Answer:
Option D, quiet, regular, appears effortless
Explanation:
Normal breathing is fairly quiet -- free from wheezing, chortles, hoarseness or rasp, rattling, bubbling, crackling, or any other sounds that may indicate obstruction or some pathology.
Normal breathing should also be regular in that it is expected to be rhythmic and at a rate between 12 and 20 breaths per minute. Irregularities such as hyperventilation (excessive breathing), Kussmaul's breathing, Biot's respirations, Cheyne-Stokes patterns, bradypnea (slow breathing), or apnea (low-to-no breathing) can be a symptom of an underlying issue in need of prompt intervention.
Lastly, normal breathing should appear effortless. There is a flat muscle separating the mediastinum (which houses the heart, lungs, and lower respiratory tract) from the abdominopelvic cavity called the diaphragm. When it contracts alongside the intercostal (between rib) muscles, the chest cavity expands causing air to be inspired into the lungs like a vacuum. When it relaxes, air is expulsed into the outside environment. This process should occur involuntarily, hence why it appears so effortless. If breathing takes effort, such as the patient needing to use their abdominal muscles, their sternocleidomastoid muscles, more contract from the intercostals, along with the diaphragm, this indicates something is wrong, the patient is in need of oxygen support, or the patient is acutely fatigued. This is known as accessory muscle breathing.
Normal breathing is quiet, regular, and effortless, option D.
