Final answer:
Hyperventilation is the pathophysiologic mechanism that may be activated as a result of a flail chest and increase the patient's respiratory rate.
Step-by-step explanation:
The pathophysiologic mechanism that may be activated as a result of a flail chest and increase the patient's respiratory rate is hyperventilation. Hyperventilation is an increased depth and rate of ventilation to meet an increase in oxygen demand. It occurs in response to a flail chest as a compensatory mechanism to maintain adequate oxygenation.