The hiatus is a normal opening in the muscle that separates the chest cavity from the abdomen which moves up and down with breathing. Although the hiatus is a normal opening, there are occasions when this opening enlarges and the stomach or other organs can slip up inside the chest. This occasion of an abnormally large opening of the hiatus is called a hiatal hernia. Paraesophageal hernias account for only 5% of all hiatal hernias. A paraesophageal hernia is a type of hiatal hernia where the junction of the stomach and the esophagus remains in place, but part of the stomach is squeezed up into the chest beside the esophagus.

The esophagus is a relatively simple organ but it does have several locations where problems are more likely. The most problematic area is at the bottom (technically, in the lower thoracic section) where the esophagus connects with the stomach – the gastroesophageal junction. At the junction is the lower gastroesophageal sphincter, a hole into the stomach controlled by a set of muscles that opens to allow food to enter the stomach, and closes to prevent stomach acid from entering the esophagus. When this sphincter is not functioning properly, especially as a chronic long-term condition, there are many potential problems, some of which may lead to cancer.

Sleep apnea is a condition in which breathing is temporarily suspended during sleep. There are several forms of sleep apnea, including central, complex and obstructive sleep apnea, of which the latter is the most common. Obstructive sleep apnea (OSA) may involve two different types of breathing interruption: apnea and hypopnea. Apnea occurs when the upper airway becomes obstructed due to collapse of the muscles and soft tissues of the throat during inspiration. Hypopnea is said to occur when the blockage is only partial, resulting in a significant reduction in airflow.