Final answer:
To maximize the amount of air in the lungs for a PA projection of the chest, the patient should take a full inspiration. This increases the thoracic cavity volume and allows more air to be drawn into the lungs due to the pressure gradient created.
Step-by-step explanation:
The instructions for a patient to maximize the amount of air in the lungs on the PA projection of the chest is to take a Full inspiration. During full inspiration, the diaphragm contracts and moves down, and the external intercostal muscles help lift the rib cage. This increases the volume of the thoracic cavity and thereby the lungs, creating a pressure gradient that causes air to rush into the lungs. The patient should be instructed to breathe in deeply and hold that breath during the imaging so that the lungs are at their greatest volume, providing a clear image. Pulmonary ventilation consists of two major steps: inspiration and expiration. A full inspiration contributes to a better depiction of lung structures on the PA chest projection by allowing more air into the lungs, thus expanding them and allowing for a full evaluation of the lung fields, heart, mediastinum, and other anatomical structures within the chest.