In: Asthma27 May 2014
The prevalence of asthma is increasing worldwide, and it increased from 3.5% to 5% in the United States between 1982 and 1992. Gastroesophageal reflux (GER) is frequently found in association with asthma. Approximately one half of asthmatics attending an asthma clinic experienced symptomatic GER on a regular basis. Physiologic studies confirm the high rates of GER in asthmatics. Sontag et al> found that 40% of asthmatics had erosive esophagitis, 58% had hiatal hernias, and more than 80% had abnormal GER based on ambulatory pH monitoring criteria. Asthmatics may experience reflux-associated respiratory symptoms (RARS) including cough, dyspnea, and wheezing, and they may require [3-agonist inhalers during periods of symptomatic GER. canadian health and care mall
Although the nature of the relationship between GER and asthma remains controversial, most authors have focused on the adverse effects of GER on asthma control. Proposed mechanisms of asthma worsening include tracheal aspiration of gastric contents and vagally mediated bronchospasm triggered by the presence of acid in the lower esophagus.
Aspiration of gastric acid causes inflammatory changes in the airway. In cats, Tuchman et al found that tracheal instillation of hydrochloric acid had a greater effect on airway resistance than esophageal instillation. This observation suggests that microaspiration has a greater potential to cause bronchospasm. However, studies designed to demonstrate the importance of microaspiration in asthma have been disappointing. To document microaspiration, asthmatics with suspected GER have ingested a radioactive tracer meal at night and then have undergone chest and abdominal scanning the following morning. The presence of tracer activity over the lungs has been presumed to represent reflux and aspiration. Less than half of the patients studied had positive tracer studies, however, which suggests that either the technique is not sensitive enough to document GER or GER exerts its effect on asthma by a different mechanism.
Harding et al measured peak expiratory flow rate (PEFR) and esophageal pH with a dual probe monitor during acid perfusion (AP) of the esophagus. They assumed that if microaspiration had an important effect on airway tone, falls in pH in the upper esophagus would correlate with falls in peak expiratory flow (PEF). Changes in pH in the upper esophagus did not correlate with PEFR, which led them to conclude that microaspiration was not important. Gastal et al also found that proximal reflux does not appear to be a specific etiologic factor in asthma.
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