In addition to history and physical examination findings, clinical signs of respiratory disease provide diagnostic clues and information about respiratory lesion localization. Most patients with respiratory disease are presented for evaluation because of the following clinical signs:
sneezing and "reverse sneezing"
coughing (including hemoptysis)
nasal discharge (including epistaxis)
tachypnea and labored breathing
adventitious breath sounds
exercise intolerance
A sneeze is a protective reflex that occurs in reaction to particulate matter or an irritation of the nasal cavity or nasopharynx. Sneezing is a nonspecific clinical sign that can occur in association with a wide range of infectious and inflammatory conditions, neoplasia, congenital anomalies, foreign bodies, and other underlying disorders.
In contrast to a sneeze, which involves expiratory airflow through the nasal passages, a reverse sneeze (also called paroxysmal respiration) is characterized by a sequence of repeated, forceful, abrupt, and rapid inhalations. This can occur in patients with nasopharyngeal irritation.
Irritation of the central airways triggers a cough (a short, forceful expulsion of air from the lungs), leading to the expulsion of particulate matter from the respiratory tract. A cough is a protective reflex and involves a complex reflex arc. Cough is a common, nonspecific clinical sign indicating disease along the respiratory tract from the larynx to the lung. An irritant might have to be cleared from the airway, or there could be expectorant within the airways secondary to infection. Qualities of the cough can provide clues to the underlying cause. For example, a cough can be dry or productive and can vary in pitch. A high-pitched, dry cough (often described as a “goose honk” cough) is a characteristic of upper airway irritation or obstruction in dogs and is most commonly associated with tracheal collapse or kennel cough.
Nasal discharge can be serous, catarrhal, purulent, or hemorrhagic, depending on the extent of mucosal or turbinate damage. Nasal discharge indicates increased production of normal secretions, sometimes supplemented by neutrophils (purulent) or blood (hemorrhage). It likely also indicates decreased “grooming” of the nostrils with the tongue in ill animals.
Epistaxis, or bleeding from the nose, is often caused by vascular rupture (as can occur with mycotic infection of the guttural pouch or exercise-induced pulmonary hemorrhage in horses) or by intranasal fungal infection or neoplasia, systemic coagulopathy, vasculitis, thrombocytopenia (immune-mediated or a result of rickettsial infection), hyperviscosity syndrome, hypertension, or nasal trauma.
Hemoptysis, or coughing up of blood, occurs after rupture of pulmonary aneurysms in the lungs of cattle with chronic lung abscesses. Bleeding can also result from polyps, neoplasms, granulomas, trauma, thrombocytopenia, and bracken fern or sweet clover poisoning.Other than neoplasia, heartworm disease is a major cause of hemoptysis in dogs.
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Tachypnea, or increased rate of breathing, can be a clinical sign of disease (eg, sepsis, pleural effusion); however, it can also occur in healthy animals (eg, after vigorous exercise or in response to anxiety). Tachypnea is distinguished from hyperventilation, which is defined not solely by an increased respiratory rate but also by the development of hypocapnia (ie, carbon dioxide is eliminated at a rate that exceeds metabolic production). Hyperventilation cannot be determined on the basis of physical examination findings alone.
Accompanying or subsequent to tachypnea, compromised ventilation might manifest as increased respiratory effort (labored breathing), often followed by alterations in the normal respiratory pattern. The objective, observable signs of labored breathing are referred to as respiratory distress. The term "dyspnea" is commonly used as a synonym but is formally defined as the subjective sensation of breathing discomfort (shortness of breath), as reported by the patient; because dyspnea is a subjective experience, it must be inferred by the clinician on the basis of observable clinical signs and behavior, rather than self-reported symptoms.
Orthopnea is a postural adaptation that is a clinical indicator of respiratory distress. In dogs, this typically manifests as standing with the elbows abducted, the back arched or weight shifted caudally onto the hindlimbs, and the head and neck extended to optimize airway patency. Cats, in contrast, often assume a crouched position on all four limbs, with the sternum slightly elevated.
Other clinical signs of respiratory distress include open-mouth breathing and changes in mucous membrane color, including gray, dark pink, or blue discoloration (cyanosis). These findings reflect major impairment of pulmonary function and might precede respiratory arrest.
Adventitious breath sounds include crackles (rales), wheezes, rhonchi, and pleural friction rub. Increased sounds on inhalation (stertor and stridor) are typically observed and can occur with upper airway obstruction or obstructions cranial to the thoracic inlet (eg, laryngeal paralysis, cervical tracheal collapse). Labored expiration occurs in obstructive diseases caudal to the thoracic inlet (eg, diffuse bronchitis, principal bronchial collapse, or pulmonary edema). Fixed airway obstructions (eg, tracheal neoplasia, foreign body, or stenosis) or a combination of upper and lower airway diseases (eg, pleural effusion with congestive heart failure) result in marked respiratory distress or respiratory failure. Cough, clear nasal exudate, and shallow breathing with grunting are often associated with the pain caused by pleuritis.
Exercise intolerance is a common clinical sign in patients with respiratory disease, reflecting impaired oxygen delivery and decreased ventilatory efficiency during periods of increased physical demand. Affected animals fatigue quickly during activity and might exhibit other clinical signs of respiratory disease (including increased respiratory effort, cough, or respiratory distress).
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