Final answer:
The third step in checking lung sounds involves auscultation with a stethoscope, listening for abnormal lung sounds while the patient breathes deeply.
Step-by-step explanation:
The third step to checking lung sounds in a patient is auscultation of the lungs. This process involves using a stethoscope to listen for abnormal sounds such as crepitation, which is a crackling sound that can be indicative of a condition like pneumonia. During the physical examination, the clinician may ask the patient to breathe deeply while listening over various lung fields. This practice not only allows the clinician to assess airflow but also helps to amplify any heart murmurs that may be present due to changes in blood flow dynamics related to the respiratory cycle. Crepitation, heard as cracking sounds, and other abnormal lung sounds can signify increased resistance in the lungs, fluid, or infection among other issues.