Quadriplegia, or paralysis of all four limbs resulting in inability to move without assistance, may result from traumatic injury to the head or spinal cord or from a variety of congenital or acquired diseases and conditions. Immobility without quadriplegia may occur in severe forms or advanced stages of many conditions including neuromuscular weakness disorders, cerebral palsy, multiple sclerosis, ALS and spinal muscular atrophy. Because quadriplegic/immobile patients have impaired chest wall and diaphragm muscle function, their lungs will not work as well. As a result, mechanisms for mobilizing airway secretions, including cough and effective mucociliary clearance (MCC) functions, are diminished or absent. Consequently, secretions accumulate in the lungs, triggering recurrent episodes of respiratory illness. In patients with quadriplegia/immobility, the most common cause of death is acute respiratory failure due to pneumonia and severe mucus plugging precipitated by retention of stagnant airway mucus.

Regular airway clearance therapy is recognized as an essential component in the standard respiratory care plan for quadriplegic/immobile patients. Many physicians prescribe vest therapy for those patients who cannot mobilize airway secretions without therapy. Airway clearance therapy methods requiring a lot of effort on the part of patients are generally unsuitable for this population. In patients with ineffective cough, additional techniques or devices to clear secretions from central airways are also required