Coughing in Dogs and Cats

Coughing is commonly mentioned as a symptom caused by cardiac disease in dogs. While dogs certainly can cough from heart disease, it has been found to be an inconsistent and unreliable indicator of cardiac disease and congestive heart failure. Therefore, it is important to consider other possible etiologies and obtain the whole clinical picture for a given patient. Cats very rarely cough from heart disease; generally if a cat is coughing or wheezing, it is due to airway or pulmonary diseases, such as asthma.

Physiology of the Cough Reflex

Understanding the physiologic mechanism of coughing helps inform our diagnostic and therapeutic approach. The cough reflex is initiated by several different sensory nerve fibers primarily in the larynx, carina, and also to a lesser degree in the bronchioles.

Afferent nerve impulses pass from the respiratory passages mainly through the internal laryngeal nerve and then the vagus nerve to the medulla of the brain. An efferent pathway then follows with signals transmitted back from the cerebral cortex and medulla via the vagus, superior laryngeal, and phrenic nerves to the glottis, intercostal muscles, diaphragm, and other major inspiratory and expiratory muscles.

Phases of Coughing

The cough mechanism proceeds through three distinct phases:

Inspiratory phase: Air is drawn into the lungs in preparation for the cough.

Compression phase: The epiglottis closes to entrap the air in the lungs. The abdominal muscles contract forcefully, pushing against the diaphragm, while other expiratory muscles, such as the intercostals, also contract forcefully. This creates pressures up to 100 mmHg.

Expiratory phase: The epiglottis suddenly opens widely, allowing air to be expelled at velocities ranging from 75-100 mph. This serves to expel mucus and debris.

Clinical History and Characterization

To help determine a possible etiology for the coughing, it is essential to characterize the cough in detail. A comprehensive patient history should explore several key questions:

Temporal Characteristics

• Has the coughing been chronic with little or slow progression, or has the cough been more acute in onset?
• When does the coughing occur? Are there any activities that tend to be associated with the coughing (while the patient is active, at rest, predominantly during the night, eating/drinking, etc.)?

Associated Clinical Signs

• Are there any other adverse respiratory signs besides the coughing (increased resting respiratory rate, labored breathing, fainting/collapsing, exercise intolerance, etc.)?

Additional Historical Considerations

Other patient history information may also be important in determining the cause of the cough:

• History of cardiac and/or pulmonary disease?
• Any recent history of travel?
• Any recent vomiting?
• Is the patient on regular heartworm prophylaxis?
• Has the patient been dewormed recently?
• Has the patient had exposure to other dogs?
• Is the patient on any medications?
• Has there been any chance for toxin exposure?
• Has there been any recent trauma?
• Any recent changes in appetite?
• Any recent changes in drinking or urination?

Physical Examination Findings

Physical examination findings are critical for helping to determine cough etiology. Key findings to assess include:

Cardiovascular Assessment

• Presence of a heart murmur: While significant, this does not definitively indicate cardiogenic cough
• Heart rate: Patients with congestive heart failure typically will have tachycardia due to increased sympathetic tone; the presence of bradycardia should prompt consideration of other etiologies

Respiratory Assessment

• Tracheal palpation: Can the coughing be induced on gentle tracheal palpation?
• Lung auscultation: Are there any abnormal lung sounds, such as crackles?

Diagnostic Approach

A comprehensive diagnostic assessment should ideally be performed for any coughing patient. Since coughing is a respiratory sign, thoracic radiographs should always be one of the first tests recommended.

Recommended Diagnostics

• Thoracic radiographs: Essential first-line imaging to assess cardiac silhouette, pulmonary parenchyma, and airways
• TFAST/thoracic POCUS: Point-of-care ultrasound can rapidly identify pleural effusion or pulmonary edema
• Echocardiography: Indicated when cardiac disease is suspected based on physical examination or radiographic findings
• Comprehensive laboratory work: Including heartworm testing, complete blood count, biochemistry panel, and urinalysis
• Airway evaluation: An internal medicine consultation for diagnostics to assess non-cardiogenic coughing, such as an airway wash or bronchoscopy, should be considered in order to provide a definitive diagnosis and tailor therapy

The Cardiac Connection: What the Evidence Shows

Studies in dogs have shown variable results regarding the correlation between cardiac disease severity and coughing. Even increased left atrial size has not been definitively demonstrated to result in airway compression or collapse. This challenges the traditional teaching that left atrial enlargement mechanically compresses the mainstem bronchi, leading to cough.

Treatment Approach

Non-Cardiogenic Cough

If the coughing is confirmed or suspected to be non-cardiogenic, therapy should be directed at the underlying disease process. Treatment options may include:

• Cough suppressants (e.g., hydrocodone, butorphanol)
• Antibiotics for bacterial infections
• Bronchodilators for airway disease
• Corticosteroids for inflammatory conditions
• Treatment of parasitic infections if identified

Suspected Cardiogenic Cough

If, based on history, physical examination findings, and diagnostic results, left-sided congestive heart failure is confirmed or strongly suspected, loop-diuretic therapy should be initiated.

Species-Specific Considerations

Cats

It bears repeating that cats very rarely cough from cardiac disease. When a cat presents with coughing or wheezing, primary differential diagnoses should focus on:

• Feline asthma
• Chronic bronchitis
• Pneumonia
• Parasitic disease (heartworm, lungworm)
• Neoplasia
• Foreign body

Cardiac disease should be far down the differential list unless there are other clinical signs suggesting heart failure, such as respiratory distress, pleural effusion, or pulmonary edema documented on imaging.

When to Refer

Consider referral to a veterinary cardiologist when:

• Diagnostic imaging reveals significant cardiac disease but the relationship between the cardiac pathology and cough is unclear
• Cough persists despite appropriate therapy for both cardiac and non-cardiac etiologies
• Advanced cardiac imaging (echocardiography) is needed to guide treatment decisions
• The patient has concurrent cardiac and respiratory disease requiring specialized management
• Client requests specialist consultation for complex cases