Relationship between supramaximal flow during cough and mortality in motor neurone disease

The main function of cough is clearance of intrathoracic airways. A normal cough is characterized by a transient increase in expiratory flow above the maximal flow-volume loop envelope, known as cough "spikes". They may be absent in patients with motor neurone disease. The relationship between cough pattern, pulmonary function and survival was studied. Fifty-three patients were recruited (25 bulbar). Vital capacity, maximal inspiratory and expiratory mouth pressures and cough flow/volume curves were performed on all patients, and the presence or absence of spikes were recorded. The primary endpoints were mortality or initiation of ventilatory support over a period of 18 months. Thirty-five patients died over the 18-month period of the study (including the six who were started on noninvasive ventilation). Twelve of the 24 patients with spikes died compared to 23 out of 29 patients without spikes (p<0.05). Patients without spikes were more likely to be bulbar on clinical grounds (p<0.0001) and had poorer lung function. The results showed an association between the absence of cough spikes and increased mortality. However the main determinants of survival in motor neurone disease are age, vital capacity and inspiratory mouth pressure, and it remains to be shown whether regular monitoring of cough conveys any additional advantage.