Saturday, June 16
Hiatal hernias contribute to reflux, although the way in which they contribute is not clear. A majority of patients with GERD have hiatal hernias, but many do not. Therefore, it is not necessary to have a hiatal hernia in order to have GERD. Moreover, many people have hiatal hernias but do not have GERD. It is not known for certain how or why hiatal hernias develop.
Normally, the LES is located at the same level where the esophagus passes from the chest through the diaphragm and into the abdomen. (The diaphragm is a muscular, horizontal partition that separates the chest from the abdomen.) When there is a hiatal hernia, a small part of the upper stomach that attaches to the esophagus pushes up through the diaphragm. As a result, a small part of the stomach and the LES come to lie in the chest, and the LES is no longer at the level of the diaphragm.
It appears that the diaphragm that surrounds the LES is important in preventing reflux. That is, in individuals without hiatal hernias, the diaphragm surrounding the esophagus is continuously contracted, but then relaxes with swallows, just like the LES. Note that the effects of the LES and diaphragm occur at the same location in patients without hiatal hernias. Therefore, the barrier to reflux is equal to the sum of the pressures generated by the LES and the diaphragm. When the LES moves into the chest with a hiatal hernia, the diaphragm and the LES continue to exert their pressures and barrier effect. However, they now do so at different locations. Consequently, the pressures are no longer additive. Instead, a single, high-pressure barrier to reflux is replaced by two barriers of lower pressure, and reflux thus occurs more easily. So, decreasing the pressure barrier is one way that an hiatal hernia can contribute to reflux.
There is a second way in which hiatal hernias might contribute to reflux. When a hiatal hernia is present, there is a hernial sac, which is a small pouch of stomach above the diaphragm. The sac is pinched off from the esophagus above by the LES and from the stomach below by the diaphragm. What's important about this situation is that the sac can trap acid that comes from the stomach. This trap keeps the acid close to the esophagus. As a result, it is easier for the acid to reflux when the LES relaxes with a swallow or a transient relaxation.
Finally, there is a third way in which hiatal hernias might contribute to reflux. The esophagus normally joins the stomach obliquely, which means not straight on or at a 90-degree angle. Due to this oblique angle of entry, a flap of tissue is formed between the stomach and esophagus. This flap of tissue is believed to act like a valve, shutting off the esophagus from the stomach and preventing reflux. When there is a hiatal hernia, the entry of the esophagus into the stomach is pulled up into the chest. Therefore, the valve-like flap is distorted or disappears and it no longer can help prevent reflux.