From the Guidelines

Typical breath sounds in COPD patients are often quiet or diminished.

The presence of quiet or diminished breath sounds can be a moderately strong predictor of COPD, with a positive likelihood ratio of greater than 5.0 when combined with hyperresonance 1.
Other physical signs, such as wheezing during tidal breathing, prolonged forced expiratory time, and hyperresonance, may also be elicited in patients with COPD 1.
However, the sensitivity and reproducibility of physical examination for detecting or excluding COPD are poor, and the absence of these signs does not exclude the disease 1.
The clinical significance of breath sounds in COPD patients is influenced by the degree of airflow limitation, pulmonary hyperinflation, and body build 1.
Additional diagnostic tools, such as chest radiography and computed tomography (CT) scans, may be used to support the diagnosis and assess the severity of COPD 1.
The use of accessory muscles, pursed-lip breathing, and central cyanosis may indicate severe airflow obstruction, while peripheral oedema, raised jugular venous pressure, and signs of pulmonary hypertension may suggest the development of cor pulmonale 1.

From the Research

Normal breath sounds occur when no respiratory problems exist, and are typically clear and without any additional noises 2
Adventitious lung sounds, such as wheezes, rhonchi, and crackles, are usually associated with certain pulmonary pathologies 2

Detection of abnormal respiratory sounds with a stethoscope is important in diagnosing respiratory diseases and providing first aid 3
Accurate interpretation of respiratory sounds requires a clinician's considerable expertise, and trainees may sometimes misidentify respiratory sounds 3
Automated classification of breath sounds using deep learning techniques can aid in the rapid diagnosis and appropriate treatment of respiratory diseases 3
Lung sound patterns can help distinguish between different respiratory conditions, such as congestive heart failure, chronic obstructive pulmonary disease, and asthma exacerbations 4
Breath sound intensity can vary between different respiratory conditions, and can be used to evaluate the severity of disease 5

Normal breath sounds have a consistent intensity and frequency, while adventitious sounds can have varying intensities and frequencies 2
Wheezes are typically high-pitched sounds, while rhonchi are lower-pitched sounds 2
Crackles are typically heard during inspiration, and can be fine or coarse 2
Breath sound intensity can be affected by factors such as airflow, lung volume, and airway resistance 5