Causes of Stridor and Wheeze (Breathing Sounds)

stridor vs wheezing

Stridor and wheezing are two terms for different breathing sounds that are often used synonymously although there is a difference. Wheezing refers to the high-pitched or whistling sound, which is most prominent when breathing out (expiration). A wheeze is usually heard clearly upon auscultation (use of a stethoscope) although at times it may be audible, especially to the patient, without any need for a stethoscope. A stridor is also high pitched but ‘rough’ sound sometimes described as crowing. It  easily audible without the use of a stethoscope (auscultation) and while it is present when breathing in (inspiration) or out (expiration), it is usually more prominent on inspiration.

Anatomy of the Respiratory System

Tracheobronchial tree leading to the lungs

The respiratory system is made up of the organs that allow ventilation, which is the entrance and exit of gas or air passages, and the lungs, which is responsible for gas exchange between the air and the blood. Starting from the nose, air travels through the nasal cavity, into the pharyng, larynx and trachea (air or wind pipe). Here the air will diverge into the two bronchi, each of which divide multiple times to form bronchioles that empties air into the air sacs (alveoli) of the lungs. The tracheobronchial tree is a series of ‘tubes’ that lead to the lungs. These tubes are thin walled, lined with membranes that secrete mucus, and contain smooth muscle in the wall. Under certain conditions, the membranes may produce more mucus, the smooth muscle may contract or the wall of the tubes may become inflamed resulting in swelling. All these mechanisms will cause constriction (narrowing) of the tubes to varying degrees thereby affecting the flow of air. However any mass within the airways, whether a foreign body, abscess or tumor will also affect the passage of the air. The disrupted airflow is often the reason for abnormal breathing sounds like a wheeze or stridor, similar to the changes in the flow of air through a flute.

Abnormal Breathing or Chest Sounds

Wheezing is a result of irregular narrowing of the lower airways, often seen in asthma, while a stridor is a mechanical (physical abnormalities) or functional (impaired functioning) of the air passages, including the throat.A stridor is more often seen in respiratory infections, disorders of the vocal cords, tumors or allergic reactions. Irrespective of the type of sound, any abnormal chest sounds heard upon breathing should be investigated by a medical doctor to verify the extent to which the air flow is affected. Subsequently the cause of the wheeze or stridor has to be identified and treated accordingly.

It is difficult to always ascertain whether a sound is a stridor or a wheeze, and a stridor is often described as a wheeze by most people. There are a number of causes of wheezing and a stridor and some of the causes may overlap. It is therefore important to take note of other signs and symptoms or the results of clinical tests and diagnostic techniques to make a final diagnosis.

Causes of Wheezing and Stridor

There are various causes of wheezing and stridor, all of which affect the flow of air through the respiratory passages to some degree. Some of these causes include the following conditions.

  • Asthma is probably the most well known cause of a wheeze. There is usually a history of asthma and it is triggered by certain stimuli, like inhaled allergens (dust, pollen, etc) or ingested allergens (dairy, nuts, etc), environmental conditions like cold or wet weather, or strenuous physical activity (exercise induced asthma).
  • Acute bronchitis is usually the result of a respiratory tract infection and fever, pain and persistent coughing along with a stridor may be noticed. The cough is often productive, meaning that mucus (phlegm) is expectorated upon coughing.
  • Allergic reaction or anaphylaxis occurs after exposure to an allergen. Examples include hypersensitivity to shellfish, certain drugs, insect bites like a bee sting. The reaction causes narrowing of the airways shortly after exposure to the allergen and requires immediate medical attention to restore airway integrity.
  • Bronchiectasis is a lung disease that results in excessive mucus accumulation due to widening of the airways. The mucus build up causes an irregular air passage, affecting the flow of air and resulting in abnormal breathing sounds like a wheeze or stridor.
  • Common childhood respiratory infections that cause stridor include bronchiolitisand croup. Bronchiolitis is a common childhood infection of the respiratory system, which is common in the “cold and flu” season. Bronchiolitis is usually caused by the respiratory synctial virus (RSV) and presents with typical symptoms of a “chest infection”, along with rapid, shallow breathing. Croup is a respiratory tract that causes swelling of the trachea (wind pipe) and larynx and may be accompanied by stridor. It mainly affects children and has a characteristic barking-like cough.
  • Chronic obstructive pulmonary disease (COPD), like emphysema or chronic bronchitis, is progressive lung disease that typically occurs as a result of long term exposure to toxins that irritate the respiratory passages. This is often seen in cigarette smokers and may also be present in those with long term exposure to noxious fumes, air pollution, airbone particles and dust. Excessive mucus secretion, a “tight chest”, wheezing or stridor and difficulty in breathing are the characteristic symptoms of COPD.
  • Drugs like non-steroidal antiinflammatories, including aspirin and certain anti-hypertensive medicines may cause wheezing. This may be a result of the drug side effects or due to an allergic reaction to the active ingredient, filler (or bulking) substances in the drug or preservatives and colorants. In certain cases, drug interactions may occur when more than one drug is used simultaneously and can cause various signs and symptoms.
  • Tumors affecting the airway or lung may be the cause of a stridor. Endobronchial tumors or laryngeal tumors are more likely to be the cause of a stridor as it affects the passage of air to the lungs. However lung cancer will also cause abnormal breathing sounds, especially if the mass is at multiple sites or the tumor has grown to a substantial size.
  • Foreign object(s) that lodge in the airway passages are more likely to occur in children and will cause pain, along with wheezing and depending on the size of the object, difficulty breathing may also be present. In the cases of larger objects, the child may be in respiratory distress, turn “blue” (cyanosis) due to a lack of oxygen and urgent medical attention is required.
  • Gastroesophageal reflux disease (GERD) may cause aspiration, where gastric acid enters and irritates the airway lining, often causing spasm of the larynx. This is more likely to occur in chronic cases of GERD and develops slowly if the GERD is untreated. Typical symptoms include heartburn and/or chest pain.
  • Epiglottitis is a serious condition that results from a infection like strep throat. The epiglottis is a small flap that prevents food and drink from entering the lungs during swallowing. In a case of epiglottitis, the epiglottis becomes inflamed and swollen thereby impairing normal air flow. It may also occur as complication to chickenpox and in fungal infections of the throat and respiratory passages, often seen in HIV/AIDS.
  • Airborne irritants like smoke and fumes from certain chemicals can cause constriction of the respiratory passages when inhaled. This affects the airflow, resulting in a wheeze or stridor.
  • Most respiratory tract infections may cause a wheeze or stridor due to narrowing of the air passages as a result of inflammation or excess mucus production. Cases of a retropharyngeal abscess or peritonsillar abscess (quinsy), which are more likely in children, are uncommon and may require immediate medical attention as a retropharyngeal abscess can cause almost total obstruction of the airway and even result in death.
  • Vocal cord paralysis or dysfunction will result in a stridor along with changes in voice quality or even a loss of the voice. There are numerous causes from viral infections, to tumours, neck injury or neurological disorders like Parkinson’s disease.
  • Congenital (birth) anomalies of the tracheobronchial tree will result in stridor. These defects requires specialist medical attention as episodes may cause a total collapse or obstruction of the airway and can be fatal. Laryngomalacia is one of the more common anomalies in infants, where the airway collapses during inspiration due to impaired airway development and stridor is one of the defining features along with feeding difficulties.
  • Congestive heart failure is a slow progressing cardiac condition and a wheeze or stridor may be present for a long period of time. Other signs and symptoms of congestive heart failure include swelling of the legs, fluid in the lungs, shortness of breath and fatigue.
  • Swelling and spasm of the larynx may occur after intubation or even a bronchoscope and s stridor may be audible. This gradually settles and further treatment may not be necessary.
  • Pulmonary embolism is the result of blockage of one or more arteries of the lung. It causes sudden shortness of breath, severe chest pain and a cough. A wheeze or stridor may also be present.

Please note that any information or feedback on this website is not intended to replace a consultation with a health care professional and will not constitute a medical diagnosis. By using this website and the comment service you agree to abide by the comment terms and conditions as outlined on this page

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  • Rosemary Jones

    My son had a head injury resulting in cranial arterial blockages and he now wheezes when watching television or listening to the radio. I cannot find any info on why this is. He takes risperidone and procyclidine daily.

    • Dr. Chris

      Hi Rosemary

      Both risperidone and procyclidine can aggravate a preexisting case of asthma. As to the association with watching television or listening to radio, this is difficult to explain and you should speak to your doctor. He may be getting excited by something on TV or the radio which can result in wheezing if he is asthmatic. You should speak to your doctor about this or discuss it with the neurologist who may be more knowledgeable about this peculiar side effect of the drug.

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  • Phani Kumari

    I have a baby girl. She suffered from Mechonium Aspiration Syndrome and she was there in NICU for 1 month. Now her lungs are clear but she is still suffering from Wheezing. We are using BudeCort Inhealer and Levolin if there is high wheezing sound. I heard that, Mechonium Aspired babies will suffer from wheezing for atleast one year. Is it true?

    • Dr. Chris

      Hi Phani

      Yes, newborns with MAS are more likely to suffer with wheezing and recurrent chest infections, especially within the first year of life. It is often most prominent in the first 6 months. However, you should take your baby to a pediatrician to exclude other underlying causes like allergic asthma, etc.

  • Scott Henning

    I got the flu really bad which resulted in a lot of extreme coughing. Now i hear and feel a buzzing on exhaling fully and feel like it is hard to breath deeply without effort. It feels like Im struggling to breathe fully when i lay down or try to sleep. Do I have asthma? Or is this from over working bronchial area from coughing to much? Do I need medication or will it go away after awhile? I was concerned about pneumonia.

    • Hi Scott. It is not uncommon for a secondary bacterial infection of the airways and lungs to occur after a flu (if these symptoms are not a continuation of the flu itself). It leads to conditions like bronchitis and sometimes even pneumonia. The mucus build up in the bronchi and narrowing of these airways can cause the wheezing that you hear. It does not mean that you have asthma. However, there is no way of saying for sure through an online platform. You should consult with a doctor. While there is no cure for the flu, these secondary bacterial infections can be effectively treated with antibiotics. Failure to seek treatment early for these conditions can lead to complications.

      • Scott Henning

        Thank you I did go to see my physician and he not only gave me a nebulizer treatment but an inhaler and put me on Z-pak for what he felt was the start of pneumonia in my left lung. 5 days later i am feeling better but still coughing and raspy when exhaling. Getting better though.

        • Hi Scott. Glad to hear that you are improving. If it was pneumonia then it will take some time to recover. Monitor your symptoms closely and if there is any deterioration in your condition then see your doctor immediately. Also ensure that you take the antibiotics as prescribed.

  • Lisa

    Hi my name is Lisa I went to the dr. For an antibiotic, I felt a sinus infection coming on and didn’t want it to get worse. Went in and the dr. Said I have copd. Because she heard a little wheezing when I coughed. My oxygen was 97/98 and I had no trouble breathing? She did no X-ray or breathing test… she telling the truth??? Help thanks