Adventitious Lung Sounds: Types and Causes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

Adventitious lung sounds are abnormal noises added on top of normal breathing sounds when a veterinarian listens to the chest with a stethoscope. The three main categories are crackles (short, discontinuous popping sounds), wheezes (continuous musical sounds from narrowed lower airways), and stridor (a continuous, harsh, high-pitched sound from a narrowed upper airway). Each points toward a different part of the respiratory tract, but none of them is a diagnosis on its own. Adventitious breath sounds tell your veterinarian where to look next, not what the final answer is.

This article explains what each adventitious chest sound means, how veterinarians distinguish them, which conditions cause them in dogs, cats, and other species, and what you should do if you hear something unusual at home.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

At a Glance: The Three Core Adventitious Sounds

This table is a starting framework. Your veterinarian will interpret any sound in the context of your pet's history, physical examination, and imaging.

What "Adventitious" Actually Means

The word adventitious means "added from outside." In respiratory medicine, adventitious lung sounds are sounds that are not part of normal breath sounds. Normal breathing creates a soft, low-pitched airflow noise heard over the lung fields. Anything extra, popping, whistling, squeaking, or harsh, is adventitious.

Veterinarians divide breath sounds into three broad groups:

1. Normal breath sounds. Soft airflow heard over healthy lung.
2. Decreased or absent breath sounds. Not truly adventitious, but abnormal. These suggest fluid, air, or tissue between the stethoscope and the lung, or a lung that is not moving air. A toddler with complete left lung collapse from a mucus plug had absent breath sounds over the entire left hemithorax [5].
3. Adventitious sounds. Added noises such as crackles, wheezes, stridor, stertor, and rattles.

The distinction matters because adventitious breath sounds are a sign, not a disease. Two pets can make the same sound for completely different reasons. A wheeze in a cat usually means lower airway narrowing. A wheeze in a horse with severe asthma means the same thing, but the underlying triggers and treatment differ [1].

The Anatomy Behind the Sounds

To understand adventitious chest sounds, it helps to picture the airway as a tree that gets narrower as it branches.

• The upper airway includes the nose, pharynx, larynx, and trachea. Problems here tend to create loud, harsh sounds heard without a stethoscope, especially during inspiration.
• The lower airways include the bronchi and bronchioles. Problems here create wheezes and crackles heard through the stethoscope over the chest.
• The alveoli are the tiny air sacs where gas exchange happens. Fluid or collapse here creates fine crackles.

Air moving through a tube is silent when the tube is wide and smooth. It becomes noisy when the tube narrows, when the walls vibrate, or when liquid and air mix. That single principle explains almost every adventitious sound.

Crackles: Discontinuous Added Sounds

Crackles are short, explosive, discontinuous sounds. They are sometimes called rales in older human medical texts. Each crackle is a tiny pop, and many crackles together sound like hair being rubbed between the fingers, Velcro separating, or salt sizzling in a pan.

Crackles come from two main mechanisms:

• Airway reopening. A small airway that has collapsed during expiration pops open during inspiration.
• Fluid and secretions. Air bubbling through liquid in the airways creates a series of small explosions.

Veterinarians split crackles into fine and coarse types.

Fine Crackles

Fine crackles are soft, high-pitched, and brief. They cluster at the very end of inspiration. They sound like the noise of rubbing a lock of hair near your ear.

Fine crackles usually point to disease in the small airways or the lung interstitium, the tissue between air sacs. Common causes include:

• Pulmonary edema from left-sided heart failure
• Early or interstitial pneumonia
• Pulmonary fibrosis
• Interstitial lung disease

In horses, fine crackles and wheezes were significantly more frequent in horses with severe asthma during an exacerbation compared with healthy controls, mild to moderate asthma cases, and severe asthma cases in remission [1]. That study used a digital auscultation device to record sounds from 11 locations on each horse for one hour, which allowed researchers to detect sounds that a brief examination might miss.

Coarse Crackles

Coarse crackles are louder, lower-pitched, and longer than fine crackles. They can occur earlier in inspiration and may extend into expiration. They sound wetter, like bubbling or gurgling.

Coarse crackles usually mean larger airways contain secretions or fluid. Common causes include:

• Bronchopneumonia
• Aspiration pneumonia
• Chronic suppurative lung disease
• Bronchiectasis

In dogs with aspiration pneumonia, most affected dogs had increased, decreased, or adventitious lung sounds on examination [2]. That study of 88 dogs found that auscultation abnormalities were common even when body temperature, heart rate, and respiratory rate were normal. This is one reason a veterinarian listens carefully even when a dog looks stable.

Cattle with chronic suppurative pneumonia also produce crackles. In a study of 12 cows, researchers recorded lung sounds alongside ultrasound findings and found that adventitious sounds did not always line up neatly with the underlying lesions [3]. That is an important limitation of auscultation in every species.

What Crackles Do Not Tell You

Crackles are not specific. The same sound can come from heart failure, pneumonia, or fibrosis. A study of adult sheep with lung abscesses found that auscultation failed to detect adventitious sounds in any of the ten sheep, even though ultrasound clearly showed the abscesses [6]. Wheezes and crackles heard in some sheep with ovine pulmonary adenocarcinoma did not correlate well with the lesions seen on ultrasound.

That finding is a useful reality check. Adventitious lung sounds are a clue, not a conclusion.

Wheezes: Continuous Musical Sounds

Wheezes are continuous, musical, high-pitched sounds. They last longer than crackles and have a clear tone, like a whistle or a tea kettle. The pitch can be single or multiple.

Wheezes come from air flowing through narrowed lower airways. The narrowing can be caused by:

• Smooth muscle constriction (bronchoconstriction)
• Mucus plugging
• Swelling of the airway wall
• External compression of the airway

Expiratory Versus Inspiratory Wheeze

The timing of a wheeze gives a clue about where the problem is.

• Expiratory wheeze. The airways naturally narrow during expiration. If they are already narrowed by disease, expiration becomes the hardest phase and the wheeze is loudest then. This pattern is typical of lower airway disease such as asthma or chronic bronchitis.
• Inspiratory wheeze. This can occur with lower airway disease too, but a prominent inspiratory wheeze should make your veterinarian think about the upper airway or a fixed obstruction.

In horses with severe asthma during an exacerbation, wheezes were detected in 68.6 percent of breaths analyzed, compared with zero percent in healthy controls, mild to moderate asthma cases, and severe asthma cases in remission [1]. That is a striking difference and shows how strongly active lower airway disease can produce wheezes.

Feline Asthma and Wheeze

Feline asthma is a classic cause of wheeze in cats. The airways narrow because of allergic inflammation and bronchoconstriction. Affected cats often cough, breathe with effort, and make a wheezing sound. Some cats have a chronic cough that owners mistake for hairballs.

A wheeze in a cat is never normal. It deserves a veterinary examination and usually chest imaging.

Canine Chronic Bronchitis and Wheeze

Dogs with chronic bronchitis also wheeze. The airway walls thicken and produce mucus, narrowing the lumen. Small breed dogs are overrepresented in many practices, though any dog can develop chronic bronchitis.

Wheeze Versus Stridor

Wheezes are lower airway sounds. Stridor is an upper airway sound. The two can sound similar to an untrained ear, but they have different timing and character. Stridor is harsh and usually inspiratory. Wheeze is musical and usually expiratory. Your veterinarian can often tell them apart just by listening at the neck versus the chest.

Stridor: A Harsh Upper Airway Sound

Stridor is a continuous, harsh, high-pitched sound caused by turbulent airflow through a narrowed upper airway. It is usually heard during inspiration, but it can be biphasic if the obstruction is severe. Stridor is often loud enough to hear without a stethoscope.

Stridor is a red flag. It means the upper airway is narrowed, and upper airway narrowing can progress quickly to complete obstruction.

Common Causes of Stridor in Dogs

• Laryngeal paralysis. The arytenoid cartilages fail to open the larynx during inspiration. Older large-breed dogs are most commonly affected. The classic sign is a harsh inspiratory noise that worsens with exercise, heat, or excitement.
• Laryngeal masses. Tumors or polyps in the larynx narrow the airway.
• Tracheal collapse. The trachea flattens during breathing, creating a honking cough and sometimes stridor.
• Laryngeal edema. Swelling from trauma, surgery, or an allergic reaction.
• Brachycephalic airway syndrome. Bulldogs, pugs, and similar breeds have multiple upper airway abnormalities that together create noise and effort.

Stridor in Cats

Cats can develop stridor from laryngeal disease, nasopharyngeal polyps, or tumors. Any cat with a new harsh breathing noise needs prompt evaluation.

Stridor in Other Species

Stridor is not limited to dogs and cats. In human neonates, inspiratory stridor is most often caused by laryngomalacia, vocal cord paralysis, or subglottic stenosis. Less commonly, a vascular anomaly such as a ductus arteriosus aneurysm can compress the recurrent laryngeal nerve and cause vocal cord paralysis [4]. That case report describes a neonate with progressive, position-dependent inspiratory stridor and episodic oxygen desaturation. The principle applies across species: stridor means something is narrowing the upper airway, and the cause may be distant from the airway itself.

Stertor: The Snoring Sound

Stertor is a low-pitched, snoring sound caused by vibration of soft tissue in the nose, pharynx, or soft palate. It is usually inspiratory. Stertor is not the same as stridor.

• Stertor is low-pitched and fluttering. It sounds like snoring.
• Stridor is high-pitched and harsh. It sounds like air forced through a tight opening.

Brachycephalic dogs often stertor because their soft palate is elongated and their nostrils are narrow. Stertor can also occur with nasal obstruction, nasal masses, or pharyngeal disease.

Stertor is sometimes normal in flat-faced breeds at rest, but it is never normal if it is new, progressive, or accompanied by effort.

Rattles and Other Terms

Rattles are a category used more often in equine medicine. They are coarse, bubbling sounds from secretions in larger airways. In the horse asthma study, rattles were significantly more frequent in horses with severe asthma during exacerbation, though at a lower rate than wheezes or crackles [1].

Terminology differs between human and veterinary medicine. Human clinicians often use the term rales for crackles and rhonchi for low-pitched continuous sounds. Veterinary clinicians tend to use crackles, wheezes, stridor, and stertor. The same physical sound may carry different names depending on who is listening and where they trained. This is one reason auscultation findings are described in plain language in a medical record rather than relying on a single label.

How Veterinarians Distinguish the Sounds

Auscultation is a skill built on pattern recognition. Veterinarians use several strategies to sort out adventitious breath sounds.

Listen in Multiple Locations

A veterinarian listens over the trachea, the mainstem bronchi, and multiple points on both sides of the chest. A sound heard only over the trachea suggests an upper airway source. A sound heard over the lung fields suggests a lower airway or parenchymal source.

Compare Inspiration and Expiration

Timing is one of the most useful clues.

• Late inspiratory crackles suggest small airway or alveolar disease.
• Expiratory wheezes suggest lower airway narrowing.
• Inspiratory stridor suggests upper airway narrowing.

Check for Synchrony of Chest and Abdominal Movement

In a study of 176 dogs and cats with respiratory distress, researchers systematically recorded respiratory rate, heart rate, temperature, type of breathing, movement of the thoracic and abdominal wall during inspiration, presence of stridor, presence and type of dyspnea, and thoracic auscultation findings [7]. They categorized abdominal and chest wall movement as synchronous, asynchronous, or inverse, and then assigned animals to groups based on the anatomical localization of the distress. Inspiratory dyspnea was associated with upper airway disease. This kind of structured examination helps localize the problem before imaging.

Use Imaging to Confirm

Auscultation narrows the differential. Imaging confirms it.

• Thoracic radiography shows lung patterns, heart size, and masses.
• Thoracic ultrasound shows pleural surfaces and superficial lung. In the cattle study, ultrasound allowed researchers to compare recorded sounds over normal lung and defined pathology in the same animal, removing confounders such as respiratory rate and chest wall thickness [3].
• Computed tomography gives detailed anatomy for upper airway and lung disease.
• Bronchoscopy allows direct visualization of the airway.

In the sheep study, ultrasound detected lung abscesses, fibrinous pleurisy, and ovine pulmonary adenocarcinoma lesions that auscultation missed [6]. That does not make auscultation useless. It makes auscultation one tool among several.

Causes by Anatomical Location

Sorting causes by location is the most practical way to think about adventitious lung sounds.

Upper Airway Causes

• Laryngeal paralysis
• Laryngeal masses
• Laryngeal edema
• Tracheal collapse
• Brachycephalic airway syndrome
• Nasopharyngeal polyps in cats
• Foreign bodies

These produce stridor or stertor.

Lower Airway Causes

• Feline asthma
• Canine chronic bronchitis
• Equine asthma
• Bronchoconstriction from any cause
• Mucus plugging

These produce wheezes and sometimes coarse crackles.

Lung Parenchyma Causes

• Pneumonia (bacterial, viral, fungal, aspiration)
• Pulmonary edema
• Pulmonary fibrosis
• Interstitial lung disease
• Neoplasia

These produce crackles and sometimes wheezes.

Pleural Space Causes

• Pleural effusion
• Pneumothorax
• Fibrinous pleurisy

These typically reduce or eliminate breath sounds rather than add adventitious sounds. In the sheep study, normal breath sounds were reduced over the area of fibrinous pleurisy, and no pleuritic rubs were heard [6].

Risk Factors and Predispositions

Several factors increase the chance that a pet will develop adventitious breath sounds.

• Age. Laryngeal paralysis is most common in older large-breed dogs. Congenital causes of stridor are more common in young animals.
• Breed. Brachycephalic breeds have a higher risk of upper airway noise. Small breed dogs are overrepresented in chronic bronchitis.
• Body condition. Obesity worsens respiratory effort in brachycephalic dogs and can worsen lower airway disease.
• Environment. Allergens and irritants trigger feline asthma and equine asthma.
• Underlying disease. Heart disease predisposes to pulmonary edema. Neurologic disease or esophageal disease predisposes to aspiration pneumonia. In the aspiration pneumonia study, most affected dogs had increased, decreased, or adventitious lung sounds, and many had normal temperature, heart rate, and respiratory rate [2].
• Species. Horses with severe asthma during exacerbation had wheezes in 68.6 percent of breaths, crackles in 66.1 percent, and rattles in 17.7 percent [1]. Healthy horses, horses with mild to moderate asthma, and horses in remission had near-zero rates.

What to Do If You Hear an Abnormal Sound

If you hear a new breathing noise in your pet, stay calm and observe carefully. Note:

• Whether the sound is on inspiration, expiration, or both
• Whether it is high-pitched or low-pitched
• Whether it is continuous or intermittent
• Whether your pet is working hard to breathe
• Whether the gums are pink or pale or blue
• Whether your pet can eat, drink, and rest comfortably

Record a short video with sound if you can. Your veterinarian may find it useful.

Emergency Signs

Seek emergency veterinary care immediately if you see:

• Blue, gray, or white gums
• Open-mouth breathing in a cat
• Collapse or fainting
• Extreme effort with each breath
• Inability to lie down or rest
• A sudden change in the sound, especially if it becomes quieter (which can mean the airway is closing)

Stridor that appears suddenly is an emergency. Upper airway obstruction can progress rapidly.

Veterinary Examination and Diagnostics

A veterinarian will start with a full history and physical examination. They will listen to the chest and neck, check mucous membrane color, assess respiratory effort, and palpate the neck and chest.

Auscultation

Auscultation is the first-line tool. It is inexpensive, non-invasive, and repeatable. It has limits. In the sheep study, auscultation failed to detect adventitious sounds in all ten sheep with lung abscesses [6]. In the cattle study, adventitious sounds did not always correlate with lesions seen on ultrasound [3]. A normal auscultation does not rule out lung disease.

Imaging

Radiography and ultrasound are the next steps. Ultrasound is particularly useful for pleural space and superficial lung disease. Radiography is useful for lung patterns and heart size.

Advanced Testing

Depending on the findings, a veterinarian may recommend:

• Airway sampling (tracheal wash or bronchoalveolar lavage)
• Bronchoscopy
• Computed tomography
• Blood gas analysis
• Cardiac evaluation

In dogs with aspiration pneumonia, hypoxemia and a high alveolar-arterial gradient were common, and neutrophilia with a left shift was a frequent finding [2]. These tests help assess severity and guide treatment.

Evidence-Based Management

Treatment depends on the cause. There is no single treatment for adventitious lung sounds.

Upper Airway Disease

• Laryngeal paralysis may require surgery to open the airway.
• Tracheal collapse may be managed with medication, weight control, and sometimes stenting.
• Brachycephalic airway syndrome may require surgical correction of the obstructing tissues.

Lower Airway Disease

• Feline asthma is managed with bronchodilators and anti-inflammatory medication, often delivered by inhaler.
• Canine chronic bronchitis is managed with anti-inflammatory medication, bronchodilators, and sometimes antibiotics.
• Equine asthma is managed with environmental control and medication.

Lung Parenchyma Disease

• Pneumonia is treated with antibiotics guided by culture when possible.
• Pulmonary edema from heart failure is treated with diuretics and cardiac medication.
• Aspiration pneumonia is treated with antibiotics and supportive care. In the dog study, most dogs had a predominantly alveolar infiltrate on radiography, and the right middle lung lobe was most commonly affected [2].

Pleural Space Disease

• Pleural effusion is drained with thoracocentesis.
• Pneumothorax is managed with thoracocentesis or chest tube placement.

Treatment duration varies. Your veterinarian will set a recheck schedule based on the diagnosis and response.

Unsafe Home Remedies

Do not try to treat adventitious lung sounds at home.

• Do not give human asthma inhalers to a pet without veterinary guidance.
• Do not give over-the-counter cough suppressants.
• Do not use essential oils or humidifiers with additives around pets with respiratory distress.
• Do not wait to see if stridor resolves on its own.

Some home measures are safe and helpful. Keep the air clean, avoid smoke and strong fragrances, use a harness instead of a neck collar for dogs with tracheal collapse, and keep your pet at a healthy weight. These support veterinary care rather than replace it.

Prevention

Not all causes of adventitious lung sounds are preventable, but some are.

• Maintain a healthy weight. Obesity worsens respiratory effort.
• Avoid airway irritants. Smoke, dust, and strong chemicals can trigger lower airway disease.
• Control allergens. This is especially important for cats with asthma and horses with equine asthma.
• Treat dental disease. Poor dental health is a risk factor for aspiration pneumonia in some animals.
• Manage underlying heart disease. Good cardiac care reduces the risk of pulmonary edema.
• Use a harness for dogs with tracheal collapse.
• Schedule regular wellness examinations. Early detection of heart or lung disease improves outcomes.

Prognosis

Prognosis depends entirely on the cause.

• Feline asthma is usually manageable with lifelong treatment.
• Laryngeal paralysis has a good prognosis after surgery in many cases, though aspiration risk exists.
• Tracheal collapse varies from mild to severe.
• Pneumonia has a good prognosis with prompt treatment.
• Pulmonary edema from heart failure carries a guarded prognosis but can be managed for months to years.
• Lung masses carry a variable prognosis depending on type and stage.

Adventitious lung sounds themselves do not determine prognosis. The underlying disease does.

Limitations and When to Contact a Veterinarian

Auscultation is a useful screening tool, but it has real limits. In the sheep study, auscultation missed lung abscesses in every affected animal [6]. In the cattle study, adventitious sounds did not always match ultrasound findings [3]. A normal chest examination does not rule out serious lung disease, and an abnormal sound does not confirm a specific diagnosis.

Contact a veterinarian promptly if your pet has:

• A new or worsening breathing noise
• Increased respiratory effort at rest
• A cough that lasts more than a few days
• Exercise intolerance
• A change in gum color
• Difficulty eating or sleeping because of breathing

Seek emergency care immediately for blue gums, open-mouth breathing in a cat, collapse, or sudden severe distress. Individual cases need a veterinarian who can examine your pet in person.

Frequently Asked Questions

What are adventitious lung sounds?

Adventitious lung sounds are abnormal added breath noises heard with a stethoscope. The main types are crackles, wheezes, and stridor.

Are adventitious breath sounds always serious?

No. Some are mild and reversible, but any new adventitious sound deserves veterinary evaluation because the underlying cause can range from minor to life-threatening.

What is the difference between crackles and wheezes?

Crackles are short, discontinuous popping sounds from airway reopening or fluid. Wheezes are continuous musical sounds from narrowed lower airways.

What does stridor mean in a dog?

Stridor is a harsh, high-pitched inspiratory sound from a narrowed upper airway. In dogs, common causes include laryngeal paralysis, laryngeal masses, and tracheal collapse.

Can cats have adventitious lung sounds?

Yes. Cats with feline asthma commonly wheeze. Cats can also develop crackles from pneumonia or heart failure and stridor from upper airway disease.

Is stertor the same as stridor?

No. Stertor is a low-pitched snoring sound from soft tissue vibration. Stridor is a high-pitched harsh sound from a narrowed airway.

Do adventitious lung sounds always mean lung disease?

No. Stridor and stertor come from the upper airway, not the lung. Even lower airway sounds can come from heart disease, airway disease, or other causes.

When should I take my pet to the emergency room?

Go immediately for blue or pale gums, open-mouth breathing in a cat, collapse, severe effort with each breath, or a sudden change in breathing sound.

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Sources

1. Breath characteristics and adventitious lung sounds in healthy and asthmatic horses.
2. Clinical, clinicopathologic, and radiographic findings in dogs with aspiration pneumonia: 88 cases (2004-2006).
3. Clinical presentation, auscultation recordings, ultrasonographic findings and treatment response of 12 adult cattle with chronic suppurative pneumonia: case study.
4. Ductus arteriosus aneurysm in a neonate with inspiratory stridor.
5. Life-Threatening Acute Hypoxemic Respiratory Failure Caused by Complete Left Lung Collapse Secondary to Mucus Plug Obstruction in a Toddler: A Case Report.
6. Antibiotic Treatment Response of Chronic Lung Diseases of Adult Sheep in the United Kingdom Based upon Ultrasonographic Findings.
7. Evaluation of respiratory parameters at presentation as clinical indicators of the respiratory localization in dogs and cats with respiratory distress.