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by Noah Lechtzin, MD, MHS

Wheezing is a relatively high-pitched whistling noise produced by movement of air through narrowed or compressed small airways. It is a symptom as well as a physical finding.

Prolonged expiratory phase with wheezing.



Airflow through a narrowed or compressed segment of a small airway becomes turbulent, causing vibration of airway walls; this vibration produces the sound of wheezing.

Wheezing is more common during expiration because increased intrathoracic pressure during this phase narrows the airways. Wheezing during expiration alone indicates milder obstruction than wheezing during both inspiration and expiration, which suggests more severe airway narrowing.

By contrast, turbulent flow of air through a narrowed segment of the large, extrathoracic airways produces a whistling inspiratory noise (stridor—see Stridor).


Small airway narrowing may be caused by bronchoconstriction, mucosal edema, or external compression, or partial obstruction by a tumor, foreign body, or thick secretions.

Overall, the most common causes are

  • Asthma

  • COPD

But wheezing may occur in other disorders affecting the small airways, including heart failure (cardiac asthma), anaphylaxis, and toxic inhalation. Sometimes, healthy patients manifest wheezing during a bout of acute bronchitis. In children, bronchiolitis and foreign body aspiration are also causes (see Table: Some Causes of Wheezing).

Some Causes of Wheezing


Suggestive Findings

Diagnostic Approach*

Acute bronchitis

URI symptoms

No known history of lung disease

Clinical evaluation

Allergic reaction

Sudden onset, usually within 30 min of exposure to known or potential allergen

Often nasal congestion, urticaria, itchy eyes, sneezing

Clinical evaluation


Often known history of asthma

Wheezing arising spontaneously or after exposure to specific stimuli (eg, allergen, URI, cold, exercise)

Clinical evaluation

Sometimes pulmonary function testing, peak flow measurement, methacholine challenge, or observation of response to empiric bronchodilators


In children < 18 mo (usually from November to April in the Northern Hemisphere)

Usually URI symptoms and tachypnea

Clinical evaluation

COPD exacerbation

In middle-aged or elderly patients

Often known history of COPD

Extensive smoking history

Poor breath sounds


Pursed lip breathing

Use of accessory muscles

Clinical evaluation

Sometimes chest x-ray and ABG measurement

Drugs (eg, ACE inhibitors, aspirin, β-blockers, NSAIDs)

Recent initiation of a new drug, most often in a patient with a history of reactive airway disease

Clinical evaluation

Endobronchial tumors

Fixed and constant inspiratory and expiratory wheezes, especially in a patient with risk factors for or signs of cancer (eg, smoking history, night sweats, weight loss, hemoptysis)

May be focal rather than diffuse

Chest x-ray or CT

Bronchoscopy (usually preceded by spirometry with flow volume loops that indicate obstruction)

Foreign body

Sudden onset in a young child who has no URI or constitutional symptoms

Chest x-ray or CT


GERD with chronic aspiration

Chronic or recurrent wheezing, often with heartburn and nocturnal cough

No URI or allergic symptoms

Trial of acid-suppressing drugs

Sometimes esophageal pH monitoring

Inhaled irritants

Sudden onset after occupational exposure or inappropriate use of cleaning agents

Clinical evaluation

Left-sided heart failure with pulmonary edema (cardiac asthma)

Crackles and signs of central or peripheral volume overload (eg, distended neck veins, peripheral edema)

Dyspnea while lying flat (orthopnea) or appearing 1–2 h after falling asleep (paroxysmal nocturnal dyspnea)

Chest x-ray


BNP measurement


*Most patients should have pulse oximetry. Unless symptoms are very mild or are clearly an exacerbation of a known chronic disease, chest x-ray should be done.

BNP = brain (B type) natriuretic peptide; GERD =gastroesophageal reflux disease.


When patients are in significant respiratory distress, evaluation and treatment proceed at the same time.


History of present illness should determine whether the wheezing is new or recurrent. If recurrent, patients are asked the previous diagnosis and whether current symptoms are different in nature or severity. Particularly when the diagnosis is unclear, the acuity of onset (eg, abrupt or gradual), temporal patterns (eg, persistent vs intermittent, seasonal variations), and provoking or exacerbating factors (eg, current URI, allergen exposure, cold air, exercise, feeding in infants) are noted. Important associated symptoms include shortness of breath, fever, cough, and sputum production.

Review of systems should seek symptoms and signs of causative disorders, including fever, sore throat, and rhinorrhea (respiratory infection); orthopnea, paroxysmal nocturnal dyspnea, and peripheral edema (heart failure); night sweats, weight loss, and fatigue (cancer); nasal congestion, itching eyes, sneezing, and rash (allergic reaction); and vomiting, heartburn, and swallowing difficulties (gastroesophageal reflux disease with aspiration).

Past medical history should ask about conditions known to cause wheezing, particularly asthma, COPD, and heart failure. Sometimes the patient’s drug list may be the only indication of such diagnoses (eg, inhaled bronchodilators and corticosteroids in COPD; diuretics and ACE inhibitors in heart failure). Patients with known disease should be asked about indicators of disease severity, such as previous hospitalization, intubation, or ICU admission. Also, conditions that predispose to heart failure are identified, including atherosclerotic or congenital heart disease and hypertension. Smoking history and exposure to secondhand smoke should be noted.

Physical examination

Vital signs are reviewed for presence of fever, tachycardia, tachypnea, and low O 2 saturation.

Any signs of respiratory distress (eg, accessory muscle use, intercostal retractions, pursed lip breathing, agitation, cyanosis, decreased level of consciousness) should be immediately noted.

Examination focuses on the lungs, particularly adequacy of air entry and exit, symmetry of breath sounds, and localization of wheezing (diffuse vs localized; inspiratory, expiratory, or both). Any signs of consolidation (eg, egophony, dullness to percussion) or crackles should be noted.

The cardiac examination should focus on findings that might indicate heart failure, such as murmurs, a 3rd heart sound (S 3 gallop), and jugular venous distention.

The nose and throat examination should note appearance of the nasal mucosa (eg, color, congestion), swelling of the face or tongue, and signs of rhinitis, sinusitis, or nasal polyps.

The extremities are examined for clubbing and edema, and the skin is examined for signs of allergic reactions (eg, urticaria, rash) or atopy (eg, eczema). The patient’s general appearance is noted for constitutional signs, such as the cachexia and barrel chest of severe COPD.

Red flags

The following findings are of particular concern:

  • Accessory muscle use, clinical signs of tiring, or decreased level of consciousness

  • Fixed inspiratory and expiratory wheezing

  • Swelling of the face and tongue (angioedema)

Interpretation of findings

Recurrent wheezing in a patient with a known history of disorders such as asthma, COPD, or heart failure is usually presumed to represent an exacerbation. In patients who have both lung and heart disease, manifestations may be similar (eg, neck vein distention and peripheral edema in cor pulmonale due to COPD and in heart failure), and testing is often required. When the cause is known asthma or COPD, a history of cough, postnasal drip, or exposure to allergens or to toxic or irritant gases (eg, cold air, dust, tobacco smoke, perfumes) may suggest a trigger.

Clinical findings help suggest a cause of wheezing in patients without a known history (see Table: Some Causes of Wheezing).

Acute (sudden-onset) wheezing in the absence of URI symptoms suggests an allergic reaction or impending anaphylaxis, especially if urticaria or angioedema is present. Fever and URI symptoms suggest infection, acute bronchitis in older children and adults, and bronchiolitis in children < 2 yr. Crackles, distended neck veins, and peripheral edema suggest heart failure. Association of wheezing with feeding or vomiting in infants can be a result of gastroesophageal reflux.

Patients with asthma usually have paroxysmal or intermittent bouts of acute wheezing.

Persistent, localized wheezing suggests focal bronchial obstruction by a tumor or foreign body. Persistent wheezing manifesting very early in life suggests a congenital or structural abnormality. Persistent wheezing with sudden onset is consistent with foreign body aspiration, whereas the slowly progressive onset of wheezing may be a sign of extraluminal bronchial compression by a growing tumor or lymph node.


Testing seeks to assess severity, determine diagnosis, and identify complications.

  • Pulse oximetry

  • Chest x-ray (if diagnosis unclear)

  • Sometimes ABGs

  • Sometimes pulmonary function testing

Severity is assessed by pulse oximetry and, in patients with respiratory distress or clinical signs of tiring, ABG testing. Patients known to have asthma usually have bedside peak flow measurements (or, when available, forced expiratory volume in 1 sec [FEV 1 ]).

Patients with new-onset or undiagnosed persistent wheezing should have a chest x-ray. X-ray can be deferred in patients with asthma who are having a typical exacerbation and in patients having an obvious allergic reaction. Cardiomegaly, pleural effusion, and fluid in the major fissure suggest heart failure. Hyperinflation and hyperlucency suggest COPD. Segmental or subsegmental atelectasis or infiltrate suggests an obstructing endobronchial lesion. Radiopacity in the airways or focal areas of hyperinflation suggest a foreign body.

If the diagnosis is unclear in patients with recurrent wheezing, pulmonary function testing can confirm airflow limitation and quantify its reversibility and severity. Methacholine challenge testing and exercise testing can confirm airway hyperreactivity in patients for whom the diagnosis of asthma is in question.


Definitive treatment of wheezing is treatment of underlying disorders.

Wheezing itself can be relieved with inhaled bronchodilators (eg, albuterol 2.5 mg nebulized solution or 180 mg metered dose inhalation). Long-term control of persistent asthmatic wheezing may require inhaled corticosteroids and leukotriene inhibitors.

Intravenous H 2 blockers (diphenhydramine), corticosteroids (methylprednisolone), and subcutaneous and inhaled racemic epinephrine are indicated in cases of anaphylaxis.

Key Points

  • Asthma is the most common cause, but not all wheezing is asthma.

  • Acute onset of wheezing in a patient without a lung disorder may be due to aspiration, allergic reaction, or heart failure.

  • Reactive airway disease can be confirmed via spirometry.

  • Inhaled bronchodilators are the mainstay of acute treatment.

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