2. Breath stacking. Inspiratory lung volume can be increased by 'stacking' repeated inhalations. This allows a greater cough flow with improved secretion clearance. The simplest method is to use a bag, face mask and a one-way valve. Inspiratory volume can also be augmented using mechanical or non-invasive ventilators although care must be taken to avoid over-inflation and barotrauma(14). The cough phase after insufflation is often augmented by external compression of chest or abdomen (manually assisted cough). While there is evidence that breath stacking, with or without manually assisted coughing, can increase lung volume and peak cough flows(15), there are no prospective studies to study long term effects.