An acid reflux refers to the movement of stomach contents upwards into the oesophagus or swallowing tube.
A valve system between the lower oesophagus and the stomach opens to allow fluids and solids to be swallowed, but closes to prevent the upward movement of stomach contents into the oesophagus.
When stomach contents, which are normally acidic, move into the oesophagus, they can irritate it. This may give rise to heartburn - a sensation of burning rising behind the middle of the breast bone.
The problem is not that the stomach produces too much acid, but that the movements of the stomach are no longer coordinated.
A contributing factor is the presence of a hiatus hernia, where a weakness of the diaphragm allows the upper end of the stomach to be pulled up into the chest. In this case, the valve may not close completely.
So, when the stomach contracts to discharge food to the intestines, some food goes upwards into the oesophagus. This condition is called gastro-oesophageal acid reflux disease (Gerd).
Gerd may cause cough and throat symptoms. This condition is known as laryngo-pharyngeal reflux (LPR). It is unclear what gives rise to LPR. It is possible that different mechanisms give rise to LPR in different patients.
A possible mechanism is that acid refluxes into the oesophagus and microscopic sprays of acid reach the throat and causes direct irritation.
Another explanation is that when acid makes contact with the lower oesophagus, it stimulates the nerve endings there, which then activate a nervous reflex involving the throat and airway, thereby inducing cough.
Acid reflux is suspected to be present in less than 30 per cent of patients with throat irritation. In some patients, it may not be acid, but gas from the stomach that induces the cough reflex.
A small number of patients may have a weakness in the wall of the pharynx - the tube behind the mouth that joins the oesophagus - that traps food. Others could have either physical obstruction in, or weak propulsion of the oesophagus, which makes it difficult for food to go down.
You should eat slowly and chew food well before swallowing. This reduces the risk of choking on food and swallowing of air, and stimulates the production of saliva, which is alkaline and may help neutralise any acid that refluxes from the stomach.
Staying upright and walking may help promote downward movement of food and acid. Avoid lying down for four hours after a meal, to allow time for the food to go from the stomach to the intestine.
It may be helpful to avoid citrus fruit, food that contains vinegar and spicy food, especially curry, as these could either directly irritate the throat or trigger acid reflux.
Patients with Gerd symptoms are usually prescribed a class of drugs called proton pump inhibitors, which are highly effective in suppressing acid production.
Another useful treatment is to improve the emptying functions of the stomach with drugs called prokinetic agents, and to reduce the sensitivity of the nerves involved in the throat and oesophagus.
Anti-depressants may be useful to target the nerves, even though the patient may not be suffering from depression.
Dr Gwee Kok Ann, gastroenterologist at the stomach, liver and bowel centre at Gleneagles Hospital and adjunct associate professor at the department of medicine at Yong Loo Lin School of Medicine at National University of Singapore.
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