3. Mechanical insufflation-exsufflation. Devices in this group inflate the lung with an inspiratory positive pressure phase followed rapidly by a negative pressure exhalation phase(16). They are widely used and recommended but prospective research support is lacking. As with breath stacking, there is evidence of short term improvement in lung volume and cough flows(17) following MI-E treatment. There are also retrospective reviews to suggest that the technique is effective and well tolerated in children(18). However, there are no prospective controlled studies of MI-E either in adults or children.