In a pre-post study by Stiller et al. (1992), the effectiveness of intermittent positive pressure breathing on lung capacity was studied. The authors found that this style of mechanical ventilation significantly increased lung volume, as well as vital capacity (Stiller et al. 1992).
There is level 4 evidence (from one pre-post study: Stiller et al. 1992) that intermittent positive pressure breathing may increase lung volume as well as vital lung capacity in acute SCI individuals.