<qa>  What is the natural elasticity of the chest wall?Tidal volumes can also be increased by electrical stimulation of the surface of abdominal muscles during expiration. During stimulation the patient expires below functional residual capacity the amount of air left after normal expiration. The natural elasticity of the chest wall then causes a recoil increase in the size of the next inspired breath. Functional electrical stimulation FES of the abdominal muscles is theoretically an attractive technique to augment respiration. It is non-invasive, it mimics natural physiological processes and tetraplegic patients cannot sense abdominal discomfort. There are potential applications in acute SCI patients to prevent the need for artificial ventilation and to aid ventilator weaning. The technique could also be used in chronically injured patients to augment ventilation. 