To cancel the lower-frequency portions of the noise, noise-cancelling headphones use active noise control. They incorporate a microphone that measures ambient sound, generate a waveform that is the exact negative of the ambient sound, and mix it with any audio signal the listener desires.
Esophageal hiatus. In human anatomy, the esophageal hiatus is an opening in the diaphragm through which the esophagus and the vagus nerve pass. It is located in the right crus, one of the two tendinous structures that connect the diaphragm to the spine. Fibers of the right crus cross one another below the hiatus.
Any time an internal body part pushes into an area where it doesn't belong, it's called a hernia. The hiatus is an opening in the diaphragm-the muscular wall separating the chest cavity from the abdomen. Normally, the esophagus goes through the hiatus and attaches to the stomach. In a hiatal hernia, the stomach bulges up into the chest through that opening. There are two main types of hiatal hernias: sliding and paraesophageal (next to the esophagus). In a sliding hiatal hernia, the stomach and the section of the esophagus that joins the stomach slide up into the chest through the hiatus.