During which phase of respiration does the diaphragm move to its lowest position when performing chest radiography?

• A. Resting expiration
• B. Second full inspiration
• C. First full inspiration
• D. Forced expiration

Answer: (B)

The diaphragm moves to its lowest position during the second full inspiration of the respiratory cycle. This phase of respiration is characterized by a deep inhalation, where the diaphragm contracts significantly and descends further into the thoracic cavity. As the diaphragm lowers, it creates a negative pressure within the thoracic cavity, allowing the lungs to expand fully and draw in maximum air.

During the first full inspiration, while the diaphragm does contract and lowers, it does not typically reach its maximum descent compared to the second full inspiration. Resting expiration involves the diaphragm relaxing and moving upward, and forced expiration further increases intrathoracic pressure but does not contribute to the diaphragm's lowest position as effectively as a full inspiration does. Therefore, the second full inspiration is the key phase when the diaphragm is at its lowest, making it the correct answer.