## Chapter 34. Introduction to Pulmonary Structure & Mechanics

A group of friends from San Francisco, California, where the sea level barometric pressure is 760 mm Hg traveled to the summit of Mt. Everest, where the barometric pressure is about 250 mm Hg. Before leaving the Bay Area, the travelers measure the partial pressure of O2 (Po2) and they again measure Po2 at the top of Mt. Everest. Assuming they are measuring “dry air,” what is the difference in Po2 at the two sites?

A. 21%

B. 52.5 mm Hg

C. 107.5 mm Hg

D. 160 mm Hg

E. 510 mm Hg

The correct answer is C. The O2 composition in dry air is the same at sea level or on top of Mt. Everest, 21%. The Po2 is calculated by the multiplying the O2 composition by the barometric pressure. Thus, at sea level, Po2 = 0.21 × 760 mm Hg, or 160 mm Hg (ruling out D); and on top of Mt. Everest, Po2 = 0.21 × 250 mm Hg, or 52.5 mm Hg (ruling out B). The difference, then, between sea level and Mt. Everest is 160 − 52.5 = 107.5 mm Hg. The barometric pressure difference shown in (E) does not take into account the 21% oxygen in the air (B), both of which can be used to arrive at the correct answer (0.21 × 510 mm Hg = 107.1 mm Hg).

A nurse in the pulmonology clinic administered respiratory tests on a subject. After speaking with the subject, he reported to the patient that the FVC measured at 4 L. Which statement below best describes what the nurse measured?

A. The amount of air that normally moves into (or out of) the lung with each respiration.

B. The amount of air that enters the lung but does not participate in gas exchange.

C. The amount of air expired after maximal expiratory effort.

D. The largest amount of gas that can be moved into and out of the lungs in 1 min.

The correct answer is C. The maneuver is described is generally used to measure both the maximal respiratory effort, or FVC, and the forced expiratory volume during the first second (FEV1). Both measurements, and more specifically, the ratio, FEV1/FVC are important indicators of lung health. Answer A refers ...

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