Which of the following statements about alveolar pressure (Palv) during normal quiet breathing is true?
a. It is positive during inspiration and nega-tive during expiration.
b. It is the same as intrapleural pressure (Ppl).
c. It is negative during inspiration and posi-tive during expiration.
d. It always remains less than atmospheric pressure.
ANS: C
During inspiration the pleural pressure drops, the transpulmonary pressure gradient widens, caus-ing the alveoli pressure to become sub-atmospheric and gas to enter the lung. During expiration the passive recoil of the lungs cause a supra-atmospheric pressure in the alveoli that causes gas to exit the lung.
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