Answer:

Posture has a dramatic effect on FRC. When a patient goes from upright to the supine position, FRC decreases approximately 30%. Body position does not affect CC.

Conversely, age has a greater effect on CC than on FRC. CC increases with age, whereas FRC does not change or increases only slightly. Therefore, CC will exceed FRC in healthy adults over the age of 44 years when in the supine position and in healthy adults over the age of 70 years in the upright position.

During general anesthesia, FRC is reduced approximately 20%, whether breathing is controlled or spontaneous. The anatomic basis of the FRC reduction under anesthesia is not well understood. Traditionally, it was thought to be due to the cephalad shift of the diaphragm, induced by anesthesia and muscle paralysis. Although the role of the anatomic position of the diaphragm remains debatable, the current understanding is that FRC is reduced due to loss of respiratory muscle tone.

CC was previously reported to be unchanged during anesthesia, but later studies concluded that CC reduced in parallel to FRC during anesthesia.

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