Compared with negative-pressure ventilation, positive-pressure ventilation occurs when:

• A. Air is drawn into the lungs
• B. Air is forced into the lungs
• C. The chest wall expands outward
• D. The diaphragm relaxes

Answer: (B)

Positive-pressure ventilation pushes air into the lungs by delivering gas under positive pressure, inflating the lungs from within the airways. This is different from negative-pressure ventilation, which enlarges the chest cavity and pulls air into the lungs by creating a sub-atmospheric pressure around the thorax. So the defining action of positive-pressure ventilation is that air is forced into the lungs. The other statements describe drawing air in, normal inspiratory chest movement, or expiratory diaphragm relaxation, which are not the mechanisms that distinguish positive-pressure ventilation.