Canine and Feline Respiratory Medicine. Lynelle R. Johnson
to pneumothorax is usually acute; however, pleural effusive disorders can result in either an acute presentation with respiratory distress or a more chronic development of signs due to slow accumulation of fluid. Usually, the degree of respiratory distress is associated with the rapidity of fluid or air accumulation rather than with the specific volume present. Cats seem to be particularly sensitive to addition of a final, critical volume of fluid that overcomes their ability to compensate.
Physical Examination
Cervical and thoracic auscultation, as described for evaluation of animals with cough, is important for animals that present with tachypnea, because many diseases will result in both cough and tachypnea. In addition to listening for increased sounds, it is important to determine if there is an absence of lung sounds, which might indicate the presence of fluid or air in the pleural space.
A notable clinical sign associated with parenchymal or pleural disease is a rapid, shallow breathing pattern, although with pleural disease, exaggerated chest wall motion or hyperpnea can sometimes be present in conjunction with a rapid respiratory rate. In animals with severe respiratory distress, elbows are abducted and the neck is extended to facilitate movement of air into the alveoli. Parenchymal diseases are characterized by increased lung sounds or detection of adventitious sounds. When pleural effusion is present, lung sounds are ausculted in the dorsal fields only and muffled sounds are heard ventrally; heart sounds are also muffled. Pneumothorax leads to an absence of lung sounds dorsally due to compression by air, and lung sounds are present in the ventral fields only. In some cases, a line of demarcation can be ausculted between normal and abnormal lung sounds, indicating a fluid line or the boundaries of air accumulation.
Figure 1.5 Each region of the thorax should be percussed to detect regional differences in the air/soft tissue sounds that are created. One hand is placed against the thorax and is rapped quickly and sharply with the curved fingers of the alternate hand.
In addition to auscultation, thoracic percussion aids in determining if pleural disease is present. Percussion can be performed using a pleximeter and mallet or by placing the fingers of one hand on the chest and rapidly striking them with fingers of the opposite hand (Figure 1.5). The sound that develops will vary depending on whether an air or fluid density is present within the thoracic cavity. Percussion of the chest in a region filled with fluid reveals a dull sound, while in an animal with pneumothorax or air trapping, percussion results in increased resonance. This technique is somewhat limited in a cat or small dog because of the small size of the thoracic cavity.
Exercise Intolerance
History
In general, exercise intolerance can result from respiratory, cardiac, musculoskeletal, neurologic, or metabolic diseases. Respiratory disorders that result in exercise intolerance usually do so through airway obstruction in diseases such as laryngeal paralysis in the dog, asthma in the cat, or chronic bronchitis in either species, or through hypoxemia associated with parenchymal disease. Historical features in animals with airway obstruction can include loud breathing noises as well as progressive tiring and a reduced level of activity. Upper airway obstruction due to laryngeal disease can be accompanied by reports of dysphonia, decreased vocalization, gagging, or retching, while lower airway obstruction due to bronchoconstriction or inflammation is usually associated with cough.
Physical Examination
In the older, large breed dog presented for evaluation of exercise intolerance, careful attention should be paid to laryngeal auscultation for stridor suggestive of laryngeal paralysis. Increased tracheal sensitivity and loud or adventitious lung sounds in cats or dogs with exercise intolerance but no systemic signs of illness suggest that bronchial narrowing, collapse, or inflammation could be responsible for exercise intolerance. Animals that display tachypnea on physical examination, abnormal lung sounds, and systemic signs of illness likely suffer from some form of pneumonia.
Differentiating Cardiac from Respiratory Disease
It can be difficult to distinguish animals with heart failure from those with respiratory disease because of the similarity in clinical signs, physical examination findings, and sometimes even radiographic changes. In addition, some animals suffer from heart and lung or airway diseases concurrently, although in most situations one clinical disease predominates as the cause for clinical signs. It is also important to understand that the presence of disease in one organ can lead to secondary disease in the other thoracic organ. Disorders of the respiratory tract that cause clinical complaints similar to those found in cardiac disease include asthma in cats and bronchitis in dogs, and pneumonia, pulmonary edema, and interstitial diseases in both species. In addition, respiratory or systemic causes of pleural effusion must be distinguished from hydrothorax due to biventricular heart failure.
History
As suggested earlier, the presence and character of cough can sometimes be helpful in distinguishing cardiac from lung or airway disease. Typically, the cough in dogs with airway disease is chronic, harsh, paroxysmal, and can be dry or productive. In contrast, dogs in congestive heart failure will have a soft, moist cough, as do some dogs with pneumonia. Cats with bronchial disease virtually always have a history of cough, while only 5–25% of cats with congestive heart failure might have cough in the history (Dickson et al. 2018). Cats with airway disease can present with rapid breathing, although in a study of cats presented to the veterinarian for respiratory distress, severe tachypnea was more common in cats with cardiac disease (Dickson et al. 2018). Pulmonary edema is often associated with an acute onset of clinical signs referable to the respiratory tract in association with constitutional signs of lethargy, inappetence, and depression. Animals with pneumonia frequently have a vague history of illness that can be acute or chronic but is also characterized by anorexia, malaise, and weight loss. Dog with cardiac disease are often cachectic and lethargic, while dogs with chronic bronchitis are typically robust or obese and have a healthy appetite. Dogs or cats with pulmonary fibrosis generally display a gradual deterioration in exercise tolerance, and tachypnea or difficulty breathing is noted later during the course of disease.
Signalment
Signalment can be an important clue to determining whether heart or lung disease is more likely in a given case. A young animal with a heart murmur and clinical signs of cardiopulmonary disease is a likely candidate for congenital heart disease. Young to middle‐aged cats can be affected by hypertrophic cardiomyopathy or feline bronchial disease. The presence of a gallop sound or arrhythmia makes cardiac disease more likely. It is more difficult to identify the primary cause of clinical signs in middle‐aged to older small breed dogs, because they can be affected by airway collapse, chronic bronchitis, and degenerative valvular disease concurrently. Exacerbation of any of these disease processes could be the cause for clinical presentation to the veterinarian.
Dobermans, Golden Retrievers, and giant breed dogs are commonly affected by cardiac disease, while primary respiratory conditions are less common in these dogs, with the exception of aspiration pneumonia associated with laryngeal paralysis, which is common in Retriever breeds. It is also important to recall that large breed dogs can be affected by airway collapse, chronic bronchitis, and pneumonia. Idiopathic pulmonary fibrosis is most commonly reported in older West Highland White terriers, but other terrier breeds can be affected as well as cats, and younger dogs can also occasionally develop interstitial lung disease. A Maine Coon or Ragdoll cat is more often affected by hypertrophic cardiomyopathy, while a Siamese cat would be more likely to develop chronic airway disease.
Physical Examination
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