Some of the common causes of diminished breath sounds on a physical exam are heart failure, pneumonia and chronic obstructive pulmonary disease exacerbation. Reduced airflow from restrictive diseases such as fibrosis can also be a contributing factor, according to MedlinePlus.
With heart failure, reduced breath sounds are caused by fluid overload. The physician will hear crackles in the lungs and a gallop when listening to the heart. In most cases, the individual will also have lower extremity edema, according to the Merck Manual.
If the cause is pneumonia, the physician will most likely hear crackles in addition to decreased breath sounds. The patient will most likely present with a fever, productive cough, difficulty breathing, and chest pain during inspiration or expiration, according to the Merck Manual.
When COPD is the cause of diminished breath sounds, people will most likely breathe with pursed lips and have poor air movement in the lungs, an increased chest diameter, and a cough that can either be productive or nonproductive, according to the Merck Manual.
Individuals with restrictive lung diseases will either have occupational exposure or a neurological condition. They will also exhibit diminished breath sounds caused by the inability to completely expand the lungs during inspiration, according to the Merck Manual.