physical examination. In: Fox, P. R.; Sisson, D. D.; Moïse, N. S. Textbook of Canine and Feline Cardiology. Philadelphia, WB Saunders. 1999. cap. 5. p: 46-64.