A 44-year-old woman comes to her primary care physician because food and water 'just don't go down the way they should.' Over the past 9 months, both solid food and liquids have lodged behind her breastbone after swallowing — there has never been a period when only solid food was difficult; both consistencies have been equally affected from the very start. She experiences no coughing, choking, or nasal regurgitation when she swallows, and she has no trouble initiating a swallow. She has a 4-pound weight loss and no history of heartburn or acid reflux. Upper endoscopy reveals a dilated esophageal lumen with pooled saliva but no mucosal mass, stricture, web, or ring. Esophageal manometry is subsequently performed.
Which of the following best describes the swallowing disorder responsible for this patient's presentation?