Final answer:
Patient D, who experiences heartbeat irregularity and breathing problems, has symptoms consistent with damage to the medulla oblongata, which controls vital autonomic functions.
Step-by-step explanation:
The patient who experiences heartbeat irregularity and breathing problems is the one with symptoms consistent with damage to the medulla oblongata. The medulla oblongata is responsible for regulating several critical bodily functions such as heart rate, breathing, blood pressure, and reflex centers for vomiting, coughing, sneezing, and swallowing. Damage to this area can lead to problems such as irregular heartbeats (arrhythmias) and respiratory issues, which patient D is experiencing.