Negative-pressure ventilators cause air to enter the lungs by increasing ______________ pressure

a. transairway
b. transpulmonary
c. transrespiratory
d. transthoracic

ANS: B
Transpulmonary pressure maintains alveolar inflation due to the decrease in pleural pressure caused by the negative pressure surrounding the chest wall. Positive-pressure ventilators cause air to move into the lungs by increasing the pressure in the upper airways and in the conductive air-ways. Changes in transpulmonary pressure result in corresponding changes in alveolar volume. The transairway pressure is the gradient that produces airway movement in the conductive air-ways and represents the pressure caused by resistance to gas flow in the airways. The transrespir-atory pressure is responsible for gas flow into and out of the alveoli during breathing. The trans-thoracic pressure is the pressure across the chest wall. It represents the pressure necessary to ex-pand or contract the lungs and chest wall together.