How does gastroesophageal reflux disease (GERD) cause bronchospasm?

Mechanisms of Bronchospasm Induced by Acid Reflux

Acid reflux causes bronchospasm primarily through neurally-mediated reflexes between the esophagus and airways, without requiring direct aspiration of gastric contents into the lungs. 1

Primary Mechanisms

Gastroesophageal reflux disease (GERD) can trigger bronchospasm through several pathways:

1. Vagally-Mediated Reflex Pathway

   • Acid in the esophagus activates vagal afferent nerves that project to similar brainstem regions as airway afferents 1
   • These neural pathways converge centrally, triggering parallel reflex effects in both the GI tract and airways
   • This neuronal connection can initiate bronchospasm even when refluxate remains confined to the esophagus 1, 2

2. Esophageal-Bronchial Neural Connections

   • Direct neuronal projections exist between esophageal and airway autonomic ganglia 1
   • When activated by acid reflux, these connections produce physiologic effects in the airways including:
     • Mucous secretion
     • Bronchial smooth muscle contraction (bronchospasm)
     • Increased airway inflammation 1

3. Cough Reflex Sensitization

   • Acid reflux sensitizes the cough reflex, lowering the threshold for bronchospasm 1
   • Studies show acid challenges to the esophagus markedly reduce the concentration of inhaled capsaicin required to evoke cough 1
   • This sensitizing effect depends on CNS integration and amplification of vagal sensory inputs 1

4. Parasympathetic Activation

   • Acid stimulation of the distal esophagus increases parasympathetic activity 2
   • This parasympathetic activation causes concomitant bronchoconstriction in asthmatics regardless of their reflux status 2
   • The effect is mediated through a vagally-mediated esophago-bronchial reflex 2

Supporting Evidence

Research demonstrates that acid challenges to the esophagus can:

• Directly result in coughing or bronchospasm 1
• Reduce the concentration of inhaled irritants needed to trigger bronchospasm 1
• Increase parasympathetic tone as measured by autonomic function tests 2

Importantly, one study showed that the sensitizing effect of esophageal acid challenge could be prevented by inhalation of atropine, confirming that a CNS-dependent reflex initiated from the esophagus results in bronchospasm and/or mucous secretion in the airways 1.

Clinical Implications

• Bronchospasm can occur without refluxate reaching the proximal esophagus or airways 1
• Medical treatment of GERD reduces sensitivity to tussive stimuli and improves asthma outcomes in 70-80% of patients 3
• Anti-cholinergic medications may have a role in treating reflux-associated bronchospasm 2

Common Pitfalls

• Assuming direct aspiration is necessary for GERD to trigger bronchospasm
• Failing to consider GERD as a potential trigger in patients with difficult-to-control asthma 3
• Prescribing oral bronchodilators (like theophylline) which may worsen GERD and create a vicious cycle 4
• Not recognizing that some asthma medications can potentiate GERD 5

For patients with both GERD and respiratory symptoms, inhaled bronchodilators (like albuterol) are preferred over oral agents, as they cause less reflux 4.