Rhonchi Lung Sounds: Causes and Medical Evaluation

Rhonchi are low-pitched, continuous lung sounds often described as resembling snoring or a rumbling noise heard through a stethoscope. They occur when air moves through airways narrowed or partially blocked by mucus, fluid, or swelling, and their presence during a medical exam typically signals that something is obstructing the larger airways. The causes range from common respiratory infections to chronic lung disease to rarer situations like an inhaled foreign object, and the workup a clinician pursues depends heavily on the clinical picture surrounding the sound.

What Rhonchi Actually Sound Like

If you have ever heard someone snore loudly, you have a rough idea of what rhonchi sound like through a stethoscope. They are continuous sounds, meaning they last long enough to have a musical or tonal quality rather than sounding like brief pops or clicks. The American Thoracic Society defines them as low-pitched continuous sounds with a dominant frequency of about 200 Hz or less, which places them well below the higher-pitched whistle of a wheeze.¹ That low, rumbling quality is what gives rhonchi their characteristic snoring or groaning texture.

Rhonchi can occur during inhalation, exhalation, or both, though they are frequently more prominent when breathing out. They tend to change or even disappear temporarily after coughing, which is a useful bedside clue: if the sound clears when the patient coughs up mucus and then returns as secretions re-accumulate, the obstruction is likely mucus rather than a structural narrowing. A case report of a patient with a long-standing foreign body in the airway described the rhonchus heard in the left lung as “a low-pitched, continuous snoring sound, mostly heard at inspiration,” illustrating how the timing and character can vary depending on the cause.²

How Rhonchi Differ from Wheezes and Crackles

Lung sounds fall into a few broad categories of abnormal, or “adventitious,” sounds, and the distinctions matter because each type hints at a different problem. Wheezes are the high-pitched cousins of rhonchi. Where rhonchi sit around 200 Hz or below, wheezes are defined as continuous sounds with a dominant frequency of 400 Hz or more.¹ That difference in pitch reflects where the obstruction sits and how tight the airway has become: a narrower passage produces a higher-pitched sound, much the way pinching the neck of a balloon changes the squeal it makes when air escapes.

Crackles are a different animal altogether. They are discontinuous, meaning they sound like brief pops or clicks rather than sustained tones. Fine crackles resemble the sound of hair being rubbed between your fingers near your ear and tend to suggest fluid in the tiny air sacs deep in the lungs. Coarse crackles are louder, lower-pitched bursts that can indicate fluid or mucus in slightly larger airways. A computational study modeling airflow through branching airways found that when comparing rhonchi and crackles generated in the same level of airway, the dominant frequency and loudness of crackles can be slightly higher than those of rhonchi, but the two overlap enough that distinguishing them by ear alone is genuinely difficult.³

Adding to the confusion, the boundary between a “low-pitched wheeze” and a “rhonchus” is blurry in practice. Some classification systems treat the two as interchangeable, while others insist that rhonchi specifically describe sounds with a non-musical, snoring quality. This terminological overlap has real consequences for how reliably clinicians communicate their findings, a problem explored in more detail below.

Common Causes of Rhonchi

The mechanism behind rhonchi is straightforward: air forced through a partially obstructed large airway vibrates the walls and the obstructing material, producing a low-pitched hum. The causes of that obstruction, though, span a wide range of conditions.

Acute bronchitis: Viral or bacterial infection inflames the bronchial lining and stimulates excess mucus production. Rhonchi are a hallmark finding, and they often improve as the infection resolves and mucus clears.
Chronic obstructive pulmonary disease (COPD): Chronic bronchitis, one of the two main forms of COPD, involves persistent airway inflammation and mucus hypersecretion. Rhonchi may be present at baseline and worsen during flare-ups, known as acute exacerbations.
Pneumonia: Bacterial or viral infection of the lung tissue can fill airways with inflammatory fluid and debris. Rhonchi may accompany the more classic crackles associated with pneumonia.
Asthma: While wheezing is the better-known sound in asthma, rhonchi can appear when thick mucus plugs partially block the larger airways during a severe episode.
Cystic fibrosis: Abnormally thick, sticky mucus in the airways produces chronic obstruction, and rhonchi are a frequent finding on exam.
Foreign body aspiration: An inhaled object lodged in a bronchus can produce localized rhonchi on the affected side, sometimes persisting for months or years before the cause is identified.

During acute exacerbations of chronic bronchitis, the most common bacterial culprits are Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae, with viruses responsible for roughly a third of episodes overall.⁴ Whether bacterial or viral, these infections drive the mucus overproduction and airway swelling that generate rhonchi.

When Rhonchi Raise the Stakes

Rhonchi alone do not tell a clinician exactly what is wrong, but combined with other findings, they help narrow the possibilities considerably. In a primary care study examining how physicians distinguish pneumonia from bronchitis, the presence of rhonchi was one of several examination findings that helped explain the variation in diagnosis, alongside crackles (rales), fever at or above 100°F, chest pain, shortness of breath, and elevated heart and respiratory rates.⁵ Crackles and fever were the strongest individual predictors of pneumonia in that analysis, but rhonchi added diagnostic information, particularly when combined with the broader clinical picture.

Foreign body aspiration is a scenario where rhonchi can be especially important. In children, an inhaled object is usually suspected quickly because of witnessed choking. In adults, the diagnosis can be delayed for years. One documented case involved a patient whose only initial complaints were a persistent rhonchus on one side and a valve-like sensation during breathing; the foreign body had been lodged in the airway for an extended period before it was finally identified.² The takeaway for patients: a rhonchus that is persistently localized to one side and does not respond to standard treatments warrants further investigation, often with imaging or bronchoscopy.

Why Doctors Sometimes Disagree About Rhonchi

One of the less-discussed problems with rhonchi is that clinicians frequently disagree on whether they are hearing them at all. This is not a minor quibble. In a study where twelve physicians independently classified the same lung sounds from recordings, agreement on rhonchi was particularly poor and considerably weaker than agreement on crackles or wheezes.⁶ The majority of observers in that study never reached acceptable agreement levels for identifying rhonchi as a separate category. Part of the difficulty is that rhonchi sit in an acoustic gray zone: too low-pitched to be clearly a wheeze, too continuous to be clearly a crackle, and sometimes sharing features of both.

A separate study evaluating physicians and medical students found the same pattern. Rhonchi were described as an “ambiguous class” that respondents frequently misidentified, consistent with earlier research showing that rhonchi are very often incorrectly classified.⁷ The problem is compounded by the fact that different textbooks and guidelines use the terms “rhonchi” and “low-pitched wheezes” interchangeably, so two clinicians may hear exactly the same sound and label it differently while both being technically correct by their respective training.

Even broader agreement on whether airway sounds are normal or abnormal is shakier than most patients would assume. In a study of chest auscultation after cardiac surgery, agreement between two examiners on airway-related sounds was only fair, and for sounds related to the lung tissue itself, there was essentially no agreement at all.⁸ These findings do not mean auscultation is useless. They mean that the stethoscope is a screening tool, not a precision instrument, and clinicians treat it as one piece of a larger diagnostic puzzle rather than a definitive answer on its own.

The Medical Evaluation When Rhonchi Are Found

When a clinician hears rhonchi during an exam, what happens next depends on what they already know about you. A patient with a known history of COPD who comes in with worsened rhonchi during a respiratory infection will often be managed based on the clinical picture alone, perhaps with a course of antibiotics, increased bronchodilator use, or a short course of oral steroids. No imaging may be needed if the presentation fits a familiar pattern.

In situations where the cause is less clear, the evaluation typically follows a stepwise approach. A chest X-ray is usually the first imaging study, since it can reveal pneumonia, a mass, or signs of fluid accumulation. If the X-ray is unrevealing but symptoms persist, a CT scan provides more detailed images and can pick up subtle abnormalities that plain films miss. Pulmonary function testing may be ordered if COPD or asthma is suspected but not yet formally diagnosed. Blood work, including inflammatory markers and sometimes sputum cultures, helps guide treatment when infection is the leading concern.

Bronchoscopy, where a flexible camera is threaded into the airways, enters the picture when something localized or structural is suspected. A rhonchus heard consistently in one specific area of the lung, especially without an obvious infectious cause, raises the question of an obstructing lesion or foreign body. This is the scenario where bronchoscopy becomes both diagnostic and potentially therapeutic, since a foreign object or mucus plug can sometimes be removed during the same procedure.

The clinician also listens for context clues during the exam itself. Do the rhonchi clear with coughing? That points toward mucus as the culprit. Are they fixed and unchanging? That suggests a structural cause. Are they accompanied by wheezing, crackles, or diminished breath sounds in other areas? Each combination shifts the probability toward different diagnoses.

Digital Stethoscopes and AI-Assisted Classification

Given how often human listeners disagree about lung sounds, there has been growing interest in letting algorithms take a crack at the problem. Digital stethoscopes that can record, amplify, and transmit lung sounds are increasingly available, and pairing them with machine learning offers the potential to standardize what has traditionally been a subjective assessment.⁹

The results so far are promising but uneven. In one study using deep learning to classify recorded lung sounds that had been confirmed by specialists, the algorithm achieved strong performance for crackles and wheezes but notably lower performance for rhonchi. Precision and recall for crackles were around 90% and 85%, and for wheezes around 89% and 93%, but for rhonchi the numbers dropped to about 68% and 71%.¹⁰ The pattern mirrors the human difficulty: rhonchi are the hardest category for both flesh-and-blood clinicians and silicon classifiers. The ambiguity that makes rhonchi difficult for human ears does not vanish when the listener is a neural network trained on the same imperfect labels.

Still, the technology has real potential. Recorded lung sounds can be shared remotely for second opinions, tracked over time to monitor disease progression, and eventually used as part of telemedicine evaluations where a physician is not physically present to listen. Wearable devices that continuously monitor respiratory sounds are in early development and could eventually flag changes before a patient notices symptoms worsening.

Clearing Rhonchi Through Airway Management

Because rhonchi stem from obstructed airways, treatments that clear or open those airways tend to reduce or eliminate the sounds. The specific approach depends on the underlying cause.

For infection-driven rhonchi, treating the infection itself is the primary strategy. Antibiotics target bacterial causes, while supportive care and time address viral infections. Bronchodilators, the inhaled medications that relax airway smooth muscle, are used when bronchospasm contributes to the obstruction. Mucolytics and adequate hydration help thin secretions so they are easier to cough up.

Chest physiotherapy, which includes techniques like percussion (rhythmic clapping on the chest wall), postural drainage (positioning the body to let gravity help move mucus), and assisted coughing exercises, has a specific role in clearing secretions from the airways. A study of pneumonia patients in the ICU found that chest physiotherapy performed in two sessions per shift was effective at reducing rhonchi, lowering respiratory rate, and helping patients clear secretions.¹¹ These techniques are used most aggressively in hospitalized patients who cannot cough effectively on their own, such as those who are sedated, post-surgical, or profoundly weak from illness.

For patients with chronic conditions like COPD or cystic fibrosis, daily airway clearance routines become part of ongoing disease management. Devices like oscillating positive expiratory pressure (PEP) valves and high-frequency chest wall oscillation vests give patients tools to keep airways clear at home. Rhonchi in these patients are expected to some degree and serve more as a barometer of how well secretion management is going than as a sign of a new problem.

Localized Versus Diffuse Rhonchi

One detail that can change the diagnostic direction entirely is whether rhonchi are heard throughout both lungs or only in one spot. Diffuse rhonchi, heard across multiple lung fields, typically point toward a systemic process: widespread bronchitis, a COPD exacerbation, or generalized mucus buildup. The pattern makes sense because these conditions affect the airways broadly.

Localized rhonchi, confined to one region, raise different concerns. A tumor partially blocking a bronchus, a foreign body lodged in one airway, or a mucus plug in a single segment can all produce a rhonchus audible only over that area. The localized nature is what prompts clinicians to think beyond infection and consider imaging or bronchoscopy sooner. In the foreign body case report mentioned earlier, the rhonchus was heard only in the left lung, and it was precisely that one-sided quality that eventually led to the correct diagnosis after what had been a prolonged diagnostic journey.²

Clinicians also pay attention to whether the rhonchi are more prominent during inhalation or exhalation. Inspiratory-dominant rhonchi suggest obstruction that worsens as the airway tries to expand, while expiratory-dominant rhonchi are more consistent with airway collapse or narrowing during exhalation, as occurs in COPD. Both patterns are informative, and neither is inherently more alarming than the other without additional context.

How Airway Generation Affects the Sound

The branching structure of the airways matters for understanding rhonchi. Your trachea divides into two main bronchi, which divide into lobar bronchi, which divide again and again into progressively smaller passages. Computational modeling of airflow through these branches has shown that both the pitch and the loudness of rhonchi decrease as you move deeper into the airway tree. The dominant frequency of rhonchi was concentrated between roughly 290 and 420 Hz in the larger airways, dropping with each successive branching generation, and the sound pressure level followed the same downward trend.³

What this means in practice is that rhonchi originating from the larger, more central airways are louder and easier to hear through a stethoscope than those arising from smaller, more peripheral branches. A mucus plug in a main bronchus will produce a clearly audible, low-pitched rumble, while partial obstruction in a smaller airway deeper in the lung may generate a fainter sound that is harder to detect against the background of normal breathing. This is one reason why the stethoscope, for all its limitations, remains better at catching problems in the larger airways than in the lung periphery, and why imaging picks up where auscultation leaves off for deeper pathology.

1
European Respiratory Journal. Wheezes
2
PubMed Central. Rhonchus and Valve-Like Sensation as Initial Manifestations of Long-Standing Foreign Body Aspiration: A Case Report
3
PubMed. Study on the flow mechanism and frequency characteristics of rales in lower respiratory tract
4
Oxford Academic. Infectious exacerbations of chronic bronchitis: diagnosis and management
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Primary Care Respiratory Journal. Diagnosis and management of pneumonia and bronchitis in outpatient primary care practices
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PubMed Central. Wheezes, crackles and rhonchi: simplifying description of lung sounds increases the agreement on their classification: a study of 12 physicians’ classification of lung sounds from video recordings
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PubMed Central. The accuracy of lung auscultation in the practice of physicians and medical students
8
PubMed Central. Accuracy of chest auscultation in detecting abnormal respiratory mechanics in the immediate postoperative period after cardiac surgery
9
PubMed Central. Evolution of the Stethoscope: Advances with the Adoption of Machine Learning and Development of Wearable Devices
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Scientific Reports. Respiratory sound classification for crackles, wheezes, and rhonchi in the clinical field using deep learning
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Jurnal Kegawatdaruratan Medis Indonesia. The Effectiveness of Chest Physiotherapy for Pneumonia Patients with Ineffective Airway Clearance Problems in Intensive Care Unit