Final answer:
The EMT should suspect a spinal cord injury due to the paradoxical breathing pattern observed, which is not typically caused by a fractured sternum, ruptured diaphragm, or intra-abdominal bleeding.
Step-by-step explanation:
The EMT's observation that the patient's chest collapses and abdomen rises during inhalation is characteristic of paradoxical breathing, which often suggests a significant issue with the neuromuscular systems involved in breathing. Given the context of the patient having been ejected from his truck, the most likely suspect would be a spinal cord injury. Damage to the spinal cord can cause a disruption in the signals from the brain to the diaphragm and intercostal muscles, leading to the observed abnormal respiratory pattern.
While a fractured sternum, ruptured diaphragm, or intra-abdominal bleeding can also result from traumatic injury and affect breathing, they do not typically produce the described paradoxical breathing pattern that is suggestive of a neurological deficit in the control of the respiratory muscles. Therefore, spinal cord injury (A) is the most appropriate suspicion.