Mechanical insufflation/exsufflation: has it come of age? A commentary

In 1852, the English physician Meryon 1 described how a 16-yr-old male with what was to become known as Duchenne muscular dystrophy, died from acute respiratory failure during a febrile episode with “profuse secretion of mucus from the trachea and larynx”. One-hundred and fifty years later, over 90% of episodes of respiratory failure in patients with muscular dystrophy are caused by ineffective coughing during intercurrent chest colds 2. Most people with neuromuscular diseases (NMDs) still die prematurely or are hospitalised and undergo tracheotomy, because of failure to assist respiratory muscles to prevent respiratory failure. The study by Chatwin et al. 3 of cough augmentation with mechanical in‐exsufflation (MI‐E) is an important step towards ending this perennial trend. Over 700 patients with NMDs, postpoliomyelitis, high-level spinal cord injury, and other conditions with respiratory muscle weakness or paralysis have used noninvasive positive pressure ventilation delivered via mouthpieces 4 and nasal interfaces 5 for continuous ventilatory support, in many cases, for over 40 years 2, 5–9. However, it would have been impossible for these patients to have avoided tracheotomy had they been unable to effectively clear airway secretions during intercurrent chest colds. Whereas the mucociliary elevator is generally intact in patients with NMD unless they undergo tracheotomy, the cough is not. Leith 10 reported that a normal cough requires that the vocal folds enlarge airway diameter and the inspiratory muscles inspire up to ∼85–90% of total lung capacity. There is then a rapid and firm closure of the glottis for ∼0.2 s. Both glottic opening and closure require intrinsic laryngeal (bulbar) muscle contractions. Subsequent contraction of abdominal and intercostal (expiratory) muscles results in intrapleural pressures of ≤18.62 kPa (140 mmHg). Upon glottic opening, this causes an explosive decompression …