In considering the first possibility, it has long been appreciated that chronic obstructive pulmonary diseases have varied causes. Smoking has been considered to be responsible in the large majority of patients; however, careful longitudinal studies have shown that only a minority of smokers developed airways obstruction (although all develop mucous hypersecretion and, consequently, chronic bronchitis). Among other predisposing factors considered to play a part in the development of airways obstruction are hyperreactivity of the airways and abnormalities of pulmonary defense mechanisms such as abnormal cilia or anti- protease deficiencies. In the present study, we have identified a potentially far more common association in 21 of 25 patients with frequent exacerbations of COPD. We assume that the cricopharyngeal dysfunction leads to occult aspiration of small quantities of oropharyngeal contents. It is not unlikely that such repeated aspirations of oral secretions would be unrecognized and yet over a prolonged period could damage airway epithelium and promote parenchymal destruction. Presumed acute exacerbations of COPD common in this group of patients may have been related to larger aspirates.
It is possible, also, that cricopharyngeal dysfunction is secondary to COPD. Belsey has suggested that gastroesophageal reflux leads to cricopharyngeal achalasia, a mechanism protecting the larynx from aspiration of gastric acid. Since it can be speculated that COPD may favor increased gastroesophageal reflux by flattening of the diaphragm, the presence of COPD may lead to progressive cricopharyngeal achalasia. In addition, p-adrenergic drugs, theophylline, alcohol, cigarette smoking, and severe coughing paroxysms may lower or overcome lower esophageal sphincter tone and promote reflux; however, in a recent editorial, Winship stated that the role of gastroesophageal reflux in producing increased upper esophageal sphincter tone has not been clarified. While our radiologic observations are not supportive of its role, more definitive gastroesophageal reflux examinations should be performed, by ambulatory pH monitoring, for example, or acid perfusion studies (or both). There are no data suggesting an effect of drugs, tobacco, or alcohol on the upper esophageal sphincter.
Common etiologic factors that might be considered include aging. As noted previously, mild radiographic abnormalities of the upper esophageal sphincter are relatively common in the aged population, and “senile” emphysema with increasing airflow limitation is an accepted phenomenon. Nevertheless, our observations suggest that aging alone is not the cause of the swallowing disorder in these patients. While there may have been a bias in the selection of our patients, the observed incidence of 84 percent of cricopharyngeal achalasia is considerably higher than reported in the literature and, although surprising, indicates an important need for further studies. Furthermore, 17 of the 21 patients with COPD whom we studied had severe radiologic abnormalities of swallowing.
Although cricopharyngeal myotomy resulted in clinical improvement in eight patients with severe COPD dysfunction, the usefulness of this surgery has not been clarified. Swallowing rehabilitation programs may be equally beneficial. Prior to performance of this surgery, concern was raised that the myotomy could enhance aspiration secondary to gastroesophageal reflux; however, in eight patients followed up to two years after surgery, swallowing was greatly improved, and exacerbations of pulmonary distress were relieved. Furthermore, myotomy may not result in removal of the barrier to gastroesophageal reflux, as the remaining muscle may undergo axial lengthening and thereby prevent aspiration. Treatment of gastroesophageal reflux as a potential etiologic factor would also be rational and important.
The failure of the larynx to protect itself and the airway from aspiration has not been elaborated. Presumably, material that has not been cleared from the oropharynx by the preceding swallow is aspirated by the following obligatory inspiration. Other possibilities include malposition of the larynx during swallowing resulting in leakage into the airway and also possibly contributing to cricopharyngeal malfunction.
In conclusion, we reemphasize the nonrandomized aspects of this study and that the controls were unmatched. Our subjects consented to have the radiographic studies of swallowing performed after careful and intensive questioning regarding deglutition. We believe that swallowing disorders should be sought in patients with severe COPD who have frequent exacerbation of respiratory distress.