Asthma and gastroesophageal reflux

Overview
The underlying gastro-esophageal reflux disease predisposes the patient to have repetitive episodes of acid aspiration, which subsequently causes repeated airway inflammation and results in irritant-induced asthma. The incidence of GERD in patients with asthma is approximately 38%. Asthmatics resistant to therapy are commonly associated with GERD, but identification and treatment of GERD has not shown to relate to the improvement in asthmatic control.

Pathophysiology
There are three mechanisms proposed to explain the pathophysiology of development of asthma in patients with GERD:
 * 1) Vagal reflex: Both the esophagus and the bronchial tree, as they share a common embryonic origin, are innervated by the vagus nerve. Therefore, when there is reflux of acid contents from the stomach into the esophagus, the receptors in esophagus are stimulated causing firing of the vagus nerve resulting in bronchospasm. This phenomenon was demonstrated by Mansfield and Stein by intraesophageal acid provocation test resulting in increased resistance to airflow. and further strengthened by another series involving 136 subjects However, many studies failed to demonstrate a significant relationship between acid reflux and pulmonary function.
 * 2) Heightened Bronchial Reactivity: Acid reflux into esophagus, increases the bronchial response to other stimuli. This was demonstrated by increased bronchial response to methacholine challenge test.
 * 3) Microaspiration: Microaspiration of acidic contents from stomach into the upper airways and bronchial tree was shown to stimulate bronchial receptors resulting in broncho-constriction in asthmatic patients. A murine study demonstrated that microaspiration of gastric contents caused immune response similar to that observed in asthma. However, a prospective single blinded study failed to demonstrate any significant bronchoconstriction with acid reflux into the airways.

Epidemiology and Demographics
GERD is commonly seen among patients with asthma. The prevalence ranges between 34%-89%.

History and Symptoms
Patient may present with the following symptoms after eating a high fat meal or foods that lower the lower esophageal sphincter pressure:
 * Chest pain
 * Coughing in supine position
 * Dyspnea
 * Heartburn
 * Hoarseness
 * Loss of dental enamel
 * Regurgitation of foods/liquids
 * Sensation of lump in throat
 * Sore throat
 * Water Brash (regurgitation of excessive saliva)

Chest X Ray
The chest x-ray in asthmatics is often normal. It is done to exclude other causes of wheeze and aid in the diagnosis of complications such as atelectasis and pneumonia.

Other Diagnostic Studies

 * Esophageal PH testing: Presence of symptoms of GERD, which is refractory to proton pump inhibitors, should undergo esophageal PH testing. This helps in correlating the symptoms of asthma with gastro-esophageal reflux.
 * Upper GI endoscopy: Endoscopy, though not indicated in diagnosis of asthma in GERD, may be done to exclude the presence of Barrett's esophagus.

Treatment
Treatment of asthma in GERD mainly pertains to treatment of GERD. And therefore patients with poorly controlled asthma should be evaluated for GERD even in the absence of gastric reflux symptoms.

Primary prevention

 * Patients should be advised to avoid heavy meals, fried foods, caffieine and alcohol.
 * Patients should be advised to avoid meals or drinks at least for 3 hours before sleep.
 * Elevating the head end of the bed is also shown to improve the symptoms.

Secondary prevention

 * Proton pump inhibitors: Omeprazole demonstrates an improvement in the symptoms of asthma and peak expiratory flow rates in asthmatics with GERD symptoms. . Dosage of 40mg/day is recommended


 * Lansoprazole has shown to decrease the number of episodes of asthma exacerbations though it does not improve the asthmatic symptoms.


 * Esomeprazole improves peak expiratory flow in subjects with asthma who presents with both GERD and nocturnal symptoms.

Future or Investigational Therapies
The role of fundoplication in patients with asthma and GERD has not yet been established. A meta-analysis of 24 studies concluded that the surgery improved asthma symptoms by 79% but had little effect on expiratory flow rate. . Surgical therapy has been found superior to the H2 antagonist. However, the benefit from surgery was not found to be different from those treated with proton pump inhibitors.