often ascribed to bordetellosis. A honking cough is frequently described in dogs with tracheal or airway collapse and a brisk snapping sound on expiration is suggestive of large airway collapse. Animals with pneumonia might have a softer cough along with a vague history of illness characterized by anorexia and lethargy. Dogs with heart disease also can have a soft cough associated with tachypnea, exercise intolerance, or lethargy. With severe or fulminant pulmonary edema, a dog might expectorate pink foam if pulmonary edema has flooded the alveolar space and entered the airways. However, the common association of cough with congestive heart failure has been called into question (Ferasin et al. 2013).

Table 1.2 Respiratory causes of cough in dogs and cats.

	Dog	Cat
Infectious tracheobronchitis	Canine infectious respiratory disease complex^a	Mycoplasma Bordetella
Pneumonia	Bacterial Aspiration Foreign body Fungal Interstitial^b	Bacterial Aspiration Foreign body Fungalb Interstitial^b
Inflammatory disease	Chronic bronchitis Eosinophilic bronchopneumopathy	Asthma/chronic bronchitis
Neoplasia	Primary Metastatic	Primary Metastatic
Structural disorders	Bronchiectasis Airway collapse	Bronchiectasis

^a Reported causes include canine adenovirus‐2, canine parainfluenza‐3 virus, canine respiratory coronavirus, canine herpesvirus, influenza viruses, and canine distemper virus along with Bordetella, Mycoplasma, and Streptococcus equi subsp. zooepidemicus.

^b More commonly a cause of tachypnea than cough.

      Determining environmental and travel history is important for animals with cough. Exposure to a high‐density dog population should raise concern for disease associated with canine infectious respiratory disease complex. If the cough is harsh and dry, Bordetella should be considered, while a soft, chronic cough could be suggestive of canine influenza virus infection. Sporting dogs that develop an acute onset of cough or have a chronic, antibiotic‐responsive cough could have foreign body pneumonia. Fungal pneumonia should be suspected in animals with cough that have traveled to endemic regions. In those animals, cough is usually accompanied by tachypnea and systemic signs of illness. Finally, environmental history is important, because exposure to pollutants and airway irritants can exacerbate upper or lower airway diseases in both dogs and cats, although it remains unclear whether or not exposure to second‐hand smoke is an important factor in worsening cough in animals (Hawkins et al. 2010).

      Signalment

In general, younger animals might be more likely to develop infectious or foreign body pneumonias, while older animals develop bronchitis, neoplasia, airway collapse, and perhaps aspiration pneumonia. Dogs with eosinophilic or fungal pneumonia also tend to be young to middle‐aged. Asthma/bronchitis seems to affect cats of all ages, although perhaps the eosinophilic form is more common in younger animals. Cervical tracheal collapse might affect younger dogs, while older dogs get both tracheal collapse and bronchomalacia.

      The breeds affected depend on the underlying case of cough. For example, an older Retriever‐type dog is likely to develop laryngeal paralysis and subsequent aspiration pneumonia, while aspiration in a brachycephalic breed often happens at a young age. Tracheal collapse affects toy and small breed dogs, while chronic bronchitis and bronchomalacia can affect any size breed of dog.

      Physical Examination

      One of the more difficult challenges in assessing animals with respiratory disease is the development of good auscultation skills. Practice and patience are required because audible sounds are altered by age, body condition score, conformation, respiratory pattern, and the presence of disease. As mentioned earlier, careful examination should include the larynx and trachea, followed by auscultation of all lung fields. The anatomic origin for lung sounds has not been fully established; however, normal lung sounds are usually designated as bronchial, vesicular, or bronchovesicular. Bronchial sounds are loud and are heard best over the large airways near the hilus. Typically, they are louder and longer during expiration than inspiration and have a tubular character. Vesicular lung sounds are soft, heard best on inspiration, and can be detected over the periphery of the chest in normal animals. The sound resembles a breeze passing through leaves on a tree. Bronchovesicular sounds (a mixture of bronchial and vesicular qualities) are typically louder on inspiration than expiration.

      Lung sounds in animals with airway or parenchymal disease are often increased in loudness or harshness, and harsh bronchovesicular sounds can be the only physical examination finding in animals with marked bronchopulmonary disease. Adventitious (abnormal) lung sounds (crackles and wheezes) are discontinuous noises and are not found as commonly as expected in respiratory patients, but should always be taken as an indicator of disease. Adventitious lung sounds can be enhanced by inducing a cough or a deep breath, or by exercising the patient. In normal animals, it is difficult to induce a cough by palpating the trachea; however, animals with airway or parenchymal disease usually have increased tracheal sensitivity due to activation of irritant receptors by infection or inflammation.

      Crackles are thought to result from rapid opening of airways, but could also arise from equalization in pressure as air passes through fluid or mucus‐filled airways. They can be heard at any point during inspiration or expiration. Fine or soft crackles are suggestive of pulmonary edema, particularly if ausculted in the hilar region of a dog, whereas coarse crackles are more suggestive of airway or parenchymal disease. Dogs or cats with pulmonary fibrosis can display either fine or coarse crackles that are ausculted diffusely across the chest. Auscultation in dogs with airway collapse can reveal diffuse crackles because of the presence of concurrent bronchitis, or because of small airways that open and close during the phases of respiration. In the latter case, crackles are often present during both inspiration and expiration. A loud snapping sound over the hilar region at end expiration is suggestive of collapse of the intrathoracic trachea, carina, or mainstem bronchi. Wheezes result from air passing through airways narrowed by intraluminal mucus, extraluminal compression, or by collapse or constriction, and are usually heard on expiration.

Tachypnea

      History

Tachypnea is most often associated with parenchymal or pleural disease, although in the cat tachypnea can also be encountered with bronchial disease. Parenchymal diseases that lead to tachypnea are primarily pneumonia and pulmonary edema. Pneumonia (infectious, aspiration, fungal, or interstitial) can be acute or chronic and insidious in onset. Both pneumonia and pulmonary edema are typically associated with systemic signs of illness such as lethargy, anorexia, and weight loss.

      Tachypnea