Which of the following result in a decrease in functional residual capacity?

a. Shallow breathing

b. Partial airway occlusion

c. Absorption atelectasis

d. Hemothorax

A decrease in functional residual capacity is caused by incomplete alveolar inflation related to 1) shallow breathing; 2) partial or complete airway occlusion, which may be generalized (as in bronchospasm) or localized (as in gastric aspiration); 3) absorption atelectasis, which occurs when oxygen is substituted for nitrogen in the inspired gas; or 4) conditions in which air or fluid is occupying a potential alveolar space in the chest such as pneumothorax, hemothorax, or pulmonary edema.