1. A 30-year-old woman is involved in an automobile accident. The woman, who was not wearing a seat belt, hits her chest against the steering wheel . When she is brought by ambulance to the emergency room, she is noted to be cyanotic. Her blood pressure is within normal limits and her heart rate is fast but regular. Her respirations are rapid and very shallow. She receives no medications in the ambulance. Chest x-ray demonstrates multiple broken ribs, but no pleural effusion or obvious lung disease. Which of the following mechanisms would most likely account for this patient's hypoxemia?