This mechanism is similar to that of the pneumatic belt,2,4 but there is an important difference. As shown by the magnetometry tracings in Figure 2, the chest wall and abdomen move synchronously during abdominal compression by the hands, but paradoxically during use of the pneumatic belt. This indicates that use of the hands truly assists ventilation, whereas the pneumatic belt controls it. When the patient exhales, her hands apply pressure to the mid-epigastrium, forcing the diaphragm into the thorax while the chest wall deflates. The hand force is timed to synchronize with exhalation and does not increase intrathoracic pressure enough to expand the chest wall. By contrast, bladder inflation with the pneumatic belt is not synchronized with the patient's spontaneous breathing and is quite forceful. The abdominal compression is much greater than that achieved with the hands, increasing intrathoracic pressure more and causing the chest wall to expand and move paradoxically during exhalation. Because there is no paradoxical chest wall motion, manual ventilation must be more efficient than the pneumatic belt. Also, because it uses less force and allows the patient to determine the breathing pattern, the patient senses it as more comfortable.