G control: subjects treated with conventional physiotherapy according to the routine service of physiotherapy of the hospital; G Voldyne: subjects treated with incentive spirometry, Voldyne Model 5000® (Sherwood Medical, USA); G CPAP: subjects treated with "continuous positive airway pressure"; G EPAP: subjects treated with "expiratory positive airway pressure"; G IPPB: subjects treated with "intermittent positive pressure breathing"; G BIPAP: subjects treated with "bi-level positive airway pressure"; G BS: subjects treated with "breath stacking" (siliconized mask connected to a unidirectional valve allowing only inspiration).