GPC Air BagUsing a five or six liter rubber bag, inhalation and exhalation can be practiced. Since the same air is breathed, carbon dioxide, rather than oxygen, is transferred avoiding hyperventilation. Practice emptying and filling the lungs by slowly rebreathing air several times in a row. In this exercise the muscles of enlargement will learn to work apart from the muscles of reduction. It is important that the lungs go from extremes, empty to full.