There is a paucity of data regarding the physiological efficacy of MIE devices and although clinical consensus regards them as a beneficial adjunct to the management of patients with respiratory muscle weakness causing a reduction in effective secretion clearance it is less clear the optimum protocol to achieve secretion clearance. The aim of chest physiotherapy is to achieve clearance of airway secretions and allow improved gas exchange by enhancing ventilation and perfusion matching within the lung. The data suggesting optimum pressures for MIE are based around early work on achieving enhanced cough peak expiratory flow. More recently higher pressures have been suggested to achieve enhanced airway clearance. There may be potential beneficial effects with high pressure MIE by enhancing airway opening during the insufflation pressure achieving a degree of lung volume recruitment. Conversely, high insufflation pressures may adversely affect both pulmonary and cardiac physiology which may be further impacted by the large pressure swing during exsufflation. This is particularly relevant given the increasing co-morbid cardiomyopathy that occurs in many congenital neuromuscular diseases.