Respiratory expulsive efforts evoked by maximal lung emptying

Some patients exhibit cough-like expiratory efforts ("deflation cough") during slow vital capacity (SVC) and/or FVC maneuver. The cause and motor features of these expulsive efforts are unknown.

Of 1,720 consecutive patients, 43 displayed deflation cough during SVC or FVC, and 18 agreed to participate in additional examinations involving radiologic and clinical assessments. Variables of the motor pattern of deflation cough, as well as its intensity and frequency, were recorded by means of a pneumotachograph; the "integrated" surface abdominal electromyographic activity (IEMG) was recorded as well. On different occasions, participants were randomly administered either an antacid or salbutamol or matched placebos. Comparisons between deflation cough variables prior to and after drug administration were performed by means of the analysis of variance and post hoc tests.

Fourteen patients (77.8%) were affected by a respiratory disease, and all of them also reported esophageal and/or extraesophageal symptom(s) of reflux. In control conditions, maximal lung emptying was consistently accompanied by the appearance of deflation cough. Peak IEMG and peak expiratory flow rates of deflation cough correlated (r = 0.53, P < .05). Inhaled agents had no effect. Antacid abolished deflation cough in 11 patients, reduced its frequency in four, and was ineffective in three. Matched placebo was significantly less effective.

All patients with deflation cough present symptoms of gastroesophageal reflux; acidic reflux, possibly evoked by the efforts of lung emptying, may be the causative factor. Receptors sensitive to lung collapse may also contribute to deflation cough when antacid administration fails.