Review Question - QID 109695

A 55-year-old man presents to his primary care physician for trouble swallowing. He previously struggled eating food if he did not chew it thoroughly, but now he occasionally struggles with liquids as well. He has a retrosternal burning sensation whenever he eats. He feels his throat burns when he lays down or goes to bed. Otherwise, the patient has no other complaints. The patient has a medical history of obesity, diabetes, constipation, and anxiety. His current medications include insulin, metformin, and lisinopril. The patient endorses a 5-pound weight loss recently. He has a 22 pack-year smoking history and drinks alcohol with dinner. His temperature is 99.5°F (37.5°C), blood pressure is 177/98 mmHg, pulse is 90/min, respirations are 17/min, and oxygen saturation is 98% on room air. On physical exam, you note an overweight man in no current distress. The abdominal exam is within normal limits. Which of the following is the most appropriate confirmatory test for the underlying diagnosis?