Water aerosols and cough

Inhalation of ultrasonically nebulised distilled water (fog) induces cough; however, the receptor type(s) mediating this reflex are poorly defined. In humans, cough threshold can be determined by inhalation of progressively increasing fog concentrations; the intensity of the associated motor response can be indexed in terms of flow-related variables as well as of the peak and slope of the integrated electromyographic activity of the abdominal muscles. We have evaluated coughing in patients with Parkinson's disease who show a high incidence of serious chest infections. These patients turned out to have a normal cough threshold but reduced expiratory muscle force during reflex coughing; this suggests an impairment in the central mechanisms subserving muscle activation possibly leading to inefficient airway clearing. Recurrent chest infections also affect laryngectomised patients. These patients have a normal cough threshold but reduced muscle force during coughing in response to threshold stimuli. Voluntary coughing is preserved in these patients, and this should be used to facilitate mucus removal. In normal subjects, fog inhalation causes cough and increases in respiratory drive and minute ventilation, mainly accounted for by increases in tidal volume, possibly due to activation of airway rapidly adapting receptors. Nedocromil sodium administration increases cough threshold and attenuates the ventilatory responses. The assessment of sensory and motor components of coughing may represent a useful tool for those investigating cough in humans.