Wheezing

Etiology

Wheezing is commonly experienced by people who have asthma; although, it can be heard in people with foreign bodies, congestive heart failure, a malignancy of the airway, or any lesion that causes narrowing of the airways. During expiration, the presence of wheezing indicates that the individual’s peak expiratory flow rate is less than fifty percent compared to normal. The quality and duration of wheezing also depend on where in the airways the obstruction is located. In asthma, the wheezing is due to narrowing of the lower airways, whereas, with malignancies, the obstruction is usually in the upper, more proximal airways. In rare cases, wheezing may be heard both during inspiration and expiration. In severe asthma, no wheeze may be heard as the airflow will be so severely reduced, and chest auscultation will be silent. Since any process that reduces airway caliber generates wheeze, below are some of the many of the conditions that can cause wheeze:

• Respiratory infections (croup, laryngitis, bronchiolitis)
• Obstructive airway diseases (asthma) 
• chronic obstructive pulmonary disease (COPD)
• Anaphylaxis
• Pulmonary peribronchial edema (congestive heart failure)
• Vocal cord dysfunction (paradoxical vocal fold motion [PVFM], vocal cord paralysis)
• Postnasal drip
• Airway compression: Intrinsic or extrinsic (squamous cell carcinomas, goiter)
• Hyperdynamic airway collapse (tracheobronchomalacia)
• Carcinoid tumors
• Foreign body inhalation
• Forced exhalation by normal individuals[5][6][7]

Epidemiology

The reported prevalence of wheezing amongst young children between 2 to 3 years of age is 26% in the United States. The global prevalence is lower in the adolescent age range, approximately 12%. Global surveys reveal a similar prevalence in adults, with European and Australian surveys reporting the highest prevalence rates, up to 17%.[8]

Pathophysiology

Wheezes are thought to be the product of fluttering vibrations of narrowed airway walls, induced by a diminished airflow velocity. The characteristics of their sound include how loud they are (i.e., the amplitude), how long they last and how intense (i.e., high pitched) they sound. A physiologic trial done in the 1980s identified the determinants of the pitch of a sound generated within collapsible tubes. It was determined that the pitch of a wheeze is a reflection of the stiffness, thickness, and longitudinal tension of the airway's wall. Subsequent clinical studies have shown that the pitch and, more so, duration of wheeze are the only two characteristics that correlate well with the severity of airway obstruction. The degree of bronchial obstruction is also proportional to the number of airways that are producing wheeze. And so, the amplitude of auscultated wheeze has no bearing on the severity of airway obstruction. At the very severe end of airway obstruction, if there is very little to no airflow, then no wheeze will be heard despite severe airway obstruction.[9][10][11][12]

History and Physical

History should be targeted toward the various etiologies of wheezing listed above. For example, patients who have had head and neck cancer surgery and/or radiation may develop vocal cord paralysis. Additionally, a prior history of endotracheal intubation can alert one to the possibility of tracheal or subglottic stenosis.

Physical examination of the trachea and thorax will identify wheeze. Wheeze associated with asthma is most commonly heard during expiration; however, wheeze is neither sensitive nor specific for asthma, so the wheezes can certainly extend into inspiration also. Upper airway obstruction from tonsilar hypertrophy can be evaluated with an oral examination, and palpation of the neck could identify a goiter.[13]

Evaluation

When wheezing is heard, some workup is required because it is an abnormal sound. The first imaging test of choice in a patient with wheezing is a chest x-ray to look for a foreign body or a lesion in the central airway. In the non-acute setting, if asthma is suspected, the next step is to obtain baseline pulmonary function tests with bronchodilator administration. Following this, it may be necessary to perform an airway challenge test with a bronchoconstrictive agent such as methacholine. If the wheezing resolves with a bronchodilation agent, a tumor or mass as the cause is a much less likely consideration. If there is no resolution after a breathing treatment, and a tumor or mass is suspected, then a CT scan of the chest and bronchoscopy may be required if possible malignancy is suspected on CT.[7]

Treatment / Management

Treatment predominantly revolves around the suspected etiology of wheezing. The ubiquitous approach to ensuring Airway, Breathing, and Circulation (ABCs) are stable is the priority. Those with signs of impending respiratory failure may require either noninvasive positive pressure ventilation or invasive mechanical ventilation following endotracheal intubation. In cases of anaphylaxis, epinephrine would be required. Nebulized, short-acting beta2 agonists such as albuterol and nebulized short-acting muscarinic antagonists are often administered while further workup is performed.[7]

Differential Diagnosis

Other lung sounds that can be mistaken for or that overlap with wheezes are rhonchi and stridor. Rhonchi share similar characteristics to wheezes, with the main difference being a lower dominant frequency of fewer than 200 MHz. This lower frequency is described as a snoring-like sound. Stridor is a higher-pitched and higher amplitude sound due to turbulent airflow around a region of upper airway obstruction. It is typically an inspiratory sound that is far more pronounced when auscultated over the trachea than the thorax.[14]

Possible causes of wheezing include:

• Allergies
• Anaphylaxis
• Asthma
• Bronchiectasis 
• Bronchiolitis 
• Bronchitis
• Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Epiglottitis
• Foreign object
• Gastroesophageal reflux disease (GERD)
• Heart failure
• Lung cancer
• Drugs (i.e., aspirin)
• Obstructive sleep apnea
• Pneumonia
• Respiratory syncytial virus (RSV)
• Respiratory tract infection
• Smoking
• Vocal cord dysfunction