What are breath sounds and how are they defined in patients with various respiratory conditions, such as asthma (Asthma), Chronic Obstructive Pulmonary Disease (COPD), pneumonia, and pulmonary fibrosis, across different demographics, including pediatric and geriatric populations?

Breath Sounds: Clinical Definitions and Characteristics

Normal Breath Sounds

Normal breath sounds are characterized by specific acoustic properties that vary by anatomical location, with the highest frequencies observed at the trachea (inspiration: 447-1323 Hz; expiration: 206-540 Hz) and inspiratory sounds consistently demonstrating higher intensities than expiratory sounds across all chest locations. 1

Key Acoustic Properties

• Frequency variations by location: Tracheal sounds exhibit the highest frequencies, while peripheral lung fields show lower frequencies 1
• Gender and age differences: Women (444-999 Hz) and infants (250-400 Hz) present the highest frequencies at maximum power 1
• Intensity patterns: Inspiratory sounds are most intense at the left posterior lower lobe (5.7-76.6 dB), while expiratory sounds peak at the trachea (45.4-85.1 dB) 1
• Clinical significance in COPD: Quiet breath sounds combined with prolonged expiratory duration become apparent as COPD progresses from mild to moderate-severe disease 2

Abnormal Breath Sounds: Rhonchi

Rhonchi are continuous, low-pitched rumbling sounds with a dominant frequency of approximately 200 Hz or less, typically heard during forced expiration and often clearing with coughing. 3, 4

Clinical Characteristics

• Acoustic properties: Continuous adventitious sounds distinguished from crackles by their uninterrupted nature 3
• Timing: Especially prominent during forced expiration 4
• Response to coughing: May clear or change after coughing as secretions move, unlike other adventitious sounds 4

Associated Conditions

• Common in: COPD, bronchiectasis, bronchitis, and pneumonia 4
• Clinical limitation: Presence of rhonchi on physical examination is not sufficiently diagnostic to determine the specific underlying condition and requires correlation with other clinical findings 4
• Severity assessment: Rhonchi do not reliably predict the severity of airway obstruction 4

Abnormal Breath Sounds: Crackles

Crackles are discontinuous, explosive sounds heard typically during inspiration in conditions like bronchiolitis and pneumonia, representing the sudden opening of collapsed alveoli and airways filled with inflammatory exudate. 3, 5

Clinical Characteristics

• Acoustic nature: Discontinuous rather than continuous like rhonchi or wheezes 3
• Timing: Typically heard during inspiration 3
• Prevalence in pneumonia: Present in approximately 81% of pneumonia patients 5

Diagnostic Significance

• High diagnostic value: When crackles are present with fever ≥38°C, tachypnea, and dyspnea, pneumonia is highly likely and warrants chest radiography 5
• Combined findings: The absence of runny nose combined with breathlessness, crackles, and diminished breath sounds significantly increases the likelihood of pneumonia 5

Abnormal Breath Sounds: Wheezing

Wheezing is a raspy high-pitched whistling sound noted on expiration or inspiration associated with obstruction of the lower airways, commonly found in asthma and COPD. 2

Clinical Context

• Asthma presentation: Wheezing during normal breathing or prolonged phase of forced exhalation is a key finding, though absence does not rule out asthma 2
• Diagnostic limitation: In children aged 5-16 years with wheeze, asthma should not be diagnosed based on symptoms alone but requires objective testing with spirometry showing reversible obstruction 3
• Pneumonia caveat: Wheezing, cough, prolonged expirations, or rhonchi alone do not significantly increase the likelihood of pneumonia on chest radiograph 5

Diminished or Quiet Breath Sounds

Diminished breath sounds have a positive likelihood ratio greater than 5.0 for COPD when combined with hyperresonance, making this combination a moderately strong predictor of disease presence. 2

Clinical Significance

• COPD progression: Quiet breath sounds become apparent as COPD progresses from mild disease (where physical examination is often normal) to more severe stages 2
• Pneumonia: Diminished breath sounds in affected lung regions occur due to consolidation and reduced air movement 5
• Emphysema indicator: Silent inspiration in the presence of severe expiratory obstruction is a sign of primary emphysema 6

Critical Clinical Pitfalls

Diagnostic Limitations

• Physical examination alone is insufficient: The European Respiratory Society emphasizes that physical examination findings, including the presence of rhonchi, wheezes, or crackles, are insufficient for diagnosis and must be confirmed with objective testing such as spirometry 3, 2
• Poor correlation with severity: The degree of airways obstruction cannot be predicted from symptoms or signs alone 2
• Variable patient perception: Patients' perceptions of airflow obstruction are highly variable, making spirometry essential for objective assessment 2

Management Implications

Treatment decisions should be based on spirometry results rather than the presence or characteristics of breath sounds alone. 3

• COPD management: Mild COPD (FEV1 60-79% predicted) requires short-acting bronchodilators as needed; moderate COPD (FEV1 40-59% predicted) requires long-acting bronchodilators; severe COPD (FEV1 <40% predicted) requires combination therapy 3
• Asthma in children: Children with chronic cough (>4 weeks) as the only symptom are unlikely to have asthma and require evaluation per chronic cough guidelines 3
• Bronchiolitis: In infants 1-23 months with tachypnea, wheeze, and crackles, bronchiolitis should be diagnosed clinically without routine chest radiography or viral testing 3

Population-Specific Considerations

Pediatric Populations

• Stridor: Most common indication for flexible bronchoscopy in infants, usually reflecting upper airway obstruction 2
• Laryngomalacia: Most common congenital laryngeal anomaly causing persistent stridor in children 2
• Occult pneumonia: May be present in up to 26% of children with fever without source and elevated WBC count (>20,000/mm³) 5

Geriatric Populations

• Atypical presentations: Elderly patients may have absent or altered physical examination findings despite radiographic pneumonia 5
• Poor symptom perception: Individual patient perception of breathlessness varies considerably for the same degree of airflow limitation and may be particularly poor in old age 2